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STANDARDIZATION AND FLEXIBLE WORK CELLS FOR HIGH VARIETY, LOW VOLUME MANUFACTURING

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ABSTRACT

STANDARDIZATION AND FLEXIBLE WORK CELLS FOR HIGH VARIETY, LOW VOLUME MANUFACTURING

This thesis studies the opportunities for the application of lean manufacturing tools in a high mix, low-volume traditional manufacturing factory floor setting. A job shop is a manufacturing system well-known for its operational complexity due to the conditions under which it operates, such as instability of order volumes, product mix, product routings, customer bases, and etc.

A fundamental approach to improve the performance and efficiency of job shops has been to transform the Functional Layout that they traditionally use into a Cellular Layout. Cellular Layouts provide shorter production lead times, lower WIP inventory levels, simpler scheduling, and better control of product quality. However, Cellular Layouts have major disadvantages such as low machine utilization, high cost of cell reconfiguration when demand or product mix change, and high risk of disruption to production due to machine breakdowns and operator absenteeism. These disadvantages are especially harmful for job shops because they operate in a high-mix low-volume (HMLV) environment.

Consequently operations are not standardized and batch and queue operational strategies are employed. However, closer examination reveals that these operations largely consist of a small number of elemental machine functions that are exercised in various combinations.

Value stream mapping and other associated analytical tools are used to explore the opportunities to streamline the flow of products on the floor with a focus on reducing inventory and improving quality.

To complement the analysis, this thesis also examines the impact of improved floor employee involvement. It considers several aspects including the increased empowerment of the direct labor staff, stronger team participation, and a greater focus on solutions specifically tailored to the particular area. Based on the results of the work, the recommendation is in increased focus on developing team skills and empowerment, specifically within the direct labor staff. This approach is demonstrated using an industrial case study.

CHAPTER 1

Introduction

1.1 Background and Motivation

This thesis looks at the application of Lean Manufacturing principles in a highly complex, high mix, and low volume manufacturing environment. Where the process are primarily traditional machining operations with a large part complexity, schedule complexity and demand unpredictability. This work focuses on the ways to improve the flow of products using lean techniques to reduce the confusions in the shop floor .Owing to the low repeatability of jobs released to the shop floor due to the work environment, motivation for creating standardized work is usually low among the work force, thus creating a need to constantly revise the work process at regular intervals of time.

A new cutting tool path is designed in this work for reducing the cycle time in the main bottleneck operation to improve and standardize the flow in the manufacturing cell. Analytical tools such as value stream mapping are used to study and improve the flow in the process. Flow in the cell is improved with a mix of push and pull system where ever necessary.

Objectives and scope of thesis

1.2 Standardized Work

Standardized work is a fundamental element in both process improvement and process control for all organizations looking for a lean status (Yamkelani Moyo 2004). Most organizations engage in a continuous attempt to standardize all aspects of their operations if clear picture of the organization's objectives are to be created. In today's increasingly competitive world, where customers are becoming more demanding for more varieties of the product to suit their needs, it is increasingly becoming important for organizations to streamline and standardize their operations. However, the benefits of standardized work have been limited to mostly organizations that produce high-volume, low-variety products, with only a small percentage of organizations in the high-variety, low-volume (HVLV) production enjoying similar successes (Jina, Bhattacharya, and Walton 1997).

The problem of standardized work in HVLV environments is more understandable due to low repeatability of jobs in the shop floor. Lack of understanding of the need to change as well as lack in confidence in new methods of working have adverse effect on any effort of lean and standardization in long term.

Standardized work is established by considering the technical and process standards required to successfully manufacture a product at the desired quality and rate while providing for the complete safety of the operator. Standardization is the key to success of managing factories effectively. It should be realized that no matter how good a factory's equipment is, the factory cannot make good products without the people who have to operate the equipment and manage the factory. These are referred to as standardized work (Niebel Benjamin), Methods, standards and work design. Standards are created for people to use, and therefore it is important that these standards are acceptable and well communicate or otherwise they become useless and all effort used to develop them go to waste. The best way to gain universal acceptability in formulating standards as well as capturing the tremendous knowledge on the shop floor is to encourage user participation at the development stage. When people are able to participate in the development of standards, implementation become easier as there is greater acceptance of the process.

To main challenge in the process of standardization would be to observe and collect data about all the non value added activities in the process and then try to educate people about the new system with an open mind. Traditional thinking people who do not understand “why” and “how” will be human road blocks in the process of standardization. Lack of understanding of the need to change as well as lack in confidence in new methods of working may have adverse effect on any efforts at lean and standardization

The most vital solution would be to expose and make all potential problems caused due to bad practices more visible, which will require people to respond rapidly - this is the intent, to eliminate problems and implement the new system. Lean manufacturing methodologies such as Value Stream Mapping, High Performance work Teams and extensive use of concepts such as Single Minute Exchange of Dies (SMED) and 5S will help to bring about a change.

A new Kanban system is introduced in this work to improve the flow of material and information between the cells to various other supporting departments. This system accelerates people based on ordinary visual controls, that tell us precisely where things are, what needs to be done, by when, in what quantity, by whom and how. This is a very important step towards process standardization to reduce confusion. With the help of visual control, work standardization can be easily implemented where what is supposed to happen does happen on time.

1.3 Background and Approach

Schlumberger Houston Product Center is a job shop manufacturing organization that is involved in the manufacture of various types of safety valves. The products released to the shop floor are constantly changing and thus there is a need to modify and enhance standardized work procedures. It is interesting to note that the products have a low repeatability in production, but still they possess similarities in features and in the way they are machined.

In the first week of this work a team was assigned to work on developing a team charter. The goals for each week were set to track the progress of the new system. The work was started with the initial plans of implementing 5S and visual improvements in the cell. The word cell used in this work loosely refers to 6 machines which are grouped together to make a single product.

The cells are newly formed with machines moved from different locations in the shop floor to product oriented cells to improve the flow and to reduce the operator movement time. The objectives of this work were very clear as to improve the delivery time and to reduce any confusion in the newly formed cell. As the initial works of cell design and machine grouping were already done, the main job was to focus on increasing the cell throughput, with a focus on solving any practical problem.

Lean Manufacturing techniques particularly setup and cycle time reduction strategies had been introduced in this cell several times previously before this work with good initial success and were declined as time went past. So care is taken in this work to implement and sustain the changes. The first part of this work was started with a focus of making the work place friendlier and more organized to work. All the operators in the cell were formally introduced to 5S and were made aware of the work which is going to be done.

The next important focus was on setup time reduction. There was no standard way of doing the setup and each and every operator uses their own convenient way to do the setup. This inconsistent process also depends very much on the skill of the operator. As there is a mix of new less experienced operators and very high skilled experienced operators there is a need for standardization in setup to save time and to share knowledge and experience. In the newly formed cell there is a mix of both manual, old machines and highly automated machines. In order to have consistent flow, Total Productive Maintenance (TPM) concepts were introduced to the operators/machinists who could make the machines more reliable. There were cases where a series of repairs happened in a particular machine which eventually led the machine to stop for weeks for maintenance thus affecting the cell throughput.

The next important part of this work is focused on cycle time reduction. This was one of the main departmental objectives in this particular cell. A particular operation named operation C took a lot of time ranging from 60 hours to 90 hours to complete the turning operation. This time depends on the diameter of the part and the material type.

As these parts are custom made depends on the material and size there is a lot of practical difficulty in machining the parts due to their design. For each setup the jaws of the particular size has to be made and it takes a considerable amount of time to complete it which adds to the increase in non value added time in the process. So the main focus in this part is to reduce the variation when compared to the standard routings time and to reduce the non value added time.

The main tools used to solve the problems were to involve all the team members of the area and ensure individual empowerment and accountability, with a relentless focus on new process sustainability.

1.4 Objectives

The objective of this thesis is to establish methods for developing standardized work for high-variety, low-volume (HVLV) job shop environments. Ideally these methods should exhibit the following characteristics:

As jobs are continuously changing, there is a need to develop a good documentation of standardized work. These documents should be useful in the study of work methods, identifying flaws in the process and seeking remedy for the situation.

The standardized method should educate floor workers and seek acceptance of the standard work process, cultivate interest by encouraging a participative approach to standardization. This is accomplished through a learning environment where every individual on the shop floor is allowed to think and contribute to continuous improvement.

Learning that occurs gradually and intermittently over a long period of time, should not be forgotten and should be recalled and used consistently in the future for the new products that may have similarities with the previous stabilized products. This transfer of knowledge from old products to new products would save considerable amount of time. This also helps to reduce variability in process set up and facilitate rapid change over from one job to the other.

1.5 Organization of the Thesis

Following a brief introduction and overview in Chapter 1, Chapter 2 provides a more complete understanding of the problem from the literature reviews. It provides an overview of the industry thoughts to the problem. Chapter 3 gives an overview of the setup study done in the cell, and also gives solution for flow improvement in the cell. Chapter 4 describes an attempt to solve cycle time reduction issues and also looks on ways to sustain the changes and improvements made. This chapter also focuses on the importance of value streams, and the update that has been made in the current value stream to move ahead to the ideal state. Finally, Chapter 5 presents an overview of the conclusions and recommendations for future work.

CHAPTER 2

Literature Review

Lean manufacturing was probably originated in 1920s when Henry Ford and his

associates recognized the potential of flow improvement in Ford automotive production. Henry implemented synchronized assembly line production to promote continuous flow from raw materials to shipments of finished car for their Model T Ford automobile. His method has shown significant productivity leap but has been only in the special case of large-lot high-volume high-speed assembly production. Three quarters of a century later, Ohno, a chief engineer at Toyota Motor Company, conducted a thorough study of large lot American production systems in order to improve his company's production system to compete and survive in the global market competition.

It is understood that Japanese corporations cannot afford large amounts of land to warehouse finished products and parts. Adopting large-lot production to achieve economic lot size would cost even more. Therefore, he developed an alternative approach to promote continuous flow for small-lot production in Toyota plants and soon his developed production system has become one of the most productive systems in the global manufacturing industry. This production system is referred to as Toyota Production System (TPS) (Hines, Holweg and Rich 2004).

It is a special line flow production system that can produce more variety of products in lower volumes or smaller lot-sizes than the traditional large-lot American production system. The small-lot production allows TPS to operate under low inventories. When the inventories decrease, problems or wastes are exposed. Once these problems or wastes are found, they are removed and the production system improves. This is referred to as a waste identification and removal strategy in TPS.

The system continues to reduce the inventories and the next problems or wastes are then identified and removed. The repeating process of identifying and eliminating wastes is referred to as a continuous improvement strategy in TPS. Therefore, this manufacturing philosophy aims directly to attack any form of waste in the production process through continuous improvement in pursuit of perfection. TPS best practice has brought lean approach becoming the most productive approach in the manufacturing industry. It has become the general case of lean manufacturing these days. The values of the system and its strategies have proven to global manufacturing industry and a considerable number of manufacturing companies are keen to adopt this model to their own production systems (Papadopoula and Ozbayrak, 2005).

2.1 Lean Manufacturing in HVLV Facilities

Although lean manufacturing can be a universal tool for all manufacturing companies, lean strategies and techniques in TPS, may not fit to all types of manufacturing companies. According to a lean practitioner in the team who has more than 15 years of lean manufacturing experience in both low-variety high-volume and high-variety low-volume environments, Lean Manufacturing and TPS are terms that can be referred interchangeably but they may not be interchangeable. TPS is suited for manufacturing companies in a low-mix high-volume environment where flow patterns are simplified and recognized and flow line layouts are most suitable for these companies. In a HVLV environment, most manufacturing companies are job shops. Their products are wide variety and their production volumes are very small compared to the manufacturing environment in which TPS was developed. Adopting TPS to these HVLV manufacturing companies without properly adapting to the environment would not give maximum result out of the system.

The adaptation of the layout when implementing lean manufacturing in most manufacturing companies has traditionally been done by converting from the existing functional layouts to cellular layouts. However, practitioners have found that it is not advised to completely convert the functional layout of a job shop operating in a HVLV environment into a cellular layout. The main reason is that the inherent inflexibility of manufacturing cells cannot adapt to changing capacity requirements (machine and labor), product mix, and demand volume. (Smart Khaewsukkho 2008).

2.2 Four Key Production System Characteristics:

2.2.1 Mix

Mix refers to the number of different products that are produced within a certain production system. What makes one product “different” from another? One answer is the end product differences, such as number of parts, functionality, appearance, etc. This definition is not very useful; however it is helpful for the purpose of understanding mix within the production system.

A more appropriate method of understanding product differences is to compare the different processes or steps that products must take as they move through production and the difference in processing time at each step. Two products may look different to the customer, but if they are produced with identical routings through the plant, require no setups from one product to the next, and require identical processing times, then these products that appear to be similar might travel completely different routes through the factory, and even the processes they do share have unique setups and very different process times. These types of products contribute significantly to the factory mix.

2.2.2 Volume

Volume is the quantity of a product over a specific period of time. Knowing whether a product is high volume or low volume is difficult to define because it depends so greatly on one's perspective. To a company such as Intel that produces millions of semiconductor chips a year, a product with a 100 unit per month volume would be considered low volume. To the employees of a space satellite manufacture, this type of volume would seem very high. They can usually count the number of products produced per month on one hand.

Some products that might be produced continuously are run in batches by companies trying to reduce setup time and costs.

2.2.3. Demand Variability

Demand variability is defined as the changes in customer demand over time. How different are the customer's orders between order cycles? The time between cycles could be fairly long (weeks or months) in slower-moving industries such as aerospace, defense, or very short (hours in case of Dell). The more demand for specific products fluctuates from order to order, the higher the demand variability.

It is important to note that total demand could be relatively constant, but demand by product varies between order periods. If the demand differences occur on similar products with similar routings and processing times in the factory, the contribution to demand variability is minimal.

2.2.4 Degree of Customization

Manufactured products can be standardized on one end of the spectrum or customized on the other end. Standard content includes materials and parts that repeat between orders of a given product. Customized content refers to materials and parts that are unique to a particular order.

The most extreme example of a customized product is one that is designed and produced only one. The international space station is such a product: although some companies might have other uses, this is a one of a kind product that is highly customized. On the extreme “standard” end of the spectrum are highly commoditized products such as basic fasteners and electrical devices, mechanical devices. These products do not change from order to order. They remain unchanged over long periods of time and can be manufactured in a repetitive manner.

2.3 Production Control Methods:

2.3.1 Push versus Pull

All different methods for controlling the movement of products from the beginning to the end of production can be characterized as either a push or pull system (or some combination of the two). In basic push system products that completes one process step is pushed to the next step. Production does not stop as long as there is product awaiting that process step. Inventory is allowed to build up in front of less productive machines in this type of system.

In contrast to a push style of production control is pull. In a basic pull system, production does not commence at a specific processing step until the downstream process sense the signal, usually in the form a certain level of inventory between the processes. Product might be waiting in front of that processing step, but production cannot commence until the downstream process demands it (Spearman and Zazanis 1990).

2.3.2 MRP:

Material requirements planning (MRP) is a computerized system that is typically laid on top of a traditional “push” manufacturing system with a functional layout. A functional layout is one where like machines are grouped together in “work centers” or “departments”. Products usually need to pass through many of these work centers, and managing what product goes to what work center becomes a tough task as the number of work centers and products increase.

Many companies have implemented an MRP system to handle this complexity. An MRP system can be programmed with the routings of all products and a reasonable time for each product to pass from one work center to the next. By combining these routings and processing times, a promised lead time can be generated for every product that starts on the factory floor.

MRP systems can run into problems because of the variability that is present in every manufacturing system. Any delay in production, such as machine going down or a process taking quite a bit longer than expected starts a ripple in the system that usually magnifies. The product that gets behind will now reach the next work center at a different time than originally planned. This work center might now be working on the next product that MRP has planned, so either this must be broken into or the other product must be delayed further. As the variability effects add up, products get behind schedule and need to be expedited through the system (Plenert 1998).

2.3.3 Kanban:

Kanban, is a production control method used for lean manufacturing and the most widely used form of “pull”. In order for Kanban to be implemented, production must be organized in such a way that the product or group follows the same sequence through the factory on dedicated equipment.

Kanban works by limiting the inventory between each step in a production process. Cards are created for each process step. Work cannot begin at a particular step until that step receives a card from the upstream process. Work therefore does not build up between work centers because the number of cards is limited. Kanban is the ultimate form of “pull” production because every step waits from the downstream step to signal or pull material rather than just produce what is placed in front of the process (Gravel and Price 1988).

Kanban creates a very tight production system that is intolerant of variability. The failure of one step in the chain will quickly ripple through the system and shut down the other process in the chain. A similar kanban system is shown in later chapters of this work.

2.4 Manufacturing Metrics: Cost, Quality, Delivery, Flexibility

Cost, quality, delivery and flexibility are four of the most important attributes for determining the performance of a manufacturing system. Manufacturers like to make the highest quality at the lowest cost and deliver it exactly when the customer wants it. They also desire the flexibility to be able to change quickly with industry trends or changing customer demands.

To achieve better quality, costs would have to rise. Costs could be reduced by automating processes but this reduces flexibility. Delivery can be guaranteed with piles of finished goods inventory but this inventory is an added cost for the company.

2.5 Wastes Identified

Significant changes to this “trade-off” idea occurred in the latter half of the twentieth century. Proponents of lean manufacturing claim that implementing lean simultaneously improves quality, reduces cost, improves on-time delivery, and increases flexibility. This could be accomplished by the constant drive to eliminate waste from manufacturing. Toyota is a very good example of the positive effects of a Lean manufacturing system on these four attributes. Toyota manufactures lower cost, higher quality cars than non lean auto manufactures. They also have the flexibility to produce multiple models on one assembly line. Following the lean guidelines certain waste was identified through brainstorming sessions without the help of the value stream map in the manufacturing cell. The wastes that were focused on can be put into the following priority list.

  • Unnecessary movement of employees
  • Overproduction ahead of demand
  • Unnecessary transport of materials
  • Production of defective parts
  • Excess inventories

2.5.1 Unnecessary Movement of Employees

This was seen by management as the largest source of waste in production. It is often observed that operators talking to each other about non-work related topics outside of break times and wasting time by looking for parts or production instructions. Direct labor was a very important factor in the calculation of total product cost, so any time wasted by the operators hit the bottom-line directly.

This waste can be addressed by a number of initiatives. The first of these was to create accurate, easily accessible production instruction for every process in the cell. This is commonly referred to as “standard work” in the lean lexicon. The second was a way to change the material presented to the line to reduce the need to “hunt” for parts. This is reduced by introducing the new kanban system in the later parts of this work.

2.5.2 Overproduction Ahead of Demand

The main tool to address overproduction ahead of demand was to implement a pull system, which is described in detail in another chapter. As part of this initiative to reduce overproduction, all products that was on the production floor that was not needed in the next month was pulled back and products which are in demand are issued to the line for production.

2.5.3 Unnecessary Transport of Materials

This can be addressed in such a way that machine and assembly workstations are all located in the same footprint on the production floor so that product never had to leave that part of the shop floor from start to finish. This can be effective in minimizing travel distances. The work of cell formation based on product type helped to reduce the transport of materials considerably.

2.5.4 Production of Defective Parts

There is a significant amount of rework generated by production. A couple of changes were made to improve this situation. First, all rework was moved to a central location so the amount of severity and rework could be observed. Prior to this all rework was performed at employee work benches, which hid the magnitude of the problem. Second, standard work was created to better instruct operators on the right way to make parts.

2.5.5 Excess Inventories

An attempt is made to institute a rule to limit inventory in front of all work centers, but inventory still was allowed to pile up in front of certain work centers which takes very less cycle time. Queue management was done in front of the machines where there is a specific place to keep the new incoming work piece to the work center and also for the outgoing finished product to the next location. With the help of these queues it is very easy for the fork lift operator to place the work in the right location. It acts as a visual aid to see if there is enough work available for the machine.

CHAPTER 3

Setup Time Reduction and Flow Improvement

3.1 The Necessity of Determining Time Standards

The determination of time standards in manufacturing is an important aspect of standardization. As production system shifts towards high variety, low volume (HVLV) determining time standards gets more complicated Therefore, it is not surprising to find that most job shops have not attempted to standardize their operations, in most cases operators alone determine their own time standards for their operations. There has been very few successful attempts to determine the correct time standard or develop standardized work for some of the process of the cell. Although acknowledging the inherent nature of products that come from job environments makes it difficult to standardize, it is not an entirely impossible mission to accomplish.

Once the time standard for each operation has been standardized it would be very helpful for a work load balance analysis is to be carried out. Workload balance determines the amount of work that each operator is allocated in the cell. It also shows if an operator and the cell as a whole are able to meet the takt time. Takt time is the maximum time allowed to produce a product in order to meet its demand. Obviously extremes at either end are possible, in which an operator's load is far below or far above takt time.

3.2 Setup Reduction

Determining the setup time for each machine required a separate time study analysis. In order to successfully do the study, it is important to become familiar with the processes so that all the value added elements and non value added elements could be timed and sorted separately. It is common knowledge that most operators on the shop floor view time study in bad taste. It is extremely important for the time study analyst to make it known to the operator concerned that the study is being done to determine how to make the job better, not to see how fast or slow the operator is working. It is usually best not to show up with a stopwatch and immediately begin timing the operator. The best way is to get familiarized with the process, listing all the elements of the job. Observing and listing all the work elements on paper prior to the time study itself allows identifying all the non value added tasks that may be part of the job. Spending some time observing and speaking to the operator is part and parcel of shop floor courtesy that not only relaxes the operator but allows him or her to open up to making suggestions about his/her process.

Determining the setup and cycle times for the machining operation in the cell did reveal quite a number of non value added tasks. Tasks such as walking to get material, unloading the material onto the skid, filing, searching for tread protectors, making new jaws, paper works, program print outs constituted a significant amount of none-value-added time. While some of these tasks cannot be totally eliminated, knowledge about them can trigger an action response to minimize the negative effect.

Observing the setup process did understand that the operators/machinist perform a dual role of operating machine and a role of a clerk before starting the process, such as taking print outs of the program, spending a considerable amount of time on paper work. This is not recommended as it takes away the operator's production time and adds a lot of non value added time in the process as shown in the table 1.

A number of setup studies were done to reduce and highlight the non value added time in the process. All the activities which are done before start of the machine were noted and were classified as internal, external and waste. Internal refers to all activities which can be done only with the help of stopping the machine. External refers to all the activities which can be done without stopping the machine. Waste refers to all activities which are done without much use and can be directly eliminated from the system. The goal of classifying the work done by the operators/machinist is to highlight and reduce the non value added time by eliminating the external activities and reducing the internal activities.

Having a dedicated team leader playing a role to minimize the non value added time is always recommended. The team leader is also known as a coordinator for the specific area in the shop floor whose duty is to assist reducing the non value added activities, and also to get suggestions from the operators for improvement in specific areas of the cell.

As the suggestions made by simple word of mouth, quickly get drowned in the chaos and complexities dictated by production needs this kind of setup study helps the operator and the coordinator to understand the actual reality by which the time is lost in the process and how time can be saved in future setups.

Table 1: Setup study

3.3 Flow Improvement

As discussed in the earlier chapter, kanban production control method is used to create “pull” in the workplace such that all the machines get the required work piece before they start working. This could save a considerable amount of waiting time in the shop floor. To implement this, production is organized in such a way that the product follows the same sequence through the factory on dedicated equipment.

As said, Kanban works by limiting the inventory between each step in a production process. Cards are created for each process step. Work cannot begin at a particular step until that step receives a card from the upstream process. Work therefore does not build up between work centers because the number of cards is limited. Kanban is the ultimate form of “pull” production because every step waits from the downstream step to signal or pull material rather than just produce what is placed in front of the process.

This system is used to reduce the setup time in the cell, which in turn helps to reduce the non value added time found in the setup process. The main idea behind this is to make sure the part, tools and programs are made available before the start of any new work. A card system is used which links plant production control, Machinist, Tool crib and coordinator to improve the flow in the process.

The main duty of the production control in this system is to assign the material for the next job to the right machine. The material is placed on a rack near to the machine by production control, and as soon as the operation for the previous job is completed the new work piece is moved from the rack to the machine which cuts the delay in search for the next job. Production control's duty extends to complete the initial paper work so that it would be easy for the machinist to concentrate on his/her work. Production control also writes down the job id on a board near the machine to have visual control on the work which is being done.

Prior to the implementation of this system a job is picked randomly without control which drastically affects the production schedule, now with this system the machinist can understand which job is going to be next, and this helps the machinist to reduce the uncertainty in a high mix low volume environment, and to gain confidence in the process.

Once the initial duties of the production control is over the card is handed over to the tool crib. It is the place where all the tools for different works are handled in the shop floor. The role of the tool crib is to help reduce the machinist time, who spends a lot time in search of the right tools. In most cases the machinist walks around the shop floor searching the right tools which could be otherwise used for working on a new work piece. This unwanted movement increases the setup time and naturally increases the run time of the product. To cut down any unwanted movement of the machinist in the shop floor, the tool crib works in this system to collect all the tools according to the part which is going to be worked in the particular machine and they pre- kit the right tools to place it near the machine before the machinist's starts the operation. The tool crib properly calibrates the tool and makes it easier for the machinist to use the right tool. This helps the machinist to gain confidence in the tools which he is going to use. The more the number of tools used the more is the setup time. With the help of the tool crib the right number of tools is used which helps to minimize the setup time thus saving considerable amount of time and energy.

The role of a machinist is also very important in this system. The machinist reconfirms the work piece placed by the production control by checking the overall ID and OD and the material type before starting the work. This confirmation reduces the variability in the system as in case if the machinist starts working without confirming the ID and OD he may end up in part oversize or under size eventually leading to a scrap.

The machinist also checks for the right standard CNC program to be loaded in the machine before the previous job has finished. The word standard program is used because there were cases in which the machinist tends to adjust the speed and feed rate at his comfort which changes the program parameters. Thus leading to a big variation in the run time of the product each time when a similar work is performed. This also varies from shift to shift as each operator has his own standard of performing the job. It should be noted that as the program changes the tools accordingly are changed, so the importance of standardized program is emphasized to the machinists.

Once the machinist has confirmed the part dimensions, material and the program the machinist initials in the board near to the machine confirming that the setup is completed, and there could be no chance for failure. This board system also helps to reduce pinpointing other departments when some scrap part occurs.

The next in the cycle is the coordinator, who checks the complete start up process. After the coordinator completes his task, the cycle is now passed on to the production control, and the same cycle is repeated. The role of the coordinator in this system is very critical as his job would be to implement the standardized programs in the shop floor, and he has to make sure there would be no complaints or flaws during machining. If the machine could stop running it could cost a lot of resources so the coordinator takes charge and completes the paper work making sure everything is perfect.

These activities are done before the previous part is machined. There by the machinist just needs to load the part, use the right tools to complete his work on time consistently. This system help reduce the set up time for machining any given part in this high variety low volume environment.

3.4 Conditions for Implementing Standardized Work

Trouble free equipment: If equipment trouble is frequent, then repetition will not be smooth. This means irregular movement and irregular operation sequences will interrupt the work and cause standardization to fail.

Good quality input resources: If parts and materials are of insufficient quality, the processing conditions will always be changing. Since quality is built into the product in the process, every time defects occur in process due to defective input material, they will require an investigation into the cause that is beyond the scope of the process itself. This leads to unstable processes and consequently standardized work will no longer function as intended.

3.5 Types of Standard Work Documents

To avoid creating a standardized work sheet for each product, all standard work is documented on a more common basis. The standardized work is created for the following cases:

3.5.1 Set up sheet: The absence of documented set up procedure presented the biggest problem in the processes. Set up involves the elements of work that take place between completion of the previous job and start of the new job. This includes cleaning, loading the program. No documented set up procedure and time procedure was in place to guide the operator in carrying out set up. As a result, set up method and time was hugely variable with each operator claiming his or her method to be superior to that of his/her co-worker. With the new standardized set up sheet each setup time is monitored and non value added time is continuously eliminated from the process.

3.5.2 Standard Operating Procedure: This contains the work instructions needed for the operator to perform his or her work. This is used to describe a single activity. It is important to display all the knack points for the operation. Knack points are special key techniques (tricks of the trade) that enable the job to be done effectively and may relate to any aspect of performance including quality, efficiency, burden and productivity. It is helpful as a visual document with pictures that enable the operators to positively respond rather than paragraphs of text that take time and difficulty to understand. Pictures, icons and symbols can convey operator work effectively. This document will also be a very good training document for new operators.

3.5.3 Pre Job Review: This is a very important document which should be completed before the operator/ machinist can start working. This document is a combination of all the activities including the right tool, right part, material and it also includes the cost of the part which could give the machinist a sense of importance of the product he/she is handling. The pre job review document travels with the work pallet, the production control initials it confirming the right part is supplied to the shop floor, later the machinist signs it indicating he has received the right work piece later this is initialed by the tool crib indicating the right tools are supplied to do the particular job. With this document the entire history of the work piece can be found out, and in case of any mistake it is very easy to identify the place where the mistake has started.

CHAPTER 4:

Lean Production

Issues to be addressed in the cell range from developing process-level standardized work to system-level standardized work. The main part to be focused in this chapter is on the new ways to reduce the cycle time of the process. As said earlier, the word cell used in this work loosely refers to 6 machines which are grouped together to make a single product.

The main bottleneck operation is on a machine which does all the turning operations in the cell. There are two such machines in the cell to perform the same operation. These machines perform 4 different operations at different parts of the same product. The machining time for each of these four operations varies from 2 hours to 90 hours. This time variation leads to a lot of confusion to the operators in the shop floor, as many times they are not sure when the operation will start and when it will end. There are also a lot of communication problems between the first shift and the second shift operators regarding the process troubles in each part due to the unpredictable timings and also due to the low repeatability of jobs in the shop floor. This instability makes the operators not so confident in their operation eventually taking a lot of extra time to complete the task.

The actual time taken to complete the third operation in this machine varies about 60 to 90 hours depending on the diameter of the part and the material type. The standard time to complete this process is only 40 hrs. The process is not stable as per the standard guidelines and it also depends very much on the skill of the operator. The main reason for the delay in this process was observed in detail by a number of cycle time studies.

4.1 Initial Observations

A lot of time was spent in observing this bottleneck process as the machining takes a lot of time depending on the part size and material, as the working time is very long for a single part it is difficult to predict where the time is lost in the operation, so the standard routing time was compared with the actual process and there was about 50% more time used than the standard time in most cases. The difference in time was about 2 days of working time when compared to the standard. Since the opportunity is big, a time study was done to note down the time taken for each and every operation.

The entire 3rd operation was divided into 13 small operations and the time for each operation was noted and documented and was also compared with the standards. With the help of the time study it was found that 4 operations out of the 13 are taking about 50% of the time i.e. nearly 30-50 hrs.

As the impact in these 4 operations is high, the major work in this chapter is focused in reducing the cycle time in these operations. These 4 operations are used to make a pocket in the center of the work piece. The CNC program used for this turning operation was observed. As per the program there are about 12 passes to complete this operation for the part size which is of maximum demand. In reality, from the time study it was noted that each pass out of the twelve was re passed at least 2 or 3 times. This happened due to very fast insert wear, insert break or no proper cut or push offs. It was noted that the machine was stopped 57 times due to insert failure in one particular shift alone while cutting the pocket, but still the pocket operation was not completed.

At the end of the first time study it was observed that the machine was stopped 180 times to complete the pocket operation. Each time the machine is stopped due to an insert failure there is a delay of about 3-4 minutes which includes checking the insert condition to flip or change the insert. On the whole the delay is about 4 hours in one particular shift when there is a pocket operation. To complete the entire pocket the machine was stopped 180 times due to the same problem which leads to a 12 hour delay and when added with the other delays in the operation such as waiting for paper work, and other unnecessary movement around the shop floor makes the total delay very worse for each and every part. Whenever this operation is performed there is usually confusion among the workers as the process does not follow the procedure or the standard program.

Whenever there is an insert failure the operator used to take his decision based on his experience to re run at the same depth of cut until the insert performs well till the end. As the skill set of the operators working in 2 such machines and on different shifts vary, each arguing their method to be superior and correct, lead to inconsistency or lack of standardized work procedure in the cell.

Based on the time study observation for this operation it is understood that the pocket is having an interrupted cut on a high strength inconel material which is causing this potential instability and delay in the process. Based on the input from the shop floor it was understood that the problem existed for a long time and most of the solutions which were tried either did not work or worked initially and the same problem started over again in a different way. This bottleneck process in the cell is very important for improving the cell throughput which eventually satisfies the product demand. To have a brief idea about the work piece, it has two holes running all along the part for a length of about 40 inches over the sides which are first drilled in the earlier operation and then a pocket is made in the middle of the 40 inch long part which cuts these two holes leading to an interrupted cut which is solely responsible for the delay and inconsistency.

As the time delay for every part in the system is more than 2 extra days an immediate solution was required for this problem. The tool insert company was contacted to get their potential views and solutions for the problem and to solve it faster with better grade inserts to prevent insert failure. The tool insert representative who came to have a look on this issue in the shop floor quoted that the insert which is currently used for the interrupted cut pocket operation was one of the best grade of inserts and he even quoted that if a different grade or type of insert could be used it could even worsen the problem, and there was no guarantee that it may improve the situation. With these inputs from the tool insert company it was decided to use the same tool insert.

As the first contact with the tool Insert Company did not help much in the work to reduce the cycle time to meet to the standard operating time, the direction in the project was changed to fix the same insert and look on to other parameters which could be modified to solve the problem.

4.2 Initial Solution:

With more thoughts on the problem it was understood that if the effect of interrupted cut could be reduced that could naturally reduce the turning operation time by more than half which could help us to meet with the standard. Now the challenge is how to reduce the impact of the interrupted cut, as the process of drilling the side holes cannot be done at a later stage due to other manufacturing problems. With these thoughts in mind we came out with a second idea which was to eliminate the interrupted cut process itself.

The idea was to fill the side holes with some kind of similar material as such as the original cutting material. This material on the side holes could help us to reduce the impact of the interrupted cut when making the pocket operation, and once the pocket operation is completed the extra material on the side holes can be removed. When this idea was discussed it was understood that there were similar kind of trials carried out with metal rods being used on the side holes to reduce the impact of the interrupted cut in the past. It was understood that the trials failed and there was no improvement in reducing the operation time.

The reasons for failure of the project was brainstormed, and it was understood that when the rods where tried to fit into the side drilled holes there was still a small gap which eventually led to the same interrupted cut operation. So now to solve the problem of interrupted cut the side holes should be drilled and then they have to be completely filled with some other material and then the pocket has to be made to reduce the impact of the interrupted cut to save time in the operation.

From the past experience we understand that the material should be tightly packed without any small gap to make this process work. For this purpose, different kinds of materials were thought and finally a polymeric wax like substance was finalized.

This compound is a special type of tooling compound which can be melted and poured into the total length of the part through the side holes and then pocket can be made in the middle of the part, and once the pocket has been made the tooling compound can be melted and taken out. Prior permissions were taken from various department of the company and a sample of the substance was ordered for trials. As this trial involves heating the part to remove the material (tooling compound), and also melting the tooling compound to pour it in the side drilled holes of the part involved some initial preparatory steps which could add some more time to the operation, so this trial was put on hold.

4.3 CNC Program Trails

The current CNC turning program was studied in detail to start the project in the direction of optimizing the speed, feed and depth of cut parameters. As the part length is long, an extended bar is used to do the turning operation, and as there are two interrupted cuts in the process the bar intends to vibrate which causes a taper in the operation, and this taper eventually takes a lot of re pass to make it perfect and to meet the tolerance limit.

The depth of cut used was about 28 thousandths per side in the interrupted cut pocket operation and the speed was 120 SFM.

As any random trial in this standard operation involved a possibility of a scrap which could lead to a big loss in production time and part cost, so an old scrap part was taken for a trial study, and 4 trials were planned.

When too many cutting parameters could be changed there is a possibility for the process to go out of control, and so only a set of known cutting parameters were changed to observe the effect on the operation time.

As the process involves a lot of time the following were documented during the turning operation. The number of pass, the time taken for each pass, the number of rerun in each pass to complete the step, the number of inserts used for each pass and then the insert condition after each pass.

In the first trial the material worked was inconel, this material had a lot of trouble in creating work standardization as it was one of the toughest materials to work with. From the initial discussion in this chapter it could be understood that the insert could have been given too much of stress during the operation which is the reason for the failure of 53 inserts during the operation.

So the first step in this process optimization was to reduce the depth of cut and to run the other conventional cutting parameters as the same. The depth of cut was reduced from 28 thousandths to 15 thousandths per side, and the speed was run at 120 SFM with the same tool inset A.

As said the following parameters were observed and documented as follows:

Table 2: Trial 1 Observations

Pass Number

Repass / Rerun

Time for each pass

# of inserts used

Insert Cond G/B

Remarks (Start Time : 1:50 PM Jul 10 08) Trial 1 : 15 thousandths DOC

1

0

25

1

Good

2

0

23

1(1)

Good

3

0

28

1(2)

Good

4

0

28

1(3)

Good

5

0

15

1(4)

Good

6

0

14

2(1)

Good

7

0

20

2(2)

Good

8

0

19

2(3)

Good

9

0

17

2(4)

Good

10

0

21

3(1)

Good

11

0

18

3(2)

Good

We can see consistency

12

16

3(3)(4)

Broke

1

20

4(1,2)

Broke

2

20

4(3,4)

Broke

3

20

5(1,2)

Good

13

29

5(3,4)

Broke

1

30

5(3,4)

Broke

2

28

6(3)

Good

14

29

6(4)

Broke

1

30

7(1)

Good

15

30

7(3,4)

Broke

1

29

8(1,2)

Broke

2

29

8(3,4)

Broke

3

22

9(1)

Good

16

28

9(3,4)

Broke

1

32

10(1,2)

Broke

2

30

10(3)

Good

17

0

55

11

Good

18

45

12

Broke

1

41

Good

19

38

12(3)

Bad

40

Bad

41

Good

20

30

13(1)

Good

Should have Touched the side drill Holes. Repass has reduced when compared to earlier runs, but still Opportunity for improvement

Gauge Problem waiting for a long time 2 1/2 hr delay after lunch

1

40

14(1,2)

Bad

Still some material in the back rerun again

2

36

14(3,4)

Good

21

35

15(1,2)

Bad

1

38

15(3,4)

Good

22

40

16(1,2)

Bad

Noticed the Formation of hump. The Front part was good, the back Portion was rough. Should be the starting stage of a taper

1

29

16(3,4)

Bad

38 mins Delay

2

31

17(1,2)

Good

20 mins Delay due no availability of gauge

23

Finish Pass

32

17(3,4)

Bad

1

26

18(1,2)

Bad

2

25

18(3,4)

Bad

3

31

19(1,2)

Bad

4

23

19(3)

Good

5

19

19(4)

Good

Hump is built up at the back, so more number of finish pass to remove the taper.

Taper :

0.022” à 0.010” 7passes

0.010ӈ0.005 6 Passes

Check pass

31

20(1)

Taper

Clean up

6

31

21(2,3)

7

28

21(4)

Break

Taper

8

25

22(1)

Good

9

31

22(2)

Good

10

29

22(3)

Good

11

26

22(4)

Good

Completed Step 1

Squaring of pockets was started

4.3.1 Trial 1 Result

At the end of this trial a lot of background information supporting the process was observed, and it paved way for further interesting trials. This trial could be considered partially successful as the trial helped to save 3 hours of running time with the help of the reduced depth of cut. The main intention in this trial was to reduce the stress given to the tool inserts. From the table above it could be noted that there was consistency in the beginning of the trials and later as it reached the interrupted cut the real problem started and where the change didn't help much. After some analysis, the reasons for the inserts performance in the beginning and some poor performance later was understood, as this was due to some block of material for the tool insert to work before it could touch the side drilled holes where the actual interrupted cut process starts.

This study was primarily done for consistency i.e. No extra passes for the same depth of cut and the turning operation should follow as per the program. At the end of this trial it was also observed that the inserts lasted longer than the conventional depth of cut which mean that the insert failure in the middle of the cut was reduced. By this way it helped to reduce the time by 3 hrs.

In the earlier conventional way when an insert failed in the middle of a cut, the inserts are changed at the end of the cycle and is made to rerun for the same depth of cut. Thus extending the time and wasting resources. This scenario was reduced in the new trail which indicates that the process optimization is going on the right direction.

At the end of the cutting operation there were some notable taper formations which lead to more number of repass in the finish stage. This is not a new addition due to the change; rather this is happens in most parts during this operation. Further Investigation is done in this area to prevent it in the future trials.

The above diagram illustrates the current cutting path method. The insert starts to cut from one end, and the turning operation is done to the entire length of about 7 to 10 inches depends on the size of the product. After the initial sizing is done there is a 30o angle to the side of the part where there are the two side drilled holes.

The feed is maintained the same when the tool moves from the side and to the middle of the pocket. In the later steps after completing the shaping process of the pocket the tool insert is again repositioned to remove the front and the back squares. In the final stage after the squaring operation is completed the final finish pass is done to complete the process as per the tolerance.

4.4 Reasons for Change

With the first trial study which partially worked out with the help of the reduced depth of cut in the beginning, but had trouble when it entered into the mid section of the interrupted cut. At the end of the trial 1 pocket analysis it was noted that the front 30o angle is not of much help to the process, as the material in this area is removed again in subsequent steps, and it can be concluded that the operation is repeated which adds more time to the operation, which can be eliminated by combining it with the first step.

This extra squaring not only adds time but also eats a few more inserts. The tool holder was analyzed and it was confirmed that the tool can go straight and could perform the combined operation. With the current working tool head it was observed that the back squaring operation cannot be done in the same process as it involves the tool head direction to be changed in the middle of the process, so back squaring operation is maintained as a separate step. The above ideas were brain stormed with the operators to get their views and opinions for any potential problems.

The process was given a positive feedback and it was supported for time reduction. It was noted that when the feed rate was kept the same when the tool insert moves at an angle during the initial pocket sizing, and also when it comes to horizontal in the middle of the pocket may lead to insert failure or poor performance of the insert due to sudden impact. So it is suggested in the second trial to try with a reduced feed rate of 6 thousandths when the tool insert comes at an angle and at a feed of about 10 thousandths when the tool is in horizontal position. The first trials depth of cut of about 15 thousandths worked out better than the original depth of cut so it was planned to maintain the same.

4.4.1 Reasons for Taper and Solutions

At the end of the first trial analysis it was observed that the new change worked out well in the beginning and in the later stages it lead to the formation of taper during the final finish pass. This taper took a very long time to clear off to meet the tolerance, and the problem existed in almost all the production parts costing a lot of extra time and work leading to the violation of standard time.

The reasons for this taper was analyzed in detail in the shop floor with the production staff and it was decided to have a study on a part where the taper was about to start. The operator was able to judge that the part is going to have a taper in the operation, but the measures taken by the operator by reducing the speed hardly helps the process to be in control.

At one stage the author personally stopped the machine and with the help of an iron rod and a focus light, the author was able to observe that the front side of the pocket is turned well, but whereas the back side of the pocket is having a lot of problems with uneven cuts. The potential reasons for this kind of scenario may be the insert is not performing the same extent as it should do in the front and in the back side of the pocket. The material in the front side of the pocket is pushed to the back end, and this push offs and humps leads to taper formation which adds up to the extra time.

This hump and taper formation is a very common situation which takes a lot of time could be considered as a non value added activity in this operation. With the help of the iron rod when the taper was observed it was noted that the taper occurred in the middle of the part.

The total length of the pocket is about 7 inches, and with observation of a few parts it was noted that the taper starts at about 3.5 inches from the back end. The two side squaring is done in the latter stage which leads to potential hump formation near the ends and requires a lot of extra passes to remove the material. It is known for sure that the problem persists at the back end of the pocket the following two solutions were drawn to solve it.

4.4.2 Solution 1

The first modification idea is to prevent the formation of humps and taper and to make the tool insert move in both the directions. In the first pass the tool insert is made to work in the front direction and in the second pass the tool insert can be made to do the turning operation in the opposite direction. By this way there will be consistency in the process, and the inserts action can be equally felt throughout the process.

A potential implementation problem which was felt during this process to remove the taper was that in the first pass the tool insert has to go in one direction and for the second pass the insert has to move in the opposite direction with the currently used tool holder it was not able to perform this kind of work. Every time the tool holder position has to be changed to perform this action. As changing the tool holder direction for each pass would cost more time and is a much intensive process than earlier so the idea was put on hold. Discussions were held to buy a tool post which can move in both directions to meet the requirement. At the same time new ways to solve the problem was also tried to solve the problem in a fast way.

4.4.3 Solution 2

As the first idea required investment to solve the problem. An improved version of the same plan was executed in a different way in this solution. The problem was restudied and was understood that it was clear that the inserts performance is not the same throughout the pocket length of 7 inches. With the earlier study it was found that the insert can perform well for about 3-4 inches. So in the second modification plan the tool insert is made to work for 3.5 inches i.e. the middle of the pocket and later the tool insert is checked if the insert has worn out then the insert can be changed and the insert can start its action back from the middle of the pocket. By this way we can avoid any extra pass in the pocket turning operation. The simple policy of divide and conquer can be implemented to solve the problem. A lot of time can be saved by making the process work correctly in the first time.

The initial idea of removing the front squaring as well the idea of checking the insert in the middle of the operation was clubbed together and further trials were planned.

4.5 Trial 2

With a lot of experience and understanding from the first trial the second trial was planned carefully. In the second trail the above cutting method was implemented. A scrap part was used for this trial, and a pocket was made in the same position and place as per the production part specifications.

The cutting parameters like depth of cut, speed, feed were also modified based on the results of trial 1. The depth of cut of 15 thousandths per side used in the first trial was performing good in the beginning so it is planned to increase the depth of cut from 15 thousandths per side to 33 thousandths per side before it touches the interrupted cut, and once the tool starts its action in the interrupted cut the depth of cut is maintained the same as 15 thousandths as there were poor results in the first trail in this area. The feed is maintained as 10 thousandths before it touches the interrupted cut and thereafter it is made to run at a reduced feed rate of 8 thousandths.

The cutting speed is maintained the same as in earlier trial as 120 SFM before it touches the interrupted cut, and during the interrupted cut process it is maintained at 100 SFM to improve and make the process under control, and once all the shaping is done in the pocket operation it is planned to run at higher speeds of 140 SFM. This high speed would be helpful to clear off all the humps and the taper in the pocket. With the above changes the insert is also checked 2 times for each pass.

4.5.1 Results

This trail was again made for consistency i.e. how far can we go safely with the same insert without any trouble, and this trial proved successful. The pocket operation was reprogrammed according to the new cutting parameters and a simulation was done using edge cam software and the time to complete this operation was observed to be 6 hours of working time. The time taken to check the insert was not taken into consideration in this simulation. The actual operating time to complete the pocket was 10 hours in the actual machine. The change proved to be successful and it almost matched the results, when the insert change time and some common delay are added to the simulation time.

At each pass the insert conditions were studied and it was observed that there was no insert breakage in the middle of the pass, and it was observed to be normal insert wear. This good performance of the insert helped to reduce the taper thus saving time in the final pass. In this trial a lot number of re pass which was a usual scenario earlier was avoided and the turning operation followed the original program.

Some noticeable points in this operation was that during the final finishing stage there was some push offs and some hump formation in the back squaring area. The increased speed helped to reduce the taper formation in a quick way thus saving a considerable amount of time. This proved to be a good trial ground for removing taper. At the end of this trial it could be said that the pocket operation can be made in this new way at a rough average of 3 times the simulation time done in edge cam software. This is due to the extra time required to check the inserts and other usual delays in the shop floor. This new cutting path helped to reach the standard times for this operation.

4.6 Trial 3

The second trial was successful with the help of the lessons learned from the first trial. The second trial was made on a less tough material, and so the third trial was planned on a bigger size part and also on the toughest material of the product range i.e. on inconel. This trial is also a check for consistency for the new process.

New cutting parameters were tried in this trial, the depth of cut of 33 thousandths used in the previous trial before it touched the interrupted cut performed better, so in this trial the depth of cut is increased to 55 thousandths per side to save some more time. The depth of cut of 15 thousandths in the interrupted cut process worked good in the previous trials and it is maintained the same in this trial as it is a critical factor for insert failure in this operation.

The final finish pass in the process is divided into 4 passes of 10 thousandths each. There is also a check pass at the end of the 4 passes just to make sure to complete the piece with the right tolerance limit. The cutting speed of 100 SFM in the interrupted cut process worked out well and the speed of 120 SFM before the interrupted cut process also worked well. So in this trial a constant speed of 125 SFM is tried throughout the process. In the final stages of the pocket a very high speed of 200 SFM is intended to try in this process.

The lessons learned from the earlier trials proved that by increasing the speed could help in removing the taper very easily rather than reducing the speed. Unlike other trials the feed is reduced, and is maintained the same throughout the process in this trial as 8 thousandths. This is intended to make the process standardize.

As the pocket/part to be worked is a bigger size and the material to be worked is also a tougher grade. The number of insert checks has been increased from 2 to 3 times for each and every pass. This could help us to improve the consistency and could also help us to make the part production more standardized.

4.6.1 Results

The trial 3 results were very impressive as the time taken as per the simulation to complete one pass is about 12 minutes and the actual time taken was about 15 minutes. This trial was a very good proof about the working of the new cutting path method. The part was made as per the program and a lot of repass was avoided by this new cutting method. This method and parameters proved that it could work with tougher grade materials also. The insert check of 3 times in each cycle was helpful to make the inserts work better. After each trial the insert condition was studied and the wear was found normal which showed that the amount of stress given to the insert is minimized than the earlier conventional way.

4.7 Trial 4

This is the final trial in the cycle time reduction and process optimization in the cell for this process. This trial is again a check for consistency in the new process so that all the programs of different part sizes and material types can be changed. Due to the high mix, low volume environment there is variation in cycle times in the pocket turning operation every time.

This trial was planned to get an exact idea of the time saving and the process improvement done in the process. There are two machines in which the pocket turning operation can be done in the cell. So in one of the machines a production part is made and in the other machine the new process is tried for consistency in a scrap part of the same size and material as that of the production part. This could help us to gain confidence among the workers in the new pocket turning process.

The depth of cut is maintained the same as 15 thousandths in the interrupted cut and 33 thousandths before the interrupted cut process, and 4 passes of 10 thousandths depth of cut with a final finish pass. The production part is run at the conventional cutting parameters of 55 thousandths dept of cut per side and without any insert check in the middle of the process. The cutting speed is maintained the same as 120 SFM, but where as in the new process the cutting speed is maintained at 125 SFM and during the final shaping process the speed is maintained at 140 SFM.

This higher speed as discussed above would help to remove the taper and complete the part with the desired finish, with the experience from the previous trials it is completely convinced that higher the speed after shaping the pocket would help to save a lot of repass in the process. The feed rate is maintained the same as 8 thousandths throughout the process in the new cutting method. As this is a bigger size part and a tougher material the insert check is made 3 times for each pass. By this trial it is also very clear that the insert checks in the middle of the operation proved to be working.

4.7.1 Results

At the end of this final trial it is fully convinced that the process is made under control and some of the important learning's were the increased speed helped to shape the process to avoid rerun, this study was helpful for the operators to reduce time in their operation as they are used to reduce the speed in case of any humps. The conventional way of doing it is the speed is being reduced by 20% to remove the taper. The increased number of insert checks in the process helped to make the process more stabilize. The work once completed was perfect with the new insert check action and there was no reason for turning the part at the same depth of cut. With the comparison of the old and new process we can understand that the old process took 55 reruns to shape the part i.e. 55 times it is run on the same depth of cut, but in the new process it took 10 reruns to complete the pocket. The 10 reruns were made on the finishing stage to remove the humps formed due to the back squaring. The total time taken by the old process is about 45 hours just to complete the pocket. The new process took 20 hours to complete it.

4.8 Lessons Learned

In the case of humps and taper increasing the speed would help rather than slowing down. This is because if the speed is reduced we are just pushing the material or rubbing the material, we are not cutting it. A lot of re pass would lead to work hardening, and eventually it becomes much tougher to cut.

Insert wear should be carefully taken into account. If the inserts wear faster it would lead to taper formation, this would lead to a large number of reruns in the final stage. So the wear of the insert should be studied in each pass to have an idea about the stress pattern in the insert. This one improvement in turning operation helped to save almost 2 full working days in non value added time.

4.9 Sustaining Improvement

As in the past a number of improvements were made which were typically successful in the beginning and later lost its control in the long run. As the new process gained attention among the workers a standardized CNC program for different part sizes and materials types were made. The old programs were removed phase by phase new programs with the proven changes were implemented. Earlier each operator had their own customized programs and methods which led to increased run time. Now a more common program is being used by all the operators.

4.9.1 Routing Updates

As said, the entire 3rd operation in this machine is divided into 13 sub operations and the clocking time is made during the start of the operation and at the end of the operation. Clocking time is used to find out the total time used by each operator to complete his/her task. All the 13 operations in total take an average time of about 70 hours. In due course this time has increased from 70 to 90 hours and the operation has gone out of control. If there is an increase in time it would be very difficult to track the reason for the increase in extra time. It may be very difficult to say in which operation the program has gone out of control.

In order to have a control and an understanding such that which operation could have gone wrong and in what point could help us target the problem very easily. So it is decided to divide the operator clocking time into two. As observed the pocket operation takes a long time, so the clocking time is divided as before the pocket and after the pocket.

By this way even after months of production of a part, we can backdate and could identify the time taken for the pocket operation alone. This could help us to keep the process under control and the improvement is not lost in due course. The update in all the CNC programs and routing would play a commendable role to sustain the change.

4.10 Other Improvements

The improvements in the third operation in the part in the bottleneck machine helped to reduce the confusion and to meet the standards in the cell. The improvements were not stopped when an opportunity was seen in any operation. The second operation in the same bottleneck machine took a lot of time to turn down the OD.

Conventional carbide inserts were used for this operation. The depth of cut for this operation was very high and the process usually takes 7 hours to complete roughing the OD operation. The number of passes as per the program was 2 to complete the operation, but due to insert failure the number of passes required to complete it has been increased from 2 to 4 passes.

To solve this problem and to reduce the time in the operation new ideas were implemented. All new ceramic inserts were ordered for this purpose as the ceramic inserts are capable of running at high speeds thus reducing expensive machining times.

Turning is an almost ideal operation for ceramics. In general, it is a continuous machining process that allows a single insert to be engaged in the cut for relatively long periods of time. This is an excellent vehicle to generate the high temperatures that make ceramic inserts perform optimally.

The time taken to complete one single pass in the turning operation with this new insert takes only 17 minutes, but where as in the old method the time taken to complete it is about 2 hours. Although the new ceramic insert was able to perform extraordinarily well it is recommended to have an insert check in every half pass so that the process is under control and the change could be sustained. The depth of cut used for this operation is 100 thousandths per side and the feed is maintained at 10 thousandths, roughing speed at 500 SFM and the final finish speed is at 600 SFM.

This change helped to save 70% of the operation time. The usual time to complete this operation is about 7 hours and now with the new amended changes its only takes 2 hours to complete the entire operation.

4.11 Pull System

There is no consistency in the number of completed products made from the cell, as much of the process in the newly formed cell takes a lot of time than the standard time to complete the process. In order to make a consistent supply of products from the cell a pull system is implemented. All the problems in the cell which cause an inconsistent variation to meet the standard time is listed and the main cycle time reduction problems were solved.

Based on the working hours per day and the total available working time per week, and with the help of a new consistent target of products per week based on the market demand, the maximum time in the bottle neck process are fixed, and accordingly the cycle time is brought down in all the machines in the cell to meet the requirements.

As in the earlier case, before the cells are formed there is no proper control over the time limit to complete the work piece. This over a period of time with the uncertainties of a high mix low volume environment created a lot of confusions in the shop floor resulting in variations from the standard time. A pull system with visual controls which could fix a time limit for each and every operation in the cell could help in achieving the target on time. In general the operating hours of the day can be divided and a time frame is set for each variety of product and also for each type of material.

4.12 Value Stream Mapping

Value Stream Mapping (VSM) is a key component of transformation. Identifying the value stream is considered by Womack and Jones to be the important lean principle. The purpose of value stream mapping is to sort every action required to design, order, or make a specific product into three categories. (1) Those which actually creates value as perceived by the customer; (2) Those which create no value but are currently required by the system and cannot be eliminated yet; and (3) those actions which do not create value as perceived by the customer and can be eliminated.

4.12. 1 Overview

The VSM management tools create a system by which teams and management can choose the important value streams to focus improvement, identify the key improvements within those streams, schedule the work, and track, and review progress. The absence of this type of system would hinder fully realizing the benefits of value stream mapping. This is because all too often, daily production issues would take priority over the longer - term value stream improvements. The VSM management system attempts to create an agreement and framework between the value stream teams and management that the improvements are of the same importance as daily activities. It does this through a set of tools.

  • Opportunities are identified, quantified and prioritized,
  • Teams are chartered, supported by management and lean experts, with clear responsibilities and boundaries,
  • Detailed work plans are created,
  • Metrics are tracked,
  • Progress is reviewed,
  • And the system is stabilized.

4.13 Current State Map

Once a strategic value stream has been selected, a team is formed and charted to map the current state. This team should consist of person from the area being mapped, along with any support personnel (such as manufacturing engineering, design engineering, facilities, customers, or lean coordinators) that may be desired.

The objective of the current state map is to walk the process from customer to supplier in order to identify all process steps, process step metrics (cycle time, process time, and change over time, number of people required, number of shifts, reliability, inventory, and information flow. This sets the stage for creating the future state map- in the next step.

Frequently, the current state value stream map will reveal the inefficiencies of the existing production process. These inefficiencies are sometimes a result of unreliable machines, long setup times, and the use of batch and queue production processes, typically leading to large amounts of inventory between each process step and long production lead times (Seth and Gupta 2005).

The “lead time ladder” at the bottom of the value stream map attempts to quantify the amount of processing time required at each step (on the lower steps of the ladder) and the amount of lead time ahead of each process step based on the inventory ahead of each process step (the upper steps of the ladder). By summing across the lower steps and upper steps, the team can get an indication of the ratio of total production lead time. Often, this ratio is very low, indicating a high amount of non-value added activity in the system

The problems in the current cell are mapped in a value stream with the help of IGrafx flow charter software. It is a very user friendly software available for analyzing a process and for modeling the system. It helps the organization to understand the current scenario in a very visual way. From the value stream map the bottleneck situation is analyzed and the overall lead time is reduced for the product.

4.13.1 Background

The current value stream map was already designed by the management as some initial lean techniques were implemented in the cell prior to this work. The problems in the current cell are mapped in a value stream with the help of IGrafx flow charter software. It is an user friendly software available for analyzing a process and for modeling the system. It helps the organization to understand the current scenario in a visual way.

The changes and improvements made in this work helped to achieve the targets in the future state map by reducing the lead time. The new techniques used in this work were updated in the current state value stream to make the journey of lean continue to achieve the ideal situation. With the help of the current value stream map the need for throughput increase, quality and delivery time is understood.

The reasons for the gap between the current state and the future state map are that there is a Push system with WIP built up between each process in the shop floor. The plans based on MRP forecasts are not ideal scheduling rule for queues. One of the other important points which should be noted is that the process is not driven by the customer, and batch processing is inflating the lead times. There is a lot of scope for improving the quality of products in terms of rework to achieve perfection. The flow of the parts is not smooth between the processes and there is delay due to transportation.

4.14 Future State Map

The future state map shows the first evolution of waste removal. It ideally represents a chain of production where the individual processes are linked to the customers either by continuous flow or pull, and each process gets as close as possible by producing only what the customer needs, and when they need it.

It is recommended that the future state map should be created by the same team that created the current state map, and it is usually done within a day of creating the current state map so that the team does not forget the learning from the current state.

Value stream improvement process is a never ending cycle. Therefore, the team developing the future state map should try to achieve the ideal state; the first generation of future state map will often assume that the existing product design, and existing machinery and technology remains the same. The team will therefore look for sources of waste not caused by these items. After the first phase of waste - removal is achieved; the team can go back and create a new current state and future state map in the spirit of continuous improvement, perhaps challenging some of the original assumptions.

The future state will likely contain numerous “kaizen bursts” or process improvements, supporting the transition to flow or pull. Some of these bursts may be perceived as simple, while others may be complex.

The new process improvements done in this work helped to reduce the setup time, improve the flow and helped reduce the cycle time were updated in the value stream map and a new current value stream map was created; this work helped to move forward to the most ideal state.

CHAPTER 5

CONCLUSION

The goal of this work is to typically develop a process design that meets customer requirements best in the "least waste way". The biggest challenge in applying lean standardized work principles in a HVLV lies in developing and educating people to accept the core values of lean standardized work. Success in implementing lean standardized work in HVLV environments lies in the active participation of an integrated cross section of people from all functional areas of the organization. If there is a way of getting people excited about lean standardization and its core principles, this would be a big boost in achieving a lean status.

It is the beliefs that focus should be shifted more too developing programs that have the ability to encourage the worker to develop interest and actively participate in any form of lean initiatives. From a consultant standpoint, there is lot that can be done to improve the performance of HVLV environments as far as reducing the chaos that is associated with them. It will be noted that operators in HVLV environments may fall into three different categories: the skilled, semi skilled and general personnel. It is an opinion that erasing or reducing the separation of skill level can go a long way in accelerating the progress of lean initiatives in the organization.

It was noted that where separation of skill exists, workers on the shop floor exhibit strong ownership of processes and this tends to impact negatively on the rest of the workforce whose interest in the particular processes is diminished.

Improving the flow and reducing variation should be secondary goals in an HVLV environment. The flow concepts shown in this work to improve the work piece flow is a very good example that would help to achieve lean status in a short period of time.

At the end of this work it should be quoted that there was a 50% reduction of non value added activities in various operations of the cell. This helped to cut the production time by a direct 2 working days. The setup time reduction work helped to initiate the workers about the various non value added activities which could be eliminated to make the process work more efficiently.

Carrying out this project was a worthwhile experience from a learning point of view, and it has revealed opportunities that can be explored to achieve better performance for HVLV environments.

References

Jay Jina, Arindham K. Bhattacharya and Andrew D. Walton. 1997. Applying lean

principles for high product variety and low volumes: some issues and

propositions. Logistics Information Management 10(1)

(Yamkelani Moyo 2004). Function - based approach to establishing standardization and

flexible work cells for high variety, low volume manufacturing.

(Niebel Benjamin), Methods, standards and work design

Peter Hines, Matthias Holweg and Nick Rich. 2004. Learning to evolve: A review of

contemporary lean thinking. International Journal of Operations & Production

Management 24(10)

Papadopoula, T.C. and Ozbayrak, M., “Leanness: experience from the journey to

date,” Journal of Manufacturing Technology Management, Vol. 16, No. 7, pp. 784-

807 (2005)

Smart Khaewsukkho. 2008 NEW APPROACHES FOR DESIGN OF HIGH-MIX LOW-VOLUME FACILITIES. Ohio state university.

Mark L. Spearman and Michel A. Zazanis 1992. Push and Pull production systems:

issues and comparisons. Operations Research 40(3)

Gerhard Plenert 1998. Focusing Material Requirements Planning(MRP) towards performance. European Journal Of Operations Research 119(1999)

Marc Gravel and Wilson L. Price 1988. Using Kanban for Job Shop Environment. International Journal of Production research 26(6)

Dinesh Seth and Vaibhav Gupta 2005. Application of value stream mapping for lean operations and cycle time reduction: an Indian case study production planning and control 16(1).

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