The topic of reducing cycle time

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Chapter II

Literature Review

This chapter reviews previous research and theories that cite the topic of reducing cycle time, which is relevant to lean concepts and simulation. The topic of this chapter are below.

  1. Product cycle time improvement
  2. Principles of lean
  3. Simulation Modeling
  4. Review literature
  5. Research Frame work

In the past, most research focused on the development of dispatching and releasing rules to improve cycle time. With less restriction on the equipment, batch size reduction would be another alternative to shorten cycle time which considered setup time and capacity constraints to solve the batch size problem. Some concepts use lean manufacturing to eliminate waste and non-value-added time. Some scholars used simulation methods to do the cycle time analysis by combining simulation and computer algorithms to search for the batch size for each individual product in a multi-product environment. Most of the past studies regarding batch size concentrated on traditional manufacturing environments, with fixed demands and production rates. The primary goal of this framework was to minimize the total production cycle time.

2.1 Product cycle time improvement

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Cycle time reduction involves identifying and implementing more efficient ways to do things. Reducing cycle time requires eliminating or reducing non-value-added activities, which is defined as any activities that do not add value to the product.

Examples of non-value-added activities in which cycle time can be reduced or eliminated include repair due to defects, machine set-up, inspection and schedule delays. Explained by Kivenko (1994)

1.2.1 The element of manufacturing lead time can be further divided into:

  1. Queue time before processing.
  2. Set up time.
  3. Run (processing) time.
  4. Waiting time after processing.
  5. Move time.

There is an important follow-on effect to reducing the frequency of set-ups. Just as introducing computer integrated manufacturing removes operator involvement and operator skills atrophy (Coble and Bohn, 1997), decreasing set-up frequency drives set-up proficiency down. The danger is an ever downward spiral of reducing set-up frequency and increasing batch size. Even when the operator element is reduced or replaced in "flexible" manufacturing systems, the performance is in some cases worse than the manual system. Rather than producing more variety of lower volume, these systems often produce less variety of higher volume (Meyer, 1993). That is to say, set-up time is reduced and batch size increased. (Youngman, 2003)

2.1.2 Bottleneck

A bottleneck is the resource that constrains or limits the output of the overall operating unit. In a line flow process design, the bottleneck is the process stage with the highest cycle time. In a job shop or batch process design, the bottleneck can be more difficult to identify. Certain pieces of equipment and/or specific people may be used at multiple process stages. (Prasad, 1995)

2.1.3 BATCH SIZE

Page (2003) explained "batch" is the term normally used for the quantity of a particular product to be made all in one go. An entire batch of work might take several days to complete. Traditionally, this would involve the batch going through one operation at a time, and it wouldn't be allowed to go to the next operation until the entire batch quantity had gone through the current stage of processing. The batch is kept together like this to allow the inspector a chance to compare the components from the beginning, middle and end of the batch to specification all at the same time. It is easy to keep WIP on process.

Schragenhein and Dettmer (2000) said that increasing batch size affects work-in-process inventory levels, manufacturing lead time, local and global safety time issues, and finished goods stock levels by increasing them. Increased batch size affects quality and throughput by decreasing them. However, well thought-out changes to critical batch sizes can hugely change these parameters within a process. It does so not by speeding up machine or process time, but by reducing idle time when work sits on the workshop floor (or office desk, or computer hard disk) between process points after reduce batch size found that smaller batches can move much faster.

Batch size issues at a formal level have tended to be treated as a trade-off analysis or optimization between set-up or ordering costs, storage and holding costs, and stock out costs (Jaber and Bonner, 1996). The resultant optimal batch size is known as the Economic Order Quantity or EOQ. (Trigeiro, Thomas and Jo, 1989). However, while most everyone knows about Economic Order Quantity, very few people ever bother to calculate it. There is a far more fundamental driver to batch sizing. The fundamental driver is reducing "non-productive" set-up time, and maximizing "productive" processing or machine time. There are usually very strong measurement incentives - timesheets - which cause workshop floor personnel to minimize set-up time and maximize process time. The easiest way to do this is to decrease the frequency of set-ups by increasing the batch size. There is, however, another more subtle and less often expressed driver at work as well. (Spearman, 1996)

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Some considerations when choosing the number for batch size: Koskela (1992)

  • If the number is too large, the amount of queue space taken up on both ends of the link becomes excessive. Messages take up queue space when they are not committed, and cannot be removed from queues until they are committed.
  • If there is likely to be a steady flow of messages, you can improve the performance of a channel by increasing the batch size. However, this has the negative effect of increasing restart times, and very large batches may also affect performance.
  • If message flow characteristics indicate that messages arrive intermittently, a batch size of 1 with a relatively large disconnect time interval may provide better performance.
  • Even though nonresistant messages on a fast channel do not wait for a sync point, they do contribute to the batch-size count.

Lean principles can be used to improve productivity driven by workers, based on their knowledge of the work and equipment, with the goal of increasing value added work (Holly and Gaskins, 2004)

2.1.4 Cycle time is linked to other aspects of Lean

  1. Continuous improvement leads to step improvements in cycle time once takt times come down for all steps.
  2. Standardized work is a key to making cycle time work on the floor.

2.2 Principles of Lean

Lean was started at Toyota because they wanted a clear definition of customer value. It acknowledges that all value is created by some process. Therefore, Lean can develop processes that are waste or "muda" is defined by Shoichio Toyoda, founder of Toyota, as "anything other than the minimum amount of equipment, materials, parts, space and worker's time which are absolutely essential to add value to the product." Lean is a methodology that is used to increase speed and reduce the cost of any process by eliminating waste. A Lean initiative is to give a simple way of understanding the impact of efforts through planning improvement activities, checking the results and making appropriate adjustments. In addition, Lean tools help to determine the financial impact of improvements such as increasing inventory turns, reducing work-in-process and reducing changeover time. (Ohno, 1990)

The Toyota Production System (TPS) identifies seven forms of waste in manufacturing, which Ohno calls "The Seven Deadly Wastes." The wastes can be classified as follows:

  1. Overproduction : making more than needed
  2. Inventory: stuff laying around (often a symptom of another waste)
  3. Defects: Time spent fixing defects, including defect that get thrown away and the time make the product correctly
  4. Waiting: Waiting time for doing something..
  5. Over processing: making to a higher quality standard than expected by the customer.
  6. Transportation: excess moving of material.
  7. Motion: inefficient people movement.

Lean Manufacturing is an operational strategy oriented toward achieving the shortest possible cycle time by eliminating waste. It is derived from the Toyota Production System and its key thrust is to increase the value-added work by eliminating waste and reducing incidental work. The technique often decreases the time between a customer order and shipment, and it is designed to radically improve profitability, customer satisfaction, throughput time, and employee morale. ( Michael and Kentaro, 1998)

2.2.1 Characteristics of a Leans process

The characteristics of Lean process assist to flow of process run as continuously as possible with a rapid cycle time. The precise description of each work station activity specifying cycle time, take-time, the work sequence of specific tasks, and the minimum inventory of parts on hand needed to conduct the activity (Stenzel, 2007).

The characteristics of lean processes are:

  • Make to order
  • Single-piece production
  • Just-In-Time materials/pull scheduling
  • Short cycle times
  • Quick changeover
  • Continuous flow work cells
  • Compressed space
  • Multi-skilled employees
  • High first-pass yields with major reductions in defects

2.2.2 Lean tools

Lean manufacturing tools can resolve many problems in production lines. In This chapter we will focus on lean tools that concern this study by using standard work and rapid changeover.

2.2.2.1 Standard Work: DEFINITION

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The definition of standard work was explained by Jeff Hajek (2009) a common term given to any collection of time value. The format of the data is as tables or worksheets. The data can be utilized in conjunction with calculated cycle time but cannot decide the operating parameters for a plant providing a lean manufacturing environment. Standard Work has three main components:

  1. It is balanced to the takt time.
  2. It specifies standard work-in-process (WIP).
  3. It defines the sequence of operations for a single operator.

The precise description of each work activity specifying cycle time, task time, the work sequence of specific tasks, and the minimum inventory of parts on hand needed to conduct the activity. Henry Ford said that " If you think of standardization as the best that you know today, but which is to be improved tomorrow - you get somewhere. But if you think of standards as confining, then progress stops."

Somnath Kundu (2008) studied the application of design automation to reduce cycle time of hydro turbine design. Because of the rapid growth in the demand for electricity and increased credit risks in the financial markets, there is a strong business deriver ? To reduce the design to commission cycle time of process. The first step that is important is standardization. The key to success for any design automation project is standardization: The standardization of the product structure and design practice and automating the same has given the user an edge over its competitors.

Front Line Professionals (2001): said that Standardized work is one of the most powerful lean tools. Professionals that do the work on the floor can often best document the current best practices. Establishing standardized work relies on

Collecting and recording data as it actually happens. Such standardized practices serve as the baseline for kaizen or continuous improvement. As the standard is improved, the new standard becomes the baseline for further improvements, and so on. Standardizing the work adds discipline to the culture, an element that is frequently neglected but essential for lean transformation. Standardized work also supports audits, promotes problem solving, and involves team members in developing safety guards (poka-yokes). All of the standardization efforts need to be surrounded and embedded in the culture of the lean organization.

2.2.2.2 Takt time: DEFINITION

Takt Time comes from a German word 'takt' meaning rhythm. The definition of Take time was explained by Jon Miller ( 2003 ) is a one of the key principles in a Lean Enterprise. Takt Time sets the 'beat' of the organization in synch with customer demand. Takt Time balances the workload of various resources and identifies bottlenecks.

Takt Time is a simple concept, yet counter-intuitive, and often confused with cycle time or machine speed. In order for manufacturing cells and assembly lines to be designed and built Lean, a thorough understanding of Takt Time is required. Takt Time is used to match the pace of work to the average pace of customer demand. Takt is not a number that can be measured and is not to be mistaken with cycle time, which is the time it takes to complete one task. Cycle time may be less than, more than, or equal to Takt Time.

The formula for Takt time is:

Takt time = Net Available Time per Day Customer Demand per Day

2.2.2.3 Rapid change overtime

SMED (single minute exchange of die) is a theory and tools set of techniques that make it possible to set up or change overtime equipment. Change overtime is the time from when the last goods item/piece comes off a machine or out of a step until the first good item/piece of the next service/product is made. Changeover time includes set up, warm up, trial run, adjustment, first-piece inspection, etc. Changeover Time is the amount of time it takes to change over equipment/programs/ files/documents from the end of the previous step to the beginning of the current step. Changeover is the total of Set-up time and Run-up time. Changeover can be the time and make the difference between a good product and a good product at the right speed. If can reduce change overtime, can reduce cycle time of process as well. Jaikumar (1986) while Dave (1996) need to reduce machinery change overtime because have two biggest wastes are overproduction and WIP queues. There is one "real" issue that must be overcome in order to greatly reduce batch size without increasing cost. The component of change overtime following list:

  1. Internal setup takt that can be performed only while the machine is shut down.
  2. External set up takt that can be performed while the machine is running

2.2.2.4 Effects of change overtime Reduction

  1. Batch size can be reduced.
  2. Help to reduce inventory.
  3. Increase the capacity on bottleneck equipment.
  4. Help to eliminate the setup scrap

2.2.3 Traditional vs. Lean Manufacturing

A key difference in Lean Manufacturing is that it is based on the concept that can be driven by real customer demand. Instead of producing what you hope to sell; Lean Manufacturing can produce what your customer wants with shorter lead times. Instead of pushing product to market, it's pulled there through a system that's set up to quickly respond to customer demand.

2.2.3 Traditional vs. Lean Manufacturing

A key difference in Lean Manufacturing is that it is based on the concept that production can and should be driven by real customer demand. Instead of producing what you hope to sell; Lean Manufacturing can produce what your customer wants with shorter lead times. Instead of pushing product to market, it's pulled there through a system that's set up to quickly respond to customer demand.

2.3 Simulation Modeling

Simulation is the dynamic representation of a real system by a computer model which behaves in the same manner as the system itself. In the manufacturing industry, simulation represents the dynamic manufacturing process in the computer model, and shows graphically and over simulated time the effects of a potential scenario to support the decision-making process. Bielunska and Gun (2002).A schematic information flow of manufacturing simulation is shown in Figure 2-4.

Manufacturing simulation converts the detailed operational data into the management information. It enables various scenarios to be tested without large investment on setting up a pilot line or disrupting the production. It eliminates the common problem in manufacturing industry: bottlenecks

2.3.1 Application Areas of Manufacturing Simulation.

In the manufacturing companies, managers and engineers are able to evaluate the performance of manufacturing process under several different sets of condition to identify the proper layout and operational policy. That can contribute to achieve better production performance such as high throughput, short lead time, low work-in-process (WIP), and high resource utilization. Instance of the application of manufacturing simulation by the current users are:

Implementing new manufacturing concept

Imperfect design from the introduction of this concept can cause the production output reduction; however, the potential problems can be identified by simulation. The re-layout project of National Semiconductor Malaysia studied in one process Tung, Wang and Sun(1995) by using simulation is the good instance. Before application of new layout, the dynamics of simulation benefit indentified the potential problems, helped the involving department to understand the process of new layout, and saved 5% on the capital investment.

Improving existing process; the existing process need to be adapted to handle the new requirement when new products are launched or demand pattern becomes different from the past. Simulation is very effective to study the impact of modification to smooth the change. Motorola Malaysia was reported the saving to be US$250,000 equivalent of capacity gain within one year after the company use simulation to study the product mix and batch size to improve the setup time and machine assist time Yong (1994).

Reducing Work-In-Process (WIP); a high WIP is often built because of unexpected breakdowns, leading to a high inventory cost, slow material flow, and inflexible product mix. Simulation is used to analyze the sensitivity of WIP levels. Flextronics Singapore used simulation to study the most economical way to reduce WIP and the result reported at more than 50% reduction, significantly improved others company performance such as inventory, delivery performance Chang and Kum (1994).

Product timing: Simulation is superb for deciding the order loading sequence and operation timing. It was arranged a systematic instruction to the product shop level. It is easy to find this simulation on a daily basis to generate timing instructions to the operations of PCB Manufacturing CIMTEX (1994) at Digital Singapore. These also greatly reduced WIP and stabilized operations.

2.3.2 Core leaning concept and Simulation

To arrange the instruction learning by following a description of how simulation is being use since it increasing learning perception. Along predictive simulation leaning model. Learning period is greatly reduced and eliminates waste. Majority companies have been using simulation to find solution to creating value or product improvement process. Simulator process created an idea tool for developing alternative process scenarios to assist the performance of current operation inefficiencies. Furthermore, the role model to eliminate through the leaning implementation.

2.4 Review of related studies.

2.5 Researching Model Work:

The core concepts of the model are a type of intermediate theory that attempt to connect to all aspect of inquiry (e.g., problem investigation, purpose, literature review, methodology data collection and analysis). This model is able to create the maps that give coherence to empirical inquiry. Due to the models are potential similarity to empirical inquiry, they take different forms depending upon the research question or problem in figure 2-5.

2.5.1 The component of the cycle time decision elements:

  • Processing time: timing that the thing is being worked on by an operation. To studying this matter seriously by using tool; a stopwatch from camera - following unit being processed by one operator - all the way through the process (or sub-process).
  • Waiting time: timing between sub-process that the thing gets shuffled around or sits around waiting for someone to work on it. As well as knowing "Waiting & Transportation Time" or "Inventory/Transpiration Time. In this case have effect from waiting time in each work station and wait time of part of car model.
  • Change overtime; the amount of time takes to change over the making or program from the end to previous step to the current step. If you have to takes always will effect with total cycle time.
  • Since a batch size of one has been unpracticed the goal is in improve productivity periodically. The ultimately reduces inventory carry costs, work in progress, and cycle time. Also this enabling the company operates profitably at lower margins.

2.5.2 The meaning of element of the determination in cycle time reduction.

  • Productivity: From studying shown way to improve productivity by reduce cycle time in order to protect loss sale, reduce cost in manufacturing and increase customer satisfaction.
  • A cost incurred by a business when it is unable to fill an order and must complete it later. A back order cost can be discrete, as in the cost to replace a specific piece of inventory, or intangible, such as the effects of poor customer service.
  • On time deliver: one of the reason why is company need to reduce cycle time. The actual measurement will be the percentage of units you produce that meet your customer's deadline. Isn't it interesting that it has to do with the customer's deadline.

In this chapter, the researcher has discussed relevant concepts in cycle time reduction by use simulation to optimal batch size as well as proposing the concept framework for this research project. In the next chapter, the researcher will explain the methodological approach this project.