Techniques For Evaluating Layout Planning Computer Science Essay

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In corporate world, especially manufacturing organizations, designing the precise fit layout for the volume of production, variety and managing a smooth flow is very critical and also essential. So it's mandatory to come out with the layout planning which fits into specific type of organization. Layout planning enables the efficient utilization of machines, effective flow of work, and thereby reducing the lead time of process which in turn will enable the faster delivery of the service by the organization.

Product layout and process layout is used in discrete manufacturing industry. Each type has its own advantage and disadvantages. So selecting an appropriate design is an challenge for an organization. Decision on the design on layout is usually made by assessing the interdepartmental flow and the material handling cost. Process layout can be designed by computer programs also. Some of those are CORELAP, ALDEP COFAD and CRAFT.

To meet the targeted production level with the minimum resources, resources should be arranged strategically so that the process is balanced. This technique of balancing is called as line balancing technique. This technique ensures that the resources are used optimally and the process is smooth. Entire designing is done by calculating the cycle time, workstations required, resource utilization and drawing the required precedence relationships.

Mid-volume and mid-variety manufacturing system can benefit from group layout. These layouts subdivide machine components into subgroups such as part families and machine groups. Methods of designing GT layouts are Production Flow Analysis, Rank Order Clustering, Mathematical Programming and Clustering Method.

While designing a layout for service organizations two factors that should be kept in mind are customer contact and the line of visibility. In this report, we shall briefly discuss the significant techniques used in the evaluation of layout planning.

CHAPTER 2. LAYOUT PLANNING, TYPES AND PROCEDURES

LAYOUT

Plant layout refers to the arrangement of physical facilities such as machinery, equipment, furniture etc. within the factory building in such a manner so as to have quickest flow of material at the lowest cost and with the least amount of handling in processing the product from the receipt of material to the shipment of the finished product.

According to Riggs, "the overall objective of plant layout is to design a physical arrangement that most economically meets the required output - quantity and quality."

According to J. L. Zundi, "Plant layout ideally involves allocation of space and arrangement of equipment in such a manner that overall operating costs are minimized.

PROCESS LAYOUTS:

Process layouts, functional layouts, or job shops as they are sometimes called, are designed to accommodate variety in product designs and processing steps. If a manufacturing facility produces a variety of custom products in relatively small batches, the facility probably will use a process layout.

Process Layouts typically use general-purpose machines that can be changed over rapidly to new operations for different product designs.

Process layout

Advantages

Limitations

1.Smooth,simple, logical and direct flow lines result.

1. machine stoppage stops the line.

2. Small work-in-progress inventories should result.

2.Product design changes cause the layout to become obsolete.

3. Total production time per unit is short

3.Slowest station paces the line.

4. Material handling requirements are reduced.

4.general supervision is required.

5. Less skill is required for personnel.

5.Higher equipment investment usually results

6.Simple production control is possible.

 

7.Special-purpose equipmenet can be used.

 

PRODUCT LAYOUTS:

Product layouts, often called production lines or assembly lines are designed to accommodate only a few product designs. Such layout is designed to allow a direct material flow through the facility for products. Auto-manufacturing plants are good examples of facilities that use a product layout.

Product layout typically uses specialized machines that are set up once to perform a specific operation for a long period of time on one product. To change over these machines to a new product design requires great expense and long down times.

Product Layout

Advantages

Limitations

1. Material movement is reduced

1.Personal and equipment movement is increased

2. When a team approach is used, continuity of operations and responsibility results

2. May result in duplicate equipment

3. Provides job enrichment opportunities.

3. requires greater skill for personnel.

4.Promotes pride and quality because an individual can complete the "whole Job".

4. Requires general supervision.

5. Highle flexible; can accommodate changes in product design, product mix, and production volume.

5. May result in increased spacec and greater work-in-progress.

 

6.Requires close control and coordination in scheduling production.

CELLULAR LAYOUTS:

In cellular manufacturing (CM), machines are grouped into cells, and the cells function somewhat like a product layout island within a larger job shop or process layout. Each cell in a CM layout is formed to produce a single parts family - a few parts all with common characteristics, which usually means they require the same machines and have similar machine settings. The main advantages of using CM layout are

Machine changeovers are simplified.

Training periods for workers are shortened.

Materials-handling cost is reduced.

Parts can be made faster and shipped more quickly.

Less in-process inventory is required.

Production is easier to automate.

FIXED-POSITION LAYOUTS

Some manufacturing and construction firms use a layout for arranging work that locates the product in a fixed position and transports workers, materials, machines and subcontractors to and from the product. Missile assembly, large aircraft assembly, ship construction, bridge construction are examples of fixed-position layouts.

Fixed position layouts are used when a product is very bulky,large, heavy or fragile. The fixed-position nature of the layout minimizes the amount of product movement required.

Fixed Position Layout

Advantages

Limitations

1. By grouping products, higher machine utilization can result.

1.General supervision required.

2.Smoother flow lines and shorter travel distances are expected than for process layouts.

2.Greater labor skills required for team members to be skilled on all operations,

3. Team atmosphere and job enlargement benefits often results.

Critically dependent on production control balancing the flows through the individual cells.

4. Has some of the benefits of product layouts and process layouts; it is a compromise between the two.

4. If flow is not balanced in each cell, buffers and work-in-progress storage are required in the cell to eliminate the need for added material handling to and from the cell.

5. Encourages consideration of general-purpose equipment.

5. Has some of the disadvantages of product layouts and process layoutsl it is a compromise between the two.

 

6. Decreases the opportunity to use special-purpose equipment.

HYBRID LAYOUTS:

Most manufacturing facilities use a combination of layout types. In this type of layout, the departments are arranged according to the types of processes but the product flow through on a product layout. A classical example of a hybrid layout is the final assembly of Boeing's commercial aircraft. Although hybrids make the identification of layout types fuzzy, it is important to understand the characteristics, advantages and disadvantages of each basic type of layout.

FEATURES OF A GOOD LAYOUT

The layout of plant can be planned in a number of ways but a good layout should possess some basic characteristics, namely:

(i) There should be sufficient space for the workers as well as for the equipment to perform their functions. This will ensure smooth and continuous flow of production process.

(ii) Must provide adequate safety and security to workers against accidents or injury e.g. Provision of fire fighting equipment, first-aid boxes etc.

(iii) Sufficient gang-way space for materials, workers and semi-finished goods. This leads to increase in efficiency.

(iv) Arrangement of machines and equipment should be such that minimum material handling's necessary for low cost processing.

(v) Stores for in-process material should be provided at some convenient place i.e. not far from the place of operations.

(vi) Supervision, co-ordination and control of the activity should be effectively and easily executed.

(vii) There should be sufficient scope for making adjustments and modifications whenever any need arises i.e. the layout should be flexible.

A scientific criterion for determining a good Plant Layout:

Integration.

Cubic space utilization.

Minimum distance.

Floor.

Maximizing coordination.

Minimum flexibility.

Maximum accessibility.

Safety security.

Minimum handling.

PROCEDURES FOR LAYOUT PLANNING:

There are various procedures for layout planning, 3 of which are mentioned below. During evaluation of layout planning, these procedures play an important role as these determine the basic criteria for the evaluation techniques deployed.

1. Apple's Plant Layout Procedure

1. Procure the basic data

2. Analyse the basic data

3. Design the productive process

4. Plan the material flow pattern.

5. Consider the general material handling plan

6. Calculate equipment requirements.

7. Plan individual workstations.

8. Select specific material handling equipment.

9. Coordinate groups of related operations.

10. Design activity interrelationships.

11. Determine storage requirements.

12 Plan service and auxiliary activities.

13. Determine space requirements.

14. Allocate activities to total space.

15. Consider building types.

16. Construct master layout.

17. Evaluate, adjust and check the layout with the appropriate persons.

18. Obtain approvals.

19. Install the layout.

20. Follow up on implementation of the layout.

2. Reed's Plant Layout Procedure.

1. Analyse the product or products to be produced.

2. Determine the process required to manufacture the product.

3. Prepare layout planning charts.

4. Determine workstations.

5. Analyze storage area requirements.

6. Establish office requirements.

7. Establish office requirements.

8. Consider personnel facilities and services.

9. Survey plant services.

10. Provide for future expansion.

3. Muther's Systematic Layout Planning Procedure:F:\Vinopugazh\Official\Great Lakes\Curriculum\Trimester 2\Operations Management\Project\muther's systematic layout planning.jpg

CHAPTER 3 - EVALUATION TECHNIQUES

3.1Activity Relationship Analysis

Activity Relationship diagram shows the relationship of every department, office, or service area with every other department and area. In order to establish this relationship, we use closeness codes to "weight" the decision

Code

Definition

A

Absolutely required proximity

E

Especially important

I

Important

O

Ordinary importance

U

Unimportant

X

Closeness undesirable

A" Codes between Departments:

Restricted to massive materials movements

Used for great movements of people

Limit it to no more than eight (8) with one department

Example - raw steel storeroom to the shearing department

Figure : Activity relationship Chart activity

E" Codes between Departments:

Used if there is any doubt that it is an "A"

Much material or people movement, but not all at one time

Example- restrooms, or break rooms

I" & "O" Codes between Departments:

Used when some level of importance is desired

Some consultants omit these codes, however, use them on the first few layout designs

U" Codes between Departments:

Useful because they tell us that no activity or interface is needed

Indicates that these departments can be placed far away from each other

"X" Codes between Departments:

As important as "A" codes

The opposite of "A" codes

Indicates less than desired closeness

Example- Welding next to flammables, or paint areas near grinding operations

Relationship or Affinity Code :

The relationship or affinity code states the desired degree of closeness between two activity centers.

A rule of thumb is that you should not exceed the following percentages for a given code: A - 5%, E - 10%, I - 15%, and O 25%.

The total number of relationships, N between all possible pairs of work centers (n) can be determined by: N = n (n-1) / 2

For example with 25 different departments or work centers there will be N = 25 (25-1) / 2 = 300 relationship codes.

The facilities designer should have no more than 15 A relationships (300 x 5% = 15).

WORKSHEET

The worksheet can serve as an interim step between the activity relationship diagram and the dimensionless block diagram

Step-by-step procedure for the worksheet

1. List all the activities down the left hand side of a sheet of paper.

2. Make six columns to the right of the activity column and title them A,E,I,O,U, and X (relationship codes).

3. Taking one activity at a time, list the activity numbers under the proper relationship codes. Be sure each activity number appears on each line.

DIMENSIONLESS BLOCK DIAGRAM

The dimensionless block diagram is the first layout attempt.

It will be the basis for the master layout and plot plan.

Step by step procedure

1. Cut up a sheet of paper into 2 x 2 inch squares.

2. Place an activity number in the center of each square.

3. Taking one square at a time, make a template for that activity by placing the relationship codes in the following positions: A relationship in the top left hand corner. E relationship in the top right hand corner. I relationship in the bottom left corner. O relationship in the bottom right corner. U relationships omitted. X relationship at the center under the activity number.

4. Each activity center is represented by one square.

5. Once the templates are ready, you place them in the arrangement that will satisfy as many codes as possible.

All As should have a full side touching. All Es should have at least one corner touching. No X relationship should be touching.

FLOW ANALYSIS

Flow analysis is now performed on the dimensionless block diagram.

For Example, Start with receiving and show the movement of materials to stores, to fabrication, to welding, to paint, to assembly and pack out, to the warehouse, and to shipping We would not want shipping or receiving to be located in the middle of the building.

We would not want material to jump over one or more departments

SOFTWARE PACKAGES

Software packages are available to aid facility planners in achieving solution to a layout problem.

FactoryPLAN via a series of interactive menus and on-screen prompts assists the user in arranging a layout based on the closeness ratings between pairs of activity centers or work areas.

The analysis is performed in 3 steps:

1. Create a data file containing activity center names.

2. Once the list is complete, the user is prompted to enter the affinity code and reason code between pairs of work centers.

3. The third step of the analysis is the generation of the activity relationship chart and the flow path diagrams.

The software will generate an optimized layout based on the data that are entered by the user

ACTIVITY RELATIONSHIP FACTORS

Do they share common utilities?

Are they part of a common process?

Does one department supply the other?

What are the management and personnel common between the departments?

Is the process in one department harmful to the other?

NON-FLOW FACTORS

Usually collected through interviews with the operators, management, etc.

These areas include:

Maintenance

Tool storage

Lunchroom

Restrooms

Offices

Use the same charting/weighting concept

RELATIONSHIP DIAGRAMS C:\Users\Vinoth Kumar\Desktop\rd.jpg

Relationship diagrams positions activities spatially.

Proximities are typically used to reflect the relationship between pairs of activities.

A sample of relationship diagram is shown in the figure.

3.2. LINE BALANCING

The analysis of production lines is the central focus of the analysis of product layouts. The product design and the market demand for products ultimately determine the technological process steps and the required production capacity of production lines. The number of workers, attended and unattended machines, and tools required to provide the market demand must then be determined, the information is provided by line balancing.

Line Balancing.

Line balancing is an analysis process that tries to equally divide the work to be done among workstations so that the number of workers or workstations required on a production line is minimized. The table below summarizes some of the terms often used in line balancing.

Terminology of Production Line Analysis

Tasks - Elements of work.

Task Precedence - The sequence or order in which tasks must be preformed. Precedence for each task is known from a listing of the tasks that must immediately precede it

Task Times - The amount of time required for a well-trained worker or unattended machine to perform a task. Task times are usually expressed in minutes.

Cycle Time - The time in minutes between products coming off the end of a production line.

Productive time per hour - The number of minutes in each hour that a workstation is working on the average. A workstation may not be working because of such things as lunch, personal time, breakdowns, start-ups, and shutdowns.

Workstation - Physical location where a particular set of tasks is performed. Workstations are usually of two types: a manned workstation containing one worker who operates machines and/or tools, and an unmanned workstation containing unattended machines like robots.

Work center - A physical location where two or more identical workstations are located. If more than one workstation is required to provide enough production capacity, they are combined to form a work center.

Number of workstation working - The amount of work to be done at a work center expressed in number of workstations. 28 hours of work at a work ceneter during an 8-hour shift would be equivalent to 28/8 ot 3.5 workstations working.

Minimum Number of Workstations - The least number of workstations that can provide the required production, calculated by:

Sum of all task times Sum of all task times x Demand Per hour

------------------------------- = -------------------------------------------------------------------

Cycle Time Productive time per hour.

Actual number of workstations - The total number of workstations required on the entire production line, calculated as the next higher integer value of the number of workstations working

Utilization - The percentage of time that a production line is working. This is usually calculated by

Minimum number of workstations

--------------------------------------------------- x 100

Actual number of workstations

Line - Balancing Procedures:

1. Determine which tasks must be performed to complete one unit of a particular product.

2. Determine the order or sequence in which the tasks must be performed.

3. Draw a precedence diagram. This is a flowchart wherein circles represent tasks and connecting arrows represent precedence.

4. Estimate task times.

5. Calculate the cycle time.

6. Calculate the minimum number of workstations.

7. Use one of the heuristics to assign tasks to workstations so that the production line is balanced.

Production lines have workstations and work centres arranged in sequence along a straight or curved line. A workstation is a physical area where a worker with tools, a worker with one or more machines, or an unattended machine like a robot performs a particular set of tasks. A work center is a small grouping of identical workstations, with each work station performing the same set of tasks. The goal of analysis of production lines is to determine how many workstations to have and which tasks to assign to each workstation so that the minimum number of workers and minimum amount of machines are used to provide the required amount of capacity.

Let us assume that we need a product to come off the end of a production line every 5 minutes; then the cycle time is 5minutes. This means that there must be a product coming out of every workstation every 5minutes or less. If the time required to do the tasks at a workstation were 10minutes, then two workstations would be combined into a work centre such that two products would be coming out of the centre every 10minutes, or equivalent of one every 5minutes. On the other hand, if the amount of work assigned to a workstation is only 4minutes, that workstation would work 4minutes and be idle for 1minute, It is practically impossible to assign tasks to workstations such that each one produces in exactly 5minutes. In line balancing, our objective is to assign tasks to workstations such that there is little idle time. This means assigning tasks to workstations and work centres such that a finished product is completed very close to but not exceeding the cycle time.

Line balancing Heuristics:

Research had proved the use of linear programming, dynamic programming and other mathematical models to study line balancing problems. However large problems cant be solved using this methods. Heuristic methods or methods based on simple rules, have been used to develop good solutions to these problems - not optimal solutions, but very good solutions. Among these methods are the

(i) Incremental Utilization Heuristic and

(ii) Longer-Task-Time (LTT) Heuristic.

(i) Incremental Utilization Heuristic:

The incremental utilization Heuristic simple adds tasks to a workstation in order of task precedence one at time utilization is 100 percent or is observed to fall. Then this procedure is repeated at the next workstation for the remaining tasks.

The incremental utilization heuristic is appropriate when one or more task times is equal to or greater than the cycle time. An important advantage of this heuristic is that it is capable of solving line-balancing problems regardless of the length of task times relative to the cycle time. Under certain circumstances, however, this heuristic creates the need for extra tools and equipments. If the primary focus of the analysis is to minimize the number of workstations or if the tools and equipments used in the production line are either plentiful or inexpensive, this heuristic is appropriate.

Figure 1: Steps in Incremental Utilization Heuristics.1-s2.0-S0305054812000998-gr8.jpg

(ii) Longer-Task-Time (LTT) Heuristic

The longest-task-time heuristic adds tasks to a workstation one at a time in the order of task precedence. If a choice must be made between two or more tasks, the one with the longest task time is added. This has the effect of assigning as quickly as possible the tasks that are the most difficult to fit into a solution. Tasks with shorter times are the nssaved for fine-tuning the solution. This heuristic follows the steps as shown in the figure 2.

The conditions of the longest-task-time heuristic's use are:

1. It can be used only when each and every task time is less than or equal to the cycle time.

2. There can be no duplicate workstations.

Because there are no duplicate workstations, the amount og tools and equipment required is low. This restriction also reduces the flexibility, however. If each and every task time is less than or equal to the cycle time, and if the primary focus of the analysis of production lines is minimizing the number of workstations and the amount of tools and equipment required, then this heuristic would be appropriate. Fortunately, there are modifications of this heuristic that allows task times to be greater than the cycle time. For example, th POM software Library, allows the use of a modified longest-task-time heuristic that permits times to be as much as twice the cycle time.

Figure 2 : Steps in Longest-Task-Time Heuristics.longest - task time heuristic -.jpg

The two line balancing heuristics discussed here are representative of a large group of such heuristics. So which one should we use in analysing a particular time-balancing problem? In some circumstances, we may not have a choice because only one heuristic may accommodate the conditions that fit our line-balancing problem. For example, if one or more task times are equal to or greater than the cycle time, we may have to choose the incremental utilization heuristic. At other times, if the use of more than one heuristic seems appropriate, we would be advised to use several line-balancing heuristics on the same problem to determine which one yields the best solution.

4. CONCLUSION:

Each and every manufacturing and service facility will have different types of layout, owing to its nature of construction and ease of operations. Determining the exact layout during the planning stage facilitates the proper and profitable function of the plant. This determination by both quantitatively and qualitatively means is influenced by different evaluation techniques, many of which we have been discussed in detail in this report. Evaluation of all layouts in the planning stage will result in higher efficiency, increased profits, proper forecast of cost and manpower and eventually its savings.

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