Plant or facility Plant or facility LayoutLayout

Dr A R M Harunur RashidDr A R M Harunur Rashid Room FAB405Room FAB405

What is plant layout?What is plant layout? According to Moore According to Moore ““Plant Plant

layout is a plan of an optimum layout is a plan of an optimum arrangement of facilities arrangement of facilities including personnel, operating including personnel, operating equipment, storage space, equipment, storage space, material handling equipment and material handling equipment and all other supporting services all other supporting services along with the design of best along with the design of best structure to contain all these structure to contain all these facilities”.facilities”.

CLASSIFICATION OF CLASSIFICATION OF LAYOUTLAYOUT

1. Process layout1. Process layout

2. Product layout2. Product layout

3. Combination layout3. Combination layout

4. Fixed position layout4. Fixed position layout

5. Group layout5. Group layout

Process layoutProcess layout In process layout the arrangement of facilities In process layout the arrangement of facilities are grouped together according to their are grouped together according to their functions. A typical process layout is shown in functions. A typical process layout is shown in Fig. Fig.

Process layout is normally used when the Process layout is normally used when the production volume is not sufficient to justify a production volume is not sufficient to justify a product layoutproduct layout

Usually the paths are long and there will be Usually the paths are long and there will be possibility of backtracking.possibility of backtracking.

Product LayoutProduct Layout The product layout is selected when The product layout is selected when

the volume of production of a product the volume of production of a product is high such that a separate is high such that a separate production line to manufacture it can production line to manufacture it can be justified.be justified.

In this type of layout, machines and In this type of layout, machines and auxiliary services are located auxiliary services are located according to the processing sequence according to the processing sequence of the product.of the product.

Combination LayoutCombination Layout A combination of process and product A combination of process and product

layouts combines the advantages of layouts combines the advantages of both types of layouts.both types of layouts.

A combination layout is possible A combination layout is possible where an item is being made in where an item is being made in different types and sizes. Here different types and sizes. Here machinery is arranged in a process machinery is arranged in a process layout but the process grouping is layout but the process grouping is then arranged in a sequence to then arranged in a sequence to manufacture various types and sizes manufacture various types and sizes of products.of products.

Combination LayoutCombination Layout

Fixed Position LayoutFixed Position Layout This is also called the project type of layout. This is also called the project type of layout. In this type of layout, the material, or major In this type of layout, the material, or major

components remain in a fixed location and components remain in a fixed location and tools, machinery, men and other materials tools, machinery, men and other materials are brought to this location. are brought to this location.

This type of layout is suitable when one or a This type of layout is suitable when one or a few pieces of identical heavy products are few pieces of identical heavy products are to be manufactured and when the assembly to be manufactured and when the assembly consists of large number of heavy parts, the consists of large number of heavy parts, the cost of transportation of these parts is very cost of transportation of these parts is very high.high.

Group Layout (or Cellular Group Layout (or Cellular Layout)Layout) Group layout is a combination of the product Group layout is a combination of the product

layout and process layout. It combines the layout and process layout. It combines the advantages of both layout systems. If there are advantages of both layout systems. If there are m-machines and n-components, in a group m-machines and n-components, in a group layout (Group-Technology Layout), the m-layout (Group-Technology Layout), the m-machines and n-components will be divided machines and n-components will be divided into distinct number of machine-component into distinct number of machine-component cells (group) such that all the components cells (group) such that all the components assigned to a cell are almost processed within assigned to a cell are almost processed within that cell itself. Here, the objective is to that cell itself. Here, the objective is to minimize the intercell movements.minimize the intercell movements.

In-group technology layout, the objective is to In-group technology layout, the objective is to minimize the sum of the cost of transportation minimize the sum of the cost of transportation and the cost of equipments. So, this is called as and the cost of equipments. So, this is called as multi-objective layout.multi-objective layout.

The basic aim of a group technology layout The basic aim of a group technology layout is to identify families of components that is to identify families of components that require similar of satisfying all the require similar of satisfying all the requirements of the machines are grouped requirements of the machines are grouped into cells. Each cell is capable of satisfying into cells. Each cell is capable of satisfying all the requirements of the component all the requirements of the component family assigned to it.family assigned to it.

A typical process layout is shown in FigA typical process layout is shown in Fig

DESIGN OF PRODUCT DESIGN OF PRODUCT LAYOUTLAYOUT Assembly lines are a special case of product Assembly lines are a special case of product

layout.layout. A more-challenging problem is the A more-challenging problem is the

determination of the optimum configuration of determination of the optimum configuration of operators and buffers in a production flow operators and buffers in a production flow process. A major design consideration in process. A major design consideration in production lines is the assignment of production lines is the assignment of operation so that all stages are more or less operation so that all stages are more or less equally loaded.equally loaded.

LINE BALANCINGLINE BALANCING The total work to be performed at a workstation The total work to be performed at a workstation

is equal to the sum of the tasks assigned to is equal to the sum of the tasks assigned to that workstation. The line-balancing problem is that workstation. The line-balancing problem is one of assigning all tasks to a series of one of assigning all tasks to a series of workstations so that each workstation has no workstations so that each workstation has no more than can be done in the workstation cycle more than can be done in the workstation cycle time, and so that the unassigned (idle) time time, and so that the unassigned (idle) time across all workstations is minimized.across all workstations is minimized.

The problem is complicated by the relationships The problem is complicated by the relationships among tasks imposed by product design and among tasks imposed by product design and process technologies. This is called the process technologies. This is called the precedence relationship, which specifies the precedence relationship, which specifies the order in which tasks must be performed in the order in which tasks must be performed in the assembly process.assembly process.

The steps in balancing an The steps in balancing an assembly lineassembly line1. Specify the sequential relationships among 1. Specify the sequential relationships among

tasks using a precedence diagram.tasks using a precedence diagram.

2. Determine the required workstation cycle time 2. Determine the required workstation cycle time C, using the formulaC, using the formula

3. Determine the theoretical minimum number of 3. Determine the theoretical minimum number of workstations (Nt) required to satisfy th workstations (Nt) required to satisfy th workstation cycle time constraint using the workstation cycle time constraint using the formulaformula

4. Select a primary rule by which tasks are to be 4. Select a primary rule by which tasks are to be assigned to workstations, and a secondary rule assigned to workstations, and a secondary rule to break ties.to break ties.

5. Assign tasks, one at a time, to the first 5. Assign tasks, one at a time, to the first workstation until the sum of the task times workstation until the sum of the task times is equal to the workstation cycle time, or no is equal to the workstation cycle time, or no other tasks are feasible because of time or other tasks are feasible because of time or sequence restrictions. Repeat the process sequence restrictions. Repeat the process for workstation 2, workstation 3, and so on for workstation 2, workstation 3, and so on until all tasks are assigned.until all tasks are assigned.

6. Evaluate the efficiency of the balance 6. Evaluate the efficiency of the balance derived using the formuladerived using the formula

7. If efficiency is unsatisfactory, rebalance 7. If efficiency is unsatisfactory, rebalance using a different decision rule.using a different decision rule.

ILLUSTRATION :ILLUSTRATION : The MS 800 car is to be assembled on The MS 800 car is to be assembled on

a conveyor belt. Five hundred cars a conveyor belt. Five hundred cars are required per day. Production time are required per day. Production time per day is 420 minutes, and the per day is 420 minutes, and the assembly steps and times for the assembly steps and times for the wagon are given below. Find the wagon are given below. Find the balance that minimizes the number of balance that minimizes the number of workstations, subject to cycle time workstations, subject to cycle time and precedence constraints.and precedence constraints.

SOLUTION:SOLUTION:1.1. Draw a precedence diagram as follows:Draw a precedence diagram as follows:

2. Determine workstation cycle time. Here we 2. Determine workstation cycle time. Here we have to convert production time to seconds have to convert production time to seconds because our task times are in secondsbecause our task times are in seconds

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3. Determine the theoretical minimum number 3. Determine the theoretical minimum number of workstations required (the actual number of workstations required (the actual number may be greatermay be greater))

4. Select assignment rules.(a)Prioritize tasks in order of the largest number of following tasks:

Our secondary rule, to be invoked where ties exist from our primary rule, is

(b) Prioritize tasks in order of longest task time. Note that D should be assigned before B, and E assigned before C due to this tie-breaking rule.

5. Make task assignments to form workstation 5. Make task assignments to form workstation 1, workstation 2, and so forth until all tasks 1, workstation 2, and so forth until all tasks are assigned. It is important to meet are assigned. It is important to meet precedence and cycle time requirements as precedence and cycle time requirements as the assignments are made.the assignments are made.

6. Calculate the efficiency.6. Calculate the efficiency.

7. Evaluate the solution. An efficiency of 77 per cent 7. Evaluate the solution. An efficiency of 77 per cent indicates an imbalance or idle time of 23 per cent indicates an imbalance or idle time of 23 per cent (1.0 – .77) across the entire line.(1.0 – .77) across the entire line.

In addition to balancing a line for a given cycle In addition to balancing a line for a given cycle time, managers must also consider four othertime, managers must also consider four other

options: pacing, behavioural factors, number options: pacing, behavioural factors, number of models produced, and cycle times.of models produced, and cycle times.