PROCESS LAYOUT Process layouts are found primarily in job shops, or firms that produce customized, low-volume products that may require different processing requirements and sequences of operations. Process layouts are facility configurations in which operations of a similar nature or function are grouped together. As such, they occasionally are referred to as functional layouts. Their purpose is to process goods or provide services that involve a variety of processing requirements. A manufacturing example would be a machine shop. A machine shop generally has separate departments where general-purpose machines are grouped together by function (e.g., milling, grinding, drilling, hydraulic presses, and lathes). Therefore, facilities that are configured according to individual functions or processes have a process layout. This type of layout gives the firm the flexibility needed to handle a variety of routes and process requirements. Services that utilize process layouts include hospitals, banks, auto repair, libraries, and universities.

Improving process layouts involves the minimization of transportation cost, distance, or time. To accomplish this some firms use what is known as a Muther grid, where subjective information is summarized on a grid displaying various combinations of department, work group, or machine pairs. Each combination (pair), represented by an intersection on the grid, is assigned a letter indicating the importance of the closeness of the two (A = absolutely necessary; E = very important; I = important; O = ordinary importance; U = unimportant; X = undesirable). Importance generally is based on the shared use of facilities, equipment, workers or records, work flow, communication requirements, or safety requirements. The departments and other elements are then assigned to clusters in order of importance.

Advantages of process layouts include: Flexibility. The firm has the ability to handle a variety of processing requirements. Cost. Sometimes, the general-purpose equipment utilized may be less costly to purchase and less costly and easier to maintain than

specialized equipment. Motivation. Employees in this type of layout will probably be able to perform a variety of tasks on multiple machines, as opposed to

the boredom of performing a repetitive task on an assembly line. A process layout also allows the employer to use some type of individual incentive system.

System protection. Since there are multiple machines available, process layouts are not particularly vulnerable to equipment failures. Disadvantages of process layouts include:

Utilization. Equipment utilization rates in process layout are frequently very low, because machine usage is dependent upon a variety of output requirements.

Cost. If batch processing is used, in-process inventory costs could be high. Lower volume means higher per-unit costs. More specialized attention is necessary for both products and customers. Setups are more

frequent, hence higher setup costs. Material handling is slower and more inefficient. The span of supervision is small due to job complexities (routing, setups, etc.), so supervisory costs are higher. Additionally, in this

type of layout accounting, inventory control, and purchasing usually are highly involved. Confusion. Constantly changing schedules and routings make juggling process requirements more difficult.

PRODUCT LAYOUT Product layouts are found in flow shops (repetitive assembly and process or continuous flow industries). Flow shops produce high-volume, highly standardized products that require highly standardized, repetitive processes. In a product layout, resources are arranged sequentially, based on the routing of the products. In theory, this sequential layout allows the entire process to be laid out in a straight line, which at times may be totally dedicated to the production of only one product or product version. The flow of the line can then be subdivided so that labor and equipment are utilized smoothly throughout the operation. Two types of lines are used in product layouts: paced and unpaced. Paced lines can use some sort of conveyor that moves output along at a continuous rate so that workers can perform operations on the product as it goes by. For longer operating times, the worker may have to walk alongside the work as it moves until he or she is finished and can walk back to the workstation to begin working on another part (this essentially is how automobile manufacturing works).

On an unpaced line, workers build up queues between workstations to allow a variable work pace. However, this type of line does not work well with large, bulky products because too much storage space may be required. Also, it is difficult to balance an extreme variety of output rates without significant idle time. A technique known as assembly-line balancing can be used to group the individual tasks performed into workstations so that there will be a reasonable balance of work among the workstations.

Product layout efficiency is often enhanced through the use of line balancing. Line balancing is the assignment of tasks to workstations in such a way that workstations have approximately equal time requirements. This minimizes the amount of time that some workstations are idle, due to waiting on parts from an upstream process or to avoid building up an inventory queue in front of a downstream process.

Advantages of product layouts include:

Output. Product layouts can generate a large volume of products in a short time. Cost. Unit cost is low as a result of the high volume. Labor specialization results in reduced training time and cost. A wider span of

supervision also reduces labor costs. Accounting, purchasing, and inventory control are routine. Because routing is fixed, less attention is required.

Utilization. There is a high degree of labor and equipment utilization.

Disadvantages of product layouts include:

Motivation. The system's inherent division of labor can result in dull, repetitive jobs that can prove to be quite stressful. Also, assembly-line layouts make it very hard to administer individual incentive plans.

Flexibility. Product layouts are inflexible and cannot easily respond to required system changes—especially changes in product or process design.

System protection. The system is at risk from equipment breakdown, absenteeism, and downtime due to preventive maintenance.

FIXED-POSITION LAYOUT

A fixed-position layout is appropriate for a product that is too large or too heavy to move. For example, battleships are not produced on an assembly line. For services, other reasons may dictate the fixed position (e.g., a hospital operating room where doctors, nurses, and medical equipment are brought to the patient). Other fixed-position layout examples include construction (e.g., buildings, dams, and electric or nuclear power plants), shipbuilding, aircraft, aerospace, farming, drilling for oil, home repair, and automated car washes. In order to make this work, required resources must be portable so that they can be taken to the job for "on the spot" performance.

Due to the nature of the product, the user has little choice in the use of a fixed-position layout. Disadvantages include:

Space. For many fixed-position layouts, the work area may be crowded so that little storage space is available. This also can cause material handling problems.

Administration. Oftentimes, the administrative burden is higher for fixed-position layouts. The span of control can be narrow, and coordination difficult.

COMBINATION LAYOUTS Many situations call for a mixture of the three main layout types. These mixtures are commonly called combination or hybrid layouts. For example, one firm may utilize a process layout for the majority of its process along with an assembly in one area. Alternatively, a firm may utilize a fixed-position layout for the assembly of its final product, but use assembly lines to produce the components and subassemblies that make up the final product (e.g., aircraft).

CELLULAR LAYOUT Cellular manufacturing is a type of layout where machines are grouped according to the process requirements for a set of similar items (part families) that require similar processing. These groups are called cells. Therefore, a cellular layout is an equipment layout configured to support cellular manufacturing.

Processes are grouped into cells using a technique known as group technology (GT). Group technology involves identifying parts with similar design characteristics (size, shape, and function) and similar process characteristics (type of processing required, available machinery that performs this type of process, and processing sequence).

Workers in cellular layouts are cross-trained so that they can operate all the equipment within the cell and take responsibility for its output. Sometimes the cells feed into an assembly line that produces the final product. In some cases a cell is formed by dedicating certain equipment to the production of a family of parts without actually moving the equipment into a physical cell (these are called virtual or nominal cells). In this way, the firm avoids the burden of rearranging its current layout. However, physical cells are more common.

An automated version of cellular manufacturing is the flexible manufacturing system (FMS). With an FMS, a computer controls the transfer of parts to the various processes, enabling manufacturers to achieve some of the benefits of product layouts while maintaining the flexibility of small batch production.

Some of the advantages of cellular manufacturing include:

Cost. Cellular manufacturing provides for faster processing time, less material handling, less work-in-process inventory, and reduced setup time, all of which reduce costs.

Flexibility. Cellular manufacturing allows for the production of small batches, which provides some degree of increased flexibility. This aspect is greatly enhanced with FMSs.

Motivation. Since workers are cross-trained to run every machine in the cell, boredom is less of a factor. Also, since workers are responsible for their cells' output, more autonomy and job ownership is present.

Product or Line Layout In a product (or line) layout, various facilities, such as machine, equipment, work force, etc., are located as per the sequence of operation on parts. Even if a facility (or machine) is needed again after few other operations, we duplicate the facility at every required sequence. Product layout is preferred when production is continuous, part variety is less, production volume is high and part demand is relatively stable.Suitability of Product LayoutAssembly line such as automobile factory.Low variety, high volume production system.3.     For standardized products, which have quite stable demand in near future.

Advantages of Product Layout Less work in process (WIP) inventory, as the flow of material is continuous along a line. Compared to process layout, it requires less space for same volume of production. Conveyorized material handling or automation in the material handling is cost effective, as the flow of material is well known. The through-put time (or product cycle time) is less as compared to process layout. This is due to less chances of congestion and less waiting time on machine. Simple production planning and control and better coordination of different activities may be achieved. The skill level of workers may be lesser, as a particular worker has to do a particular operation, which seldom changes due to standardized production line. The flow of material is smooth and continuous.

Limitations of Product Layout1.     Change in product design is difficult to accommodate.2.     Product variety is very much limited.3.     Breakdown of a particular machine in line halts the production output.4.     Capital investment in machines may be higher as compared to process layout as duplication of machines in line may be needed.5.     The flexibility to increase the production capacities is limited

Process Layout Process layout is also called as functional layout. Similar machines or similar operations are located at one place as per the functions. For example, all milling operations are carried out at one place while all lathes are kept at a separate location. Grinding or finishing operation is kept at a separate location. This functional grouping of facilities is useful for job production and non-repetitive manufacturing environment.

Advantages of Process LayoutInitial investment in process layout is low.Varied degree of machine utilization may be achieved in process layout as machine is not dedicated to a single product. Greater flexibility and scope of expansion exist in this layout.

 Disadvantages of Process LayoutThere is high degree of material handling. Parts may have to backtrack in the same department.Large work in-process inventory is common. This may lead to more storage area.Workers are more skilled. This is because of variety in products and difference in design. Therefore, labour cost is higher.Total cycle time is high. This is due to waiting in different departments and longer material flow. Inspection is more frequent which results in higher supervision cost. It is difficult to fix responsibility for a defect or quality problem. The work moves in different departments in which the machine preference is not fixed. Therefore, which machine or which operator was faulty during a quality lapse may be difficult to trace in some cases. The production planning and control is relatively difficult.

Suitability of Process Layout  For non-standardized product.  For low volume, high variety manufacturing environment. For frequent change in product design.  For job-shop manufacturing.  For very expensive machines like CNC milling, co-ordinate measuring machine, etc.

Fixed Position Layout In fixed position layout, the main product being produced is fixed at a particular location. Resources, such as equipment, labor and material are brought to that fixed location. This type of layout is useful when the product being processed is very big, heavy or difficult to move. Some examples of fixed position layout are shipbuilding, aircraft assembly, wagon building, etc.

 Advantages of Fixed Position Layout1.     Easy for products which are difficult to move.2.    Flexibility for change in design, operation sequence, labor availability, etc., exists in this layout.

3.    This layout is very cost effective when many orders of similar type are existing in different stages of progress.4.    Large project type of jobs such as construction are suited in this layout.

LIMITATIONS OF FIXED POSITION LAYOUT1.     High capital investment due to long duration to complete a product.2.     Space requirement for storage of material and equipment is large.It requires careful project planning and focussed attention on critical activities otherwise confusion, delay and conflict may arise.

INTRODUCTION OF MRP MRP stands for material requirement planning. It is a computer based system that takes master production

schedule (MPS) to explode it into required amount of raw materials, parts, sub-assemblies, and assemblies needed in each of the planning

horizon, and then reducing these material requirements to account for materials that are in inventory or on order and finally developing a

schedule of order for purchased materials and produced parts over the planning horizon. In simple terms American Production and Control

Society (APICS) defines it:     MRP constitutes a set of techniques that use bill of material, inventory data, and the master production

schedule to calculate requirements for materials.- APICS Dictionary

          The core of MRP is its relationship with bill of materials and use of MRP records to calculate the time-phased release of orders for

manufacturing, planning and control (MPC) system. We will explain the entire methodology of MRP through an example but before that we

will understand some concepts.

DEFINITIONS AND TERMINOLOGY IN ASSEMBLY LINE

1. Work Element (i)The job is divided into its component tasks so that the work may be spread along the line. Work element is a part of the

total job content in the line. Let TV be the maximum number of work element, which is obtained by dividing the total work element into

minimum rational work element. Minimum rational work element is the smallest practical divisible task into which a work can be divided.

Thus, the work element number (i) is 1 < i < N

The time in a-work element, i say (TjN), is assumed as constant. Also, all TiN are additive in nature. This means that we "assume that if work

elements, 4 and 5, are done at any one station, the station time would be (T4N + T5N). Where N is total number of work elements.

 2. Work Stations (w) It is a location on the assembly line where a combination of few work elements are performed. Since minimum number of work stations (w) cannot be less than 1, we have w > 1

 3. Total Work Content (Twc) This is the algebraic sum of time of all the work elements on the line. Thus;  Twe ∑Ni=1 TiN

4. Station Time (Tsi) It is the sum of all the work elements (i) on work station (s). Thus, if there are n, to n2 work elements assigned at station s, then Tsi ∑n2

n1 TiN

 5. Cycle Time (Tc)Cycle time is the rate of production. This is the time between two successive assemblies coming out of a line. Cycle time can be greater than or equal to the maximum of all times, taken at any station. Necessary clarification is already given in the previous example. Tc > Max {Tsi} If, Tc = max {Tsi}, then there will be ideal time at all stations having station time less than the cycle time. 

6. Delay or Idle Time at Station (Tds) This is the difference between the cycle time of the line and station time.

--- d = nTc  - Twe / nTc  = nTc - ∑Ni=1 TiN / nTc

Where; Tc = total cycle time;Twe = Total work content;n = Total number of stations.  

9. Line Efficiency (LE) It is expressed as the ratio of the total station time to the cycle time, multiplied by the number of work stations (n):

 LE = ∑Ni=1 TiN  / (n) (Tc) X 100% ×

HEURISTIC: HELGESON-BIRNIE (RANKED POSITIONAL WEIGHT) METHOD Following steps are followed:

Step 1:  Draw the precedence diagram.Step 2:  For each work element, determine the positional weight. It is the total time on the longest path from the beginning of the operation to the last operation of the network. Step 3:  Rank the work elements in descending order of ranked positional weight (R.P.W). Calculation of RPW would be explained in the example to follow.Step 4:  Assign the work element to a station. Choose the highest RPW element. Then, select the next one. Continue till cycle time is not violated. Follow the precedence constraints also.Step 5:   Repeat step 5 till all operations are allotted to one station.

problem 1:Design the work stations for an assembly line shown below. Use RPW method. Desired cycle time is 10 minutes.

   Solution Twe = ∑N

i=1 TiN = Total work content = 2 + 4+ 1 + 2 + 2 + 3 + 3 + 2+ 1 + 5 + 3 + 2 + 1 + 3 = 34 Range of cycle time: Max (TiN) < Tc < (b)  Line Efficiency = [1– Balance delay] * 100      = [1 – 0.15] * 100       = 85% (c) Smoothness Index =  √∑Ni=1 [(Ts)max - Tsi]2

HEURISTIC: LARGEST CANDIDATE RULEstep 1: List all work elements (i) in descending order of their work elements (TiN) value. Step 2: Decide cycle time (Tc). Step 3: Assign work element to the station. Start from the top of the list of unassigned elements. Select only feasible elements as per the precedence and zoning constraints. Select till the station does not exceed cycle time.Step 4: Continue step 3 for next station.Step 5: Till all work elements are over, repeat steps 3, 4.Problem 1: Refer the figure below. Decide cycle time.KILBRIDGE-WESTER HEURISTIC FOR LINE BALANCING In this heuristic, work element is selected as per its position in precedence diagram.Step 1: Construct precedence diagram. Make a column I, in which include all work elements, which do not have a precedence work element. Make column II in which list all elements, which follow elements in column I. Continue till all work element are exhausted. Step 2:Determine cycle time (Tc) by finding all combinations of the primes of ∑N

i=1 TiN

 which is the total element time. A feasible cycle time is selected. Number of stations would be: n = ∑Ni=1 TiN / Tc 

Step 3: Assign the work elements in the work stations so that total station time is equal to or slightly less than the cycle time. Step 4: Repeat step 4 for unassigned work elements: 

                                          Seven column initial assignment

 

 Now, selecting cycle time is equal to 18 seconds we follow the steps:

Column Work Element, i

TiN Column Sum Cumulative Sum

I 1 8 8 8

II 234

433

  9

  

17

III 56

67

 13

 30

IV 7 5 5 35

V 8910

325

  

10

  

45

VI 1112

85

 13

 58

VII 13 10(tmax)

10 68

  Total elemental time is 68 minutes which is 2 × 2 × 17. The cycle time must lie between 68 (for one station) to 10 min. (which is max of all TiN). 10 < Tc < 68 The possible combinations of primes (17, 2 and 2) of work content time (68 min) are as follows: 

Feasible Cycle Time Infeasible Cycle Time

17 2

17 × 2 = 34 2 × 2 = 4

17 × 2 × 2 = 68  

 Line Efficiency =  68/ 5 X 17 X 100 = 80%Smoothness Index = √ 02 + 42 + 22 + 42 + 72 = √85 = 9.22 Balance Delay = 5 X 17 - 68 / 5 X 17 X 100 = 20%

now, looking at the previous table, little readjustment it work element is possible if the cycle time is extended to 18 min. This is apparent when we consider the following grouping: 

Column Work Element, i TiN Station Sum (Tsi)

(Tc – Tsi) for Tc

= 18 min.

I 123

833

  

17

  1

II 4567

3675

   

18

   0

III 891011

3258

   

18

   0

IV 1213

510

 15

 2

  Line Efficiency =  68 /4 X 18 X 100 = 94.44% Smoothness Index = √12 +22 = √5 = 2.24 Balance Delay = 4 X 18 - 68 / 4 X 18 X 100 = 5.56%

 Total work content = 68 min.Largest work element time = 10 min. Thus, cycle time (Tc) must satisfy  T > 10 min.

For minimum cycle time of 10 min., number of stations would be 68/10  = 6.8. Therefore, we must take stations lesser than this. Let us select 5 stations design. For 5 stations, the station time should be nearly 68 equal to 68/5  = 13.6 min.

 List work elements in descending order of their work element.

Work element TiN Immediate Precedence

13 10 9, 11, 12

1 8 —

11 8 8

6 7 4

5 6 2

7 5 3, 5, 6

10 5 7

12 5 10

2 3 1

3 3 1

4 3 1

8 3 -7

9 2 7

 Step 3

Station Element TiN iN  at stations

I 123

833

  

14

II 465

376

  

16

III 7108

553

  

13

IV 11129

852

  

15

V 13 10 10

 

Here, final cycle time is maximum station time which is 16 min.

 Balance delay =  nTc - ∑TiN/ ∑nTc- = 5 X 16 - 68 / 5 X 16 X 100% = 15%×-×× 

Station Element TiN iN