cellular manufacturing system

CELLULAR MANUFACTURING SYSTEM

ByRakesh Chander Sainircsaini.blogspot.com

Cellular Manufacturing is an application of group technology in which dissimilar machines or processes have been aggregated into cells, each of which is dedicated to the production of a part or product family or a limited group of families.

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A manufacturing cell is a cluster of machines or processes located in close proximity and dedicated to the manufacturing of a family of parts.


Machine Cell Design

Machine cells can be classified as the following:

1. Single machine cell: Consists of one machine, supporting fixtures and tooling. One or more part families with one basic type of process (such as milling) can be processed.


2. Group machine cell with manual handling: This type of cell is often organized into a U-shaped layout. Includes more than one machine to process one or more part families. Material handling is performed by the human operators who run the cell.

3. Group machine cell with semi-integrated handling: A mechanized handling system, such as a conveyor, is used to move parts between machines in the cell. If the parts made in the cell have identical routings, in-line layout is selected.


Machine Cell Design

4. Flexible manufacturing system (FMS): Most highly automated machine cell. Combines automated processing stations with a fully integrated handling system.

The cell design process involves issues related to the system structure and system operation:

Structural issues:Structural issues:Selection of part families and grouping of parts into

familiesSelection of machine and process populations and

grouping of these into cellsSelection of tools, fixtures, and palletsSelection of material-handling equipmentChoice of equipment layout


Machine Cell Design

Issues related to procedures:Issues related to procedures:Detailed design of jobsOrganization of supervisory and support personnel around

the cellular structureFormulation of maintenance and inspection policiesDesign of procedures for production planning, scheduling,

control, and acquisition of related software and hardwareModification of cost control and reward systemsOutline of procedures for interfacing with the remaining

manufacturing system


Machine Cell Design

Evaluation of Cell Design Decisions

Evaluation of structural issues:

• Equipment and tooling investment (low)

• Equipment relocation cost (low)

• Inter- and intracell material-handling costs (low)

• Floor space requirements (low)

• Extent to which parts are completed in a cell (high)

• Flexibility (high)


Performance variables related to system operation:

• Equipment utilization (high)

• Work-in-process inventory (low)

• Queue lengths at each workstation ()

• Job throughput time (short)

• Job lateness (low)


Evaluation of Cell Design Decisions

Best Machine Arrangement

The important factors about determining the type of machine cell :-

• Volume of work to be done in the cell:

• Includes the number of parts per year and the amount of work required per part. Required to determine the number of machines in the cell, total cost of operating the cell, and the amount of investment needed to organize and equip the cell.


• Variations in process routings of the parts: Determines the work flow. One of straight-line, U-shape or loop flows is selected.

• Part size, shape, weight, and other physical attributes: Determines the size and type of material handling and processing equipment that can be used.


Best Machine Arrangement

Cell Formation Approaches

1. PRODUCTION FLOW ANALYSIS

• A method for identifying part families and associated groupings of machine tools.

• It groups parts with identical or similar routings together.

• These groups are used to form logical machine cells in a group technology layout.


PFA Procedure

Step 1: Data Collection: Decide on the scope (population of parts to

be analyzed) collect the necessary data (part number,

machine routing, lot size, annual production rate).

Step 2: Sorting of Process Routings: Arrange the parts into “packs” (group of parts with

identical process routings).

- Give each pack an identification number or letter



Step 3: PFA Chart: Plot the process code numbers for all the packs on a PFA

chart.

Step 4: Analysis: Most subjective and most difficult step in PFA. Rearrange the data on the PFA chart to bring the packs

with similar routings together to determine the logical machine cells.



Rank Order Clustering Algorithm

• A simple algorithm used to form machine-part groups

• Based on sorting rows and columns of the machine-part incidence matrix.

Step 1: Assign binary weight and calculate a decimal weight for each column and row using the formulas

Decimal weight for row i=

Decimal weight for column j=


Step 2: Rank the rows in order of decreasing decimal weight values

Step 3: Repeat steps 1 and 2 for each column

Step 4: Continue preceding steps until there is no change in the position of each element in each row and column


Rank Order Clustering Algorithm

Single-Linkage Cluster Analysis (SLCA) Algorithm-I

• Similarity coefficients between machines are used to construct a tree called dendrogram. A dendrogram is a pictorial representation of bonds of similarity between machines as measured by the similarity coefficients.

• Similarity coefficient between two machines is the ratio of the number of parts visiting both machines and the number of parts visiting one of the two machines.

Xijk=operation on part k performed both on machine i and j,

Yik=operation on part k performed on machine i,

Zjk= operation on part k performed on machine j.


Single-Linkage Cluster Analysis (SLCA) Algorithm-II

Step1: Compute similarity coefficients for all possible pairs of machines.

Step 2: Select the two most similar machines to form the first machine cell.

Step 3: Lower the similarity level (threshold) and form new machine cells by including all the machines with similarity coefficients not less than the threshold value.

Step 4: Continue step 3 until all the machines are grouped into a single cell.


Part ‘Number’

Machine ID

X 1 2 3 4 5 6

A 1 1

B 1 1

C 1 1

D 1 1 1

E 1 1 1


Part Number

B. WT. 1 2 3 4 5 6

Machine ID

E 24 1 1 1

C 23 1 1

D 22 1 1 1

B 21 1 1

A 20 1 1

D. Equiv24+23 = 24

22+21= 6

22+21+20=7

24+23=24

22+20=5

24=16

Rank 1 5 4 2 6 3


Part Number D. Eqv Rank

1 4 6 3 2 5

B Wt: 25 24 23 22 21 20

Machine ID

E 1 1 125+24+ 23=56

1

C 1 125+24= 48

2

D 1 1 122+21+ 20 = 7

3

B 1 1 22+21=6 4

A 1 1 22+20=5 5


Exceptional Parts and Bottleneck Machines

• The creation of independent machine cells is one of the important goals of cell design

• In practice, some parts need to be processed in more than one cell

• These parts are known as “exceptional” parts and the machines processing them are “bottleneck” machines


• The problem of exceptional elements can possibly be eliminated by

Generating alternative plansDuplication of machinesSubcontracting these operations


Exceptional Parts and Bottleneck Machines

Typical Objectives of Cellular Manufacturing:-

• To shorten manufacturing lead times by reducing set up, work handling ,waiting times and batch sizes.

• To reduce work-in-process inventory-smaller batch sizes and shorter lead times reduce work-in-process.

• To improve quality- This reduces process variations.

• To simplify production scheduling- This reduces the complexity of product on scheduling.

• To reduce set up times- This is accomplished by using group tooling that have been designed to process the part family.


Benefits of Cellular Manufacturing

Engineering Design• Reduction in new parts design

• Reduction of drafting effort in new shop drawings

• Reduction of number of similar parts, easy retrieval of similar functional parts, and identification of substitute parts


Layout Planning

• Reduction in production floor space required

• Reduced material-handling effort

Equipment, tools, jigs, and fixtures

• Standardization of equipment

• Reduced number of tools, pallets, jigs, and fixtures

• Significant reduction in costs of releasing new parts



Process Planning

• Reduction in setup time and production time

• Improved machine loading and shortened production cycles

• Reduction in number of machining operations and numerical control (NC) programming time



Production Control

• Reduced work-in-process inventory

• Easy identification of bottlenecks

• Improved material flow and reduced warehousing cost

• Faster response to schedule changes

• Improved usage of fixtures, pallets, tools, material handling, and manufacturing equipment



Quality Control

• Reduction in number of defects leading to reduced inspection effort

• Reduced scrap generation

• Better output quality



• Purchasing

• Coding of purchased parts leading to standardized rules for purchasing

• Reduced number of parts and raw materials

• Economies in purchasing because of accurate knowledge of raw material requirements

• Simplified vendor evaluation procedures leading to just-in-time purchasing



• Customer Satisfaction

• Accurate and faster cost estimates

• Efficient spare parts management, leading to better customer services



• Employee Satisfaction

• The workers in a cell observes the parts from raw material state to the finished part state. They visualize their contribution to the firm, and are more satisfied.

• Work part quality is more easily traced in group technology, and so the workers are more responsible for the quality of work they accomplish.



cellular manufacturing system

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