Chapter 10 - LayoutChapter 10 - Layout

Layout planning involves decisions about the physical arrangement of economic activity centers within a facility. Basically, anything that consumes space: people/teams, machines, work benches, aisles, timecard rack, storage room. The goal: allow workers and equipment to operate effectively.

1. What centers should the layout include?

2. How much space and capacity does each center need?

3. How should each center’s space be configured?

4. Where should each center be located?

• Relative location: place of a center relative to other centers

• Absolute location: particular space that the center occupies

Layout TypesLayout Types

(a) Layout of a job shop

FoundryMilling

machines

LathesGrinding

Painting Drills

Office

Welding

Forging

Layout can:• facilitate flow of materials and information.• Increase utilization of labor and equipment• Reduce hazards to workers• Improve employee morale• Improve communication

Process layout: groups workstations according to function: most common when the same operation must intermittently produce many different products or serve many customers.

Product layout: centers are arranged in a linear path; continuousflow; high volume; L, O, S U - shapes

Advantages/disadvantages on page 448!

Station 1 Station 2 Station 3 Station 4

(b) Layout of a production line

Flexible Manufacturing Systems (FMS) were born out of the desire to make small batch production more efficient and recently to improve the company’s market performance by improving manufacturing flexibility (Chen et al, 1992). There are three key components to FMS:

Several CNC machines (only one CNC would be a FM Cell not FMS) and the hierarchy of the communication and levels of control (Stecke)

An automated material handling system for moving materials and parts from one machine to another (conveyor, guided carts, AGV)

A host computer controlling the CNC’s FMS are designed around families of parts for mid-volume production. FMS

completes a given number of operations on an item before it leaves the system. The root process is still batch. Manufacturers should consider several important implications before implementing FMS:

Technological – CNC machines, CAD, Robots, AGV (auto guided vehicles). Early in FMS development, FMS technology was purchased to reduce environmental uncertainty (threats). Research by Chen et al (1992) proposed that FMT can assume an offensive role to turn threats into opportunities and firms can achieve benefits of manufacturing flexibility.

Financial – capital appraisal techniques Political – management, skills, commitment Sociological – fewer jobs

Layout TypesLayout Types

Hybrid Layouts

One-worker, multiple-machines cell: worker operates several different machines simultaneously to achieve a line flow.

Can change setupsto produce differentproduct/part

Reduces inventory

Machine 1

Machine 2

Machine 3

Machine 4Machi

ne 5

Materials in

Finished goods out

Group TechnologyGroup Technology

Product layouts with low-volume processes. Creates cells not limited to just one worker and groups parts or products with similar characteristics into families and sets aside groups of machines for production.

Goal is to minimize setup or changeovers for similar processing requirements

Group TechnologyGroup Technology

(a) Jumbled flows in a job shop without GT cells

Drilling

D D

D D

Grinding

G G

G G

G G

Milling

M M

M M

M M

Assembly

A A

A A

Lathing

Receiving and

shipping

L

L L

L L

L L

L

(b) Line flows in a job shop with three GT cells

Cell 3

L M G G

Cell 1 Cell 2

Assembly area

A A

L M DL

L MShipping

D

Receiving

G

First image is grouped to function (lathing, milling, drilling) After lathing, part is moved to next function where it waits until it has a higher priority than any other job competing for the machine. Second image is grouped into product families – simplified the flow.

Designing Process LayoutsDesigning Process Layouts

Line Balancing – assignment of work stations in a line to achieve desired output rate with the smallest number of workstations. Line is as only as fast as the slowest workstation.

Work elements –smallest unit of work that can be performed independently and immediate predecessors – work elements that must be done before the next can begin.

Precedence diagram – work elements are circles and time required to perform work is below the circle. Arrows lead from immediate predecessors to next work element.

Line BalancingLine Balancing

A Bolt leg frame to hopper 40 NoneB Insert impeller shaft 30 AC Attach axle 50 AD Attach agitator 40 BE Attach drive wheel 6 BF Attach free wheel 25 CG Mount lower post 15 CH Attach controls 20 D, EI Mount nameplate 18 F, G

Total 244

Work Time ImmediateElement Description (sec) Predecessor(s)

40

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FC

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G

Line BalancingLine Balancing

40

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FC

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Desired output rate = 2400/weekPlant operates 40 hours/week

r = 2400/40 = 60 units/hour

c = 1/60 = 1 minute/unit= 60 seconds/unit

Matching output to demand decreases inventory. After determining desired output rate for a line, calculate the line’s cycle time. This is the maximum time allowed for work on a unit at each station. If the time for work elements at a station exceeds the line’s cycle time, causes bottlenecks. Cycle time = 1/r where r is the desired output rate.

Line BalancingLine Balancing

c = 60 seconds/unitTM = 5 stationsEfficiency = 81.3%

Desired output rate = 2400/weekPlant operates 40 hours/week

TM = 244 seconds/60 seconds= 4.067 or 5 stations always round up

Efficiency = [244\5(60)]100 = 81.3%

40

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Theoretical minimum: to achieve the desired output rate, use line balancing to work to a station, satisfying precedence relations and minimizing the number of workstations. Minimizing n, the number of workstations also maximizes worker productivity.

Line BalancingLine Balancing

Theoretical minimum = t / cWhere t = total time required to assemble each unit

(the sum of all work element standard times)c = cycle time

Idle time, efficiency, and balance delay: Minimizing n automatically ensures minimal idle time, maximum efficiency, and minimal balance delay.

Idle time is the total unproductive time for all stations in the assembly of each unit:

Idle time = nc – t

Efficiency – ratio of productive time to total time, as a percent:t / nc (100)

Balance delay – amount by which efficiency falls short of 100%: 100-Efficiency

Finding a solution

Longest work-element time: assigns, as quickly as possible, those work elements most difficult to fit into a station and saves work elements having shorter times for fine tuning

Largest number of followers – reduces unnecessary station idle time

Line BalancingLine Balancingc = 60 seconds/unitTM = 5 stationsEfficiency = 81.3%

40

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S1

S2S3

Finding a Solution

S1 A A 40 20

S2 B,C C 50 10

S3 B,F,G B 30 30E,F,G F 55 5

Cumm IdleStation Candidate Choice Time Time

S4 D,E,G D 40 20E,G G 55 5

S5 E,I I 18 42E E 24 36H H 44 16

Line BalancingLine Balancing

40

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G

c = 60 seconds/unitTM = 5 stationsEfficiency = 81.3%

S1

S2S3

S5S4