7. Layout and Safety Issues_TS_L7

Layout Strategies

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What is Facility Layout? Location or arrangement of everything within & around

buildings Pay attention to following to decide layout design

Customer satisfaction Level of capital investment Utilization of space, equipment, & people Ease of equipment maintenance Amount of flexibility needed Efficient flow material and worker Employee safety

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Types of Layouts Product - Product layout involves locating the machines

and equipment so that each product follows a pre-arranged route through a series of processes. The products flow along a line of processes, which is clear, predictable and relatively easy to control.

Process - In process layout, similar manufacturing processes (cutting, drilling, wiring, etc.) are located together to improve utilisation. Different products may require different processes so material flow patterns can be complex.

Group Technology / Cellular (HYBRID) – product families Fixed-position - large bulky projects such as ships and

buildings

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Product Layout

Station 1 Station 2 Station 3 Station 4

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Process Layout

Lathe Drill

Grind

Lathe Weld

Assembly

Drill

MillWar

ehou

se Lathe PaintLathe

Weld

Paint

Mill

Mill

Mill Grind

Assembly

War

ehou

se

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Product Layout - Advantages Reduces materials handling.

Accommodates small amounts of work in process.

Reduces transit times.

Simplifies production planning and control systems.

Simplifies tasks, enabling unskilled workers to learn task quickly.

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Product Layout - Limitations Disadvantages of product layout

Lack of process flexibility. Lack of flexibility in timing: the product can not flow

through the line faster than the slowest task can be accomplished unless that task is performed at several stations.

Large investments: special-purpose equipment and duplication is required to offset lack of flexibility in timing.

Dependence of the whole on each part: a breakdown of one machine or absence of enough operators to staff all work stations may stop the entire line.

Worker fatigue: workers may become bored by the endless repetition of simple tasks.

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Product Requirements Standardized product High production volume Stable production quantities

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Product-Oriented Layout Types

Assembly Line • Assembles fabricated parts • Uses workstation • Repetitive process • Paced by tasks

Fabrication Line • Builds components • Uses series of machines • Repetitive process • Machine paced

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Process-Oriented Layout Department areas having similar processes located in close

proximity

Design places departments with large flows of material or people together

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Process Layout - Advantages Better utilization of machines Fewer machines required High degree of flexibility relative to equipment or

manpower allocation for specific tasks Comparatively low investment in machines is

required The diversity of the task offers a more interesting

and satisfying occupation for the operator Specialized supervision is possible

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Process Layout - Limitations Since longer flow lines usually result, material

handling is more expensive Production planning and control systems are more

involved Comparatively large amounts of in-process

inventory results Space and capital are tied up by work-in-process Because of the diversity of the jobs in specialized

departments, higher grades of skill are required Total production time is usually longer

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Comparison Of Product And Process Layouts PRODUCT LAYOUT PROCESS LAYOUT1. Description Sequential arrangement Functional grouping

of machines of machines

2. Type of Process Continuous, mass Intermittent, job shopproduction, mainly batch production,

assembly mainly fabrication

3. Product Standardized Varied,made to stock made to order

4. Demand Stable Fluctuating5. Volume High Low6. Equipment Special purpose General purpose7. Workers Limited skills Varied skills

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Comparison Of Product And Process Layouts PRODUCT LAYOUT PROCESS LAYOUT 8. Inventory Low in-process, High in-process, high finished goods low finished goods 9. Storage space Small Large10. Material Fixed path Variable path handling (conveyor) (forklift)11. Aisles Narrow Wide

12. Layout decision Line balancing Machine location13. Goal Equalize work at Minimize material each station handling cost14. Advantage Efficiency Flexibility

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Line balancing is the process of assigning tasks to workstations in such a way that the workstations have approximately equal time requirements.

Design Product Layouts: Line Balancing

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Cycle time is the maximum time allowed at each workstation tocomplete its set of tasks on a unit.

Cycle Time

Maximum cycle time is given by the summation of the task times.

Minimum cycle time is given by the longest of the task times.

6-17D

OT = timecycle = CT

rateoutput desired = D

dayper timeoperating OT

CTOT = rateOutput

Determine Maximum Output

Steps in Product LayoutStep 1: Develop the precedence diagram showing the sequence and performance times for each task.

Step 2: Calculate cycle time to meet the output requirement. Take the demand per day and divide it into the productive time available per day (in minutes or seconds).

productive time Demand per day or production rate per day

Step 3: Determine the theoretical minimum number of workstations. This is the sum of all task times divided by the cycle time. Fractions are rounded to the next higher whole number.

time for task i

Cycle timeStep 4: Perform the line balance by assign specific assembly tasks to each workstation. An efficient balance is one that will complete the required assembly, follow the specified sequence, and keep the idle time at each workstation to a minimum.

Cycle time =

Minimum number of workstations =

1. Longest operating task time

Choose the available task with the longest task time

2. Greatest number of following tasks

Choose the available task with the largest number of following tasks

3. Ranked positional weight Choose the available task for which the sum of following task times is the longest

4. Shortest operating task time

Choose the available task with the shortest task time

5. Least number of following tasks

Choose the available task with the least number of following tasks

Line-Balancing Heuristics (Rules of Thumb)

Rule Meaning

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Precedence diagram: Tool used in line balancing to display elemental tasks and sequence requirements

A Simple Precedence Diagrama b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min. 0.2 min.

Figure 6.11Precedence Diagram

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task timeof sum = t

CT t)(

=N

Determine the Minimum Number of Workstations Required

What is the minimum number of workstations for the previous precedence diagram? (assume minimum cycle time)

mins 2.5 = t

35.2min 1

mins 2.5 = N

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• Arrange tasks shown in Figure 6.11 into three workstations.– Use a cycle time of 1.0 minute– Assign tasks in order of the most number of

followers

– There is another rule called the order of greatest positional weight

Example 1: Assembly Line Balancing

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Workstation

TimeRemaining Eligible

AssignTask

RevisedTime Remaining

StationIdle Time

1 1.00.90.2

a, ccnone

ac–

0.90.2

0.22 1.0 b b 0.0 0.03 1.0

0.50.3

de–

de–

0.50.3 0.3

Example 1 Solution

Total idle time = 0.5

6-25

%100*(N)(CT)cycleper timeIdle

= timeidle %

Efficiency = 100% – Percent idle time

Calculate Percent Idle Time

What’s the % idle time and efficiency for the above example?

%7.16%100*(3)(1.0)

0.5 = timeidlePercent

Efficiency = 100% - 16.7% = 83.3%

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• Assign tasks in order of most following tasks.

– Count the number of tasks that follow

• Assign tasks in order of greatest positional weight.

– Positional weight is the sum of each task’s time and the times of all following tasks.

Some Heuristic (intuitive) Rules:

Line Balancing Rules

Example

A manager wants to assign workstations in such a manner that hourly output is 4 units. Working time is 56 minutes per hour. What is the cycle time?

Cycle time = operating time/output rate= 14 mins.

What is the positional weight for each task?A= 3+2+4+9+5 = 23 E = 4+9+5 = 18B= 2+4+9+5 = 20 F = 5+6+4+9+5 = 29C= 9+5 + 4 =18 G= 6 + 4 + 9 + 5 = 24D= 7+4+9+5 = 25 H = 14

Example

Numbers above the circles indicate task times

Assign the tasks above to workstations in the order of greatest positional weight.

Steps:1)Arrange the task in the decreasing order of positional weights.2) Find out the number of workstations

# of workstations = sum of task times/cycle time = 45/14 = 3.2 =4

Task - Task time F = 5 D = 7 G = 6 A = 3 B = 2 C = 4 E = 4 H = 9 I = 5

Task - Task time F = 5 D = 7 G = 6 A = 3 B = 2 C = 4 E = 4 H = 9 I = 5

%64.19%100*(4)(14)

11 = timeidlePercent

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1 min.2 min.1 min.1 min. 30/hr. 30/hr. 30/hr. 30/hr.

Bottleneck

Bottleneck Workstation

Theoretically, the line should be able to produce at 60 units per hour.

But the 3rd station has a task time of 2 mins, therefore limiting the output to 30 units per hour.

The problem: Pproduce 500 Model J Wagons per 8-hour day

Setup time and work breaks total 45 minutes Production time available = 480 – 45 = 435 minutes Assembly steps and times for the Model J Wagon are

given below:

Assembly Line Balancing Illustration

ABCDEFGHIJK

Position rear axle support and hand fasten 4 screws to nutsInsert rear axle

Tighten rear axle support screws to nutsPosition front axle assembly and hand fasten with 4 screws to nuts

Tighten front axle assembly screwsPosition rear wheel #1 and fasten hub capPosition rear wheel #2 and fasten hub capPosition front wheel #1 and fasten hub capPosition front wheel #2 and fasten hub cap

Position wagon handle shaft on front axle assembly and fasten bolt and nutTighten bolt and nut

Task Task Description4511950151212121289

195

AA,B

DA,B,CA,B,CD,ED,E

A,B,C,D,E,F,G,H,IJ

Tasks ThatMust Precede

Time

A

B C

F

G

D E H

I

J K

Step 1: Draw the precedence diagram

45

11 9

50 15

12

12

12

12

8 9


Step 2: Calculate the cycle time

Cycle Time = time available / output required

= 435 minutes / 500 units = 0.87 minutes = 52.2 seconds

Step 3: Calculate the minimum number of workstations

Minimum number of work stations = total task time / cycle time

= 195 seconds / 52.2 seconds = 3.74 = 4 stations

Step 4: Balance the line using the following heuristics (rules of thumb):

1. According to Greatest-Number-of-Following-Tasks rule2. According to the Longest-Operating-Time rule


Station 1

Station 2

Station 3

Station 4

Station 5

A

D

B/E/C/F

G/H/I/J

K

45

50

11/15/9/12

12/12/12/8

9

7.2

2.2

41.2/26.2/17.2/5.2

40.2/28.2/16.2/8.2

43.2

None

None

C,E/C,H,I/F,G,H,I/None

H,I/I/J/None

None

C,E/C/F,G,H,I

H,I

Workstation Task Task Time Idle TimeFeasible Remaining

TasksTasks With

Most Followers

Step 4: Balancing the line using the Greatest-Number-of-Following-Tasks rule:


Station 1

Station 2

Station 3

Station 4

D

A

E/H/I/B

C/F/G/J/K

50

45

15/12/12/11

9/12/12/8/9

2.2

7.2

37.2/25.2/13.2/2.2

43.2/31.2/19.2/11.2/3.2

None

None

H,I,B/I,B/B/None

F,G/G/J/K

E/H/I/B

C/F/G/J/K

Workstation Task Task Time Idle TimeFeasible Remaining

TasksTasks With Longest

Operating Time

Efficiency of the line = total task time / (number of stations * cycle time):

Step 4: Balancing the line using the Longest-Operating-Time rule:

Efficiency of line balance using the greatest-number-of-following-tasks rule= 195 / (5 x 52.2) = .747 = 74.7%

Efficiency of the line using the longest -operating-time rule= 195 / (4 x 52.2) = .934 = 93.4%


Facility Layout

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Designing Process LayoutsMain issue in the design of process layouts concerns the relative

positioning of the departments involved. Process layouts features:1. Some departments benefit from adjacent locations.2. Some departments must be kept separate.3. External factors such as the location of entrances, loading docks,

elevators, windows, and areas of reinforced flooring have to be considered.

4. Flow costs for material and personnel within the building are critical.

Facility Layout

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Steps for Process LayoutStep 1: Construct a “from-to-matrix showing the flow of parts or materials from

department to department.Step 2: Determine the space requirements for each department.Step 3: Develop an initial schematic diagram showing the sequence of

departments through which parts will have to move. Try to place departments with a heavy flow of materials or parts next to one another.

Step 4: Determine the cost of this layout by using the following equation: Minimize cost = XijCij

where: n = number of work centres or departments i,j = individual departments Xij = number of moves between department i and department j

Cij = cost of a move between department i and department j

Step 5: Try to improve this layout by trial and error or by use of a computer program.

Step 6: Prepare a detailed plan considering space or size requirements of each department.

Facility Layout

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1 2 3 4 5 6 7 8

175 25 0 30 200 20 25 0 100 75 90 80 90 17 88 125 99 180 20 5 0 25 0 180 187 374 103 7

Flows Between Departments

(number of moves)

12345678

12345678

Department

Shipping & receivingPlastic molding & stamping

Metal formingSewing departmentSmall toy assemblyLarge toy assembly

PaintingMechanism assembly

Activity

1

2

3 5 7

4 6 8

160 ‘

80 ‘

Step 1

Step 240’ 40’ 40’ 40’

40’ 40’ 40’ 40’

40’ 40’ 40’ 40’

40’ 40’ 40’ 40’

Process Layout Illustration - Minimizing Flow Costs for a Toy Company

Facility Layout

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1 2 3 4 5 6 7 8

175 25 0 60 400 60 75 0 100 150 180 240 270 17 88 125 198 360 20 5 0 50 0 180 187 374 103 7

12345678

Cost Matrix - First SolutionAssume flow cost = 1 for adjacent movesAssume flow cost = 2 for moves over 1 deptAssume flow cost = 3 for moves over 2 depts (Assume diagonal moves are possible)

Sample Calculations: 1 to 2 = 175 x 1 = 175 1 to 6 = 200 x 2 = 400 1 to 8 = 25 x 3 = 75, etc.

Total cost = $3,449

Step 4

Step 31 3 5

2 4 6

25 88

200 20

100 5

175


Facility Layout

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4 3 5 7

2 1 6 8

Revised LayoutExchange 1 & 4

Why 1 & 4? Youwant to bring 1 and6 next to each other,and this is one way

to do it!

Costs affected:1&5, 1&6, 1&7,1&8, 4&5, 4&6,

4&7, 4&8

1 2 3 4 5 6 7 8

175 50 0 30 200 40 50 0 100 150 180 240 270 17 88 125 198 360 40 10 0 75 0 180 187 374 103 7

12345678

Cost Matrix - Second SolutionCost reductions:

1&5 = 30, 1&6 = 2001&7 = 20, 1&8 = 25

Cost additions:4&5 = 20, 4&6 = 54&7 = 0, 4&8 = 25

Total cost = $3,234

Step 5


Facility Layout

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Small ToyAssembly

5

MechanismAssembly

8

Shipping andReceiving

1

Large ToyAssembly

6

MetalForming

3

Plastic Mldg. / Assb.

2

Sewing

4

Painting

7

A final,feasiblesolution

after severaliterations

Step 6


Facility Layout

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Process Layout Illustration - Systematic Layout PlanningEven though the approach of minimizing flow costs is widely used, it suffers from the limitation of being able to focus on only one objective, and many situations involve multiple criteria.A more general approach, systematic layout planning (SLP), allows for subjective input from analysts or managers to indicate the relative importance of each combination of department pairs.

The following is an example of SLP for the floor of a department store:

From

1. Credit dept

2. Toy dept.

3. Wine dept.

4. Camera dept.

5. Candy dept.

To 2 3 4 5 I U A U 6 --- 1,6 --- U I A --- 1 1,6 A E 2,3 1 X 1

Area (sq. ft.)

100

400

300

100

100

Letter

Number

Closeness Rating

Reason for Rating

Facility Layout

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Reason

Type of customer

Ease of supervision

Common personnel

Contact necessary

Share same space

Psychology

Code

1

2

3

4

5

6

5 2 4

13

Initial layout based upon relationship requirements

(ignoring space and building constraints)

2 4

3 15

20 ft.

50 ft.

Final layout adjustedby square footageand building size

Facility Layout

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Process Layout - Additional Illustration # 1

A small printing shop wishes to locate its seven departments in a one-floor building that is 40 unitswide and 50 units long. Department sizes are :

Department Length (units) Width (units)Layout 10 10Cutting 20 10Shipping 10 10Supply Storage 20 15Printing 25 20Binding 20 20Art 20 20

The average number of loads flowing between departments is expected to be:

From Dept Layout Cutting Shipping Supply Storage Painting Binding ArtLayout --- --- --- --- --- --- ---Cutting --- --- --- 100 --- 400 ---Shipping --- --- --- 500 --- --- ---Supply Storage --- 600 100 --- 400 100 ---Printing --- --- --- --- --- 1200 100Binding --- 100 1000 --- 200 --- ---Art --- 100 --- --- 100 --- ---

What is your layout recommendation?

Facility Layout

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Eight work centres must be arranged in an L-shaped building. The location of centres A and E are designated as shown in the accompanying diagram. Assuming transportation costs are $2 per load per metre, develop a suitable layout that minimizes transportation costs using the information below.

From / To A B C D E F G H A -- 40 40 60 120 80 100 110 B -- 60 40 60 140 120 130 C -- 45 85 40 70 90 D -- 40 50 40 45 E -- 90 50 40 F -- 40 60 G -- 60 H --

A * B

C D E *

F G H

From / To A B C D E F G H A -- 10 5 90 365 135 125 0 B 0 -- 140 10 0 35 0 120 C 0 220 -- 110 10 0 0 200 D 0 110 240 -- 10 0 0 170 E 5 40 100 180 -- 10 40 10 F 0 80 40 70 0 -- 10 20 G 0 45 20 50 0 40 -- 20 H 0 0 0 20 0 0 0 --

Loads per day

* cannot be moved

Distances (metres)

Facility Layout

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Hercules Manufacturing, a producer of corrugated cardboard boxes, is planning a 3600 square foot layout. The operations manager has obtained SLP ratings for locating departments next to each other.

From / To Storage Corrugator Folder/Gluer Taper/Bailer Inspection ShippingStorage --- AN U U I U Corrugator --- --- I U U XFolder/Gluer --- --- --- AN I UTaper/Bailer --- --- --- --- U IInspection --- --- --- --- --- AN Shipping --- --- --- --- --- ---

AN = Absolutely Necessary I = Important U = Unimportant X = Undesirable

Area(sq.ft.)1200400400400400800

What should be the layout used by Hercules Manufacturing?

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Before Group Technology

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

Jumbled flows in a job shop without GT cellsJumbled flows in a job shop without GT cells

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Group Technology / Cellular

Cell 3

L M G G

Cell 1

Cell 2

Assembly area

A A

L M DL

L MShipping

D

Receiving

G

G

Hybrid Layouts: Cellular layouts

Notice:The distancedistance that each part must travel before

completionthe irregularityirregularity of the part routingsAmount of “paperwork”“paperwork” needed to direct the flow of each

individual part and to confirm that the right operation has been performed

Original Process Layouts


In its current form, there is no apparent pattern to the routings.

PRODUCT FLOW ANALYSIS (PFA) reorders part routing matrices to identify families of parts with similar processing requirements.

If we reorder the matrix listing which parts have four machines in common, three...Part Routing Matrix


Part Routing Matrix Reordered to Highlight Cells

Revised Layout with Three Cells

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Group Technology / Cellular - Advantages Increased machine utilization

Compromise between product layout and process layout, with associated advantages

Shorter travel distances and smoother flow lines than for process layout

Reduced Material flow path

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Work Cell Advantages

Decreased: Inventory Floor space Direct labor costs

Increased: Equipment utilization Employee participation Quality

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Group Technology / Cellular - Limitations General supervision is required Higher skill levels required of employees than for product

layout Depends on balanced material flow through the cell;

otherwise, buffers and work-in-process storage are required Lower machine utilization than for process layout

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Fixed Position Layout

Lathe Grind

Drill

Press

War

ehou

se

Paint

War

ehou

se

Assembly

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Fixed-Position Layout Design is for stationary project Workers and equipment come to site Limited space at site Changing material needs

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Fixed-Position Layout - Advantages Material movement is reduced Continuity of operations and responsibility results from team High flexibility; can accommodate changes in product

design, product mix, and production volume Independent of production centers allows scheduling to

achieve minimum total production time

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Fixed-Position Layout - Limitations Increased movement of personnel and equipment Equipment duplication may occur Higher skill requirements for personnel General supervision required Cumbersome and costly positioning of material and

machinery Low equipment utilization

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Types of LayoutsHigh

Medium

Low

Low Medium High

Product Layout

Fixed LocationLayout

Group Technology / Cellular Layout

ProcessLayout

Volu

me

Variety

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Safety Issues

Safety for workerSafety for machine and

workplace

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WHY do we need safety precautions???

Accident must be avoided. An accident is an unexpected action that results in

injury to people or damage to property. Causes of accident:• Carelessness• Use of wrong tools• Unsafe work practices• Horseplay• Ignore safety rules• Inadequate maintanence

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WHY do we need safety precautions???

Sources of accident:• Machines with moving parts• Electrical equipments• Sharp equipments• Chemicals

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Safety Issues for Prevention of accidents

Safety features in machines; Limit switches, part detector, machine in operation signal, robot teach pendant normally open switch

Individual attitude towards safety: proper attire, safety shoes, Knowledge about Standard Operational Procedure, FIRST AID ect.

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Safety IssuesLockout/Tagout

Machine needs maintenance / Servicing must be locked out .

To minimize injuries. Machine cannot be used until tagout/lockout device

is removed. Only authorized service person can use. If the machine cannot be locked out then go for

tagout option.

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Lockout procedure

Notification Understanding about the machine. Stop the machine with proper procedure if in

operation. Deactivate energy isolating devices Lock energy isolating devices with dedicated locks. Stored energy should be dissipated (ie grounding of

Capacitors) Final checking Confirm locked out.

Homework

A shop wants an hourly output of 33.5 units per hour. The working time is 60 minutes per hour. Assign the tasks using the rules:

a)In the order of greatest positional weight.

Homework

unitper minutes 80.1hourper units 33.33hourper minutes 60

output Desired timeOperatingCT

7. Layout and Safety Issues_TS_L7

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