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ch02


Methods, Standards, and Work Design : (2)

Problem – Solving Tools
? 13 basic tools: Select the project – 5 tools Get and present data – 5 tools Develop the ideal method – 3 tools

METHODS STUDY
? Systematic recording of existing and proposed ways of doing work in order to simplify the job
? Improve procedures ? Improve layout ? Reduce human fatigue ? Improve use of materials, machines, labor ? Improve physical workplace

Aim at: Productivity & Health Safety

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Fig. 2.1 – Steps in Methods Study
5 tools

5 tools

3 tools
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#1 – Select Project
? Human factors – ? Technical factors – ? Economic factors –
Accidents, Injuries Error rates, Defects ? Quality Medical, Waste, Rework, Bottlenecks, Long Distances

? Exploratory tools ? Pareto analysis ? Gantt chart Office survey ? Fish diagram ? PERT chart ? Job/Worksite Analysis Guide
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On the floor

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1.1 PARETO ANALYSIS (80-20 Rule) ? Vilfredo Pareto – economist ? 80% of money held by 20% of people ? 80% of costs, accidents, injuries, accounted for by 20% of jobs/individuals ? Concentrate on those 20% ? Plot in descending order as a cumulative probability distribution (DesignTools)

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1.2 GANTT CHART
? Horizontal bar chart of activities ? Shade in bar as completed ? Any given point in time, a snapshot of the status of all activities ? Some behind, some ahead of schedule ? Again focus efforts where needed ? Use DesignTools

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1.3 FISH DIAGRAM
? Cause-and-Effect Diagram ? Event or problem (Effect) as “fish head” ? Contribution factors (Cause) as “fish bone” attached to backbone and fish head. ? The principle cause further subdivided into categories: human, machine, methods, materials, environment, admin; until all possible causes are listed ? A good one have several levels of bones and provide a good overview of problem and contribution factors
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1.4 PERT CHART
? Program Evaluation and Review Technique ? Network diagram or critical path ? In terms of time ? U.S military project ? Longest path is the critical path.

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2

21

23

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Example (p27)
? To calculate: how to shorten project duration? ? To estimate the cost of various alternatives?

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1.5 JOB/WORKSITE ANALYSIS GUIDE

? Time to go out on the floor ? Meet with supervisor first
? Explain study (production?) ? Select jobs/workers

? May need to meet with union also ? Never express opinions ? Fill out Job/Worksite Analysis Guide

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#2 Recording and analysis tools
? Operation process chart

? Flow process chart
? Worker/Machine process chart ? Gang process chart ? Flow diagram

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2.1 Operation process chart
? Indicates the general flow of all components in a product. ? Two symbols:
? Operation -? Inspection --

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Basic element

Indicate Process flow Parts / supply

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Conclusion:
? Identifies operations, inspections, materials, moves, storages, delays. ? Shows all events in correct sequence. ? Shows relationship between parts and fabrication complexity. ? Distinguishes between produced and purchased parts.

? Provides info. on the num of employees and time required.
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2.2 Flow process chart
? More detail than operation process chart, (in addition to op/inspec, also moves & storage delays) ? Is especially valuable in recording nonproduction hidden costs, like distance traveled, delays, and temporary storage. ? 2 types:
? product or material ? Operative or person

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2.3 FLOW DIAGRAM
? Pictorial plan of the flow of work ? Is a helpful supplement to the flow process chart. ? Plant layout

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Original Flow Diagram

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Revised layout Flow Diagram

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2.4 WORKER & MACHINE PROCESS CHARTS
? Shows the exact time relationship between work cycle of the person and the operating cycle of the machine. ? indicates both idle machine time and worker time – effecting improvement ? Determines the most economical num of machines one worker can operate.

1 worker ? n machines

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2.5 GANG PROCESS CHARTS
? Instead of 1 worker ? n machines (worker machine process chart),

1 machines ? n workers.

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#3 Quantitative Tools
? Using Math Model can compute the number of facilities that can be assigned to an operator in less time. ? 3 types worker and machine relationship:
? Synchronous servicing
? Random servicing ? Combination

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3.1 Synchronous servicing
? ideal case for 1 worker ? n machines
Both worker and machines are fully occupied during the whole cycle

l?m ? Calculated by: n ? l Where,
l – total operator servicing time per machine m – total machine auto running time

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Figure 2-18 (p45)

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What –if ?
? N > n, ? at least 1 machine can have idle time

N < n, ? man idle time
?? How to determine which one is better?

Criterion – minimum total cost per piece
cost of idle machine hourly rate of the operator

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TEC calculation
l?m n1 ? l?w
Where, n1 -- lowest whole number w -- total worker time (not directly interacting with machine) To calculate Total Expected Cost (TEC), K1 – operator rate, $/time K2 – cost of machine, $/time
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TEC calculation

(Cont.)

? Case 1: n1 machines ? worker - idle ; machine - no idle time ? The cycle time = ( l + m )
TECn1 ? K1 ?l ? m? ? n1K 2 ?l ? m? ?l ? m??K1 ? n1K 2 ? ? n1 n1

?Case 2: n2 machines ? worker - no idle ; machines - idle n2 ? n1 ? 1 ? The cycle time = n2( l + w )
TECn2 ?
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K1n2 ?l ? w? ? K 2 n 2 n 2 ?l ? w? n2

? ?l ? w??K1 ? n2 K 2 ?
39

Method, Standards, and Work Design

TEC calculation

(Cont.)

? Alternate Approach for TEC calculating: To calculating Production Rate per hour ( R )
60 R? ?n cycle tim e
K 1 ? nK 2 TEC ? R
Cost of labor and machine

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Example 2.1 (p46)

? 10% increase in production (60 compared to 54.5) ? 3.6% decrease in unit costs (from 1.56 to 1.5) ? Reduction of idle time for operator from 0.7min to machine idle 0.1min

3.2 Random servicing
? Cases:
? when the facility needs to be served -- unknown ? how long servicing takes -- unknown

? to calculate the probability of m machine down n! P?m of n ? ? p m q n?m m!?n ? m? !
Where, p – the probability of down time q – the probability of runtime, q =1- p
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Example
? p = 40% ; q= 60%; n=3
Machine down (m) 0 1 2 3
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Probability
3! 0.4 0 0.6 3 ? 0.216 0!?3 ? 0?! 3! 0.410.6 2 ? 0.432 1!?3 ? 1?! 3! 0.420.61 ? 0.288 2!?3 ? 2?! 3! 0.430.60 ? 0.064 3!?3 ? 3?!

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Example( cont.)
No. of machines down 0 1 2 3 Total: Probability 0.216 0.432 0.288 0.064 1.0 Machine hours lost per 8-hr day 0 0 0.288*8=2.304 2*0.064*8=1.024 3.328

? proportion of machine time lost = 3.328 / 24 = 13.87 % ? By changing no. of machines assigned to a worker, ? different proportion value K 1 ? nK 2 ? Criterion – minimum TEC TEC ?
R
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Example 2.2
? 1 operator ? 3 machines ? Expected downtime 40% ? When running, each machine can produce 60 units/hr ? Operator wage $10/hr, machine cost $60/hr ? Question: Is it worth hiring another operator?
No. of machines down 0 Probability 0.216 Machine hours lost per 8-hr day (1 operator) 0 Machine hours lost per 8-hr day(2 operator) 0

1
2 3 Total:
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0.432
0.288 0.064 1.0

0
0.288*8=2.304 2*0.064*8=1.024 3.328
Method, Standards, and Work Design

0
0 0.064*8=0.512 0.512
47

Example 2.2 (cont.)
? Production rate R: ? Case 1: (1 operator) R1 ? 3 ? 60 ? (1 ? 3.328 ) ? 155 .04 24 0.512 ) ? 176 .16 ? Case 2: (2 operators) R2 ? 3 ? 60 ? (1 ? 24 ? Total Expected Cost (TEC): TEC ? K1 ? nK2
R

? ? ? ?
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TEC1 =(10+3*60)/155.04 = 1.23 $/unit TEC2 =(2*10+3*60)/176.16 = 1.14 $/unit More efficient if hiring another operator TEC3 =(3*10+3*60)/180 = 1.17 $/unit
Method, Standards, and Work Design 48

3.3 Combination
? Combination of synchronous and random servicing
? Servicing time is relatively constant ? but the machines are serviced randomly ? Particular distribution in time between breakdown

? One Approach assumes an expected workload for operator based on :
? No. of machines assigned Empirical Curve Formula ? Mean machine running time ? Mean servicing time
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? For n<=6

? For n>7, Wright Formula
2 I ? 50 ? ?1 ? X ? N ? ? ?1 ? X ? N ?? ? ? ? ?

3.4 LINE BALANCING
? ? Operators ? a production line ? Line balance :
? several operators, each performing consecutive operations, work as a group ? Production rate depends on the slowest operator n ? Line efficiency S .M . ? Where, 1 E? n ?100% S.M. – Standard Min per op. A.M – Allowed standard min per op. ? A.M .

?

N ? R?

S .M . ? A.M . ? R E
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? Assembly line involves 8 op. ? Line produces 700 units per day (R = 700/480=1.458units/min; 1/R=0.685
min/unit)

(example: see page 58)

? S.M for each op (shown in table)
S .M . ? N?R ? 1.458? (1.25 ? 1.38 ? ... ? 1.28) / .95 ? 23.6 E
Op.
Op1. Op2.

S. M.
1.25 1.38

S.M./min/unit
1.25/0.685=1.83 2.02

No. of op.
2 2

S.M./no.op
1.25/2=0.625 0.69

Op3.
Op4. Op5.

2.58
3.84 1.27

3.77
5.62 1.86

4
6 2

0.645
0.64 0.635

Op6.
Op7. Op8. total

1.29
2.48 1.28 15.37

1.88
3.62 1.87

2
4 2 24

0.645
0.62 0.64

The strategy in assembly line balancing ? Work element sharing

? Dividing a work element
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The strategy in assembly line balancing
1→2 operators

Work element sharing Operation improvement Add operator

Dividing
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Re-assignment

Improvement-combination
54

Method, Standards, and Work Design

Steps for assembly line balancing
? 1. Determine the sequence of work elements
? fewer restriction on order ? greater balancing chance ? Precedence chart

? 2. Zone Restraint consideration
? More zoning restraints ? fewer combinational possibilities

? 3. Precedence Graph & Precedent Matrix
? 4. Positional weight
? = sum of all work unit following

? 5. Assign work element to various workstations according to positional weight
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Figure 2-21 Precedence Chart

BACK

Precedence Graph

BACK
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Precedence Matrix

BACK

Positional weight
Work element Positional weight Immediate predecessors

00
01 03 04

6.26
4.75 4.4 4.18

00,01 03

02

3.76
3.51 2.64 2.36 1.76 1.04 0.55

00
02 05 04,06 04 07,08 09
59

? Positional weight (00) = Sum (00, 02,03,04,05,06,07,08,09,10) =0.46+0.25+0.22+…+0.55 = 6.26
BACK
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05 06 08 07 09 10

Method, Standards, and Work Design

Table 2-2

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Conclusion: ? Pareto analysis and fish diagram – select a critical op. and identify the root causes and contributing factors leading to the problem ? Gantt chart and PERT chart – project scheduling tools ? Job/worksite analysis guide – in particular site

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? Operation process chart – overview of relationship between different op. and inspections. ? Flow process chart – detail info. to find hidden or indirect cost due to delay, storage and material handling. ? Flow diagram – supplement to flow process chart in developing plant layout
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? Worker/machine, gang process chart -show machines in conjunction with operators, analyze idle time. ? Synchronous, Random servicing calculation and line balancing – develop efficient ops. through quantitative methods

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Assignment
? Page 66 –
? ? ? ? ? Problem 1 Problem 4 Problem 5 Problem 6 Problem 9

? Deadline : Next Wednesday (25, Mar, 2009)

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