1. Organization of Workstations
Chapter 9
Organization of Workstations
Supplementary Material from:
Groover, M.P. (2007). Work Systems and the Methods, Measurement, and Management of Work, Upper Saddle River, NJ: Pearson Prentice Hall, pp. 59 – 112.

2. Overview Work Flow Konz & Johnson Guidelines 1 – 3 Work Cell Layout
K & J Guideline 4: Line Balancing
K & J Guidelines 5 - 9

3. Work Flow
Physical movement of work units through a sequence of unit operations.
Unit operations examples
Manual operations
Move box
Load furniture into van
File document into filing cabinet
Operations involving tools & equipment
File part
Paint trim around doorway
Measure shaft diameter with micrometer
Handwrite entries into ledger
Apply adhesive
Drill hole
Mill slot
Work Flow Patterns
Pure Sequential Operations
Mixed Sequential Operations

4. Pure Sequential Work Flow1 2 3 4

5. Mixed Sequential Work Flow6 1 2 3 4 5 7 8

6. Types of Movement In a Sequential Workflow
Bypassing
In-sequence 1 2 3 4
Backflow
Repeat

7. From-To Charts
Daily quantities (Qij) of work units moving between 5 workstations. 15 1 40 2 30 3 20 4 10 5 10 25

8. Bottlenecks Blocking Starving Reasons
Upstream operations limited by rate of downstream operations.
Starving
Downstream operations limited by rate of upstream operations.
Reasons
Technological factors
Work allocation decisions
Human factors (ergonomic limitations)
Downstream 1 2 3 4
Upstream

9. Konz & Johnson Guidelines
1. Use Specialization Even Though It Sacrifices Versatility
2. Consider Group Technology
3. Consider Both Non-progressive and Progressive Assembly
Konz & Johnson Guideline 1
Use Specialization Even Though It Sacrifices Versatility
Special-purpose equipment
Specialized materials and supplies
Specialized labor
Group technology
K & J Guideline 2
Consider Group Technology
Product families/classes
based on similarities
form (geometry)
process
Work cells
workstations organized around families
K & J Guideline 3
Consider Both Non-progressive and Progressive Assembly
Consider an assembly of N elements that requires m people to work.
Non-progressive assembly: Each worker does all N elements.
Progressive assembly: The job is split so each worker does N/m elements.
Which is better?

10. Non-Progressive Assembly
Advantages
Neutral Characteristics
Disadvantages
Advantages of Non-Progressive Assembly
Balance delay time is eliminated.
Scheduling flexibility is increased.
Shocks do not have multiple effects.
Musculoskeletal disorders reduced.
Satisfaction may increase.
Neutral Characteristics
Quality may be higher or lower with each type of assembly.
Material handling has advantages and disadvantages in both.
Space requirements could favor either.
Walking may be required in either.
Disadvantages of Non-Progressive Assembly
Direct labor cost/hour is higher.
Skill requirements and training costs are higher.
Equipment capital cost is higher.
In-process inventory is higher.
Supervision is more difficult.

11. In-Class Exercise
What are the work units in your project’s work system?
Is the work progressive “assembly” or non- progressive?
If non-progressive, what (if anything) would justify progressive?

12. U-Shaped Work Cell With Manual Handling
Common Work Cell Layouts For Progressive Assembly
Manual Handling
U-shaped
Mechanized Handling
In-line (linear)
Loop

13. In-Line Work Cell

14. Loop Work Cell

15. U-Shaped Work Cell With Mechanized Handling

16. K & J Guidelines 4. Balance Flow Lines Before balancing flow lines:
Ask whether it is appropriate to balance the line.
Gather the givens:
Table of work elements and times
Precedence diagram
Required units/minute from line
Determine:
Number of stations
Number of workers at each station
Elements to be done at each station.

17. Line Balancing Determine quantity to be made and time allowed.
20,000 units in 1,000 hours
Cycle time = 1,000 h / 20,000 = 0.05 h / item
Sum of element times = h
Estimate an approximate number of stations.
( h/item) / (0.05 h/station) = 3.63 ≈ 4 stations
One operator at each station
Make a trial solution by inspection (K & J).
Or use a line balancing heuristic.
Or use a line balancing program.

18. Line Balancing (K & J) 1 2 5 3 4 6 7 8 9 10

19. Balanced Line (K & J) S1 1 2 5 S3 3 S4 4 6 7 S2 8 9 10 S1 S2 S3 S4 S4
1,2 S2
8,9 S3
3,4,6 S4
5,7,10 S4
6,7

20. Line Balancing Determine quantity to be made and time allowed.
20,000 units in 1,000 hours
Cycle time = 1,000 h / 20,000 = 0.05 h / item
Sum of element times = h
Estimate an approximate number of stations.
( h/item) / (0.05 h/station) = 3.63 ≈ 4 stations
One operator at each station
Make a trial solution by inspection (K & J).
Or use a line balancing heuristic.
Or use a line balancing program.

21. Largest Candidate Rule Heuristic
Sort work elements in decreasing order of work times.
Assign elements to first workstation by starting at top of list and selecting first element that satisfies precedences and does not cause cycle time to be exceeded. Start back at top for more assignments.
When no more elements can be assigned without exceeding cycle time, proceed to next station.
Repeat steps 1 & 2 until all elements have been assigned.

22. Element Times and Precedence Diagram1 2 5 3 4 6 7 8 9 10

23. Solution (Setup)

24. Solution (completed)

25. Balanced Line 1 2 5 3 4 6 7 8 9 10

26. Balanced Line S1 1 S2 2 5 3 S4 4 6 7 S3 8 9 10 S1 S2 S3 S4 S4 1,2
Modifications
Consider element (human, machine) sharing.
Remember that cycle times are not fixed.
Remember that elements often can be redefined.
Interchange elements from the assembly task and the subassembly tasks. 10 S1
1,2 S2
5,3,8,10 S3
4,9 S4
6,7 S4
6,7

27. Konz & Johnson Guidelines
5. Minimize Material Handling Cost
6. Decouple Tasks
7. Make Several Identical Items at the Same Time
8. Combine Operations and Functions
9. Vary Environmental Stimulation Inversely with Task Stimulation
K & J Guideline 5
Minimize Material Handling Cost
Consider how utilization affects capital costs vs. operating costs.
Eliminate peak loads through scheduling.
Replace transportation with communication.
Reduce number of trips through scheduling and combining.
Reduce fixed costs by using line production.
Move more product/labor hour.
Reduce distances by efficient layout and arrangement.
Use a “bus” instead of a “taxi” system.
Emphasize reducing total MH costs rather than individual elements (system perspective).
K & J Guideline 6
Decouple Tasks
Line Balancing
Buffering Techniques
Buffers at or between stations
Buffers due to carrier design
Buffers off-line
Decouple by moving operators
Utility operator
Help your neighbor
K & J Guideline 7
Make Several Identical Items at the Same Time
Task stages:
Get ready Do
Put away
Reduce cost/unit by prorating get-ready and put-away over more units.

28. Checklist To Be Used With Process Charts and Flow Diagrams (1) From Work Systems, by Mikell Groover (2007)
Questions Related to Material
What alternative materials can be used?
Could the part be purchased as a commercially available item?
Could the functions of several components be combined into one component?
Should this part be made or purchased (make/buy)?
Questions Related to Processing Operations
What is the purpose of each processing operation?
Is the processing operation necessary?
Can operations be eliminated, combined, or simplified?
Is the operation time too high?
Could the processing operation be automated?
Where else could this be performed to reduce move distances?

29. Checklist To Be Used With Process Charts and Flow Diagrams (2)
Questions Related to Inspection Operations
What is the purpose of the inspection operation?
Is the inspection operation necessary?
Can the inspection operation be combined with the previous processing operation?
Could 100% inspection be replaced with sampling inspection?
Could the inspection operation be automated?
Questions Relating to Moves
How could moves be shortened or eliminated by combining or eliminating operations?
Could the items to be moved be batched to reduce trips?
Could the moves be mechanized or automated?
Could the operations sequence be changed to reduce move distances?

30. Checklist To Be Used With Process Charts and Flow Diagrams (3)
Questions Relating to Delays
What is the reason for the delay? Can the reason be eliminated?
Is the delay avoidable?
Why can’t the next operation be started immediately?
Questions Relating to Storage
Is the storage necessary?
Why can’t the item(s) be moved immediately to the next operation?
Can just-in-time delivery be used to eliminate storage?