1. Uses of Performance Analysis in High Speed Assembly
Arne Thesen
Department of Industrial Engineering
University of Wisconsin-Madison
4/14/2019
Arne Thesen

2. A Headlamp assembly system
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Arne Thesen

3. Steps in designing a high-speed assembly system
Task Analysis
Identify all steps and decide how they are to be performed
Group related steps
Design jobs, and estimate their duration
Line balancing
Identify longest job
Reduce duration of this job
Repeat
Design hardware
Job-specific
Material handling
Integration
Performance analysis of complete system
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Arne Thesen

4. Assembly of headlights for a Ford Aero
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Arne Thesen

5. Assembly of headlights for a Ford Aero
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Arne Thesen

6. Elements of a typical high-speed assembly system
65 meters of conveyors
25 stations, some with multiple machines
Eight second cycle times for single machine stations
Inspect/Repair loop
About 50 circulating pallets
Asynchronous flow
Very limited room for pallets in front of stations
Difficult to access inside of loop
Initial cost: US$3.000,000
Cell did not perform as expected when first installed
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Arne Thesen

7. Typical complaints Cell does not produce at the expected rate.
Ford Aero headlights, Parker Pens
Not meeting production targets even though I have sufficient capacity
HP inkjet line
Our WIP is excessive.
Ohmeda
Unplanned overtime almost every day.
Marquip shipping dept.
Although all elements have sufficient capacity, the system does not produce at the expected rate.
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Arne Thesen

8. Common excuses Cell manufacturer cell lied! Workers are lazy!
Production scheduler is incompetent!
Customer is too picky!
Sales people promised too early a shipping date!
It is not my fault that the machines always jams.
More likely explanation:
The system is not properly integrated!
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Arne Thesen

9. How to improve performance
Reallocate pallets
Balance workloads at stations
Use multiple machines at some station
Reallocate buffer spaces
Revise the handling of rework
System vendors often do not have the time or tools to evaluate effect of these choices.
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Arne Thesen

10. Steps in the performance analysis
Identify bottleneck
Spreadsheet analysis
Queuing models
Simulation
Eliminate bottleneck
Reduce workload
Increase capacity
Repeat
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Arne Thesen

11. Three case studies Assembly of Automobile headlight assemblies
Problem: System did not produce at contracted rate
Solution: Redesign two of 24 stations. Change number of pallets
Assembly of anesthetic vaporizers
Problem: WIP was excessive
Solution: Increase quality to reduce rework
Building of Ink-jet cartridges
Problem: Production rate too low, stations idle
Solution: Increase the number of circulation pallets Increase space for pallets at some stations
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Arne Thesen

12. A Headlamp assembly system Production target not met
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Arne Thesen

13. Headlamp assembly Initial system did not meet specifications
Not clear how many pallets to use
Blocking due to limited buffer sizes
Difficult to spot bottlenecks
Design of parallel stations difficult
Findings
Reduce the number of pallets
Synchronization or parallel stations increased cycle times
Repair loop caused deadlock
Inefficient routing of pallets to Aimer stations
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Arne Thesen

14. Using different number of pallets
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15. Deadlock Loops cannot be full
This works
This does not work
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Arne Thesen

16. Assembly of Vaporizers 1:
Very high WIP
Excessive Rework
Production target not met
1. Based on a study by C. Coleman,R. D’Onghia and J. Schluter
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Arne Thesen

17. Assembly of Vaporizers Mexican v.s American Production rate
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Arne Thesen

18. Assembly of Vaporizers An unexpected result
WIP will always increase.
Must slow arrival of work orders
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Arne Thesen

19. Assembly of Vaporizers Relationship between workload and repair rates
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20. Assembly of Vaporizers Results: Rework Reduction
Output Increase from Std.
% Reduction
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Arne Thesen

21. Assembly of Vaporizers Results: Cool vs. Standard
Cooling vs. Standard
Output
Model
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Arne Thesen

22. Assembly of Vaporizers Recommendations
New work release policy
Limit Work In Progress (WIP)
Rework Reduction
Improve quality of incoming part
Selective assembly to improve tolerances
Cooling Machine
Reduces WIP in cooling area
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Arne Thesen

23. Making HP Inkjet cartridges
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Arne Thesen

24. HP Inkjet cartridges Findings
Production rate very sensitive to the number of pallets used
Repair-loop frequently causes deadlock
Increase buffer spaces in repair area
Discard bad cartridges when deadlock about to occur
Line was poorly balanced
Increase speed on 4 machines
Add parallel station
Need to re-allocate buffer spaces
Moving four station increased space in front of key station
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Arne Thesen

25. HP Inkjet cartridges Production rates when allocating 9 spaces to 3 stations
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Arne Thesen

26. Lessons learned from the cases
Production rates may be increased by
Changing the number of kanbans or pallets
Improving quality of incoming parts
Doing repairs off-line to avoid deadlock
Adding machines to the bottleneck stations
Not synchronizing parallel machines
Speeding up critical stations
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Arne Thesen

27. Lessons Learned Rework Allocation of pallets
May significantly increase workload on bottleneck station
Allocation of pallets
Wrong number of pallets leads to starvation or blocking
Way to many pallets causes deadlock
Allocation of buffer spaces
Insufficient number of buffer spaces leads to blocking
Workload balancing
Difficult with random processing times
Multiple machines at a station
Difficult to implement
Synchronization may increase cycle time
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Arne Thesen

28. Conclusion Performance depends on how well system is integrated
Simulation can estimate performance of specific designs
No simple way to optimize performance
A strategy of bottleneck identification and elimination usually works well
4/14/2019
Arne Thesen