1. Mechanical and Industrial Engineering
Manual Assembly
Corrado Poli
Mechanical and Industrial Engineering
UMass Amherst
©Fall 2001

2. Two Phases of Assembly Handling Insertion Can be done Manually
Automatically
Handling
Insertion

3. Manual Handling (Affected primarily by geometry)
Bins
Workstation
Fixture
Operator
Operator
Reaches into the bin
Grasps the part
Transports and orients the part
Pre-positions it

4. Manual Insertion
(Affected by both the part geometry AND the part/parts to which it is placed/fastened/mated to.)
Bins
Workstation
Fixture
Operator
Operator - places/fastens part onto a partially completed assembly/subassembly

5. Automatic Assembly (free transfer/non-synchronous system)
Gravity Feed Track
Bowl
Feeder
Workhead
Assembly Machine -
Workstations
Buffer Stock
Workcarrier
Partially completed assembly transferring to next station
Buffer
Space
Parts emptied into a bowl feeder which contain orienting devices.
Parts exit feeder go down track in preparation for insertion.

6. Schematic of assembly system
Four Station Automatic Assembly System for Irrigation Mini-Drippers (Rotary Indexing Machine)
Schematic of assembly system
Mini-dripper has a base, body, regulator and cover.

7. Orienting system for cup shaped parts
Automatic Handling (From “Handbook of Feeding and Orienting Techniques for Small Parts,” by Boothroyd, Poli and Murch)
Bowl Feeder
Orienting system for cup shaped parts

8. Cost of An Assembly Number of parts
Ease with which the parts can be > Handled > Inserted

9. Rule #1 - Eliminate Parts
Outright elimination of parts. (screws, nuts, washers, etc.- use snap fits)
Combining 2 or more distinct parts into a single molded, cast or stamped part.
9 parts
2 parts

10. Eliminate Fasteners If not possible, reduce the number or variety
Incorporate the fastening function with another feature
1 screw
4 screws
Snap
Screws aren’t expensive - driving them is!

11. Can Parts Be Combined?
Since there is no relative motion between the parts - and
Since these parts can be made of the same material
Why not combine them?

12. Rule #2 -Design Parts So they can be easily handled and Inserted Bins
Workstation
Fixture
Operator

13. Factors Affecting Manual Handling Time (Cost)*
Part
Symmetry > End-to-end > Rotational
Size
Thickness
Mass
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992

14. If the part is Easy to Grasp and Manipulate with One Hand and No Tools

15. Examples of Symmetry Parts with end-to-end symmetry
Parts with no end-to-end symmetry
Dowel pin
washer
pin
bulb
nail
screw
disk
key

16. Examples of Rotational Symmetry
Parts with rotational symmetry.
Parts with no rotational symmetry.
bulb
pin
screw
washer
Kollmorgen
disk
key

17. Illustrations of Size and Thickness

18. Illustrations of Light and Heavy Mass

19. Parts are Difficult to Grasp and Manipulate
Flexible - two hands to keep orientation prior to insertion (belts, chains, gaskets)
Do not nest or tangle
Nest or tangle (and degree of severity)
Slippery (ball bearings with oil)

20. Parts are Difficult to Grasp and Manipulate - continued
Due to obscured view/access
Need Grasping Tools (tweezers, magnets, snap rings, )
Due to part size/thickness
Two hands
Heavy
Large
Expansion board
Computer chip
Fragile

21. Parts are Difficult to Grasp and Manipulate - continued
Sharp/hot/ undesirable to touch
Grease on ball bearing
Part with adhesive
Sticky

22. Factors Affecting Manual Insertion*
Dog point
No chamfers
Chamfers
Ease of alignment (provide feature to ease insertion)
Ease of insertion
(affected by clearance, jamming, wedging, pushing against a force)
Part jams on corners
Same clearance, no jamming
chamfers
Negative clearance (press fit) Push against a force
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992

23. Factors Affecting Manual Insertion - continued
Obstructed view and/or obstructed access
Task: Place battery in shaver.
View clear? Need to rely on tactile sensing?
Access clear? Is there a feature that restricts access to the operator?
Self-locating, no need to hold

24. Additional Considerations
Insert vertically from above (i.e. don’t fight gravity)
Yes No
Provide features/obstructions to prevent incorrect assembly of the part.

25. Additional Considerations
Eliminate difficult to control operations - - welding, brazing, gluing, etc
Eliminate extra operations such as special adjustments, torque adjustments etc.

26. Additional Considerations
Design products into sub-assemblies that can be assembled and tested separately.
‘De-couple’ manual and machine operations.
Group manual assembly operations to optimize line balancing.

27. Precision needed if you need to do process planning.
Assembly Analysis
Three choices to analyze an assembly:
Precise quantitative method - such as the Boothroyd approach*.
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992
Precision needed if you need to do process planning.
Use an approximate approach during configuration stage of design?
Assembly Advisor
Allow 7-9 sec/part
(Compromise approach)
(Fails to focus attention on characteristics that make assembly difficult)

28. Assembly Advisor

29. Combining Parts
If Cdcx<5:
yes!
Question: Is the design on the right, which contains fewer parts, less costly?