The Fine Line Between Honest and Evil Comics by Salty Vixen
Reduce manual assembly costs
1. Product design for manual assembly
DFA tool: To reduce manufacturing and assembly costs.
Effectively analyses the ease of assembly, Quick results simple and
easy to use.
Free association of ideas, comparison of alternative designs,
identification of assembly problem areas, evaluation of solutions
logically,
Ideas, reasoning and decisions made during the design process
become useful for future reference.
Database for assembly times and cost factors for various design
situations and production conditions.
The ease of assembly depends on manual or general purpose
automation or special purpose automation.
2. Manual assembly: Handling, insertion and fastening
Guide lines for part handling:
Design parts with end to end symmetry and rotational
symmetry about the axis of insertion
Provide features that will prevent jamming of parts stacked in
bulk
Avoid features that allow tangling of parts
Guide lines for part insertion and fastening:
Provide chamfers to guide insertion of two mating parts
Generous clearance should be provided
Where ever possible avoid holding down of parts
Use pyramid assembly, progressive
3. Manual insertion and fastening consist of a finite variety of basic
assembly tasks.
Peg in hole, screw, weld, rivet, press fit.
Factors effecting handling times.
Part symmetry, Part thickness and size, Part weight
Parts requiring two hands: Heavy, Very precise, large, flexible, part
does not posses holding features
Combination of factors
Parts that severely nestle or tangle: Small, vision obscured, high
temp.
Chamfer on insertion operations: peg into a hole, part with a hole
onto peg.
Chamfer on peg is better, curved chamfers are better.
Insertion time depends on length, diameter ,chamfer and clearance.
Avoid jams and disc assembly problems: length and clearance
Holding down time: clearance, grip size and insertion length
4. Further Design guidelines
Avoid connections
Design so that access for assembly operations is not
restricted.
Avoid adjustments
Use kinematic design principles
Design parts to prevent nesting. Nesting is when parts that are
tacked on top of one another clamp to one another, for example,
cups and coffee lids.
Design parts with orienting features to make alignment easier.
5. To determine whether it is possible to combine neighboring parts:
•Must the parts move relative to each other?
•Must the parts be electrically or thermally insulated?
•Must the parts be made of different material?
•Does combing the parts interfere with assembly of other parts?
•Will servicing be adversely affected?
If the answer to all questions is “NO”, you should find a way to
combine the parts.
During the assembly of the product, generally a part is required only
when;
1.A kinematic motion of the part is required.
2.A different material is required.
3.Assembly of other parts would otherwise be prevented.
If non of these statements are true, then the parts do not need to
be separate entities and may be combined.
6. Design for Assembly Principles
• Minimize part count
• Design parts with self-locating features
• Design parts with self-fastening features
• Minimize reorientation of parts during assembly
• Design parts for retrieval, handling, & insertion
• Emphasize ‘Top-Down’ assemblies
• Standardize parts…minimum use of fasteners.
• Encourage modular design
• Design for a base part to locate other components
• Design for component symmetry for insertion
7. DFA Process
Product Information: functional requirements
Functional analysis
Identify parts that can be standardized
Determine part count efficiencies
Step 2
Step 1
Analyze data for new design
Step 3
Identify handling (grasp & orientation) opportunitiesStep 4
Identify insertion (locate & secure) opportunitiesStep 5
Step 6 Identify opportunities to reduce secondary operations
Identify quality (mistake proofing) opportunities
Benchmark when possible
Determine your practical part count
Step 7
9. Product Information: functional requirements
Functional analysis
Identify parts that can be standardized
Determine part count efficiencies
Step One
10. Considerations/Assumptions
• The first part is essential (base part)
• Non-essential parts:
– Fasteners
– Spacers, washers, O-rings
– Connectors, leads
• Do not include liquids as parts
(e.g.. glue, gasket sealant,)
13. Count Parts and Interfaces
• List number of parts
(Np)
• List number of
interfaces (Ni)
14. Determine if Parts Can be Standardized
• Can the current parts
be standardized?:
• Should they be?
• (Only put a “Y” if
both answers are
yes…)
15. Theoretical Part Count Efficiency
Theoretical Part
Count Efficiency
Theoretical Min. No. Parts
Total Number of Parts
Theoretical Part 1
Count Efficiency 10
Theoretical Part
Count Efficiency
=
= * 100
= 10%
* 100
GoalRule of Thumb – Part
Count Efficiency Goal >
60%
16. DFA Complexity Factor – Definition
• Assessing complexity of a product design
• Two Factors
• Np – Number of parts
• Ni – Number of part-to-part interfaces
– Multiply the two and take the square root of the
total
– This is known as the DFA Complexity Factor
S Np x S Ni
17. DFA Complexity Factor – Target
• Smaller is better (Minimize Np and Ni)
• Let Npt = Theoretical Minimum Number of parts
– from the Functional Analysis
– Npt = 5
• Let Nit = Theoretical minimum number of part to part interfaces
– Nit = 2(Npt-1)
– Nit = 2(5-1) = 8
Part 2
Part 3
Part 4
Part 5
Part 1
DCF = S Np x S Ni
DCFt = S Npt x S Nit
DCFt = 5 x 8 = 6.32
18. Determine Relative Part Cost Levels
• Subjective estimate only
• Low/Medium/High
relative to other parts
in the assembly and/or
product line
19. Cost Breakdown
• Media paper 21.4%
• Centertube 3.6%
• Endplates (2) 3.0%
• Plastisol 2.6%
• Inner Seal 4.0%
• Spring 0.9%
• Shell 31.4%
• Nutplate 21.0%
• Retainer 4.8%
• Loctite 0.3%
• End Seal 7.0%
27. Mistake Proofing Issues
• Cannot assemble wrong
part
• Cannot omit part
• Cannot assemble part
wrong way around.
symmetrical parts
asymmetrical parts
29. Quantitative criteria
• Handling Time: based on assembly process and
complexity of parts
– How many hands are required?
– Is any grasping assistance needed?
– What is the effect of part symmetry on assembly?
– Is the part easy to align/position?
30. Handling Difficulty
• Size
• Thickness
• Weight
• Fragility
• Flexibility
• Slipperiness
• Stickiness
• Necessity for using 1) two hands, 2) optical
magnification or 3) mechanical assistance
34. Quantitative criteria
• Insertion time: based on difficulty required for
each component insertion
– Is the part secured immediately upon insertion?
– Is it necessary to hold down part to maintain location?
– What type of fastening process is used? (mechanical,
thermal, other?)
– Is the part easy to align/position?
42. Error = Sum all Y’s in Error Columns
Proofing Theoretical Min. No. Parts
Handling = Sum all Y’s in Handling Columns
Index Theoretical Min. No. Parts
Insertion = Sum all Y’s in Insertion Columns
Index Theoretical Min. No. Parts
2nd Op. = Sum all Y’s in 2nd Op. Columns
Index Theoretical Min. No. Parts
Assembly Metrics
43. Analyze All Metrics
First consider:
Reduce part count and type Part Count Efficiency
and DFA Complexity Factor
Then think about:
Error Proofing Error Index
Then think about:
Ease of handling Handling Index
Ease of insertion Insertion Index
Eliminate secondary ops. 2nd Op. Index
Set Target Values for These Measures
45. Minimize part count by incorporating multiple functions into single
parts. Several parts could be fabricated by using different
manufacturing processes (sheet metal forming, injection molding).
47. Design to allow assembly in open spaces, not confined spaces
Do not bury important components
48. Parts should easily indicate orientation for insertion.
Parts should have self-locking features so that the precise alignment
during assembly is not required, or provide marks (indentation) to
make orientation easier.
53. Design the mating parts for easy insertion.
Provide allowance on each part to compensate for variation in
part dimensions.
Case 1
Case 2
54. Design the first part large and wide to be stable and then
assemble the smaller parts on top of it sequentially.
Case1
Case 2
55. If you cannot assemble parts from the top down exclusively, then
minimize the number of insertion direction.
Never require the assembly to be turned over.
Case 1
Case 2
56. Joining parts can be done with fasteners (screws, nuts and bolts,
rivets), snap fits, welds or adhesives.
