1. ME 330 Manufacturing Processes MECHANICAL ASSEMBLY: Joining Methods (cont.)

2. Two Major Types of Mechanical Assembly
allow for disassembly
create a permanent joint with no possibility of disassembly
Use of the third part component
Use of the deformation between two components to be assembled.
For example, adhesion and bonding
Why would you ever want to make a part with a permanent joint??
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Principle: elasticity and plasticity

3. Mechanical Assembly Approach: Deformation to make two parts fit or lock each other together

4. Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation

5. Law 1: Force-deformation effect: elasticity and plasticity.
Law 2: Thermal-deformation effect: varying the temperature of an object can lead to the expansion or contraction of an object in geometry.
Principle 1: Part A is in a forced state and Part B constrains Part A, which leads to the interference fit or assembly of A and B due to Law 1.
Principle 2: Part A is in an thermal or cooled state and Part B constrains Part A, which leads to the interference fit or assembly of A and B due to Law 2.
Principle 3: mutual interlock of A and B, which leads to a joint of A and B; the assembly process further follows Principles 1 and/or Principle 2.

6. The principle of a process explains why and how a process works.
In the case of assembly of two parts A and B without a third part, the principle of a process explains why and how A and B can be assembled.

7. Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation

8. Mechanical approach to introduce an interference fit in assembling two parts
Press
Shrink and expansion
Snap
Retaining ring
Mold (permanent)
Integral

9. Press Fitting  Press and then fit
A straight cylindrical pin of a certain diameter is pressed into a hole which has a slightly smaller diameter than the pin.
Diameter of the hole (inner) is smaller than diameter of the pin.
After pressing on the perimeter of the pin, the diameter of the pin is smaller so that it can be inserted into the hole.
Roll Pin
Spiral Pin
Hole
- Parts do not need to be cooled/heated to fit together
- Show example of tool to push pin in, and tool to push pin out
Aside: gunreports.com for pin types
Remark 1: Press assembly follows Principle 1

10. Press Fitting Functions: Locate and lock components in place.
Facilitate the formation of pivot joint - to create shafts to allow one component to rotate about the other.
Facilitate the formation of safety device - to break in overload conditions to save the rest of the assembly from failure.
- Parts do not need to be cooled/heated to fit together
- Show example of tool to push pin in, and tool to push pin out
Aside: gunreports.com for pin types

11. Facilitate the formation of a safety device - to break in overload conditions to save the rest of the assembly from failure due to high stress created in the shaft.
(a)
(b)
- Parts do not need to be cooled/heated to fit together
- Show example of tool to push pin in, and tool to push pin out
Aside: gunreports.com for pin types
Assume the gray is the pin. In (a), pin (gray) is fixed with shaft (green). Suppose the assembly of the gray and blue is based on the press fit, and the assembly of the gray and green is permanent joint. When there is a overloading along the shaft (green), the whole assembly comes to the situation (b).

12. Shrink and Expansion
Shrink fitting - external part is enlarged by heating and internal part is inserted into the external part. Shrink to create interference fit when back to room temperature.
Expansion fitting - internal part is contracted by cooling and inserted into external part, then expands to create interference fit when back to room temperature.
Commonly used to fit gears, pulleys, and sleeves onto shafts
Principle 2: Part A is in an thermal or cooled state and Part B constrains Part A, which leads to the interference fit or assembly of A and B due to Law 2.
Remark 2: This assembly process follows Principle 2

13. Snap Both parts are deforming during the assembly process
Joining two parts in which mating elements possess a temporary interference during assembly, but once assembled they interlock.
During assembly, one or both parts elastically deform to accommodate the temporary interference.
Both parts are deforming during the assembly process
Remark 3: Snap follows Principle 3 with Principle 1

14. Retaining Rings Remark 4: The assembly process follows Principle 1
Fastener that snaps into a circumferential groove on a shaft or bore to form a shoulder
Function: to locate or restrict movement of parts on a shaft or bore
Internal
External
Used to locate or restrict movement of parts on a shaft
like bearings
Remark 4: The assembly process follows Principle 1
E-clip
Push-on

15. Molding Inserts
Placement of a component into mold prior to plastic molding or metal casting, so that it becomes a permanent and integral part of the molding or casting: (a) threaded bushing, and (b) threaded stud

16. Pros of molding Inserts
Insert has better properties than molded or cast material.
Insert geometry is too complex or intricate to incorporate into mold cavity.
Applications:
Internally threaded bushings and nuts
Externally threaded studs
Bearings
Electrical contacts
Remark 5: The assembly process follows Principle 2

17. Integral Lanced tabs Seaming
Both parts are deformed, so they interlock as a mechanically fastened joint. Methods include:
Lanced tabs
Seaming

18. Integral - lanced tabs
Lanced tabs to attach wires or shafts to sheet metal
Many different shapes
Remark 6: This process follows Principle 3 with Principle 1

19. Integral - Seaming
Edges of two separate sheet metal parts or the opposite edges of the same part are bent over to form the fastening seam
Canned food
I will show another joint: It is a proprietary joint called the Loc-L-joint:
Alternative for rivets
Remark 6: This process follows Principle 3 with Principle 1

20. Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation

21. Design for Assembly (DFA)
Keys to successful DFA:
Design products with as few parts as possible.
Design parts such that they can be easily assembled.
Knowing how a product can be assembled as well as assembly costs.
DFA is done during the design stage.
Keep in mind: high volume of products may need to be assembled, so costs add up quick

22. DFA Guidelines Reduce the number of threaded fasteners
Use quicker fastening methods such as snap fits, retaining rings, and integral fasteners.
2. Use threaded fasteners where disassembly is required.
Reduce the variety of fasteners

23. DFA Guidelines
Use modularity in product design: Design the subassembly around a base part to which other components are added.
Reduce the need for multiple components to be handled at once: Use separate operations for each component.
Limit the required directions of access: Adding all components vertically from the bottom to top is the ideal.
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24. Summary
Assemble without a need of the third party but two parts themselves.
Two laws in physics and three principles for the assembly process design.
Laws  Principles  Structuring  Applications/Functions.
Design For Assembly (DFA).
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Promoting innovation: new principle, new process, new equipment