# Two Major Types of Mechanical Assembly

## Presentation on theme: "Two Major Types of Mechanical Assembly"— Presentation transcript:

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

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?? Pass around phone

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

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

Law 1: Force-mechanical effect: elasticity and plasticity.
Law 2: Thermal-mechanical effect: varying temperature of an object can lead to expansion or contraction in geometry of the object. 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 assemble process further follows Principles 1 and/or 2.

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

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

Press Fitting  Press and then fit
Straight cylindrical pin of a certain diameter is pressed into a hole of a slightly smaller diameter. 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 Spirol 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

Press Fitting Functions: Locating and locking 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

Facilitate the formation of a safety device - to break in overload conditions to save the rest of the assembly from failure. (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 yellow is the pin. In (a), yellow is fixed with green and grey. Suppose the assembly of the yellow and green is based on the press fit, while the assembly of the yellow and grey is permanent joint. When there is a overloading along the shaft, the whole goes to the situation (b).

Shrink and Expansion Shrink fitting - external part is enlarged by heating and internal part is inserted, then shrinks to create interference fit when back at room temperature Expansion fitting - internal part is contracted by cooling and inserted into external part, then expands to create interference fit when back at room temperature. Commonly used to fit gears, pulleys, and sleeves onto shafts

Snap 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. Remark 3: Snap follows the interlock principle with Principle 1

Retaining Rings 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 Used to locate or restrict movement of parts on a shaft like bearings External E-clip Push-on

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

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

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

Integral - lanced tabs Lanced tabs to attach wires or shafts to sheet metal Many different shapes

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

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

Design for Assembly (DFA)
Keys to successful DFA: Design product with as few parts as possible Design parts so they are easy to assemble Important to how a product will be assembled and the assembly costs. DFA is done during the stage. Keep in mind: high volume of products may need to be assembled, so costs add up quick

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

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 from above is the ideal Remember the phone

Summary Assemble without a need of the third party but two parts themselves. Two laws in physics and three principles of such kind of assembly governs the process. Laws  Principles  Structuring  Applications/Functions. Design For Assembly (DFA). Remember the phone