Mechanical Fastening, Casting and Forming Processes for Parts

Wedge Prisms and Shaft Connections

A wedge prism is generally a rectangular section used to transmit rotation and unite two mechanical parts. There are two main orientations:

• Longitudinal: used to provide a secure connection along the length of a shaft.
• Transverse: used to join two shafts that rotate on the same axis.

Tabs, Pins and Cylindrical Elements

Several small components are used to adjust, fasten and secure parts:

• Tab: a special kind of adjustment pin. Tabs typically have a straight section and the adjustment or locking action occurs through the sides.
• Pin: a rounded, elongated piece used as a fastener to secure two components together. Pins are commonly subjected to shear.
• Cylinders: one piece positioned over another but not rigidly fixed; they allow relative positioning or rotation when required.
• Cone: used for fixation by taper fit and alignment.
• Security elements: components used to immobilize a part once positioned.

Riveting and Tubular Rivets

Riveting: rivets are fasteners provided with a cylindrical shank and a head that can be deformed by compression to join parts.

Tubular rivet: a variant of rivets where the rivet has a hollow section and is used in a rivet hole; it is deformed to create the permanent fastening.

Welding Types and Definitions

Welding is the stable union of two parts (or two portions of a workpiece) obtained by the application of heat.

• Heterogeneous: welding where the filler material is different from the base metal.
• Homogeneous: welding performed without filler material so the weld is essentially identical to the base metal.

Wax Properties for Casting Patterns

Important wax characteristics for lost-wax and similar processes include:

• Plasticity: ability to retain the imprint of the pattern and sufficient strength to endure handling.
• Fineness: produces smooth molds without losing detail or contact with the metal.
• Permeability to gases: facilitates evacuation of gases during casting.
• Refractoriness: the mold must withstand casting temperatures.
• Contraction: minimal shrinkage of the molding sand when drying.
• Disaggregation: allows removal of the casting without leaving sand particles adhered to the part.

Molding Sand and Mold Assembly

Molding-sand and mold assembly steps (preserving original sequence): construction of the model; configuration of the bottom of the mold, which is filled with sand; configuration of the upper mold as before; installation of accessories for the sprue and vent; assembly of the complete mold; discharge (pouring) of molten material; and procurement (removal) of the finished piece.

Casting and Mold Operations

Casting-molding typical steps include:

• Preheating: empty mold or pan is heated before pouring.
• Pouring: the molten metal (fusion mass) is poured into the mold.
• Solidification and cooling: allow the casting to solidify and cool to room temperature.
• Opening: opening the mold and removing the piece.

Lost-Wax Molding Process

Lost-wax molding sequence (maintaining original content order): pattern/model preparation; construction of the casting system; elaboration of the wax model; preparation of the sand mold around the wax model; obtaining the sand mold after dewaxing; and finally obtaining the finished part.

Pressure Molding: Pros and Cons

Pressure-molding advantages and drawbacks are noted as follows:

• Advantages: thinner parts can be produced and there are fewer cracks.
• Drawbacks: it is expensive and some alloys cannot be processed by this method.

Elastic and Plastic Deformation

Elastic deformation is when, after the applied force stops, the material regains its original form.

Plastic deformation: after cessation of the force, the material remains permanently deformed.

Forging Operations and Terms

Forging operations include several basic processes (original terms preserved and clarified):

• Drawing: lengthening the piece while reducing its cross section.
• Upsetting (disgorging / emphasized): the reverse of drawing; increases cross section and reduces length.
• Punching: drilling or producing holes.
• Cutting: separation of material to size the part.
• Bending: plastic deformation to produce angles or curves.

Hot Imprinting and Finishing

Hot-imprinting: the preparation step that gives the piece a rough form close to the final geometry by forging or stamping. The piece is placed hot between dies or prints; finishing removes burrs or excess material.