Chapter 16 Manufacturing Products
Types of Manufacturing Processes There are thousands of manufacturing processes. Used to change the size and shape of materials, to fasten materials together, to give materials desired properties, or to coat the surfaces of products.
All secondary manufacturing processes can be classified into six groups; • Casting and molding. • Forming. • Separating. • Conditioning. • Assembling. • Finishing.
Casting and Molding Processes Three groups of processes give size and shape to pieces of material. First of theses is casting and molding. Casting and molding give materials shape by introducing a liquid material into a mold. Mold has a cavity of the size and shape that is wanted. Liquid material is poured or forced into the mold. Material is allowed to solidify before being removed.
All casting processes involve five basic steps: • Producing a mold of the proper size and shape. • Preparing the material. • Introducing the material into the mold. • Allowing the material to harden. • Removing the completed part from the mold.
Molds Two major types of molds used in casting and molding processes. These are expendable molds and permanent molds.
Expendable Molds Most cast products are made in molds that are used once. The mold is destroyed to remove the cast item.
Types of Expendable Molds Green sand casting uses sand held together with a binder. The sand is rammed around the pattern to form the mold cavity. Shell molding uses a sand and rein mixture. This mixture is poured over a heated metal pattern.
Investment casting uses molds made from plaster. The pattern is normally made from wax. Permanent Molds A second type of mold is called a permanent mold. Withstand repeated use.
Often made of steel, aluminum, or plaster. Mold must withstand temperatures above the melting point of the material being cast. Processes that use permanent molds are die casting, injection molding, and slip casting.
Forming Processes Forming is the second family of processes that give materials size and shape. All forming processes apply force through a forming device to cause the material to change shape.
All materials react to outside forces, small forces cause a material to flex. When the force is removed the material returns to its original shape. If the force increases, there is a point where the material will not return to its original shape. This point is called the yield point. The range between rest and the yield point is called the material’s elastic range.
Above the yield point the material will be permanently deformed. The greater the force the more the material will be stretched, compressed, or bent. This range is called its plastic range. Finally, the material cannot withstand any more force and it breaks. This point is called the fracture point.
Forming Devices • Forming processes are used to produce specific shapes in a material. Their must have a way to insure that the shape is correct and consistent. This is done by using one of two devices: • Dies. • Rolls.
Separating Processes Separating processes remove excess material to make an object of the correct size and shape. Casting and forming processes change the shape and size of materials without any removal. Remove material by either machining or shearing.
Machining is based on the motion of a tool against a work-piece to remove material. Shearing uses opposing edges of blades, knives or dies to fracture the unwanted material away from the work.
Machining • Machining removes excess material in small pieces. Machining cuts material away using three methods: • Chip removal: Using a tool to cut away the excess material in the form of chips.
Frame cutting: using the heat from burning gases to shape and size the material. • Nontraditional: using electric sparks, chemical action, sound waves, or light waves to separate material.
Shearing The second group of separating processes is shearing. Cuts material to create the desired size and shape. Shearing can be used to cut material to length, produce an external shape or generate an internal feature.
Conditioning processes Casting, molding, and separating operations change the external features of a work-piece. The material is given a new size and shape. In some cases this is not enough. Internal structure of the material needs to be changed, The material may need to be harder, softer, stronger, or be more easily worked.
To change internal properties, conditioning processes are used. Three types of conditioning processes are thermal, mechanical, and chemical conditioning.
Mechanical conditioning uses mechanical forces to change the internal structure of the material. Most metals become harder as they are squeezed, stretched, pounded, or bent. • Chemical conditioning uses chemical actions to change the properties of a material. The lenses of many safety glasses are chemically treated to make them more shatter-proof.
Most common conditioning processes use heat. These are called thermal conditioning and include heat treating, drying, and firing.
Assembly Processes Most of the things you see are made from more than one part.
Bonding Bonding holds plastic, metal, ceramic, and composite parts to each other. Bonding uses cohesive or adhesive forces to hold parts together.
Mechanical Fastening Mechanical fastening uses mechanical forces to hold parts together, friction between the parts can be used. The most widely used method to hold parts together are mechanical fasteners. Examples of fasteners are staples, rivets, screws, nails, pins, bolts, and nuts.
Finishing Processes The last secondary process most products go through is finishing. These techniques protect the product and enhance its appearance.