FORMING AND
SHAPING PROCESSES AND EQUIPMENT
Rolling
Rolling is one of the most important processes in
the primary working of metals. Rolled plates, sheets, shape, pipe and tubing, and foil are
used in a wide variety of products, ranging from beverage cans and packaging to car
bodies, boilers, and ship hulls. In additional to flat rolling, shape rolling is used to
make products with various cross-sections, such as bars, rods, and structural shapes for
buildings and transportation equipment. An important development is continuous casting of
billets, which are rolled directly into semifinished products. As in all metalworking
processes, rolling involves a number of process and material variable that should be
controlled in order to roll products having high quality, properties, surface finish, and
dimensional accuracy. These variables include rolling temperature and speed, lubrication,
and the condition of the rolls and the characteristics of the equipment.
Forging
Forging is a metalworking process and is
capable of producing a wide variety of parts with favorable characteristics of strength,
toughness, dimensional accuracy, and reliability in service. Die design and material
behavior during deformation, as well as friction, heat transfer, and material-flow
characteristics in a die cavity, are important consideration. Also important is the proper
selection of die materials, lubrications, temperatures, speeds and equipment. Defects can
develop if the process is not controlled properly.
A variety of forging machines is available, each
with its own characteristics and capabilities. Forging processes have been highly
automated with industrial robots and computer controls. Computer-aided design and
manufacturing techniques are now being used extensively in die design and manufacturing,
as well as in perform design and predicting material flow and possibility of internal and
external defects during forging.
Extrusion and Drawing
The extrusion process is capable of producing
lengths of solid or hollow sections with constant cross-sectional area. Important factor
in successful extrusion are die design, extrusion ratio, lubrication, billet temperature,
and extrusion speed. Cold extrusion, which is a combination of various extrusion and
forging operation, is capable of economically producing discrete parts with good
mechanical properties.
Rod, wire and tube have numerous important
applications. These products are made basically by a drawing process in which the material
is pulled though or more dies. Although the cross-sections of most drawing products are
round, rectangular and other can be drawn. Drawing tubular products usually require
internal mandrels. Proper design and selection of die material and lubrications are
essential to obtaining the product with good quality and surface finish, dimensional
accuracy and strength.
Sheet-Metal Forming
Sheet-metal forming processes are among
the most versatile of all forming operations and generally are used with workpieces having
high ratios of surface area to thickness. Unlike bulk deformation processes, such as
forging and extrusion, the cross-sectional area of the material in sheet forming is
generally prevented from being reduced, avoiding necking and tearing. The important
material parameters are capacity of the sheet metal to stretch uniformly and its
resistance to thinning. Various tests have been developed predict the formability of sheet
metals.
Because of the thin sheet used, springback, buckling
and wrinkling are significant problem in sheet forming. This problem can be avoided by
proper tool and die design and by minimizing the unsupported length of material during
processing. The forces and energy required in sheet forming can be transmitted to the
workpiece through solid tools and dies; flexible rubber or polyurethane members; and
electrical, chemical, magnetic, and gaseous means.
Powder Metallurgy
The powder-metallurgy process consists of
preparing metal powders, compacting them into shape, and sintering them to impart
strength, hardness and roughness. Although size and weight are limited, the process is
capable of producing relatively complex parts economically, in net-shape form to close
tolerances, from a wide variety of alloy and metal powders. Control of powder shape and
quality, process variables, and sintering atmosphere are important considerations in
product quality. Parts may be subjected to additional metalworking, machining and
finishing operations to impart certain geometric features and to improve properties and
dimensional accuracy.
Tooling design compacting pressure can control
density and mechanical and physical properties. Some critical parts, such as jet-engine
component, are now being made by P/M techniques. By controlling porosity, products such as
filters and oil-impregnated bearing can be made. The P/M process is suitable for medium-to
high-volume production runs, and has competitive advantages over other methods of
production, such as casting, forging, and machining. Among newer developments in P/M
techniques is selective laser sintering as a method of prototyping?
Forming and Shaping Plastics and Composite Materials:
Rapid Prototyping
Plastics can be formed and shaped by variety of
processes, such as extrusion, molding, casting and thermoforming. The starting material is
usually in the form of pellets and powders. Thermosets are generally molded and cast, and
thermoplastics are formed by these processes as well as by thermoforming and techniques
used for metalworking. The high strain-rate sensitivity of thermoplastics allows extensive
stretching in forming operations; thus complex and deep shapes can be produced. The design
of plastic parts should include consideration of their low strength and stiffness, as well
as physical properties such as high thermal expansion and low resistance to temperature.
Reinforced plastics are shaped into important
structural components using liquid plastics, prepregs, and bulk-and sheet-molding
compounds. Fabricating techniques include various molding methods, filament winding, and
pultrusion. Important factors in fabricating reinforced-plastic components are the type
and orientation of the fibers and the strength of the bond between fibers and matrix and
between different layers of materials. Inspection techniques are available to check the
integrity of these products.
Forming and Shaping Ceramics and Glass
