author owes much to many people. I am grateful to my son Sasha, who labored countless hours at converting AutoCAD drawings into a format compatible with commercial printing. In addition, I would like to acknowledge John F. Carleo, editorial director at Industrial Press, who worked with me during the manuscript preparation and persuaded me of the continuing interest of Industrial Press in publishing my fourth book. Finally, I wish to thank Em Turner Chitty for her help.
Vukota Boljanovic
Knoxville, Tennessee
Classification Of Shaping Processes
Production Equipment And Tooling
Manufacturing is the procedure by which materials are transformed into desired shapes. Materials are first formed into preliminary shapes, and then refined into more precise shapes, after which the final shaping and finishing operations are performed. The shaping process is one broad category of manufacturing processes. In the shaping process, a component or product can be created from a solid, granular, particle state, or liquid state, meaning the state of the work material in the shaping phase. In the design of a shaping process, the only factors that are known at the outset are the final product shape and the material with which it is to be made. It is the engineer who must design a process to make a defect-free product; the engineer always operates under constraints due to the shape of the desired object, the material’s properties, the cost of production, the time available, and many other factors. Shaping processes influence the vast majority of products bought or used by consumers. This is the reason why in this book so much space will be devoted to discussing particular shaping processes. These are processes that you, as a designer or manufacturing engineer, will most likely use or encounter while engaged in the practice of mechanical or industrial engineering.
CLASSIFICATION OF SHAPING PROCESSES
Classification of technological shaping processes may be based on many different criteria, depending on the purpose of the processes. In general, shaping process can be classified into two main categories: primary and secondary shaping processes. The primary shaping processes form the overall shape of the product or the component that will, with other parts make up the final product’s shape. The purpose of secondary processes is to provide the final, precisely shaped surfaces that will meet product requirements, such as surface or dimensional tolerances.
The classification used in this book refers to primary shaping processes and is based on the state of the starting material. There are four broad categories of primary shaping processes for metals (Fig. I.1):
Fig. I.1 Classification of primary metal shaping processes.
1.Casting, molding, and other processes, in which the starting material is in the form of a heated liquid.
2.Particulate processing (powder metallurgy), in which the starting material is a powder.
3.Deformation processes, in which the starting material is a solid that is deformed to shape the components.
4.Metal removal processes, in which the starting material is a solid whose size is sufficiently large for the final geometry of parts to be circumscribed by it; in these processes, the unwanted material is removed as chips, particles, and so on.
Casting and molding. In this category starting material is heated to transform it into a liquid state; after that, the material is poured or in some other way forced to flow into a die cavity and allowed there to solidify, thus taking the shape of the cavity, which is nearly the shape, or the “net” shape, of the part. This type of primary shaping process is called casting. Casting processes use two types of mold: expandable mold (sand casting, shell mold casting, investment casting, and ceramic mold casting); and permanent mold (permanent-mold casting, die casting, centrifugal casting, and squeeze casting).
Particulate processing. In this category the starting materials are metals or ceramics in powder form. In this process, metal powders are compressed into desired shapes (often complex) and sintered (heated without melting) to form a solid component. This type of primary shaping process is called powder metallurgy.
Deformation processes. In this category the starting material is in a solid state. The initial shaping of the workpiece is accomplished through the application of external forces to the solid work material, with these forces being in equilibrium. Wit the application of load to the workpiece, internal stress and displacements are generated, causing shape distortions. This type of shaping process is called “deformation”.
Deformation processes can be conveniently classified into bulk deformation processes (rolling, extrusion, and forging) and sheet metal processes (shearing, bending and drawing, and forming). In both cases the surfaces of the deforming material and of the tools are usually in contact, and the friction between them has a major influence. In bulk forming the input material is in billet, rod, or slab form, and a considerable increase in the surface-to-volume ratio occurs in the formed part. In sheet metal processes a sheet blank is plastically deformed into a complex three-dimensional configuration, usually without any significant change in sheet thickness and surface characteristics.
Bulk deformation processes have the following characteristics:
•The workpiece undergoes large plastic deformation, resulting in an appreciable change in shape or cross section.
•The portion of the workpiece undergoing permanent plastic deformation is generally much larger than the portion undergoing elastic deformation. Therefore, elastic recovery or spring-back after deformation is negligible.
The characteristics of sheet metal processes are as follows:
•The workpiece is a sheet or a part fabricated from a sheet. The deformation usually causes significant changes in shape but not in the cross-section of the sheet.
•In some cases the magnitudes of permanent plastic and recoverable elastic deformations are comparable; therefore, elastic recovery or springback may be significant.
Material removal processes. Machining processes are frequently used as primary or secondary processes. In these processes the size of the original workpiece is large enough so that the final geometry of the finished piece can be achieved by employing one or more removal operations. The chips or scrap are necessary to obtain the desired geometry, tolerance, and surface finish. The amount of scrap may vary from a few percent to more than 70% of the volume of the starting workpiece material. Machining as a primary process used for low-production volume parts, for the production of prototypes, and for production of the tooling used in processes such as stamping, injection molding, and other processes, generates a part’s shape by changing the volume of the workpiece through the removal of material.
Machining is also used as a secondary process. Thus, machining
