Introduction to shaping operations

INTRODUCTION TO SHAPING OPERATIONS

Shaping operations take raw materials and modify their form to make the intermediate and final product shapes. The component or product can be created from a solid, granular, particle state or liquid state based on the state of the work material in the shaping phase.

In general, the shaping operations are classified into two main types: primary and secondary.

Primary shaping operations form the overall shape of the product or the component such as sheet, bar, plate, or some other preliminary form.

Secondary shaping operations take the preliminary form and alters its shape further to a final, precisely shaped version of the product that will meet the product requirements. Secondary operations further improve the properties, surface quality, dimensional accuracy, tolerance, etc. These operations are primarily used to remove metal to develop a specific form from the unfinished piece.

1. Primary Shaping Operations

There are four broad categories of primary shaping operations for metals as follows:

(a) Casting and moulding:

In this category, the raw material is heated to transform it into a liquid state. Then the material is poured or in some other way forced to flow into a die cavity and allowed there to solidify. Thus the material is taking the shape of cavity which is nearly the shape of the part. This type of primary shaping operation is called casting. The detailed explanation of casting and moulding processes are available in Chapter 1 of this book.

(b) Particulate processing (powder metallurgy):

In this category, the raw materials are metals or ceramics in powder form. In this process, metal powders are compressed into desired shapes and sintered (heated without melting) to form a solid component. This type of primary shaping operation is called powder metallurgy.

(c) Deformation processes:

In this category, the raw materials is in a solid state. The initial shaping of workpiece is obtained through the application of external forces to the solid material. With the application of load to the workpiece, internal stresses and displacements are generated which causes the shape distortion. This type of shaping process is called deformation.

Deformation processes can be conveniently classified into bulk-forming processes (e.g., rolling, extrusion, and forging) and sheet-forming processes (e.g., stretching, flanging, drawing, and contouring). In both cases, the surfaces of the deforming material and of the tools are usually in contact, and 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 forming, a sheet blank is plastically deformed into a complex three-dimensional configuration, usually without any significant change in sheet thickness and surface characteristics.

(d) Material removal processes:

Material removal processes are frequently used as primary or secondary operations. 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 scarp may vary from a few percentage to more than 70% of the volume of the starting workpiece material.

Machining as a primary operation used for low-production parts, for the production of prototypes, and for production of the tooling used in processes such as stamping, injection moulding and other processes. Machining operation generates a part's shape by changing the volume of the workpiece through the removal of material.

Machining is also used as secondary operation. Thus, machining is used to improve a basic shape that has been produced by casting or deforming processing, as well as to produce basic shape itself.

2. Secondary Shaping Operations

As large number of components require further processing after the primary operations. These components are subjected to one or more number of machining operations in machine shops, to obtain the desired shape and dimensional accuracy on flat and cylindrical jobs. Thus, the jobs undergoing these operations are the roughly finished products received through primary shaping operations. The process of removing the undesired or unwanted material from the work piece or job or component to produce a required shape using a cutting tool is known as machining.

This can be done by a manual process or by using a machine called machine tool (traditional machines namely lathe, milling machine, drilling, shaper, planner, slotter). In many cases these operations are performed on rods, bars and flat surfaces in machine shops. These secondary operations are mainly required for achieving dimensional accuracy and a very high degree of surface finish. The secondary operations require the use of one or more machine tools, various single or multi-point cutting tools (cutters), job holding devices, marking and measuring instruments, testing devices and gauges etc. for getting desired dimensional control and required degree of surface finish on the workpieces. The example of parts produced by machining processes includes hand tools machine tools instruments, automobile parts, nuts, bolts and gears etc. Lot of material is wasted as scrap in the secondary or machining process.

Some of the common secondary or machining operations are: turning, drilling, boring, cutting and shaping, milling, reaming, threading, knurling, broaching, grinding, stamping, polishing, hobbing, planning etc. Various unconventional machining operations namely machining with Numerical Control (NC) machines tools or Computer Numerical Control (CNC) machines tools using Electro Discharge Machining (EDM), Electro Chemical Machining (ECM), Laser Beam Machining (LBM), Abrasive Jet Machining (AJM), Ultrasonic Machining (USM) setups etc. will also come into this category.