Manufacturing processes can be broadly divided into two groups and they are primary manufacturing processes and secondary manufacturing processes. The former ones provide basic shape and size to the material as per designer’s requirement. Casting, forming, powder metallurgy are such processes to name a few. Secondary manufacturing processes provide the final shape and size with tighter control on dimension, surface characteristics etc. Material removal processes are mainly the secondary manufacturing processes. Material removal processes once again can be divided into mainly two groups and they are “Conventional Machining Processes” and “Non-Traditional Manufacturing Processes”. Examples of conventional machining processes are turning, boring, milling, shaping, broaching, slotting, grinding etc. Similarly, Abrasive Jet Machining (AJM), Ultrasonic Machining (USM), Water Jet and Abrasive Water Jet Machining (WJM and AWJM), Electro-discharge Machining (EDM) are some of the Non Traditional Machining (NTM) Processes. (ii) Classification of Non Traditional Machining Processes
To classify Non Traditional Machining Processes (NTM), one needs to understand and analyse the differences and similar characteristics between conventional machining processes and NTM processes. Conventional Machining Processes mostly remove material in the form of chips by applying forces on the work material with a wedge shaped cutting tool that is harder than the work material under machining condition. Such forces induce plastic deformation within the work piece leading to shear deformation along the shear plane and chip formation. Fig. 9.1.1 depicts such chip formation by shear deformation in conventional machining.
Thus the major characteristics of conventional machining are: • Generally macroscopic chip formation by shear deformation • Material removal takes place due to application of cutting forces – energy domain can be classified as mechanical • Cutting tool is harder than work piece at room temperature as well as under machining conditions
Non Traditional Machining (NTM) Processes on the other hand are characterised as follows: • Material removal may occur with chip formation or even no chip formation may take place. For example in AJM, chips are of microscopic size and in case of Electrochemical machining material removal occurs due to electrochemical dissolution at atomic level • In NTM, there may not be a physical tool present. For example in laser jet machining, machining is carried out by laser beam. However in Electrochemical Machining there is a physical tool that is very much required for machining • In NTM, the tool need not be harder than the work piece material. For example, in EDM, copper is used as the tool material to machine hardened steels. • Mostly NTM processes do not necessarily use mechanical energy to provide material removal. They use different energy domains to provide machining. For example, in USM, AJM, WJM mechanical energy is used to machine material, whereas in ECM electrochemical dissolution constitutes material removal.
Thus classification of NTM processes is carried out depending on the nature of energy used for material removal. The broad classification is given as follows: • Mechanical Processes
⎯ Abrasive Jet Machining (AJM)
⎯ Ultrasonic Machining (USM)
⎯ Water Jet Machining (WJM)
⎯ Abrasive Water Jet Machining (AWJM)
• Electrochemical Processes
⎯ Electrochemical Machining (ECM)
⎯ Electro Chemical Grinding (ECG)
⎯ Electro Jet Drilling (EJD)
• Electro-Thermal Processes
⎯ Electro-discharge machining (EDM)
⎯ Laser Jet Machining (LJM)
⎯ Electron Beam Machining (EBM)
• Chemical Processes
⎯ Chemical Milling (CHM)
⎯ Photochemical Milling (PCM) etc.
(iii) Need for Non Traditional Machining
Conventional machining sufficed the requirement of the industries over the decades. But new exotic work materials as well as...