By definition, machining is one of the secondary manufacturing processes by which excess material is gradually removed by shearing from a pre-formed blank in the form of solid chips using a wedge shaped cutting tool in order to get desired shape, finish and tolerance. It follows subtractive manufacturing approach to fabricate desired object. Examples include turning, threading, facing, drilling, boring, milling, shaping, etc. Such conventional machining processes are unable to cope up with the ever-growing demands for miniaturized products with high surface quality and close dimensional tolerance. Moreover, newly developed materials display unacceptable machinability in many occasions. All these limitations paved the way for finding out alternative machining processes that can satisfactorily process wide variety of materials and produce surface finish in the range of nanometers with improved accuracy. Subsequently many non-traditional machining (NTM) or unconventional machining processes have emerged that to cater the need of market.
In NTM processes, neither shearing occurs nor chips form. In fact, such processes don’t even utilize a so called cutting tool. Instead of only mechanical energy, various forms of energy (mechanical, thermal, electrical, chemical, electro-chemical, light, etc.) are used in their direct form in such NTM processes to remove material. Material removal is also realized in several ways such as by erosion, melting and vaporization, ionic dissolution, etc. There are several NTM processes, for example abrasive jet machining, ultrasonic machining, electro-chemical machining, electro-discharge machining, laser beam machining, etc. Each process has distinct capabilities and is suitable for specific purposes. Various similarities and differences between conventional machining and non-traditional machining (NTM) processes are given below in table format.
Similarities between conventional machining and NTM
- Both are machining processes and thus used for removing excess material.
- Both are subtractive manufacturing processes (top-down approach).
- Both are secondary manufacturing processes.
- Both can produce sufficiently smooth and finished surface with close tolerance, although different processes have different capability.
Differences between conventional machining and NTM
| Conventional Machining | Non-Traditional Machining (NTM) |
|---|---|
| Only mechanical energy (power) is utilized to gradually remove excess material from workpiece. | Various forms of energy (like electrical, mechanical, thermal, chemical, light, etc. or a combination of two or more such forms) are directly utilized to remove excess material. |
| Materials are removed in the form of tiny sharp chips. | So called ‘chip’ is not produced here. Material is removed in various forms, such as tiny metal particles, ions, molten or vapor, etc. |
| ‘Shear deformation’ is the only phenomenon that causes removal of material. | Shear deformation plays an insignificant role in material removing in most of the NTM processes. Instead, erosion, dissolution, evaporation, sputtering, etc. occur here. |
| A sharp wedge shaped cutting tool having specific geometry, material and properties is required for cutting action. | So called cutting tool does not exist here. However, in few cases (for example ECM, EDM) tool is required and its profile & property must match with the requirement. |
| Physical contact between cutting tool and workpiece and also relative velocity in between them are indispensably necessary in order to remove materials. | Although no physical contact occurs between cutting tool and workpiece, in few processes such as AJM, AWJM, & USM solid abrasive grits strike the work surface to erode material. |
| These processes are age old and thus physics of the processes are well-understood. Skilled labors are also readily available at comparatively cheaper cost. | Most of these processes are developing. Labor cost is also high due to less number of skilled labors available in this field. |
| It can provide a wide range of surface finish depending on the process that is employed and also the process parameters. However, getting surface finish below 10µm is quite difficult and that requires costly CNC system. | Achievable surface finish is much better than that for conventional processes. It can easily provide a surface finish in nanometer range. |
| These processes are suitable for bulk removal of material. In this sense, these are fast, reliable, and economic (higher material removal rate—MRR). | These are suitable for highly accurate and precise requirements. For bulk removal of materials, these processes are time consuming, less reliable, and uneconomic. |
| There are certain shapes that cannot be produced by conventional machining. | NTM processes sometime become a reliable option for producing such critical shapes. Buy this book |
| Examples of conventional machining processes— Turning, Facing, Grooving, etc.Drilling, Boring, Reaming, etc.Shaping, Planing, Milling, etc.Grinding, Lapping, Honing, etc. | Examples of non-traditional machining processes— AJM, AWJM, USM, etc.EDM, ECM, CHM, etc.LBM, PAM, EBM, IBM, etc.Hybridization of above processes |
References
- Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
- Advanced Machining Processes by V. K. Jain (Allied Publishers Private Limited).
- Nonconventional Machining by P. K. Mishra (Narosa Publishing House).