NON-TRADITIONAL MACHINING

NON-TRADITIONAL MACHINING

Non-traditional manufacturing processes is defined as a group of processes that remove excess material by various techniques involving mechanical, thermal, electrical or chemical energy or combinations of these energies but do not use a sharp cutting tools as it needs to be used for traditional manufacturing processes.

Extremely hard and brittle materials are difficult to machine by traditional machining processes such as turning, drilling, shaping and milling. Non traditional machining processes, also called advanced manufacturing processes, are employed where traditional machining processes are not feasible, satisfactory or economical due to special reasons as outlined below.

Very hard fragile materials difficult to clamp for traditional machining

When the workpiece is too flexible or slender

When the shape of the part is too complex

Several types of non-traditional machining processes have been developed to meet extra required machining conditions. When these processes are employed properly, they offer many advantages over non-traditional machining processes. The common non-traditional machining processes are described in this section.

Definition

A machining process is called non-traditional if its material removal mechanism is basically different than those in the traditional processes, i.e. a different form of energy (other than the excessive forces exercised by a tool, which is in physical contact with the work piece) is applied to remove the excess material from the work surface, or to separate the workpiece into smaller parts.

Non Traditional Machining (NTM) Processes 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,

Need for development of Non Conventional Processes

The strength of steel alloys has increased five folds due to continuous R and D effort. In aero-space requirement of High strength at elevated temperature with light weight led to development and use of hard titanium alloys, nimonic alloys, and other HSTR alloys. The ultimate tensile strength has been improved by as much as 20 times. Development of cutting tools which has hardness of 80 to 85 HRC which cannot be machined economically in conventional methods led to development of non –traditional machining methods. 8888

1.Technologically advanced industries like aerospace, nuclear power, ,wafer fabrication, automobiles has ever increasing use of High –strength temperature resistant (HSTR) alloys (having high strength to weight ratio) and other difficult to machine materials like titanium, SST,nimonics, ceramics and semiconductors. It is no longer possible to use conventional process to machine these alloys.

2. Production and processing parts of complicated shapes (in HSTR and other hard to machine alloys) is difficult , time consuming an uneconomical by conventional methods of machining 3.Innovative geometric design of products and components made of new exotic materials with desired tolerance , surface finish cannot be produced economically by conventional machining.

4.The following examples are provided where NTM processes are preferred over the conventional machining process:

Intricate shaped blind hole – e.g. square hole of 15 mmx15 mm with a depth of 30 mm with a tolerance of 100 microns

Difficult to machine material – e.g. Inconel, Ti-alloys or carbides, Ceramics, composites , HSTR alloys, satellites etc.,

Low Stress Grinding – Electrochemical Grinding is preferred as compared to conventional grinding

Deep hole with small hole diameter – e.g. φ 1.5 mm hole with l/d = 20

Machining of composites

NON-TRADITIONAL MACHINING
NON-TRADITIONAL MACHINING


SELECTION OF PROCESS

The correct selection of the non-traditional machining methods must be based on the following aspects.
i) Physical parameters of the process
ii) Shape to be machined
iii) Process capability
iv) Economics of the processes

Physical parameter of the process

PAM and ECM require high power for fast machining. EBM and LBM require high voltages and require careful handling of equipment. EDM and USM require medium power . EBM can be used in vacuum and PAM uses oxygen and hydrogen gas.

Shapes cutting capability

The different shapes can be machined by NTM. EBM and LBM are used for micro drilling and cutting. USM and EDM are useful for cavity sinking and standard hole drilling. ECM is useful for fine hole drilling and contour machining. PAM can be used for cutting and AJM is useful for shallow pocketing.

Process capability

The process capability of NTM is given in Table 2.0 EDM which achieves higher accuracy has the lowest specific power requirement. ECM can machine faster and has a low thermal surface damage depth. USM and AJM have very material removal rates combined with high tool wear and are used non metal cutting. LBM and EBM are, due to their high penetration depth can be used for micro drilling, sheet cutting and welding. CHM is used for manufacture of PCM and other shallow components.

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