Modern Manufacturing Technology

Introduction

Ms Shikha Kashyap Assistant Professor Dept of Mechanical Engineering The NorthCap University, Gurgaon

Need For Unconventional Machining Methods

Last few decades have witnessed a rapid growth in the development of harder and difficult to machine metal and alloys.

It has been realized that such materials are difficult to machine by conventional methods, and therefore their machining is not only costly but also results into poor surface finish and shorter tool life.

To overcome these difficulties a number of Newer Machining Methods have been developed.

Machining of intricate and complicated shapes, thin and fragile components and accurate and economical forming of very hard, high strength materials which are being extensively used in aerospace and nuclear industries, have forced the scientists, engineers and technologists to search for new techniques of machining which can readily provide an effective solution to these problems.

As a result of research and development for the last fifty years or so, several new methods of machining have emerged which can be grouped under the name of:

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Unconventional machining methods, or Non-traditional machining methods, or Physical machining process, or New technologies, or Modern machining methods

Characteristic features of modern machining processes that distinguish them from conventional machining processes:

The following are the characteristic features of non-traditional machining processes when compared with traditional or conventional machining processes:

Material is removed from the work piece without mechanical contact (with work piece).

In many processes, material removal rate is independent of the hardness of the work piece.

Cutting forces are independent of the hardness of the work material. The tool material need not be harder than the work material.( In

many cases, softer materials can be used as tool material) Almost any work material irrespective of its hardness and strength

can be machined.

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Generally tool wear is negligible; hence tool wear is not a problem. No burr is left on the work piece. Generally no residual stresses are left on the surfaces machined. In most of the cases entire shape can be obtained in one stage or in

one setting. This is possible since material removal takes place uniformly over the entire area below the tool simultaneously.

In majority of cases “surface integrity" (Surface integrity is the surface condition of a work piece after being modified by a process.) of the surfaces produced by modern machining methods is superior.

Modern machining methods can be integrated easily with micro-processors and numeric controls for better control of the processes and for improving the versatility and productivity of the machines.

Intricately shaped contours and fine machining of precision holes are possible.

Basic Principle of New Machining Methods

The basic principle of machining by these new methods is to apply some form of energy to the work piece directly without almost any physical contact between the tool and the work piece and have the desired shape by material removal from the work piece.

Different forms of energy applied to the work piece are:

1) Mechanical Energy

2) Electrical (Electro-chemical energy)

3) Thermal Energy

4) Chemical Energy

The actual mechanism or mode of metal removal for different processes are given below:

Machining Process

1. Conventional Machining Process (e.g. turning, milling, drilling)

2. Abrasive jet machining (AJM)

3. Ultrasonic Machining

4. Chemical Machining

Predominant Mechanism of Metal Removal

1. Shear failure of work material

2. Erosion of work material.

3. Erosion of work material.

Cavitation phenomenon.

4. Etching

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5. Electrochemical Machining

6. Electrochemical Grinding

7. Spark Erosion Machining

8. Electron beam machining

9. Laser beam machining

10. Ion beam machining

11. Plasma Arc Machining

5. Ion Displacement

6. Ion Displacement, Erosion of work material (due to grinding action of abrasive wheel)

7. Vaporization of work metal

8. Vaporization of work metal

9. Vaporization of work metal

10. Vaporization of work metal

11. Fusion of work metal

Advantages of Non-traditional

Material removed without mechanical contact with the work piece. (ECM, EDM,LBM,CHM)

Material removal rate is independent of work piece hardness. (ECM, EDM,LBM)

Cutting forces are independent of work piece hardness. (ECM, EDM,LBM,CHM)

Tool material need not be harder than work piece material. (ECM, EDM,LBM,CHM,USM)

Tool wear is not a problem. (ECM, LBM,CHM) Ability to machine any material. (LBM) Burr-free machining. (ECM,EDM,CHM) Stress-free machining. (ECM, ECG, CHM)

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Uniform material removal over the entire area below the tool surface simultaneously. (ECM,CHM)

Superior surface integrity possible. (ECM,CHM,ECG) Intricately shaped, very hard and fragile materials can be

machined. (USM) Finely focused micro-machining possible. (EDM,LBM,EBM) Easy compatibility with numeric control and computer controls.

(EDM,LBM,EBM,ECM)

Limitations of Non-traditional Machining Processes

All modern machining processes are generally costly. Their specific power consumption(kW/cm3/min) is quite high. The following are some of the specific limitations of the non- traditional machining process:

Work piece and tool must be electrically conductive (EDM,ECM) Depth of hole drilled is limited. (LBM) Heat-affected zones (HAZ) produced are not desirable.

(EDM,LBM,EBM) For this purpose the compatibility of the process with the

metallurgical state of the work piece material can be studied before using a particular non-traditional machining process for production work.

There may be taper in the sidewalls of holes or cavities (EDM,LBM)

Most of these limitations can be overcome and controlled, that the advantages can be obtained with good product quality assurance.

Classification of new machining methods

The classification is done on the basis of the type of energy used I the working zone for material removal action. Four distinct type of energy used are:

Mechanical Energy Electrical Energy (Electro-chemical energy) Thermal Energy (Thermo- electric energy) Chemical Energy

Mechanical Energy Conventional machining Abrasive Jet Machining (AJM) Water Jet machining (WJM) Ultrasonic machining (USM)

Electrical Energy

Electro-chemical machining Electro-chemical grinding Electro-chemical Deburring Electro-chemical Honing

Thermal Energy Spark erosion machining or Electro-discharge machining (EDM) Electron-Beam machining (EBM) Ion-Beam machining Laser-Beam machining Plasma-Arc machining

Chemical Energy Chemical machining Electro-polishing Photo-chemical machining

Abbreviations used for Unconventional Machining Methods

USM - Ultrasonic machining ECM - Electro-chemical machiningAJM - Abrasive Jet MachiningEDM - Electro-discharge machiningLBM - Laser-Beam machiningEBM – Electron-Beam machining PAM – Plasma-Arc machiningECG – Electrochemical grinding

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