Unconventional Manufacturing Processes

1 Introduction of Unconventional Manufacturing Process 1.0 INTRODUCTION Since beginning of the human race, people have evolved tools and energy sources to power these tools to meet the requirements for making the life more easier and enjoyable. In the early stage of mankind, tools were made of stone for the item being made. When iron tools were invented, desirable metals and more sophisticated articles could be produced. In twentieth century products were made from the most durable and consequently, the most unmachinable materials. In an effort to meet the manufacturing challenges created by these materials, tools have now evolved to include materials such as alloy steel, carbide, diamond and ceramics. A similar evolution has taken place with the methods used to power our tools. Initially, tools were powered by muscles; either human or animal. However as the powers of water, wind, steam and electricity were harnessed, mankind was able to further extend manufacturing capabilities with new machines, greater accuracy and faster machining rates. HSTR Alloys

Ultimate tensile strength Kgf/cm

2

14000 Titanium 7000 Al alloy

3500

1400

700 350

Al

1915

1930

1945 1960 Year of development

Fig. 1.1. Trend of increase of material strength 1

Comp-1/Newage/Uncmp-1—II print/22.5.07

7.6.07

30.6.07

13.9.07

18.9.07

2

UNCONVENTIONAL MANUFACTURING PROCESSES

Every time new tools, tool materials, and power sources are utilized, the efficiency and capabilities of manufacturers are greatly enhanced. Since 1940’s, a revolution in manufacturing has been taking place that once again allows manufactuers to meet the demands imposed by increasingly sophisticated designs and durable but in many cases nearly unmachinable, materials. In the figure 1.1, Merchant had displayed the gradual increase in strength of material with year wise development of material in aerospace industry. This manufacturing revolution is now, as it has been in the past, centered on the use of new tools and new forms of energy. The result has been the introduction of new manufacturing processes used for material removal, forming and joining, known today as non-traditional manufacturing processes. The conventional manufacturing processes in use today for material removal primarily rely on electric motors and hard tool materials to perform tasks such as sawing, drilling and broaching. Conventional forming operations are performed with the energy from electric motors, hydraulics and gravity. Likewise, material joining is conventionally accomplished with thermal energy sources such as burning gases and electric arcs. In contrast, non-traditional manufacturing processes harness energy sources considered unconventional by yesterday’s standards. Material removal can now be accomplished with electrochemical reaction, high temperature plasmas and high-velocity jets of liquids and abrasives. Materials that in the past have been extremely difficult to form, are now formed with magnetic fields, explosives and the shock waves from powerful electric sparks. Material-joining capabilities have been expanded with the use of high-frequency sound waves and beams of electrons and coherent light. During the last 55 years, over 20 different non-traditional manufacturing processes have been invented and successfully implemented into production.

1.1 CLASSIFICATION OF UNCONVENTIONAL MANUFACTURING PROCESSES The non-conventional manufacturing processes are not affected by hardness, toughness or brittleness of material and can produce any intricate shape on any workpiece material by suitable control over the various physical parameters of the processes. The non-conventional manufacturing processes may be classified on the basis of type of energy namely, mechanical, electrical, chemical, thermal or magnetic, apply to the workpiece directly and have the desired shape transformation or material removal from the work surface by using different scientific mechanism. Thus, these non-conventional processes can be classified into various groups according to the basic requirements which are as follows : (i) Type of energy required, namely, mechanical, electrical, chemical etc. (ii) Basic mechanism involved in the processes, like erosion, ionic dissolution, vaporisation etc. (iii) Source of immediate energy required for material removal, namely, hydrostatic pressure, high current density, high voltage, ionised material, etc. (iv) Medium for transfer of those energies, like high velocity particles, electrolyte, electron, hot gases, etc. On the basis of above requirements, the various processes may be classified as shown in table 1.1.

Processes

Transfer energy medium

Source of immediate energy

Basic mechanism

Energytype

Ultrasonic machining

Mechanical contour grinding

Physical contact

Cutting tool

Shear

Pneumatic or hydraulic pressure

Erosion

Abrasive jet machining

High velocity particles

Mechanical

Electro chemical grinding

Whirling jet machining

High velocity liquid

Electro chemical machining

Chemical etching

Electrolyte

High current

Iondisplacement

Electro-chemical

Thermo-electrical

Electron

Electrical discharge machining

Electron beam machining

Fusion

Plasma arc machining

Hot gases

Ionised material

Ion beam machining

Laser beam machining

Radiation

High voltage amplified light

Vaporisation

Chemical Hot chlorine machining machining

Environment

Chemically reactive agent

Ablative action

Chemical

Non-conventional manufacturing processes

INTRODUCTION OF UNCONVENTIONAL MANUFACTURING PROCESS

3

4


1.2 COMPARATIVE ANALYSIS OF UNCONVENTIONAL MANUFACTURING PROCESSES A comparative analysis of the various unconventional manufacturing processes should be made so that a guide-line may be drawn to find the suitability of application of different processes. A particular manufacturing process found suitable under the given conditions may not be equally efficient under other conditions. Therefore, a careful selection of the process for a given manufacturing problem is essential. The analysis has been made from the point of view of : (i) Physical parameters involved in the processes; (ii) Capability of machining different shapes of work material; (iii) Applicability of different processes to various types of material, e.g. metals, alloys and non-metals; (iv) Operational characteristics of manufacturing and (v) Economics involved in the various processes.

Physical parameters The physical parameters of non-conventional machining processes have a direct impact on the metal removal as well as on the energy consumed in different processes. (Table 1.2) TABLE 1.2. Physical Parameters of the Non-conventional Processes Parameters

USM

AJM

ECM

CHM

EDM

EBM

LBM

PAM

220

220

10

—

45

150000

4500

100

12 (A.C.)

1.0

10000 (D.C.)

—

50 (Pulsed D.C.)

0.001 (Pulsed D.C.)

2 (Average 200 Peak)

500 (D.C.)

Power (W)

2400

220

100000

—

2700

150

—

50000

Gap (m.m.)

0.25

0.75

0.20

—

0.025

100

150

7.5

Vaccum

Air

Argon or hydrogen

Potential (V) Current (Amp)

Medium

Abrasive Abrasive Electrolyte in water in gas

Liquid Liquid chemical dielectric

5


From a comparative study of the effect of metal removal rate on the power consumed by various non-conventional machining processes shown in fig. 1.2.

Power consumption, watts

10

ECM

5

PAM 10

10

10

10 10 10

4

3

USM

EDM

MCG

3

4

AJM

2

EB

M

1 0

LBM

–1

10

–1

10

0

1

2

10 10 10 10 3 Metal removal rate mm /min

10

5

Fig. 1.2. Effect of metal removal rate on power consumption.

It is found that some of the processes (e.g. EBM, ECM) above the mean power consumption line consume a greater amount of power than the processes (e.g. EDM, PAM, ECG) below the mean power consumption line. Thus, the capital cost involved in the processes (EBM, ECM etc.) lying above the mean line is high whereas for the processes below that line (e.g., EDM, PAM, MCG) is comparatively low.

Capability to shape The capability of different processes can be analysed on the basis of various machining operation point of view such as micro-drilling, drilling, cavity sinking, pocketing (shallow and deep), contouring a surface, through cutting (shallow and deep) etc. TABLE 1.3. Shape Application of Non-conventional Processes Holes Process

Precision small holes

Trough cavities Standard

Precision standard

Surfacing

Trough cutting

Double contouring

Surface of revolution

Shallow

deep

Dia Dia Length Length < .025 > .025 < 20 mm > 20 mm mm mm USM AJM ECM

— — —

— — —

good fair good

poor poor good

good poor fair

good fair good

poor — good

— — fair

poor good good

— — good

CHM EDM

fair —

fair —

— good

— fair

poor good

fair good

— fair

— —

good poor

— —

LBM PAM

good —

good —

fair fair

poor —

poor poor

poor poor

— —

— poor

good good

fair good

6


For micro-drilling operation, the only process which has good capability to microl < 20, drill is laser beam machining while for drilling shapes having slenderness ratio, D the process USM, ECM and EDM will be most suitable. EDM and ECM processes have good capability to make pocketing operation (shallow or deep). For surface contouring operation, ECM process is most suitable but other processes except EDM have no application for contouring operation.

Applicability to materials Materials applications of the various machining methods are summarised in the table 1.4 and table 1.5. For the machining of electrically non-conducting materials, both ECM and EDM are unsuitable, whereas the mechanical methods can achieve the desired results. TABLE 1.4 Metals Alloys Process USM AJM ECM CHM EDM EBM LBM PAM

Aluminium

Steel

Super alloy

Titanium

Refractory material

Poor Fair Fair Good Fair Fair Fair Good

Fair Fair Good Good Good Fair Fair Good

Poor Good Good Fair Good Fair Fair Good

Fair Fair Fair Fair Good Fair Fair Fair

Good Good Fair Poor Good Good Poor Poor

USM is suitable for machining of refractory type of material while AJM are for super alloys and refractory materials. TABLE 1.5 Non-Metals Process

Ceramics

Plastic

Glass

USM AJM ECM CHM EDM EBM LBM

Good Good — Poor — Good Good

Fair Fair — Poor — Fair Fair

Good Good — Fair — Fair Fair

PAM

—

Poor

—

7


Machining characteristics The machining characteristics of different non-conventional processes can be analysed with respect to : (i) Metal removal rate (ii) Tolerance maintained (iii) Surface finish obtained (iv) Depth of surface damage (v) Power required for machining The process capabilities of non-conventional manufacturing processes have been compared in table 1.6. The metal removal rates by ECM and PAM are respectively one-fourth and 1.25 times that of conventional whereas others are only a small fractions of it. Power requirement of ECM and PAM is also very high when compared with other non-conventional machining processes. This involves higher capital cost for those processes. ECM has very low tool wear rate but it has certain fairly serious problems regarding the contamination of the electrolyte used and the corrosion of machine parts. The surface finish and tolerance obtained by various processes except PAM is satisfactory. TABLE 1.6 Process

MRR (mm3/min)

Tolerance (µ)

Surface (µ) CLA

Depth of surface damage (µ)

Power (watts)

USM AJM ECM CHM EDM EBM

300 0.8 15000 15 800 1.6

7.5 50 50 50 15 25

0.2–0.5 0.5–1.2 0.1–2.5 0.5–2.5 0.2–1.2 0.5–2.5

25 2.5 5.0 50 125 250

LBM PAM Conventional machining

0.1 75000 50000

25 125 50

0.5–1.2 Rough 0.5–5.0

125 500 25

2400 250 100000 — 2700 150 (average) 2000 (peak) 2 (average) 50000 3000

Economics of the processes The economics of the various processes are analysed on the basis of following factors and given in Table 1.7. (i) Capital cost (ii) Tooling cost (iii) Consumed power cost (iv) Metal removal rate efficiency (v) Tool wear.

8


TABLE 1.7 Process

Capital cost

Tooling cost

Power consumption cost

Material removal rate efficiency

Tool wear

USM AJM ECM CHM EDM EBM LBM PAM MCG

L VL VH M M H L VL L

L L M L H L L L L

L L M H* L L VL VL L

H H L M H VH VH VL VL

M L VL VL H VL VL VL L

* indicates cost of chemicals.

The capital cost of ECM is very high when compared with traditional mechanical contour grinding and other non-conventional machining processes whereas capital costs for AJM and PAM are comparatively low. EDM has got higher tooling cost than other machining processes. Power consumption is very low for PAM and LBM processes whereas it is greater in case of ECM. The metal removal efficiency is very high for EBM and LBM than for other processes. In conclusion, the suitability of application of any of the processes is dependent upon various factors and must be considered all or some of them before applying nonconventional processes.

REVIEW QUESTIONS 1. Justify the need of unconventional manufacturing process in today’s industries. 2. What are the basic limitations of conventional manufacturing process ? Explain. 3. What are the basic factors upon which the unconventional manufacturing processes are classified ? Explain. 4. List five conventional and five related unconventional manufacturing processes used in industries. 5. Distinguish between conventional and unconventional manufacturing processes. 6. Why are the unconventional manufacturing processes not completely taking over the conventional manufacturing processes ? Explain. 7. Unconventional machining processes yield low rates of material removal compared to conventional processes even then they have gained wide popularity. Discuss why ? 8. Enumerate the limitations of conventional manufacturing processes particularly in the light of present day manufacturing environment. 9. ECM, EDM, USM etc. are commonly referred to as unconventional machining processes, what is unconventional in these processes ? Explain.

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Unconventional Manufacturing Processes

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