ME6004 -UNCONVENTIONAL MACHINING PROCESSES

1. ME6004 -UNCONVENTIONALMACHINING PROCESSES UNIT I INTRODUCTION

2. Conventional Machining Process • In conventional machining processes, metal is removed by using some sort of tool which is harder than the work piece and it is subjected to wear. • #In this process, tool and work piece being in direct contact with each other. • #In other words, the conventional machining processes involve removal of metal by chip formation.

3. Demerits of Conventional Machining Processes: • 1. Metal is removed by chip formation which is an expensive and difficult process. • 2. Chips produced during this process are unwanted by-products. • 3. Removal of these chips and their disposal and recycling is a very tedious procedure, involving energy and money. • 4. Very large cutting forces are involved in this process. so proper holding of the work piece is most important. • 5. Due to the large cutting forces and large amount of heat generated between the tool and the work pieceinterface, undesirable deformation and residual stresses are developed in the work piece.

4. UnConventional Machining Process Definition: • The Unconventional machining processes do not employ a conventional or traditional tool for metal removal, instead, they directly utilize some form of energy for metal machining(removal). • #In this process, there is no direct physical contact between the tool and the work piece. • #Therefore the tool material need not be harder than the work piece material as in conventional machining.

5. Definition: • Nonconventional Machining is a recent development in machining techniques. It is based on unconventional machining techniques using Laser beam, Electron beam, Electric arc etc. • #Conventional machining involves the direct contact of tool and work piece, whereas unconventional machining does not require the direct contact of tool and work piece. • #Conventional machining has many disadvantages like tool wear which are not present in Nonconventional machining. • #Examples : Abrasive water jet machining, Electric arc machining, Laser cutting , electric discharge machining etc

6. Needs for UnConventional Machining Process • #A harder and difficult to machine materials such as carbides, stainless steel, nitralloy, hastalloy and many other high strength temperature resistant alloys find wide application in aerospace and nuclear engineering industries. • Many of these materials also find applications in other industries, owing to their high strength to weight ratio, hardness and heat resisting qualities. • #For such materials the conventional edged tool machining is highly uneconomical and the degree of accuracy and surface finish attainable are poor. • #The unconventional machining processes have been developed to over come all these difficulties.

7. Why Unconventional Machining? Situations where traditional machining processes are unsatisfactory or uneconomical • – Work piece material is too hard, strong, or tough. • – Work piece is too flexible to resist cutting forces or too difficult to clamp. • – Part shape is very complex with internal or external profiles or small holes. • – Requirements for surface finish and tolerances are very high. • – Temperature rise or residual stresses are undesirable or unacceptable.

8. Classification for UnConventional Machining Process 1.Based on the type of energy required to shape the material a) Thermal energy method b) Electrical energy method c) Electro chemical energy methods d) Chemical energy methods e) Mechanical energy methods 2. Based on the mechanism involved in the process • Erosion • Ionic dissolution • Vaporisation

9. Contd. Classification for UnConventional Machining Process 3. Based on source of energy required for material removal • Hydrostatic pressure • High current density • High voltage • Ionised material 4. Based on medium of transfer of energies: • High voltage particles • Electrolyte • Electron • Hot gases

10. Contd. Classification for UnConventional Machining Process • Mechanical energy methods : In mechanical energy methods, the material is removed by mechanical erosion of the work piece material. Example:Ultrasonic Machining(USM) Abrasive Jet Machining(AJM) Water Jet Machining(WJM) • Thermal energy methods : In this method, heat energy is concentrated on a small area of the work piece to melt and vaporise the tiny bits of work material. The required shape is obtained by the continued repetition of this process. Example: Laser Beam Machining(LBM) Plasma Arc Machining(PAM) Electron Beam Machining(EBM) Iron Beam Machining.(IBM)

11. Contd. Classification for UnConventional Machining Process • Electrical energy methods : In this method, electrical energy is directly used to cut the material to get the final shape and size. Example: Electric Discharge Machining(EDM) Wire Cut Electrical Discharge Machining(WEDM) • Electro chemical energy methods :In these methods, material is removed by ion displacement of the work piece material in contact with a chemical solution Example: Electro Chemical Machining(ECM) Electro Chemical Grinding(ECG) Electro Chemical Honing(ECH) Electro Chemical Deburring(ECD) • Chemical energy methods : These methods involve controlled etching of the work piece material in contact with a chemical solution Example: Chemical Machining(CHM)

12. Material Vs Method of machining • All methods are not suitable for all materials. Depending on the material to be machined, following methods can be used

13. PROCESS SELECTION In order to make use of non-traditional machining processes efficiently, it is necessary to know the exact nature of the machining problem. The following points must be considered for the correct selection of the unconventional machining process • 1. Physical parameters • 2. Shapes to be machined • 3. Process capability or machining characteristics • 4. Economic consideration

14. Process Selection- Physicalparameters Physical Parameters : • #Potential : potential energy is the energy of an object or a system due to the position of the body or the arrangement of the particles of the system. • #Current • #Power : • #Gap • #Medium • #Work material

15. Physical parameters of modern machining processes

16. Process Selection- Shapes to be machined The application of the unconventional machining processes is also influenced by the shape and size of the work piece to be produced • For producing micro holes-LBM is best suitable • small holes –EBM is best suitable • deep holes (L/D >20) and contour machining-ECM is best suitable • For shallow holes-USM and EDM is best suitable • Honing-ECM is best suitable • Grinding-AJM and EDM is best suitable • Deburring –USM and AJM is best suitable • Threading-EDM is best suitable • shallow pocketing –AJM is best suitable • For clean, rapid cut and profiles-PAM is best suitable

17. Process Selection – Process Capability Process Capability ( or) Machining Characteristics : The machining Characteristics can be analyzed with respect to • #Metal removal rate obtained • #Tolerance maintained • #Surface finish obtained • #Depth of surface damage • #Power required for machining

18. Process capability

19. Process Selection -Process Economy Process Economy : The economics of the various processes are analyzed by considering the following points • #Capital Cost • #Tooling Cost • #Power requirement • #Metal removal rate efficiency • #Toll consumption

20. Process Economy

21. Advantages of UnConventional Machining Process: • #Increases productivity • #Productivity : Productivity is a measure of the efficiency of production. Productivity is a ratio of production output to what is required to produce it (inputs). The measure of productivity is defined as a total output per one unit of a total input. • #Reduces number of rejected components • #Close tolerance is possible • #The tool material need not be harder than the work piece material as in conventional machining. • #Harder and difficult to machine material can be machined by this process. • The machined surface do not have any residual stresses

22. Contd. Advantages of UnConventional Machining Process: • Tool wear is not a problem (eg. ECM, LBM, CHM) • Finely focused micro-machining possible • Micro hole drilling possible • Easy compatibility with numerical control and mini computer controls.

23. Limitations of UnConventional Machining Process: • #Unconventional machining processes are more expensive. • #Metal removal rate is slow. • #AJM, CHM, PAM and EBM are not commercially economical processes • There may be taper in the side walls of holes or cavities. (eg.EDM, LBM) Most of these limitations can be overcome and controlled.

24. Applications of UCMP • AJM is suitable for machining super alloys and refractory materials such as ceramics glass and plastics. • USM has good machining performance for refractory type materials such as ceramics glass and plastics. • ECM is used for machining steel and super alloys, ECM cannot be used for machining non-conducting materials like ceramics, plastics and glass • EDM is used for machining steel, super alloys, titanium and refractory materials. EDM cannot be used for machining non conducting materials such as ceramics, plastics and glass • EBM is most suitable for machining refractory materials and has a medium performance on glass and plastics • LBM can machine any substance and is suitable for refractory materials such as ceramics and has a medium performance on glass and plastics • PAM is suitable for machining aluminium, steel and super alloys. PAM is not suitable for machining ceramics and glass.