NTMM

Name:- Sourabh TailorRoll no :- 2013btechme041

Content• INTRODUCTION

▫ Need of unconventional machine▫ Unconventional machining▫ Classification of NTMM▫ Limitations of NTMM

• ECM▫ Electro Chemical machining▫ ECM Equipment▫ Electrolyte▫ Tool▫ Advantageous▫ Disadvantageous▫ Application▫ Electro chemical Grinding(ECG)

• EDM▫ Physical principle▫ Characteristics Of EDM▫ EDM Tool▫ Dialectical fluid▫ Advantages▫ Disadvantages▫ Applications▫ Wire EDM▫ Electric Discharge Grinding (EDG)

Content

Need for Unconventional ProcessesNew materials having high strength and hardness, such as nimonic

alloys and alloys with alloying elements such as tungsten,

molybdenum, and columbium are difficult to machine by the

traditional methods.By conventional machining the MRR reduces with an increase in the

work material hardness.

Need for development of non-traditional machining processes

which utilize other methods such as electrochemical processes for the

material removal.

Introduction

Need for Unconventional Processes

Complex shapes.

A very high accuracy is desired besides the complexity of the

surface to be machined.

Unconventional MachiningDifferent forms of energy directly applied to the workpiece to have shape transformation or material removal from work surface.No chips, No lay pattern on work surface, no direct physical contact between the tool and the workpiece .The tool material does not have to be harder than the work material.Tool forces do not increase as the work material gets harder.

Classification of NTMMThe Non-traditional Machining Methods are classified according to the major energy sources employed in machining.1.Thermal Energy Methods2.Electro - Chemical Energy Method3.Chemical Energy Methods4.Mechanical Energy Methods

Limitations of NTMM

Expensive set up, low MRR and skilled labour required.

The limitation of electrical machining methods is that the

work material must be an electrical conductor. Also,

consumption of electrical energy is very large.

The NTMM which have not been proved commercially

economical are: USM, AJM, CHM, EBM and PAM.

ECM

Electro Chemical Machining

Electrochemical machining is the reverse of electro plating.The work-piece is made the anode, which is placed in close proximity to an electrode (cathode), and a high- amperage direct current is passed between them through an electrolyte, such as salt water, flowing in the anode- cathode gap.Metal is removed by anodic dissolution and is carried away in the form of a hydroxide in the electrolyte for recycling or recovery.MRR in ECM depends on atomic weight of work material.

Fig. :- Principle of ECM

Electrochemical MachiningVariation in the current density will result in work taking the electrodes shape.The electrode is fed with a constant velocity, and the electrolyte is fed through the tool

Fig. :-ECM Equipment

ECM EquipmentSupply Voltage 2 to 35 V DC and Current 500 to 40,000 A.

The tool-to-work gap needs to be maintained at a very small value 0.1 to 0.25 mm. A servo drive is provided on the tool axis for this purpose.

The electrolyte needs to be pumped through this gap at high pressures ranging from 0.70 to 3.00 MPa. This introduces a large amount of load on the machine, because of the large working areas involved. Hence the machine structure will have to be made rigid to a withstand such forces.

The electrolyte consists of the metal debris removed from the anode, which will have to be filtered before it is re-pumped into the system.

Also a large amount of heat is generated during the electrolysis, which heats up the electrolyte, and hence it needs to be cooled.

ElectrolyteThe electrolyte is so chosen that the anode (workpiece) is dissolved but no deposition takes place on the cathode (tool).

Properties electrolyte should be1.High electrical conductivity2.Low viscosity3.High specific heat4.Chemical stability5.Non-corrosive and non-toxic6.Inexpensive and readily available.

Tool

The properties of tool materials should be:1.High electrical and thermal conductivity2.Easy machinability3.Good stiffness4.High corrosion resistance

Tool materials: Copper, brass, bronze, Al, Stainless Steel,

nickel, etc.Material wear / Tool wear: Infinite

Advantages

1.Complex three-dimensional surfaces can be machined accurately. Good for low machinability or complicated shapes.

2.As ECM leads to atomic level dissolution, the surface finish is excellent (Ra 0.2 to 0.6 μm) with almost stress free machined surface and without any thermal damage.

3.The tool wear is practically nil which results in a large number of components produced per tool.

4.MRR is highest (1600 mm3/min) among NTMM and comparable with conventional machining.

Disadvantages1. Use of corrosive media as electrolytes make it difficult to

handle.2. Sharp interior edges and corners re difficult to produce.3. Very expensive machine.4. Forces are large with this method because of fluid pumping

forces.5. Very high specific energy consumption.(about 150times of

conventional processes.6. Not applicable with electrically non-conducting materials and

jobs with very small dimensions.

Applications

•Any electrically conductive work materials irrespective of their hardness, strength or even thermal properties.

•Shape application – blind complex cavities, curved surfaces , through cutting , large through cavities.

•It is used for marching of gas turbines blades.•Die sinking •Profiling and contouring•Trepanning •Grinding•Drilling•Micro-machining

Electrochemical Grinding (ECG)

•In ECG, the tool electrode is a rotating , metal bonded diamond grit grinding wheel.•As the electric current flows between the workpiece and the wheel, through the electrolyte, the surface metal is changed to a metal oxide, which is ground away by the abrasives. As the oxide film is removed, new surface metal is oxidized and removed.ECG is a low-voltage high-current electrical process.The purpose of the abrasive is to increase the efficiency of the ECG process and permit the continuance of the process.The abrasive particles are always nonconductive material such as aluminium oxide, diamond, or borazon . Thus they act as an insulating spacer maintaining a separation of from 0.012 to 0.050 mm between the electrodes.

Fig :- Equipment setup and electrical circuit for electrochemical grinding.

Electrochemical Grinding (ECG)

The process is used for shaping and sharpening carbide cutting tools, which cause high wear rates on expensive diamond wheels in normal grinding. Electrochemical grinding greatly reduces this wheel wear.Fragile parts (honeycomb structures), surgical needles, and tips of assembled turbine blades have been ECG- processed successfully.Inter electrode gap in ECG is controlled by Controlling the size of diamond particle in the wheel.

EDM

Physical PrincipleBasic process

Physical PrincipleAn arc jumps between two points along the path of least resistance.

Physical PrincipleThe energy of the arc is so concentrated that it causes the electrode, and the work to melt. But the electrode material is chosen so that it melts less.

Physical PrincipleThe metal and dielectric fluid is partly vaporized, causing sudden expansion.

Physical PrincipleThe blast from the expanding vapours knocks some molten particles loose, and the remaining molten metal hardens.

Characteristics of EDM

Mechanics of material removal - melting and evaporation aided by cavitations.

The process is based on melting temperature, not hardness, so some very hard materials can be machined this way.

The arc that jumps heats the metal, and about 1 to 10% of the molten metal goes into the fluid. The melted metal then recast layer is about 1 to 30 μm thick, and is generally hard and rough.

The electrode workpiece gap is in the range of 10 μm to 100 μm.

EDM Tool

• Prime requirements EDM tool Material1.It should be electrically conductive.2.It should have good machinability, thus allowing easy manufacture

of complex shapes.3.It should have low erosion rate or good work to tool wear ratio.4.It should have low electrical resistance.5.It should have high melting point.6.It should have high electron emission.

EDM ToolThe usual choices for tool(electrode) materials areCopper, brass,alloys of zinc and tin,hardened plain carbon steel,copper tungsten,silver tungsten,tungsten carbide,copper graphite, and graphite.

Electrical & thermal conductivity Good

Servo-Mechanism The gap between the tool and work has a critical importance. As the

workpiece is machined, this gap tends to increase. For optimum

machining efficiency, this gap should be maintained constant. This is

done by servo- mechanism which controls the movement of the

electrode.

Dielectric FluidFluid is used to act as a dielectric, and to help carry away debris.

If the fluid is pumped through and out the end of the electrode, particles will push out, and mainly collect at the edges. They will lower the dielectric resistance, resulting in more arcs. As a result the holes will be conical.

Quite often kerosene-based oil.

The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less. To free it from eroded metal particles, it is circulated through a filter.

Advantages•Hardness, toughness or brittleness of the ,material poses no problem. Due to this EDM can be used for machining materials that are too hard or brittle to be machined by conventional methods.•The method does not leave any chips or burrs on the work piece.•Cutting forces are virtually zero. So very delicate and fine work can be done.•The process dimension repeatability, and surface finish obtained in finishing are extremely good.•The characteristics surface obtained, which is made up of crates, helps in better oil retentions. This improves die life.•Because the forces between the tool and the workpiece and virtually zero, very delicate work can be done.

Disadvantages1.Only electrically conductive materials can be machined by EDM.

Thus non - metallic, such as plastics, ceramics or glass, cannot be machined by EDM.

2.Electrode wear and over-cut are serious problems.

3.A re-hardened, highly stressed zone is produced on the work surface by the heat generated during machining. This brittle layer can cause serious problems when the part is put into service.

4.Perfectly square corners cannot be made by EDM.

5.MRR is quite low.

6.High specific energy consumption ( about 50 times that in conventional machining)

ApplicationsEDM can be used for machining any material that is electrically conductive, thus including metals, alloys and most carbides.

EDM is widely used for machining burr free intricate shapes, narrow slots and blind cavities etc., for example, sinking of dies for moulding, die casting, plastic moulding, wire drawing, compacting, cold heading, forging, extrusion and press tools.

EDM is particularly useful when dealing with internal cuts that are hard to get tools into. Machining tends to work best with external cuts.

Almost any geometry (negative of tool geometry) can be generated on a workpiece if a suitable tool can be fabricated (the use of punch as a tool to machine its own mating die is commonly employed in EDM method).

The method is also employed for blanking parts from sheets,

cutting off rods of materials, flat or form grinding and sharpening

of tools, cutters and broaches.

In EDM method, small holes, about 0.13 mm, in diameter and

as deep as 20mm diameters can be drilled with virtually no

bending or drifting of hole. Due to this, EDM is particularly useful

for machining of small holes, orifices or slots in diesel-fuel

injection nozzles, or in aircraft engines, air brake valves and so on.

Application

Wire EDM

Wire EDM is a special form of EDM wherein the electrode is a continuously moving conductive wire.

A thin wire of brass, tungsten, or copper is used as an electrode.

The electrode wire is typically made with a 0.05 to 0.25- mm diameter,

which is wire electrode wound between the two spools.Deionised water is used as the dielectric. This process is much faster than electrode EDM.

This process is widely used for the manufacture of punches, dies, and

stripper plates, with modern machines capable of cutting die relief,

intricate openings, tight radius contours, and corners routinely.

Geometrically accurate but moderately finished straight toothed metallic spur gears, both external and internal type, can be produced by wire type Electro discharge Machining (EDM).

Fig. :- wire EDM

Electric Discharge Grinding (EDG)

EDG is similar to EDM except that the electrode is a rotating wheel (usually graphite).Positively charged work pieces are immersed in or flooded by a dielectric fluid and fed past the negatively charged wheel by servo-controlled machine table.Metal is removed by intermittent high frequency electrical discharges passing through the gap between wheel and workpiece.Each spark discharge melts or vaporizes a small amount of metal from the workpiece surface, producing a small crate at the discharge sit, as in EDM.

Fig :- EDG Machine