Non Traditional Machining

Manufacturing Technology II Sub Code – MEC330

Non-Traditional Manufacturing (NTM)

Non-Traditional Machining (NTM) Processes

Introduction

 We all know that the term machinability refers to the case with which a metal can be machined to an acceptable surface finish

 Nontraditional machining processes are widely used to manufacture geometrically complex and precision parts for aerospace, electronics and automotive industries  In ordinary machining we use harder tool to work on workpiece,

this limitations is overcome by unconventional machining

 Unconventional machining is directly using some sort of indirect

energy for machining

 Ex: Sparks, Laser, Heat, Chemical etc.

 Applied in EDM , Laser Cutting Machines , etc.

Non-Traditional Machining (NTM) Processes

Introduction

 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, residual stresses which are not present in Non-conventional machining.

Non-Traditional Machining (NTM) Processes The requirements that lead to the development of nontraditional machining.

 Very high hardness and strength of the work material

 The work piece: too flexible or slender to support the cutting or grinding forces  The shape of the part is complex, such as internal and external profiles, or small diameter holes

 Surface finish or tolerance better than those obtainable conventional process  Temperature rise or residual stress in the work piece are undesirable.

Non-Traditional Machining (NTM) Processes Machining characteristics

• The machining characteristics of different non-conventional processes can be analyzed with respect to :  Metal removal rate

 Tolerance maintained

 Surface finish obtained

 Depth of surface damage

 Power required for machining

Non-Traditional Machining (NTM) Processes

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

Non-Traditional Machining (NTM) Processes

NTM Processes are characterised as follows:

 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, whereas in ECM electrochemical dissolution constitutes material removal

Non-Traditional Machining (NTM) Processes

Advantages of Non-conventional machining: • High accuracy and surface finish • Less/no wear

• Tool life is more

• Quieter operation

Disadvantages of non-conventional machining: • High cost

• Complex set-up

• Skilled operator required

Classification of NTM Processes

Classification of NTM Processes

• The classification of NTM processes is carried out depending on the nature of energy used for material removal. •

Mechanical Processes

– Water Jet Machining (WJM)

– Abrasive Jet Machining (AJM)

– Abrasive Water Jet Machining (AWJM) •

– Ultrasonic Machining (USM)

Electrochemical Processes

– Electrochemical Machining (ECM) – Electro Chemical Grinding (ECG) – Electro Jet Drilling (EJD)

Classification of NTM Processes

• Electro-Thermal Processes

– Electro-discharge machining (EDM) – Electron Beam Machining (EBM) – Laser Beam Machining (LBM)

• Chemical Processes

– Chemical Milling (CHM)

– Photochemical Milling (PCM) etc.

Classification of NTM Processes

Schematic representation of various NTM metal cutting operations

Water jet machining (WJT)

 Water jet acts like a saw and cuts a narrow groove in the material  Pressure level of the jet is about 400 MPa  Advantages

 No heat produced

 Cut can be started anywhere

 Without the need for predrilled holes  Burr produced is minimum

 Environmentally safe and friendly manufacturing

 Application – used for cutting composites, plastics, fabrics, rubber, wood products etc. Also used in food processing industry.

Water jet machining (WJT)

Abrasive Jet Machining (AJM)

 In AJM a high velocity jet of dry air, nitrogen or CO2 containing

abrasive particles is aimed at the work piece

 The impact of the particles produce sufficient force to cut small hole or slots, deburring, trimming and removing oxides and other surface films

Abrasive Jet Machining (AJM)

Abrasive Jet Machining (AJM)

Common applications:

 Fast and precise cutting of fabrics

 Vinyl, foam coverings of car dashboard panels

 Plastic and composite body panels used in the interior of cars  Cutting glass and ceramic tiles

Limitations of AJM

 MRR is rather low (around ~ 15 mm3/min for machining glass)

 Abrasive particles tend to get embedded particularly if the work material is ductile  Tapering occurs due to flaring of the jet  Environmental load is rather high.

Abrasive Jet Machining (AJM)

Different engineering components machined with AWJ

Abrasive Jet Machining (AJM)

Abrasive Water Jet Machining (WAJM)

 Abrasive Water Jet Machining (AWJM) belong to mechanical group of non-conventional processes

 In AJWM processes, the mechanical energy of water and abrasive phases are used to achieve material removal or machining.

Advantages of WJA and WAJM

WJM and AWJM have certain advantageous characteristics, which helped to achieve significant penetration into manufacturing industries.  Extremely fast set-up and programming  Very little fixturing for most parts

 Machine virtually any 2D shape on any material  Very low side forces during the machining  Almost no heat generated on the part  Machine thick plates

The applications and materials, which are generally machined using WJ and AWJ

Applications

Materials

Ultrasonic Machining (USM)

 Ultrasonic machining is a non-traditional machining process.  USM is grouped under the mechanical group NTM processes.  Fig. briefly depicts the USM process.

Ultrasonic Machining (USM)

 In USM, a tool of desired shape vibrates at an ultrasonic frequency over the workpiece  Generally the tool is pressed downward with a feed force, F.

 Between the tool and workpiece, the machining zone is flooded with hard abrasive particles generally in the form of a water based

slurry

 As the tool vibrates over the workpiece, the abrasive particles act

as the indenters and indent both the work material and the tool

 The abrasive particles, as they indent, the work material is removed, particularly if the work material is brittle

 Due to crack initiation, propagation and brittle fracture of the

material.

 Hence, USM is mainly used for machining brittle materials

Summary

Ultrasonic Machining (UM)

 In UM the tip of the tool vibrates at low amplitude and at high frequency.  This vibration transmits a high velocity to fine abrasive grains between tool and the surface of the work piece.  Material removed by erosion with abrasive particles.  The abrasive grains are usually boron carbides.

 This technique is used to cut hard and brittle materials like ceramics, carbides, glass, precious stones and hardened steel.

Ultrasonic Machining (USM)

Up-down vibration of tool hammers the abrasive particles against workpiece, causing cutting

Ultrasonic Machining (UM)

Applications

Ultrasonic Machining (USM)

machining hard and brittle semiconductors, glass, ceramics, carbides etc

 Used

for

metallic

alloys,

 Used for machining round, square, irregular shaped holes and

surface impressions

 Machining, wire drawing, punching or small blanking dies

 Welding plastics (package sealing), Wire-bonding (IC chips)

Limitations

 Low MRR

 Rather high tool wear  Low depth of hole

Diffusion Coating

Surface Coatings *

 Diffusion Coating is a process in which an alloying element is diffused into the surface of the substrate, thus altering the properties  The alloying elements can be supplied in solid, liquid or gaseous states  This process has different names, depending on the diffused element

Electroplating, Electroless plating and Electroforming Plating as with other coating processes,

 Imparts the properties of resistance to wear and corrosion  High electrical conductivity

 Better appearance and reflectivity

*Review

Electroplating

Surface Coatings *

 In electroplating, the workpiece (cathode) is plated with a different metal (anode), while both are suspended in a bath containing a water-based electrolyte solution

 Although the plating process involves a number of reactions, basically the process consists of the following

1. The metal ions from the anode are discharged using potential energy from the external source of electricity 2. The metal ions combine with the ions in the solution and 3. They are deposited on the cathode

 Chemical cleaning, degreasing and thorough soaking of the workpiece prior to the plating are essential  All the metals can be electroplated

*Review

Electroplating

Surface Coatings *

*Review

Electroplating

Surface Coatings *

 Electroplate thickness range from a few atomic layers to a maximum of about 0.05 mm  Complex shapes may have varying plating thickness

 Chromium, nickel, cadmium, copper, zinc and tin are common plating materials

 Chromium Plating is done by plating the metal first with copper, then with nickel and finally with chromium

 Hard Chromium Plating is done directly on the base metal and results in a hardness of up to 70 HRC

 This method is used to improve the resistance to wear and corrosion of tools, valve stems, hydraulic shafts, diesel and aircraft engine cylinder liners and used to rebuild worn parts *Review

Electroless Plating

Surface Coatings *

 Electroless plating is done by chemical reaction and without the use of an external source of electricity  The most common application utilize nickel and copper

 In electroless plating, nickel chloride (a metallic salt) is reduced, using sodium hypophosphite as the reducing agent to nickel metal, which is then deposited on the workpiece  The coating has excellent wear and corrosion resistance

 Cavities, recesses and the inner surfaces of the tubes can be plated successfully

*Review

Electroless Plating

Surface Coatings *

*Review

Electroless Plating

Surface Coatings *

 Electroless plating process can also be used with nonconductive materials, like, plastics and ceramics  Electroless plating is more expensive than electroplating

 However the coating thickness of electroless plating is always uniform

*Review

Electrochemical Machining (ECM)

 Electrochemical machining is one of the newest machining process of

metal removal by controlled dissolution of anode of an electrolytic cell  Reverse of electroplating and is based on Michael Faraday’s classical laws of electrolysis

 This process is particularly suit to metal and alloys which are difficult

or impossible to machining

 An electrolyte acts as a current carrier and high electrolyte movement

in the tool-work-piece gap washes metal ions away from the work piece (anode) before they have a chance to plate on to the tool (cathode).  Tool – generally made of bronze, copper, brass or stainless steel.  Electrolyte – salt solutions like sodium chloride or sodium nitrate mixed in water.  Power – DC supply of 5-25 V.

Electrochemical Processes

 Electrochemical Machining (ECM) requiring basically two-electrodes,

an electrolytes, a gap and a source of D C power of sufficient capacity  ECM can be thought of a controlled anodic dissolution at atomic level of the w/p that is electrically conductive by a shaped tool  Due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution - Reverse of electro-plating (workpiece is anode)

Schematic principle of Electro Chemical Machining (ECM)

Electrochemical Machining (ECM)

 In actual process, the cathode tool-shaped, like mirror image of the     



finished workpiece and is connected to the anode The tool is advanced towards the w/p through the electrolyte that completes the circuit The metal is then removed from the w/p through electrical action, and the cathode shape is produced on the w/p The electrolyte is pumped at high pressure through the gap b/w the tool & w/p and must be circulated at a high rate to carry heat The electrolysis process that takes place at the cathode liberates hydroxyl ions (negatively charged) and free hydrogen The hydroxyl ions combine with the metal ions of the anode to form insoluble metal hydroxides and the material is removed from the anode This process continues and the cathode (tool) reproduces its shape in the w/p (anode). The tool does not contact w/p

Electrochemical Machining (ECM)

Electrochemical Machining (ECM)

Electrochemical Drilling

Electrochemical Grinding

 Combines electrochemical machining with conventional grinding.

 The equipment used is similar to conventional grinder except that the wheel (bonded with diamond or Al oxide abrasives)

 The tool is a rotating cathode wheel with abrasive particles where abrasives serve as insulator between wheel and work piece.

 A flow of electrolyte (sodium nitrate) is provided for

electrochemical machining.

Electrochemical Grinding

Suitable for grinding very hard materials where wheel wear is very high in traditional grinding process .

Electrochemical Machining (ECM)

An electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible. • Characteristics of Electrolyte  Good electrical conductivity  Non toxicity and chemical stability  Non corrosive property  Low viscosity and high specific heat • Function of electrolyte  Carrying current between tool and work peice  Remove products of machining and other insoluble products from cutting region  Dissipate heat produced in the operation.

Electrochemical Machining (ECM)

Tool materials for ECM

The general requirements on the tool material in ECM are  It should be conductor of electricity

 It should be rigid enough to take up load due to fluid pressure  It should be chemically inert to the electrolyte  It should be easily machinable to make it in the desired shape

Main uses:

- Dies and glass-making molds, turbine and compressor blades, Holes, Deburring Due to low forces on tool, ECM can be used to make holes at very large angle to a surface – an example is shown in the turbine nozzle holes in the figure here. [source: www.barber-nichols.com]

Electrochemical Machining (ECM)

Advantages of ECM

 Tool does not contact w/p producing no heat, no friction and does not wear and no heat built-up occurs  Process leaves a burr free surface.

 Does not cause any thermal damage to the parts.  Lack of tool force prevents distortion of parts.

 Capable of machining complex parts and hard materials

 ECM systems are now available as Numerically Controlled machining centers with capability for high production, high flexibility and high tolerances.

Electric Discharge Machining (EDM)

 EDM is based on erosion of metals by spark discharges  EDM system consist of a tool (electrode) and work piece,

connected to a dc power supply and placed in a dielectric fluid  When potential difference between tool and work piece is high, a transient spark discharges through the fluid, removing a small amount of metal from the work piece surface  This process is repeated with capacitor discharge rates of 50-500 kHz.

Electric Discharge Machining (EDM)

 A dielectric is an electrical insulator that can be ionized by an applied electric field.

 When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization.  Dielectric fluid – mineral oils, kerosene, distilled and deionized water etc. Role of the dielectric fluid 1. Acts as a insulator until the potential is sufficiently high. 2. Acts as a flushing medium and carries away the debris. 3. Also acts as a cooling medium.

 Electrodes – usually made of graphite.

 EDM can be used for die cavities, small diameter deep holes, turbine blades and various intricate shapes.

Electric Discharge Machining (EDM)

Characteristics of dielectric fluid Low viscosity  High fluidity  Controlled level of toxicity  Cheap and easily available

Electric Discharge Machining (EDM)

- Inexpensive, precise, complex shapes - Workpiece must be a conductor

i.

ii.

Characteristics of EDM

The process can be used to machine any work material if it is

electrically conductive & tool has to be electrically conductive as well Material removal depends on mainly thermal properties of the work material rather than its strength, hardness etc

iii. In EDM the tool and geometry of the tool is the positive impression of the hole or geometric feature machined iv. The tool wear once again depends on the thermal properties of the tool material v.

Though the local temperature rise is rather high, still due to very small pulse time, there is not enough time for the heat to diffuse and thus almost no increase in bulk temperature takes place. Thus the heat affected zone is limited to 2 – 4 μm of the spark crater

vi. However rapid heating and cooling and local high temperature leads to surface hardening which may be desirable in some applications vii. Though there is a possibility of taper cut and overcut in EDM, they can be controlled and compensated.

Wire EDM Wire EDM

 This process is similar to contour cutting with a band saw.  A slow moving wire travels along a prescribed path, cutting the work piece with discharge sparks.  Wire should have sufficient tensile strength and fracture toughness.  Wire is made of brass, copper or tungsten. (about 0.25 mm in diameter).

Wire EDM

Wire-cut EDM

[source: www.magnix.co.kr]

Electric Discharge Machining (EDM)

Electron Beam Welding (EBW)*

 Fusion welding process in which heat for welding is provided by a highly-focused, high-intensity stream of electrons striking work surface  Electron beam gun operates at: High voltage (e.g., 10 to 150 kV typical) to accelerate electrons  Beam currents are low (measured in milliamps)

 The electron gun melts the parent metal, and the molten metal flows to fill the gap  Heat affected zone is very narrow

 Welds can be several inches deep, and leaves a very clean weld.  Welding must be done in a vacuum.

Electron Beam Welding (EBW)*

Electron Beam Welding (EBW)*

Electron Beam Welding Vacuum Chamber

 EBW had to be carried out in a vacuum chamber to minimize disruption of electron beam by air molecules  Three Vacuum Levels in EBW 1. 2. 3.

High-vacuum welding – welding in same vacuum chamber as beam generation to produce highest quality weld

Medium-vacuum welding – welding in separate chamber but partial vacuum

Non-vacuum welding – welding done at or near atmospheric pressure, with work positioned close to electron beam generator

Electron Beam Welding (EBW)*

EBW Advantages and Disadvantages

Advantages:

High-quality welds, deep and narrow profiles

Limited heat affected zone, low thermal distortion No flux or shielding gases needed Disadvantages:

High equipment cost

Precise joint preparation & alignment required Vacuum chamber required

Safety concern: EBW generates x-rays

Electron beam machining (EBM)

 Similar to LBM except laser beam is replaced by high velocity electrons.

 When electron beam strikes the work piece surface, heat is produced and metal is vaporized.  Surface finish achieved is better than LBM.

 Used for very accurate cutting of a wide variety of metals.

Electron beam machining (EBM)

Electron Beam Machining (EBM)

Laser Beam Welding (LBW)*

 Fusion welding process in which combination is achieved by energy of a highly concentrated, coherent light beam focused on joint  LBW normally performed with shielding gases to prevent oxidation  Filler metal not usually added

 LBW often used for small parts

 The heat from laser can be used to heat the surface of material or

penetrate the entire depth of the joint (good for thin gauge metals).

 The major problems with the current lasers is the cost and bulk of the power source.

Laser Beam Welding (LBW)*

 A laser beam that becomes highly focused is an excellent source of

concentrated energy.

 This energy is used for many welding applications and also

cutting and heat treating.

 Two basic types of lasers are used in welding:  Solid-state and  Gas Lasers.

 Solid-state lasers are made of a single elongated crystal rod. Nd:YAG is the most common solid-state laser used for welding.

 The most common gas laser is the carbon dioxide laser. It is used most widely for welding.

Laser Beam Welding (LBW)*

• Single pass weld penetration up to 3/4” in steel • Materials need conductive

not

• No filler metal required

be

• Low heat input produces low distortion • Does not require a vacuum

CO2 lasers:     

Laser Beam Welding (LBW)*

higher power,

better beam quality in terms of focusability, higher speeds and

deeper penetration for materials that don’t reflect its light, lower start-up and operation costs.

Nd:YAG lasers:    

easy beam alignment, easier maintenance, smaller equipment,

more expensive safety measures

Laser Beam Welding (LBW)*

Advantages:      

Laser Beam Welding (LBW)*

Deep and narrow welds can be done.

Minimal heat affected zones in welds created.

Excellent metallurgical quality will be established in welds. Ability to weld smaller, thinner components. Increased travel speeds. Non-contact welding.

Laser Beam Welding (LBW)

Disadvantages:     

High initial start-up costs

Part fit-up and joint tracking are critical Not portable

Metals such as copper and aluminium have high reflectivity and are difficult to laser weld High cooling rates may lead to materials problems

Laser Beam Welding (LBW)*

Applications Laser Beam Welding (LBW):  Aerospace.

 Defense/military.  Electronics.

 Research & development.  Medical.

 Sensors & instrumentation.  Petrochemical refining.

 Communications & energy.

Comparison: LBW vs EBW*

 No vacuum chamber required for LBW  No x-rays emitted in LBW

 Laser beams can be focused and directed by optical lenses and mirrors

 LBW not capable of the deep welds and high depth-to-width ratios of EBW  Maximum LBW depth = ~ 19 mm (3/4 in),  Whereas EBW depths = 50 mm (2 in)

LaserLaser Beambeam Machining

machining (LBM)

 In LBM laser is focused and the work piece which melts and evaporates portions of the work piece.

 Low reflectivity and thermal conductivity of the work piece surface, and low specific heat and latent heat of melting and evaporation – increases process efficiency.  Application - holes with depth-to-diameter ratios of 50 to 1 can be drilled. e.g. bleeder holes for fuel-pump covers, lubrication holes in transmission hubs.

Laser Beam Machining

1. 2. 3. 4. 5. 6. 7.

Difference between EDM & ECM

Uses dielectric fluid as a conducting medium between tool and work piece. Wear of tool takes place during the process. Heat is generated during the process. Low metal removal rate. It works on the principle of spark erosion. Metal is removed by melting and vaporization. Tools used are oversize for machining inside surfaces and undersize for machining outside surfaces.

1. 2. 3. 4. 5. 6. 7.

Using electrolyte as a conducting medium between tool and work piece. No wear of tool during process so tool life is high. No heat is generated during the process. Metal removal rate is high. It works on principle of Faraday’s law of electrolysis. Metal is removed by electrochemical reaction. Tool used are of required size of the work piece.

Difference between Dielectric & Electrolyte Dielectric

1. It is used as conducting medium in EDM process. 2. It act as conductor and insulator both. 3. Tool wear takes place in the dielectric fluid. 4. It may or may not be corrosive in nature.

Vs

Electrolyte

1. It used as conducting medium in ECM process. 2. It always provide passage for supply of electricity. 3. The electrolyte selected is such that there is no wear of tool. 4. It should be non corrosive in nature.

1. 2. 3. 4. 5. 6.

Difference between EBM & LBM

EBM

Vs

LBM

When high velocity electrons 1. strikes the work piece its kinetic energy converted into heat energy.

When excited atoms releases photons in the form of chain, a LASER beam is generated which strikes on w/p & melts it.

Accuracy is good.

Accuracy is comparatively more.

Electron gun is used as a tool.

2.

Metal removal rate is low.

4.

3.

The complete process should 5. kept in vacuum. Usually only metals.

6.

LASER material is used as tool. Metal removal rate is high.

Vacuum is required between flash lamp and ruby rod. Any material.

Text Book

References

Work Shop Technology, Volume II - Machine Tools, choudhury

by Hajra