production engineering

RWTC PRODUCTION ENGINEERING

ContentsChapter Page no.

Chapter 1 – Machining Processes 1 Cutting tool materials 1 Tool geometry 2 Machinability, Turning, Boring 3 Drilling, Reaming, Milling, Broaching, Grinding, Honing, Lapping 4 EDM, ECM 5

Chapter 2 – CNC machines 1 Principles of numerical control, CNC machine tools 1 Features of CNC machines, Application & economics of CNC machining 1

Chapter 3 – Sheet metal forming 1 Shearing, Blanking, Piercing, Routing, Nibbling, Bending, Forming 1 Advanced sheet metal forming 2

Chapter 4 – Welding 1 Type of weld process 1 Electric arc, Resistance, Submerged arc, EBW 2 Atomic Hydrogen welding, Weld jigs 3

Chapter 5 – Pipe lines & tubular conduit fabrication 1 Types of pipe lines, Cleaning of pipe lines, Inspection of pipe lines 1

Chapter 6 – Heat treatment processes 1 Heat treatment of Al. alloys, Steels 1

Chapter 7 – Surface finishing processes 1 Purpose of surface treatments 1 Cleaning & Surface preparation 2


1. Machining processes

- Machining or Metal cuttingMetal cutting, commonly known as machining, is the removal of unwanted material from a work piece in the form of chips so as to obtain a finished product of desired size, shape, and finish. The vast majority of manufacturing stage in their production, ranging from relatively rough or non precision work, such as cleanup of castings or forgings, to high precision work involving tolerances of 0.002mm or less. Thus it is the most important of the basic manufacturing processes.

- Cutting tool materialsThe materials selected for cutting tools must combine hardness and strength (toughness) with good wear resistance at elevated temperatures.

TOOL STEEL: Plain carbon steel of 0.9 to 1.3% carbon when hardened and tempered has good hardness and strength, adequate toughness, and can be given a keen cutting edge. However it loses its hardness above 204C because of tempering, and it has largely been replaced by other materials for metal cutting.

HIGH SPEED STEEL (HSS): First introduced in 1900, this high alloy steel is remarkably superior to tool steel in that it retains its cutting ability at temperatures up to 593C, exhibiting “Red Hardness”. Compared to tool steel, it can operate at about double the cutting speed with equal life. Although several compositions are used, a typical composition is that of 18-4-1 type (W 18%, Cr 4%, V 1%), Comparable performance can also be obtained by the substitution of approximately 8% Molybdenum for the Tungsten. High speed steel is widely used for drills and many types of general purpose milling cutters and single point tools used in general machining. It has been almost completely replaced for high production machining by carbides and coated tools.

CEMENTED CARBIDE: These non ferrous alloys are used for most metal cutting operations. They are also called sintered carbides because they are manufactured by powder metallurgy techniques. These materials became popular during world war II as they afforded a four or five fold increase in cutting speeds. The early versions, which are still widely used, had tungsten carbide as a major constituent, with a cobalt binder in amounts from 3 to 13%. Recent types utilise very fine micro particles dispersed in the carbide structure, improving their toughness and tool life, particularly when subjected to impact, as in making interrupted cuts. Various other carbides, especially titanium, tantalum and columbium, can be added or substituted for the tungsten. Another type is composed of titanium carbonitrides, titanium-molybdenum transition phases, and nickel alloy binder.

Carbide tools are extremely hard (90-95RA) and can be operated at cutting speeds 200 to 500% greater than those used for HSS. Consequently, they have replaced HSS in many metal machining processes. Carbides are not as tough as HSS and some times react chemically with iron and steel during cutting. At high speeds, they lose hardness and can plastically deform

Many carbide tools are made in the form of throwaway inserts. They contain from 2 to 8 cutting edges and are held mechanically in a tool holder.

CERAMICS: They are made of pure aluminium oxide. Very fine particles are formed into cutting tips under pressure of 267 to 386 Mpa and sintered at about 982 C. Unlike the case with ordinary ceramics, sintering occurs without vitreous phase. Ceramics are in the form of disposable tips. They can operated at 2-3 times the cutting speeds of tungsten carbide, almost completely resist cratering, usually require no coolant, and have about same tool life at their higher speeds as tungsten carbide does at lower speeds. Ceramics are usually as hard as carbides but more brittle and therefore require more rigid tool holders and machines in order to take advantage of their capabilities. Their hardness and chemical inertness makes ceramics a good material for finishing.

Chapter 1Nov 01 Page 1


DIAMONDS: Diamond is the hardest material known (Knoop 7000). Industrial diamonds are now available in the form of polycrystalline compacts which are finding industrial application in machining of aluminium, bronze, and plastics., greatly reducing the cutting forces as compared to carbides. Diamond machining id done at high speed with fine feeds for finishing and produces excellent finishes. Single crystal diamonds, with cutting edge radius of 100 angstroms or less, are being used for precision machining of large mirrored surfaces. They have, for many years, been used to slice biological materials into thin films for viewing in transmission electron microscopes.

CUBIC BORON NITRIDE (CBN): Is a man made tool material, developed by General Electric, and is the hardest material known to man other than the diamond. It retains its hardness at elevated temperature (Knoop 4700 at 20C, 4000 at 1000C) and has low chemical reactivity at the tool/chip interface. This material can be used to machine hard aerospace materials like Inconel 718 and Rene 95 as well as chilled cast iron.

COATED CARBIDE: Coated inserts of carbide are finding more success in many metal cutting applications in recent years. The basic idea is to coat a tough, shock resistant carbide with a thin, hard, crater resistant surface layer to provide for a long lasting, tough tool material. TiC coated tools were introduced in 1969. These tools have 2-3 times the wear resistance of the best uncoated tools with the same breakage resistance. This results in a 50-100% increase in speed for the same tool life. Most coated inserts cover a broader application range, so fewer grades are needed, resulting in lower inventory costs for the user. Other materials which have found success as coating materials for carbides are titanium nitride (less flank resistance but better crater resistance), hafium nitride (better wear resistance than TiC in steel turning), and aluminium oxide coating for carbides, Al2O3 coated carbides permit the cutting speed to be increased to 90% in machining AI1045 steel. Aluminium oxide coatings also demonstrated excellent crater wear resistance by providing a chemical / diffusion reaction barrier at the tool / chip interface. Recent improvements in control of thickness, porosity, and the interface metallurgy have resulted in improved coating adhesion and suppression of strength degrading interface reactions.

- Tool geometryThe geometry of a single point tool is critical to the performance of the tool during metal removal. There are essentially 6 angles to be defined. These are shown in the figure. This is the typical HSS tool used in turning or shaping operations. In order to provide greater strength at the cutting edge and better heat conductivity, zero or negative rake angles are commonly employed on sintered carbide and ceramic cutting tools. These materials tend to be brittle, but their ability to hold their superior hardness at high temperatures makes them preferred for high speed and continuous machining operations. A negative rake angle increases tool forces to some extent , but this minor disadvantage is offset by the added support to the cutting edge. This is particularly important in making intermittent cuts and in absorbing the impact during the initial engagement of the tool and work. The following table specifies tool geometries for cutting various materials.

Chapter 1

Nov 01 Page 2


Work material ToolRake angle (deg) Cutting speed

mm/minBack Side

B1112 steel HSSWCCeramic

160-5

223-5

69168427

1020 steel HSSWCCeramic

160-5

143-5

55152366

4140 steel HSSWCCeramic

120-5

143-5

4091274

18-8 steel (stain less)HSSWCCeramic

84-5

148-5

2784152

Grey cast iron (medium)HSSWCCeramic

50-4-5

122-4-5

3469244

Brass (face machining) HSSWC

00

04

76221

Aluminium alloys HSSWC

3510-20

1510-20

91122

Magnessium alloys HSSWC

010

1010

91213

Titanium (turning) WC 0 5 46

- Machinability & cost of machiningThe machinability of material is defined as follows: “The most machinable meterial is one which permits the removal of material with a satisfactory finish at lowest cost.” Factors affecting the machinability of metals are

Material of the work piece Tool material Tool geometry Machining operation Cutting speed Coolant Coefficint of friction between tool & the work piece Shear strength of work piece material

Factors which come into play while evaluating the machinability are Tool life Form & size of chip and shear angle Cutting forces and power consumption Surface finish Cutting temperature Rate of cutting under standard force Uniformity in dimesional accuracy of successive parts

- TurningTurning provides a widely used means for machining external and internal cylindrical, conical and spherical surfaces. Turning is done on the lathes.

- BoringBoring is variation of turning. Essentially, it is internal turning where in a single point cutting tool produces internal cylindrical, conical or spherical surfaces. Consequently, boring can be done on most machine tools that can do turning. However, boring can also be done using a rotating tool with the work piece remaining stationary. Also, specialised machine tools have been developed that can do boring drilling and reaming but will not do turning (Jig boring).



- DrillingIn manufacturing it is probable that more internal cylindrical surfaces (holes) are produced than any other shape, and a large proportion of this are made by drilling. Most drilling is done with a tool having 2 cutting edges. In recent years, new drill point geometries have resulted in improved hole accuracy, longer life and increased feed rate capabilities.

- ReamingReaming is done for 2 purposes. To bring holes to a more exact size, and to improve the finish of an existing hole by machining a small amount from its surface. Multi edged cutting tools are used and no special machines are built especially for reaming. It is usually done on the same machine as that was employed for drilling the hole that is to be reamed.

- MillingMilling is a basic machining process by which a surface is generated progressively by the removal of chips from a work piece as it is fed to a rotating cutter in a direction perpendicular to the axis of the cutter. In some cases the work piece remains stationary and cutter is fed to the work. In nearly all the cases, a desired surface is obtained in a single pass of the cutter or work and, because very good surface finish can be obtained, milling is particularly well suited, and widely used , for massive production work.

- BroachingBroaching is one of the most productive, basic machining process. As a process, it is similar to shaping, competes economically with milling and boring and is capable of producing precision machined surfaces. The heart of this process lies in the broaching tool wherein roughing, semi finishing, and finishing teeth are combined into one tool.

- GrindingGrinding is an abrasive machining process. Chips are formed by very small cutting edges that are integral part of abrasive particles. The results obtained by abrasive machining range from the finest and smoothest surfaces produced by any machining process, in which very little material is removed. Aluminium oxide is the most widely used artificial abrasive. Other abrasives are silicon carbide and diamond.

- HoningHoning uses fine abrasive stones to remove very small amounts of metal. It is used to size and finish bored holes, removing common errors left by boring (taper, waviness, and tool marks) or to remove the tool marks by grinding. The amount of material removed is typically about 0.13mm.

- LappingLapping is an abrasive surface finish process wherein fine abrasive particles are charged into a soft material, called a lap. The material of the lap may range from cloth to cast iron or copper, but is always softer than the material to be finished, being only a holder for the hard abrasive particles. Lapping is applied to both metals and non metals.

Materials of almost any hardness can be lapped. However it is difficult to lap soft materials because the abrasive tends to become embedded. The most common lap material is fine grained cast iron. Copper is used quite often and is the common material for lapping diamonds. For lapping hardened metals for metallographic examination, cloth laps are used. Lapping can be done either by hand or by special machines. In hand lapping the lap is flat, similar to a surface plate, grooves are usually cut across the surface of the lap to collect excess abrasive and chips. The work is moved across the surface of the lap, using an irregular, rotary motion., and is turned frequently to obtain uniform cutting action.



Various types of lapping machines are available for lapping round surfaces. A special type of center less lapping machine is use dfor lapping small, cylindrical parts, such as piston pins and ball bearing races.

- Electric discharge machiningEDM has long been of greatest interest to end user industries, especially the automotive, aerospace, tool, mould, and die making, and heavy engineering industries. Its primary attraction has been its ability to take a raw piece of stock, machine it, and finish it on one machine using EDM’s ability to create contours, fine pitch, independent top and bottom profiles, and perform multi axis simultaneous machining. EDM machines cut to 0.003mm accuracy.

- Electro chemical machiningElectro chemical machining, commonly designated ECM, removes material by anodic dissolution with a rapidly flowing electrolyte. It is basically a deplating process in which the tool is a cathode and the work piece is the anode, so both must be conductive. The electrolyte, which can be pumped rapidly through or around the tool, sweeps away the waste product (sludge) and captures it by settling in filters. The shape of the cavity is the mirror image of the tool, which is advanced via a servo mechanism which controls the gap (0.003 to 0.03”) between the electrodes. The tool advances into the work at a constant feed rate which matches the dissolution rate of the electrodes. The electrolytes are highly conductive solutions of inorganic salts, usually NaCl, KCl, NaNO3 (or other proprietary mixtures) and are operated at about 90 to 125 F with flow rates ranging from 50 to 200 feet per sec. Tools are usually made of copper or brass and some times stain less steel or fibre glass. There is no wear of the cutting tool during the actual cutting as the tool is protected cathodically. The process produces a stress free surface, and the ability to cut the entire cavity simultaneously aids productivity.

Electrochemical hole drilling processes have been developed for drilling very small holes using high voltages and acid electrolytes. The tool is a drawn glass nozzle with an internal electrode. Multiple sets of glass tubes are employed and over 50 holes per stroke can be done. This technique was developed to drill the cooling holes in gas turbine blades. Stress free holes from 0.004 to 0.03” in dia with 50:1 depth to dia ratios are routinely accomplished in nickel and cobalt alloys. Acid is used so that the dissolved metals go into solution instead of forming sludge.



2. CNC MachinesNumerical control is a method and system of controlling a machine or process by instructions in the form of numbers.

- Principles of numerical controlMachine control functions done by operator in conventional machines are translated into numeric instruction that can be understood by the machine control unit. This is done by preparing part programs and running the programs on the machine control unit. The following steps are involved in the preparation of part programs.

Define sequence of operations Write program in APT (nowadays CAD/CAM systems generate APT program automatically) Post process the APT program to generate machine code, which will be understood by the

machine control unit Punch the program on the paper tape or send the part program to the machine control unit directly

through communication port

- CNC machine toolsNC machines are classified into the following 4 groups

Group I – Machine tools with rotating tools either on vertical spindle or on horizontal spindle. These include vertical knee milling machines, drilling machines, horizontal boring machines, horizontal machining centres etc.

Group II – Machine tools with rotating work pieces like lathes, grinding machines, etc.

Group III – Machine tools with non- rotating work pieces and non-rotating tools like shaper, planner etc.

Group IV– Machines other than machine tools like NC drafting etc.

- Features of CNC systems X,/Y/Z axes movement control (linear) A/B/C axes rotation control (rotary) Automatic tool changer Automatic pallet changer Multi axes machining Multi spindle heads In process gauging

- Application and economics of usage of CNC machiningCNC machines are used in almost all the industries where accuracies and complicated geometries are involved. The following are the advantages of using CNC machines.

It provides ability to perform more work faster. e.g a combination of operation like milling, turning, drilling, tapping, boring, reaming can be done in a single setup on multiple sides of work piece. Because of less setting time, effective machine utilization is increased.

Because most NC machine tools have contouring ability, the cost of special tools is eliminated. Increased productivity, reduced setup and lead time, better scheduling, reduced tooling

requirement and reduced tooling cost, increased accuracy, reduced material flow time, greater safety, complete interchangeability, reduced work piece handling, increased cutting tool life

Fewer jigs & fixtures Design modifications can be readily implemented



3. Sheet metal formingThe following are the usual sheet metal operations being carried out to form different shapes out of thin metal sheets.

- ShearingIt is the process of separation of the metal by means of two blades of identical contours

- BlankingShearing of closed contours where the metal inside the contour profile is used for subsequent operations. The blanks may be with or without holes.

- PiercingIt is the opposite of blanking, where remaining portion is used for subsequent operations

- RoutingIt is a metal cutting operation in which a cutter rotating at speeds of 15000 to 18000 rpm cuts the material to the profile of the template

- NibblingA circular punch moving with a rapid reciprocating strokes from 300 to 900 per minute, operate in conjunction with a circular die, fixed to the machine. The cut is made by holding against the pilot of the punch and taking a small bite with each stroke of the punch, following either a template or a scribed line on the work. Internal holes must be started from previously drilled holes.

- BendingNormally Press brake is used to do the bending. In bending the plane of the original metal is changed and very often the action takes place along a straight line. For bending the bend allowance is calculated unsing the following empirical formula.BA=(0.01743R+0.0078T)xA where R=Bend radius, T=Sheet thickness, A=Dend angle in deg.

- FormingThis is same as bending except the difference that the bending need not be along a straight line. The following are the usual forming processes

Hand forming Rubber press forming Stretch forming

- SpinningIt is a forming process where sheet is pressed against a rotating form tool to get the required shape.



- Advanced sheet metal Forming Fluid forming

o Rubber pad formingo Fluid cell formingo Fluid forming

Dual forming Hot forming

o Hot jogglingo USI hot forming

Age creep forming Super plastic forming / diffusion bonding Explosive forming (high energy rate forming Fine blanking CNC routing CNC spinning CNC stretch forming



4. WeldingWelding is process in which two materials, usually metals, are permanently joined together through localised coalescence, resulting from a suitable combination of temperature, pressure, and metallurgical conditions. Because the combination of temperature and pressure can range from high temperature with no pressure to high pressure with no increased temperature, welding can be accomplished under a very wide variety of conditions, and numerous welding processes have been developed and are used routinely in manufacturing.

- Type of weld and processo Oxy fuel gas welding (OFW)

Oxy acetylene welding pressure gas welding

o Arc welding (W) Shielded metal arc welding Gas metal arc welding

Pulsed metal arc welding Short circuit arc Electro gas

Gas tungsten arc welding (formerly known asTIG) Flux cored arc welding Plasma arc welding Stud welding

o Resistance welding (RW) Resistance spot welding Resistance seam welding Projection welding

o Solid state welding (SSW) Forge welding Cold welding Friction welding Ultrasonic welding Explosion welding Roll welding

o Unique processes Thermit welding Laser beam welding Electroslag welding Flash welding Induction welding Electron beam welding Atomic hydrogen welding



- Electric arc weldingAll arc welding processes employ essentially the same basic circuit except that alternating current is used at least as much as direct current is used. If the work is made positive and the electrode is made negative, straight polarity is said to be employed. When the work is negative and electrode is positive, the polarity is reversed. When bare electrodes are used, greater heat is liberated at the anode. Certain shielded electrodes, however, change the heat conditions and are used with reverse polarity.

The various arc welding processes require selection or specification of the welding voltage, welding current, arc polarity (straight polarity, reverse polarity, alternating current), arc length, welding speed, arc atmosphere, electrode or filler material, and flux. The filler metal is selected to match the base metal with respect to properties and/or alloy content.

- Resistance weldingIn resistance welding, both heat and pressure are utilised in producing coalescence. The heat is the consequence of the electrical resistances of the work pieces and the interface between them. A certain amount of pressure is applied initially to hold the work pieces in contact, there by controlling the electrical resistance at the interface, and is increased when the proper temperature is attained to facilitate coalescence. Because of the pressure utilised, coalescence occurs at a lower temperature than with oxyfuel gas or arc welding. Resistance spot welding is the simplest and most widely used of this type of welding.

- Submerged arc weldingIn submerged arc welding the arc is maintained beneath a blanket of granular flux. Either AC or DC current can be used as the power source. The flux is deposited just ahead of the electrode, which is in the form of coiled wire copper coated to provide good electrical contact. Because the arc is completely submerged in the flux, only a few small flames are visible. The granular flux provides excellent shielding of the molten metal and, because the pool of the molten metal is relatively large, good fluxing action occurs, so as to remove impurities. Consequently very high quality welds are obtained.Atomic hydrogen welding

- Electron beam weldingEBW is fusion welding process in which heating results from the impingement of a beam of high velocity electrons on the metal to be welded. A high voltage current heats a tungsten filament to about 2200 C, causing it to emit high velocity electrons. By means of control grid, accelerating anode, and focussing coils, the electrons are converted into concentrated beam and focussed on to the work piece in a spot ranging from 0.8 to 3.2mm in dia. The work is enclosed and moved under the electron gun in the vacuum chamber. Under these conditions, the vacuum assures degasification and decontamination of the molten weld metal, and very high quality welds can be obtained. However the size of the vacuum chamber required naturally imposes serious limitations on the size of the work piece that can be accommodated and productivity.

Materials that are difficult to weld by other processes, such as Zirconium, beryllium and tungsten can be welded successfully by EBW. Very narrow welds can be obtained as well as remarkable penetrations. The high power and heat concentrations can produce fusion zones with depth to width ratio of 25:1, with low heat input, low distortion, and very narrow heat affected zone. Heat sensitive materials can be welded without damage to the base metal. High welding speeds are common. No filler material is required. The process can be performed in all positions. Pre heat or post is not necessary. However the equipment is quite expensive and extensive joint preparation is required. Further more the vacuum chamber tends to limit production rate and the size of piece that can be welded.



- Atomic hydrogen weldingThis process combines gas welding with electric arc welding. The electrode holder incorporates two tungsten electrodes arranged in inclined position and hydrogen is ejected from the hydrogen nozzle in between the tips of these electrodes. The electric arc between the electrodes breaks down the molecular hydrogen into atomic hydrogen. This atomic hydrogen, when touches the relatively cold metal, recombines into molecular hydrogen, thus liberating considerable heat which melts the metals to be welded and creates molten puddle into which a consumable welding rod to supply the material for welding may be added. The hydrogen also provides reducing gas atmosphere under which the fusion takes place. Usually alternating current supply is used and temperature of the order of 4200C is achieved. This process is best suited for tool and die parts where alloy control and heat input are important.

- Weld JigsWeld jigs are used to keep the welding details in place during the welding process and to avoid distortions



5. Pipe lines & tubular conduit fabrication

- Types of pipe lines & conduits Hydraulic pressure lines – Most of the hydraulic lines used in ALH are of AMS 4943 or

AMS 4944, Thin walled titanium tubes. These lines manufactured using red band samples taken on the actual aircraft and end fittings are attached using permaswage swaging process or by orbital welding.

Hoses – Different types of hoses are used in ALH for carrying hydraulic fluids and carrying fuel from tank to tank and supply tank to the engine. Normally they are used for transferring fluids and gases at lower pressures. End fittings are crimped using Aeroquip hose crimping machine.

Beadings – Beadings are done to facilitate rubber hoses to be connected on the beadings and tightened with worm clamps.

- Cleaning of pipe lines (HPS 103)Aircraft pipe lines are cleaned using alkaline cleaner as per HPS 101 and paint removed as per HPS 102. The following is the usual procedure to clean the stainless steel pipes.

De-grease the pipes in trichloroethylene Pickle the tubes to remove any rust formed as per HPS 101 Scrub and clean Rinse thoroughly Passivate the pipes for 30 minutes as per HPS 101 Rinse thoroughly in hot water Dry the bores with dry compressed air Flush the bores with the medium for which it is meant

- Inspection of pipe linesAfter cleaning, the pipes shall be checked for their cleanliness by means of wetting test and ends covered with blanking plugs or heat shrinkable plugs. Pressure testing is done to find out if any leakages are there.



6. Heat treatment processesHeat treatment is an important operation in the manufacturing process of machine parts and tools. It may be defined as an operation of heating and cooling of metals in the solid state to induce certain desired properties into them. Heat treatment can alter the mechanical properties of the steels by changing the shape & size of the grains of which it is composed, or by changing micro constituents. It is generally employed for the following purposes.

To improve machinability To change or refine grain size To relieve stresses of the metal induced during cold or hot working To change mechanical properties. e.g tensile strength, hardness, ductility, shock resistance to

corrosion etc. To improve magnetic and electrical properties To increase resistance to wear, heat and corrosion To produce a hard surface on a ductile interior

- Heat treatment of aluminium alloysAluminium alloys are usually formed in annealed or solutionised condition and artificially aged

Annealing – Heat to 410-420C. Furnace cool to 250C at the rate of 30C/hr and cool in air. Solutioning - Heat to upper critical temperature (4955C for 2024 alloy) for the required time

in the air furnace and quench in UCON quench solution. Artificial ageing – Ageing gives the required strength to the aluminium alloys. Heat to1905C

for 16hrs, and cool in air.

- Heat treatment of steels Annealing – It is the softening process in which iron base alloys are heated above the

transformation range, held there for a proper time and then cooled slowly at the rate of 30-150 C per hr, below the transformation range in the furnace itself.. Alternatively the steel may be transformed into a furnace at about 650C, and held there until the austenite has transformed into pearlite. Final cooling can be done in still air.

Normalising – Is done to improve the machining characteristics, refine grain size and homogenise micro structure, modify and refine cast dendrite structures and provide desired mechanical properties. Iron base alloys are heated to 40-50C above the upper transformation range and held there for a specified period ( to ensure that a fully austenitic structure is produced) and followed by cooling in still air at room temperature.

Hardening – Hardening is done to improve the strength of the steels. Steel is heated to 20C above the transformation range , soaking at this temperature for a considerable period to ensure through penetration of the temperature inside the component, followed by sudden cooling to room temperature by quenching in water or oil or brine solution

Tempering – It is used to relieving the internal stresses produced by quenching while hardening



- Case hardening of steelThis process is used to produce a high surface hardness for wear resistance supported by a tough, shock resisting core and better fatigue limit. The following are some of the case hardening processes.

Carburising Nitriding Cyaniding Induction hardening Flame hardening

- Heat treatment of titanium alloysGenerally aircraft industry uses the Titanium alloy Ti6Al4V . It can annealed , solution treated and precipitated to obtain the final strength requirements.

Annealing – Heat to 700-840C, soak for required time depending on the thickness, and cool in furnace at 30C/hr (max) to 540C

Stress relieving – To relieve internal stresses formed by heavy machining. Heat to 550-700C. soak for required time and cool in furnace at 55C/hr (max) to 480C, then 150C/hr upto 200C, then cool in air

Solution treatment – Heat to 925-940C. soak for required time and quench in water. Precipitation treatment – Heat to 495-565C. soak for 2-6 hrs. cool in air.



7. Surface finishing processes

- Purpose of surface treatmentDifferent types of coatings are given to the finished parts to avoid corrosion and impart special properties like wear resistance and masking. The following coating processes are normally used in aircraft industry.

Anodising of aluminium alloys (HPS 201) . Used for corrosion protection Chromating of Mg alloys (HPS 202). Used for limited degree of protection against corrosion

and acts as a good base for painting Chromate passivation of Cadmium & Zinc plated parts (HPS 203). Increases corrosion

resistance of Cd & Zn plated surfaces in humid conditions. Improves resistance to organic vapours from varnishes and plastic insulating materials. Improves the performance of the subsequent painting schemes applied on the surface

Tin plating (HPS 204). Used for protection against corrosion up to 180C, chiefly carbon and low alloy steels & copper base alloys, and to facilitate soldering or masking during nitriding

Cadmium plating (HPS 205). Used for protection against corrosion, wear and easy solderability.

Copper plating (HPS 206). Used as un under coat for nickel, chrome and silver plating, protection against fretting corrosion, anti seizure coating when press fitting a component, to build up worn out surfaces such as bearing diameters, stop ooffs during case hardening treatments such as carburising & nitriding, to assist thread rolling on stainless steel studs, for electroforming.

Hard chromium plating (HPS 207). Used for high surface hardness on steels and heat resisting copper base alloys.

Nickel plating (HPS 208). Used for protection against corrosion especially on copper base alloys, resistance to wear mainly on steel, Ni based alloys and aluminium alloys, to restore worn out or over machined surfaces of steel and heat resisting alloys, lubrication and protection against oxidation during forging of stainless steels.

Silver plating (HPS 209),used for resistance to corrosion, anti seizure, anti galling, bearing surface, electrical conductivity, solderability

Zinc plating (HPS 210). Used for protection against corrosion especially on tools, jigs and ground equipment.

Lead plating (HPS 211). Used for corrosion protection especially in sulphurous atmosphere, bearing application and protection of storage battery parts

Decorative chromium plating (HPS 214). Used to obtain non-tarnish and durable coating on any metal except nickel.

Temporary protection (HPS 215).Used for temporary protection against corrosion or mechanical damage during storage & transit. Lacquers, de-watering oils, lanolin based protectives, hot dip oil and retention coatings, solvent strippable coatings.

Dallic process (HPS 216). Used for repair of damaged or reworked areas of parts treated with cadmium plating.

Alodine1200Alocrom treatment of Al. alloys (HPS 217) for corrosion Passivation (HPS 218). Used for stainless steel pickling, passivation and decontamination. Anodising of titanium alloys (HPS 221). Used for protection against galling & galvanic

corrosion, improved wear resistance and pre treatment in the application of dry film lubrication.

Chromium plating of aluminium alloys (HPS 219). Used for better appearance, better corrosion resistance, prevention of seizing and wear resistance

Plasma flame deposition (HPS 226). Used to confer the surface with special properties like corrosion resistance, wear resistance, oxidation, protection, electrical and thermal barriers etc. Dimensional buildup for salvage of worn parts. Repair and recondition on existing coating. To provide under coat with high bond strength for other sprayed materials.



- Cleaning & surface preparation (HPS 101)Various surface cleaning processes are used for inspection purposes, as a preparation for further processing, for cleaning before assembly and as a preparation for storage. There are two types of cleaning processes, chemical and mechanical. The following are some of the cleaning processes used in the aircraft industry.

Solvent de-greasing – using kerosene other organic solvents Vapour de-greasing (HPS 109) Pickling & de-scaling – the process depends on the metal to be treated. Generally acid

pickling and salt bath descaling are used Abrasive blast cleaning (HPS 108) – Used for removal of sand particles from castings,

removal of scales formed during heat treatment or welding, Cleaning and preparing for metal spray or any other subsequent operations, Cleaning of steel forgings in preparation of for inspection. There are three types of blasting processes.

o Shot blasting,o sand blastingo wet blastingo Glass bead blastingo Cocoanut shell-grit blasting

Barrel cleaning or tumble cleaning Alkaline cleaning Emulsion cleaning Electrolytic alkaline cleaning. Used where extreme cleanliness is required, especially prior to

electroplating Ultrasonic cleaning- Ultrasonic energy is used along with organic or inorganic solvent media.

The process is usually used as a final cleaning method especially for complicated and precision jobs, requiring extreme cleanliness.

Chemical or electrochemical etching (HPS 110) – used as a preparation for plating or inspection.

Chemical or electrolytic polishing – Used as a preparation for plating, anodising, inspection etc., or as a final treatment.


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