Workshop technology

Compiled by Rabin
Some very important definitions
The temperature at which new stress-free grains are formed in a metal is known as recrystallization temperature.
Spring back is the geometric change made to a part at the end of the forming process when the part has been released from the
forces of the forming tool. It is a common phenomena in cold working.
Some metals, such as lead and tin, have a low recrystallization temperature and can be hot-worked even at room temperature,
Cold working
Plastic deformation of metals below the recrystallization temperature is known as cold working.
It is generally performed at room temperature.
ADVANTAGES OF COLD WORKING
1. No heating is required because the T < Trecryt and at room temperature.
2. Better surface finish is obtained.  Better dimensional control  no secondary machining  Products possess better
reproducibility and interchangeability. Explanation- Since the working is done in cold state, no oxide would form on the surface
and consequently good surface finish is obtained.
5. Better strength, fatigue, hardness and wear properties of material due to strain hardening.
6. Directional properties can be imparted.
7. Contamination problems are almost negligible as the metal surfaces must be clean and scale-free.
8. Excessive cold working gives rise to the formation and propagation of cracks in the metal. The loss of ductility during cold
working has a useful side effect in machining. With less ductility, the chips break more readily and facilitate the cutting operation.
9. There is no possibility of decarburization of the surface.
10. The recrystalline temperature of steel is increased.
DISADVANTAGES OF COLD WORKING
1. Higher forces and more energies are required for deformation.
2. Heavier and more powerful equipment is required.
3. Less ductility, Less impact strength, less resistance to corrosion is available.
4. Strain hardening occurs ( may require intermediate annealing ).
5. Undesirable , internal residual stresses may be produced.
6. Imparted directional properties may be detrimental.
7. Material is not uniform after this working. There is more risk of cracks as the existing cracks propagate and new cracks may
develop.
8. It does not require pickling because no oxidation of metal takes place. Embrittlement does not occur in cold working due to no
reaction with oxygen at lower temperature.
9. It generally distorts grain structure. But crystallization does not occur.
10. The stress required for deformation increases rapidly with the amount of deformation. The amount of deformation, which can
be performed without introducing other treatment, is limited and as per the ductility of the material.
11. Spring back is a common phenomenon present in cold-working processes.
Hot working
Plastic deformation of metal carried out at temperature above the recrystallization temperature, is called hot working.
Under the action of heat and force, when the atoms of metal reach a certain higher energy level, the new crystals start forming.
This is called recrystallization. When this happens, the old grain structure deformed by previously carried out mechanical
working no longer exist, instead new crystals which are strain-free are formed.
ADVANTAGES OF HOT WORKING
1. No strain hardening.
2. Even brittle materials can be hot worked.
3. No internal or residual stresses are set-up in the metal in hot working process.
4. If cracks and blow boles are present in the metal, they can be finished through hot working. There is less risk of cracks.
5. Since the shear stress gets reduced at higher temperatures, this process requires much less force to achieve the necessary
deformation.
6. Greater ductility of material is available, and therefore more deformation is possible. It is preferred where large deformations
have to be performed that do not have the primary purpose of causing work hardening.
7. Favourable grain size is obtained leading to better mechanical properties of material
8. Equipment of lesser power is needed.
9. Material is uniform throughout. Compositional irregularities are ironed out and non-metallic impurities are broken up into
small, relatively harmless fragments, which are uniformly dispersed throughout the metal instead of being concentrated in
large stress-raising metal working masses.
10. If process is properly carried out, ultimate tensile strength, yield point, corrosion resistance are unaffected
DISADVANTAGES OF HOT WORKING
1. Most commercial metals require some heating. However, this temperature should not be too high to reach the solidus
temperature; otherwise the metal will burn and become unsuitable for use. Therefore one has to be very careful as regards the
temperatures at which to start hot work and at which to stop because this affects the properties to be introduced in the hot
worked metal. Too high a temperature may cause phase change and overheat the steel whereas too low temperature may result
in excessive work hardening.
2. Fibre and directional properties are produced.
3. Due to high temperature in hot working, rapid oxidation or scale formation and surface de-carburization take place on the
metal surface leading to poor surface finish and loss of metal.
4. Some metals cannot be hot worked because of their brittleness at high temperatures.
5. Because of the thermal expansion of metals, the dimensional accuracy in hot working is difficult to achieve.
6. Handling and maintaining of hot working setups is difficult and troublesome.
7. The process involves excessive expenditure on account of high cost of tooling.
8. Heavy oxidation occurs during hot working so pickling is required to remove oxide.
9. There is chance of embrittlement by oxygen in hot working hence metal working is done at inert atmosphere for reactive
metals.
HW process associated terms
Bloom has a square cross section with minimum size of 150mm × 150mm. Blooms are used for rolling structural products such
as I-sections, channels, rails etc.
Billet is smaller than a bloom and has minimum size of 50mm × 50mm. Billets are rolled into bars, rods. Bars and rods are raw
materials for extrusion, drawing, forging, machining etc.
A slab can be considered as a special case of bloom i.e., a bloom with lesser thickness. A slab is rolled from an ingot or a bloom
and generally has a rectangular cross section of about 250 mm by 40 mm. Slabs are meant for rolling sheets, strips, plates etc.

Hot spinning -
1. It involves spinning a piece of metal on a lathe while high heat from a torch is applied to the workpiece.
2. Once heated, the metal is then shaped as the tool on the lathe presses against the heated surface forcing it to distort as it spins.
Parts can then be shaped or necked down to a smaller diameter with little force exerted, providing a seamless shoulder.
Generally, parts of circular cross section which are symmetrical about axis of rotation can be produced.
Rolling mills
1. A three high rolling mill has three rolls. First rolling in one
direction takes place along one direction. Next the work is
reversed in direction and fed through the next pair of roll. This
improves the productivity.
2. Rolling power is directly proportional to roll diameter. Smaller
diameter rolls can therefore reduce power input. Strength of
small diameter rolls are poor. Therefore, rolls may bend. As a
result, larger diameter backup rolls are used for supporting the
smaller rolls. Four high rolling mill is one such mill. Thin sections
can be rolled using smaller diameter rolls. The smaller size rolls
are known as working rolls which concentrate the total rolling
pressure over the workpiece. The larger diameter rolls are called
back-up rolls and their main function is to prevent the deflection
of the smaller rolls, which otherwise would result in thickening of
rolled plates or sheets at the centre.
3. Cluster mill and Sendzimir mill are used for rolling thin strips of
high strength materials and foils [0.0025 mm thick].
Hot spinning
Hot drawing or cupping
Drawing is pulling of metal through a die or a set of dies for achieving a reduction in a diameter. The material to be drawn is
reduced in diameter.
It is used to produce thick-walled seamless cylinders and tubes

Fig. Two stages of hot drawing.

Hot piercing or seamless tubing
CW associated process
Cold forging (swaging) is widely used in forming ductile material. Commonly used swaging processes are – sizing (slightly
compressing to obtain close dimensional tolerance) , heading ( making bolts, rivets and similar headed elements) and rotatory
swaging (reducing the diameter of tubes and bars)
 Cold spinning is best suited to aluminum and other soft metals making kitchen utensils.
Cold extrusion – the most common process is impact extrusion. Limited to soft and ductile material like Pb, Sn, Al, Zn and their
alloys. Items of daily uses such as tooth pastes shaving creams
Cold drawing – bars, wire and tubes
Cold bending
Cold or shot peening- to improve the fatigue strength
Tube drawing using a moving mandrel
Conclusion
Hot rolled steel is typically cheaper than cold rolled steel due to the fact that it is often manufactured without any delays in the
process, and therefore the reheating of the steel is not required (as it is with cold rolled).
Hot rolled steel is used in situations where precise shapes and tolerances are not required.
Cold rolled steel is essentially hot rolled steel that has had further processing. The steel is processed further in cold reduction
mills, where the material is cooled (at room temperature) followed by annealing and/or tempers rolling. This process will produce
steel with closer dimensional tolerances and a wider range of surface finishes.
Cold rolling also improves machinability in the cold rolled part by conferring the property of brittleness, a condition, which is
conducive to smooth tool, finishes with broken chips.
Tandem or continuous or multistage drawing of wires and tubes is necessary because annealing is needed between stages.
In order to get uniform thickness of the plate by rolling process, one provides hardening of the rolls.
Thread rolling is a cold forging process that can be performed on any ductile metal. The blank diameter of a rolled thread is at
the pitch diameter, a theoretical point between the major diameter and minor diameter. READ THIS LAST SENTENCE VERY
CAREFULLY.
Facts
The recrystallization temperature for steels is typically between 400 and 700 °C.
The process of increasing the cross section of the bar at expense of its length is upsetting while process of decreasing the cross
section of the bar by increasing the length is drawing down.
Welding process entails joining similar or dissimilar metals by fusion wherein
1.There may or may not application of pressure
2.There may or may not be use of filler metals
Types of joints
Lap joints < 3mm plates
Butt joints < 5mm plates without beveling
The plates measuring between 5mm to 12.5mm in
thickness are butt joint only with beveling ( V or U) the
edges.
Above 12.5mm, double bevel is must.
Electric resistance welding
ERW facts
Time – short duration
Voltage - low ( 6 to 10V)
Amperage – high ( 60 to 4000 Amp)
Pressure varying from 25 to 55 Mpa
Types – Spot for joining two or more sheets of metal. ( electrode tip diameter = 𝑡 , distance between nearest edge of the plate
and center of weld = 1.5d, spacing between two spot welds should not be less than 3d)
Conventional vs Roll spot vs seam welding
For Conventional or seam welding, best adopted
thickness is 0.025 to 1.25mm thickness
For seam welding,, it is between 0.025mm to
3mm. It is used for stainless steel, aluminium and
its alloys, nickel and its alloys etc. Less overlap
required of two parts than spot or projection
welding. Several parallel seams can be produced.
Gas tight or liquid tight welds can be produced.
Do you know the welding process which is used for the mass production in the automobile
sector?
The answer is projection welding.

Please Note-
Projection should be made on plates with highest thermal conductivity and
thicker metal in case of any confusion.
Flash vs butt (upset) welding
Similarity –
1. Coalescence is produced simultaneously over the entire area of two abutting surfaces.
2. Heat for welding is obtained by the resistance to electric current between the two facing surfaces.
Dissimilarity
1. Upset welding is done without a change in current or pressure throughout the cycle, adopted in rods and pipes . But flash
welding is a two-stage process namely, flashing action and upset or forging action, adopted in steel container and MS.
Arc welding facts and figures
Temperature between 6000 to 7000 degree Celsius
Both AC and DC can be used , but DC is most preferred.
DCSP – when work is connected to +ve terminal, DCRP- when work is connected to –ve terminal.
Types of Arc welding
1. Carbon Arc Welding - a pure graphite or baked carbon rod is used as a non-consumable electrode ; Weld can be made with or
without the addition of filler material. Carbon arc welding may be classified as (1) Single electrode (carried out in air or in
inert atmosphere, heat source for brazing DCSP) , & (2) Twin carbon (AC, more heat)
2. Metal arc welding – 2400 to 2700° C
3. MIG (aka Gas Metal Arc Welding) – It uses consumable electrode. It is fully automatic process as the electrode is a roll of
wire which the welder feeds out of a ‘gun’ to the work piece. You control the speed of the wire, so you can make long welds
without stopping to replace a rod. MIG welding is a very simple and easy process to learn. A variety of materials such as
mild steel, stainless steel and aluminium and a range of material thicknesses can be welded from thin gauge sheet metal right
up to heavier structural plates.
4. TIG - TIG stands out in that the tungsten electrode carries the arc, but is not consumed. Tungsten withstands the heat of
welding. TIG takes the most skill, since you have to hold a filler rod in one hand and the gun in the other in order to
accomplish this type of welding. It is usually reserved for specialized types of welds. If the metal you're using is thin,
TIG could be a better option.
NOTES -
DCSP – Copper alloys and Stainless steel. (@ Cass); DCRP – Magnesium ; A/C - steel, CI, Al, Mg (@SCAM)
5. Atomic H2 welding – the non consumable electrode
6. Submerged MAW- Bare electrode; low carbon, alloy steel and non-ferrous alloys
7. Thermit – iron oxide + Al (1500°C)
Contd.
Flame temperature in oxyacetylene gas welding is about 3200°C (≈ two times the temperature of thermit welding)
Low pressure (injector) type welding torch operates oxygen pressure in between 70kN/m2 to 280kN/m2 and at acetylene
pressure less than 7kN/m2 and for positive or equal pressure torch, the pressure of acetylene should be more than 7kN/m2.
The welding tip is made of high thermal conductivity material like copper.
Desired pressure range for oxygen is 70 kN/m2 to 280 kN/m2 and that of acetylene is between 7 kN/m2to 103kN/m2.
Color code for oxygen is black and for acetylene is red.

Flames
Neutral flame दागबिबिन इस्पात, कास्ट आईरोन , तामा र अल्मुबनयम (३२००से ल्सियस ;
१२५० सेल्सियस)
Oxidizing flame कास्य र बितल

Carburizing flame  stellite (कोिाल्ट र क्रोबमयमको बमश्र धातु जु न प्रबतरोध गनन प्रयोग हुन्छ ),
अलौबिक बमश्र धातु
Welding techniques
Left ward or fore-hand or forward टर्न अिरे टरको दायााँ िाथ (right hand)मा | welding दायााँ दे ल्सि िायााँ | टर्न ६०-७० बिग्री ; रि ३०
– ४० बिग्री | ६ बमबलमीटर भन्दा माबथ मोटाईलाइ िर्ान लु हुने |This technique is used for unbevelled steel plates up to 3 mm and
bevelled plates up to 6mm. For plates above 3mm thickness the plate edges are bevelled to produce ‘ V’ of 80-90°.
Right ward or back hand or backward  टर्न अिरे टरको िायााँ िाथ (right hand)मा | welding िायााँ दे ल्सि दायााँ | टर्न ४०-५० बिग्री ; रि
३० – ४० बिग्री | ६ बमबलमीटर भन्दा माबथ मोटाईलाइ िर्ान लु हुने | For plates above 8mm thickness, the plate edges are bevelled to
produce ‘V’ of 60.
The welding is started from the bottom of the welded joint and goes towards top of the joint. This may be carried out either by
the leftward or rightward technique. The torch makes an angle of 25°v to 90°, depending upon the thickness of the plates to be
welded vertical welding .
Linde’s welding- This is a special welding technique used for butt welding of steel pipes. The edges of the pipes are bevelled at
70° and butted together with a gap of approximately 2.5mm. The seam is welded with excess acetylene flame. While welding,
the pipes are rotated constantly so as to weld the seam in the horizontal position only. Rightward welding is adopted in this
technique to weld the pipes.
Conclusions
Less voltage means less penetration whereas more current means high metal deposition rate. Therefore for shallow and heavy
work application ,we use low voltage and high current.
The cutting of iron and steel by using oxygen is extensively used now-a-days in industry. The welding torch is replaced by
cutting torch which has four openings.
Sheet metal work
Sheet metal operation

Planishing

Drawing is a metalworking process which

uses tensile forces to stretch metal or
glass. The process is considered
"deep" drawing when the depth of
the drawn part exceeds its diameter.
Two process
Two processes
Difference between blanking, punching n’ piercing
1. Disk or plane washers are manufactured with blanking operation.
2. Punching operation removes scrap from the larger piece of sheet metal.
3. Piercing operation produces extruded hole or slot using punch and dies.
Dies type (female parts)
Simple die – only one operation is performed, i.e., only cutting or only forming operation
Compound die – Two types of only one kind operation can be performed like blanking and piercing (both cutting operation) or
bending or drawing (both are forming operation) . Eg making a washer
Combination – Both cutting and forming operation can be performed simultaneously.
Progressive die- two or more operation are performed simultaneously but in different stations
Vice – pipe, leg and pin
Hammers-
A ball-peen (also spelled ball-pein) hammer, also known as a machinist's hammer, is a type of peening hammer used in
metalworking. Its steel head is harder than that of a claw hammer, so is less likely to chip on impact. Ball peen hammers are
commonly used to drive cold chisels, set rivets, and bend and shape metal.
Cross peen
Straight peen
Double faced
Soft hammer
Straight, cross, ball peen and double faced
Chisel

The cross cut (or cape) chisel is

designed for those who want to
get into those tight areas.
The design of the tool is such that
the handle is thinner than the
cutting edge, which narrows on
two sides until it reaches a point.
This chisel is designed not to get
stuck where a flat chisel might.
Half round n’ diamond pointed chisel
1. The half round chisel is a type of chisel which has a
rounded shape, although the top of the tool is
actually flat.
2. It is designed to create grooves/channels with
rounded bottoms.
3. Such grooves may be found in bearings, acting as
"oil ways". Sometimes this chisel may be called a
"round nose chisel".

1. The diamond point chisel has a diamond shaped tip

and is used to create grooves with a "V" shape,
something which may be desirable in many
instances, including carving.
2. It is also used in corners and in the moving of
incorrect marks left by a centre punch.
3. Some diamond point chisels may be better suited to
use on brickwork.
Cookies for your thoughts
While working near flammable substances, one should avoid iron or steel hand tools. Why?
Explanation:
Steel or iron hand tools can produce sparks, serving as a source of ignition when adjacent to flammable substances. To avoid
this, stick to non-ferrous materials in flammable environments.
However, non-ferrous materials don’t contain iron and are spark-resistant, so they should be utilized wherever highly volatile
liquids, flammable gases, or any explosive materials are used or stored.
MCQ with hint – a type of edible fungus
Wedges, chisels, and draft pins are unsafe to use if they have...
(A) Flat heads
(B) Mushroomed heads
(C) Pointed heads
(D) All of the above

Impact tools including wedges, chisels,and drafts are unsafe to use if they have mushroomed heads. This is because the head of the
tool might shatter on impact into sharp fragments that are dangerous to any worker in the vicinity.
Nip point
1. In-running nip points (or pinch points) are a special danger arising from
rotating or reciprocating parts.
2. They occur whenever machine parts move toward each other or when
one part moves past a stationary object.
3. Figure shows some in-running nip points that may be encountered in
the woodworking industry.
4. The nip points in this figure are located where the belts or chains
approach the pulleys or gears, or where the rotating parts approach
the stationary components.
Common practices-
While tightening a nut with an adjustable wrench, always face (and pull) the sliding jaw of the wrench in your direction. That
way, most of the pressure is now on the fixed jaw, which doesn’t slip. Do not push on a wrench - losing your balance is more
likely if the wrench slips.
Pneumatic tools (such as drills, hammers, chippers, and sanders) run on compressed air. Operation of pneumatic tools is a risky
business and includes dangers like getting hit by one of the tool’s attachments’ fasteners. Eye or face protection, but not head
protection, is required when using a power grinder.
Wire cutting pliers that have plastic-covered handles should not be used to cut low-voltage, live electric wire. Plastic handles are
affixed to pliers for comfort only and do not provide electrical insulation. Electric currents should be disabled before cutting a
live wire.
MCQ with hint – seks
Q. Jacks used continuously at one site must be inspected
(A) Before each use
(B) Weekly
(C) Monthly
(D) Every 6 months
(E) Yearly
MCQ with hint – an auditory test
Q. An abrasive wheel is checked for cracks or defects with a…
(A) Sound or ring Test
(B) Hit and trial Test
(C) Forward or rewind Test
(D) X-ray machine
According to OSHA, an abrasive wheel must be sound- or ring-tested for cracks and defects before it is mounted. To test the
wheel, one should tap the wheel lightly with a nimble, non-metallic instrument. If the wheel sounds dead or cracked, it should not
be used, as it can break apart during operation. If a “ring” or clear metallic tone is heard, it means that the wheel is undamaged.
hacksaws
Made of Carbon or HSS.
Blades come in two lengths – 250mm and 300mm (most common)
Hacksaws cut on the push stroke, which means the blade should always be placed in the frame with the teeth pointing away
from the handle.
Hacksaw is specified by its length and point per inch (aka pitch which is number of teeth per 25 mm length)
Teeth are bend left and right alternately (setting of the teeth in order to cut wide groove and to prevent body of the blade
jamming or rubbing the saw cut) , every 3rd and 5th teeth are left straight to break up the chips and help the teeth clean
themselves.
Stroke- push and pull
Push stroke are designed for cutting through tougher materials. This is because it’s easier to exert pressure on the saw when
pushing it rather than pulling it.
Pull saws have thinner blades which are designed for making more delicate and precise cuts. As well as this, the motion of
pulling the saw towards you rather than pushing it gives the user more control over each stroke of the saw. This makes it easier to
cut in a straight line and achieve a neat finish.

Question of the centuries - How to tell if the saw cuts in pull or push stroke?
Typically, if the teeth are not angled back or forward, and instead, point straight down, then the saw cuts on both the push and pull
stroke.
Files
HAND FILE: Used for general filing of metals such as steel. They are rectangular in section and are the most common type of
file used in workshops.
HALF ROUND FILE: Used for filing curved surfaces.
THREE SQUARE FILE: Is triangular in section and very useful when filing ‘tight’ corners / angles.
 KNIFE FILE: Knife files are very useful when filing where there is little space. Knife files are very thin and can fit into small
gaps.
SQUARE FILE: The square file is quite thin and fits into corners well. They can be used to file slots in metal or for filing
where there is little space.
Please note-
1. Files are often graded according to the roughness / smoothness of cut.
2. The file that has the least harsh teeth is graded as ‘very smooth’. The most abrasive of files is graded as ‘rough’.
3. Larger the file coarser the pitch, smaller the file smoother the pitch.
X-section
Some marking, measuring and testing tools
Surface plate
Steel rule
Outside and inside calipers
Dividers
Scriber
Universal surface gauge
Punch- 2 types solid (for heavy duty application) & hollow (for low duty application)
V-block - precision metalworking jigs typically used to hold round metal rods or pipes for performing drilling or milling
operations. They consist of a rectangular steel or cast iron block with a 90-degree channel rotated 45-degrees from the sides,
forming a V-shaped channel in the top.
Angle plate
Try square
Combination set
Universal Surface gauge

Q. The part of USG used to draw parallel lines along the datum
surface is guide pins.
Instruments

Photo of angle block

Photo of try square
Angle plate and Combination set

Photo of Combination set

Measuring instrument and gauges
A Vernier scale on caliper may have a least count of 0.1 mm while a micrometer may have a least count of 0.01 mm.
Instruments – outside and inside micrometer
Other types
1. Screw thread micrometer
It measures the pitch of the thread directly.
It has a 60-degree pointed spindle and a double V-shaped swivelling anvil.
Fixed anvil screw thread micrometers are those types of screw thread micrometers that can only measure thread pitches within
a limited range.
2. Depth micrometer
Micrometer’s parts – The ratchet stop
This is a device placed on the end of the thimble.
Only a relatively slight pressure on the thimble can result in a considerable force being exerted between the two anvils. If the
force were to be excessive then it would be possible to overstress the frame thus causing permanent damage to the micrometer
which would in turn lead to incorrect readings being obtained.
To overcome this problem the ratched stop is fitted and this drives the thimble through a ratchet device.
Ring Gauges- diameter of shaft and studs
A plug gage is a cylinder designed to check the component
tolerance of a hole in a product
The ‘Go’ plug gauge is the size of the low limit of the hole while the ‘Not-Go’ plug gauge corresponds to the high limit of the
hole.
Snap Gauge is used to check external dimensions like diameter

The ‘Go’ snap gauge is the size of the high (maximum)

limit of the shaft while the ‘Not-Go’ snap gauge
corresponds to the low (minimum) limit of the shaft.
Slip gauges are used as references for the setting of measuring equipment
1. also known as Gage blocks, Johansson gauges are precision ground and lapped measuring standards.
2. Micrometers, gap gauges, sine bars, dial indicators (when used in an inspection role) are checked for their accuracy using slip
gauge.
3. Use the minimum number of blocks for high accuracy.
4. The length of each block is actually slightly shorter than the nominal length stamped on it, because the stamped length
includes the length of one wring film, a film of lubricant which separates adjacent block faces in normal use. This nominal
length is known as the interferometric length.
Thickness or Feeler Gauge measure clearances between components.
One of the major use of feeler gauge is to adjust the spark
gap between the distributer points of an automobile.
Pin gauge – to measure diameter of small hole(>75mm)
Caliper Gauge to check both the inside and outside dimensions
One end check the inside dimensions (hole diameter) while it’s another end checks outside dimensions (shaft diameter).
A calliper gauge is similar to a snap gauge
Radius or Fillet Gauge
(a) To check concave and convex radii on corners or shoulders.
(b) For layout work and inspection of components.
(c) As a template when grinding of cutting tools.
The gauge is placed against the edge to be checked and any light leakage between the blade and edge indicates a mismatch that
requires correction. Radius gauges require a bright light behind the object to be measured.
A thread gauge, also known as a screw gauge or pitch gauge, is used to
measure the pitch or lead of a screw thread.