3DefinitionThe process in which permanent change is obtained in a metal shape by plastic deformation under the action of external forces.
4Why Metal Forming is required? Economical and time saving process to obtain desired shape from the given material.To improve mechanical properties.To minimize defects such as holes, cracks etcTo distribute impurities equally in metal.
5Classification of Metal Working Hot Working of metals.Cold Working of metals.
7DefinitionIt can be defined as the plastic deformation of metals and alloys at a temperature above recrystallisation and below melting point such that fine refined grain is obtained.Maximum working temperature is 0.7 to 0.9 times the melting point.
8AdvantagesProperties such as strength, ductility and toughness is improved.Density increases by removing voids.Desired shape can be easily obtained under plastic deformation.Effect of impurities can be reduced.Good grain structure.Atoms in same direction leads to better strength.
9Disadvantages Surface finish is not good. Required accuracy is not obtained.Process takes place at higher temperature, so tool life is minimum.Thus handling cost is high.
16Recrystallization temperature Cold Working of MetalsHot Working of metalCold Working of metalNormal Temperature Temp RiseMelting PointRecrystallization temperature
17DefinitionThe process in which plastic (permanent) deformation occurs when the process is carried out at a temperature lower than recrystallisation temperature.The temperature is half of absolute melting temp.Theoretically, it is room temperature. (25 to 30 “C)
18Advantages Improves hardness and strength Desired accuracy is possible.Heating is not required.Thus, cost and time is reduced.
19Disadvantages Reduces ductility, thus difficult to process. Force required is more.Produce internal and residual stresses.Atoms are deformed.Low ductility -> Difficult to process.Cost increases.
20Cold working Methods Cold Rolling Cold Drawing Cold Extrusion Cold SpinningSqueezingBendingPeeningCoiningHobbing
21Difference between Hot and Cold Working Hot WorkingCold WorkingProcess is done above recrystallisation temperatureProcess is done on hot metal.Less force is required.No residual stress is formed in the metal.Below recrystallisation temperature.Process is done on metals at room temperature.More force is required.Residual stresses formed is more.
22Difference between Hot and Cold Working Hot WorkingCold WorkingImproves ductility, stiffness and toughness.Accuracy in surface finish is less.Maintenance cost is high.Improves strength and hardness.Accuracy in surface finish is more.Maintenance cost is low.
28What actually happens in Rolling Process???? Rolls or rollers are arranged.The metal piece which is to be deformed is drawn between the space of the rollers (by using frictional force between the rolls and metal surface)Metal is squeezed (compressive force)
29Angle of Contact V2 V1 O R Angle of contact Feed direction B New grain Old GrainNormal ForceFriction Force
30Angle of ContactFrom the fig. we can say that, when the roller and work piece make contact, then we get arcAB.Here arc AB is the contact portion.Now, arc AB makes an angle “θ” with O.This angle formed is known as angle of contact.
31t2 = thickness after rolling R = radius of roll Angle of Contact:Cosθ = 1- (t1-t2)2RWhere, t1 = thickness before rollingt2 = thickness after rollingR = radius of rollθ = Angle of contact or bite
32Coefficient of Friction Now, coefficient of friction is given by,µ = Frictional ForceNormal Force=tanβWhere, β = Friction angle
36Stage 2: V2 V1 O R Angle of contact Feed direction B New grain A C t1 Old GrainNormal ForceFriction Force
37Stage 2:Between B and C, speed of work piece is less than roller speedStage 3: At point C, the speed of work piece and roller is same. This point is known as no slip point.Stage 4: From point C to A, the speed of work piece is more than the rolleri.e. V2 > V > V1
38Forward SlipForward slip is the slip that is caused due to difference between, the strip velocity and roller velocity.i.e if the strip velocity is greater than roller velocity, then a slip occurs, which is known as forward slip.Forward Slip = V2 –V where, V2 = Strip VelocityV V = Roller peripheral velocity
43Points to rememberThe metals are recrystalized parallelly along with deformation.Temperature is made constant during the rolling process.The distance between the roller is less than the thickness of the metal (ingot), the thickness of metal reduce and length increases.
44AdvantagesThe grains become finer, thus mechanical properties improve.Productivity increases.Due to high temperature, high pressure is created. This pressure reduces the cavity and voids.The grains are equally divided. Thus,shape is uniform.
45AdvantagesSince the impurities are distributed equally, its effect is minimized.Entire process is economic.
46Disadvantages Surface finish is not good due to oxidation. Since the process is carried out at high temperature, its handling and tooling cost is more.Metal (output) of desired measurement is not obtained.
47COLD ROLLINGDefinition: It is defined as the process that is carried out at room temperature or temperature below recrystallisation temperature.
49Points to rememberSince in cold working, tremendous force is applied and when such force is removed, some residual forces remain inside the metal.Before cold working is carried out, the scale (formed due to hot rolling) are removed by submerging the metal into sulphuric acid. Then, it is washed with water and cold working is done.It is done for softer metals. Eg. Aluminum, copper, silver.
51Advantages Surface finish is good. Measurement accuracy is achieved. Tool handling cost is less.Porosity (sponge like) is reduced.Mechanical properties improve.Here also, the impurities are evenly distributed. Thus, its effect is minimized.
52DisadvantagesSince this process is carried out at room temperature, higher amount of force is required.Ductility is decreased.Residual stresses are formed.
53HOT ROLLING COLD ROLLING Process is carried out at above recrystallisation temperature.Process is carried out at below recrystallisation temperature.Pressure applied is less due to high temperature.High pressure is applied.Coarse grain becomes fine grains.The grains becomes longer and distorted.No residual stresses are generated.Residual stresses are generated.Tool handling cost is more.Tool handling cost is less.Improves ductility.Ductility reduces.Surface finish and accuracy is less.Surface Finish and Accuracy is more.
54Basic DefinitionsIngot : The metal in a square shape obtained from casting process is known as ingot.Area range : 300 to 500 mm^2Length is between 1.5 to 2m400mm1.5 m400mm
55Basic Definitions Bloom: Metal piece smaller than ingot. Area range : 200 to 300 mm^2Length is between 3.5 to 5.5 m250 mm4.5 m250 mm
56Basic DefinitionsBillet : Metal piece produced from bloom is known as Billet. Further billet is rolled into bars.BilletBillet100 mmBars100 mm
57Basic DefinitionsSlab: The rectangular cross section type metal obtained from rolling of bloom or billet is known as slab.Thickness: 50 to 150 mmWidth : 0.5 to 1.5 mSLAB
58Basic Definitions Plate : Further rolling slabs, we get plates. Width : 750 to 1200 mmThickness: 2.7 to 7mmLength: 1.5m to 3mPLATE
59Basic Definitions Sheet : Rolling of Slab will result into sheets. Thickness: 0.21 to 2.64mmWidth and length same as plate.SHEET
60Basic DefinitionsFlat : 2.5mm to 6mm thickness strip is known as flat.Strip : 0.1 mm to 2.5 mm thickness is known as strip. The width is very less compared to length.
76DefinitionThe force that occurs due to friction between the area of contact between the roller and work piece is known as frictional force or metal friction.
77Function of Friction.Initially, the angle of friction (β) should be higher than angle of contact (θ).Thus, because of this, the work piece does not come back.i.e θ< βAlso, based on angle of contact, we can find out mill drive design, number of passes, draft (t1-t2) and power requirement.
783) Presence of tensionWhen the work piece is pulled from one end, tensile stress is created.Thus, this will reduce, the roller diameter and amount of power to be applied through rollers.Tensile force
794) Operation speed Refer slide 36 – 38. Conclusion: Due to forward slip, the exit velocity increases. Thus, we can say that, the effect of coefficient of friction decreases.So, operational speed is also important for rolling process.
80Roll Mills used in Rolling Process: Two – high rolling mill2 high pull over mill2 high reversing mill2. Three high rolling mill3. Four high rolling mill4. Cluster rolling mill5. Continuous rolling mill6.Special mill
81Two – High Rolling mills 2- High Pull Rolling MillIn this type of rolling mill, the direction of feed is from one side only.It uses two rollers.i.e when the first pass is over, the work piece is again brought back to its original position and the rolled back again, which lesser space between the rollers.Sugarcane mc
82Two – High Rolling mills Two High Reversing MillIn this method of rolling, the direction of feed is from both direction.Here also, 2 mills are used.During this process, handling of work piece is easier.(1)(2)
83Two – High Rolling mills Two high rolling mills are used for bloom, billet or slab rolling.Two high roll mills are normally used for obtaining medium change in cross section.For every pass in reverse mill, the direction of roller is to be changed.
84Three – High Rolling mills Here total three rollers are used. Upper, middle and lower roller.As shown in figure, we can easily see that the gap between upper roll and middle roll is more compared to middle and lower roll.
85Three – High Rolling mills The reason for this is, initially, the ingot or bloom is fed between upper and middle roll to decrease the cross section.Thereafter, in the reverse pass, the work piece is passed between middle and lower roller to further decrease its cross section.
86Three – High Rolling mills In this process, there is no need to change the direction of roller.Thus, minimum power is required.Bloom, billet, channel, rail can be manufactured.It is cheaper.
87Four High Rolling Mills Here total four rolls are used, of which two are bigger rolls and two smaller ones.The bigger rolls are known as back up rolls.The smaller rolls are known as working rolls.
88Four High Rolling Mills Here, metal with bigger size are rolled by passing them between the working (smaller) rolls.Since, these rolls are used to roll bigger sizes metals, they have to face shocks and vibrations.
89Four High Rolling Mills Also, huge amount of pressure is to be applied.For this purpose, back up rolls (bigger rolls) are used.The work piece can be entered between the rolls in both direction by changing the roll direction and space between the working rolls.
90Cluster Rolling MillAs from the figures, we can say cluster mills are the type of rolling mills, which has 6 or more rolling mills in operation.It is used for cold working of metals.
91Continuous (Tandom) Rolling Mill Its arrangement is similar to two – high rolling mill.Here, the metal work piece passes from one roll pass to another and we get continuous reduction in size.Used for mass production.
92Schematic illustration of various roll arrangements: (a) two-high; (b) three- high; (c) four-high; (d) cluster (Sendzimir) mill (e) Tandom rolling mill.
93Special Mill Universal Rolling Mill Planetary Rolling Mill Nowadays, usage of special type of rolling mills are increasing in industries at higher rate.There are main two types of Special Rolling Mill. They are as followsUniversal Rolling MillPlanetary Rolling Mill
94Universal Rolling Mill In this type of rolling mill there are two vertical rolling mills, and two horizontal rolling mills.This mill generally produces H-section and I-section.This mills are used for producing accurate edges.
95Planetary Rolling Mill Here the rolls are arranged in the shape of sun and planets, thus its named as planetary rolls.(only for understanding)The feed rolls, push the metal into the gap between the planetary rolls.
96Planetary Rolling Mill Further after rolling from planetary rolls, the work piece will pass through two or, four high mill.The product obtained is in form of strips.
98DEFECTS AND ITS REASON FOR CAUSE CracksRough SurfaceCracks mainly occur due to cold working of metals.Rough surface is formed due to oxidation in hot working process.
99DEFECTS AND ITS REASON FOR CAUSE FinLapExcess material pass during rolling.Over filling at roll pass.
100DEFECTS AND ITS REASON FOR CAUSE Non uniform deformation.Blow holes, pit holes.Due to unequal shape.Gas inside the metal mould.
101DEFECTS AND ITS REASON FOR CAUSE Pipes8. WarpageDue to uneven cooling.8. Due to uneven cooling and residual stresses.
102Basic Elements of Rolling Mill RollsMain components of rolling process.It is rolled and gives shape to the metal.Two types of rolls are used, (1) Working (2) Back up rolls.Working rolls contact with work piece.While Back up rolls provide strength to working rolls, do minimize deflection and add up force.
103Basic Elements of Rolling Mill Bearing and HousingThey provide support to the rollers shaft.The rollers shaft are fixed at both the endings by bearings and housing for proper alignment.If not, the product will be defective.
104Basic Elements of Rolling Mill DriveDrives are of two typesChain DriveGear driveThese drives are used to roll the rollers in rolling process