DEPARTMENT OF MECHANICAL ENGINEERING

DEPARTMENT OF MECHANICAL ENGINEERING2013-14

Processes Involved in Production of Aluminium Sheets1) Direct Chill Casting Process2) Scalping Process3) Hot Rolling4) Cold Rolling 5) Finishing Process1. Direct Chill Casting Process:In DC casting, the metal is melted in a holding furnace and then treated in a two-stage process to remove any remaining microscopic non-metallic particles and gases. The holding furnace is tilted and molten metal is poured into a water-cooled casting unit. As the metal flows into the molds, it is chilled by jets of cool water pumped around and through the base of the mold. The ingot solidifies gradually during the casting process, which takes approximately three hours. We continuously monitor the temperature, speed and water flow so that each sheetingot is of the highest quality. Individual ingots can weigh up to 20 tons and can be 500 600 mm thick, two meters wide and eight meters long. A finished 18-ton ingot contains a volume of source aluminium equivalent to approximately one million beverage cans.In this process, critical variables such as temperature, speed and water flow are carefully managed, and the metal's chemical composition and cleanliness tested on each cast. Once DC casting is complete, ingots are transferred to a hot rolling mill.

Fig.

2. Scalping Process:Aluminium ingots are moved from direct chill (DC) casting and cooled down to room temperature. It is necessary to remove the surface layer of the entire ingot to eliminate surface oxides, ensuring a uniform, high-quality surface finish. The outer surface of ingots (both flat surfaces and edges) contains more of impurities, oxides and has greater alloy segregation. For any critical application like rolling. It is necessary to get rid of these surfaces to ensure cleaner stock for hot rolling. The depth of unsound casting zone is about 10-15 mm .Therefore to producing sheets from ingot it is necessary to machine imperfect zones of solidification. This operation is carried on typical milling machine called as scalper and the process of machining is called as scalping. This operation is carried on typical milling machine called as scalper and the process of machining is called as scalping.

Fig.

3. Hot Rolling:The rolling ingot is send to a pusher furnace, which pre-heats it to a point above its recrystallization temperature (around 500C) in order to prepare it for hot rolling. This process is called annealing, and it allows the various alloy constituents in the ingots to distribute themselves, evening out differences in microstructure and ensuring a homogeneous structure within the ingot.Finally, the rolling ingot is passed back and forth between the two high non-reversible mill, which reduces the ingot's gauge until it approaches that of a strip with the desired thickness for cold rolling.Also the Butt portion, i.e. bottom part of ingot is generally unsound due to curls and initial splash of metal. Both these ends shows tendency of opening out at central plane during hot rolling operation. This phenomenon is called as alligatoring which could be serious in alloys having high percentage of Mg, Mn and Zn. Therefore, for quality reasons the ends are cut off by cutter.

Fig.

4. Cold Rolling:Hot-rolled aluminum strip is cooled toroom temperature and fed into the cold roll mill line. The strip is then passed several times between a series of rollers until it is gradually reduced to the desired gauge and wound into a coil. The resulting coil can be rolled to a thickness of 0.05 millimeters (mm). Automatic gauge and flatness control systems ensure coils of precise dimensions. Intermediate heat treatments may be used, depending on the degree of rolling and final thickness desired for particular applications, to modify mechanical features of the cold-rolled coils. For example, by heating and maintaining the aluminum at precise pre-defined temperatures, transforms the final product to fit the customers' exacting needs for tensile strength, yield strength and elongation. This process is also called annealing.

Fig.

5. Finishing Process:Numbers of finishing processes are performed to ensure that the aluminium products delivered lead the industry in consistent quality and reliability of properties for customer applications. For instance: Cold-rolled aluminium coils are flattened to a precise thickness by running them through a series of levelling rollers, in a process called tension levelling. Slitters are used in order to achieve a precise width to the coil. A protective film can be applied to rolled products. The films differ in composition depending upon the particular product application.

Fig. no (Tension leveling)

By using KENNAMETAL.COM we can get the results directly. As in the beginning it was necessary to study dependency and variation of cutting parameters with respect to each other. By using web page we got the important parameters like Force, Torque and Power.On the website user needs to input cutting parameters and in output we can get important parameters such as Force ,Torque and Power. Snapshot of the page will look like as follows.

Home / Resources / Engineering Calculators / Face Milling / Force, Torque, and Pow er

Force, Torque, and Power

For Face Milling Applications with High Shear Cutters

Unit: metric

Conversion of Workpiece Material Rockwell (Optional)

Hardness HRB OR HRC into Rockwell HRC:Brinell Hardness (HB)Calculate Hardness

Characteristics of Workpiece Materials

Brinell Hardness: 30 HB

Ultimate strength: N/mm 2

Face Mill Nomenclature

d1 Effective cutting diameter: 1500 mm

z Number of inserts in the cutter: 12

Machining Conditions

Vc Cutting speed: 400 m/min

ap Axial depth of cut: 3 mm (DOC)

ae Radial width of cut: 6 mm (WOC)

fz Required feed per tooth: 2 mm

Calculated Machining Conditions

n Spindle speed: 84.9 rpm

Vf Feed rate: 2037.6 mm/min (no productivity f ormula)

Reduced feed per tooth: 0.2525 mm (no productivity f ormula)

Fp Feed rate: 16140.9567 mm/min (w ith productivity f ormula)

Qp Metal removal rate: 36.68 cm3/min (no productivity f ormula)

Q Metal Removal Rate: 290.5 cm3/min (w ith productivity f ormula) A Cross-sectional area of the chip: 6 mm2

Calculated Required Power

Ft Tangential cutting force: 194.2 N

T Torque at the cutter: 145.65 Nmm 145650 Nm

Machining power

Ps at the cutter: 1.3 KW Pm at the motor: 1.86 KWaxial depth of cut(ap)chip areametal removal ratecutting forcestorque @ cutterpower @cutterpower @ motor

1212.2364.748.530.40.57

2424.45129.597.130.91.29

3636.68194.2145.651.31.86

4848.9258.9194.181.72.43

51061.13323.6242.72.23.14

61273.35388.4291.32.63.71

71485.58453.1339.8334.29

81697.8517.8388.353.55

918110.03582.5436.883.95.57

1020122.26647.3485.484.36.14

EFFECT OF DEPTH OF CUT

EFFECT OF CUTTING SPEEDCutting Speed (m/min)chip Area (mm2 )Metal Removal Rate (cm3/min)Cutting Force(N)Torque at Cutter(Nm)Ps(cutter) (KW)Pm (KW)

10069.16194.2145.650.30.43

150613.74194.2145.650.50.71

200618.32194.2145.650.60.86

250622.94194.2145.650.81.14

300627.52194.2145.6511.43

350632.1194.2145.651.11.57

400636.68194.2145.651.31.86

450641.26194.2145.651.52.14

500645.84194.2145.651.62.29

550650.41194.2145.651.82.57

EFFECT OF FEED PER TOOTHfeed per tooth(mm)chip area(mm2)metal removal rate(cm3/min)cutting force(N)torque at cutter(Nm)Ps(cutter)(kW)Pm(kW)

1318.3497.172.830.60.86

2636.68194.2145.651.31.86

3955.02291.3218.481.92.71

41273.35388.4291.32.63.71

51591.69485.5364.133.24.57

618110.03582.5436.883.95.57

721128.37679.6509.74.56.43

824146.71776.7582.535.27.43

927165.05873.8655.355.88.29

1030183.38970.9728.186.59.29

EFFECT OF CHANGE OF ANGLES AND CHIP THICKNESS RATIOFormulae used are as follows :-

Where,r = Chip Thickness ratiot1 = Uncut chip Thickness (Depth of cut ) =6mm (assumed)t2 = Chip Thickness = Shear Angle= Rake angleFc= Cutting Force Fs= shearing ForceAs = Shear areas= Shearing Strength = 70 Mpa for 1050(http://www.azom.com/article.aspx?ArticleID=2798 )b = Width of chip = 10 mm(assumed)V= 3100 m/min (Provided )rRake Angle ( )Shear angle

0.7536.60

0.75538.64

0.8540.59

0.85542.44

0.9544.21

0.7034.99

0.7536.60

0.7837.52

0.71038.12

0.71338.99

0.71539.55

0.72040.85

Rake angle Thrust Force (KN) (Fc=const. for 4.839 KN )Thrust Force (KN) ( =const. for 5 )

02.952.4

52.42.88

82.0923.12

131.6083.36

151.4223.6

Derivation: Finding different forces by knowing the tool Geometry, Shear Force and Thrust force.Nomenclature:-r = Chip Thickness ratiot 1= Uncut chip Thickness t2 = Chip Thickness = Shear Angle= Rake angle , Fc= Cutting ForceFs= shearing ForceAs = Shear area= Shearing Strength b = Width of chip , f=Feed per Tooth. = Co-efficient of friction (for carbide and Al. =0.61) from Wikipedia=Friction angleVc=Cutting velocityR=Resultant force under equilibriumF=Friction Force , N=Normal to friction Force , Ft=Thrust Force , Fn=Normal to Fsd =depth of cut, Angle between Fs and RCs=side cutting edge angle (from tool geometry=44)

Fig 1.1 Face milling operation force diagram in equilibriumReference:- PREDICTING CUTIING FORCES IN FACE MILLINGHONG-Tsu YOUNG,t P. MATHEW:j: and P. L. B. 0XLEY:j:(Received 28 July 1993)Merchant circle for face milling:-

Fig 1.2 Merchant circle for face millingFor finding FS resolve Fc and FT along FS Component of Fc along FS is Fc cos andComponent of FT along FS is FT sin.So force FS can be given asFS = FC cos FT sin

Fig1.3 FC and FT resolved along FS

For finding the force FN resolve force FC and FT along FNThe component of FC along FN is FC sin andThe component of FT along FN is FT cosSo force FN can be given asFN= FC sin +FT cos

Fig 1.4 FC and FT resolved along FNSimilarly we can find the forces F and N

Fig 1.5 FC and FT resolved along F and NFor finding force F, resolve forces FC and FN along FThe component of force FC along F is FC sin andThe component of force FT along F is FT cos.So force F can be given asF = FC sin + FT cosFor finding force N, resolve forces FC and FN along NThe component of force FC along N is FC cos andThe component of force FT along N is FT sin.So force N can be given asN = FC cos - FT sinCoefficient of friction can be given as = Substitute the value of F and N in above equation we get = By dividing numerator and denominator by cos we get = This is expression for .Relationship between s(shear stress), feed(f), depth of cut(d):-From above relationship we haveFS = FC cos FT sin..................................(1)Force Fs can be given as the product of shear stress and shear area.Fs = *As But we knowAs = ........................................................................From P.C.SharmaSo, Fs = Substitute this value of Fs in equation (1) we getFc cos - FT sin = (2)We know from above equation = On rearranging the terms we will get the value of FT asFT = Substituting this in equation (2) we getFc cos - sin = Taking Fc commonFc{ cos - sin} = Transferring sin to left side we getFc{ sin cos - sin2} = b*t1*Fc{ tan cos2 - tan2} = b*t1*We know, tan = ,where r =..........from P.C.SharmaFc{ cos2 - ()2 cos2} = b*t1*Taking cos2 commonFc cos2 ( ) {1 - ()} = b*t1* (3)

We have the expression for tan, So we can find the value of cos.cos2 = In our case rake angle = 0Substituting value of =0 in above equation and equation (3) we getcos2 = Fc cos2 r{1 - r} = b*t1* (4)Substituting the value of cos2 and r in equation (4)Fc (){1- } = b*t1*Fc( ) = *b= ( )Substituting t1 = f cosCs and b = ................P.C.Sharmat2=We*cosFrom Journal Paper

= ()This is the relationship between , d and f.

Future plan:-Flowchart for use of above equation for analyzing scalping process.

Calculating Values Of Depth Of Cut and feed:-Length Of Ingot=132 inch = 3353 mmFeed of ingot =100.32 mm/sCutter RPM=520 rpmSo. 8.66 revolutions takes place in 1second.In terms of Ingot Feed, 1revolution of cutter = 11.58 mm travel of ingot.So feed per tool =11.58/10 = 1.158 mm/tool.So. f =1.158mm/tool.We know,For aluminium AA1050 , Current=225 APower= Fc *V =49m/sPower= V*I =440*225 = 99000 WSo Solving equation Fc =2020 NNow, Solving equation for f=1.158 mm/tool , Mpa., Cs=44o,t2=2mm,=0.61 = ( ) From equation d=5.76 mm.For second case put d=6mm and calculate feed .By solving equation = ( ) Feed=114 mm/s

Conclusion:- For softer materials we can use higher feed rates. While for harder materials we have to use lower feed rates. For softer materials we can take higher values of depth of cut. While for harder materials we have to take lower values of depth of cut. Surface finish may affect due to use of different values of depth of cut instead of calculated values of depth of cut.References:- Hong-Tsu Young, Predicting cutting forces in face mlling(1993). S. Paul, Geometrical modification of coated carbide inserts for improved face milling, Machine tool manufacture Vol.34(1994). Metal cutting theory -P.C. Sharma. Metal cutting theory- Amitabh Bhattacharya.

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