Modified of metal sheet into a 3-D cylindrical

Modified beverage cansHAMZA PERVEZ                                15-ME-91                                                  Mujahid Hussain                                 15-ME-92                                                  Muhammad Tariq                               15-ME-94                                                 Muhammad Ishaq                                15-ME-95     Raw materialBeverage can consistsmostly of aluminum, but it contains small amounts of other metals as well.These are typically 1% magnesium, 1% manganese, 0.4% iron,0.2% silicon, and 0.15% copper.Before understanding themanufacturing process for beverage cans, we will have to understand theprocesses of drawing of sheet and plate.

DRAWINGOF SHEET AND PLATEIn drawing process, acombination of a punch and a die is used which draw a circular blank of metalsheet into a 3-D cylindrical cup. Basically the punch descends, pushing metalthrough die, converting circular blank to a cylindrical cup. Heightof cup walls is determined by difference between the diameter of original blankand diameter of punch .The drawing operation is done in multiple stages and isnot a one stage process. Wrinkles can appear in cup walls as circumference isreduced, or punch can act as a piercing tool. If gap between punch anddie is less than thickness of incoming material, cup wall is thinned andelongated.

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This process is often called ironingor wall ironing.The punch and die must have corner radii, given by Rp and Rd.­­ The sides of the punch and die are separated by a clearance c. For Drawing, the clearance isgreater than the stock thickness as follows :  As the punch first begins to push into the work, the metal is subjectedto a bending operation. As the punch moves further down, a straightening actionoccurs in the metal that was previously bent over the die radius. Holding force is critical for a successfuldrawing operation.

If too small, wrinkling occurs and if too large, it preventsthe metal from flowing properly toward the die cavity. This results instretching and possible tearing of the sheet metal.Drawing RatioFor a cylindrical shape the drawing ratio is the ratio of blank diameterDb to punch diameter Dp.

The greater the ratio, the more severe the operation. An approximateupper limit of drawing ratio=2.0ReductionFor a given drawing operation, the reduction ‘r’ is also used as : Thicknessto diameter ratioA third measure in deep drawing is the thickness-to-diameter ratio,which gives the tendency for wrinkling It is desirable for the t/Dbratio >1%. As t/Db decreases, tendency for wrinkling increases.

In cases wherethese limits on drawing ratio,reduction, and t/Dbratio are exceeded by the design of the drawn part, the blank must be drawn intwo or more steps, sometimes with annealing between the steps.DRAWING FORCEForce equation estimates the maximum force in the operation Where, F=drawing force, N, t=original blank thickness, mm, TS=tensilestrength, MPa, and Db and Dp are the starting blankdiameter and punch diameter, mm. The constant 0.7 is a correction factor toaccount for friction.HOLDING FORCEAs a rough approximation, the holding pressure can be set at avalue=0.

015 of the yield strength of the sheet metal. This value is thenmultiplied by that portion of the starting area of the blank that is to be heldby the blank holder. In eq. form Holding force is usually about one-thirdthe drawing force.Ironing of sheet metalIf gap between punch and die is less thanthickness of incoming material, cup wall is thinned and elongated.

This processis often called ironing or wall ironing Ironing of sheet metal is amanufacturing process that is mostly used to achieve a uniform wall thicknessin deep drawings.. Ironing of sheet metal can be incorporated into a deepdrawing process or can be performed separately. A punch and die pushes the partthrough a clearance that will act to reduce the entire wall thickness to acertain value.

While reducing the entire wall thickness, ironing will cause thepart to lengthen. The percentage reduction in thickness for an ironingoperation is usually 40% to 60%. Percentreduction can be measured (ti – tf)/ti X100%. With ti beinginitial thickness and tf beingfinal thickness.

Many products undergo two or more ironing operations. Beverage cans are a common product ofsheet metal ironing operations.  MANUFACTURING PROCESSIt consists of the following processes.Cutting the blankInitial drawing of the blankRedrawing the cup formed via initial drawingTrimming the earsCleaning and decoratingThe lidFilling and seaming These processes will now be explained in detail .Cutting the blank  The process starts with analuminum ingot (a material, usuallymetal, that is cast into a shape suitable for further processing) which is rolled into a thin sheet. Initially it is cut intoa circle, called a blank, which willbe used to form the bottom and sides of the can.

Material is definitely lostbetween each circle .Material loss will be minimum when the sheets contain 2 staggered rows of 7 blanks per row. (staggered rows)Only 12-14% of the sheet iswasted.Redrawingof cupAfter the initial draw the cup is redrawn to further decrease itsdiameter and increase its height. Then ironing is done which will stretch thecan and reduce the wall thickness. All this process is done in one single punchwhich takes 1/5th of a second.

An another punch gives an inwardbulge in the base of the can and this is basically done to sustain the pressureand also the bottom base and walls are also a little thicker than the upperwalls. Trimming the earsAfter the above described processes, the can becomes slightly wavy atthe top and such ripples formed in the metal are called “ears.” Quarter inch of the metal will be trimmed from that portion tostraighten the upper walls.   CLEANING AND DECORATINGThe above mentioned process leaves the outer wall of the can with asmooth and shiny surface, thus it will not require any finishing such aspolishing. Then the next procedure is the trimming of the ears and finally thecan is cleaned and a label is imposed or printed over it.

FORMATION OF A NECK AT THE TOPThe can is squeezed at the top to make a neck and from the very topportion of it, outward flanges are made which will be folded over the lid atthe time of application of the lid.THE LID The alloy used for the formation of lid is slightly different than thatused for making the base and walls of the can. At the bottom of the can aninward bulge was provided so that the it can sustain the pressure of the liquidfilled inside but as the upper lid is flat it must be stronger to sustain thepressure so it is made with aluminum with higher percentage of magnesium andless percentage of manganese.

Diameter of the lid is kept smaller than thewalls and after that with the help of a rivet a pull tab is attached on lid andthe lid is scored so that a proper opening can be made when the pull tab isopened.Filling and seamingAfter the formation of the neck , the can is filled and thus it isfilled and then the lid is added and the upper flanges made during the neckformation  are now bent around the lidand closed.After these processes the can is ready to be saled.                   


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