INTRODUCTION:SHEET METAL FORMING is the process ofconverting a flat sheet of metal into apart of desired shape without fracture orexcessive localized thinning. The processmay be simple, such as a bendingoperation, or a sequence of very complexoperations such as those performed inhigh-volume stamping plants.
Characteristics of sheet Metal. Formability Of Sheet Metal Tube Bending And Forming Bending Of Sheet And PlateTHERE ARE FOUR MAIN FOLLOWINGPROCESSES OF SHEET METAL FORMING.
SHEET METAL:“SHEET METAL IS SIMPLY METAL FORMED INTO A THINAND FLAT PIECE CALLED A SHEET METAL.”
In prehistoric times, metal sheets were used to makearmor of soldiers, swords , canons, etc.Before the discovery of Glass, it was also used tomake common home articles like plates, bowls, liquidjars, etc.Later on the sheet metal found its way in the makingof vehicles, blades of helicopters.HISTORY OF SHEET METAL
Sheet metals are characterized by a high ratio of surfacearea to thickness.Sheet metal forming is basically conversion of a flat sheetmetal into a product of desired shape without defect likefracture or excessive thinning.WHY IS IT NECESSARY?
GENERAL METAL CHARACTERISTICSMetals are… Solid at room temperature, exceptmercury, which is liquid !Metals have…Very high melting point.Metals are… Shiny when they cut.Metals are… Good conductors of heat and electricity.Metals are… Usually strong & malleable so they can behammered into shape.
Sheet metal parts are usually made by formingmaterial in a cold condition , although many sheetmetal parts are in a hot condition because thematerial when heated has a lower resistance to thedeformation.Spring or blanks are very often used as initialmaterials, and are formed on press usingappropriate tools. The shape of the part generallycorresponds to the shape of tool.Intro to Sheet Metal Characteristics:
Elongation -This is the characteristic of the sheetmetal to stretch without necking and failure.Strength - The ability of a material to stand up toforces being applied without bending, breaking ordeforming it in any way. Elasticity - The ability of a material to absorb forceand flex it in different directions, returning to itsoriginal position.
Plasticity - The ability of a material tochange in shape permanently. Ductility - The ability of a material tochange shape (deform) usually bystretching along its length.
Toughness - A characteristic of a material thatdoes not break or shatter when receiving ablow or under a sudden shock. Conductivity - The ability of a material toconduct electricity.
Tensile Strength – The ability of a materialto stretch without breaking or snapping. Grain Size – Determines surface roughnesson stretch sheet metal. It affects materialstrength. Anisotropy –Determine thinning behaviour0f sheet metal during stretching; importantin deep drawing operation.
In automobiles: The sheet metal is deformed intothe desired and brought into the required form to getauto body pressings likebonnet, bumpers, doors, etc. In aircraft’s: Sheet metal is used for making theentire fuselage wings and (body). In domestic applications: Sheet metal is used formaking many parts like washing machine body andcovers, iron tops, clock cases, fan blades andcasing, cooking utensils etc.Applications of Sheet Metal:
DEFINITION:“The ability of the sheet metal toundergo the desired shape changewithout such failure as necking ortearing.
TESTING METHODS FOR FORMABILITYWe can determine the formability ofthe sheet metal by following tests.DUCTILITYTESTDENT TESTERTENSILETESTCUPPING TEST
DUCTILITY TEST Good ductility tests are in great demand forthin sheet.Typical forming procedures suchas deep drawing and stretch forming arecharacterized in standardized test methods .It is an important but complex test is thedetermination of the forming limitcurve, from which designers canderive limit strains which should not beexceeded during forming processes.
TENSILE TEST: Tensile testing is the most basic mechanical testfor sheet metal. Tensile testing is relativelysimple and inexpensive. It also followsestablished standards to ensure uniformity ofapplication and results suitable for comparison.Simply put a standardized sample in tensile testapparatus an pull it along a single axis until itfails. We measure the material as it is pulled todetermine the materials elongation, tensilestrength, yield strength, and the range ofengineering stress and strain.
CUPPING TEST:The very first test is the cuppingtest, for checking the formability ofsheet metals. In which test the sheetmetal specimen is clamped between twocircular flat dies, and a steel ballor round punch is pushed hydraulicallyinto the sheet metal until a crackbegins to appear on the stretchedspecimen.
Formability ofsheet metal isdirectlyproportional tothe punch depth“d”. This test isinsufficient insimulating exactconditions ofactual sheet-formingoperations.
DentTester:The DentTester is animportant part of the steel producer’sformability testing. Its primary function istesting for dent resistance.A punch appliesforces up to 1,100 lbs., speeds up to 100inches/second and a punch travel of 2". Alarge work area of 10 by 12 enables the denttester to accommodate full size automotivepanels or sheet stock for testing.
“In this process an induction coil is placedaround a small section of the pipe at the bendpoint. It is then heated between 430 TO 1,200C. While the pipe is hot, pressure is placedon the pipe to bend it. The pipe is thenquenched with either air or water spray”HEAT INDUCTION:
“During the roll bending process the pipe ispassed through a series of rollers that applypressure to the pipe gradually changing thebend radius in the pipe.”This method of bending causes very littledeformation in the cross section of the pipe.This process is suited to producing coils of pipeas well as long gentle bends like those used intruss systems.ROLL BENDING:
“In the sands packing process, the pipe isfilled with fine sand and the ends arecapped. The pipe is then heated in afurnace to 1,600 F (870 C) or higher.The pipe is then placed on a slab withpins set in it. The pipe is then bent aroundthe pins using any mechanical force.”The sand in the pipe minimizes distortionin the pipe cross section.SANDS PACKING:
ADVANTAGES OF TUBE BENDINGExceptional accuracy and repeatabilityRound and square tube capabilitiesMandrel bendingBending is a cost effective process when usedfor low to medium quantities.
Comparison:Press Bending Heat InductionBending No heating is required Bending is done after heating It is used for smaller pipes It is used for larger pipes Mandrel is used. Mandrel is not used. More force is required Less force is required
YAMAHA & HONDA:In the making of Handles of bikes.SUZUKI,TOYOTA & HONDA:In the making of Exhaust pipes.APPLE FURNITURE INDUSTRIES:In the making of chairs and tables,etc.SUPER ASIA:In sanitary products.APPLICATIONS OF TUBE BENDING.
“Bending is a manufacturing process thatproduces a V-shape, U-shape, or channelshape along a straight axis in ductilematerials, most commonly sheet metal.”BENDING OF SHEET METAL:
ROLL BENDING AIR BENDING BOTTOMING COINING FOLDING WIPING ROTARY BENDINGTYPES OF SHEET & PLATE BENDING
A Roll bending is that process in which threerollers used to form a metal bar into a circular arc.The rollers freely rotate about three parallelaxes, which are arranged with uniform horizontalspacing.Two outer rollers, usually immobile, cradlethe bottom of the material while the innerroller, whose position is adjustable, presses on thetopside of the material. Roll bending may be doneto both sheet metal and bars of metal.ROLL BENDING:
Air bending is the process in which the punchtouches the work piece and the work piece doesnot bottom in the lower cavity. As the punch isreleased then work piece springs back a littleends up with less bend than that on the punch.Spring back is usually 5 to 10 degrees in thisprocess.Air Bending:
It is a process where the punch and the work piece touchesthe bottom of the die. This makes a controlled change ofangle with very little spring back. The inner radius of workpiece should be a minimum of a 1 material thickness.In bottom bending, spring back reduced by setting the finalposition of the punch. Such that the clearance b/w thepunch and die surface is less than the blank thickness. As aresult, the material yield slightly and reduces the springback. Bottom bending requires consequently more forceabout 50%-60% more than air bending.BOTTOMING:
“Coining is a bending process inwhich the punch and the work piecebottom on the die and compressionstress is applied to the bending regionto increase the amount of plasticdeformation. This reduces the amountof spring back. The inner radius of thework piece should be up to .75 of thematerial thickness.”COINING:
A rotary bending die is a special type of punch diecombination which bends the sheet metal using arotating cylinder with a v opening cut into the side ofthe cylinder. The cylinder is seated into a saddlemaking up the punch section of the die. The sheetmetal lays on an anvil and the rotary die is pushed downon top of it. As the die engages the sheet it begins torotate and bends the metal around the tip of the anvil.The rotary die will clamp the sheet metal beforebending providing a secure work piece without anysliding. Rotary dies can also bend beyond 90 ° liketraditional tooling to compensate for Spring Back.ROTARY BENDING:
“In this process one edge of the sheet is bentto 90 degree while the other end is restrainedby the material itself and by the force of bankholder and pad. The flange length can beeasily changed and the bend angle can becontrolled by the stroke position of the punch”WIPING:
“In folding, clamping beams hold the longerside of the sheet. The beam rises and folds thesheet around a bend profile. The bend beamcan move the sheet up or down, permitting thefabricating of parts with positive and negativebend angles.”Folding:
Comparison:Air Bending Bottoming Coining Spring back is more Spring back is less No spring back Work piece doesnttouches the bottom ofthe dieWork piece touches thebottom of the dieWork piece touches thebottom of the die Bend angles aredetermined by thepunch strokeSetup of the die ischanged to change thebend angleSetup of the die ischanged to change thebend angle Less force is required Relatively more force isrequiredGreatest force requiredamong all
SUPER ASIA :Outer body of Room Coolers and Geysers.G.F.C & ROYAL FANS :Blades of Fan.AUTOMOBILE INDUSTRIES :Toyota, Honda & Suzuki.RAFFLES:CPU Casings.PEL & DAWLANCE:In the outdoors units of A.C.APPLICATIONS OF SHEET METALBENDING IN PAKISTAN: