Sheet Metal Bending By-
BENDING n Bending is a manufacturing process by which a metal can be deformed by plastically deforming the material and changing its shape n Deformation about one axis
PROFILES
BAR FOLDER n Making bends or folds along the edges n For folding small hems, flanges.. n Set the machine before use
FLANGE ATTACHEMENT
ROLL FORMER
STRAIGHT BRAKER
BOX PAN
BEND ALLOWANCE n When sheet metal is bend, the inside surface of the bend is compressed and the outside surface of the bend is stretched. n Somewhere within the thickness of the metal lies the neutral axis
Total Length = A + B + Bend allowance A BEND ALLOWANCE B
BEND ALLOWANCE Cont..1 n Is the length of material required for the bend n This amount of metal must be added to overall length of the layout pattern n Depends on q q q q Degree of bend The radius of bend Thickness of the metal Type of metal n Radius of bend is proportional to the thickness of the metal
BEND ALLOWANCE Cont..2
BEND ALLOWANCE Cont..3 n Shaper radius; less material for bend n Soft material can be bent sharply n Bending compresses the inside material and stretches outside material n The neutral line will not be affected by any of these forces n Neutral line will be approximately 0.445 times the metal thickness (0.445 * T) n Formula charts are available for calculating bend allowance
BEND ALLOWANCE Cont..4
BEND ALLOWANCE Cont..5 n Method #1 n 2µ (R + ½ T) n 90 Bend is a quarter of a circle; divide by 4 n 2µ (R + ½ T) 4
BEND ALLOWANCE Cont..6 n Method #2 (1 to 180 ) n Use 2 constant values. n B A = (0.01743 * R + 0.0078 * T) * N n R The desired bend Radius n T Thickness of the material n N- Number of degree
BEND ALLOWANCE Cont..7 n Method # 3 n Use of chart n For 90 use the upper number n For other values use the lower number
BEND ALLOWANCE TERMS n Leg: The longer part of a formed angle n Flange: the shorter part of the formed angle n Mold line (ML): The line formed by extending the outside surfaces of the leg and flange n Bend Tangent Line (BL) the line at which the metal starts to bend and the line at which the metal stops curving
BEND ALLOWANCE TERMS Cont1 n Bend Allowance: The amount of material consumed in making a bend n Setback: the distance from the bend tangent line to the mold point n Bend line: the layout line as a guide in bending. n Flat: the portion not included in the bend
BEND ALLOWANCE TERMS Cont2 n Base Measurement: The outside dimensions of a formed part. (original final size) n Closed Angle: An angle that is less than 90 n Open Angle : An angle that is more than 90 n K : Constant value
SETBACK n Know the starting and ending point of the bend n Two factors determine the setback q Radius q Thickness
SETBACK Cont 1 n Setback is the distance from the q Bend Tangent line to the q Mold point n Bend tangent line Starting and end points of the bend n Mold point Point of intersection
SETBACK Cont 2 n Formula # 1 n Setback = R + T n Formula # 2 (angle other than 90 ) n Setback = K (R + T)
MAKING LAYOUT n Make a layout before forming to q prevent waste of material q Get a greater degree of accuracy q do minimum amount of forming n Layout Procedures q Flat layout q Duplication of pattern q Projection through a set of points.
FLAT LAYOUT n Left hand flat A = 1in High n Right hand flat C = 1-1/4 in high n The distance between the outside surface B= 2 inch n Material thickness = 0.051 inch n Bend radius = 3/16 inch n Bend angle= 90
n A = 1 in n B = 2 in n C = 1-1/4in T = 0.051 in R = 3/16 in Angle =90 A C B
CALCULATION n Determine the setback q Setback for first bend q Setback = R+T = 0.188 + 0.051 = 0.239 n The first flat A = 1-0.239 = 0.761 in
Cont.. 1 n Bend allowance for first bend q BA = 0.3307 or 0.331 n Second flat layout n Flat B = 2-(0.239 +0.239) q 2 0.478 q 1.522 in n BA for second bend = 0.331
Cont 2 n The flat C = 1.250-0.239 = 1.011 inch n Total = Flat A + Flat B + Flat C + BA +BA = 0.761 + 1.522 + 1.011 +0.331 + 0.331 = 3.956 in n Flat A +B+C = 4.25inch n After calculation = 4inch Saves.0.25 inch
RELIEF HOLE n Wherever two bends intersect, material must be removed to make room for the contained in the flanges. n Holes are drilled at the intersection n Provides a neatly trimmed corner from which excess material may be trimmed n Size of the relief holes varies with thickness of the material n Should be not less than 1/8 inch diameter
RELIEF HOLE Cont..1 n Must touch the intersection of the inside bend tangent lines
LIGHTENING HOLES n Lighting holes are cut at q q q rib sections Fuselage frames Other structural parts to decrease weight n Unless authorized, should never be cut n Can cut by any one of the following method q q q q Punching out Cutting out with a fly cutter Drilling out and file smooth Drilling out, cut with aviation snips and filing smooth
HAND FORMING n All forming involves either stretching, or shrinking or both n Use V- blocks, hammer, mallet, or formed blocks, wedge blocks n Joggling