Sheet Metal Bending. By- Prem Mahendranathan

Transcription

1 Sheet Metal Bending By-

2 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

3 PROFILES

4 BAR FOLDER n Making bends or folds along the edges n For folding small hems, flanges.. n Set the machine before use

5 FLANGE ATTACHEMENT

6 ROLL FORMER

7 STRAIGHT BRAKER

8 BOX PAN

9 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

10 Total Length = A + B + Bend allowance A BEND ALLOWANCE B

11 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

12 BEND ALLOWANCE Cont..2

13 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 times the metal thickness (0.445 * T) n Formula charts are available for calculating bend allowance

14 BEND ALLOWANCE Cont..4

15 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

16 BEND ALLOWANCE Cont..6 n Method #2 (1 to 180 ) n Use 2 constant values. n B A = ( * R * T) * N n R The desired bend Radius n T Thickness of the material n N- Number of degree

17 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

18 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

19 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

20 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

21 SETBACK n Know the starting and ending point of the bend n Two factors determine the setback q Radius q Thickness

22 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

23 SETBACK Cont 2 n Formula # 1 n Setback = R + T n Formula # 2 (angle other than 90 ) n Setback = K (R + T)

24 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.

25 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 = inch n Bend radius = 3/16 inch n Bend angle= 90

26 n A = 1 in n B = 2 in n C = 1-1/4in T = in R = 3/16 in Angle =90 A C B

27 CALCULATION n Determine the setback q Setback for first bend q Setback = R+T = = n The first flat A = = in

28 Cont.. 1 n Bend allowance for first bend q BA = or n Second flat layout n Flat B = 2-( ) q q in n BA for second bend = 0.331

29 Cont 2 n The flat C = = inch n Total = Flat A + Flat B + Flat C + BA +BA = = in n Flat A +B+C = 4.25inch n After calculation = 4inch Saves.0.25 inch

30 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

31 RELIEF HOLE Cont..1 n Must touch the intersection of the inside bend tangent lines

32 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

33 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