21 Precision Sheet Metal Parts

Explain the design implications of bending sheet metal to form a part. Define various terms related to sheet metal bends. Use a setback chart to calculate bend radii for precision sheet metal. Use the proper formula to calculate bend radii for precision sheet metal. Explain proper layout and fold procedures. Read and interpret precision sheet metal prints.

Precision Sheet Metal Parts Sheet metal parts are made from a flat pattern that is folded into a precision part

Bending Terms Gage: Thickness of sheet metal; based on the weight of the material Thickness: Stock thickness of the sheet metal, usually identified in formulas as T Bend: Uniformly curved section of material that serves as the edge between two sides or legs

Bending Terms Bend allowance: Amount of flat metal material required to create the desired bend between legs Bend deduction (setback): Amount of material that is less than if the part were made with a sharp corner instead of a rounded corner Leg: Straight segment of stock on either side of a bend

Bending Terms Blank length: Total amount of flat metal material required to create the part Equal to the length of all legs plus the bend allowances Springback: Opening of a bend after forming due to the elasticity of the material Overbending: Bending an extra increment to compensate for springback

Neutral Plane

K-factor An understanding of the K-factor is required for sheet metal bend calculations K-factor approximates the offset position of the neutral plane

Setback Charts Developed length = X + Y – Z, where: X = overall length of side 1 as if the corner were square Y = overall length of side 2 as if the corner were square Z = setback (bend deduction)

Setback Charts Developed length = 1.000 + .750 – .106 = 1.644

Bend Allowance Developed length = L1 + L2 + Z, where: Where L1 = length of leg 1 [X – (R+T)] Where L2 = length of leg 2 [Y – (R+T)] Where Z = (bend allowance)

Bend Allowance Developed length = .835 + .585 + .224 = 1.644

What happens to the metal on the inside and outside radii of a bend? The metal on the inside radius compresses, while the metal on the outside radius stretches.

What is the difference between a bend allowance and a bend deduction? The allowance is the amount of material that must be added to the leg lengths to achieve the final folded dimension. The deduction is the amount of material that must be subtracted from the leg lengths, if they formed a square corner, to achieve the final folded dimension.

If two legs formed a square corner and each leg was then 1, what is the developed length if the setback is .106? 1.894

Using the formula A = 1/2π (R + Using the formula A = 1/2π (R + .5T), what is the allowance for a 90° bend when the stock thickness is .0625 and the bend radius is .187? .343

What is the first step in laying out and folding a precision sheet metal part? Calculate and lay out the developed length and feature locations.

What dimension is typically not shown on a precision sheet metal part drawing, rather is given as a note? The material thickness, which is usually provided in the material block.