Precision Sheet Metal Parts Unit 21 Precision Sheet Metal Parts

Learning Objectives 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

Sheet Metal Drawing Terminology ASME 14.31 standardizes some of the notations and linework for sheet metal drawings Outside Mold Line (OML) and Inside Mold Line (IML): Lines that represent the inside or outside surfaces if projected to a sharp corner

Sheet Metal Drawing Terminology Center Line of Bend (CLB): a line midway between bend tangent lines Form block line (FBL): a line representing the surface of a forming tool Bend up (BUP) Bend down (BDN)

An Undimensioned Drawing Sheet metal drawings are sometimes classified as undimensioned drawings

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 do you see? Print supplied by Perkin Elmer.