1. Precision Sheet Metal Parts
Unit 21
Precision Sheet Metal Parts

2. 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.

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

4. 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

5. 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

6. 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

7. Sheet Metal Drawing Terminology
ASME 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

8. 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)

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

10. Neutral Plane

11. 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

12. 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)

13. Setback Charts
Developed length = – .106 = 1.644

14. 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)

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

16. What do you see?
Print supplied by Perkin Elmer.