Common failures and remedies for sheet Metal forming.pptx

Shivajee Yadav

1. INTRODUCTION Sheet metal operations can be classified on the basis of stresses induced. Stresses Induced Operations Shearing Shearing, blanking, piercing, trimming, shaving, notching, nibbling Tension Stretch forming Compression Coining, sizing, ironing, hobbling Tension and Compression Drawing, spinning, bending, forming, embossing

2. INTRODUCTION SHEET METAL OPERATIONS SHEET METAL CUTTING SHEET METAL FORMING Sheet metal operations can also classified on the basis of scrap- Scrap is present Shearing, blanking, piercing, notching etc. No scrap Drawing, spinning, bending, stretching etc.

3. Common failures for Sheet Metal Forming Some common failure or defects for sheet metal forming operations are as follows. Wrinkling Spring-back Earing Miss strike Fracture Cracks Surface defects etc.

4. Wrinkling Wrinkles appear both on the flange and on the wall during cup drawing and deep drawing operation. This is like ups and downs or waviness. The tendency for wrinkling increases with decreasing thickness, nonuniform thickness, increasing length or surface area of sheet that is not constrained or supported. Remedies- Wrinkles can be eliminated by increasing blank holding pressure. But due to too high pressure, fracture may appear and in such case draw beads are used.

5. Spring-back Springback is the geometric change made to a part at the end of the forming process when the part has been released from the forces of the forming tool. Its happen d ue to this elastic recovery. It depends on material, thickness, hardness, bend radius. Remedies- Overbending can perform to compensate spring-back. Bending at elevated temperature decreases spring-back. Apply tension during bending decreases spring-back.

6. Earing Earing is a waviness in the top edge of a cup drawn from sheet metal. Due to anisotropy in sheet metal, lobes or ears appear in the drawn cup. Anisotropy means varying properties in different directions. No of ears=2 n , Where n=1,2,3,4,...…... Remedies- Earing can be reduced by modifying the initial blank shape such as use of non circular blank as in present study. Earing can also be reduced by Varying Blank Holding Force in Deep Drawing. I roning is performed to make the thickness of drawn cup uniform.

7. Fracture In sheet metal forming, fracture usually occurs as ductile fracture rarely as brittle fracture. In deep drawing this appear due to high blank holding pressure. Remedies- Forces should apply according to material strength. In deep drawing fracture can also avoided by using draw beads .

8. Miss strike Uneven flange appear due to misplacement of the blank. It occurs in deep drawing. Remedies- Proper alignment of workpiece.

9. Surface defects Orange peel: It is grainy surface appearance. Due to overly grains or uneven flow. Remedies- ASTM grain size of no. 7 or finer is preferred. Lueder’s bands: Also called stretch-strain marks. Exhibited by low carbon steels. Remedies- These marks cane be eliminated by reducing thickness of sheet from 0.5% to 1.5% by cold rolling process