Forging Defects S. Arvind Joshua Jaydev (20082203)

Defects in Forging may Arise from:

•  Inherent Defects while forging •  Faulty cuts in Forging Operations •  Improper Heating and Cooling

Types of Defects in Forging 1.  Cracks 2.  Laps/Folds 3.  Pitting 4.  Coarse Grain Wrinkle 5.  Flow-through 6.  Distributed Metal Defects 7.  Dents 8.  Underfilling 9.  Void at Base of Rib 10. Push-through of Web under Rib

1. Cracks

• Excessive working of a surface at too low a temperature leads to cracks

• Cracks may nucleate due to sulphur inclusions, etc.

• External cracks are most dangerous • Cracks may appear at flash (if flash is too thin) •  Internal cracks may develop during Upsetting

Inclusions leading to cracking

Cavity in the centre of a cleavage facet. The small inclusion appears to have initiated cleavage fracture.

“Upsetting” Forging

Flash

Combating cracks in Forging

•  Forging at increased temperature •  Stress relieving before cutting off flash • Hot-cutting of Flash • Use concave die while upsetting.

2. Laps/Folds

• Also called “Fold-shut” • Occurs when two surfaces of a metal folds

against each other without welding completely

• Metal may flow past a die cavity that has already been filled.

• May be due to Too small die radius, excessive chilling of high friction

Example of Folding during Forging

3. Pitting

Pitting

•  Pitting occurs because of incomplete cleaning of Die

• Die and workpiece should be free from scale while forging

4. Coarse grain Wrinkle

• Wrinkling occurs during forging because the Billets contains coarse grains.

•  These wrinkles fold into laps during forging.

5. Flow-through

Also…

•  Flow through may occur in cases where metal flows past the die recesses after filling.

• Die impressions are hence not completely filled. • Maybe avoided by increasing temp. of stock • Ensure lubricants are not trapped

6. Distributed Metal Defects

•  Loose oxides minimized die-slug contact

• Avoid too much lubricant

7. Dents

Dents are caused by

•  Improper positioning of stock on die •  Throwing around the forging while it is still hot.

8. Underfilling

Underfilling

• Metal does not fill the recesses of the die completely

• Because of loose scale and lubricant residue that accumulates in deep recesses of the die

9. Rib and Web defects

•  A "peeling" lap forms in an aluminum rib-web forging as the corner of the die forces surface material ahead of the contact region. With a redesign of the upper die or preform, this type of defect can be prevented

References

•  “Mechanical Metallurgy”, G. E. Dieter

•  http://www.forgemag.com • Google Images