Manufacturing Processes II: Forming Methods, Defects & Troubleshooting, Study notes of Engineering Physics

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MANUFACTURING

PROCESSES II

PROCESS CHARACTERISTICS IN

FORMING METHODS, DEFECTS

AND TROUBLESHOOTINGS

Traditional Metal Forming Processes

• Rolling
• Forging
• Extrusion
• Wire drawing
• Sheet metal forming

4

1. Material Materials with small grains have higher fracture toughness and ductility, however the higher stress is needed to deform the material. The inclusions in the material make plastic deformation difficult.

5

Tensile test gives us

information about the

mechanical properties

(tensile strength, yield

strength, Young’s modulus,

toughness, strain...) of the

material.

When the material high

yield stress, it becomes

difficult to deform the

material.

2. Mechanical Properties

As strain rate increases, ductility of the material decreases.

8 Increasing the temperature generally has the following effects on stress-strain curves; 1 - The ductility and toughness increase, and 2 - The yield stress and the modulus of elasticity decrease.

4. Temperature

Let’s remember: For cold working

Let’s remember: For hot working

13 Residual stresses can be generated due to non-uniform plastic deformation ( especially in cold working ) or non-uniform cooling gradient ( especially in hot working ).

6. Residual Stresses

14 Geometrical factors are related to dies, fixtures, tooling and presses.

7. Geometrical Factors

FORGING OPEN DIE FORGING CLOSED DIE (Impression die) FORGING

DEFECTS IN FORGING 1 - Buckling, in upsetting forging. Subject to high compressive stress 2 - Mistmaching; This occurs due to improper alignment between the top and bottom forging dies 3 - Internal crack; due to the secondary tensile stresses 4 - Pitted surface; due to oxide scales occurring at high temperature stick on the dies 5 - Surface cracking; due to temperature differential between surface and center, or excessive working of the surface at too low temperature 6 - Microcracking, due to residual stress

Excessive flash due to excessive material usage

Inclusion