Ch. 8 Bulk Deform (Rolling/Forging) Flashcards
Four Basic Bulk Deformation Processes
- Rolling
-Forging
-Extrusion
-Wire and bar drawing
What is rolling
A defromation process in which work thickness is reduced by compressive forces exerted by two opposing rolls.
Flat rolling
Based on workpiece geometry, reduce thickness of a rectangular cross section
Shape rolling
Based on workpiece geometry, square cross section formed into a shape such as an I-beam
Hot rolling
Based on work temperature, can achieve significant deformaiton
Cold rolling
Based on work temperature, produces sheet and plate stock
Draft
amount of thickness reduciton
The no-slip point
The one point along the arc where work velocity equals roll velocity
Thread rolling
Forming threads on cylindrical parts by rolling them between two dies.
Important for mass producing bolts and screws
Performed as cold working.
Ring rolling
a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter
-as thick-walled ring is compressed, deformed metal elongates, causing diameter to enlarge.
- Hot working process for large rings
-Cold working process for smaller rings
Advantages of Thread Rolling over Thread Cutting (Machining)
Higher production rates
-Better material utilization
-Stronger threads and better fatigue resistance.
Camber
The result of extra thickness in the center between rolls at the center of the material.
Forging Process
Deformation process where work is compressed between two dies.
Products created from Forging
Engine Crankshafts
Connecting rods
Gears
Aircraft structural components
jet engine turbine parts
Hot/warm forging
reduction in strength and increase in ductility
Cold forging
Increased strength due to strain hardening
Impact forging (Forge Hammer)
applies an impact force
Press Forging (Forge Press)
Applies gradual force
Open-Die Forging
Compression of work part between two flat dies.
- reduces height and increased diameter of work.
- upset forging
Friction in Open-Die Forging
Friction constrains lateral flow of work, resulting in barreling effect.
Impression-Die Forging
Compression of work aprt by dies with inverse of desired part shape
- Flash is formed by metal that flows beyond die cavity inbto small gap between die plates.
-Flash is trimmed later(usually while hot)
-Force is higher than open-die.
What happens when the flash forms in Impression-Die Forging?
As the flash forms, friciton limits metal flow into the gap, constraining metal to fill die cavity.
Advantages of Impression-Die Forging
-Higher production rates
-Less waste of metal
greater strength
-favorable grain orientation in the metal
Limitations of Impression-Die Forging
Not capable of close tolerances
-machining is often required to achieve accuracies and features needed.
