Section 4: Bulk Deformation Flashcards
Bulk Deformation
Metal forming operations which cause significant shape change by deforming metal parts whose initial form is bulk rather than sheet.
Causes plastic flow into the desired shape
plastic flow
permanent deformation when a material hits a critical stress value
What temperature processes is bulk deformation performed under
cold, warm, and hot working
Advantage of hot working bulk deformation
Significant Shape change
Advantage of cold working bulk deformation
Strength is increased
Primary benefit of bulk deformation
Little to no waste
little or no machining required
Four Basic Bulk Deformation Processes
- Rolling
- Forging
- Extrusion
- Wire and bar drawing
Rolling w/ goals
- Slab or plate is squeezed between opposing ROLLS
- the rolls act as compressive forces that reduce the crosssection (reduce thickness)
Forging
Work is squeezed and shaped between opposing DIES
Extrusion
work is squeezed through a die OPENING, thereby taking SHAPE of the OPENING
Wire and bar drawing
Diameter of wire or bar is REDUCED by PULLING it through a die opening
Difference between Extrusion and Wire & bar drawing
In extrusion the work is SQUEEZED through an opening to take the shape of that opening
In Wire & bar drawing the work is PULLED through an opening with the goal of reducing the diameter
4 Types of Rolling and their 2 respective bases and functions
Based on workpiece geometry:
- Flat Rolling: used to reduce the thickness of a rectangular cross-section
- Shape Rolling: Square cross section is formed into a shape such an I-beam
Based on Work temperature:
- Hot Rolling: can achieve significant deformation
- Cold Rolling: produces sheet and plate stock
4 types of Rolling and their bases
Workplace Geometry:
- Flat Rolling
- Shape Rolling
Work Temperature:
- Hot Rolling
- Cold Rolling
What is Thread Rolling
Bulk deformation process used to form threads on cylindrical parts by moving them between two dies
Benefits of Thread Rolling
- Important for mass production of bolts and screws
- Performed as Cold Working
Advantages of thread rolling over thread cutting
- higher production rates
- better material utilization
- stronger threads and better fatigue resistance
Ring Rolling
Deformation Process in which a thick-walled ring of smaller diameter is rolled to form a thin-walled ring of larger diameter
Roll Piercing
Formation of internal stresses and cavity by compression of cylindrical part
Can be used for seamless tubing
What is Forging
Deformation process in which work is compressed between two dies
What is the oldest metal forming operation
Forging
Common products of forging
engine crankshafts, connecting rods, gears, jet engine turbine parts
What is Impact forging
Forge hammer - applies impact
What is Press forging
Forge Press - applies gradual force
What is Open-die forging
work is compressed between two flat dies, allowing metal to flow laterally with minimum constraint to produce a desired cross-sectional shape
What is Impression-die forging
Compression of work piece by two dies
- flash is created
What is Flashless forging
compression of a work piece in punch and die tooling
- no excess flash
Importance of flash in impression-die forging
- As flash forms, friction resists continued metal flow into the gap, constraining the metal to fill the die cavity
- In hot forging, metal flow is further restricted by cooling against die plates
Advantages & Limitations of Impression-die forging
Advantages:
-higher production rates
- less waste of metal
- greater strength
- Favorable grain orientation of metal
Limitations:
- Not capable of close tolerances
- Machining is often required to achieve accuracies and features needed
Notes on flashless forging
- starting work volume must equal die cavity volume within very close tolerance
- process control more demanding than impression-die forging
- best suited to part geometries that are simple and symmetrical
- often classified as a precision forging process
Types of forging hammers and functions
gravity drop hammers - impact energy from the falling weight of a heavy ram
power drop hammers - accelerate the ram with pressurized air or steam
disadvantage of forging hammers
impact energy is transmitted through anvil into the floor of the building
What are forge hammers commonly used in
impression-die forging
In general, extrusion is used to produce what?
long parts of uniform cross-sections
two basic types of extrusion
-direct (or forward)
- indirect (or backward/reverse)
Direct Extrusion
- starting billet cross section is usually round
- Extrudate is determined by opening
- as the ram approaches the opening, the remaining portion that cannot be forced through is called the butt
- also called forward extrusion
Indirect Extrusion
- aka backward or reverse extrusion
- lower rigidity of hollow ram
- difficulty in supporting extruded product as it exits die
- can produce a solid cross-section using a hollow ram only
- can produce a hollow cross-section using a solid ram only
Advantages and Limitations of Extrusion
Advantages:
- Variety of shapes possible, especially in hot extrusion
- Grain structure and strength enhanced in cold and warm extrusion
- close tolerances possible, especially in cold extrusion
- potentially little to no waste
Limitations:
- part cross-section must be uniform throughout length
what is Hot extrusion and its goal
- prior heating of billet to above its recrystallization temperature
- reduces strength and increases ductility of metal, permitting more size reductions and more complex shapes
what is the goal of Cold extrusion
- generally used to produce discrete parts
Impact extrusion
high speed cold extrusion
Difference between wire drawing and bar drawing
stock size, equipment, and terminology
- Bar drawing: large diameter bar and rod stock
- Wire drawing: Small diameter stock
Typical Drawing practice
-cold working
- use round cross sections
Products of wire and bar drawing
- Wire: fencing, hangers
- Rod stock for nails, screws, springs
- Bar stock: metal bars for machining, forging, etc
Bar Drawing
-Accomplished as a single draft (the stock is pulled through one die opening)
-Beginning stock has a large diameter and is a straight cylinder
- requires a batch type operation
Wire Drawing
Continuous drawing machines consisting of multiple draw dies (4-12) separated by accumulating drums:
- Each drum (capstan) provides force to draw wire stock through the upstream die
- Each die provides a small reduction, so the desired total reduction is achieved by the series of dies
- Annealing sometimes required between dies to relieve work hardening
