Introduction to Manufacturing Chapter 14: Forging

Forging • Metal-forming process in which the workpiece is shaped by compressive forces applied through various dies and tools.

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Example – Blacksmith Hammer and anvil Engr 241-R1 2

Forging • Forgeability • Capability of a material to undergo deformation without cracking.

• Forging is a discrete (individual) parts process • Forging is a near net shape process Engr 241-R1 3

Metal flow and grain structure controlled – parts have good strength • Landing gear • Jet engine shafts • Bolts • Connecting rods • Hand tools Engr 241-R1 4

Forging classified cold or hot Engr 241-R1 5

Cold Forging • Requires greater forces and workpiece materials must have sufficient ductility at room temperature; good surface finish and dimensional accuracy. Engr 241-R1 6

Hot Forging • Requires smaller forces, not as good finish or dimensional accuracy; usually require additional machining.

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Open-Die Forging • • • Upsetting or flat-die forging Simplest forging process.

Solid workpiece is set between two flat dies and reduced (height) through compression.

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Barreling • • • outward bowing of material Two causes 1.) by friction at die-work piece interface • minimized by use of lubricants.

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Barreling • • (2) by hot work piece between cold dies Material cools at die interface and resists deformation Engr 241-R1 10

Cogging: • • • Drawing out Operation where the thickness of a bar is reduced by successive forging steps at certain intervals.

Typical for parts such as I-beams which must be pre-shaped before rolling Engr 241-R1 11

Fullering • Distribute material away from die Engr 241-R1 12

Edging • Gather material into die Engr 241-R1 13

Impression-Die Forging • Work piece takes shape of die cavities (impressions).

• Flash: material which flows out from dies (frictional resistance from cooling flash causes material to fill the inside of the die cavity).

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Closed-Die Forging • • • Also called precision forging flashless forging (flash does not form).

workpiece completely fills the die cavity. Volume of material is precise.

• Economical - eliminates trimming flash Engr 241-R1 15

Closed die forging (cont.) • • Greater forces to obtain fine detail Al and magnesium good because malleable • • Less material wasted Gears, connecting rods, etc.

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Coining: • • • Another closed die process Produces fine details No lubricants used – can be trapped in die cavities – don’t compress • pressures five to six times the strength of material.

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Related Forging Operations Engr 241-R1 18

(1) Heading • upsetting operation, usually performed at the end of a round rod or wire to produce a large cross section • heads of bolts, screws nails, rivets, etc.

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(2) Piercing • indenting, without breaking, the surface of a workpiece with a punch to produce a cavity or an impression Engr 241-R1 20

(4) Roll Forging • the cross section of a bar is reduced or shaped by passing it through a pair of rolls with shaped grooves • leaf springs, hand tools, discrete parts Engr 241-R1 21

(5) Skew Rolling • • similar to roll forging Ball bearing production Engr 241-R1 22

(6) Orbital Forging • upper die moves along an orbital path above the part which is also spinning.

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(7) Incremental Forging • process where a blank is forged into a shape in several small steps (the die penetrates the blank at different depths across the surface). Similar to cogging.

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(8) Isothermal Forging • • Hot die forging Dies heated to same temp as workpiece • Good for complex parts with dimensional accuracy Engr 241-R1 25

Forging die design • Most important rule in die design • Work piece material must flow in direction of least resistance • Machining allowance used Engr 241-R1 26

Die inserts • • Separate sections Reduce cost of making dies Engr 241-R1 27

Die lubricants • • • • Slow rate of cooling Improve metal flow Serve as parting agent Not for coining – precision forging Engr 241-R1 28

Forging Machines Engr 241-R1 29

Presses • • • Hydraulic Mechanical Screw Engr 241-R1 30

Hammers • • Gravity drop – free falling ram Power drop – stroke accelerated by steam, air, or hydraulic Engr 241-R1 31

Hammers (cont.) • • Counterblow (two hammers simultaneously approach each other High-energy-rate machines - ram accelerated by high pressure – part forged in one blow Engr 241-R1 32