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. Engr 241-R1

Example – Blacksmith Hammer and anvil Engr 241-R1

Forging Forgeability Forging is a discrete (individual) parts process 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

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

Forging classified cold or hot Engr 241-R1

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

Hot Forging Requires smaller forces, not as good finish or dimensional accuracy; usually require additional machining. Engr 241-R1

Open-Die Forging Upsetting or flat-die forging Simplest forging process. Solid workpiece is set between two flat dies and reduced (height) through compression. Engr 241-R1

Barreling outward bowing of material Two causes 1.) by friction at die-work piece interface minimized by use of lubricants. Engr 241-R1

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

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

Fullering Distribute material away from die Engr 241-R1

Edging Gather material into die Engr 241-R1

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). Engr 241-R1

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

Closed die forging (cont.) Greater forces to obtain fine detail Al and magnesium good because malleable Less material wasted Gears, connecting rods, etc. Engr 241-R1

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. Engr 241-R1

Related Forging Operations Engr 241-R1

(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. Engr 241-R1

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

(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

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

(6) Orbital Forging upper die moves along an orbital path above the part which is also spinning. Engr 241-R1

(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. Engr 241-R1

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

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

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

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

Forging Machines Engr 241-R1

Presses Hydraulic Mechanical Screw Engr 241-R1

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

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