MSE 440/540: Processing of Metallic Materials

NC State UniversityDepartment of Materials Science and Engineering 1

MSE 440/540: Processing of Metallic Materials

Instructors: Yuntian ZhuOffice: 308 RBIIPh: 513-0559

[email protected]

Lecture 9: Forging

NC State University

Forging

Deformation process in which work is compressed between two dies

• Oldest of the metal forming operations– Dates from about 5000 B C

• Products: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts – Also, basic metals industries use forging to establish basic

shape of large parts that are subsequently machined to final geometry and size

http://www.youtube.com/watch?v=Fa0FVYxbVWk (Axe, 5.5 min)

NC State University

Classification of Forging Operations

• Cold vs. hot forging: – Hot or warm forging – advantage: reduction in

strength and increase in ductility of work metal – Cold forging – advantage: increased strength due

to strain hardening

• Impact vs. press forging:– Forge hammer - applies an impact force – Forge press - applies gradual force

NC State University

Types of Forging Operations• Open‑die forging - work is compressed between two

flat dies, allowing metal to flow laterally with minimum constraint

• Impression‑die forging - die contains cavity or impression that is imparted to workpart– Metal flow is constrained so that flash is created

• Flashless forging (closed die forging) - workpart is completely constrained in die

NC State University

Open‑Die Forging

Compression of workpart between two flat dies – Deformation operation reduces height and

increases diameter of work – Also called upsetting or upset forging (decrease

in height, increase in diameter)

http://www.youtube.com/watch?v=dK6eZGeDjZg (Sword, 3 min)

NC State University

• (1) Start of process with workpiece at its original length and diameter, (2) partial compression, and (3) final size

Open-Die Forging with No Friction

hholnTrue strain:

Quiz: What is engineering strain?

NC State University

Actual deformation of a cylindrical workpart in open‑die forging, showing pronounced barreling: (1) start of process, (2) partial deformation, and (3) final shape

Open-Die Forging with Friction

NC State University

Impression‑Die Forging

Compression of workpart by dies• Flash is formed by metal that flows beyond die cavity

into small gap between die plates • Flash must be later trimmed, but it serves an important

function during compression:– As flash forms, friction resists continued metal flow into gap,

constraining metal to fill die cavity

NC State University

Impression‑Die Forging Practice

• Several forming steps are often required– With separate die cavities for each step

• Beginning steps redistribute metal for more uniform deformation and desired metallurgical structure in subsequent steps

• Final steps bring the part to final geometry

http://www.youtube.com/watch?v=mySkT0Gw_X0 (1 min)

NC State University

Advantages and Limitations of Impression-Die Forging

• Advantages compared to machining from solid stock:– Higher production rates– Less waste of metal– Greater strength– Favorable grain orientation in the metal

• Limitations:– Not capable of close tolerances– Machining is often required to achieve accuracies and

features needed

Quiz: why forging improve the strength?

NC State University

Flashless (closed die) Forging

Compression of work in punch and die tooling whose cavity does not allow for flash

• 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

NC State University

• (1) Just before contact with workpiece, (2) partial compression, and (3) final punch and die closure

Flashless Forging (Closed Die Forging)

NC State University

• Upset forging to form a head on a bolt or similar hardware item: (1) wire stock is fed to stop, (2) gripping dies close on stock and stop retracts, (3) punch moves forward, (4) bottoms to form the head

Upset Forging

NC State University

• Examples of heading operations: (a) heading a nail using open dies, (b) round head formed by punch, (c) and (d) two common head styles for screws formed by die, (e) carriage bolt head formed by punch and die

Heading (Upset Forging)

NC State University

Swaging

Accomplished by rotating dies that hammer a workpiece radially inward to taper it as the piece is fed into the dies

• Used to reduce diameter of tube or solid rod stock

• Mandrel sometimes required to control shape and size of internal diameter of tubular parts

NC State University

• Swaging process to reduce solid rod stock; dies rotate as they hammer the work

• In radial forging, workpiece rotates while dies remain in a fixed orientation as they hammer the work

Swaging and Radial Forging

http://www.youtube.com/watch?v=ilL8ViUDUKc (cartoon, 1.5 min)

NC State University

HW assignment

• Reading assignment: Chapters 13

• Review Questions: 13.10, 13.11, 13.12, 13.14,

• Problems: 13.10, 13.12, 13.14

Department of Materials Science and Engineering 17