DSG325 - Intro to Forging

Lecture 08

what is forging?

shaping and compression of metal to form desired geometry

• metal ingot is heated to increase ductility

• ductile ingot is forcibly hammered/pressed into its new shape

• tempering is often done after to restore desired mechanical characteristics

What are the benefits of forging?

• high strength and durability

• very little metal waste compared to other metal manufacturing methods

  • flashing

• very little finishing required

• very little downtime/human intervention required

• varied precision - forging can achieve average tolerances of 0.2%-10% depending on material and part/die complexity

what are the characteristics of hot forging?

material is heated above recrystallization temperature

• prevents strain hardening

• makes the material more malleable, able to flow into more complex forms

• promotes recrystallization

what is the process of hot forging?

die is heated to prevent heat loss during process

• cooling complications failure to form, stick, die wear

pressure applied by die to material to form shape

what is the cold forging process?

die and material at room temperature

• material is often pre-annealed or chosen for ductility at room temperature

compressive forces squeeze material between punch and die

what are some techniques that are used in cold forging?

• rolling

• pressing

• drawing

• spinning

• heading

• extruding

What are the advantages of hot forging?

increased ductility and more complex parts

what are the advantages of cold forging?

very little waste

near-net production (very little minishing required)

higher dimensional accuracy

what are the disadvantages of hot forging?

risk of warping

less dimensionally accurate

additional cost from supporting heating equipment

what are the disadvantages of cold forging?

less complex geometry possible

risk of residual stress - often requires post-forming heat treat

What is open die forging?

(also known as drop forging)

• type of hot forging

  • shapes the workpiece without fully enclosing the metal within the die

What kind of parts are usually made using an open die forge

• very large

• fairly simple shapes with low tolerance

• custom shaped or hand forged parts

• parts with subsequent forging steps or post machining

What is closed die forging?

(also known as impression die forging)

• type of hot forging

• heated billet is roughly the volume and shape of a finished part

• billet placed in bottom die, force on die compressed billet into desired shape

• higher up-front cost - shaped dies are expensive and have to hold up to many reptations of high forces and wear

• produces fairly precise, complex geometry

• usually leaves flash

What is upset forging?

(AKA “heading”)

• can be performed hot or cold

• shaped die ‘upsets” end of wire that is fed through

  • commonly used to produce nails, screws, nuts, and bolts

what type of forging likely created this?

open die

what type of forging likely created this?

closed die

what type of forging likely created this?

open die

what type of forging likely created this?

upset die

what type of forging likely created this?

closed die

Does hot or cold forging have greater dimensional accuracy?

cold forging

Does hot or cold forging waste less material?

cold forging

Is hot or cold forging at risk of warping?

hot forging

Does hot or cold forging have a risk of retaining residual stress if not heat treated

cold forging

All else held in common (material, geometry, heat treat, etc.) will a forged or machined part be tougher?​

A forged part because you are not cutting in the grain, so it is not starting and stopping which makes the part weaker

What happens to a part when it cools in the mold?

shrinkage occurs and part pulls away from walls on the outside, hugs walls on the inside

How do we prevent a part from sticking or getting caught in the mold?

add draft to the sides and increase that draft on the inside surfaces of the part

What are some guidelines for parting lines?

• typically, perpendicular to mold pull direction

• must intersect part all the way through - no undercuts

• draft inflect point lies on this

Why should small radii be avoided?

• can case disruption to material flow and “folding”

• can cause extreme die loads to force material into tight corners

• can cause stress concentration and cracking on exterior corners shortening die life

what plane should the parting line go on and what features should be added to make it better suited for forging?

line c

• draft and fillets