Introduction to Cold Forming

Introduction to Cold Forming

March 6, 2007Independence, Ohio

Presented by Carpenter Technology Corporation

Copyright 2007 CRS Holdings, Inc.

Introduction Terminology Processes Benefits Material Characteristics Applications Steps to Manufacture Coatings and Lubricants

The information and data presented herein are typical or average values and are not a guarantee of maximum or minimum values. Applications specifically suggested for material described herein are made solely for the purpose of illustration to enable the reader to make his/her own evaluation and are not intended as warranties, either express or implied, of fitness for these or other purposes.

March 23, 1794 Josiah Pierson – “Cold Header” Rivet

Machine

November 16, 1796 Isaac Garretson – U.S. Patent for nail cutting

& heading machine

History and Development of Cold Forming

Cold Forming terms:

Cold Heading: cold forming process in which the force of

the punch must exceed the material’s elastic limit to cause plastic flow

elastic limit = yield strength

forging operation without the heat

Cold Forming Terminology

Cold Forming terms: Cold Extrusion

decreasing the diameter of the blank by pushing it through a smaller hole

reduces size without yield loss

Cold Forming: generic term describing the combination of

cold heading with cold extrusion

Cold Forming Terminology

Applications:

Cold forming machines - by the number of dies and blows for example:

1 Die/2 blow

2 Die/3 blow

2 Die/4 blow

• The wire is fed in through the cut-off die to a wire stop.

• The cut-off knife shears the blank.

• The cut-off knife transfers the blank to the heading die.

• Now the blank is ready to receive the first punch operation.

• Proper cut-off of blank is critical.

• Blank mass equals mass of finished part.

• Upsetting of a fastener head is accomplished by using one of these 4 methods.

• Typical 1-Die/2-punch method is common in producing headed fasteners.

• The first blow combines coning with shank extrusion.

• Coning is a partial head upset.

• The second blow finishes the head shape.

• Knockout pin acts as a blank support, during heading operation.

• Then ejects finished part.

• Rule of thumb:• Unsupported pin not

to exceed 8D• Supported pin is

recommended over 8D

Open Extrusion Trap Extrusion

30% area reduction 75% area reduction

• Examples using trap extrusion and open extrusion.

7 Station Cold Forming Process







Advantages of Cold Forming Design Versatility

High strength parts from non-heat-treatable alloys

Most cost effective way vs. milling, machining, hobbing and chemical etching

High production rates Metallurgical Effects

Grain flow Improves strength, hardness, toughness &

fatigue resistance Material Savings

Benefits of Cold Forming

• Heading improves the finished part’s grain structure by making it conform to the flow of the design.

• The machined diagram shows how the grain structure is weakened by cutting operations.

Benefits of Cold Forming

Material DescriptionTensile

(ksi)Yield Formability

Cost IndexSteel = 1

Aluminum Alloys

Tensile strength of mild steel with 1/3 the weight. Ex: 2024

55 50 Excellent 5.0

Brass

Alloy of Cu & Zn. Tough, rustproof. Relatively inexpensive. Ex: 274 Yellow Brass

60 min 40 min Excellent 6.0

Copper

High corrosion resistance. Expensive. Ex: 110 Electrolytic Tough Pitch

35 – 40 10 – 35 Excellent 6.5

Nickel Alloys

Approximately 2/3 Nickel, 1/3 Cu with small amounts Fe. High strength, resistance to heat and corrosion. Ex: NiCu400

80 min 60 min Excellent 18.0

Materials - Characteristics

Material DescriptionTypical max Tensile as annealed

Typical max Tensile w/ 50% cold

work

FormabilityCost IndexSteel = 1

1010 Low carbon 55 62 Excellent 1

1018 Low carbon 65 98Good to

Excellent1

1022Medium carbon

70 108Good to

Excellent1

1038Medium carbon

85 157 Fair to Good 1

4037Medium

carbon low alloy

83 166 Fair to Good 1.5


Material DescriptionTypical max Tensile as annealed

Typical max Tensile w/

5% cold workFormability

Cost IndexSteel = 1

410 Martensitic Stainless Steel 78 90 Fair 4.0

430 Ferritic Stainless Steel 75 86 Fair 4.0

302HQ Austenitic Stainless Steel 75 83 Fair 4.5

305 Austenitic Stainless Steel 83 93 Fair 4.5

A-286 Austenitic Stainless Steel 95 95 Fair to Poor 6.5

Pyromet® 718

Hi Temperature Alloy

120 135 Poor 12.0


Pyromet is a reg. tm. of CRS Holdings, Inc.

Applications for Cold Formed Parts

Automotive brake parts ball joints & steering parts starter pinions oxygen sensors constant velocity joints manifold bolts engine valves

Appliance Industry gears fasteners for assembly


Construction, Off-road equipment bolts, nuts screws – tapping, window,

roofing, deck transmission gears similar parts for automotive

Aerospace rivets, fuselage engine bolts fasteners - landing gear,

interior


Production of Formed Parts

Equipment Material Part

Cold, Warm or Hot Forming

Decision Process for Cold Forming

Equipment

Material

Part

which machine which tools skill of personnel

formability incoming condition

accuracy tolerances additional

treatments


Production of Headed Parts

Cold Heading Hot Heading

Room Temperature Forming of heated Forging temperatures No heat slugs at temperatures from 950 – 1250 °C

from: 550 – 950 °C (1740 – 2300 °F)(1020 – 1740 °F)

WarmHeading


Cold HeadingWarm

HeadingHot Heading

Carbon Steel>0.3% carbon, >3.0% alloy

Room temp 550 - 850oC

1020 - 1560oF>950oC>1740oF

Austenitic Steels

Room temp 400 - 450oC 750 - 840oF

Blue Brittleness Problem

550 - 850oC1020 - 1560oF

Aluminum alloys Room temp

420 - 480oC 790 - 900oF

Not applicable

Brass alloys Room temp 350 - 620oC 660 - 1150oF

Not applicable


Forming Type Cold Warm HotTemperature Room 550 - 950oC 950 - 1250oC

1020 - 1740oF1740 - 2300oF

accuracy high good low

formability restricted good good

material restricted large variety large variety

energy costs low moderate high

surface quality high good low

tolerances close closer low

grain structure good good variable

heat treatments few few definite

machining least less necessary

General Aspects of Heading Methods


Tooling Loads in Heading Operations

0%

20%

40%

60%

80%

100%

120%

Cold Warm Hot

Re

lati

ve

Lo

ad


Steps to Manufacture:

From raw material to finished parts

Raw Material

HeatTreatment

SurfaceTreatment

Cold Forming

FormedPart

Metal Removal

HeatTreatment

Metal Removal

Finishedpart

Process Chain of Cold Forming

Raw Material Wire/Rod

hot rolled shaved - ‘seam’ free cf/anl

material in the ‘softest’ condition optimum for cold forming

anl/cf uniform volume uniform diameter specific incoming mechanical properties desired

Steps to Manufacture

Heat Treatment of Raw Material

Benefits Improves ability of deformation

Reduces hardness

Improves metal structure towards better forming


Heat Treatment of Raw Material

Types of heat treatment Tempering to form spherical cementite

Annealing to remove strain hardening

to set the desired mechanical properties

to normalize the microstructure


Surface Treatment Alkaline cleaning

warm 170o-190oF/ 77o-88oC Cold rinsing

removes alkaline cleaner Acid pickling

sulphuric hydrochloric nitric/hydrofluoric

Cold/warm/hot rinsing removes acids


Surface Treatment Pre-coating

carbon zinc phosphate

stainless potassium sulfate lime

Drying approx. 250oF/ 120oC

Metallic Coating copper plating


Surface Treatment

Non-metallic coatings

molybdenum disulfide – MoS2

Soaps sodium stearates

calcium stearates


Cold Forming Single stage presses Multi stage presses

up to 5 or 6 stages, as many as 8

Secondary forming operations threading

rolled machined


Heat treatment after Cold Forming

Annealing relieve stress

re-crystallize

normalize

Hardening increase the hardness after forming


Metal Removing Hard Surfaces

turning grinding honing lapping

Soft Surfaces turning drilling milling


Surface Treatment Cleaning of parts

de-phosphate washing acid to remove copper coating

Corrosion protection passivation – stainless steel

Plating zinc chromate - Cr+6 (hexavalent chrome) can

be a problem


Coatings Uses

prevent metal to metal contact with tooling, galling act as a carrier for machine lubricants

Types precoat lime copper plating zinc phosphate molybdenum disulfide oxalate

Coatings and Lubricants

Lubricants Types

soaps calcium stearate sodium stearate

drawing oils Metal-removing coolants

oil emulsion synthetics


Process Lubricant

Hot Rolling Water

Drawing

Pre-coat: phosphate, lime, oxalateLubricants:

Soaps, Oils

Cold Forming Oils

Thread rollingMetal removal coolant:Emulsion, Solution, Oil

Cutting/slottingMetal removal coolant:

Emulsion, Solution


Sources:

“Heading Hints: A Guide to Cold Forming Specialty Alloys” - Carpenter Technology Corporation (2001)

“Steel Wire Handbook Vol. 3” – The Wire Association, Inc.(1972)

“Tool Design and Part Shape Development for Multi-die Cold Forming” - National Machinery Co.(1976)

“Cold Forming 101” - Fastener Technology International (June 2005)

Thank you for your interest in cold forming of wire.

More information about Carpenter is available on this website including technical datasheets and articles, Products and Markets. Visit Product Literature to request a free copy of “Heading Hints: A Guide to Cold Forming Specialty Alloys.”

To contact Carpenter, call 1-800-654-6543 in the U.S. or refer to the Contact Us page for the location nearest you.

Documents

Introduction to Cold Forming