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
7 Station Cold Forming Process
7 Station Cold Forming Process
7 Station Cold Forming Process
7 Station Cold Forming Process
7 Station Cold Forming Process
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
Materials - Characteristics
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
Materials - Characteristics
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
Applications for Cold Formed Parts
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
Applications for Cold Formed Parts
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
Decision Process for Cold Forming
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
Decision Process for Cold Forming
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
Decision Process for Cold Forming
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
Decision Process for Cold Forming
Tooling Loads in Heading Operations
0%
20%
40%
60%
80%
100%
120%
Cold Warm Hot
Re
lati
ve
Lo
ad
Decision Process for Cold Forming
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
Steps to Manufacture
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
Steps to Manufacture
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
Steps to Manufacture
Surface Treatment Pre-coating
carbon zinc phosphate
stainless potassium sulfate lime
Drying approx. 250oF/ 120oC
Metallic Coating copper plating
Steps to Manufacture
Surface Treatment
Non-metallic coatings
molybdenum disulfide – MoS2
Soaps sodium stearates
calcium stearates
Steps to Manufacture
Cold Forming Single stage presses Multi stage presses
up to 5 or 6 stages, as many as 8
Secondary forming operations threading
rolled machined
Steps to Manufacture
Heat treatment after Cold Forming
Annealing relieve stress
re-crystallize
normalize
Hardening increase the hardness after forming
Steps to Manufacture
Metal Removing Hard Surfaces
turning grinding honing lapping
Soft Surfaces turning drilling milling
Steps to Manufacture
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
Steps to Manufacture
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
Coatings and Lubricants
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
Coatings and Lubricants
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.
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