The Cold Forging Process: Part One

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Introduction to Cold Forging

Cold forging, also known as cold forming, is a metal fabrication process in which a metal is plastically deformed at room temperature through the application of extreme pressure. This manufacturing technique not only transforms the shape of the material but also significantly improves the properties of the forged components through grain size refinement.

Throughout industrial history, cold forging has gained increasing prominence and developed into one of the most widely utilized methods for component manufacturing. The process involves work hardening, also referred to as strain hardening, which occurs due to dislocations in the metallic crystal structure during deformation. Unlike hot forging, the material's yield strength is maintained rather than decreased, ductility remains controlled, and work hardening progresses rapidly—factors that make cold forging technically challenging.

Cold Forging Process Characteristics

Executing cold forging requires substantial force, and multiple operations are frequently necessary to achieve more complex geometries. However, with appropriate lubrication, tool lifespan is considerably extended compared to hot or warm forging alternatives. The resulting grain structure exhibits enhanced strength, and repeated hardening through heat treatment becomes unnecessary due to the natural work hardening that occurs during the forming process.

Both ferrous and non-ferrous metals can undergo cold forming. The forgability of these materials and their potential deformation extent largely depend on chemical composition and annealed properties of the specific grade. Critical material properties that determine formability include hardness and ductility. An important consideration is that mechanical properties significantly improve after cold forming.

In some cases, this improvement is so substantial that material grades previously deemed unsuitable for machining, warm forging, or hot forging may develop appropriate mechanical properties for new applications after cold forming. The degree of improvement in mechanical properties partially correlates with the amount and type of deformation applied. Sections of the forging experiencing minimal deformation will show less improvement than areas subjected to greater deformation.

Materials Suitable for Cold Forging

As previously mentioned, both ferrous and non-ferrous metals can undergo cold forming. While the process accommodates various materials including brass, copper, aluminum, and precious metals, steel remains one of the most commonly cold forged materials. The tables below show the different types of steels that are most suitable for cold forging.

Table 1A. Chemical compositions of carbon steels for cold forging

Sr.	Grade	C%	Si%	Mn%	S% Max	P% Max	C%	B%	Mo%	Pb%	N%	Others
1.1	AISI 1006	0.06 Max	0.10 Max	0.25-0.40	0.05	0.04
1.2	AISI 1008	0.10 Max	0.10 Max	0.30-0.50	0.05	0.04
1.3	AISI 1010	0.08-0.13	0.10 Max	0.30-0.60	0.05	0.04
1.4	VS 14250	0.10-0.14	0.13 Max	0.21-0.45	0.04	0.03
1.5	VS 13111	0.07-0.13	0.07 Max	0.20-0.40	0.04	0.03
1.6	AISI 1015	0.13-0.18	0.15 Max	0.30-0.60	0.05	0.04
1.7	AISI 1018	0.15-0.20	0.05-0.10	0.60-0.90	0.05	0.04
1.8	EN1A	0.08-0.15	0.10 Max	0.85-1.15	0.26-0.35	0.04-0.09			0.25-0.35
1.9	EN1A	0.07-0.15	0.10 Max	0.80-1.20	0.20-0.30	0.060 Max

Table 1B. Chemical compositions of boron steels for cold forging

Sr.	Grade	C%	Si%	Mn%	S% Max	P% Max	C%	B%	Mo%	Pb%	N%	Others
2.1	AISI 10821M	0.18-0.23	0.30 max	0.80-1.10	0.03	0.03	0.10-0.20	0.0005-0.003
2.2	AISI 15B25	0.23-0.28	0.30 max	0.90-1.30	0.03	0.03	0.10-0.20	0.0005-0.003
2.3	DIN 19MnB4M	0.20-0.25	0.15-0.30	0.80-1.10	0.03	0.03	0.30-0.40	0.0006-0.003
2.4	AISI 15B41	0.36-0.44	0.15-0.30	1.35-1.65	0.03	0.03	0.10-0.20	0.0006-0.003
2.5	AISI 10B36M	0.34-0.39	0.15-0.30	0.80-1.10	0.03	0.03	0.20-0.40	0.0006-0.003
2.6	DIN 36CrB4	0.34-0.38	0.10 max	0.60-0.90	0.015	0.015	0.90-1.20	0.0015-0.003
2.7	AISI 51B35M	0.34-0.40	0.15-0.30	0.35-0.50	0.025	0.025	0.90-1.15	0.0006-0.003	0.10 Max		0.15 Max

Table 1C. Chemical compositions of alloy steels for cold forging

Sr.	Grade	C%	Si%	Mn%	S% Max	P% Max	Cr%	B%	Mo%	Pb%	N%	Others
3.1	SCM 415 H	0.12-0.18	0.15-0.35	0.55-0.90	0.03	0.03	0.85-1.25		0.15-0.35		0.25 max
3.2	SCM 435	0.32-0.39	0.15-0.30	0.55-0.90	0.03	0.03	0.80-1.25		0.15-0.35		1.30-1.80
3.3	AISI 4135	0.33-0.38	0.15-0.30	0.70-0.90	0.04	0.035	0.80-1.10		0.15-0.25		0.25 max
3.4	EN 24	0.35-0.45	0.10-0.35	0.45-0.70	0.04	0.035	0.90-1.40		0.15-0.35		1.30-1.80
3.5	AISI 4140	0.38-0.43	0.15-0.30	0.75-1.00	0.04	0.035	0.80-1.10		0.15-0.25
3.6	AISI 4140 M	0.38-0.43	0.15-0.30	0.75-1.00	0.005	0.015	0.80-1.10		0.15-0.25
3.7	AISI 5140	0.38-0.43	0.15-0.30	0.70-0.90	0.04	0.035	0.70-0.90
3.8	AISI 1541	0.36-0.44	0.15-0.30	1.35-1.65	0.05	0.04

The formability of these materials depends primarily on their chemical composition and annealed properties, with hardness and ductility being critical factors. Cold forming significantly improves mechanical properties, sometimes enabling materials previously considered unsuitable for traditional processes to find new applications. Property improvements correlate directly with deformation extent and distribution, with areas experiencing greater deformation showing more significant enhancement.

Advantages and Challenges of Cold Forging

Table 2. Advantages and associated difficulties of the cold forging process

Advantages	Difficulties
Near-net-shape forming	Extensive treatment of the work piece
Higher dimensional accuracy than with forged parts	Less degree of forming than with hot forming
Very high degree of material utilization	Complex forms difficult to realize
No scaling	Higher tool expenditure
High surface quality
High work piece strength through strain hardening
Expedient grain flow as with hot forming
No heating necessary

The cold forging process offers numerous advantages, including near-net-shape capability, superior dimensional accuracy, and excellent material utilization. The process produces high surface quality and enhanced workpiece strength through strain hardening, while maintaining optimized grain flow without requiring additional heating.

However, significant challenges exist, including extensive workpiece preparation requirements and limited forming capability compared to hot forming. Complex geometries present particular difficulties, and the process demands higher tooling costs and maintenance requirements.

Industrial Applications and Process Optimization

Cold forged components serve crucial roles across multiple sectors. In automotive manufacturing, applications include brake components, ball joints, steering parts, and engine valves. The appliance industry utilizes cold forged precision gears and assembly fasteners, while aerospace applications encompass structural rivets, engine bolts, and landing gear components. Construction and off-road equipment benefit from cold forged fasteners, transmission components, and specialized hardware.

Proper lubrication plays a crucial role in cold forging, significantly extending tool life compared to hot or warm forging processes. The resulting grain structure demonstrates superior strength, often eliminating the need for repeated heat treatment cycles due to the work hardening that occurs during forming.