Cold Forging Process: Principles, Advantages, Applications, and Key Technologies

Forging is a manufacturing process in which compressive forces are applied to a solid metal workpiece, causing plastic deformation and reshaping it into the desired form. Unlike casting (pouring molten metal) or machining (removing material), forging refines the grain structure of the metal as it flows, resulting in more uniform mechanical properties and higher strength—often superior to cast or machined components of the same material.

Based on processing temperature, forging is generally divided into three categories:

• Cold Forging:Performed at room temperature up to the lower limit of the metal’s recrystallization temperature (no high-temperature heating).
• Warm Forging:Conducted above room temperature but below recrystallization (typically 300–800°C), balancing accuracy and deformation effort.
• Hot Forging:Executed above the metal’s recrystallization temperature (e.g., steel 800–1250°C, copper alloys 700–800°C).

1.0Core Definition and Characteristics of Cold Forging

Cold forging, also known as cold forming, is a precision forming process performed at room temperature or below the recrystallization threshold (e.g., steel <400°C, aluminum 100–200°C, copper 200–300°C). Under high pressure from a die set (typically 500–2000 MPa), the metal undergoes plastic flow, producing components of the required shape and size with little to no material removal. The process relies on plastic deformation at low temperatures to achieve near-net-shape results.

Key characteristics include:

• Defined Temperature Range:No high-temperature heating is required; forming is done at room or near-room temperature. Friction may raise the metal temperature slightly to 250–300°C, but this remains below recrystallization levels.
• High-Pressure Deformation:Mechanical or hydraulic presses apply axial or radial loads, forcing atoms to realign along the die cavity. The process follows the principle of volume constancy (minimal mass or volume loss).
• High Accuracy and Fine Surface Finish:Dimensional accuracy can reach IT6–IT9 (tolerances ±0.01–±0.1 mm). Surface roughness values can be as low as Ra 0.4–3.2 μm, often eliminating or minimizing the need for secondary machining such as drilling or grinding.
• High Material Utilization:Material utilization rates reach 85–95%, far exceeding traditional machining (50–70%), which significantly reduces scrap.

2.0Working Principle of Cold Forging

The essence of cold forging is the plastic flow of metals at low temperatures. The process typically involves three key stages:

• Billet Preparation:
  • Raw Material:Select ductile metals such as wire rod or bar stock (commonly low-carbon steel, aluminum, or copper alloys), cut into billets of fixed length.
  • Surface Treatment:Apply treatments when necessary—such as phosphating and soaping for steel, or solid lubricant coatings for aluminum—to reduce the friction coefficient between metal and die (kept below 0.05). This minimizes die wear and improves metal flow.
• Die Pressing:
  • Place the billet into a precisely engineered die cavity, and apply high pressure using a mechanical or hydraulic press.
  • The metal gradually fills the die cavity, transforming from a billet into a near-net-shape part.
  • For complex components, multiple forming stages (e.g., pre-forging → final forging) are required. This avoids excessive deformation in one step (generally limited to ≤50%), which could otherwise cause cracking.
• Post-Processing:
  • Stress Relief:Cold forging induces work hardening (increased strength and hardness, but reduced ductility). Some parts require low-temperature annealing (e.g., steel heated to 200–300°C) to restore plasticity.
  • Finishing Operations:For components with extremely tight tolerances, additional fine pressing, polishing, or other secondary processes may be applied to further enhance dimensional accuracy and surface quality.

Recommended Reading：Forging Process Explained: Types and Techniques

3.0Advantages and Limitations of Cold Forging

The strengths and weaknesses of cold forging are directly linked to its low-temperature forming characteristics. The comparison is as follows:

4.0Eight Core Cold Forging Processes and Their Industrial Applications

With the advancement of metal forming technologies, cold forging has developed into several specialized processes. Each is optimized for specific forming requirements, with the common goal of achieving high-efficiency production with minimal or no secondary machining.  

Extrusion:

• Principle:A billet is subjected to extremely high pressures (up to 20,000 kN, or ~2007 tons), forcing metal through a die opening to form a part profile, later cut to length.
• Subtypes:
  • Forward Extrusion:Metal flows in the same direction as the applied pressure; suitable for solid long parts (e.g., shafts).
  • Backward Extrusion:Metal flows opposite to the applied pressure; used for parts with thicker bottoms, such as bearing sleeves or cups.
  • Lateral Extrusion:Pressure is applied perpendicular to the main axis, adding secondary features such as side holes or ribs.
• Applications:Efficient for forming complex cross-section components like multi-tooth gears and hollow tubing.

5.0Lubricant Selection as a Critical Support Process in Cold Forging

Although cold forging is performed at room temperature, operations such as bending and extrusion generate frictional heat. Lubricants are therefore essential to ensure process stability, prevent defects, and extend die life.

• Functions:Reduce forming defects, minimize sticking, and improve tool longevity.
• Common Types:
  • Chemical Coatings:Zinc phosphate, phosphate, calcium aluminate, aluminum fluoride (suitable for steel and aluminum, forming a protective wear-resistant layer).
  • Polymer/Solid Lubricants:Various polymer coatings, graphite lubricants, and graphite-free types (graphite offers strong lubrication; graphite-free coatings are preferred for high-cleanliness applications such as electronic parts).
• Selection Principles:Must be tailored to metal type (e.g., steel uses phosphating soaping; aluminum uses solid lubricants) and process type (e.g., extrusion requires high-pressure-resistant lubricants, drawing requires low-friction lubricants). Complex processes may require custom lubricant formulations.

6.0Typical Applications of Cold Forging

Thanks to its precision, efficiency, and material savings, cold forging is widely adopted in industries where components must meet high standards of accuracy and strength. The automotive industry alone accounts for more than 60% of cold-forged parts.

7.0Key Differences Between Cold Forging and Hot Forging

Cold and hot forging differ fundamentally in processing temperature, deformation characteristics, achievable accuracy, and suitable applications. The comparison is as follows:

8.0Key Technologies in Cold Forging

The successful implementation of cold forging relies on three core technologies that directly determine part quality and production efficiency:

Die Design and Manufacturing:

• Die Materials:High-strength tool steels such as Cr12MoV or DC53 are used. Vacuum heat treatment is applied to achieve hardness levels of HRC 58–62, ensuring the dies can withstand high pressures.
• Cavity Design:Metal flow must be simulated to prevent folding, cracking, or other defects. For complex parts, transitional fillets are incorporated to guide uniform filling of the die cavity.

Lubrication Technology:

• Core Objective:Maintain a friction coefficient below 0.05 between the metal and die to minimize wear and extend die life.
• Common Solutions:Steel components typically undergo phosphating + soaping treatment, forming a phosphate film that absorbs the soap layer. Aluminum components are coated with solid lubricants such as molybdenum disulfide (MoS₂).

Materal Selection and Pre-Treatment:

• Material Requirements:Metals with good ductility and low yield-to-tensile strength ratios are preferred, such as low-carbon steels (10#, 20#), low-alloy steels (20Cr, 40Cr), pure aluminum (1060), and brass (H62).
• Pre-Treatment:High-carbon and high-alloy steels require spheroidizing annealing before forging to reduce hardness, improve ductility, and prevent cracking during deformation.

9.0Cold Forging Process: Frequently Asked Questions (FAQ)

Q1: What is the main difference between cold forging and hot forging?

A1: Cold forging is carried out at room temperature or below the metal’s recrystallization point, offering high dimensional accuracy and excellent surface finish. Hot forging, performed above the recrystallization temperature, allows larger deformation with lower force but typically requires secondary machining for accuracy.

Q2: Which materials are most suitable for cold forging?

A2: Cold forging works best with ductile metals such as low-carbon steels, aluminum, copper, and their alloys. Brittle materials like cast iron are not suitable.

Q3: What are the biggest advantages of cold forging?

A3: High precision (IT6–IT9), smooth surfaces (Ra 0.4–3.2 μm), material savings (utilization up to 95%), and low energy consumption (only 1/5–1/10 of hot forging).

Q4: What are the main limitations of cold forging?

A4: High die costs, limited material options, reduced ductility due to work hardening, and complex shapes often requiring multiple forging stages.

Q5: In which industries is cold forging most widely applied?
A5: The automotive sector dominates (over 60% of parts), followed by electronics, machinery, hand tools, and heavy equipment manufacturing.

 

References

https://www.iqsdirectory.com/articles/forging/cold-forging.html

https://www.tfgusa.com/cold-forging/#FAQs

https://www.fictiv.com/articles/hot-forging-vs-cold-forging

https://www.forcebeyond.com/cold-forging/

https://ecenarro.com/blog-en/from-machining-to-cold-forging/