Barton International

What’s the Difference Between Hot and Cold Forging?

Introduction

Hot and cold forging are ancient processes that remain vital manufacturing methods to this day. Discover the definitions, advantages, and disadvantages for each forging type.

Forging is a process that changes metal through compression. Each forging type is classified by temperature, from cold to warm to hot. Hammers such as power hammers or dies are the traditional tools used to deliver the necessary blows that shape the metal. 

Forging is an ancient skill and has been performed by smiths for thousands of years. Traditional forged parts began with tools, weapons, and jewellery. However, things have changed in recent years. Forging has since evolved to manufacturing. During the industrial revolution, it began revolving around large machinery and mechanisms for production.

Metal forging remains a major worldwide industry. Its necessity will always be in demand, while components of metal manufacturing require the highest strength. But the question is, which type of forging does your business require?

Discover the key differences behind hot and cold metal forging. This informative comparison guide explains the advantages and disadvantages of both cold and hot forging.

What Is Hot Forging?

Hot forging is when the metal workpiece, also known as a billet, is worked into a predetermined shape. It involves hammering, pressing, or upsetting the metal while it’s heated to at least 75% of its melting temperature.

The temperature required for hot forging depends on the type of metal you’re working with. For example:

Steel – Up to 1150°C

Al-Alloys – 360 to 520°C

Cu-Alloys – 700 to 800°C

When hot forging, you start by:

  • Heating the dies to prevent loss of temperature during the process.
  • Ensure crystallisation doesn’t occur until the foaming is finished.
  • Under intense heat, the workpiece will become more pliable and ductile.
  • Pressure the metal with the die to transform the metal.

A crucial factor to consider is managing the temperature. If the metal is allowed to get too cold, it will finish the forging and require reheating to start again.

The Advantages of Hot Forging

Hot forging is the best process for deforming metal of a high formability ratio, such as steel. Here are the main advantages.

Ductility: The workpiece can be forged into various configurations thanks to the high ductility.

Efficiency: Forging is a quicker and more effective process, especially steel.

Surface quality: Hot forging allows for a wide range of surface finishes on completion, such as polishing.

Crystallisation: Any strain hardening effects during the forging process are negated by recrystallisation.

Homogenised grain structure: Homogenised heat treatment allows metallurgical reactions to uniform the chemicals.

The Disadvantages of Hot Forging

The downside of the hot forging process are as follows:

Additional costs: The high-intensity heat required for hot forging requires time, money, and energy.

Dimensional tolerance: The dimensional tolerance is less precise.

Warping: Due to the high temperature, warping can become an issue if the forger is not careful during the cooling process.

Grain structure: The grain structure is varied and can be unreliable.

Unprecedented reactions: The metal can react with the surrounding atmosphere, known as scale formation.

The manufacturing of metals offers a range of production techniques at different stages of the production journey. These stages can be divided into fabrication, forging, formwork, and casting. Here are some specific examples of metal manufacturing.

Metal forging remains a major worldwide industry. Its necessity will always be in demand, while components of metal manufacturing require the highest strength.

What Is Cold Forging?

Cold forging is the process of deforming metal at low temperatures, typically room temperature. Compressive forces pressure the metal between a punch and a die till the metal conforms to the die’s contours.

Techniques used during cold forging include:

Whenever cold forging, important aspects to consider are:

Annealing: Annealing makes the metal softer to improve the material flow. Apply this intermediately during the hardening process before the forging is finished. 

Bonderize: ‘Bonderizing’ improves the surface area as a coating process to help strengthen the metal.

Material colume: Control over material volume will reduce damage and overall stress upon the material.

Lubrication: Apply lubrication to protect the material from damage during metal-on-metal procedures.

The Advantages of Cold Forging

Cold forging is often preferred with softer metals such as aluminium. Here are some key benefits of opting for this type of forging:

Better finish: Cold forging parts require very little to no finishing work.

Net material: Cold forging produces net shapes or near net shapes for overall material saving.

Cheaper: It’s typically cheaper than hot forging because you don’t have to heat the metal. Plus, there are fewer processes involved.

Zero contamination: Cold forging is much less likely to have any contamination issues.

Reproducibility: Cold forging can be reproduced reliably and consistently.

Dimensional accuracy: Cold forging has close dimensional tolerances for increased control.

The Disadvantages of Cold Forging

On the flip side, cold forging also has its disadvantages:

Cleaning: The forger must ensure the metal surface is clean before they begin forging.

Less Ductile: The metal is much less ductile compared to hot forging.

Residual stress: Residual stress can occur during the deformation process.

Equipment: Heavier and more powerful machinery and tools are required.

Hot or Cold Forging for Manufacturing?

Overall, both hot and cold forging have various advantages and disadvantages that complement each other. While cold forging increases the strength of the material, it’s less flexible. In contrast, hot forging can create more complex shapes but is more expensive and requires extra energy to heat the metal at very high intensities.

The answer to the question solely depends on your individual needs. If you need a hand deciding between hot and cold forging, Barton International is here to help. Since 1898, we’ve specialised in the forgery of metal. As a 100% British owned business operating for over 100 years, we understand the importance of metal forgery in the manufacturing industry.

To find out more about our metal forging services, please get in touch. A member of our team will be happy to answer any of your questions.     

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