Hot Forging vs. Cold Forging
How to Define Hot Forging and Cold Forging
Forging is one metal working process, its history can be traced back to 4000 BC. People must have seen this familiar picture, a block of metal were beaten into specified shape by a blacksmith with hammer, and this is the early stage forging. We can find that early stage forging only working on heated metals. As technology advances, a new forging process (Cold Forging) was invented to prevent from cracking in 1960’s. Since then, metals no longer must be heated before forging. Today, according to the working temperature, forging can be classified into hot forging, cold forging and warm forging.
Metal must be heated significantly before hot forging, its temperature can approach as high as 1200℃. Usually the headed temperature should be higher than metal’s recrystallization point, high temperature makes metal soft and easy to re-shape. Therefore, hot forging is more common used for “hard” metal, such as steel, alloy and etc.
Use of Hot Forging
Drop Forging is one typical Hot Forging, it is commonly used in rigging industry. Hot forging is proficient in volume production, because the high costs of dies must be shared by at least thousands of components to make this process viable.
- Elimination of Chemical Impurities
- Enhanced Ductility
- Homogenized Grain Structure
- Scale Formation
Possible Disadvantages of Hot Forging
- Reaction with Surrounding Atmosphere
- Varying Grain Structure
- Less Precise Tolerances
In contrast with hot forging, cold forging offers a more precise and economic metal working process. Metal does not need to heat in advance, its original temperature could be the same as surrounding atmosphere. The temperature of metal and die may both go up, as the energy of transformation has been exchanged into heat. Cold forging is also an environmentally-friendly choice for manufactures, due to its non-heated process.
There are two type of cold forging machine, one is horizontal press style, and another one is vertical press style. The vertical press style machine is more common in use, while the horizontal press style machine is designed for specialized use only.
Use of Cold Forging
The characteristic of high accuracy makes cold forging an ideal option for those manufacturers who have a high-level demand on precision. Automobile manufacturers are the most typical consumers of cold forging product, and cold forging industry has been progressing with the prosperity of automobile industry.
Advantage of Cold Forging
- Near Net Shape
- Increased Dimensional Control
- Improved Reproducibility
- Improved Interchangeability
Possible Disadvantages of Cold Forging
- High Strength Requirement for tooling
- High Powerful Requirement for Equipment
- High Cleanliness Requirement for Metal Surface
- Residual Stress may Occur
- Less Ductility
To sum up, cold forging and hot forging are two sub-class of forging, they offer similar results. Manufacturers should make their best decision according to their real needs.