Metal forging is a process that has been used for centuries to create strong and durable metal products.
While there are many different metal forging methods available today, the two main types that will be discussed here are cold forging and hot forging.
Due to their efficiency and cost-effectiveness, both methods have become an essential component of the fabrication process.
In the following sections, we will explore the differences between the two techniques, specifically their advantages, disadvantages, key differences, and when each one should be used.
Cold forging is a metalworking process that is performed near or at room temperature, below the metal’s recrystallization point.
During the process, cooler forging temperatures are commonly used to form raw metals into desired shapes.
The process typically requires two dies and a press, which together shape and compress the metal between them.
The cold forging process involves the following steps:
While the above steps are generally employed during the cold forging process, many other forming techniques can be added to deliver a more unique and finished component.
Let’s go over the most widely used ones in the following sections!
Rolling is a forming process that involves passing the sheet metal between two or more rolls to reduce its thickness and shape it into a desired product.
There are several different types of rolling methods, including flat rolling, ring rolling, roll bending, profile rolling, and controlled rolling.
This forming process offers several advantages, including low-cost production, minimal wastage of materials, and high accuracy in terms of size and shape precision.
In metalwork, drawing refers to the process of stretching metal into the desired shapes and sizes.
It can be used for making products like wire mesh, screws, nuts and bolts, and other complex engineering parts.
Drawing done in cold form is often preferred because it does not require any additional heat treatment to achieve final product strength requirements.
Forge pressing is the process of using pressure to shape metal into a specific form.
In some cases, this process can be used to join together two or more pieces of metal.
This type of forming is often used in industrial applications when large-scale production of parts needs to take place quickly and efficiently.
Metal spinning includes rotating a metal disc or tube at high speed to create a metal part. The resulting product will be axially symmetric.
The process is also referred to as spin forming or spinning.
It is common in the production of components for cars, aircraft, and architectural applications such as handrails and decorative trim.
The extrusion process is commonly used in the production of metal parts and components, such as pipes, rods, and tubes, in order to join two pieces of material together.
The process involves pushing a heated piece of metal through a die to create any desired shapes or contours.
During the process, an electric motor is used to push the heated metal through the die at high speeds.
This results in reduced waste when compared with other forging techniques, as well as increased accuracy in terms of the final shape and design.
Heading, also known as upset forging, is a cold-forming process used to create parts with increased strength and durability.
It involves the application of compressive forces to the end of a workpiece so that its cross-section increases in size and length while its volume remains unchanged.
Heading can be done either manually or mechanically, depending on the size and material of the workpiece being formed.
The cold forging techniques listed here are all ideal for parts that require precise tolerances or complex geometries.
In fact, cold forging should be considered anytime precise forging is needed.
Hot forging is a manufacturing process that is performed at high temperatures—above the metal’s recrystallization point.
High temperatures prevent strain hardening from occurring during the forging process.
The temperatures which are usually used during hot forging range anywhere between 950 °C-1250 °C (1742 °F-2282 °F).
The process includes the following steps:
There are many cooling methods and heat treatments that can be applied to the hot forging process. However, the most common, and perhaps the most effective one, is stamping.
Stamping is often used during the hot forging process to increase the strength of the finished product by providing additional support and structure.
The stamping process consists of several steps which must be followed to ensure accuracy and quality:
Hot forging is often used in place of machining and casting operations because it allows for better control over the finished product.
It also helps improve surface integrity and dimensional stability, reduces waste generation, improves mechanical properties, increases fatigue strength, and offers better part consistency.
Depending on the application, hot forging may be more cost-effective than other kinds of metalworking, as it is an inherently fast process that requires minimal tooling costs.
The most obvious difference between cold and hot forging lies in the temperatures that both processes employ to shape metal components.
Cold forging usually requires no more than room temperature, while the temperature used for hot forging can run up to 1150 °C (210 °F), depending on the alloy being worked with.
Of course, the exact temperatures used for each forming process vary depending on the hardness of the metal and other factors, such as lubricants or other materials added during manufacturing.
Another key difference between cold and hot forging is the way they increase the strength of the metal during each process.
For instance, cold forging increases material strength through strain hardening by introducing stress-induced plastic deformation that strengthens the material’s crystalline structure.
This process creates a more uniform grain size which enhances the mechanical properties of the component.
Hot forging, on the other hand, restricts metal from strain hardening by keeping the structure of the metal intact during its transformation into a new shape or size.
This ensures that the most appropriate yield strength is achieved, and that the resulting product isn’t too hard, while remaining highly ductile.
In the table below, you can see the pros and cons of each method.
| Cold Forging | Hot Forging |
|---|---|
| Advantages | Advantages |
| Greater dimensional accuracy High surface quality Reduced costs (no machining needed) Shorter lead times (fewer steps) Less material wastage | Superior strength Durability No additional treatments Complex geometries Stronger grain structures Customization options |
| Disadvantages | Disadvantages |
| Requires expensive metals Tooling machine limitations (only certain sizes and shapes can be achieved) Residual stress | Expensive (a large amount of energy is required to heat the metal) Material wastage (higher amounts of scrap material) Limited material selection (some metals cannot be hot forged because they become too brittle when subjected to high temperatures) Low dimensional tolerances |
The characteristics listed above will determine which process is the most suitable for your project, depending on which metal you plan to use.
Using either method for forging steel, for example, will depend on the class of steel being used, as some types of steel can be forged at room temperature while others cannot.
Cold forging should be used when softer metals are required for custom metal parts.
During cold forging, the stress on the metal is applied gradually, so there is less risk of cracking or other damage compared to similar processes like hot forging or machining.
The metals that are most suitable for cold forging are as follows:
That is not to say that some harder metals cannot be cold forged.
For instance, several types of steel—like carbon steel, alloy steel, and stainless steel—can all be cold forged with little risk of material deformation or mechanical damage.
Some of the more popular applications of cold forging include:
In general, cold forging should be used when parts have relatively simple geometries that require high precision and strength with minimal weight.
Hot forging is recommended for metals that have high formability.
In other words, for metals that can withstand heavy deformation without developing severe defects.
Since hot forging uses high temperatures and high pressure to deform metals into customizable shapes, the material used should be resistant to brittleness, cracking, and corrosion.
The most common metals used for hot forging Include:
Hot forging has a range of applications that span various industries, including automotive, aerospace, defense, energy, and medical technology.
Some of the more common applications which utilize hot forging include:
When determining whether hot forging should be used or not, there are several factors to consider.
For starters, it’s important to look at whether the material being forged can withstand extreme temperatures and pressures without losing its structural integrity.
All the metals that were previously mentioned in this section fit that description.
Second, if items require precise tolerances or close dimensional accuracy, hot forging should probably be avoided since heat can cause the material to shrink or expand unpredictably during the process.
Finally, if the application requires a high surface finish, then hot forging may not be as desirable as cold forging since the latter allows for a more polished look.
Cold forging and hot forging are both effective manufacturing processes that use metal to create intricate parts.
While the two methods require the same starting material (metal), their end result is vastly different.
Cold forging generally requires less energy, produces a superior surface finish, and can create complex shapes in a single operation, while hot forging is better suited for larger parts with greater strength requirements and more ductility.
Ultimately, the choice of which process to use depends on the desired application and should be determined carefully to ensure optimal results.
Before choosing which method is right for your project, consider reaching out to a metal manufacturer who has expertise and experience working with both processes.
From a contract manufacturing firm, BuntyLLC evolved into a full service custom machined, forged and cast metal parts fabrication enterprise. We supply global solutions from our headquarters in Greenville, South Carolina.
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