Some Like it Cold

Cold forming, also known as cold forging or cold working, encompasses all metalworking processes that shape metal anywhere from just below its recrystallization temperature down to room temperature. Where hot forming allows the metal to recrystallize into the new shape, cold forming changes the pattern of the crystalline structure within the material through bending, compressing or other shaping actions, increasing the ultimate tensile strength of the metal (a process known as work hardening or strain hardening). Metal that has been cold rolled—made flatter by rolling it between two high pressure rolls—can become up to 20% stronger than its original form.

Cold forming is a relatively simple procedure that can create metal parts at lower temperatures and do so without removing any material—everything is generally just compressed or stretched or bent. Where machining can remove a considerable amount of material from a workpiece (perhaps over 50% of a blank to form a single rivet), cold forming wastes nothing, leaving the mass of the finished piece the same as the blank it was formed from. However, some features of a part that cold forming cannot make directly can be added in a secondary operation that may remove material, such as threading.

While many cold forming operations can be conducted at room temperature, the friction created by them can increase the temperature of the metal by several hundred degrees Fahrenheit (but still cooler than the recrystallization temperature, so it is still considered “cold forming”). 

Items that are often made using cold forming include aerospace parts, bolts, electrical contacts, medical components, nuts, rivets, and screws, among many others.

Types of Cold Forming Processes

Cold forming techniques are usually classified into four major groups: bending, drawing, shearing, and squeezing. The following are some of the cold forming processes that are used, listed with their classifications:

  • Angle Bending (Bending)
  • Blanking (Shearing)
  • Burnishing (Squeezing)
  • Coining (Squeezing)
  • Cutoff (Shearing)
  • Dinking (Shearing)
  • Draw and Compression (Bending)
  • Embossing (Drawing)
  • Extrusion (Squeezing)
  • Flanging (Bending)
  • Forging (Squeezing)
  • Heading (Squeezing)
  • Hubbing (Squeezing)
  • Ironing (Drawing)
  • Lancing (Shearing)
  • Metal Spinning (Drawing)
  • Nibbling (Shearing)
  • Notching (Shearing)
  • Peening (Squeezing)
  • Perforating (Shearing)
  • Piercing (Shearing)
  • Punching (Shearing)
  • Riveting (Squeezing)
  • Roll Bending (Bending)
  • Roll Forming (Bending)
  • Rolling (Squeezing)
  • Seaming (Bending)
  • Shaving (Shearing)
  • Sizing (Squeezing)
  • Slitting (Shearing)
  • Staking (Squeezing)
  • Stamping (Squeezing)
  • Straightening (Bending)
  • Stretch Forming (Drawing)
  • Superplastic Forming (Drawing)
  • Swaging (Squeezing)
  • Thread Rolling (Squeezing)
  • Trimming (Shearing)
  • Tube Drawing (Drawing)
  • Wire Drawing (Drawing)

Metals That Can Be Cold Formed

While some materials are too brittle for cold forming—like cast iron—others are very suited to the method, such as soft metals that are difficult to machine because they have chip-breaking issues that can jam conventional machine tools.

Some metals that are ideal for cold forming include:

  • Alloy Steel (1045, 1117, 1215, 4140, 4150, 4340, 8620, H-11)
  • Aluminum (2024, 6061)
  • Brass and Naval Brass
  • Bronze
  • Carbon Steel (with a carbon content below .5%)
  • Copper
  • Gold, Palladium, and other precious metals
  • Lead
  • Nickel and Nickel Alloys
  • Stainless Steel (316, 416, 17-4)
  • Tantalum
  • Tin
  • Titanium
  • Tool Steel and other materials up to 44 HRC

Disadvantages of Cold Forming

Despite its growing popularity, cold forming does have a few disadvantages compared to hot forming that metalworkers should be aware of, including the following:

  • Heavier equipment is required that can exert higher pressure due to the hardness of the metal.
  • It’s more expensive up front than hot forming (though hot forming may require secondary operations that can bring up the overall costs).
  • Because of the costs, cold forming is generally reserved for large volume manufacturing.
  • It is limited to only certain types of material.
  • The metal becomes less ductile and malleable.
  • While becoming harder, the metal also becomes more brittle.
  • Cold forming can potentially crack or even break the workpiece.
  • Metal surfaces must be cleaned and free of dirt, scale, and imperfections.
  • Not a good solution for creating custom pieces because the metal isn’t malleable.
  • The surface of cold forged parts may have to be heated afterwards to allow for some types of finishing work.
  • Annealing—heating and cooling—may be required to relieve stress from the workpiece, adding additional costs.
  • Cold forming metal leads to the condition known as springback, where the part moves back slightly towards its original shape after deformation. This must be compensated for in some way, such as overbending an angle so it will settle to the desired position.

Advantages of Cold Forming

Compared to hot forming and machining, cold forming has many advantages, including:

  • It can usually be performed at room temperature.
  • It can create harder parts.
  • It can create parts with a higher yield point.
  • It increases the tensile strength of the metal through strain hardening.
  • It creates a superior surface finish on the product.
  • It is a high-speed process. For example, one or two parts might be created per minute through machining, compared to 50 to 400 parts per minute in cold forming.
  • It produces consistent parts.
  • It provides for better control of the final dimensions of the part.
  • It is a much safer process because of the lower temperatures.
  • It is cost effective since no heating of the metal is required.
  • Most secondary operations are eliminated, giving additional savings in money and time.
  • There is no waste of material—nothing is machined off, except possibly during a secondary process. The same amount of metal that was in the blank is in the finished part.
  • It is ideal for working with precious metals like gold, silver, and palladium, since there is no waste of material.
  • There is less chance of contamination of the metal.
  • Dies used in cold forming last longer than those used in hot forming.
  • There is no risk of warping metal with cold forming like there is with hot forming.
  • Cold formed metal has a natural radius on almost every edge, corner and undercut due to the material flow as it fills a die under the extreme pressures used in cold forming.
  • Cold forming techniques are usually simpler to perform than hot working ones.

Picking the Perfect Process for Your Projects

Which is better, cold forming or hot forming? The answer is simple: it depends.

Different types of metal respond differently under each type of forming, so that is a critical question to look at before buying equipment. If your operation works frequently in several different materials, you may need to consider both hot and cold forming machinery.

The ultimate determination for the process is the type of product you need to produce. Does it need to be malleable? Does it need to be extremely hard? Is their risk of damage if it is too brittle or too soft? All potential factors need to be considered before settling on a final solution to your forming needs. As with any metalworking equipment purchase, be sure to consult with friends in the industry and trusted machinery dealers to look carefully at all the advantages and disadvantages of each process to help you select the ideal one for your upcoming projects and overall operation.