Steel and Metal Extrusion Vs. Cold Drawing

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Steel and Metal Extrusion Vs. Cold Drawing

steel metal extrusion cold drawing

When it comes to the steel and metal manufacturing world, the need to form metals into various shapes is a common — and sometimes challenging — requirement. Certain forms of metal are relatively easy to form into different shapes, but others — including steel tubes, steel beam and other types of channel bar — may require certain special forming processes during their manufacturing.

At Wasatch Steel, we’re proud to provide a wide range of steel bar, steel tube and numerous other steel products for any project you require them for. We’re also happy to recommend the ideal processes for any kind of metal shaping you may require, including two specific approaches that are often used for this need: Extrusion and cold drawing, which have certain similarities but also some important differences that separate them. What are each of these two processes, what are their advantages, and what are some common metals often shaped or formed using them? Here’s a general primer.

Metal Extrusion

Within the metal world, extrusion refers to a process that’s used to create complex shapes out of metal bars. By passing the bar through a die that matches the shape, some simple shapes can be made; by using more than one die (each step shaping the bar to a smaller size), more complex tube shapes can be created.

Extrusion is somewhat ideal for cases where you need strong but simplistic tubing, including things like light posts and lamp posts. Extruded metal tubes are often welded together in order to create even more complex structures, and the process can also be used to add simple holes or special shapes into a bar in certain cases.

Here are the typical steps involved in the metal extrusion process:

  • A metal billet is shaped using smelting, solidifying and rolling processes.
  • The billet is then heated for the extrusion process, making the metal more malleable and easier to shape.
  • Pressure is applied on the billet, with the dies used for the extrusion process machined with great precision to ensure a proper fit.
  • The metal is fully forced through the die, after which it cools and hardens.
  • The extruded metal is then cut into the desired length, which may require a milling step depending on the shape of the final piece.
  • Various other processes, including annealing, coating or others, may also be applied to the metal once it’s been extruded.

Extrusion may be performed on a variety of metals, but aluminum and steel are especially common materials given their strength and malleability. It has several advantages over the cold drawing process depending on your needs:

  • Extruding is a faster process than cold drawing.
  • Extrusion produces more accurate dimensions compared to cold drawing.
  • The surface of extruded metals is smoother than that of drawn metal, making it ideal for certain applications like food processing equipment and medical devices.
  • Extruded products generally cost less than cold drawn products.
  • Plastic deformation is a much smaller concern with extruded products, and it’s easier to achieve a perfectly round shape.

There are several common examples of extruded metal products found throughout our world today. Square metal tubing, for instance, is a common metal bar that’s often used for frame housing and other purposes, while steel I beams are often used in complex building applications. Other options include round tubing, 80/20 framing, channeled tubing, and various forms of metal rod and wire.

Cold Drawing

Cold drawing, on the other hand, is a process that’s similar to extrusion in some ways — for instance, the use of a metal billet that’s pre-formed prior to the process — but also differs with other major concepts. During cold drawing, the billet itself is not actually part of the process; rather, metal is fed through a series of molds, each shaped slightly differently to change the size of the metal as it’s fed through.

Since each pass produces a smaller piece of metal, you can actually force more total metal through the process compared to extrusion — however, this is offset by one key difference: Draw molding requires more passes in order to produce a finished product. Unlike extruded tubes and beams, cold drawn pieces must be pulled through the dies multiple times in order to reach their final shape; while extrusion simply forces metal through a die that matches the desired shape, draw molding requires each pass to gradually decrease in size until you reach your target.

The number of dies a billet will go through during cold drawing depends on the complexity and thickness of the metal you’re trying to produce. A billet may go through as many as 20 dies during draw molding, after which it’s often post-processed and cut to length once again — this is entirely separate from any other processes used on extruded metal bars or rods, like coating or milling.

Some advantages of cold drawing include:

  • Ability to achieve extremely tight tolerances in any metal being formed
  • Round shapes like pots, pans and containers are easy to make
  • Mechanical properties are fantastic, including both hardness and durability

However, as we noted above, the cold drawing process does leave metal vulnerable to plastic deformation. You must take great care to avoid these side effects, since they can decrease the strength and accuracy of your final product.

Properly applied to many types of metals, cold drawing is an excellent method for manufacturers who want to produce extremely accurate metal products. It’s commonly used in square and round forms of tubing, including steel and stainless steel products. It’s also regularly used to create pots and pans for major use, plus for various cans and other custom shapes.

For more on the extruding and cold drawing processes for steel and other metal shaping, or to learn about any of our steel services, speak to the staff at Wasatch Steel today.