Steel Vs. Aluminum

Whether this is your first time to reconsider the injection mold tooling material that you are using or it's your first time to work with injection molding, it's always a good idea to consider that various options that are available to understand what kind of an impact they can make to your overall production process. In this article, we will be discussing the pros and cons of working with the two tools: aluminium and P20 steel. We will be outlining why each is the best for the purpose they are intended for.

To better understand the various pros and cons that are involved with selecting steel or aluminium for injection molding, it is very important to note that mold materials all have different applications and properties. In order to obtain the best results, you should select the material that is the most appropriate for the core and mold base based on the requirements of your project.

P20 steel is the material that is most commonly used for molds for the plastic manufacturing industry based on its unique characteristics. The following are some of its major properties:
  • Good thermal stability
  • Good resistance to wear and tear
  • Good corrosion resistance
  • Heat treatment potential after machining
  • Good polishing ability
  • Hardness

P20 material is a low alloy steel that is very versatile and characterized by its moderate strength level and hardness. Typically, it is sold in a pre-hardened state at a hardness of around 40 to 50 HRC (with the Rockwell Hardness Scale going up to 100). O20 steel has a homogenous mix of alloys which enables it to obtain uniform hardness within the entire material. The presence of metals like nickel and chromium in P20 steel enhances its hardness and strength, which makes it more desirable compared to other materials and is one of the best to find such high-performance metals for critical industry processes

The major impact that the properties have on a finished part is the capacity for the mold to create thousands of parts with minimal wear and tear. That is ideal for big production runs of more than 50,000 parts.

While searching for materials for injection mold tooling, you might have encountered Berlin Copper, PAS 940, and Maraging 300. They all have properties that are similar to P20 steel, but their selection is quite specific for niche industries. The materials can be costly due to their special properties and makeup.

Most people are surprised to learn that there are leveraged advantages offered by aluminum. Some of these include the following:

The heat transfer rate of aluminum is 5x better. With improved conductivity, the cooling line position is not as critical which allows for the placement of more mold components.

Aluminum has been shown to reduce the time of the production cycle by as much as 30%.

Aluminum's heat treatment process is a lot better than steel since it doesn't need to be sent out to get annealed. Anneas is a type of heating treatment process used on metal to toughen the material and remove internal stresses.

Compared to steel, aluminum is a lot more cost-effective.

Although there are advantages to aluminum molds, it is capable of only producing one to two thousand units. Steel, on the other hand, can guarantee 50,000 units minimum. Therefore, if you just need a small production run, then aluminum will most likely be the tooling method you prefer at a fraction of what steel would cost.

However, there are downfalls to aluminum. It has a low-density nature, so compared to steel there is fairly limited texture selection. Carving more than a single undercut also can be an issue due to the surface of the mold receiving constant wear and tear. That results in modifying the whole mold instead of just one specific area, which in turn can cause more difference in the final product's output quality. After several thousand production cycles, the mold's cavities will start wearing, which will cause your product to have nonconformities, which will lead to higher tooling costs. To get aluminum to the same hardness level as steel, it would need to either be plated with nickel or anodized.

Whether you are considering aluminum or steel, it is essential to remember that a majority of molds are made precisely using a Computer Numerical Control (CNC) tooling machine. These are computer programmed machines that automatically run, and make special finishings, cavities, and cuts to a block of material through the use of saws, drills and/or other tools. It is particularly important to choose a material that a CNC machine is capable of cutting. Also, harder materials such as P20 need more effort and special tools to be milled compared to aluminium, which increases the overall cost.

It is up to you to decide which rout of tooling you want to use, but looking at the requirements of your overall project, such as the production volume, can be a great guide to help you choose the best material to use for your project. The selection you make can save you money in both the short and long term.