Steel Vs. Aluminum

Whether this is your first time reconsidering the injection mold tooling material that you are using or it's your first time working with injection molding, it's always a good idea to consider the various options that are available to understand what kind of 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: aluminum and P20 steel. We will be outlining why each is the best for the purpose they are intended for.

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

P20 steel is the material most commonly used for molds in plastic manufacturing based on its unique characteristics. The following are some of its significant 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, enabling 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, making it more desirable than other materials, and is one of the best to find such high-performance metals for critical industry processes.

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

Most people are surprised to learn that aluminum offers leveraged advantages. 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, allowing for more mold components to be placed.

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

Aluminum's heat treatment process is much better than steel since it doesn't need to be sent out to get annealed. Anneas is a 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, they are capable of producing only one to two thousand units. On the other hand, steel can guarantee a minimum of 50,000 units. Therefore, if you just need a small production run, aluminum is 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 there is relatively limited texture selection compared to steel. Carving more than a single undercut can also 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 can cause more differences 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, leading to higher tooling costs. To get aluminum to the same hardness level as steel, it must either be plated with nickel or anodized.

Whether you are considering aluminum or steel, it is essential to remember that most molds are made precisely using a Computer Numerical Control (CNC) tooling machine. These computer-programmed machines automatically run and make special finishings, cavities, and cuts to a block of material using saws, drills, and/or other tools. It is essential to choose a material that a CNC machine can cut. Also, more complex materials such as P20 need more effort and special tools to be milled than aluminum, increasing the overall cost.

It is up to you to decide which route 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 for your project. Your selection can save you money in both the short and long term.