Aluminum Molds Vs. Steel Molds | Plastic Injection Molding

Aluminum Molds vs. Steel Molds: Five Critical Points of Comparison for Product Designers and Engineers 

Choosing between steel and aluminum tooling is a critical decision for product designers. This is because the tool impacts part quality, cycle time, cost, and even time-to-market.

For more information, please visit WIT MOLD.

Therefore, understanding how each material will perform during the injection molding process will help you to make more informed decisions&#;for today and future needs.

In this blog we provide a critical comparison between P20 Steel and QC-10 Aluminum for five key areas:

• USA vs China: Where you quote tooling impacts the cost/time to create and change molds
• Tool life comparison: how many parts can be produced with steel vs. aluminum molds?
• Thermal conductivity and the ability to control the temperature of each mold type can influence fill, form, and cycle time
• Part size and complexity by mold type
• Material and surface finish options for aluminum and steel

Where you quote tooling matters: USA vs. China

Deciding between an overseas and domestic supplier for tooling can influence your entire injection molding project&#;from supply chain management and production cost to the time it takes to build and change your mold.

For one, vast discrepancies in material cost between the USA and other countries, notably for this discussion, between aluminum and steel as raw material.*

 

In the USA, for example, aluminum is the default material used to create molds because it is cheaper than steel. Conversely, in China raw steel is used as the default material because it is cheaper than aluminum. One country uses a soft material while the other uses a hard material.

Therefore, if you quote tooling in different locations, chances are you will not be looking at an apples-to-apples comparison. This is because soft and hard materials perform differently during the injection molding process. Which can impact cycle time, cost, and time-to-market.

Cost and time to create or change steel molds vs. aluminum molds

When quoting tooling there are two critical costs to consider. First, the initial cost to create the mold. And second, the cost to make changes to the mold. Below is a comparison of cost and time for steel vs. aluminum tooling.

 

Cost  to create or change steel molds vs. aluminum molds

The cost to create an aluminum mold is about ¼ to ½ the cost of creating a steel mold. In general, aluminum tooling will prove to be the most cost-effective option even when comparing a quote from a China-based vendor for steel tooling to a USA aluminum quote.

The type of mold you choose can also impact the cost of making changes. For example, aluminum tooling is roughly 1/10 the cost of changing a steel tool&#;regardless of where it is manufactured. This is because it takes much longer and is harder to machine steel versus aluminum.

Time to create or change steel molds vs. aluminum molds

The time required to create an aluminum tool, on average, is about 15-25 business days. In contrast, the average time required to create a steel tool is about 35-60 business days.

On average, the time required to change an aluminum tool is about 5 business days. Compared to an average of 20 business days required to change a steel tool.

What is the tool life of P20 Steel Tooling vs. QC-10 Aluminum Tooling?

(And how much volume can I produce with each tool before investing more money to keep it running?)

 

Please note, the estimated volume for steel and aluminum molds will depend on material selection for use during the injection molding process:

• P20 Steel tooling, average life of 50,000-100,000 parts
• QC-10 Aluminum tooling, average life of 10,000-25,000 parts

According to Taylor Foster, Account Executive at Xcentric, quantity often determines whether to choose steel or aluminum tooling.

&#;Simply put, steel tooling will always offer a longer tool life than aluminum tooling,&#; Taylor said. &#;This means, it can produce a higher volume of parts before the mold requires maintenance due to wear and tear, or total replacement.&#;

Therefore, if you are going to need hundreds of thousands&#;or millions of parts in a year, steel tooling is likely going to be the best option.

Alternatively, Taylor said &#;if you do not anticipate this level of production volume, and instead plan to stay in the 10s of thousands over the next year or so, then aluminum will be the best option.&#;

When moving parts to production, product designers are faced with a choice: steel or aluminum tooling? Watch the webinar to learn common misconceptions between the two along with a side-by-side comparison that will help you to make more informed decisions.

Thermal Conductivity of Aluminum is 5 times greater than Steel

Thermal conductivity is a material&#;s intrinsic ability to transfer heat. The thermal conductivity of aluminum is about five times greater than steel. This is important because it directly impacts the fill, flow, and cycle time of aluminum molds.

Fill, flow, and cycle time: benefits of aluminum molds

• Material fills the mold faster and more evenly than steel molds
• Plastic can flow longer distances with less injection pressure in aluminum
• Cycle time is less due to quicker heating and cooling, meaning faster creation of your parts using aluminum molds
• Parts have minimal warp and much better dimensional stability &#; giving a higher acceptance rate on parts

Aluminum molds&#; superior thermal control can reduce cycle time up to 40%

In an article published in Moldmaking Technology1, Douglas Bryce provides details about an IBM tooling study of aluminum molds for high-volume production. The five-year study used identical steel and aluminum molds to produce identical plastic parts.

According to the study, the aluminum molds cost up to 50% less to build than steel molds and produced higher-quality parts. Further, the aluminum molds&#; superior thermal control made it easier to manipulate areas of the tooling which resulted in cycle times up to 25-40% less than the steel molds.

Achieve better temperature control with aluminum molds, reduce cost and cycle time

Controlling the temperature of a mold is often a challenge because it depends on variables such as the material, design, ejection process, and other issues within the tool.

Still, achieving better temperature control can help to optimize cost and reduce cycle time. This has been tested and proven in studies like the one featured in Flow Front by Claudia Zironi2. (Table 1)

QC-10 Aluminum vs. P20 Steel; Polystyrene vs. Nylon

In this study, Claudia Zironi conducted a side-by-side comparison of two materials, polystyrene and nylon, being injected into a QC-10 aluminum mold and a P20 steel mold.

Both materials were run in the same process to showcase a completed part within the same spiral tool design. When completed, the overall cycle time for QC-10 Aluminum was much faster than that of the P20 Steel.

Per the study, the P20 steel molds retain more temperature during the molding process than the QC-10 aluminum molds.

Also, recovery after each shot does not come down as fast as the temperature in aluminum tooling. This is because thermal temperature releases out of aluminum faster than steel. Because of this, there was a 20-second freeze time in the P20 steel to ensure the part was cooled for ejection.

Table 1 Claudia Zironi, Flowfront Magazine, &#;Competitive Advantages of Aluminum Molds for Injection Molding Applications: Process Simulation Used to Evaluate Cycle Times,&#; April .

Part size and complexity by mold type

Based on the data discussed so far, aluminum has more to offer than prototyping and low-volume production. Though it is softer than steel, aluminum molds can be a cost- and time-efficient option for high-volume production and larger parts.

Of course, there are applications where a steel mold would be a more optimal choice.

Will the type of tooling limit material selection, surface finish, or secondary operations? 

Choosing aluminum tooling instead of steel tooling will not drastically&#;if at all, compromise your options for material, finish, or secondary operations. Here is a brief overview when comparing P20 steel and QC-10 Aluminum tooling.

Plastic Material Selection

In general, you can expect the same material options for both steel and aluminum tooling. Please note two exceptions where steel tooling is likely to be the best option due to wear and tear:

•  Exotic materials like Ultem which requires very high heat
• Abrasive material such as glass fill or other ad

For more detailed information about materials, visit Xcentric&#;s plastic material selection guide.

Surface finish options

Whether using steel or aluminum, your options for surface finish will be the same. Please note, to achieve an SPI A-1 finish, you need special facilities and/or equipment.

Are you interested in learning more about automotive mould tooling? Contact us today to secure an expert consultation!

Also, Finish and clarity are reliant on the material you choose; some materials are not capable of achieving an optically clear finish no matter the level of polish used.

Choosing the optimal surface finish for your material is critical when designing plastic parts for injection molding. Our 8-piece surface finish plaques can help you to make more informed decisions early in the process.

Aluminum molds advantage: flow and fill rates

Aluminum molds demonstrate better thermal conductivity, flow rate, and fill advantages over steel molds. Which makes aluminum a better option when you are producing long, large parts.

Also, considering the superior temperature control, aluminum is a better option for part designs with complex geometries that could cause fill issues.

Steel molds advantage: thin walls and complex features

In contrast to aluminum, steel tooling proves to be a more effective for injection-molded parts and tooling that require extremely thin walls. This is because of the increased hardness of the mold material. The thin features and areas in the tool will hold up much better to the pressure during the molding process when using steel.

Conclusion: Steel Molds vs. Aluminum Molds

In conclusion, aluminum molds provide value beyond prototyping. Instead of choosing steel molds for high-volume production, consider aluminum molds instead. They prove to be a cost- and time-effective solution for plastic injection molding.

Xcentric is located entirely in the USA with two production facilities in Michigan. Though we specialize in aluminum tooling, we also offer steel tooling. Our on-site material experts are eager to help you make the most informed decision for your next injection molding project. Please contact an Xcentric Application Engineer with questions or concerns. We are here to help bring your concept to market on time and on budget.

Taylor Foster is an Account Executive at Xcentric. He has a background in Mechanical Engineering and Business, attended the University of Kentucky, and has been working in the manufacturing industry, specializing in injection molding consultation and education as well as customer experience for the past 2 years. Get connected on LinkedIn with Taylor Foster

Working on a project?

Let us help you get that first prototype underway and have that part in your hands in as few as five days. Our engineers help you through the design process. Get your project started now!

1. Douglas Bryce, Moldmaking Technology, &#;Why Offer Aluminum Molds for Production&#;, April
2. Claudia Zironi, Flowfront Magazine, &#;Competitive Advantages of Aluminum Molds for Injection Molding Applications: Process Simulation Used to Evaluate Cycle Times&#;, April

* While steel as a raw material is cheaper than aluminum in both geographies, several other factors including market share, labor, and production costs must be factored into the material of choice in each country.

Production aluminum tooling has become a cost-effective technology solution for the entire supply chain in high-volume automotive applications, freeing up production capacity, driving cycle-time reduction and reducing total program cost. 

When properly executed, aluminum tooling brings massive efficiencies and cost savings to the molding process. First, consider this comparison: a steel mold designed to run 150,000 shots per year with a 50-second cycle time would need to run 95 days to produce the necessary 1,584 shots per day. Using a very conservative estimate, that same part in an aluminum mold would run a 35-second cycle time, so producing the same number of shots would only require 66 days. This equates to nearly 700 hours saved. In other words, the aluminum tooling has created free capacity. In addition, an aluminum mold is half the weight of a P-20 steel mold, resulting in less wear and tear on molding machines and crane equipment, which further saves a shop energy and other costs. 

Despite these benefits, misconceptions still persist about the availability of aluminum grades suitable for high-volume molding projects and about aluminum&#;s effectiveness in high-volume and large-part applications. The wheel liner on the Honda Civic is a well-known project that serves as proof of the success of aluminum tooling in a high-volume application. The part for this project measured 44 by 13 by 24 inches, and the mold was cut from a forged -series Alumold block measuring 70 by 52 by 31 inches, the largest block ever forged to produce a high-volume aluminum production injection mold. This mold withstood more than 597,000 shots before it was retired. 

There are essential best practices for using aluminum as a mold material that only come with experience, however. For example, our shop has found that olefin materials (polypropylene, polyethylene and thermoplastic olefin) are best suited for aluminum tooling in higher volume applications. Crystalline materials with glass filler can also be used, but in our experience, the mold will wear more quickly.

The single most important best practice when making the move to aluminum tooling may be to develop a true partnership among the OEM, molder and mold builder involved in a project, establishing and sharing roles, responsibilities and expectations. Without buy-in from all parties, an aluminum mold project is less likely to succeed. 

Change of Plans
A business plan can ease the execution of aluminum tooling throughout a customer&#;s supplier base, as it requires changes to a molder&#;s machine operating guidelines, and service and maintenance procedures. Training of molding personnel (or, more accurately, re-training, often led by an experienced mold builder) will be needed with the first job, because once the potential for a massive reduction in cycle time is realized, different production techniques may make sense, which in turn, can drive investment decisions. 

For example, if the molder is producing a less complex part, it may make sense to limit the amount of secondary operations performed at the machine. The logic here is that the full benefit of the potential cycle-time savings can be realized, and then any secondary operations can be completed offline, at a different location in the plant.

When we built the mold for the Honda Accord&#;s rear deck 10 years ago, the mold was used in a production cell that was originally designed for a P-20 steel tool. While the aluminum tool produced an impressive 20-percent cycle-time savings over the course of nearly 900,000 shots before the tool was retired, the potential for even more significant cycle time savings was lost due to the number of secondary operations that were performed on the part in the cell. The molder would have needed to add more manpower at the cell to realize that additional time savings, but it chose not to do so. 

Several design and processing considerations should be taken into account when building an mold from aluminum instead of a comparable steel, including:

&#; Establishing new operating press guidelines for presses that normally use steel molds. This requires working closely with the molder to test and set the new protocols which allow for the softer material&#;s different thermal expansion rates and thermal conductivity. If you&#;re an automotive molder using aluminum for the first time and you treat the aluminum like you would steel, you&#;ll likely fail. 
&#; Adjusting the design of parting lines and the part&#;s periphery to help distribute the tonnage of the machine, despite the fact that aluminum&#;s compressive strength can easily withstand the rigors of the injection molding process. 
&#; Distributing water differently to optimize its distribution within the tool.
&#; Engineering tool growth into the tooling. For example, changes in parting lines, locks and many other items need to be considered when using hybrid aluminum tooling because of the differences in each material&#;s coefficient of thermal expansion.
&#; Slightly increasing tool size to account for molding pressures. 

The bottom line is that moldmakers today continue to fight against the oversimplified label of &#;supplier of commodities&#; placed upon them. One way to win that battle is to learn and become proficient in the design and construction of aluminum molds for high-volume automotive applications, which will bring significant added value to the production process. 

If you are looking for more details, kindly visit china automotive plastic mold tool.