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What is the difference Between Aluminum And Steel Injection Mold

Aluminum or Steel Injection Mold

You can only make wise decisions on aluminum mold vs steel mold if you know their capabilities, cost, and compatibility with manufacturing scenarios. Let’s break down this comparison by discussing different aspects.

aluminum vs steel injection mold

Why Need Aluminum or Steel Mold for Injection Molding?
First, why do we need aluminum or steel molds? Well, molds are the cavities of the intended shape that define the contours of a molded part. Thus, we need these molds to manufacture our designed plastic components into exact geometry.

Although they have different capabilities, both have fundamental properties to facilitate the production of injection molded parts. Aluminum and steel alloys provide the strength, thermal conductivity, precision, and surface finish detail required to accept and shape molten plastic on solidification. Furthermore, aluminum and steel molds are corrosion-resistant, which makes them durable.

Overall, using these molds ensures the seamless injection molding of thermoplastics. That’s why we need them, even though they are preferable in distinct molding conditions.

Comparing Aluminum vs Steel Injection Mold

Aluminum and steel injection molds have differences in various aspects, such as thermal capability, durability, dimensional accuracy, surface finish of molded parts, production cycle time, etc.

aluminum injection mold
This comparison is often done as the soft tool vs the hard tool. Next, let’s elaborate on the main differences between them.

Thermal Properties
Thermal properties of mold materials directly impact the process efficiency as it determines how uniform heat will transfer within the mold and the time it takes to cool down. In this context, aluminum has almost five times more thermal conductivity (237 W/ m/K) than steel, which offers faster heat dissipation. Hence, aluminum molds heat and cool in much less time than steel molds.

The fast heat conduction ensures injected material fills the cavity uniformly because it allows liquid to flow across more distance. In comparison, steel cools slower, resulting in longer production cycle time. However, the longer cycle time gives more control over temperature and cooling rate.

Durability and Wear Resistance
The composition of carbon and other alloying elements provides steel superior strength, hardness, fatigue resistance, and thermal resistance. As a result, molds made from steel are highly wear and abrasion-resistant, can withstand injection molding pressure over time, and are more sustainable. They can repetitively go for molding cycles, up to millions.

In contrast, the quick heat flow in aluminum molds leads to rapid expansion and contraction of the material. Furthermore, it causes dimensional instability and misalignment in the molds over time. Additionally, an aluminum softer surface is more prone to scratching and denting. For all these reasons, molds made from aluminum are less durable and relatively less wear-resistant in comparison to steel vs aluminum injection molds. They are suitable to create a few hundred to ten thousand identical injection molding parts.

Surface Finish
The smooth surface of mold cavities enhances the flowability and provides a quality finish to the molded parts. If we compare aluminum and steel injection molds, aluminum molds produce plastic parts with better finish. Although, it degrades over time and alters the surface roughness.

If you want SPI A-1 finish (Ra 0.012 – 0.025 µm), any mold can achieve that. Otherwise, the parts can be processed with further finish options like polishing and powder coating to achieve the desired aesthetic appearance.

Machinability and Modification Ease
Steels are comparatively more challenging to machine than aluminum because of their hardness and stiffness. On the other hand, aluminum is softer and quickly machinable, reducing mold production time and cost.

Next, the aluminum one is easy to modify between aluminum vs steel injection molds. This is again because of the hardness difference. Soft aluminum can be easily machined and modified, whereas steel mold modification requires more time and advanced machining setup.

Impact on Molding Cycle Time
The total cycle time of creating an injection molded part includes tool setup time, injection time, time to fill & form, and cooling time. Among these, mold cooling takes up to 50 to 80% of cycle time.

As aluminum has a higher heat dissipation rate, molds cool down in significantly less time than steel. So, they reduce the overall molding cycle time. Conversely, the low conductivity of and more complicated tooling increases the cycle time while molding with steel molds.

 Comparison Criteria Aluminum Mold Steel Mold
Thermal Properties Five times higher thermal conductivity than steel mold and faster cooling rate. Relatively low thermal conductivity and slower cooling.
Durability and Wear Resistance  Highly wear-resistant and can produce millions of parts. Prone to wear and abrasion, and can be used for up to 10,000 parts.
Surface Finish  Better smoothness  Less smooth surface
Machinability and Modification Ease Excellent machinability and easy to modify and repair.  Steel is less machinable and modification is also complicated.
Impact on Molding Cycle Time A higher cooling rate significantly reduces the cycle time.  Slower heal release increases the molding cycle.

Advantages and Disadvantages of Aluminum and Steel Molds

Understanding the advantages and disadvantages of aluminum vs steel injection molds helps to identify which mold appeals and which restricts your molding requirements.

Pros of Aluminum Molds

  • It is fast to create and costs less, often 2-3 times less tool investment than steel injection molds.
  • Low upfront cost makes them cost-effective in small-volume injection molding.
  • Its low weight also facilitates easy installation & handling and easy modification to address new issues.
  • A higher dissipation rate of heat lowers the time to production cycle significantly. Also, uniform heating and cooling eliminates the risk of shrinkage, voids, or marks.

Cons of Aluminum Molds

  • These molds are unsuitable for some advanced high melting-point resins like PEEK and PSU.
  • The lifetime is too short, only up to ten thousand cycles.
  • The softness of aluminum makes mold more prone to abrasion and wear. For example, even periodic maintenance can form scratches.

Pros of Steel Molds

  • Steel is superior in injection molds in terms of durability. For instance, a steel mold can produce multiple millions of complex parts under periodic maintenance.
  • They can process any type of resin, including abrasive and high melting-point.
  • Steel-made molds maintain dimensional stability for critical applications such as medical and aerospace.
  • The longevity of mold makes it ideal for mass production, reducing per-part cost significantly.

Tool Life & Maintenance
The strength, hardness, wear & fatigue resistance, and thermal stability of steel & its alloys are higher than aluminum. As a result, steel has a longer injection mold life expectancy. So, you need to identify whether your requirement is mold longevity or not.

Next, both mold types demand maintenance over time for repetitive production of identical items. Some typical maintenance activities include cleaning, lubrication, frequency checks, and wear inspections.

Product Volume & Production Scale

It is another critical consideration before choosing between steel and aluminum injection molds. Steel is suitable for high-volume production due to its longevity and capability of withstanding high temperatures continuously. It can create parts in millions with consistent quality and accuracy.

On the other hand, aluminum molds are better options if you are looking for small-batch production or rapid prototyping.

Cost Analysis

Aluminum toolings are less expensive if we see steel price vs aluminum price in the context of injection molding. Steel might cost twice or more compared to aluminum mold of the same size and specification.

Although steel molds have high upfront investment, they return the value in long-run production. What’s more, steel is a wise option for low per-unit cost during mass production. Conversely, the aluminum option is cost-effective for prototyping to a few thousand runs.

Material Properties

Steel and aluminum have distinct physical, mechanical, and chemical properties. For this reason, they behave accordingly during the injection molding process. Aluminum is soft and ductile, but it offers excellent heat conduction. On the contrary, steel is a robust and highly wear-resistive material with relatively low conductivity.

Compatibility of Advanced Resins

The type of material you will mold also influences the decision of steel vs aluminum injection molds. For example, aluminum molding cannot process some abrasive and high melting point thermoplastic polymers like Polyetheretherketone (PEEK), glass-filled nylon, and Polysulfone (PSU). However, steel mold tooling can create parts from almost any advanced resin. Thus, evaluate the molding material properties and consider its compatibility with both types of injection mold.

Acceptance of Complex Design

Can the chosen mold accept the extremely intricate design? It is another consideration before choosing the mold. The soft nature of aluminum does not allow for complex inserts and cavities. The reason is it cannot maintain the hole’s accuracy over time. In contrast, the steel’s stiffness and strong nature enable the higher complexity. So, it can hold the accuracy of complex cavities for long production runs.

How to Manufacture Aluminum or Steel Injection Mold

Mold creation for injection molding typically has three manufacturing approaches: CNC machining, EDM, and 3D Printing. In many cases, manufacturers combine CNC and EDM machining to leverage the capabilities of both methods. Moreover, raw steel and aluminum are also crafted into plastic injection molds using these techniques.

3D Printing

Manufacturing steel or aluminum molds with 3D Printing involves adding layer by layer of molten metal to obtain desired cavities. Fundamentally, it prints or physically replicates the computer 3D model (CAD) using a 3D Printer. It can achieve the utmost complex mold shapes in a short time. Saying that mold printing is best in situations where you are continuously changing the designs or for prototyping.


XTJ is a leading OEM Manufacturer that is dedicated to providing one-stop manufacturing solutions of Aluminum 7075 Parts from prototype to production. We are proud to be an ISO 9001 certified system quality management company and we are determined to create value in every customer relationship. We do that through collaboration, innovation, process improvements, and exceptional workmanship.




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