Aluminum Injection Molds: Pros, Cons, and Making the Right Choice

Aluminum injection molds have long been considered an attractive option for various manufacturing processes, primarily driven by cost considerations and the need for shorter turnaround time.

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While aluminum molds are not a new concept and have been used in the past, they haven’t gained widespread popularity in recent years. In this article, we will explore the advantages and disadvantages of aluminum molds to understand why their usage has fluctuated over time.

Aluminum injection molds do not signify the complete mold is constructed from aluminum; rather, it means that the mold’s core and cavity are crafted from aluminum, while the mold base remains constructed from steel. This approach offers a valuable advantage in maintaining mold rigidity. The steel mold base provides essential support to the mold core, ensuring structural stability. Simultaneously, the mold core often features intricate shapes, making its fabrication more complex. In contrast, the mold base’s manufacturing process is relatively straightforward, allowing for the retention of necessary mold rigidity while minimizing processing time.

1. Cost-Efficiency

Aluminum is relatively affordable when compared to other mold materials. While the price per unit weight may not be the lowest, the cost per unit volume is notably lower than many mold steels. This affordability makes it an attractive choice for manufacturers on a budget.

2. Speedy Machining

One of the standout features of aluminum is its exceptional cutting speed. The fast machining capabilities of aluminum significantly reduce processing time. This, in turn, translates to cost savings and shorter production cycles. In fact, aluminum molds can be processed in approximately one-third to one-half the time required for steel molds.

3. Rapid Thermal Conductivity

Aluminum boasts impressive thermal conductivity, facilitating efficient heat dissipation. This characteristic helps maintain the optimal mold temperature, preventing issues like slow mold ejection, excessive product shrinkage, and warping due to inconsistent cooling. As a result, aluminum molds are well-suited for applications where precise temperature control is crucial.

1. Limited Surface Finish

One of the key drawbacks of aluminum molds is their inability to be polished to the same degree as steel molds. This limitation can affect the surface quality and dimensional accuracy of the molded parts, making them less suitable for applications where a pristine finish is essential.

2. Tool Sticking Issues in Aluminum Machining

When working with aluminum, a common challenge arises: aluminum tends to adhere to the tool, resulting in the formation of built-up burrs. This adhesion issue can significantly impact the machined surface’s smoothness and dimensional accuracy due to alterations in the tool’s size and shape. Consequently, the quality and dimensions of plastic products are compromised as a result.

3. Mechanical Limitations

Compared to steel, aluminum has inferior mechanical properties and is less capable of withstanding high-injection speed and high-pressure conditions. This limitation can lead to flashings, even in new molds. Therefore, aluminum molds are best suited for applications involving simple product designs, materials with high fluidity, and lower temperature and pressure requirements. Materials like ABS and PP are well-suited, while materials like PC and glass fiber-reinforced plastics are less compatible due to their higher temperature and pressure demands.

4. Welding and Repair Challenges

Aluminum’s poor welding performance and difficulty in polishing make it challenging to repair molds once flaws occur. This can result in increased maintenance costs and downtime.

How Much Can Aluminum Injection Molds Save?

When considering aluminum injection molds, cost savings can be substantial. While the material itself is less expensive, the primary source of savings lies in reduced processing time. In general, aluminum molds tend to be 20-40% cheaper than their steel counterparts.

Understanding Mold Lifespan

The lifespan of an aluminum injection mold varies depending on factors such as the material being molded and the complexity of the product. For instance, for a product made from PA6+GF30 with a straightforward design, an aluminum mold can typically produce around - shots. When working with materials like PP or ABS, the number of shots can increase to -, assuming no unexpected issues arise during production.

However, mold longevity is also influenced by the acceptance of flash, which refers to the presence of excess material at the parting line of the molded product. If strict requirements for flash-free production are in place, it can shorten the mold’s lifespan.

Considering the approximately 30% cost savings offered by aluminum molds, it becomes essential to weigh the pros and cons. While aluminum molds provide significant cost advantages, it’s important to remember that steel molds have a significantly longer lifespan, often lasting hundreds of times longer than their aluminum counterparts. The choice ultimately depends on the specific needs and budget of the project at hand.

Injection moulding is one of the most commonly used methods of producing identical plastic products in high volumes. However, as with every process, it is important to understand the specific design restrictions that must be adhered to in order to facilitate the obvious benefits of successfully producing cost-effective, high-quality parts.

To help, we have very simply laid out the advantages and disadvantages to consider.

Please be aware, however, that the following guidelines apply to what we would consider to be conventional injection moulding (quantities of 100,000+) and may appear at first glance to be fairly prohibitive if you are looking to develop a product with numbers out of this norm.

Low volume production possibilities

The good news is Plunkett Associates have spent many years developing strategies and techniques in order to take away some of the issues identified below, particularly for parts that would traditionally be considered too difficult or unusual to mould.

In addition, we are specialists in making injection moulding far more cost effective for much lower quantities of parts than is more commonly expected. Using a hybrid of techniques, our low volume production tooling allows us to customise to client/geometry/quantities. The result is a mould tool that reflects the requirement and opens up an exciting option to produce high quality, yet low volume components.

Are you interested in learning more about daily necessities molds? Contact us today to secure an expert consultation!

As an ISO:: Quality System certified supplier, we are confident we can help with your requirements, so please feel free to give us a call.

Advantages of injection moulding

1) Fast production and highly efficient. Injection moulding can produce an incredible amount of parts per hour. Speed depends on the complexity and size of the mould, anywhere between 15-120 seconds per cycle time.

2) Low labour costs. Plastic injection moulding is an automated process whereby a majority of the process is performed by machines and robotics, which a sole operator can control and manage. Automation helps to reduce manufacturing costs, as the overheads are significantly reduced.

3) Design flexibility. The moulds themselves are subjected to extremely high pressure. As a result, the plastic within the moulds is pressed harder and allows for a large amount of detail to be imprinted onto the part and for complex or intricate shapes to be manufactured.

4) High-output production. Thousands of parts can be produced before the tooling needs to be maintained.

5) Large material choice. There is a large selection of polymer resins to choose from. Multiple plastic materials can also be used simultaneously; for example, TPE can be overmoulded onto PP parts.

6) Low scrap rates. Injection moulding produces very little post-production scrap relative to traditional manufacturing processes. Any waste plastic typically comes from the sprue and runners. Any unused or waste plastic, however, can be reground and recycled for future use.

7) Ability to include inserts.  Metal or plastic inserts can be insert moulded.

8) Good colour control. Plastic parts can be manufactured in any required colours with the use of masterbatches or compounding.

9) Product consistency. Injection Moulding is a repeatable process; in other words, the second part you produce is going to be identical to the first one etc. This is a huge advantage when trying to produce high tolerances and part reliability in high volumes.

10) Reduced finishing requirements. There is often very little post-production work required as parts usually have a good finished look upon ejection.

11) Enhanced Strength. When plastic injection moulding, it is possible to use fillers in the moulding material. These fillers reduce the density of the plastic whilst it is being moulded, and can help add greater strength to the completed part.

Disadvantages of injection moulding

1) High tooling costs and long set up lead times. Up-front costs are high due to the design, testing, and tooling required. There is the initial design and prototyping (probably via CNC or 3D printing), then the design of a prototype mould tool to produce replicas of the part in volume. Lastly, and only after extensive testing during both stages, you can finally injection mould a part.

2) Part design restrictions. Plastic parts must be designed with injection moulding consideration and must follow the basic rules of injection moulding, for example:

• Avoid under cuts and sharp edges as much as possible
• Use uniform wall thicknesses to prevent inconsistencies in the cooling process resulting in defects like sink marks.
• Draft angles are encouraged for better de-moulding.

Don’t forget, because tools are typically made from steel or aluminium, it can be difficult to make design changes. If you need to add plastic to the part, you can make the tool cavity larger by cutting away steel or aluminium. But in order to take away plastic, you need to decrease the size of the tool cavity by adding aluminium or metal to it. This is extremely difficult and in many cases might mean scrapping the tool (or part of it) and starting over.

Also, the weight and size of the part will determine the tool size and necessary press size. The larger the part, the more difficult and expensive it will be.

3) Small runs of parts can be costly. Due to the complexity of tooling, and the necessity to rid the machine of all previous material before the next product can be made, the setup time can be quite lengthy. Therefore small runs of parts have traditionally always been thought of as too expensive to injection mould.

In summary

Injection moulding is a great process! The range of materials and colours is huge, and there is no “abs like’ that we get in 3D Printing, it’s the real thing. Parts are repeatable and tight tolerance. The only potential downside is the tooling, but as we said at the beginning of this article, we’ve got that covered, with options to suit most requirements.

Want more information on hardware mold? Feel free to contact us.