You may know injection molding as a widely-used process in product manufacturing with many industrial applications. Its efficiency, low cost of labor, decreased waste, and repeatability make it an ideal production method for complex parts.
However, the results of this process depend on the materials used and the part design, and manufacturers often look for ways to reduce costs. To achieve this, they sometimes prefer using molds made from aluminum rather than steel.
In this article, you will learn more about aluminum injection molding, and the advantages, disadvantages, and features associated with them. So let’s begin.
What is Aluminum Injection Molding?
Aluminum injection molding involves using aluminum molds in the popular manufacturing technique known as injection molding. Having been in use since the early 1990s, the parts produced can be prototypes as well as actual products.
Aluminum molds can be used instead of steel ones as aluminum has a higher thermal conductivity (around 235 W/mK) as compared to steel (around 45 W/mK).
This allows it to transfer heat from the mold more efficiently, which results in faster products being produced. Moreover, products made from aluminum molds are structurally consistent, and the surfaces have high precision and accuracy.
Aluminum Injection Molding vs Steel Injection Molding
The traditional molds in injection molding were made of steel. They continue to be used, but manufacturers always seek alternative metals to make molds from due to overcome several limitations of steel.
This is where aluminum molds come in. Both have their set of advantages and disadvantages.
Here, we will compare some main features of these two types of molds. However, your choice will also depend on your project specifications.
Compared to steel, aluminum is a softer material. This facilitates the machining of the material when the mold is being produced. This also allows aluminum mold makers to machine the mold parts separately.
On the other hand, the hardness of steel is further increased by heat treatment, which necessitates the use of specialized equipment to machine it into the shape of the mold. This results in less flexibility in terms of design.
Mold Turnaround Time
Aluminum molds for injection molding are produced either by using computerized numerical control (CNC) machining, or the electrical discharge machining (EDM) process.
You do not need extra processing in addition to these automated processes, which results in aluminum molds being produced in a relatively short time i.e. around ten to fifteen days.
Conversely, the hardness of steel prevents short mold production times. Steel mold makers need to apply advanced equipment in addition to CNC machining to make them.
Further heat treatment is also applied to increase the mold’s lifespan. All this contributes to a longer mold turnaround time, which can be more than a month in the case of steel molds.
Mold manufacturers can measure the expected life of a mold in terms of the number of parts it can successfully make in its lifespan before it undergoes extreme deformation. This is known as mold robustness, and is subject to the material of the mold as well as its design.
Aluminum injection molds are softer and do not undergo heat treatment. Hence, they last for a shorter time as compared to steel molds.
You can expect such molds to last from 3,000 to 10,000 cycles depending on the design features. This can increase the costs every time you have to produce a new mold.
On the contrary, steel molds are harder. The extra thermal processing they undergo allows them to last much longer than aluminum molds, often longer than 100,000 cycles.
Hardened tool steel, while expensive, can last for more than a million cycles. Hence, you avoid the cost of scrapping and replacing molds regularly.
In injection molding, a part is considered to have been made only when it has cooled in the mold and has been ejected from it. This production time depends on the type of mold used, and the molding temperature and pressure.
Aluminum molds work best if the temperature is controlled. Production times are around one minute per part. However, steel molds have a better ability to endure extreme temperatures and pressures, which results in production times lasting just a few seconds.
Features of Aluminum Tooling for Injection Molding
The above comparison between aluminum and steel injection molds suggests that aluminum molds are better suited for low-volume or prototype applications.
When deciding on your mold material, you should also keep in mind your project details as well as the following features of aluminum injection molds:
Thermal Expansion and Cooling rate
Aluminum has almost twice the coefficient of thermal expansion than steel. This enables it to cool down without difficulty. This makes it a suitable material to be used for injection molding purposes, where rapid heating and cooling cycles are involved.
To ensure the pars produced by injection molding are structurally accurate and similar to each other, you need to use a tool that has high strength, rigidity, and ductility in the face of high temperatures and pressure conditions.
Aluminum is a strong metal and lends its robustness to its tough nature. Its use as a mold in injection molding is enhanced by setting the right geometries and design parameters. This is why you see various alloys of aluminum being used for injection molding.
Advantages of Aluminum Injection Molding
Since the cost of producing the mold is a significant expense in the whole injection molding process, it is important to keep an eye on it. All things equal, aluminum injection mold costs are much lower compared to steel.
However, how much you spend in reality depends on your mold usage. High-volume productions may require you to make several aluminum molds, thus increasing your costs.
Lower Lead Times
Whereas steel molds take several months to manufacture and come up with a final product, aluminum molds for injection molding do the job in just a few weeks. Therefore, they are several times faster at delivering your product.
Good for Low Volumes
As we have learned before in this article, aluminum molds are your go-to mold for your prototyping and low-volume projects. At low production scales, they offer good quality results at affordable rates.
Low Machining Time
Aluminum molds can heat up and cool down at a faster rate. This enables shorter cycle times as these heating and cooling phases form a substantial proportion of the total cycle time. This helps you achieve faster production of parts.
Not only do aluminum molds allow faster heating and cooling, but they also ensure that the heat dissipation from the molten plastic material is uniform.
This helps prevent defects caused by uneven cooling, such as sink marks and burn scars. You get fewer defective products, which saves material costs.
Effortless Repair and Modification
Imagine spending a lot of time perfecting the design of your mold and then forwarding it to your mold maker. But when the mold is produced, it is defective or deformed.
If your mold was made of steel, you would have very few options except for ordering a completely new mold, thus incurring another heavy expense.
However, if your mold material was aluminum, you could have avoided this hefty cost by simply repairing the deformities. The relatively soft nature of aluminum permits you to change the shape of an imperfect mold, which is seldom possible in steel molds.
Disadvantages of Aluminum Injection Molding
We have already mentioned that aluminum molds are a better option if your production is low-volume. Unlike steel, which is more resistant to corrosion and wear, aluminum is less durable.
For high-volume production, will not last as long as steel molds, and you will have to produce new ones, raising your costs.
To increase an aluminum injection mold’s durability, it is sometimes suggested to nickel-plate it or anneal it to remove internal stresses.
While these will make your aluminum mold last longer, your costs will again increase, thus offsetting any savings you might have expected to achieve.
Limited Surface Finish
The density of aluminum is around 2.7 g/cm3compared to 7.8 g/cm3 for steel. This lower density limits the range of surface finish processes that can be applied to aluminum molds.
This problem is not usually encountered with steel molds, as steel inserts enable several custom finishes and texture choices.
Another disadvantage of aluminum molds’ lack of durability is that after thousands of production cycles, their cavities get deformed due to wear. This causes flashing in the molded parts.
You may know injection molding flash as the extra plastic that forms on the edges of molded parts. If present to a large degree, it can affect the surface finish of parts and can inhibit their mating or assembly.
As aluminum cannot bear extreme temperatures and pressures, they are not ideal for long-term use. You may not prefer to use them for high-volume production.
Sometimes, you may notice the molded parts affecting your aluminum injection mold. You may want to avoid that by modifying the mold, but it is not possible in the vase of aluminum molds.
On the contrary, you can subject steel molds to heat treatment processes to improve their toughness so they are not affected by the injection materials.
Guidelines for Aluminum Injection Molding Design
How long a mold lasts and the quality of the parts it produces depends on several factors. One of the most important of these factors is its design. Experts suggest keeping the following things in mind when designing your aluminum injection mold:
Make Provisions for Possible Revisions
Sometimes, you won’t get your mold design right the first time. Therefore, it is better to include steps in your design so you can revise it in the future if the need arises. Though it may increase your cost of mold, it may eventually prove to be a profitable measure later on when the alteration is needed.
Ensure Uniform Wall Thickness
As your part design gets more complex, the thickness of its walls does not stay uniform. This can create problems as thinner components cool faster than thicker ones.
While thicker regions can dissipate heat to these thinner regions to maintain some temperature uniformity, different cross-sectional thicknesses mean that thin parts solidify faster.
To overcome this issue, experts recommend incorporating feed paths in your design. This keeps a uniform part thickness, thus simplifying the overall molding process.
Use Suitable Alloys
Design experts also advise adding appropriate elements as alloys when designing your aluminum mold. Silicon is commonly recommended for this purpose due to its high specific heat capacity which enables it to retain heat much better than aluminum alone can.
You should keep in mind that your chosen alloy should have a limited freezing range so that it later helps in developing solid mechanical properties in products.
Take Note of Part Specifications
Your design should have fillets instead of sharp corners. This helps in avoiding the shrinkage difference that may arise if corners are included. Shrinkage has the potential to cause cracks and permanent defects in your part, which affects its quality.
To increase the lifespan of the mold and to provide hard surfaces where required, you can add inserts of different shapes and materials in your design. Brass thread inserts are one example of this.
Kemal: Aluminum Injection Molding Services
Kemal Precision Manufacturing Ltd. offers a variety of different manufacturing services including plastic injection molding. We use premium aluminum as well as steel molds to suit your every project requirement.
With the support of our professional team of industry experts, our well-equipped manufacturing facilities provide high-quality solutions for all your prototyping and mass production needs in line with international standards.
Since 1995, we have worked with more than 2,000 companies across a multitude of industries. This has helped us learn and grow so that we can serve you better.
To sum up our discussion, aluminum injection molds provide an affordable and faster substitute for steel molds and are better suited for low-volume production runs while maintaining product quality.
If you are still unsure about aluminum molds or the injection molding process in general, visit our website where you can find out more similar informative articles, or contact our experts online.