What is injection molding
The injection molding process requires an injection molding machine, raw plastic material, and a machined mold. The raw plastic material is first melted in the injection unit and is then injected into the mold — most often machined from steel or aluminum — where it cools and solidifies into the final plastic part. The key steps in the injection molding process are clamping, injection, cooling, and ejection.
Advantages:
A variety of materials with different properties can be mixed.
The parts can be made of any color desired.
The insert can be used in the molding process.
The tolerance in the design can be tighter.
High-volume orders/repetitive orders are more cost-effective.
The waste produced is very small and can be re-ground and reused.
Disadvantages:
To make steel mold, the initial start-up cost is higher.
Mold design documents require customers to have more professional knowledge and experience.
The lead time for initial mold manufacturing is longer, generally 30 days.
What is vacuum casting
The process starts by placing a two piece silicone mold in a vacuum chamber. The raw material is mixed with degassed and then poured into the mold. The vacuum is then released and the mold removed from the chamber. Finally, the casting is cured in an oven and the mold removed to release the completed casting. The silicone mold can be reused.
Advantages:
The lead time for vacuum forming on new molds is shorter, generally 10-12 days .
Lower mold start-up cost.
This method has the ability to make larger plastic parts.
Smaller batches is with relatively low cost.
Disadvantages:
The uniformity of wall thickness/uniformity of plastic products is not always achievable.
Limited to the details and complexity of the parts.
This method is not cost-effective in larger batch runs.
How to choose injection molding or vacuum casting
The following points can be taken as reference.
Quantity
For large-volume orders, injection molding is generally chosen. Although the mold cost of injection molding is high, the unit cost is very low. This means that when you need thousands or tens of thousands of parts, you can easily make up for the initial cost of the mold by saving each unit cost.
On the other hand, not everyone needs mass production. When a smaller number of parts are needed (a few prototypes or a few hundred), vacuum casting may be a better choice because the mold cost is much lower.
Detail
Since injection molds are usually made of high-quality metal, injection molding can produce finer parts compared to vacuum casting. Therefore, for highly complex parts, injection molding may be a better choice.
For simpler parts, especially parts that only need to be manufactured in a small quantity, vacuum casting can be used, and this is not just a cheap option, but vacuum casting can also provide a smooth surface finish.
Speed and quick turn
If the design needs to be modified at any stage of the manufacturing process, it is much easier and cheaper to modify the silicone mold than to rework or refurbish the injection molding steel mold. So, this also means that in the early stages of development, vacuum casting is usually a better choice. In fact, customers usually use vacuum casting to manufacture early prototypes before using injection molding to manufacture end-use parts. More importantly, compared to creating a mold for injection molding, creating a silicone mold for vacuum casting is a faster process, which means prototype process would be in a shorten lead time.
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