Vacuum casting and reaction injection molding (RIM) differ in several aspects, though they are both the machining processes of low-volume production based on simple molds at room temperature. This article dives into the differences between them and gives a glimpse of low-volume production.

What is vacuum casting?

Vacuum casting uses a prototype master and a silicone mold under vacuum to cast PU material in a vacuum environment, to reproduce the same replica as the master. It is a common rapid prototyping technology. Through this technology, it can produce parts with functional characteristics similar to engineering plastic products. At the same time, it is widely applied in low-volume production for product development or end-product manufacturing.

Short-run Production: Low Volume Plastic Manufacturing

What is reaction injection molding (RIM)?

Reaction injection molding (RIM) is an industrial molding process. This method involves adding two or more liquid monomers or prepolymers to a mixing head, mixing under pressure, then injecting them into a closed mold, where they are polymerized and cured.

It is suitable for small batch trial production in the process of product development, as well as short-run production, simple-structured coverings, and large thick-walled and uneven-wall thickness products. Therefore, it is frequently applied in the automotive and medical device industries.

Short-run Production: Low Volume Plastic Manufacturing

What are the differences between vacuum casting and reaction injection molding (RIM)?

1. The sizes of the parts are different. 

Vacuum casting is mainly used in low-volume manufacturing of relatively small plastic (ABS, PC, acrylic, etc.) and rubber components. While, RIM is widely applied to make larger plastic enclosures for low-volume production, such as automotive bumpers, medical device cases, and large-sized robots, which are usually not suitable for vacuum casting. Accordingly, the mold volumes which the two technologies employ vary, and that of RIM is surely larger in most conditions.

2. They use molds in different materials. 

Vacuum casting manufactures parts only via silicone molds no matter if it is rapid prototyping or low-volume manufacturing. However, reaction injection molding makes use of diversified molds, and the materials can be ABS, resin, aluminum, and silicone. Mold type will depend on the quantity of low-volume plastic manufacturing. Aluminum is the most widely used material for the mods of reaction injection molding.

3. Different cure reaction times.

Also, after the tool is filled with raw materials, the cure reaction time of RIM is much shorter than in vacuum casting, so the former enjoys a shorter turnaround time. So when doing the same quantity of low-volume production, RIM takes less lead time.

4. Different shrinkage rates.

The shrinkage rate of vacuum casting is larger than that of RIM. For large pieces and thin-walled products, it is necessary to consider whether there is shrinkage when making them via vacuum casting, avoiding smaller sizes of the product in the end.

5. Different product materials.

Though the raw materials for vacuum casting and RIM are both called PU, they are not the same. The properties of the parts are different. The vacuum casting parts can be ABS-like, PC-like, PMMA-like, PP-like, POM-like, rubber-like, etc. The RIM parts, in most cases, are ABS-like or PP-like. You can also check the material property list to select which one you need.

6. The applications of the products are different.

In most cases, reaction injection molding is used for low-volume plastic manufacturing and vacuum casting is used for rapid prototyping. For industries like the automotive industry which need hundreds of prototypes to do testing, RIM is also a good option.

7. The costs are different.

When making the same part, the cost of vacuum casting is relatively lower. The major reason is the mold material silicone in vacuum casting is cheaper. Accordingly, the quality of RIM is better. 

What are the advantages of low-volume production?

1. Short lead time

Molds for low-volume production can be made within several days, which largely reduces the total lead time. The lead time is usually 7 to 30 days depending on the quantities. Low-volume manufacturing enables you to bring new products to the market more quickly.

2. Cost-effective

The mold costs are much lower than injection molding mold. The costs of molds for low-volume production can be as low as hundreds of dollars. But the costs for injection molding molds are usually at least ten thousand dollars. When the quantity is less than the MOQ of injection molding, you choose to make your parts by injection molding, the mold costs cannot be offset through the volume effect. In this case, low-volume manufacturing saves you a lot of money.

3. Great design flexibility

Design modification is allowed after the first trial of low-volume manufacturing. The flexibility helps to shorten the development time and reduce risks and costs too. 

4. Faster customer feedback

With a shorter lead time, your products go into the market quicker, which enables you to gather customer feedback more fastly. Based on the feedback, you can adjust your product strategy rapidly.

How to take better advantage of low-volume manufacturing?

With technology advancing rapidly and competition intensifying, product life cycles are getting shorter and shorter, making the development of new products increasingly important for gaining a competitive advantage. Low-volume manufacturing technologies make it possible to launch new products quickly. It is the most cost-effective manufacturing method to capture the market.  In the phases of product development, financing, market testing, and end selling, low-volume production is always a good choice.

In conclusion, it is recommended that you select the best way to make your parts according to your certain needs when it comes to low-volume production. Usually, quantity is the main factor to decide the manufacturing method. Or just talk to X Rapid Technologies to help you with your low-volume plastic manufacturing projects.

FAQs of Low-Volume Plastic Manufacturing

1. How to decide on the right low-volume production method?

Vacuum casting and reaction injection molding are similar. To decide which method to use, the first factor is part size and structure. In the case of small parts or prototypes, vacuum casting is the most suitable method. The RIM is used for large parts.

2. How to choose the proper material?

X Rapid Technologies can help you to choose the material based on the material properties in need. Material data sheets are available.

3. Is there a specific requirement for the file format for low-volume plastic manufacturing?

Vacuum casting and reaction injection molding both require making molds. STP or STEP format is the best file format. In many cases, our clients only have STL format. We can offer a rough quote based on it. But it is impossible for manufacturing but for 3D printing.

4. What are the surface treatments available?

The parts by vacuum casting and reaction injection molding are easy to be finished. All surface treatments available for plastic parts can be done, including deburring, painting, electroplating, silk-screening, laser etching, etc. Contact X Rapid Technologies today to get your custom finishing solution. You can also read our blog about the finishings to learn more.

5. How will you protect my intellectual property?

We take protecting intellectual property as the basic professional ethic in our industry. We know well that rapid prototyping is for new product development. If you'd like to sign the NDA, we are more than happy to do so. And even without the NDA, your intellectual property will be well protected. All the pictures exposed have been gotten permission from our clients.