Silicone molding or vacuum casting is a manufacturing way of using silicone molds to produce plastic and rubber prototypes or parts in a low volume. On what occasions will you look for a custom silicone mold manufacturer or silicone molding company? Want to get a silicone mold for self-use to make homemade or in-house parts? In need of a small batch (10-20 pieces) of plastic or rubber parts to verify new designs? 

If the answers are yes, you indeed should turn to a custom silicone mold manufacturer. When you search for silicone mold manufacturers on the internet, you will find many to choose from. Then, how to pick a qualified one? Let’s give you some tips.

1. The manufacturer should have CNC or 3D printing abilities

To make a silicone mold, there should be a prototype model or master based on your design. It is usually made by CNC machining or 3D printing. After fastening the prototype on the shelf and surrounding it with 4 blanks, the technician pours liquid silicone into it. After about 8 hours of trying it out later, you will get a silicone mold after taking out the prototype.

If you really just want a silicone mold and don’t want the silicone mold manufacturer to produce the parts for you, it is advised to confirm with the manufacturer in advance. In most cases, the silicone molding company doesn’t consider silicone molds as deliverable goods. If it is allowed, make sure you are able to make parts yourself out of a silicone mold in the vacuum environment and control the shrinkage rate well.

2. The manufacturer should have vacuum casting machines

The silicone molding company generally uses silicone molds in vacuum casting to produce plastic or rubber prototypes or parts using PU (polyurethane) material. So the thing is that when it offers a vacuum casting service, it needs to make silicone molds. The purpose is to produce short-run plastic and rubber prototypes and parts. After 10-15 shots, the silicone molds cannot be used anymore. That’s the reason why the silicone molding company won’t ship out them.


3. The manufacturer should have experienced technicians

Injecting PU into the silicone mold in the vacuum environment under the temperature of 60-70℃, and after half an hour’s drying out you can demold and get the part. You will need to solidify the part for the second time under a temperature of 60-70℃ if it is necessary. The whole process requires skills. How to make a silicone mold? How to vacuum the machine? How long will it take to solidify the parts? How to demold smoothly? So you’d better pick a silicone molding company with skillful technicians no matter if you just want the silicone mold or need the parts to avoid quality problems.


4. The manufacturer should be good at surface finishing

In case you do not simply need a silicone mold but silicone molded parts, you’d better get them finished under one roof. That requires your manufacturer to be capable of doing surface treatment, for instance, polishing, painting, and electroplating. 

The following is a brief process of vacuum casting for your better understanding.

Materials for Silicone Molded Parts

There are hundreds of materials for vacuum casting. Because the raw material is polyurethane ( PU in short). Different material properties and hardnesses can be achieved by adjusting the proportions of the materials. They can be ABS-like, PC-like, PMMA-like, soft rubber-like, etc. It is possible to meet a variety of product development needs. A material property list can be offered for you to check which kind of PU material can meet your demands.

Silicone Molding/Vacuum Casting Process

Step 1. Prepare the Master for Making the Silicone Mold

The master can be made from any stable material. Or it can be provided by the customer. In most cases, we make it via CNC machining or 3D printing.

Master materials are usually plastic or metal, which needs to remain stable at 60-70℃ for a certain time.

Step 2. Make the Silicone Mold

The master is placed in a box and silicone is poured into it. It is then heated to 60-70℃in in an oven until the silicone has completely cured.

After taking out the box from the oven, we cut the silicone into halves and remove the master. The silicone mold is ready with a shape as same as the master.

Step 3. Making the Parts via Silicone Mold

We can inject various compound materials into the mold according to your design requirements. To ensure that the replica is the same shape as the master, the mold is placed in a vacuum environment to remove air from the cavity and fill every area with liquid silicone.

After the material inside the silicone mold is cured and demolding, the part is ready.

Step 4. Doing the Surface Treatments

X Rapid Technologies offers a wide range of finishings to ensure that the part meets your expectations entirely. Our surface treatments include deburring, sandblasting, polishing, painting, drilling, tapping and threading holes, silk-screening, laser engraving, etc. 

We also have a professional quality control team and equipment to inspect the parts to guarantee high quality.


Please be aware that there are also possibilities that you cannot use the silicone mold made by your manufacturers in the case that you don't have qualified technicians that can control the shrinkage rates well. Then you may not get the final parts you want.

Next time when you talk to a candidate manufacturer, try to ask questions about the above aspects to the very custom silicone mold manufacturer you want.

Or just contact X Rapid Technologies. We are always ready to get your projects perfectly done. In case you may have other questions about our vacuum casting services, please check the below frequently asked questions.


1. What is the highest tolerance of the silicone molded parts?

The tolerance of vacuum casting parts mainly depends on the accuracy of the master, the geometry of the part, and the material. In general, a shrinkage rate of 0.15% is acceptable. The highest tolerance can be ±0.05mm.

2. Will the masters and silicone molds be shipped to me?

No. The masters and silicone molds are not deliverable parts. The masters are used for making silicone molds. And silicone molds cannot last for a long time after manufacturing is finished. You cannot use them even if we deliver them to you.

3. When should I choose to make my prototypes with silicone molds?

Honestly, the tolerance of vacuum casting is hardly as high as that of CNC machining. Vacuum casting is a more cost-effective option if your tolerances aren't tight and the quantity is around a dozen. Then the unit price of vacuum casting would be much lower than that of CNC machining.

4. What are the advantages of vacuum casting?

Not just for prototypes, but also for end-use products, vacuum casting is the optimal low-volume production method. 

A. The silicone mold is at a relatively low cost compared with other molds for production.

B. Vacuum cast parts are with great geometrical details. So little or even no finishing is needed. 

C. Short turnaround time. After the master is ready, the silicone mold can be made within a few days. 

D. Over-molding for two different materials for one part is available.

5. Can I just order the silicone molds?

Theoretically, we just deliver silicone molds to you. However, silicone molds can be easily affected by the temperature and environment. We are not sure if you can use them well. It is technical to control the shrinkage rate. The best way is to let us produce the parts.