How to Make a Silicone Mold by Vacuum Casting

making silicone molds

 Silicone molds – those nifty and convenient shapes or mold boxes that can be used to prepare just about any item.

Now, when it comes to making a silicone mold, there are multiple approaches that can be adopted.

In this article, we focus on industrial applications for making silicone molds using methods such as vacuum casting. This is contrary to more DIY or hobbyist approaches to silicone mold making, for say crafting items at home.

Instead, here we concentrate on the creation of silicone mold prototypes particularly for plastic items.

Making a silicone mold: which way is better

Now, typically when it comes to the preparation of silicone molds for more large-scale purposes, there are two approaches that are used most commonly.

First, you have silicone injection molding, and secondly, there is vacuum casting.

Both methods have their pros and cons, and below, we will delve briefly into each of them

Injection molding

As the name suggests, this is a molding process where the raw melted plastic material is injected into the mold.


  • Greater flexibility in terms of the materials that can be used.
  • Equal flexibility on colour choices.
  • Reasonably high level of accuracy.
  • Low wastage: even the leftover materials can often be reused.


  • Not cost-effective for low volume output.
  • Initial setup cost can be rather high.
  • Relatively longer lead time for output delivery.

Vacuum casting

As the name suggests, this is a silicone molding technique that involves vacuum.


  • Low initial setup cost.
  • Shorter lead time.
  • Especially suitable for making smaller batches of products such as silicone prototypes.
  • Ideal for making large size plastic parts.

Of course, vacuum casting to create a silicone mold has its set of shortcomings too:

  • For large volume orders, this method may not be suitable.
  • Detailing in more intricate items might be minimal.

Having enlisted the pros and cons of both methods, it would now be a lot easier to choose between the two:

  1. Injection molding is preferred when more detailing is required.
  2. For low volume silicone prototypes, vacuum casting makes maximum sense.
  3. For swift turnaround times, again vacuum casting proves ideal.

How to make a silicone mold by vacuum casting

The use of vacuum, viz. a space that is completely void of matter, is at the core of making silicone molds this way.

The process starts by typically deploying two different molds – one at the top, and the other at the bottom.

The raw material is mixed separately and then placed inside the mold. Vacuum pressure ensures firm casting inside the chamber. Final casting is commonly done inside an oven to ensure complete and even curing.

Now, notwithstanding some of the minimalistic deficiencies in the process of making silicone molds by vacuum casting that we had referred to previously, it continues to be one of the most sought after ways in which silicone molds are made – for all the advantages that we had enlisted above.

Accordingly, in this section we go into greater detail about this process of making silicone molds.

Bear in mind that for the large part, the reference here would be in terms of urethane casting, viz. a casting process where additives, curatives, or polyurethane resins are poured into silicone molds for fabricating a variety of different plastic items.

how to make a silicone mold in the industry

First Step – Master Crafting

The first step to making a silicone mold by vacuum casting involves the master crafting process where digital renders are initially prepared using systems like CAD. With their help, 3D solids are made, often using 3D printing or CNC machining.

Once completed and checked for accuracy, we move on to the next step.

Second Step – Preparing the Molds

The second step involves preparing the silicone molds using liquid silicone. The casting box in this instance is usually half filled with liquid silicone and heated till it is completely cured.

Even after this initial curing process, additional curing is done in an oven, as we had referred to previously. While timelines may vary, the usual drying process takes around 16 hours.

Once fully dried, the two halves of the mold (as mentioned earlier) are cut to remove the finished master output.

Third and Final Step – Preparing Additional Copies from the Master

With the master output ready in the previous step, it is now all about preparing additional copies from it. At this juncture, the empty cavity inside the mold would be accurate enough to create precise replicas of the master, to the extent that materials other than plastic (say a blend of steel metal, among various feasible possibilities) can also be deployed.

Herein, one of the key advantages of making silicone parts by vacuum casting comes to the fore – the fact that silicone molds in this instance can be used repeatedly, at least 20 times or more, to continually create copies of the master.

A Note about Silicone Rubber

While talking about making silicone molds, it would only be apt that we delve briefly into silicone rubber.

Remember that irrespective of the method you use for making these molds – injection molding, vacuum casting, or any other, the fundamental raw material will remain the same, viz. silicone rubber.

Due to its pliability, durability as well as its unique ability to withstand extreme temperatures, silicone rubber finds frequent usage globally, for a number of diverse applications.

silicone mold materials

Silicone Molding is the right choice for Low-Volume Plastic Parts Production

When it comes to producing smaller batches of plastic items – say prototypes for larger orders that are to follow, silicone molding proves to be the ideal choice.

A major reason for this is the reusability factor; the same silicone mold can be used over and over again for at least 20 to 25 times (possibly even more) to create accurate replicas of the item in question.

This has a direct relation with costs since it helps keeping them in check. Of course, it leads to enormous time savings too!

An additional benefit is the ease with which silicone can be stored for prolonged periods. This proves especially helpful when production might have to be halted.

low volume silicone molds

Getting Started with Silicone Mold-Making for your design

While there are multiple approaches that can be adopted for making a silicone mold, vacuum casting proves to be the right choice for the production of smaller batch silicone prototypes.

In this article, we have vividly described how to make a silicone mold by vacuum casting.

As you would have noted, the steps to be followed are fairly simple in nature. Notwithstanding a more industrial level of production which is not akin to any DIY or homely approach to silicone mold making, the method we have outlined proves easy to follow and implement.

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