Vacuum casting is a widely used technique for the production of plastic prototypes. Vacuum casting is not only more economical but also the ideal process for low to medium scale production of plastic prototypes. In essence, vacuum casting allows the users to create copies of a wide range of functional plastic parts. The whole process is relatively fast-paced as compared to other manufacturing processes and parts produced through vacuum casting are of high quality and better surface finish.
Vacuum casting was actually conceptualized to solve the air entrapment problem. Researchers were able to learn that under the normal casting process, the air present in molds tends to get trapped in the final solid structure and air pockets are formed inside that compromises and weakens the overall structure of the final product. Vacuum casting has been in the news because it solves this issue.
Vacuum Casting: The process
The process of vacuum casting consists of multiple stages. The overall process is labor-intensive but still relatively fast-paced and easy to manage. The process is described as stage-wise as follows:
1. Creating a master model
First of all, a master model has to be created or obtained on the shelf. The master pattern can be an industrial part or one created through rapid manufacturing techniques like 3d printing or CNC machine tools. Parts created through 3d printing are created using the stereolithography/SLS techniques. It must be ensured that the master model used has the correct dimensions so that the final casting parts have the desired dimensions as well.
2. Producing the mold
Liquid silicone is used to create silicone mold. Once the master model is put inside the casting box, liquid silicone is poured all over it and then it is left to cure in an oven. The cured liquid silicone mold is then cut open and the master mold has removed that leaves behind an empty cavity. The empty cavity is of the exact shape and dimensions as the original master pattern. Silicone molds can typically be used 15-20 times.
3. Making the casting copies
Now suitable resins (or polyurethane that are like rubber) are mixed to ensure that the mixture has the same properties as the industrial part. The manufacturers have a list of material data sheets that have all the information about the composition and properties of the materials they used for casting. They use that information to produce a resin that best resembles the properties of the master part. The mixture is poured into the empty cavity to form the desired finished mold or product. The resin is then cured in a vacuum so that no air bubbles are trapped.
The casting machine
The casting machine consists of two chambers, one at the top and the other at the bottom. The top chamber normally has a pair of dies and a moving plate at the top. In between these two dies, the mold cavity is present. This cavity contains a vacuum. The bottom chamber consists of a crucible. Resin collects in the crucible after passing through a gating system. The gating system acts as a pathway that can control the resin inflow and is used for collecting the resin in the crucible. After the excess material is removed, the final casting product is ready.
Why vacuum casting method is preferred
Vacuum casting process comes with a host of benefits some of which are as follows:
1. Quick results
The vacuum casting process is significantly rapid and you can get a fixed volume of fully working models in almost fewer days. So this process is ideal when deadlines have to be met or urgent orders need to be delivered in less number of days. Clients can just email their CAD model to the manufacturer and get the final product ready in days.
2. Reduced cost of production
Since silicone is a comparatively cheaper material and a single mold can be used for multiple prototypes, the process is overall very economical as compared to other traditional methods.
3. Better product quality
If your company wants to provide top of the line manufacturing services, your product quality must be excellent. In vacuum casting, not only the process is fast but also the final high quality and has better structural properties, rigidity, and hardness. The air pockets are removed in the final product that enhances its mechanical properties.
4. Better product finish
Since silicone is the mold material, the final product has an excellent finish and accurately resembles the master pattern. Even the finest of details are captured in the finished product.
Use Vacuum casting for prototype mold making
Compared with rapid injection molding which is among other technologies that are used for similar kinds of manufacturing but often has more lead times and is deemed more expensive. On the other hand, vacuum casting technology can often achieve the same results with shorter lead times and if without special material requirement. When an individual company or large industries have to meet deadlines in a short period and just for functional and working prototype testing, vacuum casting can often be a better choice depending upon the requirements.