Vacuum casting (also sometimes called as polyurethane casting) is a small batch production method to produce parts out of liquid resin that are almost identical to injection molded parts. Process involves preparation of master pattern, creating a mold with silicone and casting the part into the silicone mold.
First – Preparing the master pattern. It is 3D printed in stereolithography in most cases but CNC machining can also be used to create the master pattern
Second – Creating a wooden case for pouring the liquid silicone mold
Third – Pouring liquid silicone resin over the master pattern along with the runners and gates. And then allowing the mold to solidify
Fourth – Finally casting the part into the silicone mold by pouring the polyurethane resin
By carefully cutting to split the silicone mold and removing the master pattern, it is possible to prepare the silicone mold, cast the polyurethane resin into it, split open the part and reuse the same mold for 20 to 25 cast shots. Each cast can take 1 hour and curing and post-processing can take 1 day. The overall production of a small batch can take 10 to 15 days which is much faster than injection molding that takes several months to machine the metal molds to precision. Let’s understand 2 scenarios that explain when vacuum casting is the suitable choice for production.
During Mid-Stage of Product Launch
Vacuum casting is especially right during the functional testing and marketing phase where a batch of about 20-50 parts are required for initial customer feedback before investing into mass production tooling. It can be said that vacuum casting falls in the segment that is between rapid prototyping and mass production injection molding. 3D Printed masterpiece is required for silicone mold preparation. Hence vacuum casting involves a 3D printing phase usually stereolithography to give the best surface finish to the pattern. Then it is hand polished to give it the best possible finish making sure no surface defects show up in the casted parts.
For Replicas and Spare Parts
Often at times the plastic parts or plastic components being serviced or sold are limited in number and it is a common encountered need for creating copies of parts. With vacuum casting it is possible to replicate an existing part a few times to create additional copies that are either end use parts or spare parts. The approach is to first 3D scan the original part; develop the CAD model and then 3D print the master pattern out of it for creating the silicone mold and proceed with the resin casting process. Another approach is that in case if 2 to 3 original parts are available in good condition without any damages or worn out surfaces then one of them can be directly used as a master pattern for creating the mold.
Polyurethane cast grade resins that resemble properties of ABS, PP, PE like materials can be casted with vacuum casting. For more detailed materials available you can contact us from here.
Cost of vacuum casting reduces the costs of developing and machining the metal molds that are needed for injection molding. Although cost per part can be a bit higher, the overall cost for a small batch of parts is way lower than that of a complete injection molding. You can talk to our specialists from here.
Quality and Surface Finish
It is a fascinating fact that the parts casted in vacuum casting process have really good quality in terms of strength and surface finish.