Plastic prototypes are rampantly made today using silicone rubber molds. Many manufacturers cast urethane parts from silicone rubber molds. Here is an article describing the technique used for casting urethane parts from silicone rubber molds. Factories with specialized equipment and machinery are present in making these molds.
Plastic Prototypes Using Silicone Rubber Molds
Creating the Master
It is the first step in the process. A master pattern has a material of clay, wood, or plastics. Today, people use a rapid prototyping process including stereolithography and laser sintering. They use many modern gadgets, such as CNC machined masters, PolyJet, 3DP, 3D systems, fused deposition modeling, etc. Hence, most of these machines use a layering technique in this process. So after making the basic polyurethane cast part, there is a final finish by filing, painting, or sanding.
Designing the Mold
Next, the mold using a silicone rubber is designed. The machine is set up as per the mold. Vents and gates are adjusted, and mold locators are added for the precise alignment of the mold haves. There is a selection of platinum base or a tin base silicone for mold making. While the platinum base does not shrink at all and has better chemical resistance, the tin base has outstanding resistance to inhibition and has a low durometer for flexibility. Both types can withstand casting temperatures from 390 to 590 Fahrenheit. Sometimes, to prevent inhibition due to contaminants present, there is an application of a barrier coating to the master design. These can be of acrylic sprays or polyvinyl alcohol.
Making the Mold
The silicone rubber mold is constructed. These can be very accurate and can have detailed duplication. Silicone rubber is also highly flexible for making different kinds of molds. The different types include book mold, two-part mold, and skin mold. After it has been determined which type of mold has to be made, the process of preparing silicone for mold making begins. Thus, you need to measure the right quantities of silicone base and catalyst. After undergoing a series of further processes, the mold is ready for urethane casting.
Casting the Urethane Parts
There are a wide variety of urethanes available today. These have different specifications. Hence, these are based on hardness, elongation, tensile strength, and various factors. Once the casting is ready, you proceed to the final finishing.
Finishing the Urethane Parts
The last step in part reproduction is finishing. People cut off the vent gates, and there is a removal of flash that is present to finish the prototype part. The rough edges are further smoothened and filed using sandpaper. They fill any possible voids with degassing and fine point tools. Using a fine grit or sandpaper, they remove the excess.
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