Mold design is one of the most critical steps in the initial stages of planning the production of silicone rubber keypads and components. Silicone molds come in many different shapes and sizes, and they can be made out of different metals with each having its own characteristics and benefits. Here at SiTECH, we partner with highly skilled mold makers with decades of experiences in liquid silicone injection molding.
When a customer provides us with Released for Production 3D CAD files of their design, we can begin with the process of mold design. Here at SiTECH, we utilize SolidWorks as our 3D modeling software. Our engineers utilize the 3D modeling features and components included in the latest SolidWorks release to design all of the mold parameters. The behavior of liquid silicone rubber is taken into account in the design phase as well. Because of its low viscosity, liquid silicone rubber molds fill very quickly, even at low injection pressures. This is important to understand so that critical components of the mold can be taken into account and designed into the schematics at this stage of the process.
The material that the mold is made of is another decision to take into account. Steel core and cavity sets are the most durable and long-lasting for years of LSR molding production without ill effect. Aluminum core and cavity sets are less expensive than steel and are lighter. Although rare, aluminum through extended use and thermal cycles can suffer from the annealing process, which affects the properties of the metal’s hardness and ductility. Deciding which material to use in LSR molding production should be based on the thickness of the parts being made in comparison to the thickness of the mold, as well as the intricacies of the design.
Another aspect about silicone rubber molding to consider is when heated, LSR expands. When the part is extracted, it’s calculated to shrink by 2 – 3 percent as it cools. There are few factors that affect the shrinkage of the part, tool temperature, pressure in the cavity and the thickness of the part itself. Thicker parts shrink less than thin parts. These are important factors to consider because of the tight tolerance required for most silicone component applications.
The silicone rubber part directly duplicates the surface of the mold, so the finish of the mold surface is critical to the needs of the component. Polished steel is used in the production of clear or transparent parts. An eroded or textured surface helps in the removal of silicone mold rubber parts by lessening the adhesion between the silicone and the mold. The surface of the mold can also be treated with a titanium/nickel compound to increase the life of the mold.
Many decisions have to be made in the process of design and mold manufacturing for production of silicone components. At SiTECH, we are here to help make those decisions less daunting and more transparent. From our highly skilled engineers to our advanced silicone production equipment, our team is dedicated to the successful production of all your silicone mold rubber needs.