A continuing trend within the molding business is silicone molding, which is being used in the medical, electronics, packaging and automotive industries.
The injection molding of silicone has many applications due to the hardness range of the material, from 5 to 90 durometer. All of these industries have witnessed large growth trends in silicone molding—including the multi-material/two-shot molding and overmolding market segments.
Silicone appears to be the material of choice for more and more applications, due to the following properties and benefits:
Inert, odorless, tasteless, stainless; ideal for medical and food applications
Hypo-allergenic
Thermal resistance; special compounds available
High resistance to weathering and oxidation
Excellent electrical qualities
Flexibility and durability
Colorfast and light stable with FL color pastes
Can be compounded for special properties
One needs to realize that the technology is 180 degrees opposite of what the experienced injection molder has developed throughout his or her years in the thermoplastics business.
Silicone rubbers are synthetic polymers with an alternating Si-O backbone. The molecules will cross link with the addition of a catalyst, such as platinum catalyst silicones. The two parts are mixed in a predetermined ratio, forming a compound ready to be cured.
The silicone molding process is different from that of thermoplastics in a few different ways. To mold a part, thermoplastic resin is heated in the barrel and injected into a cold mold. Typically, silicone molding of a part requires the liquid rubber to be kept cool (5 to 25oC or 60 to 77oF) and then it is injected into a heated mold (170 to 210oC or 340 to 410oF).
Silicone is a strong choice for mold-making because it offers such a diverse array of benefits. You can easily create custom designs using silicone molding. The molds themselves are also quite durable, so you can use them repeatedly without fear of breakage. Silicone’s inorganic makeup—compared to rubber, its organic counterpart—makes it highly resilient to heat and cold, chemical exposure, and even fungus. Some of the benefits of silicone molds include the following:
Flexibility
Silicone’s flexibility makes it easy to work with. Silicone molds are pliable and lightweight compared to stiffer substances like plastic and they’re also easier to remove once a part is fully formed. Thanks to silicone’s high level of flexibility, both the mold and the fabricated part are less likely to break or chip. You can use custom silicone molds to shape everything from complex engineering components to holiday-themed ice cubes or confections.
Stability
Silicone withstands temperatures from -65° to 400° degrees Celsius. Additionally, it can have an elongation of 700%, depending on the formulation. Highly stable under a broad range of conditions, you can put silicone molds in the oven, freeze them, and stretch them during removal.
Durability
In most cases, you’ll get many runs out of a silicone mold. However, it’s important to note that the life span of molds can vary greatly. The more frequently you cast, and the more complex or detailed your design, the faster your mold might degrade. To maximize the life of your silicone molds, clean them with mild soap and water, dry them thoroughly, and store them flat without stacking.
Limitations
While there are a lot of benefits to working with silicone, there are also a few limitations to be aware of:
Silicone costs more than latex and organic rubbers. A quick comparison on Amazon shows a gallon of silicone regularly topping $100—almost twice as much as latex.
Though it’s flexible, silicone can tear if stretched too far.
Not all silicone is formulated equally. Always purchase silicone and any manufacturing materials from a reputable supplier.
Benefits of Silicone Molding:
Precision and Detail
Silicon molding allows for extreme precision in the reproduction of prototypes for a manufacturer. The process even allows for complex geometries to be factored in and reproduced at a large scale. The results of silicon molding are almost identical to the finished product, making it perfect for checking for visuals.
In producing prototypes, there’s a reliance on extreme details in order to make aesthetic examination as accurate as possible.
Pricing and Economies of Scale
Other manufacturing processes could turn to steel molds to create their product prototypes, but these molds can be expensive to fabricate. Silicone molds are relatively cheaper than steel molds, and they can be used multiple times to deploy many prototypes before they break.
Economies of scale can be achieved in an average of about ten parts making it cheaper than other methods of casting utilizing molds made of aluminum or steel, or using 3D printing technology to recreate several prototypes.
Only the first product needs to be 3D-printed using this method and this saves a lot of money.
Speed in Production
Silicone molding is a pretty quick process with the possibility of producing 30 to 50 functional parts in less than one and a half weeks. This speed of output allows manufacturers to benefit from quick deployment of prototypes and speed in the decision-making process leading up to production launch.
It’s an excellent method to use if a company finds that they have urgent needs or requests that need to be fulfilled. It allows for efficiencies to occur in the entire production cycle; these efficiencies can translate into actual dollars for any company.
However, for batches over one hundred it does pose limitations to the extent that a steel mold should be considered.
Quality
Silicone is one of the best materials that producers and manufacturers can use for prototyping. In fact, a lot of science has been going into silicone for usage in different types of applications.
The quality of the part being reproducing through the vacuum casting process is almost akin to the final product due to the number of materials that can be used in the molding process.
If a manufacturer finds that a material they would be using in the final process is available for casting, then it comes at the added benefit that they’ll be receiving prototypes using the final material.
As mentioned earlier, resins can be manipulated for hardness, flexibility, rigidity, and even transparency. This allows for a variety of different types of material quality to be used for the process.