CLOSED MOLDING

Closed Cavity Bag Molding (CCBM)

With the exception of a wide perimeter flange, the rigid mold half can be constructed in exactly the same manner as an open mold. The CCBM process uses vacuum to clamp the mold halves and to help pull the resin through the reinforcement. However, the resin is injected, rather than infused as in VIP, but under relatively low pressure (the use of vacuum and injection pressure simultaneously is often referred to as a push/pull system).

CCBM is popular because it works well in many applications and because it has truly fulfilled the promise of a simple low-cost entry into the closed molding process. Don’t misunderstand; there is a learning curve, as there is with any newly adopted process, and the tooling will cost several times that of an open mold. But the process, the tooling, and the startup costs are well within the financial means and capabilities of most open and closed molders.

Each of the popular low-cost molding processes has advantages and disadvantages. A typical molder should learn all three processes, choosing the process that is most suitable for each application, based on part geometry, customer specifications, and desired production volume. If an open molder has concerns related to styrene emissions, shop working conditions, worker retention and training, or part-to-part consistency, CCBM may provide a viable alternative to open molding.

Silicone Bag Molding (SBM)

Basically, SBM is not that much different than CCBM…just an easier process to work with if you are making multiple parts. It also does not use a clamping ring like CCBM and relies solely on vacuum pressure to secure the mold in place prior to resin injections. In some cases with SBM, less than one day is needed to convert a mold to closed molding. An existing part, rather than sheet wax, may be sufficient for creating the part thickness. And no release agents are required. Silicone bags if cared for properly are good for hundreds of part cycles. And, unlike VIP, very few disposables are required for SBM.

In addition, the many advantages that CCBM offers are also experienced by the silicone bag user. However, the silicone used for the SBM process is a more environmentally pleasing product with little to no smell.

It is important to note that both CCBM and SBM eliminate virtually all styrene emissions when the process is used properly.