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Closed Mold Manufacturing

Understand the Common Types of Closed Mold Manufacturing


Silicone bag Molding

Silicone Bag Molding

Todd Johnson

What is Closed Mold Manufacturing?

Closed Molding is a technology which allows the manufacturing of better polymer composite parts in less time, with less waste, and largely reduced emissions a possibility. A wide range of industries use closed mold technologies to make precision parts. Industries include aerospace, transportation, and recreation. When identical parts need to be manufactured out of composites multiple times, closed molding is viable options

There are three primary types of closed mold technology, these include:

  • Light Resin Transfer Molding (Light RTM)
  • Closed Cavity Bag Molding (CCBM)
  • Vacuum Infusion Process (VIP) - (Not to be confused with vacuum bagging)

These three technologies are further described in the sections below.

There are many intangible advantages of using closed molding. These include higher quality control, improved surface finish, and a more worker-friendly environment. Other tangible advantages of using closed mold manufacturing include:

  • Offer new strategies to meet MACT/EPA/OSHA emission standards
  • Allow you to make superior parts in a consistent manner
  • Consistently trim parts
  • Result in lower labor costs
  • Make parts quicker with less molds, lowering overall costs
  • Require less operator control by using improved process technology
  • Require less equipment and protective clothing
  • Lower post work and finishing
  • Lower scrap rate

Simply put, closed mold manufacturing will result in a cleaner, safer, and more productive production plant. With this, employees will also be more content. Any manager can attest to the unspoken advantages of a work environment with a productive and happy work force.

Education and Training

Light RTM, CCBM, and VIP all have immense potential for improving quality and productivity when switching form open molding or other composite molding technologies. With this said, the improvements will only be maximized when employees are appropriately trained and well versed in the technology.

However, the learning curve is extremely fast in using closed molding. In fact, many say that less skill required in closed mold manufacturing. Most all composite technicians with experience in hand lamination or open molding quickly grasp the properties and theory behind closed molding.

Some composites distributors, such as Composites One, will offer educational sessions and on-site trainings to get your production plant started. 'Demo-Days" (daylong demonstrations designed to educate workers on these technologies) are also available by these distributing companies at no cost.

In the competitive global marketplace of today, it is in the material distributor's best interest to help train and improve their customer's composite manufacturing capabilities.

Process Overview

All Closed Mold technologies share the goal of getting the resin to its destination the fastest and easiest way. The difference between Resin Transfer Molding (RTM) and Vacuum Infusion Molding (VIP) is that:

  • RTM uses an above atmospheric pressure to send the resin into the your composite tool. If you are using a pressure pump as the force to drive your resin, you are using RTM.
  • VIP uses a lower than atmospheric pressure to send the resin onto your composite tool. If a vacuum pump is providing the force to drive your resin, you are using VIP.

If the resin is being "pushed" into the mold or tool, this is considered RTM, while if the resin is "pulled" into the mold, this is considered VIP, or simply "infusion."

Closed Cavity Bag Molding (CCBM) offers the advantage of flexibility over RTM and VIP. With this process, either a pressure pump or a vacuum pump may be used to drive the resin into the part.

Switching from open molding to closed molding is a big leap. When deciding on which process to use, it is important to consider:

  • How large is the part
  • How many parts are need to be made
  • The complexity and dimension of the part
  • What resin and reinforcement will be used.
  • How fast parts need to be made

Many distributors and manufacturers of the materials can help consult and advise on which route to go, and many have an experts on call.

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