Open Molding
25 February 2021

Robust, rugged, and accurate metering/pumping systems for polyester (gelcoat)/vinlyester and MEKP applications. Traditional industries for this equipment are Marine (boats, jet skis), Automotive (after-market parts, truck canopies, large truck parts), Tank building (corrosion, chemical, waste water), Amusement Parks (water slides, rides and rock walls) and Home Construction (bath tubs, hot tubs, jacuzzis, swimming pools).


What is Open Molding?

Open molding is simple, effective and low cost, allowing for rapid product development. In this process, a single-sided mold acts as the form and cosmetic surface of the part.


Open Molding Processes

Open molding employs different processes, allowing manufacturers to meet their unique part production needs. To determine what type of open molding is best for your production, you’ll need to consider each process.

Hand Lay-Up

In hand lay-up processes, which are ideal for prototype and short production runs, the mold is first treated with mold release followed by a pigmented gel coat spray to produce a high quality surface. Once the gel cures, glass reinforcing fibers are placed in the mold, followed by a poured, brushed or sprayed on catalyzed resin. Manual rolling ensures that the resin thoroughly covers the reinforcement while removing trapped air and compacting the composite. For thickness, additional reinforcement and resin may be added, and a catalyst or accelerator cures the resin system, hardening the composite without the use of external heat.


Typically used to produce larger volumes of parts, spray-up processes offer great shape complexity and fast production, using a chopper/spray gun to cut reinforcement material into short fibers that are added to the catalyzed resin and deposit mixture, then sprayed on to the molding surface. Similar to lay-up, removal of entrapped air and thorough covering of the resin is achieved through manual rolling.


What Are the Benefits of Open Molding Compared to Closed Molding?

While closed molding processes offers many advantages, including the ability to make parts faster, open molding has its own unique benefits. The open molding process represents lower start-up costs, can accommodate very large parts with the ability to change mold sizes, and enables a wide range of cost-effective versatility in part capability. Although only one side of the product will be smooth in open molding, a high gloss can still be achieved on the smooth side, with resin and gel-coats that can be color matched to eliminate the need for secondary finishing.

With a vast fluidity in part size and design options, flexible open molding processes are typically used by companies who manufacture a wide range of products where automated processes are unfeasible, or those who produce customized parts or only a small quantity of parts that cannot substantiate the greater mold costs of automated processes.


Advantages of Open Molding in Precision Part Production

Precision is vital in part production. For composite component fabrication, there are many process methods that can be employed—these processes typically involve some form of molding to shape the resin and reinforcement. Materials, part design and end-use or application all factor into the method that will be selected. However, open molding is the most accommodating of all composite fabrication and MVP equipment is the way to go when it comes to open mold processes!


CTP Open Molding Equipment – Processes Made Easier

Whichever open molding process is right for you, CTP has the equipment to guarantee precise composite fabrication, ensuring an improvement in operating efficiencies, product quality, and low-emission eco-friendliness. Our line of chopper/wetout systems deliver power, versatility and unprecedented precision in building bulk and strength to produce a stronger, more uniform laminate with minimal overspray. And our rugged, robust gelcoat application equipment eliminates the needle and seat design to provide accurate application on composite tooling for the construction of composite fiberglass parts for low and standard volumes in even thicknesses.

To learn more about CTP’s lineup of open mold equipment, click here.