Composite molds vary widely, depending on the industry and application. For instance, high-end, nickel-iron alloy tooling is commonly used in the aerospace industry, while boat and wind blade manufacturers typically use GFRP molds. This column will focus on traditional composite molds that utilize glass fiber as reinforcement and will provide guidance for manufacturers striving to invest in cost-effective molds that meet the required volume and quality standards, using the best-suited process for manufacturing.
Best practices for mold making vary based on many factors, including the following:
- Number of parts to be made with a mold
- Mold service life
- Final product specifications, tolerances and surface finish
- Material selection
- Production rate and delivery deadlines
- Staff expertise
Because there are so many decisions to make concerning molds, we’ve divided the topic into two columns. In this issue, we will discuss the influence of the final product manufacturing process, mold design and plug production. In part two, which will be published in the January/February 2018 issue of Composites Manufacturing magazine, we will examine mold building, mold maintenance and up-and-coming mold innovations.
Composite Production Processes
Prior to starting the mold-making process, it’s imperative to consider the expected production method for the final application. The method you use influences the mold you will build, and, conversely, the mold impacts the production method. Here’s an example illustrating the symbiotic relationship between the two: If you only require a few parts, then you wouldn’t build a mold for a heated resin transfer molding (RTM) process. The mold and process would simply be too costly. But if you plan on fabricating a dozen or so parts per day, then you would likely utilize heated RTM molds, which can turn out two to three parts per hour.
These are some of the factors to consider as you think about both your anticipated production process and the mold:
- Surface requirements – The gloss, profile and texture of the final part.
- Expected volume – Is the application a prototype (1-5), low volume (20-50), medium (several hundred) or high volume (several thousand)?
- Number of molds – Expected volumes determine the number of molds required.
- Accuracy – Parts are often joined together, so precision is key.
- Durability – This is often tied to required volumes, but simple design modifications (like higher draft angles) can reduce wear and damage of the mold surface.
- Speed to build – The time it takes to make one or multiple molds.
- Cost and budget
Design, plug making, mold construction, surface preparation, framing, maintenance and demolding can vary significantly depending on what type of composite manufacturing process the mold will ultimately be used for.