Author: Josh Morrison
In all manufacturing environments there are challenges presented and a need for continuous improvement. In our case, the challenge was posed in the RTV department. Certain materials required extended cure cycles to retain dimensional tolerance and mechanical strength. These cure cycles at ambient temperatures would, in some cases, extend to the better part of a week. The result: 4 or 5 days to find out if you have a good part. This was not acceptable, especially in the condition where a new tool was in the iterative, troubleshooting phase.
The answer to these lengthy dimensional instability and fragility times was in the creation of proper thermal cure cycles. One possible solution was to remove the components from their respective tools and thermally cure them in an oven. The problem with this approach was that we were frequently faced with part geometries that were too unstable or too delicate to remove from tooling in these early cure stages. The only remaining and viable way to fix this issue was to cure the parts while they were still in the tooling. This required the oven to be significantly larger than one housing only bare components. The oven size requirement then approached that of the mold chamber.
Our solution to this challenge? Heat the mold chamber.
There are two basic ways to heat a pressure vessel: conductive heat through the shell or an internal heating element. For our use, we determined that the safest (i.e. preventing possible damage to the chamber due to hot spots on the shell) and most accurate method of heating the chamber was via an internal heat source.
An internal heating system was designed and incorporated as a closed loop control system. This system required several custom designed components, two of which were favorable for production utilizing in house additive manufacturing technologies. Both components were produced in the FDM® process to utilize the low cost and high strength materials this process offers.
The first component produced internally was the control box. This box was not constrained by thin walls, nor did it have high heat requirements.
The second part produced for this system was much more stringent on the material requirement. This was the internal heater mount. Because of its location in the pressure vessel, the mount must be able to survive in excess of 200° F. The low cost FDM process offers a polycarbonate material with a service limit of around 280°F .
Internal Heating Mount
These components and the incorporating system resulted in a low cost system that has drastically improved dimensional stability and tooling cycle times. The 4-5 days, cure cycle times for RTV components has been reduced to a maximum of only 2 days, allowing us to meet tighter delivery schedules.
Do RTV molding yourself? Looking to have your own pressure pots? Contact GROWit and we can help you out! Contact us at sales@GROWit3D.com for more info.