Molds for composite part production have been increasing in size and complexity and this has caused challenges with the curing process, both in-autoclave and out-of-autoclave.  Due to the challenges associated with driving energy inside the tooling/molding platforms that are used for these composite parts, integrating heat pipes into the tool/mold can enhance the heat up and curing process due to their high level of thermal conductivity. As a result, Isobar heat pipes can speed up the curing process of the composite parts and increase productivity.

Based on test results, the new cooling chamber was not operating in an optimized manner and Acrolab was contracted to solve the problem.

Inserting ISOBAR® Heat Pipes Into the Molds

The objective of this project was to develop Isobar® heat pipe assemblies that could be inserted into either steel or carbon molds to improve the part curing process (in-autoclave). Acrolab’s Isobars® are typically used in the thermoplastic and thermoset mold industry to speed up heat transfer inside the mold structure, even out the temperature gradients in the body of the mold, improve the quality of the parts and reduce the cycle time.

This was tested and the results were very encouraging, showing that the molds with the integrated Isobar heat pipes were able to effectively deliver sufficient energy from inside the autoclave to the surface of the part and cure the composite parts uniformly and consistently, which had previously proven to be very difficult due to the complicated shape of the part.

Successful Results With 2 Concepts

Using Isobar heat pipes would significantly improve the molding process in terms of cycle time and production quality. It was very helpful to quantitatively determine the improvements after the Isobar Heat Pipes had been inserted into the mold structure, specifically as it related directly to both product quality improvement and reduced cycle time.

We narrowed our focus on two specific solutions, and pursued both of them; one concept was using direct energy inputs into the heat pipes that were inserted into the body of the mold, the second concept was to use passive energy inputs to capture the heat energy available inside the autoclave and transfer the energy to the interior surfaces of the mold through the heat pipes.

Based on the results of our analysis, Acrolab developed both concepts for prototype tools that were then tested at the client’s site. The prototype tooling was designed at approximately a quarter of the scale being used for the production part and incorporated both concepts/solutions.

The use of direct energy inputs as well as passive energy inputs to transmit heat into the composite mold structure to speed up the resin curing process yielded very good results and demonstrated that these two concepts were feasible.

Specialized Construction of Acrolab Isobar Heat Pipes

As stated above, at the client’s request, we designed both Isobar heat pipes with different lengths and different geometries according to their inherent limitations in the process. In order to accomplish the two builds we needed to source special tubing in order to build the Isobars along with the tooling necessary to achieve the design geometries proposed to the client.


We completed thorough testing onsite at Acrolab and validated performance criteria, manufacturing processes and build specifications to confirm the Isobar heat pipes were optimized for the client’s application. Once these were all documented, the Isobar heat pipes were sent to the customer for further testing and experimental runs.

Based on the customer’s feedback from their experimental runs, the Isobar heat pipes reportedly performed very well. The Isobar heat pipes clearly enhanced their process, allowing the resin to cure much faster and with better uniformity, demonstrating that they could mold more complex geometries using Acrolab’s technology, experience and thermal expertise in material processing.