HOW DPM WORKS
Differential Pressure Molding is a low-pressure compression process that utilizes a pressure differential between the inside and outside of the tool to form sheets of plastic. A unique aspect of this process is that it creates uniform pressure over the total surface of the mold, which allows the use of lightweight, thin-shell tooling that can be heated and cooled rapidly. As a result, our tools can be quickly and inexpensively.
A clamp frame holds both halves of a thin-shell composite mold. This same device also allows the mold to be opened (to insert material or remove completed parts) and closed (to form parts). Molding force can be generated either from inside the tool (called negative-pressure molding) or from outside the tool (called positive-pressure molding). Simple air or water pressure is sufficient to form the material.
As the tool closes, mold halves stop moving against each other when the pressure reaches equilibrium or stops are reached.
Cycle times are short even for large parts (in the 30-90 sec range). A number of smaller parts can also be molded via a family tool. The process can be operated by a single person loading material and removing finished parts, or it can be semi-automated.
Both thermoplastics and thermosets can be molded in DPM. With thermoplastics, the tool will be cooler than the composite sheet (which will have been previously heated prior to being placed into the tool); with thermosets, the tool will be heated to kick off the cross-link process.
A wide variety of skins / laminates can be bonded to the composite material during the molding cycle. Owing to the low pressures, there is very little material flow in the tool, limiting the amount of 3D complexity in the design but helping prevent tearing or over-stretching of face materials.
A unique feature of the DPM molding process is that 2 or more tools can be built to operate simultaneously in the same press, allowing 2 or more different sets of parts (whose size, geometry, and material can vary significantly) to be molded each cycle as long as each part is sufficiently symmetrical to balance molding pressures. As one tool opens and the part is demolded, the second tool is loaded and closed to form the next part, making it ideal for producing multiple versions of a given part on a “just-in-time” production basis. This multi-tool molding option can be setup either as a stack or via a pivot system.
This means that DPM can offer significant process efficiencies at far lower costs and far less floor space than most other competitive compression processes. The schematic and short video below show the double-molding process in action.