In IMHP technology (In-Mould Hold Pressure) from DuPont, hold pressure is applied using a separate mechanism integrated within the mould during the screw-dosing phase. This parallel arrangement of two injection moulding phases can help reduce cycle. DuPont has developed a technology, which can save between 20 and 30% in the cycle time when injection moulding semi-crystalline thermoplastics such as DuPont™ Delrin® acetal resin. By simply removing the mutual reliance on each other between the dosing and hold-pressure stages, the new In- Mould Hold Pressure (IMHP) technology allows the dosing phase in the barrel to take place simultaneously with the application of hold pressure, meaning that the cooling time can be factored out of the overall cycle time. Semi-crystalline thermoplastics require relatively long holding times, during which the volume shrinkage caused by the crystallization is compensated. In contrast to standard injection moulding procedures, the required hold pressure in the IMHP approach is generated within the mould. This allows the plasticizing unit to dose the melt for the next shot at the same time. These two phases would traditionally follow one after another, and now they can be carried out simultaneously. When the required hold pressure time has elapsed, the mould is opened and the part ejected. In general, the use of IMHP technology is confined to semicrystalline engineering plastics such as POM, PA or PBT. At the end of the hold pressure phase, only these materials have sufficient stiffness and crystallization shrinkage to permit reliable ejection from the mould. As well as significant time savings, DuPont was also able to demonstrate that there were no significant changes in terms of dimensional stability and mechanical properties between standard injection-moulded samples and those produced using the IMHP technology.