FIT Fruth Innovative Technologies Laser sintering produces tool inserts for moulding complex parts
A mould-cooling technique based on refrigeration and laser-sintered tool inserts yields undistorted mouldings and production economy.
A specialist in the manufacture of mould inserts for series production tools, Fruth Innovative Technologies GmbH (FIT) employs direct metal laser-sintering (DMLS), an additive manufacturing technique, to produce inserts with optimised cooling channels. By means of this modern tool construction technology, the company can make complex inserts from high-quality tool steels and can design them with equally complex channels for fluid or gas cooling.
FIT employs DMLS systems from EOS (the Eosint M 270) and SLM (the SLM 250 HL) to build up mould inserts of careful design and fine detail. Because of the nature of DMLS technology—the formation of tools by the layered deposition of metal powder that is sintered by laser into a solid mass according to program—these channels can have an essentially arbitrary geometry. FIT’s temperature-controlled tool inserts offer a cooling capacity far superior to classic cooling channels that are unable to follow the mould contour closely.
Within this area of expertise, the tooling supplier has introduced gas-tempered mould inserts featuring Skin Freeze, a cooling technique that makes use of refrigeration technology. Skin Freeze is basically a closed tempering circuit. Fluid from a refrigeration unit is injected directly through inlets into the tool insert. Inlet valves attached to the mould tool allow the fluid to cool the insert instantly and accurately.
The refrigerant is conducted via a highly sophisticated duct system through the mould insert and around the wall of the cavity, which is just a few millimetres thick. Owing to the heat input from the plastic melt (moulding compound) entering the cavity, when the liquid coolant enters the defined expansion spaces in the insert, which consist of inherently stable open-pored structures created in the DMLS process and are situated immediately behind the cavity wall, it soon vaporises. (This is because of the sudden change of volume behind the wall.) In so doing, it can cool the cavity wall down to –30°C within seconds. The refrigerant is then fed through a second duct system back into the cooling aggregate for reprocessing.
Because of the extremely high energy absorption involved in the cooling process, which can be as much as 20 times that of water cooling, the injected moulding compound freezes almost instantly. Cooling rates as great as 80 K/sec are possible, and mould cycle times can be reduced accordingly. Problem areas in the tool, such as hot spots, cause greater vaporisation and a higher warmth absorption, which enables the refrigerant to cool the tool evenly despite fluctuations in cavity-wall temperature. The coolant gas adapts to local temperatures.