KIMW removes visible knitlines

Friedrichshafen, Germany — The two main innovations on the booth of Kunststoff Institut Lüdenscheid (KIMW) both offer solutions to remove visible knitlines, phenomena that can be particularly noticeable in high gloss parts.

In the ThermoOpt process, a passive temperature control ceramic thermal barrier layer applied to a mold means less heat is absorbed into the mold metal. As a result, the higher temperature in the mold causes the knit line to practically melt away. Stefan Schmidt, managing director of KIMW said the ThermoOpt coating is 20-25µm thick and that this approach has been conceived for dealing with knitlines on large surface area parts.

KIMW displayed ThermoOpt examples in the form of a Gigaset telephone handset and a remote-control garage door opener housing produced by Mayweg Kunststofftechnik GmbH during the Fakuma 2015 trade show in Friedrichshafen.

The other passive temperature control knitline solution uses partial application of additional heat just in the areas where visible knitlines occur. This is applied using electric heating cartridges form Hotset Heizpatronen und Zubehör GmbH in Lüdenscheid.

In what Hotset calls its Z-System partial dynamic temperature control, developed jointly with KIMW, dynamic heating is applied to relevant points in the mold cavity at a heating rate of up to 60°K per second. This raises the temperature from just over 40°C to just over 50°C within 7 seconds, followed by cooling to 10.5°C.

Looking at a black high-gloss polycarbonate version of KIMW's standard ice scraper as a test piece, it is apparent that if there had ever been any knitlines, the Z-System solution made them melt away.

Aside from knitline removal, HotSet says the reduction of temperature in the overall mold structure enables faster cycle time and low energy cost — 100W in the case of the ice scraper. The technique has been patented, but is license-free, it was stressed in a presentation on the KIMW stand, which also showed a process for introduction of the system, starting with a secrecy agreement and ending with KIMW support in installation and start-up of the Z-System solution.

Schmidt said KIMW now has seven advanced mold rapid heating and cooling (RHC) techniques at its disposal. These include the new two knitline removal ones, Roctool induction, BFMold ball-filled molds, carbon dioxide and Greenmold. The latter involves electrically heated conductive mold coating and was one of the KIMW highlights at Fakuma 2014.

Metal direct injection molding

Meanwhile, Siegfried Kaiser, manager director of KIMW's sister institute Kunststoff Institut Südwest (KISW), discussed a new Medimold project, standing for “metal direct injection molding” and involving low melting point metal alloys. Kaiser said that unlike the new Liquid Metal process from Engel Austria GmbH, which is so far aimed at larger parts and in a specific type of alloy, KISW's project is with different alloys and aimed at multi-component applications, including additive ones. Two typical examples have been produced by conventional 3-D molded interconnection device technologies.

The Medimold project started with 12 initial partners, but Kaiser said the number has grown to 23: “It is very interesting for many companies,” he said. One of the initial project partners is plastic lens molder Polyoptics GmbH in Kleve, Germany, which Kaiser says wants to use the project to develop demisting features on lenses. And KIMW's Lüdenscheid based mold construction sister institute Werkzeugbau-Institut Südwestfalen GmbH is also among Medimold project partners.