Osram, a lighting products group, is investigating the IMPIM (intergated metal-plastics injection moulding) process as a new production method for automotive LED lamps.
Florian Petzold, Osram technology scout and manager of the technical moulding center within its innovation department, shared the group’s feasibility study for an automotive LED rear lamp cluster unit based on IMPIM (or IMKS in German) at the 2016 IKV Plastics Colloquium in Aachen, Germany in February.
Petzold showed a conventional LED cluster assembly: LEDs on separate large and small FR4 circuit boards are assembled to a plastic carrier and connected by conventional wiring to an external “light engine” driver FR4 board.
One IMPIM process moulded part can integrate all of these functions, cutting five process stages to one. “Huge design freedom” arises by avoiding rigid FR4 board shape and LED mounting position limitations, or laborious flexible circuitry assembly versions.
IKV evaluated flow length, injection speed, melt and mould temperatures and flow rate of the moulded tracks in a low melting point tin-zinc alloy conductive solder. The metal is fed to the mould via a single hot runner nozzle by a piston in an injection unit derived from metal die-casting processes.
An earlier IMPIM LED desk lamp, demonstrated by Krauss Maffei and shown by mouldmaker Krallmann at Fakuma 2012, used a third (polycarbonate) component overmoulded onto moulded metal tracks to encapsulate and firmly fix tracks to a polycarbonate base moulding.
But the 2016 Osram automotive lighting concept has been designed with undercuts in the mould. These form overlaps over the track recesses. So the moulded metal tracks are well retained, while avoiding complexity and costs involved with a second protective plastic component and associated higher mould costs.
Single plastic component design means LED electrical contacts are sealed to avoid being affected by flash from the easy-flow metal alloy. “Overmoulding of LEDs with a plastic component and contacting LEDs with solder is feasible”, Petzold stated.
IKV used Sigmasoft mould and moulding software for process simulation. The metal solder rapidly cools within 10s after LED pin contact and the 0.25s filling stage, solidifying at 133˚C. But as “soldering between solder material and LED pins is questionable, additional heating is required for the solder joint”, Petzold advised.
In its study, Osram is also: conducting automotive thermal shock tests on the IMPIM unit, investigating automated robotic production, running mould trials with different polymers and low melting metal alloys, seeking solutions to shorten machine set-up time and using process simulation to predict associated part quality with different materials. Depending on track lengths, close contour vario-thermal dynamic rapid heating and cooling may be required.
For a conventional LED lamp cluster unit, the total cost based around FR4 type glass fibre fabric reinforced epoxide resin laminate circuit boards, amounts to €4.95; for the IMPIM hybrid moulded version, the cost is €4.85. Within total cost, “bill of material” (BOM) costs account for respectively €4.42 and €3.77. While IMPIM direct material and machine costs are higher at €0.49 and €0.34 against respectively €0.20 and €0.18 for the FR4 laminate design, IMPIM labour cost at €0.25 is lower than a FR4 unit’s €0.33.
(According to www.plasticsnewseurope.com)