Osram integrates metal and plastic in car lamp

Osram's 2016 automotive LED lamp cluster concept produced in the IMPIM process

Integrative plastics technology was the major theme at IKV’s 2016 Plastics Colloquium. In this feature for Plastics News Europe David Vink reviews Osram’s work on a highly integrated LED lamp cluster with moulded metal tracks.

Lighting products group Osram is investigating the IMPIM – integrated metal-plastics injection moulding – process as a new production method for automotive LED lamps.

At the 2016 IKV Plastics Colloquium in Aachen, Germany in February, Florian Petzold, Osram technology scout and manager of the technical moulding centre within its innovation department, discussed the group’s feasibility study for an automotive LED rear lamp cluster unit based on IMPIM (or IMKS in German).

Petzold showed a cost comparison for rectangular conventional and IMPIM circuit boards made prior to development of a prototype IMPIM lamp unit. For the rectangular examples, 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.

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 KraussMaffei 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. He showed a video of a vertically rotating 2-cavity mould, metal moulding taking place in one fixed mould half cavity, during base plastic LED overmoulding in the other.

Osram 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 variothermal dynamic rapid heating and cooling may be required.

Osram’s 2016 feasibility study follows on from an earlier round IMPIM LED unit, presented at IKV’s 2014 IIMC international injection moulding conference and displayed at the 2016 IKV Plastics Colloquium.

Aside from mentioning the LED desk lamp at Fakuma 2012, Petzold said the original IMPIM idea arose at IKV in 2007. This led to IKV moulding polyamide sports sunglasses with lenses heated by metal tracks in MPC HEK’s MCP 200 alloy, at its K 2010 fair stand using Ferromatik machinery equipped with a Babyplast add-on injection unit. Mouldmaker Krallmann was among the development partners for the sunglasses and desk lamp parts, with 3?station index plate moulds, as it was also for IMPIM car key fobs shown by KraussMaffei at Fakuma 2014.

Petzold said he believes IMPIM has even more interesting potential in indoor luminaires such as down-lights, and LED street lighting using optical lens arrays, despite higher temperatures with the latter.