The additive manufacture of lightweight grippers for a robotic handling system has eliminated excessive waste in a production operation at the plastic injection moulding specialist Theo Hillers, which is based in Kall, Germany.

The company, which was looking for a way to handle plastic mesh filters for the pharmaceutical industry without damaging them, previously transferred them from injection moulding machines to the next production stage by gripping the parts by their sprue (the plastic waste left in the hole through which the mould was filled), then snapping it off and dropping the filters onto a conveyor belt.

This caused some of the filters to be damaged, resulting in an unacceptable level of wastage.

For cost reasons, the existing three-axis sprue-picking equipment had to be used, so the planned robotic gripper had to fit around it in order to place the filters gently onto the conveyor.

Other design constraints included a maximum gripper weight of 500gm and the need for eight or 12 suction cups — in a limited space.

Theo Hillers also wanted to reduce the overall complexity of the robotic gripper to ensure that it was robust and would not suffer fatigue fractures.

The task was taken on by ASS Maschinenbau. Grippers for automated handling are usually made from modular aluminium components, so when it came to using lightweight polyamide for their construction, there was little practical experience to fall back on.

For a solution, ASS turned to additive manufacturing using equipment from another German firm, EOS, which has a UK subsidiary in Warwick (www.eos.info).

Internal air ducts were integrated into the CAD design so that no additional weight was incurred by air hoses; this also resulted in the grippers being tidier and less complex. Production of the grippers took place overnight in an Eosint P 390 system from EOS.

After the CAD data had been transferred to the machine’s control, the components were produced by melting and fusing successive layers of black polyamide powder using laser power.