Developing and manufacturing grippers for handling tasks involving small quantities is time-consuming and expensive. Especially when the product to be handled is constantly changing. To meet these challenges, researchers from the Center for Additive Production (ZAP) at Fraunhofer IPA have developed a process that allows multi-component grippers to be manufactured quickly and cost-effectively.

The requirements of the industry

The project began at Henkel in Düsseldorf. At the industrial and consumer goods manufacturer, robots remove plastic bottles from a filling line and take them for further processing. They are equipped with a two-part gripper, the base body of which is made of aluminum. The gripper jaws are made of an elastomer to prevent the bottles from being damaged or slipping off. As Henkel's product range is constantly evolving, the grippers have to be replaced time and again. Previously, the molds used to manufacture the elastomer gripper elements had to be produced separately for each gripper. A fitter then screwed the gripper jaws to the base body by hand.

Automated production process reduces costs

The scientists at ZAP have therefore developed a process that allows the grippers to be manufactured faster and significantly more cost-effectively in a single production step: additive freeform casting, a combination of 3D printing and gravity casting. Manufacturing process largely automated Two print heads and a dosing unit are used during production. The base body of the gripper and the support material are printed using the FFF (Fused Filament Fabrication) process and form the rigid part of the gripper and a casting mold. The researchers use thermoplastics such as acrylonitrile butadiene styrene copolymer (ABS) as the printing material for the base body. The support structure, on the other hand, consists of a water-soluble plastic such as polyvinyl acetate (PVA).

In order to be able to cast the two-component silicone for the gripper jaws during the manufacturing process, the scientists have integrated a special dosing unit into the 3D printer. This uses silicones from Henkel that are viscous enough to fill details and cavities and also meet the requirements for dripping and curing time. Once the manufacturing process is complete and the silicone has cured, the support structure is removed in a water bath. The result is a component with both rigid and elastic material properties. "Additive freeform casting is a manufacturing process that is largely automated," says Jonas Fischer, one of the researchers involved at Fraunhofer IPA. "You only have to send the CAD data to the 3D printer and then it can manufacture the gripper independently. Post-processing by hand is not necessary and waste is avoided as far as possible."

Removing the gripper from the printer and placing it in the water bath is the only work step that currently still has to be done by hand.