Laser melting used to make metal cores for moulds

Having searched for a means of producing cooling channels in injection moulding tools, a garden tools maker is using the selected laser melting deposition process to make the cores.

MCP's selective laser melting (SLM) direct to metal technology has been applied by Gardena in the production of injection moulding tool cores with conformal cooling channels.

Gardena's Juergen Knill explained, "We required a technology which allowed us to design cooling channels in injection moulding tools, to enable simultaneous cooling of the complete part to maintain part quality as well as to speed demoulding." Using standard machining methods, the ideal position of cooling channels in parts with complex geometries often has to be compromised.

This application involved four retractable mould cores for an injection mould tool for plastics garden shear handles.

Cross sections measured just 6mm x 6mm at the critical areas - too small to machine a channel from one end of the core to the other.

Using SLM to manufacture the cores, it was possible to design and build them with a cooling circuit integrated into their most restricted areas.

Knill said, "Not only has the quality of the product been improved but also the cycle time has been reduced by 30%." Finishing operations such as grinding, spark eroding and hardened steel milling can be carried out on the cores using standard processes.

To achieve the required hardness of 52HRC, the cores were heat treated several times.

Gardena said it is very satisfied with the tolerances of the system.

Knill continued, "Retracting surfaces and surfaces requiring finishes to tolerances of 0.01mm were produced 0.3mm oversize.

Dimensionally less important free form areas were finished simply by smoothing the surfaces.

All parameters point towards a good operating life and we have already produced 66,000 problem free parts with the mould." SLM technology builds parts from single component metal powders.

The parts are built layer by layer with the metal powder being melted locally by an intensive infrared fiber laser beam that traces the layer geometry.

The Gardena cores were produced from H13 Tool Steel.

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