A03-1-TOOLING APPLICATIONS WITH EOSINT M

The other main motivation for using DirectTool is to use the unique design possibilities of DMLS to improve the performance of tooling, i.e. to gain benefits in the production process after the tool has been manufactured. Of course this can in many cases be combined with cost and/or time saving during the tool production, but especially for large series production, any savings in the plastic part production can justify even increased costs in tool production.
The best known way of improving tool performance using DirectTool is by optimizing the design of cooling and/or tempering channels to enable lower and/or more uniform temperatures in the mould, or more rapid cooling and/or heating. This can reduce both cycle time and also scrap rates due to stresses and warpage. The result is typically increased productivity and reduced cost per part in production. With conventional machining, cooling channels are added into a tool by drilling, which restricts the cooling design to combinations of straight lines, which must all be accessible for drilling and must also avoid colliding with the forming surface, ejector pins etc. With DMLS, both the positions and shapes of cooling channels (or other elements) can be designed in a freeform way. When the channels are designed to follow the moulding surfaces of the tool, this is known as conformal cooling.

Figure 4: Electrical box.
Left: conventional drilled cooling channels.
Middle: optimized conformal cooling. Right: Simulation of mould temperature. Courtesy of PEP, Legrand

Many studies and examples have demonstrated the benefits of optimized cooling. Theoretical and practical investigations by PEP [1] have shown reductions of mould temperature by approx. 20°C (Fig. 4) and/or reduction of cycle time by 20 seconds. LBC has reported cycle time reductions of up to 60 percent and in one case a scrap rate reduction from 50 percent to zero by using DirectTool with optimized cooling [2].
The project shown in Figure 5 combined conformal cooling with a further technical benefit. The product in this case was a promotional (giveaway) golf ball, which had to be produced in large quantities at very low cost. The chosen production method was blow moulding ofextruded PP combined with elastomer injection. To avoid distortion, which was important to obtain spherical balls, a good venting of the mould during blow moulding was needed.

Figure 5: Blow mould for a golf ball.
Left: conformal cooling.
Middle: venting slits (in green).
Right: DirectTool mould cavity.
Courtesy of Es-Tec, DemoCenter.

This was achieved by integrating venting slits into the rear side of the mould cavities, and selecting DMLS material and processing parameters to produce a slightly porous surface layer to allow gas to escape into the vents without creating any visible surface marks. It can be seen that the volume of the mould half was also kept to a minimum, thereby minimizing build time and costs. Eight such mould halves were combined to make a four-cavity tool, which was used to produce more than 20 million golf balls. Only around 50 hours build time was required, and the conformal cooling increased productivity by 20 percent.