The pressure to reduce cycle time is common for every molder.
In this struggle, there are several actions that can be considered:
changing the mold tempering concept, reducing wall thickness in
the molded part, changing the processing parameters or modifying
the resin formulation. There is also another possibility that is not
always considered: changing the mold material for an alloy with
a higher thermal conductivity. This article's example illustrates
the advantages of this approach. Here the mold material was only
locally modified, while a substantial reduction in cycle time was
achieved. Notably, higher thermal conductivity sometimes results
in lower hardness values and care should be taken to select the
In Germany, an automotive supplier was molding a technical product
that required a cycle time longer than expected. SIGMASOFT®
Virtual Molding was used to analyze the current production and
find a solution. The desired mold temperature was 80°C, and the
tempering channels were running in a range from 60 to 80°C.
After simulating 20 consecutive molding cycles the hotspots in
the mold, responsible for the extended cycle time, were evident.
Due to the complicated part geometry, it was not advisable to
machine new tempering channels (which could compromise the
mechanical integrity of the mold). A part redesign was also out of
SIGMA suggested changing the mold material. Two alternatives were considered: a copper-beryllium
distribution in the mold. The
temperature in the hot spots dropped from
147°C to about 92°C, and the mean mold
temperature reduced from 95°C to around 85°C. "It was a substantial improvement in the mold temperature," Schmellenkamp explained.
"However, the molder was concerned with the lower hardness of
the alloy, which may lead to wear and reduce mold life." The typical
hardness for this type of material is 33 HRC.
A second analysis considered the possibility of using special
hot-work tool steel. This material has a higher thermal conductivity
than regular tool steel (60 W/m²K), and though the ability to
remove energy from the melt is not as high as with the copperberyllium
alloy, it delivers a higher wear resistance, due to its
improved hardness (around 44 HRC).
The SIGMASOFT® Virtual Molding analysis proved that the hot spot
temperature could be reduced from around 147°C to 120°C and in
some regions from 119°C to 102°C, as shown on the right side of
Figure 1. "This material selection delivered the best compromise
between both alternatives: high wearing resistance and high
thermal conductivity," concluded Schmellenkamp. "The molding
cycle was reduced by 20% without changing the mold design."
According to Schmellenkamp, this increase in productivity is easily
achievable in existing molds. "It is not uncommon to accomplish
this reduction in cycle time for several existing molds within a
single company, resulting in up to 15% more parts produced in the
same period of time."