The Importance of a Controlled Tool Temperature
At RP Technologies we manufacture prototype injection mould tooling from aluminium. However, our service differs to other prototype tool makers & moulders as we manufacture tooling to production standard, including cooling and heating circuits.
There seems to be a common misconception in the industry that aluminium moulds do not need cooling circuits due to aluminium transferring heat more effectively than steel, so we wanted to explain the importance of controlling tool temperatures when using aluminium tools.
Part of the statement is true, aluminium has a 5x better heat transfer rate (depending on the grade) than steel. With better conductivity, the position of cooling circuits becomes less critical than with steel tooling.
However, we believe the part about aluminium moulds not needing cooling circuits is not true. Without the ability to heat or maintain a consistent tool temperature, the moulder will encounter flow issues, appearance problems but most importantly dimensional and warping problems. The cooling circuits allow the moulder to maintain a steady tool temperature, eliminating these issues.
A tool will naturally lose more heat through the core side than the cavity. This leads to a discrepancy of temperature between the two tool halves. This difference in temperature will lead to dimensional and warpage issues. Add to those problems a high potential to damage the tooling due to a difference in expansion of metal parts. The tool can seize, mating faces can dig in to each other which cause expensive repair costs. Keeping a consistent temperature across both halves of the tool is paramount to increase tool life and to produce quality mouldings.
The ability to control tool temperature also gives more flexibility in process control. Whether the control is required for dimensional stability, moulding appearance or extending the life of the tool, cooling circuits are of the utmost importance to get the correct process in order to create good repeatable components.
When processing high temperature materials such as PPS, PEEK etc a much higher tool temperature is vital to ensure the material flows correctly around the cavity. In these cases, the tool must have temperature control otherwise the material is not processed properly, and the characteristics of the material will be null and void.
Tools which utilise hot runner systems must have a cooling system, they create local hot spots on the fixed half tool face. If this is not controlled with cooling circuits, there will be a huge temperature difference between the two halves of the mould, leading to tool damage, flow issues and aesthetic problems.
Aluminium is much easier and quicker to machine than steel so there should be no reason to omit this critical part when manufacturing the tooling. To get a consistent cycle, component size & process on a moulding, cooling circuits are required to keep everything in check. It is vital for repeatability, which is essential when moulding any quantity of components that need to be fit and functional and capable of meeting specified tolerances.