Changes in toolmaking technology are driving up the quality and speed of manufacture of injection mould tools that produce plastic parts. At the heart of this is the way additive (laser sintering) and subtractive (milling) equipment work together in an integrated process. 

Mould tools incorporate cooling channels to prevent distortion in the moulds they form. These so-called ‘conformal channels’ enable cooling water to be directed close to the surface of the injection mould tool to optimise cycle times and the quality of finished parts. 

However, this limits some part geometries and it can be difficult to run straight cooling channels close enough to the mould cavity for efficient heat transfer, especially when moulded parts have elaborate shapes or complex features. 

On top of this, cooling channels often have to compete for space with other features such as ejector pins or moving inserts. This necessitates elaborate workarounds, adding cost and complexity to the mould-making process. In addition, some mould features may be too small to accommodate cooling channels altogether, leading to poor cooling performance.

All this forces moulders into a difficult trade-off. Either they accept higher levels of distortion, or they slow the production process to allow the part to cool in the mould for longer, increasing the overall cycle time, damaging productivity and driving up part costs.

Hybrid solution

There is, however, a solution, which is based on a new hybrid metal additive manufacturing and machining technology. This combines additive laser metal manufacturing and conventional CNC machining in a single integrated build process, which OGM calls ConformL Cool. 

The resulting conformal cooled inserts can incorporate complex curved, shaped or spiral cooling channels that are easily formed in small, narrow or awkwardly-shaped inserts. This allows the creation of a new generation of mould tools, with consistent and accurate cooling across the entire forming area. It also eliminates many of the problems of distortion and poor part quality traditionally associated with inefficient cooling.

OGM’s hybrid machine builds complete mould tools or inserts layer by layer, using a laser to sinter metal powder in steel or other metals. After a series of layers are completed, automated secondary machining removes any excess material. The resulting dimensional accuracy and fine surface finish allow complete tools incorporating conformal cooling channels to be manufactured automatically, without the need for separate finishing activities.

Benefits of hybrid technology

ConformL Cool hybrid machines (using both additive and subtractive technologies) combine laser sintering and milling in a single process to manufacture injection mould tools quickly and accurately, with conformal cooling channels, in an integrated build process. But, OGM says the benefits don’t stop there:

• Injection mould tools are often manufactured in the Far East to drive down cost, but it typically takes between 12 and 14 weeks before they are available for use in the UK. Using a hybrid machine locally can cut these lead times in half.

• The ability to build complete mould tools with complex cooling channel geometries and designs in a one-hit automated process also helps shorten design-to-part lead times. 

• Hybrid machines allow mould tool parts to be built in a range of metals, with conformal cooling channels printed in complex circular shapes that accurately follow the profile of the tool surface.

• The hybrid manufacturing process allows better control of fluid flow within the channels themselves. Special features encourage turbulent flow to increase heat extraction while maintaining a smooth surface finish within the channel to prevent blockages caused by mould growth or trapped debris.

• Applying ConformL Cool technology in production applications allows cycle time reductions of up to 20% and reduces defect rates on challenging parts.