plastic injection moulding

Metal additive manufacturing turns up the volume

Metal additive manufacturing is the archetypal digital manufacturing technology. When additive techniques first became commercially available, proponents claimed that they would fundamentally change the way manufacturing is done. By removing the need for traditional moulds and tools, they argued, 3D printing would replace many older manufacturing techniques.

That revolution has yet to happen.

Additive manufacturing technologies have evolved dramatically in recent years, improving in speed, precision and in the range of materials they can handle. The approach has become a mainstay of product development, prototyping and small-volume manufacturing.

Growing behind the scenes

In fact, the relationship between additive and traditional manufacturing techniques has turned out to be one of collaboration rather than competition. It might not be obvious in the end products, but many high-volume production processes increasingly rely on additive manufacturing at some point along their value chain.

In plastic injection moulding, metal additive manufacturing systems are transforming the production of mould tools, helping companies to get ideas into production faster, and driving quality and productivity up.

Staying cool at speed – Conformal Cooling

To reach the short cycle times and high productivity rates required for low cost, high volume parts, cooling water needs to be evenly distributed around the mould tool; this is typically achieved by machining water channels within both the base plate and tool inserts.

Appropriate control of the cooling rate affects the mechanical properties and surface finish of the part. If areas of the material are insufficiently cooled within the mould, or cool at a different rate to the surrounding areas, they can shrink excessively after ejection, leading to distortion, poor tolerances and unacceptably high reject rates.

Conventionally, these cooling channels are drilled through the mould material during tool manufacture; and while this approach is simple, where the part geometries are more complex, it can be difficult to run straight cooling channels close enough to the mould cavity for efficient heat transfer.

Poor cooling performance creates a dilemma for plastic injection moulders. Either they accept high levels of distortion, or they slow down the production process, allowing the part to cool in the mould for longer.

Metal additive manufacturing provides a neat solution to complex cooling challenges, allowing complex, shaped channels to be built into the structure of the tool, ensuring adequate cooling of even inaccessible areas. The process also removes the necessity for those channels to be round, elliptical, rectangular and even teardrop designs can maximise heat transfer for a variety of applications. Moulds created using this technology have demonstrated cycle time reductions of as much as 20%.

Escaping quality traps

Additive manufacturing also helps to handle some common production challenges experienced in many plastic injection moulding applications. Gas traps are caused by gas pockets forming as the ‘melt fronts’ of the molten plastic. They can lead to scorching, pinholes and poor finished part quality. Best practice in part design, tool design and the use of mould flow simulation is to alleviate the risks of gas traps, but they can still occur.

Traditionally, gas trap issues are addressed by fabricating the tool with inserts made from specialised porous materials in the critical areas, or by retrospectively adding vent pins (fixed ejector pins) to the exact site of the problem. Both these approaches add cost and time to the toolmaking process.

As a leading plastic injection moulding company, we can build inserts that incorporate large numbers of micro-pores, each just a few microns in diameter, through which gas can escape, without adversely affecting the quality of the finished part. The inserts are 3D laser sintered in steel or other metals, to match the exact requirements of each injection mould tool. The dimensions and characteristics of the gas escape channels are optimised to reduce cycle times and boost productivity, while maintaining high levels of part quality, even for extremely complex designs.

Additive and conventional production techniques are not rivals, but friends. Innovative manufacturing approaches that build on the strengths of different techniques are helping companies move faster, cut costs and deliver products that work better for their customers.

Gain additional insights from our industry expert…

Leading industry magazine, Controls, Drives & Automation, has featured an editorial from Marcel Gowers. The article explores how in plastics injection moulding, for example, metal additive manufacturing systems are transforming the production of mould tools, helping companies to get ideas into production faster, and driving quality and productivity up.

Read the full article online

To find out how OGM can help you with your next project, contact us now.

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