Thixomoulding: An almost forgotten technology is set to revolutionise the manufacture of lightweight structural components

Thixomoulding: State of the art

Thixomoulding technology is not a new technology; it is based on the processing of magnesium in a semi-solid state and has been used for decades, particularly in Asia, for the manufacture of flat components in the electronics industry, e.g. for laptops and displays. It is therefore not surprising that most thixomoulding machines (approx. 2,000) are installed in Asia.

The reason this technology has so far only been used for flat components is that, until 2019, thixomoulding machines were only available with clamping forces of up to 1,000 tonnes and screw diameters of 84 mm – and thus with shot weights of up to 1,500 g and output rates of approximately 80 kg per hour.

Since 2019, increasingly larger machines with clamping forces of up to 6,000 tonnes and screw diameters currently of up to 190 mm – with maximum shot weights of up to 22 kg and potential output rates of 500 kg per hour – have been developed and brought to market.

BOLE Intelligent Machinery is one of the pioneers in these developments and, with its MTX 4000 D-170 series machine, currently has the largest thixomoulding machine in series production on the market.

Magnesium: the infinitely available material on our planet

Why is BOLE now focusing on magnesium in combination with thixomoulding technology?
Unlike many other materials such as plastic and aluminium, magnesium is an infinitely available material on our planet.

Magnesium is a lightweight material which, unlike aluminium and plastic composites, enables a weight reduction of between 10% and 20%.

Magnesium: Is its CO₂ footprint actually lower?

If we now compare the CO₂ footprint of magnesium with that of aluminium, a significant difference can be seen per kg:

Aluminium in Europe = 6.7 CO₂/kg

Global average for aluminium = 15–16 CO₂/kg

Magnesium (Pidgeon process) = 22 CO₂/kg

However, if we consider a 1,000 cm³ component produced using die-casting, it weighs 2.7 kg when made from aluminium, with 40.5 CO₂/kg, whereas when made from magnesium it weighs 1.7 kg, with 37.5  CO₂/kg.

This corresponds to an 8% reduction in the CO₂ footprint.

If we now take a closer look at the CO₂-footprint in production, and then also consider thixomoulding technology, the following emerges:

In the thixomoulding process, the gate and flash weight accounts for between 25% and 40% of the moulded part’s weight, which is at least 50% lower than in die-casting.

If we now look at the CO₂ footprint in relation to the shot weight of the aforementioned 1,000 cm³ component, we arrive at the following comparison:

Die-casting with aluminium at a minimum of 5.4 kg at 81.0 CO₂/kg and with magnesium at 2.12 kg at 46.6 CO₂/kg.

This corresponds to a CO₂ reduction of 42 per cent compared with the global CO_2-average for aluminium.

With new Pidgeon processes and electrolysis, it will be possible to achieve 8 CO₂ per kg for magnesium in the coming years – at which point the differences will be dramatic.

Magnesium recycling

As already described, recycling is one of BOLE’s core strategies. It is therefore not surprising that we have also investigated the direct recycling of start-up parts, sprues and flash.

The results show that – when this recycled magnesium is fed back into the Thixomoulding process – there is no change in the performance of the components.

With these findings, Thixomoulding is the only process to offer the possibility of a closed-loop recycling system within your company, which further significantly reduces your costs and your CO₂-footprint.

With its Thixomoulding machine technology, BOLE offers a recycling process that produces recycled material using minimal energy and feeds it back into the machine. Customers can decide for themselves how much recycled material they wish to – or are permitted to – use in their components.

However, as mentioned: the 100 per cent recycling of your start-up parts, sprues and overflow material will have no effect on the performance of your magnesium components.

General advantages of Thixomoulding technology

1. Lower porosity in the components, as shrinkage is very minimal in magnesium due to the lower input temperature of 580 to 630°C.

1. No air entrapments, as the components are filled with a honey-like melt at a low flow front velocity during the swelling flow.
2. Better corrosion resistance: Due to the lower flow front velocity, a closed surface is achieved in thixomoulding under the pressure applied during the casting process.
3. Mechanical properties improved by at least 20 per cent and in some cases up to 40 per cent, e.g. elongation and tensile strength of the component.
4. Energy costs are reduced by at least 55% compared with die-casting processes. The average energy consumption, including melting and all peripheral equipment, is less than 0.5 kW per kilogram of magnesium cast.
5. The service life of the moulds is at least twice as long, and in some cases up to three times as long, as that required for die-casting production; this represents a massive cost saving, particularly for large components and consequently for the moulds themselves.

Component costs

When the unit costs of producing magnesium components using die-casting are compared precisely with those of producing the same components using thixomoulding, the production costs using the thixomoulding process are generally 21% to 23% lower, depending on the component.

If we also take into account the longer tool life and cleaning intervals, the cost reduction rises to 26% to 28%.

When using BOLE recycling technology in combination with a thixomoulding machine, we achieve a reduction in production costs of almost 35% for your components.

Conclusion

We at BOLE Intelligent Machinery are firmly convinced that, with thixomoulding technology, we can make our planet a little better.

We would be delighted to work together on this project.

We’ll be providing more information on thixomoulding in the near future on Foundry Planet under the hashtag ‘What on earth is thixomoulding’.