Low-pressure die-casting: A model for sustainable production

New legislation is being introduced to enforce sustainable business practices and set guidelines for future production processes. The further development of ‘clean’ technologies is not only necessary but is also being actively promoted and is gradually replacing traditional standards across various industries. Furthermore, energy efficiency has become a key priority for companies seeking to reduce their operating costs.

Weight reduction plays a crucial role in both the aerospace and automotive industries. Optimising an aircraft or vehicle to reduce weight directly lowers energy and fuel consumption. Aluminium castings offer considerable potential for lightweight construction, but one key requirement remains: maintaining or even improving structural stability whilst reducing weight. This can be achieved by minimising the amount of material used or by employing hollow casting processes with sand cores and subsequent core removal. The ongoing pressure to reduce the weight of components – and thus also CO₂ emissions – continues to drive innovation in this field.

A sustainable solution for the automotive industry: low-pressure casting

Low-pressure process

The Kurtz low-pressure process plays a crucial role in conserving resources. It enables the production of thin-walled parts with a thickness of 3 mm or less, whilst also allowing for material enrichment, high mechanical properties and a reduction in the use of recycled materials.

Key factors for successful casting:

- Optimal mould filling through low pressure

- Advanced cooling technology for precise solidification

- Innovative furnace technology for protecting the melt

- Intelligent, flexible machine design for greater efficiency

Key factor: Optimal mould filling at low pressure

At the heart of the low-pressure process is turbulence-free mould filling. The molten aluminium remains protected from external influences inside the furnace. Using controlled pressure – ranging from millibars to a maximum of 1 bar – the molten aluminium is fed through a riser into the mould cavity, usually a die-casting mould. As soon as the mould is filled, the outer shell begins to solidify, and the feeding pressure is further increased to compact the casting and ensure high-quality results.

Advantages of this process over conventional casting methods

This process offers several key advantages:

• Purity of the melt – Ensures a clean, high-quality metal melt.

• Minimal turbulence – Enables uniform, turbulence-free mould filling, thereby reducing defects.

• Optimised material usage – The dense feeding reduces the need for recycled material.

• Excellent casting quality – Improves the mechanical properties and overall performance of the component.

Efficiency and cost savings compared to gravity casting

Compared to gravity casting, this process can reduce the need for recycled material by up to 70 per cent (depending on part size), whilst simultaneously increasing casting output and minimising scrap. As compressed air is one of the most expensive resources in a foundry, there is also considerable potential for cost savings.

Kurtz’s pre-pressure technology optimises air consumption by maintaining a constant start point for casting and reduces the required air consumption to a minimum. Unlike conventional methods, the furnace is not fully vented after each casting, resulting in energy savings of approximately 80 per cent whilst simultaneously shortening cycle times and improving melt quality.

Key factor: Cooling technology

Whilst air is traditionally used for cooling, its inefficiency and high costs have led to water cooling being increasingly favoured. This method offers greater efficiency and cost-effectiveness. Furthermore, temperature- or time-controlled cooling ensures that cooling is only activated when necessary, thereby preventing excessive or inappropriate cooling.

To maintain consistent cooling quality, regulated rather than merely controlled cooling circuits are used. This process-optimised cooling system enables controlled solidification, resulting in a fine-grained cast structure. Water cooling not only improves casting quality and shortens cycle times, but also reduces energy costs by approximately 64 per cent.

Key factor: Furnace technology

Choosing the right furnace technology is crucial for efficient casting. Large, highly insulated crucible furnaces with a capacity of 600 to 4,000 kg enable long continuous casting runs and, thanks to their large circumferential diameter, allow the use of multiple risers. This flexibility ensures that the risers can be precisely positioned for optimum mould filling and feeding, particularly with large or multi-cavity moulds.

The use of direct gating via a riser eliminates the need for complex gating systems and costly feed boxes. This leads to a significant reduction in recycled material and minimises downstream machining steps such as sawing and grinding. To maintain a stable and uniform mould temperature, the furnace is switched over whilst the casting is solidifying, thereby eliminating the need for additional start-up charges to preheat the mould.

The exchange furnace concept streamlines operations by carrying out furnace charging and melt treatment outside the casting machine. This minimises machine downtime and improves Overall Equipment Effectiveness (OEE). Furthermore, the ‘in-line’ charging method, in which the melt is transferred directly from the melting furnace to the casting crucible furnace, reduces internal forklift traffic and allows the melting furnace temperature to be lowered by up to 40 °C, resulting in significant energy savings.

After filling, the melt is processed directly in the crucible furnace, ensuring excellent melt quality. Sealing the crucible furnace with a riser cover keeps the molten metal in a protected atmosphere, which further improves energy efficiency and reduces total operating costs.

Key factor: Intelligent and flexible machine design

Ribbing plays a crucial role not only in lightweight construction for castings but also in mechanical engineering, as it helps to reduce moving masses and increase efficiency. Combined with an intelligent control system, this design approach maximises operational performance. Based on the principle ‘Better data – better decisions’, the advanced machine control system enables the operator to react quickly and achieve high efficiency in series production through precisely controllable processes

Through seamless integration into data management systems, the quality management process documents every single cast component and ensures complete traceability. This data serves both as a ‘birth certificate’ for each cast part and as a valuable resource for process optimisation. By utilising intelligent data management, manufacturers can reduce the scrap rate and significantly improve Overall Equipment Effectiveness (OEE).

All these benefits clearly demonstrate that low-pressure casting technology offers an exceptional solution for making the casting process more sustainable. Not only does it reduce production costs whilst maintaining flexibility, but it also conserves valuable resources such as energy and water.

Let’s build a greener future together!