From increasing volume requirements of structural aluminum castings to implementing more digitized manufacturing processes, die casters are continually looking for new ways to optimize production.
The development of Battery Electric Vehicles (BEVs) in the automotive industry, in particular, is presenting a paradigm shift for die casting. An increasing number of car manufacturers are choosing to use ever larger structural components made of die cast aluminium in vehicle production, significantly reducing manufacturing costs and, through reducing weight, increase electric vehicle range.
To do so, however, requires investment in larger, new-generation, high-pressure vacuum die casting machines (or giga presses) which can produce complex, single structure castings. Of course, casting larger and more complex structural components doesn’t come without complications, and creates several design considerations and manufacturing challenges which need to be overcome.
The complexities of creating larger components
The world of die casting relies on precise lubrication for optimal performance and these larger components require more intricate die tools, which are increasingly difficult to lubricate using conventional water-based die release agent and spray systems.
Lack of penetration of the lubricant spray into areas such as ribs, together with the low film-forming capabilities of water-based lubricants, can be a real challenge. The spray heads used to apply water-based lubricants can often be too bulky and inflexible to deploy lubricant to all areas of the die face successfully. The inability to apply lubricant consistently can also result in less control of die temperatures, increased die maintenance and reduced die life – all of which have a large influence on cycle times, waste, efficiency and cost.
If manufacturers are to successfully reduce energy usage, material consumption, and waste, the equipment and lubricants used in the die casting process also need to advance.
The die release lubricant landscape
Die release lubricant emulsions play a critical role in the die casting process, and have an important impact on the overall quality of finished components. Typically, up to 80% of the release agent is used for cooling purposes – removing the heat energy introduced by the molten aluminium at the die surface. It also forms a protective layer that prevents the melt from sticking to the die surface so that the finished castings can be easily removed from the mould, .
Die release lubricant technology is categorized into; water-based, water-based MQL, and water-free MQL(Minimum Quantity Lubrication). For decades, it has been standard practice to use diluted water-miscible die release agents (wmFT) for die casting in the field of non-ferrous metals and their various alloys, and this is still the most common release and cooling technology today. Despite water-based die release lubricants being the most popular worldwide, there are issues it presents for businesses looking to cast larger components while maintaining product quality, improving productivity and reducing costs.
Water-based die spray’s effect on the die and mould
Due to the disparity in die temperatures (caused by the wide range of die sizes and designs), parts produced, and heat profile of each system, it can be challenging for water-based emulsions to adapt to the manufacturing demands of larger components. Whilst they can be suitable at protecting cooler areas of the die, hotter areas are susceptible to soldering. Die casters are tempted to spray more lubricant to protect hot spots, but this often leads to overspray and build-up on cooler areas. In turn, this causes a costly dilemma of lost production time and extra die maintenance.
Water-based systems can also contribute to the thermal cracking of the die or mould, reducing its expected life span. Strong thermal cycling stresses on the die surface during intensive quenching with cold mould release agents can generate high residual tensile stresses in the surface layers. This can lead to the formation of fire cracks with a c depth of fractions of a millimetre to well over 50 mm, and a width of a few 1/1000 mm to over 2 mm. Ultimately, this can lead to the premature failure of the die mould. The high water content of the wmFT can also cause corrosion of the mould, clamping tools, and machines in general.
Finished part quality
As well as reducing mould tool life, the die lubes can also affect the quality of the casted component. This includes brown spots, where discoloration of the part surface occurs due to burnt-in wax and oil residues. The corrosion inhibitors used in wmFT can decompose during the casting process, increasing the quantity and consumption of gases causing porosity in the casting.
wmFTs can also increase the risk of the Leidenfrost effect – a physical phenomenon in which an aqueous liquid – in this case, a drop of mould release agent (wmFT) – is in close contact with a mould surface that is significantly hotter than the boiling point of water . This creates an insulating vapor layer which prevents the surface from being wetted by the wmFT, causing release agent droplets to bounce off the vapor layer. In order to be able to apply a sufficient release film layer and avoid the Leidenfrost affect, hot moulds require very long spray phases to cool the die, which significantly increases the cycle time.
Maintenance
Contamination from the build-up of release agent on mould surfaces, and in spray nozzles leads to heavy deposits and even partial spray system failures which can cause unplanned downtime. A large amount of compressed air is usually required to apply the die lubricants and to blow off residues which considerably increases the energy consumption of the process.
Waste and consumption
WmFTs can also contribute to the overconsumption of release agent, water and energy which increases waste. The application of release agent is usually carried out at a spray pressure of approximately 2 - 4 bar and volumes of 12 liters and above per cycle. Up to 80 % of the actual die lubricant is misused as pure coolant, adding to the cost of production.
Heavy over-spraying produces a large quantity of contaminated wastewater which can significantly increase wastewater treatment costs over time.
Health
Heat and moisture surrounding the Die Casting Machine can lead to bacterial and fungi growth. This can cause malfunctions but also poses health risks for personnel as well as high maintenance costs. Large extraction systems must also be used to remove significant quantities of water and release agent vapors produced to prevent toxicological and direct skin contact hazards for workers.
All these challenges combine to create risks to people, machines and the environment as well as overconsumption in product and energy.
In order to mitigate these problems, the concept of minimum quantity lubrication (MQL) has emerged as a game-changer, offering targeted and efficient lubricant delivery systems.
The shift towards water-free MQL systems
Process optimization to use energy more efficiently and reduce waste enables die casters to restructure their manufacturing footprint while making significant cost savings. The key to success in water-free MQL, lies in the effective balance of energy in the moulds, intelligent conversion of the available thermal energy and reduced consumption of energy and compressed air.
Mould cooling was previously only achieved by intensive spraying of the applied die release agent, but technology today means cooling channels can be created inside the mould during manufacture meaning external cooling isn’t required with MQL. .
Thanks to intelligently designed temperature-regulated die casting moulds, MQL is possible without additional cooling. This, combined with cooling spray heads being positioned close to the surface, enables suitable mould cooling channels to be distributed over the entire surface reach.heat energy dissipates directly, and allows for the selective cooling of hot spots.
As a result, the temperature difference of the die between the filling phase and the solidification phase is significantly lower. Thanks to die temperature control channels close to the die and the use of jet cooling systems for squeezers and hotspots, cooling of the die using the spraying process is no longer necessary.
The benefits of water-free MQL systems
Water-free MQL lubricants and spray technology presents the industry with an opportunity to upgrade from conventional water-based processes and die release agents. By formulating the product to be water-free, die casters can benefit from improved tool life, reduced maintenance costs, as well as cycle time improvements.
Considerable reductions in thermally induced surface stresses reduce the formation of fire cracks in the die. With water-free MQL, there is no need to mix release agent, providing savings in both energy costs and process time as well as improving die life and cycle times.
Utlizing Water-free MQL ensures component strength and improves overall part quality by reducing porosity. The addition of sufficient cooling channels, which must be created in the mold halves when switching to water-free MQL, means there is no cooling effect on the die from the release agent. The absence of water during spraying enables a more even distribution of the release agent in the die, meaning the surface and the microstructure of the parts become significantly more homogeneous and porosity is reduced to a minimum. By addressing these porosity challenges, manufacturers can significantly reduce reject rates and substantially reduce the CO2 footprint of their operations
Another strength of water-free MQL is its ability to significantly reduce cycle times when spraying die release agent and to eliminate the air-blow phase often required when using water-miscible mold release agents. Crucially, this also removes the occurrence of the Leidenfrost phenomenon, again improving the die life and minimizing the risk of production downtime .
The removal of water from the process also eliminates wastewater and the risk of bacterial and fungal growth this reduces health risks for employees and offers significant cost savings for wastewater removal.
In summary, die casters can achieve significant cost savings and performance improvements by implementing water-free MQL technology. From tangible reductions in energy, water, waste disposal and die release lubricant usage, there are many process-efficiency improvements that can help to reduce downtime, maximise product quality, and assist with sustainability initiatives. Ultimately, water-free MQL is the logical step forward in enabling manufacturers to meet the growing trend towards larger and more complex parts.
How can Quaker Houghton help?
Quaker Houghton supplies both MQL release agents and spray system technology to effectively help manufacturers with the transition to water-free MQL processing . As such, it is uniquely placed in the industry to help customers improve their die casting performance.
Spray system technology is also part of the Quaker Houghton fully digital and automated fluid management solution, QH FLUID INTELLIGENCE™, that provides real-time monitoring and control of fluid performance and cost, providing quick, accurate, and actionable insights.
As a leader in industrial process fluids, Quaker Houghton offers a consultative approach to finding solutions that will optimize your die casting process, reduce costs, advance safety and drive sustainability. By embracing the latest technologies, die casters can reduce the impact of their products and processes whilst improving productivity and profitability.
Find out how Quaker Houghton can deliver best-in-class lubricant and equipment solutions across the entire die casting process from plunger lubricants to porosity sealing through its DieCast iQ™ intelligent die casting solution here: https://diecastiq.quakerhoughton.com/
