The Rheozamak Project

The goal

Mambretti Metalli, with the RHEOZAMAK project, investigated the feasibility and effectiveness of the semi-solid die casting process for hot chamber. The key point of the project was to achieve the formation of the Slurry at temperatures higher than those of liquidus, thus bypassing the current criticalities of application of the semi-solid to the hot chamber.
Mambretti, in order to achieve this goal, has adapted the slurry technology to hot chamber die casting machines, through some structural changes to the injection unit of the DCM, modifications to the slurry making unit, and the introduction of new digital technologies for monitoring, integration with other DCM peripherals and process management.
The filling of the die cavity takes place when the metal is not in the liquid phase but in an intermediate phase in which there are already solid particles inside the liquid metal (granular structure dispersed and suspended in the liquid phase). To obtain high quality castings, it was necessary to develop ad hoc release lubricants to overcome the difficulties of applying the semi-solid to an alloy that solidifies so quickly.

What’s slurry? See the slurry test video

Lubrication and quality control

The use of semi-solid makes it necessary to work at lower temperatures and consequently the amount of release lubricant (as well as the spray time) is lower than in the standard HPDC. The project has made the lubrication phase take place – no longer through sprayers or lubrication heads – but through the vacuum unit. In fact, when the die is closed, using the vacuum valve which constitutes a connection channel between the die cavity and the external environment, before air suction, the vacuum unit conveys the nebulised release lubricant inside the mould in the form of an aerosol. The potential advantages of this application are many: drastic reduction in the amount of release agent used and consequent reduction in wastewater disposal; significant reduction in the open mold time which implies the lower reduction of the die temperature during the open mold phase. The lower thermal shock of the mould (less temperature variation during the cycle) implies a longer life of the die itself.

The second implementation is that of the integrated vision system. In hot chamber zamak die casting, the cycle time is often very fast (between 10 and 30 seconds) and the dies often have multi-cavities. The semi-solid has a higher viscosity than the liquid and the correct filling of all cavities becomes a fundamental target that is not easily achievable. The project involved the vision system checking at each cycle that the filling of all the figures has taken place correctly (including overflows and vents) and that it can digitally communicate with the DCM/slurry maker system for any changes to the process.

Discover the lubrication @ closed mold

Improvements achieved through Rheozamak

The improvements brought about by the rheocasting process are:
• Castings without gas porosity: rheocasting allows a less turbulent flow and consequently the trapped air is reduced or eliminated (in combination with the vacuum) achieving parts of very high aesthetic quality;
• Energy savings due to keeping the furnace at lower temperatures than the standard process;
• Less use of release lubricant and lower cycle times: rheocasting requires less use of release agent, so the lubrication time is reduced, the solidification time is also reduced (starting from a lower temperature of the liquid metal) and consequently the cycle time is significantly reduced;
• Longer die life: thanks to the lower heat content exchanged between the die and the casting during the casting process, thus reducing the costs of maintenance and die repairs;
• Lower costs for wastewater management and lower environmental impact. CO2 emissions are reduced and improved and the overall environmental impact (lower Carbon Footprint) in relation to a reduced use of release agents, reduced management and disposal of sludge generated by wastewater, a lower temperature of the melting furnace and a lower waste rate of the castings produced.

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