The quality of plastic components in modern cars has increased greatly over the years in terms of accuracy of fit, visual appeal and surface feel. Companies in the supply chains, such as Czech Republic-based Innomia, therefore rely more and more on high technology production solutions, particularly for complex applications.
The firm has become an enthusiastic advocate of layer-by-layer DMLS (direct metal laser sintering) technology from EOS, which has numerous benefits including allowing components of virtually any external and internal shape to be manufactured.
Innomia’s engineers support the global automotive supplier Magna in developing production processes for injection moulded plastic parts. A recent project concerned the manufacture of a component for the central front armrest in a Škoda car and specifically involved optimising cooling of the mould. Injection moulding of the glass fibre reinforced plastic component is difficult, as uniform dissipation of heat throughout the tool has a significant effect on minimising distortion and improving component quality as it solidifies.
Moreover, temperature control plays a major role in minimising the production cycle time, as the quicker heat is removed, the sooner a component can be ejected and the next one produced.
The tool insert previously used was made of beryllium-copper alloy, which has a high thermal conductivity. Cooling was possible from one side of the insert only, so temperature distribution was uneven. The cooling water needed to be at 16°C to absorb the large amount of heat energy from the insert and component quickly. As the temperature differential was high – around 120°C – the elevated humidity accelerated corrosion, necessitating costly, intensive cleaning of the mould every one to two weeks.
Designers from Innomia began to develop a new tool insert cooling system, with optimised heat removal at the top of the list of priorities. The team decided to integrate conformal cooling channels, an established application using DMLS technology and one that only additive manufacturing (AM) can achieve. An EOSINT M 270 system from EOS was used and the metal powder chosen was Maraging Steel 1.2709.
Diameter of the cooling channels is just 3 mm. The manufacturing process involves layer-by-layer melting of the powder by a laser programmed using 3D data from a CAD model of the mould. The Czech specialist was able to increase the hardness through post-treatment to over 50 HRc, leading to high wear resistance and low maintenance costs.
Luboš Rozkošný, CEO at Innomia explained, “The DMLS process enabled us to manufacture an extremely durable component, while at the same time successfully retain the proven advantages of AM in terms of design flexibility.
“Thanks to the conformal cooling channels integrated into the component with optimum precision, we have inexpensively resolved the main challenge of the production process.”
The temperature distribution and associated heat dissipation are now substantially more homogeneous. Since the heat leaves both the tool and the component more quickly, a water temperature of 60°C is now sufficient for cooling. The insert surface temperature does not rise beyond 90°C and the consequent fourfold reduction in temperature differential has removed the air humidity problem and reduced energy consumption.
Condensation and cavity corrosion have therefore been eliminated and the maintenance interval has been extended to between five and six weeks, saving further costs.
The uniform cooling channels work so well that the production cycle is now 17 per cent faster than previously. Component deformation is no longer a problem, raising quality and repeatability. After 370,000 cycles, total cost savings amounted to around 20,000 euros.
Pavel Strnadek, head of tool maintenance at Magna added, “There is stiff competition in the European automobile industry. That is why it is very important for us to be able to produce components to the highest quality standards at the lowest price.
“The issue of injection mould cooling was something that we have been trying to deal with for a long time. We knew how we wanted improved products to look, but realising it was just not possible using conventional manufacturing methods.
“Additive manufacturing has allowed us to make the breakthrough and we are very happy with the results at every level. Maintenance, quality of the end product, costs, heat dissipation – it has been the perfect project.”
Image: The additively manufactured tooling insert on its build platform