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Contenuto archiviato il 2024-05-29

Integration of two-component ceramic injection moulding for large-scale production of novel multifunctional ceramic components for automotive and railway applications

Final Report Summary - CARCIM (Integration of two-component ceramic injection moulding for large-scale production of novel multifunctional ceramic components for automotive and railway applications)

The main goal of the CARCIM project was the integration of the two-component ceramic injection moulding (2C-CIM) as a low-cost and large-series production technique for development of complex shaped ceramic components for automotive and railway applications offering a high degree of structural and functional integrity.

The 2C-CIM technology, which is known from two-coloured plastic parts, should be qualified for the production of advanced ceramic components combining two ceramic materials with different or opposite properties without additional joining steps. 2C-CIM allows producing advanced ceramic products at a large scale with increased functionality, high degree of complexity, but at a lower cost level in comparison to other shaping techniques.

The project resulted in four 2C-CIM prototype parts.

Functional testing and verification such as techno-economical assessment of the complete processing chain had been carried out for the four parallel case studies: (1) ceramic glow plug, (2) ceramic gear wheel; (3) ceramic valve seat, and (4) ceramic braking pads for high-speed trains. For developing the 2C-CIM technology for both, low pressure and high pressure injection moulding, one case study resulted in a prototype produced by low pressure injection moulding (glow plug) and three case studies are attributed to high pressure injection moulding (gear wheel, valve seat, and brake disc).

Different types of prototypes for four case studies and appropriate material combinations have been defined by the project partners. Technical specifications of the prototypes were provided. The definition of the prototypes and the material choice was accompanied by a patent survey and a market survey in the field of the specified components and materials.

Following combinations of ceramics have been selected:
- glow plug: property combination electrical conductive / isolating: Si3N4/MoSi2 with higher and lower content of MoSi2 which serves as the conductive phase in the material;
- gear wheel : property combination high hardness / high toughness: zirconia toughened alumina (ZTA) / alumina toughened zirconia (ATZ);
- valve seat: property combination high toughness / high wear resistance: Si3N4/SiAlON;
- braking pads: property combination high friction and mechanical strength/high strength with sufficient heat conductivity: zirconia toughened alumina / Al2O3.

All feedstocks developed in the first project period have been characterised in detail by thermoanalytical, rheological and mechanical measurements for providing the input data for mould flow simulation. The injectability of the feedstock systems has been tested by producing single component parts. These parts were used afterwards for measuring the mechanical and electrical properties of the single materials.

Since defects in injection moulded components often become obvious only at the end of the processing chain after time and cost consuming debinding and sintering steps, non-destructive testing methods are getting more and more important. In the case of two-component injection moulded parts thermographic and computer tomographic investigations in the green state have been proven to be indispensable methods for characterising the accuracy of the interface between the different materials. After designing and constructing the tools for three case studies, first prototype parts had been developed and tested.

The functionality of the glow plug has been tested by ignition tests. With an applied voltage of 13 V a temperature at the tip of 1 250 degrees Celsius could be achieved within 3 seconds. Testing of the components under practical conditions will be continued beyond the project. The torque-measuring test of the sintered gear wheel showed that the components resist a torque of > 1 Nm. The components of the gear wheel have been tested concerning wear resistance, fracture toughness and hardness. Feasibility studies with another feedstock system confirmed that this component can be produced by means of two-component ceramic injection moulding.

The braking pads were inserted into a steel braking disk in a casting process. A bonding of the components in the steel disk could be obtained, and a braking test emphasised that the braking time from 180 km/h down to hold-up could be reduced by 17 %. For all components technical processing guidelines and cost estimations were established.

Following principle requirements should be taken into account for the development of two-component ceramic parts:
1. the powders chosen for two-component injection moulding must be sinterable to full density at comparable temperatures and under the same gaseous atmosphere;
2. for avoiding critical stresses during sintering the powders shall have a similar sintering behaviour, i.e. the onset of shrinkage shall fall in a narrow temperature range for both powders and the shrinking rate shall be comparable;
3. for ensuring a precise adjustment in total shrinkage the volume content of solid in the feedstocks must be the same;
4. since differences in the thermal expansion coefficients of the feedstocks may cause cracks, distortion or delaminations of the compounds already in the green state the same binder system or binder systems with comparable thermal expansion behaviour must be used for feedstock preparation;
5. the thermal expansion coefficients of the sintered ceramic materials play also a very important role as shown in this article, because differences in this property can result in stresses in the two-component part during cooling after sintering or during application of the part under cyclic heating and cooling conditions.

If stresses between both components cannot be totally excluded, they should be taken into consideration already in the design of the injection moulded parts. The CARCIM project showed the feasibility of ceramic components with novel functionalities by two-component injection moulding. It emphasised the importance of non-destructive testing methods for ensuring the quality of the products in each processing step.

Simulation of the processing chain can also be a helpful tool for avoiding problems in mould filling or with distortion and delamination of components. However, for improving the reliability of the simulation results further development work will be necessary. Tooling is a very challenging task for two-component ceramic injection moulding. For future works in this field more reworking cycles of the tool should be taken into consideration. The increase in difficulties for tooling in the case of two-component ceramic parts had been underestimated in this project.

In sum, the CARCIM project can be evaluated as a very successful European project which has strengthened the cooperation between the former project partners sustainably. A lot of tasks have been solved and a lot future challenges in this field have been pointed out.