Papers by Keyword: High Pressure Die Casting

Abstract: The use of sensors for detection, measurement and evaluation of mechanical and thermal loads is well known and essential for the implementation of »Structural Health Monitoring« (SHM). For this, sensors are mainly used for condition monitoring of mechanical loads and their impact to the castings state, which is a decisive advantage for safety-related components. The use of sensors on the surface of metallic components, in particular of cast metal components made of aluminum, is still limited to the use of strain gauges. They are usually applied on the surface of the cast metal components and get fixed by adhesives. The idea is, to integrate the sensors directly during the aluminum casting process. Since integrated sensors are naturally protected against chemical and mechanical influences, furthermore the load can be measured directly at the point of interest inside the component. Measurement data can be recorded and provide a good data basis for future calculations and dimensioning of components, which is known as »Data Mining« or »Industrial Data Space«. New technology and material combinations, which allow the fabrication of sensors capable of withstanding force and temperature during the integration process in aluminum casting, are investigated.In this paper, the design and fabrication of a strain gauge printed on an aluminum sheet is shown. These sensor sheets get integrated in aluminum during high pressure die casting (HPDC) in a way that a specimen is build up. The specimen is characterized in a fatigue bending test and the sensor data was read permanently during this test. It is shown that the new approach with printed thick film sensors on aluminum substrate sheets works properly to withstand the heavy thermal conditions during high pressure die casting. The fabricated sensor is able to sense the mechanical tiredness and detects the fatigue of the metal matrix. This a first step to use such material integrated sensors in structural health monitoring applications.

Abstract: Combining aluminum and carbon fiber reinforced plastic (CFRP) has been a key focus in realizing lightweight concepts. Manufacturing technologies for high load-bearing and ultra-lightweight CFRP structures have reached a high level of innovation. The same goes for near-net-shape high pressure die casting (HPDC) aluminum components, which can be mass-produced in a highly efficient manner. Yet for hybrid composites of these materials, the solutions to date have relied on conventionally mechanical or adhesive joining techniques. The direct joining of these two materials is problematic, due to their electrochemical intolerance and the resulting corrosive degradation. The joining technology therefore is at the center of this challenge. The DFG-sponsored joint research project of Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Fiber Institute FIBRE, and Bremen Institute for Mechanical Engineering BIME, all three institutes located at the campus of the university in Bremen, aims at combining aluminum and thermoplastic CFRP into an intrinsic hybrid composite. This is to be achieved in a single-step primary shaping process, avoiding conventional joining techniques like adhesive bonding or riveting. To this end, CFRP structures are to be recast with aluminum, creating an electrochemically decoupling layer between the two materials. This decoupling layer can therefore be considered as a key factor for realizing hybrid composites. It also needs to have a high process reliability and be long-term and mechanically stable. Polyetheretherketone (PEEK) thermoplast was identified as a suitable material for that purpose, given its stability at high temperatures and electrochemical insulation effect. First test results show the possibility of incorporating CFRP accordingly by HPDC, resulting in a continuous intact decoupling layer of PEEK. The trend indicated that different thermal treatments as well as different aluminum thicknesses of the hybrid casted sample influence the joint strength. On average, in tensile shear tests a joint strength approximately in the range of current single lap adhesive bonds could be achieved.

Abstract: Due to the growing demand for lightweight solutions in a wide range of industries, the selection and combination of various materials is becoming more and more important. As a result, the need for suitable joining technologies is increasing along with it. Within the DFG research group "Schwarz-Silber" ("black-silver"), Fraunhofer IFAM is investigating so-called transitional structures in cooperation with the University of Bremen. In this process, glass fiber structures are integrated into aluminum by a high pressure die casting process. These structures are used for the electrochemical insulation between aluminum and carbon fiber textiles, which are connected by textile processes in a subsequent production step. A solid hybrid structure is finally achieved through a resin-impregnation process. The key challenges are the positioning, pre-tensioning and infiltration of the glass fiber structures within the high pressure die casting process. In order to meet these challenges, a customized die casting tool was developed within the project. With the aid of mold-filling simulations, the die system of the die casting tool was optimized to achieve better infiltration of the fiber bundles and to additionally support the position of the glass fibers in the casting process. After the design of the molding tool, the implementation was carried out in collaboration with a toolmaker. In subsequent, up-to-date investigations, the positioning and infiltration of different variants of glass fiber structures is evaluated. The results are compared with previous attempts to position and infiltrate the glass fiber structures to assess the effect of the optimized newly designed tool.

Abstract: This paper describes the details of a quantitative experimental and numerical study on the influence of solidification conditions, including the apparent interfacial heat transfer coefficient (IHTC) between the die and solidifying metal, on the resulting local microstructure. Multiple runs of the commercial casting simulation package, ProCASTTM, are used to model the mold filling and solidification events employing a range of IHTC values. The simulation results are used to estimate the centreline cooling curve at various locations through the casting. The centreline cooling curve, together with the die temperature and the thermodynamic properties of the alloy are then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting. Finally, the local cooling rate is used to calculate the resulting grain size and skin thickness via previously established relationships. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent IHTC, which, in this study, was approximately 12000 W/m²·K. Additional useful observations from the numerical study suggest that the IHTC has a significant influence on the skin thickness and grain size in both the skin and core regions of the casting, while the effect of die temperature is limited to influencing the skin grain size only.

Abstract: High Pressure Die Casting (HPDC) is a foundry process particularly suitable for high production rates and applied in several industrial fields, but the amount of scrap, caused by defects or incomplete filling, is sometimes very high. Thus it is important to know which are the main causes of defect formation and their effects on microstructure and mechanical properties. This paper presents, within the European MUSIC project, the qualitative and quantitative results of a study conducted on AlSi9Cu3(Fe) alloy castings, referred to as Horse-shoe Reference Castings, specifically designed to generate different kinds of defects with different severity levels. The work focuses on the correlations obtained between the casting mechanical properties, their defect content in terms of porosity and oxide films and the process parameters adopted, mainly second phase plunger velocity and intensification pressure. The three point bending test was carried out on the four specimens obtained from the two appendixes of the casting. The fracture surfaces were studied by scanning electron microscopy (SEM) and optical microscopy (OM) highlighting that the defect content is clearly correlated to the mechanical properties and the process parameter settings.

Abstract: Primary AlSi10MnMg alloy is the most widely used alloy for manufacturing of vacuum assisted high pressure die castings (VPDC) with high ductility requirements. In this alloy, die soldering is avoided by a high Mn level (0.5 - 0.6 wt. %) while Fe is kept low (< 0.25 wt. %). Such combination guarantees that the Al-Fe-Mn-Si intermetallic compounds are of the α-iron rich polyhedral or Chinese script type, which is less harmful to the ductility. However, secondary alloys are cheaper and their production requires less energy than the one of primary alloys. The higher amount of Fe, a common impurity in secondary alloys, reduces ductility but also die soldering and thus manufacturing costs. Microadditions based on Mn are known to be very effective in transforming the harmful needle/platelet shaped β-compounds into α-iron compounds with a less harmful morphology. In this work a secondary alloy with 0.60 wt. % Fe and different Mn microadditions has been cast in test parts with different wall thicknesses using VPDC technology. The Mn content of the new alloy has been optimized. Mechanical properties of the optimised alloy have been determined in different heat treatment conditions and been compared to the corresponding AlSi10MnMg primary alloy. Mechanical properties similar to those of the primary alloy have been achieved.

Abstract: Among the Aluminum casting processes, High Pressure Die Casting (HPDC) is an efficient, versatile and economic way for producing large number of components. Nevertheless, because of the elevated amount of rejected castings, it is important to know which are the main causes of defect formation and their effects on microstructure and mechanical properties. This paper presents, within the European MUSIC project, an overview of the preliminary correlations obtained studying both castings with defect generator geometry, referred to as Horse-shoe Reference Castings, and industrial demonstrators, referred to as Gear Box Housing. The deduced correlations between static mechanical properties and casting defects highlighted interesting trends in both cases.

Abstract: The following paper presents results of the researches on the influence of Sr addition on microstructure and mechanical properties of EN AC-Al Si9Cu3(Fe) HPDC alloy. Two different elements were high pressure die cast for the research, one with Sr addition, second one without. Investigations involved light and scanning electron microscopy as well as hardness and tensile testing. EN AC-Al Si9Cu3(Fe) HPDC alloy microstructure is characterized by a fine dendrites of α-Al solid solution and AlSi binary eutectic mixture. What is more, many intermetallic phases are observed in the alloy. These are: α-Al₁₅(Fe,Mn,Cr)₃Si₂, β-A₅FeSi, A₂Cu, π-A₈Mg₃FeSi₆ and Q-A_l5Mg₈Cu₂Si₆. Sr modified alloy is characterized by a significant volume fraction of fine, fibrous AlSi-eutectic. The porosity in the modified alloy slightly decreased. Mechanical properties of the alloy increased after Sr modification.

Abstract: The difficulties and issues associated with the economics of the process and die life in casting aluminium alloys, as experienced by the high pressure die casting industry, were reasons behind undertaking this research project. The use of a tungsten alloy able to withstand high temperature process conditions without the welding problems experienced by standard die construction materials, such as H13, was examined in an extensive series of casting trials. The importance of operating dies at elevated temperatures to minimize heat checking has been demonstrated previously, both through theoretical thermal modelling and experimentation. This paper describes both aspects of die life extension and possibilities to reduce the amount of alloy material used in the cast part feed system, including overflows. CSIR intends using the results of this research for further development and application of high temperature die construction materials in high pressure die casting processes of light metal alloys.

Abstract: In the present paper, we introduce the development of casting an industrial component with a newly developed high strength aluminium alloy for high pressure die casting, including the introduction of property requirement, and the simulation results of temperature distribution, air entrapment, air pressure and the porosity potential in the casting, overflows and gating system. The microstructure and mechanical properties of the casting with satisfied quality are described under as-cast and heat-treated conditions.