Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with...Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with high mechanical load capacity.Moreover,forging is a cost-effective mass production process but,in spite of all its advantages,it has its limitations,e.g.in the freedom of designs.However,because of the extreme thermal loading(particularly with regard to permanent moulds) and the frequently unavoidable casting defects,hand tools are not cast.By means of thixocasting steel,technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging.Through near-net shape production,manufacturing steps and costs can be reduced.Furthermore,steels,which are difficult to forge but nonetheless have high potential for specific applications(such as high strength or corrosion resistant steels),can also be processed.In cooperation with industrial partners,X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast.Forming dies were designed and optimized by simulation,the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys.The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition(PECVD).During the experiments,combination spanners were successfully cast in the semi-solid state.Cast parts were heat-treated to enhance the toughness of components,which was subsequently measured by a standardized torque test.Moreover,a hypothetical approach of a possible,industrial batch process was carried out using the simulation software MAGMAsoft.展开更多
The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is propo...The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is proposed to simulate the cooling channel process of A356 Aluminum alloy.The three phases are liquid,solid and air respectively and treated as separated and interacting continua,sharing a single pressure field.The mass,momentum,enthalpy transport equations for each phase are solved.The developed model can predict the evolution of liquid,solid and air fraction as well as the distribution of grain density and grain size.The effect of pouring temperature on the grain density,grain size and solid fraction is analyzed in detail.展开更多
Within the project "Functional Surfaces via Micro-and Nanoscaled Structures" which is part of the Cluster of Excellence "Integrative Production Technology" established and financed by the German Re...Within the project "Functional Surfaces via Micro-and Nanoscaled Structures" which is part of the Cluster of Excellence "Integrative Production Technology" established and financed by the German Research Foundation (DFG),an investment casting process to produce 3-dimensional functional surfaces down to a structural size of 1μm on near-net-shape-casting parts has been developed.The common way to realize functional microstructures on metallic surfaces is to use laser ablation,electro discharge machining or micro milling.The handicap of these processes is their limited productivity.The approach of this project to raise the efficiency is to use the investment casting process to replicate microstructured surfaces by moulding from a laser-microstructured grand master pattern.The main research objective deals with the investigation of the single process steps of the investment casting process with regard to the moulding accuracy.Actual results concerning making of the wax pattern,suitability of ceramic mould and core materials for casting of an AlSi7Mg0.3 alloy as well as the knock-out behavior of the shells are presented.By using of the example of an intake manifold of a gasoline race car engine,a technical shark skin surface has been realized to reduce the drag of the intake air.The intake manifold consists of an air-restrictor with a defined inner diameter which is microstructured with technical shark skin riblets.For this reason the inner diameter cannot be drilled after casting and demands a very high accuracy of the casting part.A technology for the fabrication and demoulding of accurate microstructured castings are shown.Shrinkage factors of different moulding steps of the macroscopic casting part as well as the microscopic riblet structure have been examined as well.展开更多
When treated in pressure die casting processes the semi-solid aluminum alloys demand resilient cores which can bear the stress occurring during filling and the final pressure phase.The design of permanent cores is hig...When treated in pressure die casting processes the semi-solid aluminum alloys demand resilient cores which can bear the stress occurring during filling and the final pressure phase.The design of permanent cores is highly restricted in order to maintain removability.Lost cores provide the possibility of complex,undercut geometrical shapes which is mandatory for a variety of casting components.However,eligible materials which show appropriate resilience and proper decomposition properties at the same time,and in the upper echelon of cost-effectiveness,are seldom known.With the semi-solid process suited between HPDC and GDC regarding the core stress,several common and economically efficient lost core systems could be used.A selection of potentially suitable materials was identified and tested.The range of testing comprises widespread sand core-systems(amin-pur-coldbox and CO2-water-glass) as well as materials less commonly used,namely salt,plastic and zinc.Different types of conditioning are applied to enhance the surface properties.The mechanical properties of the sand cores are enhanced by different heat treatment methods during curing.The cores are tested producing a research component cast on a HPDC machine with semi-solid A356 slurry fabricated in the cooling channel process.The cast component was analyzed regarding shape stability,core removability and surface as well as the structure quality.The results show the importance of the surface conditioning for the sand-cores while salt and zinc produce good parts comparable to the reference steel core quality.展开更多
基金the German Research Foundation (DFG),which supports this work within the framework of the collaborative research centre SFB 289
文摘Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with high mechanical load capacity.Moreover,forging is a cost-effective mass production process but,in spite of all its advantages,it has its limitations,e.g.in the freedom of designs.However,because of the extreme thermal loading(particularly with regard to permanent moulds) and the frequently unavoidable casting defects,hand tools are not cast.By means of thixocasting steel,technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging.Through near-net shape production,manufacturing steps and costs can be reduced.Furthermore,steels,which are difficult to forge but nonetheless have high potential for specific applications(such as high strength or corrosion resistant steels),can also be processed.In cooperation with industrial partners,X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast.Forming dies were designed and optimized by simulation,the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys.The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition(PECVD).During the experiments,combination spanners were successfully cast in the semi-solid state.Cast parts were heat-treated to enhance the toughness of components,which was subsequently measured by a standardized torque test.Moreover,a hypothetical approach of a possible,industrial batch process was carried out using the simulation software MAGMAsoft.
文摘The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is proposed to simulate the cooling channel process of A356 Aluminum alloy.The three phases are liquid,solid and air respectively and treated as separated and interacting continua,sharing a single pressure field.The mass,momentum,enthalpy transport equations for each phase are solved.The developed model can predict the evolution of liquid,solid and air fraction as well as the distribution of grain density and grain size.The effect of pouring temperature on the grain density,grain size and solid fraction is analyzed in detail.
基金supported by the German Research Foundation DFG within the Cluster of Excellence "Integrative Production Technology for High-Wage Countries
文摘Within the project "Functional Surfaces via Micro-and Nanoscaled Structures" which is part of the Cluster of Excellence "Integrative Production Technology" established and financed by the German Research Foundation (DFG),an investment casting process to produce 3-dimensional functional surfaces down to a structural size of 1μm on near-net-shape-casting parts has been developed.The common way to realize functional microstructures on metallic surfaces is to use laser ablation,electro discharge machining or micro milling.The handicap of these processes is their limited productivity.The approach of this project to raise the efficiency is to use the investment casting process to replicate microstructured surfaces by moulding from a laser-microstructured grand master pattern.The main research objective deals with the investigation of the single process steps of the investment casting process with regard to the moulding accuracy.Actual results concerning making of the wax pattern,suitability of ceramic mould and core materials for casting of an AlSi7Mg0.3 alloy as well as the knock-out behavior of the shells are presented.By using of the example of an intake manifold of a gasoline race car engine,a technical shark skin surface has been realized to reduce the drag of the intake air.The intake manifold consists of an air-restrictor with a defined inner diameter which is microstructured with technical shark skin riblets.For this reason the inner diameter cannot be drilled after casting and demands a very high accuracy of the casting part.A technology for the fabrication and demoulding of accurate microstructured castings are shown.Shrinkage factors of different moulding steps of the macroscopic casting part as well as the microscopic riblet structure have been examined as well.
文摘When treated in pressure die casting processes the semi-solid aluminum alloys demand resilient cores which can bear the stress occurring during filling and the final pressure phase.The design of permanent cores is highly restricted in order to maintain removability.Lost cores provide the possibility of complex,undercut geometrical shapes which is mandatory for a variety of casting components.However,eligible materials which show appropriate resilience and proper decomposition properties at the same time,and in the upper echelon of cost-effectiveness,are seldom known.With the semi-solid process suited between HPDC and GDC regarding the core stress,several common and economically efficient lost core systems could be used.A selection of potentially suitable materials was identified and tested.The range of testing comprises widespread sand core-systems(amin-pur-coldbox and CO2-water-glass) as well as materials less commonly used,namely salt,plastic and zinc.Different types of conditioning are applied to enhance the surface properties.The mechanical properties of the sand cores are enhanced by different heat treatment methods during curing.The cores are tested producing a research component cast on a HPDC machine with semi-solid A356 slurry fabricated in the cooling channel process.The cast component was analyzed regarding shape stability,core removability and surface as well as the structure quality.The results show the importance of the surface conditioning for the sand-cores while salt and zinc produce good parts comparable to the reference steel core quality.
