Thixoforming : Semi-solid Metal Processing

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10.3.4 Thixoforging of Steel In this section, thixoforging parts show the possibility of producing near-net shaped components, which are not realizable in the same way in drop forging processes. They were carried out by using standard dies of hot forming tool steels X38CrMoV5-1 and X45MoCrV5-3-1. Two different geometries were chosen: a demonstrator in the form of a wheel hub and a pump housing. As thixoforming material, X210CrW12 and 100Cr6 billets were preheated into the semi-solid interval with about 35% liquidphase fraction and positioned upright in the lower die. The upper tool was lowered to close the die and, subsequently, a flexible cylinder below the lower tool frame carried out the rest of the filling operation and maintained the pressure in the cavity until the solidification was completed. The part was ejected immediately and allowed to cool in the appropriate atmosphere or medium. The demonstrator (Figure 10.14a) was chosen for basic experiments to clarify the filling behaviour of the die depending on the different diameters of the flange and different wall thicknesses of the bush [11]. It was also investigated with the rheoforming process (Section 10.3.7) and was the main part for simulations (Section 10.4.2) because of it axisymmetric geometry and the thereby reduced calculation time. Generally, the combination of a sufficient tool velocity and compression force ensures good form filling. Especially for thin-walled components there is a risk of early solidification with too slow forming operations. In the region of the bush, the material can be cooled below the solidus temperature so that the flow front breaks open and the semi-solid material of the inner part surrounds this frozen area. This can lead to cold shuts, which are characterized by strongly weakened material properties. The investigation of the pump housings produced regarding the microstructure and local inside hardness showed that no shrinkage holes and porosity can be identified on the examined cross-sections. However, some oxidized outer shell of the billet is found inside the part. Several microcracks exist around the oxide inclusion Figure 10.14 Components produced by thixoforging. Demonstrator, 100Cr6; pump housing, X210CrW12. 10.3 Heating and Forming Operationsj387
388j 10 Thixoforging and Rheoforging of Steel and Aluminium Alloys Figure 10.15 Microstructures of a processed part (100Cr6). (Figure 10.15). The use of inert gas shielding is effective in avoiding or reducing the oxidation depending on the chemical composition of the material. Figure 10.16 shows the results of local hardness investigations along the displayed lines inside the forged part. The hardness increases from the centre to the outside in a range of 250–350 HV10. This is related to the locally different cooling rates and can additionally be influenced by the occurrence of segregation. The results of the trials demonstrate the potential of semi-solid forging as a forming operation for steels but also reveal the necessity for adequate measures against scale inclusions. Countermeasures were taken by applying a fully automated semi-solid forging plant including a thorough protective atmosphere. Morphological studies of the material thus produced verify high suitability for semi-solid forging (Section 10.3.6). Figure 10.16 Distribution of hardness in pump housing (100Cr6) in vertical and horizontal directions.
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Thixoforming Semi-solid Metal Proce
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Further Reading Herlach, D. M. (ed.
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The Editors Prof. Dr. G. Hirt Insti
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VI Contents 1.3.5.2 Other Aluminium
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VIII Contents 4.6.1 Thixocasting 13
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X Contents 7.4.2 Isothermal Non-ste
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XII Contents 9.4.1.3 Simulation Res
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Preface Semi-solid forming of metal
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XVIII List of Contributors Andreas
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XX List of Contributors Alexander S
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2j 1 Semi-solid Forming of Aluminiu
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10j 1 Semi-solid Forming of Alumini
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Table 1.1 Overview of semi-solid pr
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Part One Material Fundamentals of M
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32j 2 Metallurgical Aspects of SSM
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44j 3 Material Aspects of Steel Thi
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Temperature (ºC) 1550 1500 1450 14
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100j 3 Material Aspects of Steel Th
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106j 4 Design of Al and Al-Li Alloy
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5 Thermochemical Simulation of Phas
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here it can be assumed that the dat
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Figure 5.2 Calculated temperature v
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Figure 5.4 Composition profiles of
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It is clear that C has by far the s
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Figure 5.7 The density of X210CrW12
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5.3 Calculations for the Bearing St
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Figure 5.11 Composition profiles of
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Figure 5.14 The density of 100Cr6.
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area which is available for heat tr
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Part Two Modelling the Flow Behavio
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170j 6 Modelling the Flow Behaviour
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7 A Physical and Micromechanical Mo
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3. Macroscopic averages or homogeni
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displacement boundary conditions or
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and liquid are both assumed to be i
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are the strain rate concentration t
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Semi-solid viscosity (Pa s) into cl
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Load (kN) strain to rupture, leadin
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Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
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adius R radius of the spherical inc
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Part Three Tool Technologies for Fo
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242j 8 Tool Technologies for Formin
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9 Rheocasting of Aluminium Alloys a
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Figure 9.2 Processes for the semi-s
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Two Italian companies gained the fi
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9.2 SSM Casting Processesj317 For t
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Figure 9.7 Oil pump cover for Honda
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Figure 9.9 Middle temperature cours
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Figure 9.12 Components of cartridge
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Figure 9.15 Process adapted multipa
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step-shot experiments. It is also s
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Figure 9.18 (a) Meander tool for fl
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Figure 9.19 (a, b) Wear appears in
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Table 9.2 Temperature determination
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and are plausible on the left. Furt
Page 360 and 361: Figure 9.27 Development of the micr
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Page 364 and 365: Figure 9.31 Simulation of the metal
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Page 368 and 369: Figure 9.35 Comparison of the micro
Page 370 and 371: 9.4 Rheoroutej347 If rounding of th
Page 372 and 373: 9.4.1.2 Parameters: Cooling to the
Page 374 and 375: Figure 9.36 Results of the 2D-MICRE
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Page 390 and 391: 27 Doppelbauer, M. (2003) Wirtschaf
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Page 394 and 395: 1970s [7]. Also, the quality of the
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Page 408 and 409: Figure 10.12 Segregation in compone
Page 412 and 413: 10.3.5 Thixojoining of Steel In the
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Page 426 and 427: Table 10.2 Definition of boundary c
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Page 430 and 431: References 1 Koesling, D., Tinius,
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438j 11 Thixoextrusion Figure 11.30
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440j 11 Thixoextrusion solidificati
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442j 11 Thixoextrusion GPa pressure
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444j Index arbitrary volume element
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446j Index equilibrium tests 141 eq
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448j Index - importance 273 ion flu
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450j Index oxygen-sensitive element
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452j Index - thixoforming 241 semi-
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454j Index - high pressure 131 - sc
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Thixoforming : Semi-solid Metal Processing

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