Thixoforming : Semi-solid Metal Processing

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Figure 10.20 The robot controller acts as a master controller which triggers the other components to start their respective operations [20]. 10.3 Heating and Forming Operationsj393 via a CAN BUS. Many sensors detect if operations were successfully done or an error occurred. An operator has to start the production chain by starting the programme of the robot. The programme sends a signal to the feedstock magazine that separates a billet to provide it to the robot. When this operation has been done, the feedstock magazine sends a signal for clearance. The robot engages the billet and puts it into the induction furnace. Then the robot controller gives the start signal for the heating of the billet. A separate PC controls the heating with the control scheme using a pyrometer
394j 10 Thixoforging and Rheoforging of Steel and Aluminium Alloys explained in Section 10.3.1. When the billet has reached the desired temperature, the PC sends a signal to the robot controller. The robot can now engage the heated billet and transport it into the forming press. The forging process will be started as soon as the billet has been placed in the cavity and the robot has left the area of the forging press. After the forming process, the finished part can be removed from the forming press by the unloading unit. 10.3.6.6 Control of the Forming Process The requirements for handling material in the semi-<strong>solid</strong> state are very demanding. On the one hand, the forming process has to be done as fast as possible. On the other hand, the flow of the material must not stall because this would lead to imperfections in the work piece. Therefore, the velocity of the piston has to be limited. Commonly, the velocity is constant during the forming process and the flow velocity of the material is limited by the minimum width of the cavity. Hence the forming process is not time optimal. If we could follow an optimal trajectory from form filling simulations, we would obtain a time-optimal process without imperfections in the parts. Therefore, feed-forward control for the trajectories is needed. For these reasons, the flatness-based approach is used (see Section 10.3.1). However, the velocity of the piston is not a flat output for the system of a differential cylinder [43]. To calculate the servo valve voltage from a given velocity trajectory of the piston, one has to measure the pressures in the two chambers of the differential cylinder. Therefore, offline computing of the servo valve voltage is not possible. In order to achieve a system of the differential cylinder, which has the velocity as a flat output, the compressibility of the hydraulic fluid is neglected. This leads to a simplified system without the pressure dynamics. With the simplified system, we achieve the following equation to calculate the servo valve voltage: uðtÞ ¼ 1 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi A KVBV 3 s K ð1þa3Þ AKpV m_vðtÞ FR FL T V _vðtÞþvðtÞ 1 þ T ( " V 2 m€vðtÞþ _ FR þ _ FL #) AKpV m_vðtÞ FR FL ð10:15Þ The voltage u(t) depends on the velocity v(t) of the piston, the friction force FR and the load FL. Inafirst approximation, the load is considered to be proportional to the velocity. Also, the friction force is a function of the velocity. Therefore, we can conclude that the piston velocity is a flat output of the simplified model and we can calculate the servo valve voltage from a smooth velocity trajectory. For more details, see [44]. We have to consider that the feed-forward control does not contain the pressure dynamics. Therefore, a controller is needed to make sure that the piston follows the desired velocity trajectory. A simple PID controller is sufficient. The experiments were carried out with a differential cylinder where the behaviour of the thixotropic material was simulated by a damper. Figure 10.21 shows the desired
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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
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Figure 9.27 Development of the micr
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some places can be observed as smal
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Figure 9.31 Simulation of the metal
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Page 430 and 431: References 1 Koesling, D., Tinius,
Page 432: steel billets into the semi-solid s
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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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