Toshimitsu Okane

Verification of the Simulated Residual Stress in the Cross Section of Gray Cast Iron Stress Lattice Shape Casting via Thermal Stress Analysis

The residual stresses in the thick part of the stress lattice shape casting consist of the residual stress due to the temperature differential between the thick part and the thin part and the residual stress due to the temperature differential in the radial direction of the thick part. In this study, the gray cast iron stress lattice shape castings were cast and both types of the residual stresses were separately measured. Thermal stress analyses based on the casting experiment were conducted. Next, the measurements in this study were compared with both types of the simulated residual stresses. The thermal stress analyses estimated the residual stress due to the temperature difference in the radial direction of the thick part to be significantly higher than the measurement, although the residual stress due to the temperature difference between the thick part and the thin part was successfully predicted within a 10xa0pct error. Thus, this study suggested the introduction of the mechanical melting temperature, above which the very low yield stress is applied conveniently to describe the losses of the deformation resistance of the casting, to more accurately predict the residual stress due to the temperature difference in the radial direction of the thick part. From the verification of the suggested model, this study demonstrated that the conventional elasto-plastic model must introduce the mechanical melting temperature to predict the residual stress due to the temperature difference in the radial direction of the thick part and thus the overall residual stress in the stress lattice.

Numerical and Experimental Study on Residual Stress in Gray Cast Iron Stress Lattice Shape Casting

The prediction of residual stress in a stress lattice shape casting (stress lattice) has been conducted and discussed by some researchers via the Finite Element Method (FEM). However, most of the previous studies used the first-order tetrahedral element, which has poor analysis accuracy in problems including bending. The use of the first-order tetrahedral element makes the verification of these studies uncertain because the bending deformation essentially occurs in the stress lattice casting. This study first shows that the thermal stress analysis for the stress lattice should use the element that can represent the bending deformation in principle for bending of the thin parts. Second, the simulated residual stress was compared with the measured value. The thermal stress analysis successfully predicted the residual stress of the stress lattice casting with and 11 pct difference. In addition to the prediction of the residual stress, it is important from the viewpoint of the productivity of castings to reveal the effect of the shake-out temperature on the residual stress. However, in the previous studies, conclusions concerning the effect of the shake-out temperature on the residual stress were not consistent (i.e., the one study said the higher shake-out temperature decreased the residual stress, and another study said a higher shake-out temperature increased the residual stress). Therefore, the current study first discusses the reason for the inconsistent conclusions in the previous studies. Second, stress lattice castings were cast and shaken out at various shake-out temperatures. Then, the current study validated the effect of the shake-out temperature on the residual stress. Consequently, the experimental results supported the conclusion of Kasch and Mikelonis that the shake-out at higher temperature contributed to the increase of the residual stress in the casting.

A New Theoretical Approach Based on the Maxwell Model to Obtain Rheological Properties of Solidifying Alloys and Its Validation

This paper proposes a new method for obtaining the rheological properties of solidifying alloys in the brittle temperature range (BTR). In that range, alloys show not only rheological, but also brittle behavior. Conventional methods to obtain rheological properties require steady state stress with ductility. Therefore, rheological properties of BTR alloys are unobtainable, or are otherwise including the effects of microscopic damage. The method proposed in this paper uses the stress–strain relation derived from the Maxwell model assuming that strain hardening is negligible in solid-liquid coexistence states. By removing the plastic strain term, the creep strain rate in Norton’s law is derived by the total strain rate and stress rate without the steady state stress condition. Consequently, the stress exponent n and material constant A of Norton’s law can be obtained even for alloys in the BTR. We applied this method to both tensile process before crack initiation and stress relaxation process. According to the Maxwell model, couples of the properties (n and A) obtained in both processes must be equal. Therefore, the difference can validate the obtained properties. From tensile and stress relaxation tests, we obtained the properties of solidifying Al-5xa0wtxa0pct Mg alloy. We validated results by examining the difference. This report is the first to provide a method to obtain the rheological properties of BTR alloy without damage.

Mechanical Properties of a Partially Solidified Cu-Zn Alloy

For predicting solidification cracking by thermal stress analysis, the mechanical properties in the partially solidified state based on the experimental results are the best hope. However, the Young’s modulus has never been investigated for copper alloys. In this study, stress–strain curves of a Cu-Zn alloy in the partially solidified state for various solid fractions were obtained using a specially developed horizontal tensile test device. Furthermore, by removing the load during the tensile test, the spring-back (elastic behavior) was observed and the Young’s modulus was obtained.

Training support for pouring task in casting process using stereoscopic video see-through display - Presentation of molten metal flow simulation based on captured task motion

The work support technology using augmented reality has been researched in the field of manufacturing. It is the technology that can present appropriate instructions to a worker. Thereby, the worker performs a task requiring an advanced skill even if she/he is not an expert. In this technology, most of work instructions are presented while the worker is working. However, there are many manufacturing tasks that is difficult to be retried when it fails. In order to deal with such tasks, a training support technology that a worker can train tasks beforehand using augmented reality is proposed. This technology can present simulated task results according to the motion of the worker. As a simulation result, for example, the worker can see internal state of the work object. And she/he can train as many times as she/he wants. Therefore, her/his skills can be improved through trial and error. In this paper, a concept of task training support technology is introduced. To realize the concept, the pouring task in casting process is selected as a target task and the prototype system is constructed. Then, the evaluation results of pouring task training using the prototype system are reported.

Effect of Fe Content on Hot Tearing of High-Strength Al-Mg-Si Alloy

The effect of Fe content on hot tearing of the high-strength Al-Mg-Si alloy was systematically investigated. In this study, a thermodynamic calculation software Thermo-Calc was used to calculate the solidification path under the non-equilibrium condition, and the mechanical properties of this alloy have also been investigated during solidification using an electromagnetic induction heating tensile machine. In order to confirm the calculation results of solidification path, a quenching test also was carried out. By using the Thermo-Calc, the sequence of crystallization, crystallization temperature of formed phases and their crystallized amount were systematically investigated for each alloy in which Fe content was changed. Furthermore, by comparing the fracture surfaces of the tensile testing sample and DC billet, the temperature range of crack initiation of the alloy was examined. Comparing the temperature range of crack initiation with the crystallization phase and its crystallization order, Fe content of high-strength Al-Mg-Si alloy influenced hot tearing significantly owing to the crystallization behavior of α(AlFeMn).

An instruction method of 3D task motion with stereoscopic video see-through display and its application to pouring task

Research of manufacturing support using augmented reality has been advanced. It is a technology to present the appropriate work instructions to a worker through a display device. By using the technology, the worker can perform a task that requires skill, even if a worker is not an expert. Previously, in this technology, static work instructions, such as the component mounting position and assembly procedure have been mainly presented. However, the presentations of dynamic work instructions are required in some manufacturing tasks. For example, some tasks are required the operations of the work tools including the translation and rotation in three dimensions. If the dynamic work instructions of such a complicated task can be presented, it will be possible to support more varieties of manufacturing tasks. In order to realize it, an instruction method of the three-dimensional task motion of the work tool is examined using a stereoscopic video see-through display in this paper. Then, in order to evaluate the instruction method, the pouring task in casting process is selected as an example application. Furthermore, the results of evaluation experiments are reported.