Ni-plated steel wire used for springs in electrical appliances and other devices has good corrosion resistance. It is demanded as an alternative for stainless steel wire in a mildly corrosive environment. Lubricity in spring cold working and surface gloss are required. Ni-plated steel wire drawn using conventional powder lubricants in a continuous-drawing machine exhibits lubricity, but no sufficient surface gloss. To achieve both surface gloss and lubricity, a liquid lubricant is used at the final pass, while soap powder lubricant is used at earlier passes. This basic research has been conducted to investigate the relationship between surface gloss and processing parameters at the final pass such as lubricant oil concentration, die approach angle, die bearing length and reduction in area with the use of an emulsion-type lubricant.
Shot peening is a mechanical surface treatment that is widely used in the automotive industry to improve the fatigue life and surface characteristics of machine parts. To enhance the peening effect, warm peening and double peening are effective. These processes have recently received considerable attention. Our aim in this study is to investigate the effect of warm double peening on the surface layer characteristics of high speed steel. This peening process is a combination of double peening and warm peening. The first peening was conducted in the warm state using large steel media. Then, the second peening was conducted at room temperature using microshot media. In the present study, a compressed-air-type shot peening apparatus with a heating furnace was produced experimentally. The workpiece was made of the high speed steel JIS-SKH51. The surface roughness, hardness, compressive residual stress, and fatigue strength of the peened workpieces were measured. We found that the warm double-peening method causes a significantly enhanced peening effect for high speed steel.
We have developed a numerical simulation technique of a spinning draw process using a dynamic explicit Finite Element Method (FEM) for evaluating formability. Oyane’s equation for the ductile fracture criterion was applied. In order to shorten computation time, the velocity of die roller movement and the velocity of die rotation of the material are increased in the analytical model. If the velocity of the die roller in the axial direction is increased, the velocity of die rotation is adjusted to obtain the same extent of damage as that in the actual spinning draw process. An accurate evaluation of fracture initiation in a spinning draw process can be performed within a short computation time. It was confirmed that numerical simulation is a useful tool for investigating the formability of a spinning draw process. Finally, we have developed an optimization method for forming parameters using the response surface method on the basis of the finite element analysis (FEA) results of a spinning draw process. In this study, we also presented the application of the proposed analytical model for verifying whether the optimized condition realized high-quality products without fracture.
Recently, tailored blank sheets have been widely and frequently used in automotive parts such as door inner and body side inner parts in order to reduce the weight of a car body and the number of parts. The control of the gap between batting blank sheets with different thicknesses below 0.1mm and the appropriate choice of the material for producing a tailored blank sheet are considered as main subjects in the development of new stamping parts using laser-welded tailored blank sheets. Therefore, in this study, we investigated the mechanism of gap control in a batting process and developed a dynamic explicit finite element method (FEM) for predicting the gap in a batting process in a testing machine. We also investigated a contact algorithm and friction to increase computation accuracy. The accuracy of the prediction of the gap by the proposed FEM has been verified with experimental measurement data for simple rectangle steel sheets and blanks of body side inner parts. The effects of the design variables of a batting machine on the gap were also investigated using the proposed FEM, and an equation for predicting gap was proposed.
A shaft and a thick flange can be successfully joined by forming a hole in the flange with serrations provided on the shaft, and the optimum conditions of forming depth and contact angle of the shaft were confirmed in our previous report. Under such conditions, the effects of flange diameter and serration profile on joining strength were studied. Joining strength decreased rapidly when the flange diameter was less than a certain value and the critical diameter for torsional strength was predicted using a simple deformation model. With respect to the serration profiles, a larger pitch and a smaller height of the serration resulted in a slightly lower torsional strength. The corresponding finite element simulations clearly showed the difference in torsional strength depending on serration profile, which was explained in relation to the difference between the effective strain distributions observed upon twisting the joint.
Superplastic blow forming usually poses difficulty in controlling thickness variation on formed articles because of its deformation style of free bulging. Also, when a large deformation is formed, microcavities are formed in the micro-structure of aluminum alloy, which degrade mechanical properties of the alloy. In order to overcome these demerits, a new process using two stages of forming has been proposed. In this process, a blank sheet is bulged locally by incremental forming using a bar tool in the preliminary stage, then it is superplastically formed in the finishing stage. Some forming experiments were conducted to determine the feasibility of this new forming process using fine-grain-quality 7475 aluminum alloy as blank sheets. Firstly, blank sheets were preformed into quadrilateral pans with a given depth by incremental forming. Then, their bottoms were formed into a quadrilateral cone by superplastic forming. Lastly, each article was formed successfully with a thickness distribution as predicted from the controlled height of the preformed articles. It was also found that the new forming process performs effectively under certain range conditions.
A new forming method has been developed to improve the press formability of steel sheets. Detaching die surfaces from a steel sheet blank during the forming process is a distinctive feature of the developed method, and such a motion is repeated for several times until the end of the forming process. Results of sliding tests clarified that just detaching die surfaces from a steel sheet blank during the sliding process could improve the frictional conditions between steel sheets and die surfaces. As a result, the developed method could reduce the forming load and improve the forming limit of steel sheets. Finally, it was shown that the developed method, which was automated using servo press and die cushion systems could effectively improve the deep drawability of 590MPa-grade high-strength steel sheets, even if the pressed panel was a full-scale panel for auto parts.
Most shafts have a hexagonal shape, gears and multi steps on their largest diameter. Here, we studied a method of deforming a partial diameter into the near-net outer shape required for practical machine parts. The method was clarified experimentally to be actualized by controlling the final outer shape of a partial enlarging diameter using a metal mold with a hole of final outer shape, which was fixed on the rotating-side holder and rotated together with a shaft of work. The diameter enlarging behavior was investigated experimentally by measuring the changes in the distance between holders. On the basis of the mathematical modeling of their deformation behavior, the effects of processing conditions on the enlarging shape were researched and an estimating equation for clarifying the engineering optimization of processing conditions was obtained by mathematical model analysis.
A connecting work method of tightly fixing a shaft in the central hole of a circle plate was developed for application of axial-diameter-enlarging processing. This method was successfully used in tightly connecting two pieces of different material parts such as a circle plate and a shaft. Because it is performed at room temperature without either heating or cooling such as in a traditional shrinkage fitting, this work method was clarified to exhibit high performance for industrial use.