A series of experiments have been carried out using an upsetting-extrusion-type tribometer to investigate the effect of the surface preprocessing of a workpiece on the friction behavior of dry in-place type lubricant coating. Experiments were carried out in the transition range of seizure for tool surface reduced peak height. Experiments using a typical conversion lubricant coating and dry in-place type lubricant coated on seven types of preprocessed surface showed that the tribo-performance of the dry in-place type lubricant coated on an acid-pickled and shot-blasted surface is insufficient. However, the dry in-place type lubricant coated on a shot-blasted surface in two stages using microscopic particles or phosphates as thin films gives excellent antiseizure performance and keeps the frictional shear factor low up to a tool surface reduced peak height Rpk of 0.07μm, the critical Rpk for the conversion lubricant coating is 0.05μm. The observation of a forged surface showed that the excellent performance of dry in-place type lubricant coated on a shot-blasted surface in two stages is due to its combined surface texture.
A new extrusion process with bulge deformation type tribotest has been developed to investigate the frictional behavior of lubricant coatings on the surface of steel wire in cold forging. In the tribotest, the friction behavior in forward extrusion processing can be evaluated sensitively by adding bulge deformation. The sensitivity to the frictional shear factor was optimized by changing the land part shape and angle of the taper of the die entrance. The frictional shear factor of the lubricant coating can be obtained by plotting the measured forging load or the shape of the billet after forging on the calibration curve obtained by the finite element method. A series of experiments were carried out using two types of bonderized coating and a dry in-place lubricant coating. It was revealed that the variation in the frictional shear factor at processing temperatures from 20 to 200°C is less for the dry in-place lubricant coating than for the bonderized coating.
Slide motion in hot die forging of an aluminum alloy billet was controlled by a servo press to improve the filling of die cavities and forging load. The filling of a die cavity in the hot die forging of a piston was changed by changing slide speed. The spike forging test generally used for evaluation of lubricants in cold forging was applied to the evaluation of slide motion in hot die forging. The degree of filling has a peak of the slide speed, because the distribution of temperature affecting the metal flow was changed by slide motion. The deformation of the billet continued when the dies ware held at the bottom dead center owing to the elastic recovery of the dies and press induced by the decrease in flow stress. Thus, the maximum forging load necessary for a product shape was decreased. In addition, a die quench forging process having the holding at the bottom dead center was developed to eliminate solution heat treatment in the conventional T6 process for aluminum alloy products.
Hemming is a forming method of connecting an outer panel to an inner panel by bending a hem flange at the edge of the outer panel. Depending on the complex shape of the hem flange bending line, springback occurs because the stress in panels is released after die opening. To estimate deformation by springback, a hemming simulation method using explicit and implicit finite element simulations for complex panel shapes has been developed. Because of the complexity of elastic contact conditions at hemmed portions between the inner and outer panels, it is difficult to obtain converged solutions of springback using implicit finite element simulation. In order to solve this problem, we have developed a new method that entails connecting the inner panel edge to the outer panel to avoid contact analysis. It enables the appropriate simulation of the hemming process within a short computing time based on the verification of hood parts. The proposed method can be used to investigate the strength of stiffness, the dimensions of the inner/outer panels and the hem flange shape (length/angle) to obtain geometrically accurate hemmed parts by predicting the amount of springback after the hemming process.
Wet and dry skinpass rolling experiments on tinplate were conducted with a lab rolling mill of large and small diameter work rolls. Skinpass rolling characteristics were investigated. It was found that jumping becomes easier as work roll diameter increases larger, as lubrication improves, and as what thickness at the entrance decreases smaller. The influence of back tension on rolling load is small, and the influence of front tension on rolling load is large. Transcript efficiency improves as elongation is enhanced and as lubrication is degraded.
Mechanical clinching is a mechanical joining method that has been attracting considerable attention as an alternative to spot welding or riveting, because of the many advantages it offers in assembling aluminum panel parts. However, the applications of this method are limited because it affords low peeling strength; therefore, it is necessary to improve the peeling strength. In this study, various effects of lubricant viscosity are investigated to clarify the factors influencing the peeling strength. The following observations were made with regard to the different lubricated surfaces studied. In the case of the boundary surface, peeling strength improves when the lubricant viscosity is sufficiently low for adhesion and seizing to occur. In the case of the tool surface, peeling strength decreases with a decrease in lubricant viscosity because of cross-sectional shape deformation. From the above results and results of finite element method, it is revealed that the frictional force between tools and workpiece surfaces resisting material flow plays an important role in determining the cross-sectional shape of mechanical clinching. Additionally, to achieve good cross-sectional shape, the direction of the metal flow should be controlled; this can be achieved by following some of the guidelines we proposed to achieve higher peeling strength.
The authors previously proposed the two-step cold extrusion method to shape a gear. Namely, a specially designed die, to shape a gear in two steps, is used without reducing the outer diameter of the cylindrical workpiece. This method allows complete shaping of a gear even for a solid workpiece with no hollow region. The solid workpiece results in the lowest reduction in area, and no experiment with a lower reduction in area is possible. This research is aimed at shaping a gear by a method in which a mandrel is not used and radial inward flow of the workpiece material to achieve a low reduction in area is possible. The specifications of the spur gear examined were as follows: module 1.25, number of teeth 18. The workpiece material is low-carbon S15C steel, selected as a model material for carburized quenching. The inner diameter of the workpiece was varied to investigate the effect of the reduction in area. As a result, under all shaping conditions, a gear with complete teeth could be shaped successfully at a low punch pressure even with a low reduction in area of 6%.
A flexible method of forming circumferentially variant wall thickness distributions on the same shape is attempted using two oblique sheet spinning processes. The fundamental strategy entails the inclination of the flange plane of the workpiece during forming. In one type of synchronous dieless spinning, edge-hemmed aluminum blanks of 186 mm diameter and 1.5 mm thickness are formed for truncated cone shells of 30 degrees half-angle, by synchronizing the motion of the spherical head roller in the axial and radial directions with the angle of the general purpose mandrel fixed on a bidirectionally rotating spindle. On the other hand, in the other type of force-controlled shear spinning, flat aluminum discs of 150 mm diameter and 1.0 mm thickness are formed by feeding perpendicularly to the flange plane of the workpiece and maintaining the thrust force along the plane via the roller tool, exerted onto the rotating truncated-cone-shaped die of the same half-angle of 30 degrees. The estimated wall-thickness distribution based on a simple shear deformation model nearly conformed to the measured thickness distributions of the products formed at several inclination angles of up to 15 degrees in the forming and both spinning methods.
A dieless drawing process without using any dies and tools is applied to magnesium alloy to fabricate fine tubes in this study. The extruded tube used in the experiment is made of AZ 31 magnesium alloy and has an outer diameter of 2mm, wall thickness of 0.5mm and average grain size of 5.2μm. A high-frequency induction heating apparatus with an air-cooling device is used for dieless drawing. The deformation behavior and microstructure during the dieless drawing process are investigated experimentally. A limiting reduction in area of 60% can be achieved in the experiment under a heating temperature of 400°C. In addition, it is confirmed that the ratio of inner to outer tube diameters remains a constant value during dieless drawing. In other words, the geometrical similarity with the minimization of dimensions is satisfied in this process for the AZ31 tube. Furthermore, grain growth occurs during process under a heating temperature of 400°C. Meanwhile, 4μm fine grains can be obtained after dieless drawing at a heating temperature of 300°C. Thus, it is concluded that the microstructure after dieless drawing can be controlled by adjusting the drawing conditions.