Hiroyuki Saiki

Hole flanging with ironing of two-ply thick sheet metals

Abstract Two-ply sheet metals are used in the manufacturing of electronic equipment, chemical instruments, transportation works and so on. Two-ply sheet metals are generally composed of metals that have different mechanical properties. Thus the forming process of these materials is complicated. The forming characteristics in hole flanging with ironing for two-ply sheet metals were studied. An explosively welded Al/Cu bi-metallic sheet metal was used as a model material throughout the experiments. The thickness of the matrix A1 was 2.20 mm and that of the cladding Cu was 0.83 mm. A number of experiments were performed using a conical punch with a cone angle of 45°. The experimental results were compared with FEM-simulated results, from which it was demonstrated that the rigid–plastic FEM can be used effectively for predicting the forming process and the finished shape of bi-metallic sheet metals.

Deformation analysis of hole flanging with ironing of thick sheet metals

The objective of this paper was to investigate the characteristics of hole flanging with ironing of thick sheet metals. A number of experiments were pertbrmed by using a conical punch. Several blanks of different thickness which were made from commercially pure aluminum were used. A lubricant based on aluminum fluoride and metallic stearate was applied to both sides of the blank. The effects of blank thickness on the punch load and the finished shape in the hole flanging with ironing were investigated. The experimental results were compared with the simulated results obtained by the rigid-plastic FEM. The results have demonstrated that the rigid-plastic FEM can be used effectively for predicting the punch load and the finished shape.

Evaluation of the forming limit of aluminum square cups

Abstract Combined effects of process variables (blank shapes, tool shapes, blank materials and punch lubrication) on the deep-drawability of square cups were studied. Characteristic force lines to estimate the deep-drawability were introduced. The combined effects of the process variables were explained based on the force lines, the types of fractured cups and the thickness strain distribution. Moreover, the limiting drawing ratio could be easily evaluated from the force lines. The constant fracture force and the transitional fracture force were defined. These forces were used as the target values for the improvement in the deep-drawability. The extent of the improvement in the deep-drawability was evaluated using the fracture forces.

Effects of lap sheets on the improvement of the formability of metal foil

Abstract The improvement of the deep drawability of nickel foil was investigated. The reduction in sheet thickness easily causes defects such as buckling (wrinkling) and fracturing. In order to prevent such defects and to improve the deep drawability of nickel foil, foil–lap blanks, in which thin sheets were lapped over nickel foil, were used in deep-drawing operations. Polyethylene sheets, nylon66 sheets and aluminum sheets were used as lap sheets, i.e., thin sheets for lapping over foil in deep drawing. The effects of lap sheets on the deep drawability were investigated from the viewpoint of the mechanical properties and combination of lap sheets. The deep drawability was improved using aluminum lap sheets and nylon66 lap sheets. Wrinkles on the foil cups were prevented by the lap sheet on the blank-holder side. The combination and types of lap sheets determined the deep drawability of the nickel foil cups.

Characterization of Adhesive Strength of Phosphate Coatings in Cold Metal Forming

A test method is proposed to characterize adhesive strength of phosphate coatings based on the various deformation patterns at the tool-workpiece interface. The deformation patterns were induced by tools of different surface geometrical profiles, i.e., flat surface, sinusoidal surface, saw-tooth surface and multi-surface profiles, in a localized rod drawing technique. With change in the tool geometry, three deformation regimes were observed, i.e., full film lubrication regime, mixed regime, and seizure regimes, which were categorized by the level of friction coefficient attained, and the degree of galling observed on the surface of the drawn specimens. The full film lubrication regimes were noticed when flat dies were used. In this case, the friction coefficient was maintained at nearly μ = 0.065, irrespective of the change in the surface roughness of the tools and reduction. With sinusoidal surface and other non-flat dies, mixed regime and seizure regimes were observed, and the friction coefficient varied from μ = 0.1 to 0.3. To complement the friction data, surface analysis of the tool-workpiece interface was also conducted. The frictional range of μ = 0.065 to 0.3 obtained in this study, therefore, provides for a manageable characterization of phosphate coatings for cold metal forming of objects with intricate shapes.

Influence of the roughness geometry of tool surface and the flow stress of coated solid lubricants on tribo-conditions in cold forging

Abstract In cold die forging, a sever friction sliding is often locally caused on the tool surface. It is usually preferable to smoothly finish such a portion of the tool surface. Many studies have been performed to maintain good lubrication conditions by catching lubricants to micropockets of the tool surface. This research is aimed at the detailed FEM examination of how the tool surface roughness influences the friction coefficient, the local surface enlargement at the friction surface of material and solid lubricant thinning at the edge of tool–material interface.

Influence of die geometry on the workability of conversion coatings combined with soap lubricant in cold forming of steels

Abstract Tribological conditions pertaining to the plastic deformation of zinc-phosphate coated specimens under localized bar drawing experiments were investigated. Dies of different surface profiles namely; sinusoidal, saw-tooth, flat and multi-surface profiles were used to induce various deformation patterns at the tool workpiece interface. Significant changes in the interface friction with change in both the die geometry and the mean interface temperature were observed. In order to correlate the surface expansion behavior defined by the tool geometries with the distribution of lubricant film at the tool-workpiece interface, tool indentation simulations using Two Dimensional Rigid Viscoplastic Finite Element Method (2D-FEM) were also conducted.

Combined effects of strain hardening characteristics and tool geometry on the deep-drawability of square aluminum cups

Abstract The combined effects of the corner radii of square tools and the strain-hardening characteristics ( n -values) on the deep drawability of square aluminum cups were investigated. Several materials having different n -values were prepared under various annealing conditions and used in the experiments. Typical fractured cups were observed and classified into several types, according to the location and the propagation of the cracks induced in the drawn cups. The fracture types were strongly influenced by both the n -values and the corner radii of the square punches. The maximum limiting drawing ratio was obtained under the appropriate combination of n -values and the corner radii of the square punches. However, the limiting drawing ratio decreased considerably under the following two combinations: the first, when blanks having higher n -values were drawn with square punches of small corner radii; the second, when blanks having lower n -values were drawn with square punches of large corner radii. The variation in the limiting drawing ratio with n -values and punch corner radii corresponded well to the variation in drawing forces, fracture forces and fracture types of cups.

Estimation of the deep-drawability of aluminum square cups by fracture forces

Several fracture forces for the evaluation of the forming limit are investigated. The influence of flange lubrication, blank shapes, blank materials and tool shapes on the fracture forces is examined. The increase in the critical fracture force (the ability to sustain deep-drawing forces) is required for the improvement in the deep-drawability of square cups. Constant fracture force and transitional fracture force are used as target values for the increase in the critical fracture force. Both the fracture forces are independent of the blank shapes, and influenced by the flange lubrication, the blank materials and the tool shapes. The deep-drawability of square cups is evaluated by means of the fracture forces.

Piercing process of very thin sheet metal using explosive-impulsive pressure

The characteristics of piercing a hole in amorphous alloy foil with a thickness of 0.025mm using explosive-impulsive pressure were investigated. The effects of the diameter of the die cavity and the impulsive pressure induced by explosion on the piercing of a hole were shown. The quality of the pierced holes was evaluated by means of the contour rate, that is, the ratio of the perfectly sheared contour length to the circumference of pierced holes. The contour rate approached 1.0 with increasing impulsive pressure for all diameters of the die cavity. The error in the diameter of pierced holes to the diameter of the die cavity was within 2%. Even for a small diameter, the optimum impulsive pressure distribution, i.e., the optimum amount of explosive and distance from the explosive to the specimen, enable holes to be pierced perfectly. Introduction The miniaturization of many products, mainly electronic and precision-mechine devices, apparatuses and instruments, is progressing. The formation of parts made of very thin sheets has become increasingly important. Many studies on the methods and techniques of forming precise parts with very low thickness have been performed [1-23]. Kurosaki et al. investigated the mechanical properties of electronic copper foil and sheets ranging from 5μm to 1mm in thickness [1]. Spinning and peen forming have been used to fabricate very small and thin parts [7,8]. Laser forming [2,3], spark forming [4] and incremental forming [5,6] have also been applied for forming metal foil and very thin sheets. For deep drawing, Saotome et al.[11] clarified the effect of the relative punch diameter on the deep drawability of very thin steel sheets. A friction-aided drawing process for very thin sheets was proposed and its effects were presented by Hassan et al.[12]. A technique of the controlling blankholding force by oscillating the blankholder using piezoelectric actuators was also proposed [13]. For the piercing process, Kurosaki et al. [9] developed a method by which many fine holes could be pierced through a thin sheet of 50μm, using a viscoplastic pressure medium. A small press incorporating a piezoelectric actuator was developed for press blanking of metal foil and its good performance was verified [10]. Sano et al. reported a method of punchless blanking in which a plastic material was used instead of a punch [17]. Murata et al. presented a method of punchless piercing using very high-pressure gas for a thin sheet including amorphous alloy foil [18-20]. They also investigated the characteristics of the piercing of holes by the method. An investigation of micropunching of thin sheet metals by an underwater impulsive wave induced using an Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 337-342 doi:10.4028/www.scientific.net/MSF.465-466.337