Li Qun Ruan

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

Cladding of Titanium and Magnesium Alloy by Explosive Welding Using Underwater Shockwave Technique and Effect on Interface

The wide use of clad joints in practical application has been inhibited due to the difficulty in welding certain combinations such as tungsten/-copper, molybdenum/-copper and magnesium with aluminum, titanium and stainless steel. These material combinations are generally classified as difficult to weld by conventional material joining techniques due to the vast difference in material properties and the degradation of mechanical properties of the joints. Explosive welding is here a viable alternative technique. Explosive welding is a solid-phase welding process that uses the energy of a detonating explosive to create a strong metallurgical bond. This technique has achieved impressive success in the joining of metallurgically incompatible combinations that are otherwise impossible to join by conventional welding techniques. Though the technique is suitable for joining only thin plates, it is efficient in joining some difficult to join combinations like magnesium with aluminum, titanium and stainless steel. In this paper, the result of welding titanium and magnesium was reported.

Explosive Welding Using Underwater Shock Wave Generated by the Detonation of the Detonating Code

Detonating code is a flexible code with an explosive core. It is used to transmit the ignition of explosives with high detonation velocity in the range of 5.5 to 7 km/s. However, it is difficult to use detonating code for the explosive welding of common metals since the horizontal point velocity usually exceeds the sound velocity. Hence, in the present work, a new method using underwater shock wave generated by the detonation of detonating code was tried. The details of the experimental parameters and the results are presented. From the results it is observed that the above technique is suitable to weld thin metal plates with relatively less explosives.

Basic Research on Explosive Forming of Magnesium Alloy Plate

This study has investigated the plastic forming of magnesium alloys plate. It is not easy to perform the cold-worked with the usual plastic forming method although magnesium alloys have the advantages in terms of strength-to-weight ratio. Therefore, explosive forming method which is one of the plastic forming methods with a specific forming mechanism has been applied. At first, numerical simulations have been conducted to clarify the optimal combination conditions, and then we have verified practical effectiveness of this proposed method by using experimental study.

Effect of Surface Hard Layer and Forging Conditions on the Resistance of Plastic Deformation of Hot Forging Tools

Tool damages including plastic deformation and wear are affected by forging load, thermal load and frictional slide applied to tool surface. Plastic deformation of forging tools proceeds in the tool corer owing to elevated temperature, high contact pressure and severe frictional slide. Hard layers on the tool surface increase plastic deformation resistance and thermal resistance. The optimal design of hard layer structure reduces the tool damage and improves tool life. Temperature and equivalent strain of forging tools are influenced by friction shear factor, contact thermal conductance and contact time between the tool and the workpiece. At the friction shear factor of less than 0.4, equivalent strain of the tool is reduced. At the friction shear factor of approximately 0.4 or greater, equivalent strain increases sharply and concentrates in the vicinity of the surface hard layer. This tendency becomes more significant when the contact time between the tool and the workpiece increases. Equivalent strain is reduced by low workpiece temperature.

Slide-Bend Forming of Very Thin Metal Sheet Using Slide-Ironing Tool

Characteristics of slide-bend forming were investigated. In this process, foil specimens can be bent to various shaped products by indenting and sliding a tool. The effects of the tool indentation load, the foil thickness and the number of slide repetition on the bending angle were examined experimentally for three kinds of foil materials. In addition, the deformation of bent region was examined using a rigid-plastic finite element analysis. Bending angle increased with increasing the indentation load or decreasing the foil thickness. When the number of slide repetition increased, the bending angle increased slightly. The slide repetition can be effective for adjusting bending angle slightly. By sliding a thin edge-shaped tool relative to the foil specimen, bending angle and radius of curvature of specimens can be controlled freely.

Tests on high-velocity forming of AZ31 magnesium alloy by explosive-impulsive pressure (Part II)

As reported in the previous report, increasing velocity by high-speed impulsive energy could improve the formability of AZ31 magnesium alloy. The improvement of ductility of AZ31 magnesium alloys can be observed, which is difficult to observe in usual cold forging techniques. This paper (Part II) is a coutinuation of the reported work in the previous paper. The forming of the AZ31 casting magnesium alloy was done. The hardness distribution of the test specimen was investigated for each experiment, and the microstructures are analyzed. The microstructural results indicate that adiabatic shear bands are formed and the microstructure is changed by the formation of huge amount of fine grained recrystallized structure. Furthermore, solid state is retained in the materials as well as the surface. [1]

Estimation of contact interface between tool and workpiece in cold forming using FEM analysis

The effect of the flow stress of solid lubricant for cold forging on the tribological conditions was investigated using a rigid-plastic finite element method. The thickness of lubricant film decreases with decreasing flow stress of the solid lubricant and then decreases rapidly. The apparent friction coefficient also decreases with the decrease in the flow stress of the solid lubricant. The thickness of lubricant film tends to decrease with decreasing friction shear factor. When flow stress of solid lubricant is low, the thickness of lubricant film decreases remarkably with increasing tool stroke. We can observe a good correlation between the flow stress of solid lubricant, friction shear factor, minimum film thickness and apparent friction coefficient.

Study on indentation-sliding contact conditions between semiconductor terminal and electrically testing probes

Contact conditions of the testing probes for the testing of IC electrical conductivity were investigated. A method was proposed that could clarify the conditions for designing and selecting both the optimum probe geometry and the mechanical properties of pads suitable for effectively decreasing the contact electrical resistance. The elastic deformation of contact probes and the indenting plastic deformation of the pad surface were analyzed theoretically as a coupled problem. Deformations of the pad were mainly divided into two modes depending on the relative sliding velocity: a scratch type and an indentation divergence type. When the radius at the tip of a probe was larger than the thickness of the aluminum-deposited film, the deformation tends to be an indentation divergence. The expansion of the surface area generated at the contact region (surface expansion) and the amount of swelling by bulge deformation (bulge height) were found as important factors in the design of probes. The surface expansion, which indicates the probability of the appearance of a newly generated surface due to the breaking of the insulating oxidized film, affected strongly electrical conductivity. The bulge height, together with the frictional shear factor, influenced the apparent coefficient of friction between the probe and pad. These values can provide design criteria of contact probes for achieving stable electrical conduction.