Shinya Makita

Development of cold plate produced by friction stir welding

Cooling parts consisting of copper pipes or stainless steel pipes placed on an aluminium base (hereafter, ‘cold plates’) are used in wide range of applications. These cold plates are produced by enclosing, casting, pipe expanding, and bolting attachment. There are, however, limits to the alloys that can be used in the enclosing casting method, and pipe expansion and bolt attachment involve the problem that the contact with the aluminium pipes is inadequate and the thermal performance is poor. As it is well known, in friction stir wlding (FSW) the material is softened by the heat of friction and bonding is achieved through plastic flow. It is also known that FSW is a pressure welding method in which a strong tool is strongly pressed into the material. Considering it possible that a pipe may be buried by this plastic flow and pressure, we undertook the task of developing FSW cold plate. In this, a pipe and cover are placed on a base plate, which has previously been grooved to bury the pipe, and the contact surfaces with the pipe and cover are FSW welded (Figure 1). There are gaps between the pipe and cover but, as shown in Figure 2, it is confirmed that the cover is bonded and the gaps are filled by FSW. In this study, we report a review which is made of the effects of various factors on the thermal performance, and the conditions under which the FSW cold plate could be produced stably were selected. 2. Selection of FSW tool shape

Development of a high speed MIG welding process. (Report 2) : Effect of current suppliability between contact tube and welding wire on the occurrence of surface defect

High speed MIG welding has been employed for joining the cover and the case which formed a viscous damper, a component for the reduction of vibration in truck engines; the reduction in weld strain and excess metal height and a substantial improvement in the joining strength were achieved. However, to improve high speed MIG welding, future tasks remain for bead stabilisation and the control of pit-shaped surface defects which occur on the weld surface. In order to solve these problems, as explained in the previous report, the effects of welding and pulse conditions on surface defects were investigated; from this, it became evident that pit-shaped surface defects occur with both short and long arcs. These short and long arc welding phenomena are largely dominated by the welding and pulse conditions etc. but other effects are not considered to be negligible. One of these factors is the current supply from the contact tube or tip (hereafter referred to as suppliability). For example, at practical working sites there are examples where suppliability to the welding wire is facilitated successfully by bending the end of the contact tube and a stable arc state is maintained. However, such a technique depends greatly on the experience of the welder and there is a wide dispersion in the geometry of bending; so it cannot be claimed that this technique has yet been technically established. Consequently, welding machine and torch manufacturers have been developingcontact tubes and tips which are superior in suppliability. Therefore, in this paper, the effects of suppliabilty of contact tubes and tips on the occurrence of surface defects were examined and a proposal is made to optimise tips. against the inner surface of the tube. The ball plunger mechanism was as follows: the components were a rotating ball of 1.5 mm diameter, a spacer and a spring; the rotating ball is pressed against the welding wire by the force of the spring. Type C is a commercially available tip with superior suppliability. It has the following structure: the tip end is split into 2 parts held together by attached springs to retain the welding wire; the device is attached to the contact tube. In order to investigate the contact state of the contact tube or tip with the welding wire for each type of device, the load applied upon the welding wire as it is fed through the contact tube was measured using the device shown in Fig. 2. The contact resistance was measured in the following manner using an electronic balance: the welding wire was inserted through the contact tube and tip; the welding wire, cut across its cross section, was pressed against the upper plate of an electronic balance; thus the contact resistance was measured between the welding wire and the contact tube, which was held by hand and moved downwards. The welding wire used was A5356 WY of 1.2 mm diameter, was straight and 300 mm long. Figure 3 shows the method used for the evaluation of current suppliability. The contact tube to be evaluated was attached to a feed device with a built-in pull motor and the wire was fed through the contact tube hole at 4 m/min. The contact resistance between the wire and the contact tube was evaluated by the voltage between the contact tube and the welding wire (hereafter referred to as contact voltage) when 0.2 A current flow was maintained, using a constant current power supply. In order to investigate the effects of current suppliability of these contact tubes and tips upon weld bead

Development of high-speed MIG welding process. First report: Arc phenomena and formation mechanisms of surface defects

Summary High-speed MIG welding is an effective process for reducing welding distortion and increasing the weld strength of aluminium alloys. The effects of welding conditions and the pulse duration of the pulsed current on the occurrence of pit-like surface defects in weld beads are examined to improve weld bead stability and to suppress the occurrence of surface defects during high-speed MIG welding. The formation mechanisms of surface defects are studied by observations of arc phenomena and weld bead appearances. The occurrence of surface defects during short arc and long arc welding respectively corresponds to changes in the welding current and arc voltage. Surface defects are considered to be formed by explosive scattering of the welding wire during short arc welding and solidification shrinkage during long arc welding. Surface defects can be suppressed through optimisation of the welding conditions. Reduction of the pulse duration of the pulsed current is effective for improving the appearance of wel...