A combined drawing-twisting process was developed as a new method for forming helical inner-grooved aluminum tubes. The process was applied to an extruded tube with straight inner grooves. The inner groove shape maintained that of the original tube, and no roughness or burr formation was observed. The effect of drawing reduction on the torsional buckling of the tubes was experimentally investigated. Torsional buckling can be suppressed by increasing the amount of drawing reduction. To investigate the buckling condition, the deformation in the die was analyzed by the finite element method. The stresses associated with diameter reduction and longitudinal elongation increase in the die with the amount of drawing reduction. This results in a decrease in shear stress to meet the yield condition. As a result, the torsional torque at the entry side decreases. A comparison of the experimental and analytical results shows that the experimental conditions that tend to cause torsional buckling correspond to the analytical conditions that bring the stress state at the entry side of the die close to the yield condition. The forming conditions that suppress torsional buckling can be set so that the stress state at the entry side resulting from torsional torque and backward tension does not meet the yield condition.

To improve material yield, roundness and cutting speed in the cutting of round metal tubes, a new cutting method with torsion is proposed. First, narrow grooves are made partially in the circumferential direction on the outer surface of a tube. One end of the tube is fixed and the other end is rotated. By adding torsion to the tube, a crack occurs restrictively in the narrow grooves and the crack propagates along the circumference. In conventional tube press shearing, the need to insert of precise inner cores into the tube with accurate positioning is time-consuming. Thus, in the proposed cutting method, the edges of a tube are grasped by three soft jaws attached to a power chuck of a lathe without inner cores. Even if inner cores are used to increase the holding force of the jaws, the accuracy of the diameter and positioning of inner cores is not necessary to insert them into the tube smoothly. In this report, the shape of the soft jaws and minimum chucking length were examined. Cutting trials of A6063TD and STKM11A tubes were carried out and it was confirmed that the tubes can be cut so that burrs, shear droop, and the deterioration of tube roundness do not occur.

The application of high-strength steel sheets to automobile parts is expanding year by year. As a method of processing high-strength steel sheets, cold stamping is superior in cost and productivity, but it also presents many problems. One of the major problems of cold stamping is the low dimensional accuracy of components caused by springback. Springback is an elastic recovery phenomenon at the time of tool release after press forming, and there are various deformation forms depending on the shape of the part. Although measures against each form of springback have been examined and practical applications are advancing, there are many cases in which multiple forms of springback occur in actual automobile parts but there are only a few cases in which the mutual effects of these forms and combinations of countermeasure technologies have been discussed. In this study, we evaluated the mutual effects of each shape change on parts where opening and twisting springback occur simultaneously and discussed the mechanism of these shape changes. We also describe countermeasure technologies for each springback type and give examples of how combining such technologies can effectively reduce both types of springback. In this study, both open and twist composite springback could be reduced by more than 70%.