In this paper, a number of factors influencing the joining property of sheets welded by a magnetic pulse welding are described. An electromagnetic force deforms a moving sheet, and the height of the sheet is governed by both the force and the properties of the sheet. Some information obtained from the first collision time is very useful, so two sheets with a gap can be joined with each other after the first collision. The relationship between the collision time and the gap length for an aluminum sheet is examined by 2.0kJ discharge energy experiments, and an approximation curve of this relationship is drawn. The velocity of the moving sheet is found by differentiation of the curve. The relationship between shearing load with the welded sheet and the gap length is also examined. Similar results have also been obtained for a copper sheet, and the relationship between the shearing load and the collision velocity has been shown for two materials. It has been clarified that the shearing load is distributed into three areas depending on the collision velocity. Therefore, the collision velocity is the main factor influencing the joining property of welded sheets. It has also been clarified that another influencing factor is the first collision time.
In the 1st report, the appropriate evaluation factors for void closure were revealed to be true strain εz in the z direction and the hydrostatic stress ratio σm /σeq. However, those results were obtained under the condition of single-path forging, and were not confirmed for multipass forging. In this paper, we investigated whether εz or εeq is appropriate as the evaluation factor for void closure by numerical experiments of multipath forging. The following results were obtained. 1) εeq cannot because to evaluate the void closure in multipath forging, but εz can. 2) The main factor of εz required for void closure in multipass forging is the void shape at the start of the final pass. 3) If εz required for void closure in multipass forging is less than the value of the single-pass forging, the void closure of the multipass forging can be evaluated by the single-path forging.
Compressive torsion processing (CTP) can cause huge shear strain in a cylindrical workpiece by simultaneous compressive and torsional loading without changing the cylindrical shape. In the present work, the distribution of shear strain in a specimen subjected to CTP was measured in a model experiment using two kinds of aluminum alloys, and the effect of the number of revolutions on the strain distribution was investigated. Internal shear strain of the worked specimen can be quantified by measuring the displacement of the interface between the two kinds of alloys in the cross section. The shear strain in the worked specimen has a gradient distribution not only in the radial direction owing to the geometric feature, but also in the axial direction because of the frictional constraint of the container. However, the measured shear strain was almost in agreement with value predicted by geometric calculation. The shear strain distributions were proportional to the radius and number of revolutions in the part of less than 15 mm in radius of a cylindrical specimen 41 mm in diameter and 10 mm in height.
Aluminum fluoride conversion coating has been a popular lubricant for aluminum cold forging. However, it has considerable environmental risks and problems of cost. A double-layer environmentally friendly solid lubricant has been developed as a substitute. The lubricant film was constructed of undercoat and overcoat layers. The authors applied it to three kinds of aluminum alloys. It was evaluated by a friction test based on spline extrusion. The differences in the lubrication performance caused by the season, flow stress, surface-roughing preprocesses, and undercoat film thickness were investigated. It showed better performance in rainy season, but performance was worse in winter. When it was applied to a harder material, the lubrication performance was improved by using a thicker undercoat and an appropriate preprocess. In contrast, when it was applied to a softer material, the undercoat thickness, and preprocess did not affect to the lubricating ability.