Reasons for the formation and methods to eliminate air bubbles on the surface of solder rod produced by direct extrusion

The tightening of environmental safety indicators and limiting the use of lead in new electrical and electronic equipment to a value of no more than 0.01% dictated the need to search for new low-melting alloys for use as solder. Alloy 52In-48Sn, being one of the most promising lead-free solders, is in demand by the electrical industry in the form of rods and wire. This article describes the technology for producing rods solder from the 52In-48Sn alloy in small-scale production and the problems encountered in its implementation. The article presents the results of a study of the causes of the formation of a surface defect “air bubbles” of ø8.0 and ø15.0 mm rods made by direct extrusion from the 52In-48Sn alloy. Simulation in the QForm program of the pressing process billets in a container during the extrusion showed that the reason for the formation of a defect “air bubbles” on the surface of the rods is an excessive gap between the container and the. In the billet upsetting process, the air volume is locked in the container and enters the interior of the alloy. To eliminate this defect during extrusion, it is necessary to minimize the gap between the billet and the container. The length to diameter ratio of the billet should not exceed 2.5. When designing a tool for direct extrusion, these requirements must be taken into account in order to eliminate the surface defect “air bubbles”. The research results were confirmed in the manufacture ø8.0 mm rods with high surface quality.