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Delta-stabilized plutonium, which is a soft gummy material similar to annealed copper, is difficult, if not impossible, to thread using conventional taps and dies or thread +ndt.ing techniques. This report describes a successful “plunge” threading technique and a surface preparation method which permits assembly of threaded delta-stabilized parts without galling. 4 INTRODUCTION Plutonium is easily stabilized in the delta phase by the addition of 1wt % gallium or aluminum. (1) In contrast to unalloyed plutonium which has a hardness of -275 DPH and machining characteristics similar to cast iron, the delta-stabilized material has a hardness of u 40 DPH and machines like annealed copper. The delta-stabilized material is preferred to umalloyed plutonium for many applications because it is stable at all temperatures below 450”c and can be rolled, drawn, or extruded at ambient temperature. Unalloyed plutonium undergoes a 9 % volume change at 117°C (2) at which point it transforms from the alpha to the beta phase, and fabrication operations are generally limited to casting and machining. As would be expected, difficulties were encountered in attempting to thread the soft delta-stabilized material using conventional thread-cutting tools. This report presents a tool design developed for cutting threads in delta-stabilized plutonium and a procedure for conditioning the threads so that external and internal threaded parts may be mated without galling. DEVELOPMENT WORK a. Conventional Cu~ Attempts to cut threads in the soft delta-stabilized plutonium using a standard 60° included-angle tool with the compound slide set at 30° were unsuccessful. In this method the tool was fed using the compound slide, and only one side of the thread was cut. The plutonium turnings, which tore as they were removed, slid across the tool and tended to weld to the other side of the thread. This produced gouges in the threads. These conditions occurred with cuts of from O.0025 to O.015 in. on the diameter, with or without lubricants. The tearing effeot is illustrated in Fig. 1 by the rough edge on one side of the turnings as the diameter of a delta-stabilized ingot was cut. Threading with taps and dies was equally unsuccessful. The gummy ohips loaded the taps and dies and produced severe galling. b. Plunge Cutting Threads were successfully cut in delta-stabilized plutonium by using a plunge technique. In this method the compound slide was set at 90° to the rod and the 60° included +ngle tool was fed straight into the rod so that

THREADING AND ASSEMBLY OF SOFT DELTA-STABILIZED PLUTONIUM PARTS.