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上机匣为直升机传动系统中的关键零件，几何形状复杂，性能指标要求高，成形难度大。采用纯铅为模拟材料，对上机匣成形方案进行了试验研究，确定了上机匣等温精锻成形分制坯、终锻、精整三个工步。通过对ＭＢ１５镁合金塑性图的分析，确定其变形温度范围为３５０～３８０℃。制坯、终锻时的变形温度取３８０℃，以便金属充填模膛；精整时的变形温度取３５０℃，以提高锻件力学性能。为保证锻件几何精度，采用锻后直接人工时效的热处理方案（１６４℃时效２４ｈ）。利用等温精锻工艺成功地锻制出上机匣锻件，锻件的力学性能、显微组织和尺寸精度均符合要求。
The upper case is a key part of the helicopter transmission system, which has complicated geometric shapes, high performance indexes and high forming difficulty. Using pure lead as the simulation material, the experiment of forming the upper casing was carried out. The three steps of final casing forging, final forging and finishing were confirmed. Through the analysis of plastic diagram of MB15 magnesium alloy, the deformation temperature range is 350 ~ 380 ℃. The billet, the final forging deformation temperature of 380 ° C, so that the metal filling die; finishing deformation temperature of 350 ° C to improve the mechanical properties of forgings. In order to ensure the geometric accuracy of forgings, the direct artificial aging forging heat treatment program (164 ℃ aging 24h). The mechanical properties of forgings and forgings on the upper casing were successfully forged by using the isothermal forging process, and the microstructure and dimensional accuracy all met the requirements.