押込み加工によるブラスト加工面の残留応力評価

抄録

The generating mechanism of the compressive residual stress controlled statistically is significantly complicated in practical blast process. In this paper, the residual stresses were compared in a dynamic collision process and a static indenting process using a single steel ball against a steel plate (0.5%C annealed), in order to optimize the blast process conditions in the simple indenting process.
The static indenting test was carried out using the indenting unit with low stiffness installed in NC milling machine. The tensile residual stress at the dimple center decreases with an increase in the indenting load. The tensile residual stress changes to compression when the indenting load exceeds about 20kN using a φ10mm steel ball.
The dynamic collision test was carried out using a nail strike machine which can shoot at a speed up to 56m/s. The residual stress at the dimple center changes from tension to compression at a shot speed higher than about 40 m/s. The piling-up on the dimple shoulder in the dynamic collision test is larger than that in the static indenting test, when the indenting force is loaded equivalent to the shot speed in the dynamic collision process. That is, the residual stress generated in the blast process can be evaluated using the results in the static indenting process, although the shot speed influences substantially on the dimple profile, but scarcely (<±5%) on the surface residual stress.