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The thicknesses of mold flux film and air gap are significant factors that affect the high-efficiency heat transfer, the strand lubrication and mold taper design of billet ultra-high speed continuous casting mold. Therefore, this paper established the three-dimensional fluid flow, heat transfer and solidification model, interfacial heat transfer model and two-dimensional stress-strain model to conduct multiphysics modeling. Thereby the thickness distributions of liquid slag, solid slag and air gap in the ultra-high speed billet continuous casting mold were obtained, and analyzing the effects of melting temperature of mold flux and mold taper. The results indicate that the thicknesses of liquid slag and solid slag increase and decrease respectively along the casting direction, and air gap mainly concentrates near the mold corner. The maximum thicknesses of liquid slag, air gap, and solid slag at the mold outlet are respectively 0.18 mm at the center of the strand surface (x = 0 mm), 0.28 mm at the strand corner (x = 80 mm) and 0.67 mm at x = 74 mm. The lower melting temperature of mold flux, the greater the liquid slag thicknesses and ascend from 0.14 to 0.18 mm, and conversely the maximum air gap thicknesses descend from 0.31 to 0.28 mm and existing ranges also get smaller, which is more favorable for the strand lubrication. To eliminate the air gap, the appropriate linear mold taper is 0.45% m−1 at the 6.5 m/min in casting speed.

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When machining titanium alloy parts, aside from accuracy, the other key concern when evaluating their quality is the integrity of the machined surface. Residual stress can have a significant impact upon this. A certain amount of residual stress can help to strengthen the workpiece, but excessive residual stress can lead to its deformation. In this paper, we report on an experimental study of the surface integrity of titanium alloy after milling with a microtextured ball-end cutter. Tests were conducted to assess the residual stresses on the surface of titanium alloy workpieces according to the direction of feed and milling. The impact of different micro-texture parameters was also assessed; namely, the diameter, depth, spacing and distance from the cutting edge of the individual pits. Range analysis, which is an orthogonal test, was used to analyze the results of the experiments and a prediction model of surface residual stress was established for the milling of titanium alloy with micro-textured ball-end cutters. This model can provide theoretical support for the optimization of the parameters involved in future milling processes.