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Helical milling is a high efficiency, high quality hole-making technology, which enjoys very good usage prospects for the aeronautical and aerospace industry. In the helical milling process, the chip thickness is highly variable along the cutting edges and during the tool revolution due to the special cutting trajectory. The aim of this study is to develop a cutting force model and build a new calibration method of cutting force coefficients for helical milling. First, the tool motion of helical milling and the geometry of the chip are analyzed, and then the cutting force model is established. After that the calibration method of cutting force coefficients is built. In the end, a series of cutting experiments were conducted to validate the cutting force model and the calibration method. With this model, it is possible to analyze cutting forces and optimize the cutting parameters, and then get a better quality of hole-making.

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In order to enhance the manufacturing productivity, mobile machining with industrial robots is proposed as a cost-effective and portable manufacturing alternative to large scale CNC machine tools in aircraft part machining. Combing the advantages of helical milling and parallel robot, the cutting forces and chatter stability of a novel 5-DOF hybrid PKM (named TriMule) based helical milling process are first investigated in this paper. The cutting force and dynamic model of PKM based helical milling operation are proposed, and the chatter stability diagrams at the seven representative machining positions are obtained based on the Complete Discretization Scheme with Euler's method approach. The predicted cutting forces and chatter stability diagrams are experimentally validated by the PKM based titanium alloy helical milling. It can be found that the PKM machining position has a great influence on the corresponding limit stable axial depth of cut in the helical milling operation. Meanwhile, it was indicated that the spindle speed is an important factor affecting the helical milling stability difference at different machining positions. Meanwhile, it was found that the helical milling stability is only determined by 2nd,3rd and 4th order modes of TriMule when the spindle speed is higher than 1000 rpm with the first 4 mode of the cutting system considered. The research results are expected to provide a basis for the helical milling parameter optimization and reasonable robot machining position selection.

Titanium alloys are widely used in modern aircraft manufacturing. The hole-making technology with high quality becomes a crucial aspect of aircraft assembly. Helical milling process has drawn much attention due to its high machining quality and efficiency. In this work, the cutting performance of small diameter tools (3mm) in helical milling Ti alloy is studied. The parameters of spindle speed, tangential feed speed and pitch (axial feed per revolution) are optimized to reduce cutting force and processing time. The evolutions of the cutting force, burr size, hole side wall roughness and diameter with increasing hole number are investigated. Results show that burr size and hole side wall roughness are much lower than the requirement of aircraft assembly under the optimized parameters of 7000r/min (spindle speeds), 0.1mm (pitch), 0.02mm/tooth (tangential feed). Due to the poor stiffness and large deflection of small diameter tools, excessive hole diameter error is the most prominent problem to be concerned in helical milling process.