Tool geometry analysis for plunge milling of lead-free CuZn-alloys

Plunge milling is a critical process step in mass manufacturing of rectangular shapes in electrical connector components. These shapes are manufactured by drilling a pilot hole and subsequent plunge milling with a radial offset (pitch) one or more times. The plunged cavity serves as guidance for the final broaching cut. In light of new legislative initiatives, the electronics industry is forced to use lead-free Cu-Zn-Alloys for mass manufacturing of these connectors. The plunging tool is deflected due to the higher cutting forces experienced in machining of lead-free CuZn-alloys in comparison to alloys with lead. This results in an offset of the milled cavity and negatively impacts tool guidance in the subsequent broaching process. Therefore, the geometric tolerances cannot be met. In this paper, the effect of tool geometry and cutting parameters on the workpiece geometry in plunge milling is investigated. The effect of the microstructure of the work-piece materials CuZn37, CuZn42 and CuZn21Si3P on the tool deflection and cutting force components is examined. The tools used vary regarding the design of the corner in terms of the corner chamfer and the inner shaft thickness. Friction between chips in the tools inner flutes and the cavity walls reduced workpiece accuracy. Improvements were achieved by reducing the width of the cutting corner chamfers, using large inner flutes and applying low cutting parameters.

A Study on Interferential Tool Position Correcting Algorithm in Rough Machining of 3d Impeller Variable-axis Plunge Milling

The plunge milling method has remarkably improved the rough machining efficiency of 3D impeller channel. However, in conventional cutter position planning for plunge milling, interference at the end of every cutter position due to sudden increase of radial depth is inevitable, which may seriously compromise the service life of machine tool and cutter, as well as the cutting efficiency at the interferential phase. This study optimized the cutter axis vector for the tool path of conventional rough machining of 3D impeller variable -axis plunge milling to make the angle between the normal vector for workpiece surface at the cutter contact point and the cutter-axis vector of adjacent tool position increase gradually from outlet to inlet at the smallest scale. Based on this, an iterative algorithm for tool center position and safety height for the cutter was provided, thus making the hub allowance of the optimized tool path for plunge milling as small as possible without affecting the subsequent machining on the premise of avoiding the interferential phenomenon. Finally, the correctness of the proposed method was verified by relevant numerical examples.

A modeling and prediction method for plunge cutting force considering the small displacement of cutting layer

In the process of plunge milling, the main cutting force is along the axial direction, and usually, the machining system has good axial rigidity, so it can withstand large cutting loads. This characteristic makes plunge milling particularly suitable for high-efficiency rough machining and semi-finishing of difficult-to-cut materials. The cutting force in the plunge milling process is usually large, and when the process parameters are not selected properly, the plunge milling is prone to the back-off phenomenon. In view of the characteristics of large cutting force and high cutting temperature in Inconel 718 plunge milling process, considering the small displacement of the actual tool tip caused by cutting force and cutting vibration, this article establishes a plunge milling force model based on the combination of analytical method and three-dimensional finite element method. The micro-displacement caused by vibration is obtained through dynamic modeling and modal test methods. Combined with the macro-displacement of cuter back-off under the action of the cutting force during the single-tooth run-in and run-out process, the modified cutting layer parameters are obtained, and optimized cutting force of plunge milling is obtained.

A Universal Pocket Plunge Milling Method to Decrease the Maximum Engagement Angle

Plunge milling has been proven to be an efficient strategy for machining of pockets with deep cavities and difficult-to-cut material. Previous work generates the plunge toolpath mainly by controlling the radial cutting width within the given value. However, uneven tool engagement angles may lead to excessive tool load and tool load fluctuations, which has a negative influence on tool life. In this study, a universal plunge milling toolpath generation method is proposed to improve tool life by decreasing the maximum tool engagement angle. A series of concentric circles with constant radius increment is utilized to generate a toolpath with constant cutting radial depth. Center of the concentric circle is determined based on the pocket contour. New detailed algorithms to generate plunge toolpath for basic cases have been developed. An automatic pocket subdivision algorithm has been developed by dividing the pocket into several subregions that are easy to be machined. Without loss of generality, the method is applicable for both open and closed pockets. It also works for pockets with and without islands inside. The method is implemented and verified successfully by machining experiments. The results provide strong evidence that the proposed method can reduce the maximum engagement angle over the entire toolpath and thus improve the tool life.