Abstract
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.
Highlights
Due to their combination of good electrical conductivity and good machinability, CuZn-alloys with lead contents from mPb=1 % to mPb=4 % are a preferred workpiece material in the manufacture of electronic components such as connectors due to their excellent productivity in machining
The outcomes of this study provide the base for further optimization of tool and process design in plunge milling of lead-free brass alloys
The radial force components Fx and Fy were between three and ten times higher than the axial Fz. This is disadvantageous for plunge milling since it causes tool deflection
Summary
Due to their combination of good electrical conductivity and good machinability, CuZn-alloys with lead contents from mPb=1 % to mPb=4 % are a preferred workpiece material in the manufacture of electronic components such as connectors due to their excellent productivity in machining. Compared to the popular leaded alloy CuZn39Pb3 (mPb=3 %), machining of lead-free CuZn-materials results in higher cutting force components, longer chip forms, increased friction and much higher adhesive and abrasive tool wear [6,7,8]. This leads to a crucial reduction in process reliability and productivity in all machining processes. Research regarding plunge milling of different workpiece materials suggests maximising the cutting force component axial to the tool in relation to radial force components This minimizes tool deflection and can be achieved by utilizing tools with small
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
