A methodology for helical mill-grinding of tiny internal threads made of hard brittle materials

This study proposes a methodology for helical mill-grinding of tiny internal threads made of hard brittle materials such as SiCp/Al composites. The methodology uses the helical mill-grinding method incorporating with a diamond form-grinding wheel. A mathematical model is established to predict thread form errors and provide a rational range of wheel parameters, such as variation of tool profile angle Delta alpha and ratio of the wheel diameter to the thread major diameter.. Based on the methodology, a grinding wheel is developed for processing the M2 internal threads in a validation experiment. The study demonstrates that an M2 internal thread made of the SiCp/Al composite of 45% SiC volume fraction is successfully machined in 5 min with pitch error < 0.08% and angle error < 0.3%. The thread profile on the pitch diameter is within the axial equivalent tolerance zone (0-0.016 mm), which indicates that the thread precision reaches the H4 level.