UBC Theses and Dissertations
Stress analysis of metal cutting tools Jemal, Girma
Metal cutting tools experience cutting forces distributed over a small chip-tool contact area. When the magnitude of the stresses induced by the cutting forces exceeds the tool material fatigue strength, failure of the cutting tool results. In this thesis, stress analysis in cutting tools is presented in order to predict the location and modes of tool failures. The stress analysis of cutting tools is presented using both analytical and numerical (Finite Element) based methods. First, various cutting force distributions on the rake face of the tool and analytical cutting tool stress solutions available in the literature are surveyed. It is then shown that the previous analytical solutions are in-correct because they directly applied the infinite wedge solution to determine stresses in the loaded region of the cutting tool. In this thesis, the tool and the boundary stresses are considered both in the loaded and free region. For a polynomial boundary stresses on the rake face and zero boundary stresses on the flank face, the stresses in a two-dimensional cutting tool are determined using the infinite wedge solution. The analytical cutting tool stress distributions obtained agrees well with finite element solutions and published photoelastic experimental stress distributions. From the stress distribution obtained, it is shown that the critical maximum tensile stress occurs at the end of chip-tool contact and it results in initiation of cracks and final fracture of the whole loaded region. The critical maximum compressive stress occurs on the flank face close to the cutting edge which results on cutting edge permanent deformation. The critical maximum shear stress occurs at the cutting edge and it results in cutting edge chipping. The possible extension of the two-dimensional solution to determine stresses in end mill flutes is considered. A comparison of a finite element solution of an end mill flute and the two-dimensional solution obtained above (for the same wedge angle and boundary load distribution) shows agreement at the cutting edge while at the end of chip-tool contact the two-dimensional solution gives an upper bound estimate. Thus the conclusions reached for tool failure in the loaded region from the two-dimensional solution is also applicable in end mill flutes. At the end mill shank, stress predictions using a cantilevered beam solution agrees with a finite element solution. The stress distribution shows shank fracture either at the fixed end of the end mill where it is attached to the chuck or at the flute section closest to the circular portion of the endmill. In this study for both orthogonal cutting tools and end mills, good correlation is obtained between predicted and observed in-service cutting tool failures. Therefore, the proposed cutting tool stress analysis approach may be recommended for cutting tool design and selection of optimum machining conditions.
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