Masayuki Hashimura

Analysis of Burr Formation Mechanism in Orthogonal Cutting

To prevent problems caused by burrs in machining, reduction and control of burr size is desirable. This paper presents a basic framework for and conceptual understanding of the burr formation process based upon the material properties of the workpiece. In order to verify this framework and explain the basic phenomena in the burr formation process, the deformation at the edge of the workpiece was analyzed using a finite element method (FEM). Micro-machining tests under an optical microscope and a scanning electron microscope using Al-2024-O material were also done to observe the burr formation process. The feed rate and tool edge radius were varied and the resulting burr formation observed. FEM analysis of burr formation in the 2024 material and observation of the deformation at the workpiece edge in the micro-machining tests verified the proposed conceptual understanding of the burr formation process. For the experimental conditions examined, all of the burrs in Al-2024-O were negative burrs, that is, edge breakout. As the feed was increased two effects were observed. One effect was an increase in the resulting burr thickness. Another effect, which was observed during the burr initiation stage while machining with a sharp tool, was an increase in both the distance and depth of the initial pivoting point of the burr from the tool edge.

An Investigation of Material Removal Mechanisms in Lapping with Grain Size Transition

The mechanical material removal (MRR) mechanisms in lapping were investigated, using concepts of two-body vs. three-body abrasion and ductile vs. brittle machining. The statistical nature of the depth of cut in the lapping process was described using distribution of abrasive sizes in the slurry. Through the change in abrasive size distribution, the time dependent characteristic of MRR was captured in the model. Experiments were conducted for model verification. It was found that a constant 60 deg effective inclusion angle allowed the model to fit measurement well.

Effects of microcracks in CVD coating layers on cemented carbide and cermet substrates on residual stress and transverse rupture strength

Microcracks were mechanically induced in the CVD coating layers on two types of cemented carbides with different thermal expansion coefficients, and one type of cermet. The microcracks were found to have beneficial effects on residual stress, transverse rupture strength, and chipping resistance during interrupted cutting. Residual stress in the coating on cemented carbide is tensile. Tensile residual stress decreases with increasing microcrack width and decreasing microcrack distance. Induction of 20 μm-distant and 0.025 μm-wide cracks relieves tensile residual stress by about 0.5 GPa, increases transverse rupture strength by about 0.70 GPa, and almost doubles the chipping resistance. Residual stress in the coating on cermet is compressive. Microcracks in the coating layer do not change residual stress or transverse rupture strength.

Effect of Axial Rake Angle on Burr Formation in Milling.

Burr formation in milling is a three dimensional deformation. Burr formation is different from deformation in continuous cutting. In burr formation on exit surfaces of workpieces, the continuous cutting before burr formation is considered to be an initial condition of bur formation and plastic deformation of workpiece edge formed by the tool exit is burr. Therefore, the continuous cutting and deformation by tool exit have effect on burr formation. To clarify the effect of these factors on burr formation, burrs created with various axial rake angle of the tools and cutting conditions were observed. To represent the state of the continuous cutting, the chip flow angle calculated with cutting conditions was used. To represent the deformation type at the workpiece edge, exit order of cutting edges calculated with the geometry of the tool and workpiece edges was proposed. These chip flow angle and exit order are used for understanding the burr formation in milling. To vary the chip flow angle and exit order, depth of cut, feed and axial rake angle of tools were varied. As the results, it was verified that deformation formed in continuous cutting and tool exit has effect on burr size in face milling. As the chip flow angle increased, the exit burr thickness decreased and side burr thickness increased. As the axial rake angle decreased, the exit burr thickness increased with effect of the exit order. These chip flow angle and exit order are considered to be important factors on burr formation in milling.