Katsuhiro Maekawa

Recent progress of computer aided simulation of chip flow and tool damage in metal machining

A computer simulation approach to the predictions of chip flow and tool damage in metal machining is reviewed based on the authors recent work. Not only finite element simulation theory but also material characteristics to be included in the analysis are stressed, since machining phenomena are intimately associated with elastic-plastic deformation and fracture of work materials at high strain rates and high temperatures. Temperature rise in the tool and workpiece should be incorporated in the machining simulation as well. Various simulation results together with some comparisons with experiments are shown, such as two-dimensional continuous and discontinuous chip formation, wear and fracture of a cutting tool and more practical three-dimensional machining. Finally, a new concept of computational machining or virtual machining simulation is envisaged in the light of further development of the present computer aided simulation.

High-speed end milling of Ti-6Al-6V-2Sn titanium alloy

From the view points of temperature, wear and cutting economics, high-speed end milling of an α+β type Ti-6Al-6V-2Sn titanium alloy up to a cutting speed of 628 m/min and a feed rate of 7.2 m/min has been investigated. Tool-life tests have shown that such high-speed milling operations can be achieved using a carbide tool with a large helix angle and high stiffness, in which the prevention of micro-chippings of the cutting edge plays an important role to prolong tool life. The bond strength between the carbide substrate and coatings is also essential since the separation leads to disastrous wear. In the light of the cutting economics based on the minimum-cost criterion and Taylors tool-life equation, optimum cutting conditions have been clarified: the cutting speed of a six-flute tool can be raised ten times as high as that recommended for the alloy. Finally, the finite element thermal analysis has revealed that the temperature at the cutting edge is kept low owing to the cooling action by cutting fluid during the non-cutting periods, which makes it feasible to perform high-speed end milling of the alloy.

Simulation analysis of cutting performance of a three-dimensional cut-away tool

A three-dimensional cut-away tool for turning operations has been proposed to improve machinability of difficult-to-cut materials. The tool-chip contact geometry is determined such that the restricted length is proportional to the real uncut chip thickness in the direction of chip flow. The three-dimensional elastic-plastic and thermal finite element method has been employed to simulate the cutting mechanism of an 18%Mn-18%Cr high manganese steel (HB=241) with a sintered carbide cut-away tool. The simulation has revealed that there exists an optimum restricted length of around 1.2 times the feed, where the cutting forces become minimum, leading to the reductions of cutting temperature and tool wear. Measurements of the cutting forces, cutting temperature and tool wear have been conducted to validate the analytical predictions: the cut-away tool with optimum contact geometry brings a more than 10% reduction of tool wear in dry turning of the steel with a cutting speed of 60 m/min, a feed of 0.2 mm/rev, and a depth of cut of 2 mm.

Structure Formation during Preparation of Variable Porosity Titanium Foams by Solid State Replication

Fabrication of variable porosity titanium foams through incorporation of sacrificial sodium chloride powder has been investigated. A three-dimensional solid foam pore skeleton containing macro- (200-400uf06dm), micro- (5-10uf06dm) and sub-micropores (< 1.5uf06dm) was formed during high temperature sintering of commercial purity titanium powder containing sacrificial sodium chloride particles, faceting of the interior pore powder surface being noted throughout. The largest macro-pores had a cubical topography representative of the sodium chloride powder that had been vaporized during heating to the sintering temperature. Formation of the smaller micro-pores appeared to have occurred during the compaction process these being retained in the specimen body due to incomplete sintering of the host powder. Finally formation of the smallest sub-micropores was associated with high temperature gas evolution and entrapment during sodium chloride vaporization.

Computer-Aided Simulation of Chip Flow and Tool Damage in Metal Machining

Metal machining is typical of an irreversible process, comprising large plastic deformation and fracture coupled with temperature rise at a high strain rate [1]. From a continuum mechanics point of view, suitable constitutive or governing equations that can describe these phenomena are needed to predict chip flow, cutting forces, cutting temperature, tool wear, fracture probability of a cutting tool, etc. However, the solutions of displacement or velocity, stress, strain and temperature in metal machining processes have not easily been obtained since the deformation and temperature rise are highly non-linear and time-dependent.

Machinability analysis of free-machining steels. (1st Report). Correlation between friction characteristics of low alloy resulfurized steel and cutting mechanism.

A split tool dynamometer was employed to investigate friction characteristics at the tool-chip interface. Compared to a standard steel, a calcium treated, resulfurized steel shows lower frictional stress near the chip leaving point and shorter chip contact length. The friction on the rake face can be expressed by a characteristic equation which is similar to that proposed by Shirakashi and Usui.On the other hand, high strain rate compression tests at elevated temperatures were carried out using the Hopkinson bar method to evaluate flow characteristics of the steels. On the basis of the empirical equations thus obtained, a simulation analysis was conducted to examine a correlation between the material characteristics and cutting mechanism. It shows that the difference in friction characteristics mainly causes the chip flow, temperature and cutting forces to change : the free-machining steel brings better machinability, though its flow properties are almost the same as those of the standard steel.

Plasma hot machining for difficult-to-cut materials. (3rd Report). Application to glasses and engineering ceramics.

A hot machining technique using plasma jet heating has been employed to improve the machinability of glasses and engineering ceramics such as Pyrex, mullite, alumina, zirconia and silicon nitride. Plasma heating is aimed not only at reducing the hardness of ceramics but also at changing the chip formation from discontinuous to continuous. The turning forces markedly decreased as the workpiece was heated to temperatures above 1050°C in the case of silicon nitride. Increased heating temperature changed the segmented chips produced in ordinary cutting into continuous ones, accompanied by a better finished surface with less defects. Tool wear was also decreased by means of hot machining: e.g. by a factor of 8 in turning silicon nitride with a diamond tool. However, the application to alumina and zirconia did not show sufficient improvements in machinability.