Minli Zheng

Wear characteristics of cemented carbide tool in dry-machining Ti-6Al-4V

ABSTRACT In machining titanium alloys, due to the low thermal conductivity and high chemical activity of titanium alloys, tool wear is serious and processing efficiency is very low. To avoid the effects of impurities, which were brought by the cutting fluid, the uncoated cemented carbide tool (WC-Co), which was suitable for cutting titanium alloys, was used for the experiments of dry-turning titanium alloy Ti-6Al-4V. A scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometer (EDS) was used to analyze tool wear mechanism. Based on analyzing the friction characteristic of tool–chip interface, tool wear mechanism was also studied and a physical evolution model of tool wear was established. The results showed that there existed serious adhesion, diffusion and oxidation at tool–chip interface and increasing cutting speed accelerated their occurrence. The physical evolution of tool wear behavior can reflect the loss process of tool material very well.

Study on the influence of meso-geometrical features on milling force in precision machining of titanium alloy

ABSTRACT Titanium Alloy is a typical material difficult to be processed for its characteristics of low thermal conductivity, and high chemical activity, which result in tool wear and the poor quality of the machined surface. In order to solve the problems existing in the processing of Titanium Alloy, considering the tool edge, micro-texture is implanted into the cemented carbide ball end milling cutter. The article analyzes the influence law of micro-texture and the tool edge radius of ball end milling cutter on mechanical properties of Titanium Alloy, establishes and verifies a mechanical predictive model of milling Titanium Alloy with ball end milling cutter surface based on the effect of micro-texture and the tool edge. Finally, with regard to the minimum cutting force as the target, the article uses genetic algorithm to optimize meso-geometrical features parameters of the cemented carbide ball end milling cutter. The article also provides the foundation for efficient and high-quality processing of Titanium Alloy.

Research on Character of Physical Field Distribution in High Speed Ball-End Milling Hardened Steel

In order to mend cutting instability of ball-end milling cutter caused by the changes of cutting loads in high speed milling hardened steel, we perform the modal analysis and heat-force coupling field analysis of cutter, carry out the experiment of high speed milling hardened steel, investigate the character and effect factor of physical field distribution in high speed ball-end milling hardened steel, and propose the method about the match of diameter and overhang for depressing cutter vibration. Results indicate that the decrease in the ratio of overhang to diameter can transform the first modal shape of cutter from bending modal shape into torsion modal shape. The diameter of cutter is from 30mm to 20mm, the overhang of cutter is from 125mm to 90mm, heat-force coupling field distribution changes slightly, resonance of cutter does not occur, and efficiency in machining hardened steel can be improved effectively by higher cutting speed.

Cutting Thickness of High Speed Ball-End Milling Hardened Steel

In order to solve the problem of machined surface damage and machining efficiency decline that caused by the decrease of effective cutting thickness in high speed ball-end milling hardened steel, using high speed cutting adiabatic shearing model, analyzed the adiabatic shearing deformation on hardened steel, and proposed the criterion of chip separating position. Analyzed the force in the transformation process from cutting to plowing, the influence of cutter deformation on cutting thickness was studied, and established the minimum cutting thickness model. Having done finite element analysis of cutter and experiment of high speed milling hardened steel, the validity of the minimum cutting thickness model was proved. The results show that cutting thickness changes from small to large, and then from large to small under the influence of cutting trajectory and tool edge radius. The deformation of cutter leads to the increase of the minimum cutting thickness, and further enhances chip thickness thinning effect. High feed can compensate cutting thickness thinning and the minimum cutting thickness model provides an effective way to restrain the damage of machined surface and cutter caused by cutter plowing.