Papers by Author: Yi Wan

Abstract: The first step to predict the milling stability is to identify the dynamic characteristics of cutting process. And the mass loading effects of removal material play an important role on the dynamic characteristics of milling process for thin-walled parts, such as impeller, turbine blades and automobile components, which is changing with cutting time or tool position. Therefore, how to identify the instantaneous dynamic characteristics of milling process is one of the most significant problems. In the paper, a structural dynamic modification method with variable mass to predict the instantaneous dynamic characteristics of multi-axis milling thin-walled workpiece with complex curved surface is proposed. The proposed method takes into account the variations of dynamics characteristics of workpiece with the tool position and material removal. And the material cutting process is regarded as the structural dynamic modifications of cutting system, the instantaneous dynamic characteristics of which can be estimated by the extended Sherman-Morrison-Woodbury formula to obtain the corrected frequency response function (FRF). Experiments were carried out to obtain the instantaneous dynamics of a thin-walled workpiece and the results were verified by finite element method (FEM).

Abstract: The oxide film on implant surface of biomedical titanium alloy is crucial to its bioactivity and biocompatibility in human body. A new method is proposed to obtain titanium oxide film by cutting process in oxygen-enriched atmosphere. A gas mixing system is firstly developed to provide oxygen-argon mixed gas to the flank face of insert during turning. The results show that oxygen-enriched atmosphere promote the oxidation reaction of titanium element. Thicker oxide film can be obtained in oxygen-enriched condition than that in natural atmosphere. The corrosion resistance is also improved significantly by this method in electrochemical test.

Abstract: Cutting tool temperature is the main factor that directly affects tool wear and tool life. In this paper we developed temperature model of tool insert during slot milling process, constructed by a combination of cutting time model and non-cutting model. A set of experiments are designed and carried out to obtain cutting induced temperatures at different cutting speeds during slot milling of AISI H13 steel. Experiments results indicate that tool insert temperature increases first and then decreases as the cutting speed grows, and a critical cutting speed for the tool insert temperature exists during slot milling of AISI H13 steel. Some possible reasons for the drop of tool insert temperature are proposed and discussed, and they are decreased heat flux into tool insert and increased heat convection coefficient.

Abstract: Talyor formula is widely accepted to describe tool wear and is employed to optimize cutting parameters. The common test methods and processes of cutting tool wear test are firstly investigated in this paper. The effects of interference factors on different test methods are analyzed by hypothesis test to find the reason that regression generalized Taylor formula is partly invalid or not effective. The meaning of exponentials in generalized Taylor formula is discussed and tool wear test principle for difficult-to-machine materials is proposed at last.

Abstract: Turbine blade plays an important role in aero engine and power generation equipment. As thin-walled and free-form surface component, deflection in spiral milling of turbine blade is common, which result in bad dimensional precision. In this paper, a five-axis milling experiment was firstly conducted to get the cutting force components. Then, deflections were studied at different positions. The results show that compensation can be made based on the FEM analysis.

Abstract: A difficult-to-machining material, cast supper alloy K24 has been cut with two different methods, milling and abrasive waterjet (AWJ). It is shown that milling is characterized by high tool cost, low efficiency, and good surface roughness while abrasive waterjet brings high efficiency and worse surface quality. The results have proven that the combination use of AWJ and milling is an efficient way in cutting K24.

Abstract: High-speed machining is investigated in a new viewpoint, thermodynamic theory. Many phenomena in cutting, such as heat conduction, chemical reaction, diffusion and so on, can be studied with thermodynamic theory. In this paper, entropy generation and entropy flow in cutting system are revealed as well as the interaction of sub processes. As a case study, the oxidation of cemented carbide tool was studied in thermodynamic theory and experiments. The results show that thermodynamic theory is effective.

Abstract: Flexible parts such as turbine blade, blisk and monolithic components are widely used in the aeronautical industry, and high Speed Machining (HSM) technology is used to increase productivity and reduce production costs. Chatter is an undesirable phenomenon in high speed machining processes because of deteriorative surface finish, early cutting tool failure and unexpected machine tool damage. It can be avoided in higher speed milling processes if stability lobes is determined. In this paper, a non-linear regenerative force model is applied to a bull-nose tool geometry in order to obtain the machine operation stability lobes. An analytical-experimental method is proposed to obtain the stability lobes during high speed milling flexible parts with bull-nose end mills. The method is calculated and validated.

Abstract: Five-axis milling is widely used in machining of complex surfaces parts. Part quality and productivity are extremely affected by cutting force and tool wear, especially thin-walled complex surface, such as turbine blade. Although extensive research has been conducted on cutting force and tool wear in 3-milling process, very few are on 5-axis milling and bull-nose mills. This paper presents cutting forces with various cutting conditions as well as tool wear patterns in five-axis milling super alloy, which is essential to cutting vibration and defelction analysis of thin-walled complex surfaces parts. The roles of lead angle and tilt angle in five axis milling were investigated, which provide data for NC program edit. In addition, experiments in this research proved that tool wear played affected cutting forces outstandingly.Therefore, tool wear played an very important role in tool change.

Abstract: Material constitutive model for metal machining is very difficult to obtain and establish accurately by conventional tension and compression tests. The dynamic mechanical properties and material model during machining aluminum 7050-T7451 are studied by means of orthogonal machining experiments (including quick-stop experiment, cutting force and cutting temperature measurements). Compare with compression tests (SHPB), the established material model with large strain (0.8~1.9) and high strain rate (0.45×105~1.89×105) in this paper is more valid and reliability in simulation and analyzing machining process.