Papers by Author: Jiu Hua Xu

Abstract: Ultra-high speed grinding (UHSG) is a significant and promising machining technology in grinding hard-to-cut materials. To find out the aerodynamics of the grinding wheel body when the airflow field has subsonic, transonic, and supersonic speed characteristics and clarify the corresponding influence on the grinding mechanism, the study is conducted to develop a supersonic grinding machine tool that is capable of being operated at extreme wheel speed up to 450 m/s and meanwhile accompanying with high grinding capability. In accordance with the main design objectives, a high performance grinding motorized spindle with maximum rotational speed 36000r/min and maximum power 28kW is developed. The linear motor feed driven system is also exploited to satisfy the requirement of maximum reciprocating speed up to 2m/s. Following plenty of specific design and performance analysis works, a prototype of supersonic grinding machine tool is finally developed. In the end, this paper also puts forward a number of further studies and prospective for the research activities on basis of the developed grinder.

Abstract: Honing experiments were carried out for nickel-based superalloy Inconel718 bore. The significance analysis of the four honing parameters: spindle speed, stroke speed, wedge feed per stroke cycle and grain size on the surface roughness, was studied with the orthogonal design method. And the significant degree under the rated conditions was determined. The results showed that: wedge feed per stroke cycle and grain size have a significant influence on surface roughness while spindle speed and stroke speed had no significant effect. Also, there was a positive correlation between surface roughness and wedge feed per stroke cycle and grain size. Furthermore, the honed surface topography was analyzed by the meaning of microscope.

Abstract: High-speed milling tests were performed on vol. (5%-8%) TiC_p/TC4 composite in the speed range of 50-250 m/min using PCD tools to nvestigate the cutting temperature and the cutting forces. The results showed that radial depth of cut and cutting speed were the two significant influences that affected the cutting forces based on the Taguchi prediction. Increasing radial depth of cut and feed rate will increase the cutting force while increasing cutting speed will decrease the cutting force. Cutting force increased less than 5% when the reinforcement volume fraction in the composites increased from 0% to 8%. Radial depth of cut was the only significant influence factor on the cutting temperature. Cutting temperature increased with the increasing radial depth of cut, feed rate or cutting speed. The cutting temperature for the titanium composites was 40-90 °C higher than that for the TC4 matrix. However, the cutting temperature decreased by 4% when the reinforcement's volume fraction increased from 5% to 8%.

Abstract: Single-grain grinding test plays an important part in studying the high speed grinding mechanism of materials. In this paper, a new experimental system for high speed grinding test with single diamond grain is presented. The differences of surface topography and chip morphology of Inconel 718 machined by single diamond grain and single CBN grain were evaluated. The grinding forces and corresponding maximum undeformed chip thickness were measured under different grinding speeds. The chips, characterized by crack and segment band feature like the cutting segmented chips, were collected to study the high speed grinding mechanism of nickel-based superalloy. The results show that the grinding speed has an important effect on the forces and chip formation, partly due to the temperature variation. As the speed increases, the groove surface becomes smoother.

Abstract: This study describes the theoretical basis of ultra-high-speed grinding. In addition, a new grinding machine tool whose maximum grinding speed can reach 450m/s has been recently developed, particularly, some of main components are basically discussed. Finally, this paper concludes with a presentation of current work and some future desirable plans in the area of ultra-high-speed grinding by means of the developed grinding machine tool.

Abstract: Titanium matrix composites (TMCs) possess many outstanding properties and have increasing and potential application in aerospace, automobile and other industries. However, TMCs are typical difficult-to-machining material due to the rapid tool wear rate and excessive machining induced defects. In this paper, tool wear, cutting forces, cutting temperature and surface roughness were investigated when milling TMCs with Polycrystalline Diamond (PCD) and carbide tools. The results showed that the values of surface roughness obtained by carbide tools were higher than that of PCD tools under the same cutting conditions. The value of cutting temperature for PCD tool was about 75% of the carbide tools, and the main cutting force value of PCD tool was about 85% of the carbide tool. Abrasive and adhesive wear were the main wear mechanisms of PCD and carbide tools. In all, PCD tools had a better cutting performance than carbide tools during finishing milling titanium matrix composites.

Abstract: Ti2AlNb-based alloy is regarded as lightweight high-temperature structural material, which is expected to replace the nickel-base super alloy due to its low density, high elastic modulus, strength retention at elevated temperature, outstanding oxide resistance. However, these excellent properties also make Ti2AlNb to be difficult-to-cut material. In this paper, the milling experiment of Ti2AlNb alloy was carried out using Ti(N,C)-Al2O3 coated cemented carbide tools. SEM and EDS analysis was utilized to observe the worn tools to determine the tool failure modes and wear mechanisms. Tool life when milling Ti2AlNb was short and heavily dependent on the cutting parameters. During milling, coating material of the tool was separated rapidly from the base material. When the cutting speed exceeded 100m/min, serious cracks appeared on the tool surface. Thermal fatigue, adhesive and attrition were the predominant wear mechanisms of the coated tools.

Abstract: Based on the orderly distribution alumina bubbles in working layer the porous composite-bonded CBN wheels were fabricated and grinding experiments of nickel-based alloy were carried out in comparison of the vitrified counterpart. Results show that the grinding force decreases and increases respectively with the increasing wheel velocity and depth of cut. The specific grinding energy reduces graduately from 465 to 93 J/mm³ when the maximun underformed chip thickness increases from 0.4 to 1.7 μm. Compared to the vitrified CBN wheel, the grinding forces, temperatures and specific grinding energy of the porous composite-bonded CBN wheel are always lower than that of the vitrified one. Its attributed to the graphite lubricating and alumina bubbles pore-forming effects. The larger chip storage space, sharper grit edge and less adhesion on the wheel surface surpport the advantages of the porous CBN wheel.

Abstract: This article studies the performance of ceramic grinding wheel made of micro-crystalline alumina in the creep feed grinding of nickel-based superalloy Inconel 718. The effects of abrasives and specific pore volume on the performance of wheels are experimentally discussed. Grinding force and temperature were measured and analyzed during grinding tests. The surface roughness was used to describe the quality of ground surfaces. The results indicate that the micro-crystalline alumina SG abrasive wheel with large specific volume has good grinding properties when grinding Inconel 718 in comparison of the wheels with PA abrasives or SG abrasives of small specific pore volume.

Abstract: Ti-6Al-4V alloy was hydrogenated at 800°C by thermohydrogen treatment technology. Sliding friction and wear tests were carried out in a special device assembled on CA6140 turning lathe to investigate the friction and wear mechanism between hydrogenated titanium alloys and WC-Co cemented carbide. The morphological analyses of the worn surface were made by scanning electron microscope (SEM) and the diffusion and chemical reaction behavior of elements were analyzed by X-ray energy dispersive spectrometer (EDS). It was found that the main wear mechanisms of the unhydrogenated alloys were abrasion and adhesion and surface fatigue, while the main wear mechanisms of the hydrogenated alloys were abrasion and adhesion. The main wear mechanisms of the cemented carbide were all serious adhesion and spalling, and the specific wear forms were closed related to hydrogen contents. There are all not the chemical reaction wear and element diffusion wear in the friction region of whether the unhydrogenated alloys or the hydrogenated alloys or cemented carbide.