Key Engineering Materials Vol. 693

Abstract: To avoid the influence of column vibration on machining precision, it is necessary to simulate the stiffness characteristics of the columns for CNC grinding machine, and to optimize the structure of the column by using sensitivity method. Based on structural characteristics of the grinding machine and structural characteristics of the columns, a finite element model is established to simulate and calculate the first-four models of the columns. In order to optimize the structure of the column, a sensitivity analysis is made to calculate the sensitivity of natural frequencies and mass of the column to each panel and ribbed plate. Considering a weighting factor and taking integrated natural frequency of the column as an optimization objective, the mass of the column as a constraint, an optimization equation is established. By a quadratic programming method, the parameter optimization of the column is got as follows: the mass decreased by 4%, integrated natural frequency increased by 2%. Dynamic stiffness of the column has been optimized by harmonic response analysis, the results showed that the largest column in the Z resonance peak reduced by 8.44%.

Abstract: Powder metallurgy valve seat is an important part for engine; the material has excellent properties such as the wear-resistance of high temperature, corrosion proof and high temperature stability etc. But because of its high hardness, porous nature and contains many microscopic characteristics of the hard particles and the like, common tools cut these parts wear out quickly. And the valve seat requires higher dimensional accuracy and surface roughness, so these bring a lot of difficulties to cut these parts. Because of Polycrystalline Cubic Boron Nitride (hereafter referred to as PCBN) cutting tool has such advantages as high hardness; wear resistance; minimum surface roughness, so it has a great advantage on hard cutting the powder metallurgy valve seat. By hard cutting the powder metallurgy valve seat experiments, to research on the wear form and the cutting parameters impact on the cutting force.

Abstract: In order to realize special trapezoidal thread production more quickly and simply, a new processing method is presented. Based on the shape analysis of the spiral curve, spiral surface discrete algorithm is discussed. Spiral surface is discretized in to numerous tiny straight segments, and consequently the trapezoidal thread machining can be accomplished by just using G01. Simulation and experiment results show that this processing method is feasible and with high production efficiency.

Abstract: In cam grinding process, the grinding force changes with the change of cam contour, and its change leads to create the error of X-C linkage servo-tracking position, all of the factors reduce the cam the contour accuracy. To improve the accuracy of the cam profile, and research the effect of X-C axis servo tracking, the key vector of grinding force to the position is proposed, in which the factors have been considered including the grinding depth, curvature change, cam width, length and other effects. According to the mechanical analysis of cam and grinding wheel, a cam grinding XC-axis grinding force model is established. With the flat-bottomed follower cam as an example, the grinding force of X axis and C axis is calculated. The cam grinding experiment was conducted in the grinding machine, the tangential grinding force and normal grinding force were obtained and the model was verified. The grinding force mathematical model of X-C linkage provides the theoretical basis for the servo tracking position of X-C linkage grinding.

Abstract: The invention of the Numerical Control (NC) technology have brought the new revolution of manufacturing since 20th century intermediate stage. Computer Numerical Control (CNC ) technology is the foundation of the modern manufacturing technology, integrating the traditional manufacturing technology, modern control technology and modern optical-electromechanical technology.[1,2]As the core of CNC technology, CNC system is requesting higher precision and higher speed as it develops. So it is necessary to meet the requirements of the machining surface quality and avoid the occurrences of the processing speed decline or even stall, which depends on the good controls of the acceleration and deceleration of the feed shaft [3].This article briefly analyzes some existing strategies of the acceleration and deceleration, then mainly introduces the s-shaped acceleration and deceleration curve method and the trajectory planning strategy of it.

Abstract: A series of experiments was conducted in high speed machining of powder metallurgy material with PCBN tools. The main tool wear mechanisms were discussed by observing tool wear morphology utilizing scanning electron microscopy (SEM) and detecting the element distribution of the worn tool surface using energy dispersive spectroscopy (EDS).The experimental results indicate that fragile breakage occurred before it reached its blunt standard in high-speed machining of powder metallurgy material with PCBN tools,and the tools wear mechanisms are synergistic interaction among mechanical wear,binder wear and chemical wear.

Abstract: Cutting temperature always highly reaches over to 1000¡æ when high speed machining with PCBN tools. Diffusion of tool material element may have important influence on tool wear at such high temperature., the diffusion wear and oxidation wear have become the major wear mechanism. In this paper, the rules of diffusion wear and oxidation wear for PCBN cutting tools are proposed and analyzed based on thermodynamics theory. Dissolution concentrations in typical normal workpice materials of PCBN tool material at different temperature are then calculated. Diffusion reaction rules in high temperature are developed and analyzed using Gibbs free energy criterion. The machining tests were conducted using the PCBN tools at different cutting speeds of 50, 95,100 and 180 m/min, feed of 0.1, 0.2 and depth of cut of 0.1, 0.8, 1, and 1.5 mm respectively on PUMA300LM numerically-controlled lathe. It was found that the theoretical results were uniform with the experimental data; the results will provide useful references for tool material design and selection.

Abstract: This paper presented a numerical model of a grinding wheel hub to analyze the dynamic behavior between CFRP hub and steel hub. Natural frequencies of the two different hubs were extracted with the help of finite element software ABAQUS. In addition, the vibration attenuation procedure in the process of free vibration of the hubs was also compared. The numerical results obtained from the model demonstrated that natural frequency of the CFRP hub is much higher than that made of steel owing to the great ratio of elastic modulus to density of carbon fiber. The CFRP hub has a better damping vibration characteristic which allows it to absorb vibration in grinding process to achieve a finer surface roughness.

Abstract: The existing end mill is hard to balance the tool rigidity, heat dissipation and chip evacuation. In this study, the geometries of groove and micro-blade of the end mill machining titanium are optimized, through imitating the corn leaf’s tooth based on bionics. The peripheral cutting edge is composed of linear first rake, parabolic second rake and rear face. The chip-hold groove is composed of parabolic main groove and cubic curve vice groove. The cutting process of straight tooth and designed composite tooth are simulated by constructing the two-dimensional orthogonal cutting model using ABAQUS. The results show that: compared to the straight tooth, the designed composite tooth inhibits the generation of serrated chip, and the fluctuations of cutting force are smaller, the squeezing effect on the machined surface is weaker.

Abstract: The prediction of tool wear can help understand the influence of tool wear on the machining process and result, and change or grind the worn tool in time. The two-dimensional ultrasonic vibration turning method can reduce the crack of tool and decrease the negative effect on processing thus extends the tool life. In this paper, two-dimensional ultrasonic cutting theory was applied to the precision machining of tungsten carbide. With self-developed two-dimensional ultrasonic cutting device, series of cutting experiments were carried out. During cutting process, the flank wear under different cutting length was observed; flank wear situations were compared with those in traditional cutting. In order to predict the tool wear and thus heighten the machining precision, a tool wear prediction model based on time series analysis method was built in the paper. The research results show the built AR (9) time series model can predict the flank wear condition with high precision.