CNC Grinding Research Articles

Study of Complex Helical Drill with a “S” Type Chisel Edge Tip Orient to Carbon Fiber Reinforced Plastics

In this paper, a complex helicoids’ drill tip of “S” type chisel edge grinded with a three‐parallel universal CNC grinding machine tool is carefully studied to obtain the optimum drill bit tip geometry parameters. The effects of experimental parameters, such as apex angle, chisel edge incline angle, and structure circumference rear angle, on the quality of the drilling hole and the machining force were studied from the orthogonal experiment compared with the ordinary drill bit. The range of technological parameters are confirmed which should be used during the drilling process of carbon fiber reinforced plastics (CFRP) in order to realize the reduction of cutting defects such as cutting force and spurs. The effect of spindle speed and feed on the drilling behaviour of the experiment using optimum complex helicoids’ drill tip is also analyzed. It is found that the feed has a great influence on the drilling axial force and the spindle speed has little influence on axial force, but great influence on torque.

High-resolution measurement technology for the detection of complex process influences in machining operations

Inorganic non-metallic materials are widely used in many application areas such as precision optics, semiconductor technology, high-temperature technology or medical technology. This increasingly requires the application of precise multi-axis CNC machine technology and poses great challenges for the machining processes, especially with regard to the economic production of high-quality surfaces. In the field of optics technology, high surface qualities in the nanometer range are often required. The production machines designed for this purpose must therefore guarantee a high degree of accuracy and be constant with respect to their environmental factors. An influence on the quality of the machining results that should not be underestimated is the vibrations occurring on the machine, which are caused on the one hand by the operating vibrations generated by the running spindle, and on the other hand by resonance frequencies. A side effect of these vibrations can also be damage to the workpiece or the tool. In order to detect these influences, a modal analysis and a measurement of the operating vibration mode are carried out on an ultrasonic-assisted CNC grinding machine using a three-dimensional laser Doppler vibrometer system provided by Polytec GmbH. In addition, corresponding measurements are carried out by means of a one-dimensional laser Doppler vibrometer on a 5-axis CNC universal milling machine in order to establish comparability between an ultrasound-assisted and a conventional processing machine.

Unified approach to developing analytical models of different grinding processes based on basic cutting process model

The appearance of modern CNC grinding machines allowed concentrating multipass and multistage processing of different workpiece surfaces by means of using different grinding types and different tool types. Meanwhile, the processing of different surfaces is carried out with different allowances and accuracy requirements and performed according to the specified stepwise cycles of the feeds control. As a result, there is a difficult task of quick and reliable calculation of the optimal feed cycles and other cutting modes for different types of processing of different surfaces with various grinding conditions. The solution to this problem is developing of mathematical models that link processing accuracy with cutting modes and other technological conditions of the processing. The development of such models should begin with the creation of a complex of the cutting forces` models for each grinding type. This article describes a method for deriving generalized analytical model of the cutting force for the different grinding types which is based on the functional interrelation between the intensity of the metal removal performed by the wheel and elementary volumes of metal deformable in the shear zone. The complex of the cutting forces models for different grinding types, obtained by means of using this technique, establishes functional interrelation of the cutting force with cutting modes, strength properties of the treated material, kinematics of the grinding process, geometry of the cutting zone, characteristics and geometric parameters of the grinding wheel, etc. It should also be noted that the developed models cover the majority of production conditions and they are wide-range in terms of the main technological parameters (dimensions of the treated surfaces, allowances, tolerance grades, etc.).

Φ1.05 m轻量化反射镜设计与制造

针对Ф1.05 m空间光学系统主镜的设计指标要求，提出了轻量化反射镜结构优化设计的新方法，并建立了反射镜结构自动化仿真分析与优化设计平台，基于此平台确定了性能优异的主镜结构设计方案。主镜重量小于50 kg，轻量化率已接近国外先进水平；主镜在三球铰支撑下的第一阶模态频率为361.2 Hz，自由状态下的一阶非零模态频率为501.9 Hz；在1 ℃均匀温度变化下，不去离焦和去除离焦之后的面形RMS分别为0.55 nm和0.10 nm；主镜在30g过载加速度作用下的最大应力为16.1 MPa，均满足设计要求。采用目前最先进的第三代大口径反射镜加工工艺，路线为超精密铣磨—小磨头数控研抛—离子束精修，实现主镜面形误差的确定性去除。为保证面形检测结果的天地一致性，发展了重力卸载技术和面形误差数据后处理技术，剔除重力和其他系统误差对检测的影响。主镜最终面形精度达到0.011λ RMS，获得了高精度的光学面形，也证明了方案的合理性。

Design and manufacture of the novel drum worm pair.

Although a significant amount of research on robot joint reducer was conducted, there are few systematic investigations on a novel joint reducer adopting inner worm-gear plane enveloping drum worm drive. To satisfy the development of modular robot joint, the primary objective of this paper was to systematically investigate the drum worm drive adopted in the novel joint reducer with integrated structure of drive, transmission, and support in the following aspects: meshing theory, design, analysis, and manufacture. According to the gear meshing theory, mechanical design method, classical mechanics, finite element method, and machining principle of virtual center distance, the systematic investigations around the drum worm pair applied in the novel joint reducer were conducted including the macro and micro meshing theory, structure design, mechanical and contact properties analyses, and manufacturing method. The novel joint reducer's integrated structure was designed, and the drum worm pair's mechanical and contact properties analyses were conducted, which showed: (1) the worm's bending stress and deflection, worm-gear teeth's shear stress and bending stress as well as the maximum contact stresses were all below their corresponding allowable values; (2) the maximum contact stresses appeared at the engage-in position of the worm pair opposing to the engaging-out position where the largest contact areas appeared. Then the manufacturing of drum worm's spiral tooth was conducted via the modified 4-axis linkage CNC grinder according to the conjugate motion. Finally the novel joint reducer's industrial prototype was assembled. The novel joint reducer with integrated structure of drive, transmission and support was designed and manufactured for the first time. The flowchart of design and manufacture of the reducer's drum worm pair in this process was formulated, which provides a new insight on the research of joint reducers as well as other fields.

Controlling the periodicity of grinding wheel dressing with the application of expert decision support system

The article considers the influence of the grinding wheel dressings frequency on the end product quality after processing; it describes developing of smart algorithms for CNC grinding unit as a part of Expert Decision Support System with software implementation.

Adaptive machining framework for the leading/trailing edge of near-net-shape integrated impeller

As a result of the recently increasing demands on high-performance machining technology in the aero-engine industry, the near-net shape forming technique can be suitable for many integrated impellers. However, the previous forming deformation can raise serious problems for the secondary NC machining of non-formed area, which is mostly applicable for leading/trailing edge (LE/TE) and its adjacent area. It is even worse that non-designed shape and dimension of LE/TE may be responsible for the deteriorated aerodynamic performance and subsequent high in-service cost, especially when its radius is small. Based on previous efforts, this paper presents a 5-axis adaptive machining framework for the LE/TE of near-net-shape integrated impeller. On-machine measurement (OMM) with a touch-trigger probe is utilized to digitalize the impeller. The distribution and uncertainty of sampling points are taken into account with data processing. Through the comparison between the measured and nominal geometric parameters, the impeller profile can be reconstructed sequentially on each tandem cascade. Among this, the camber line deformation emphasizes the functional significance of design intent and the thickness distribution conforms the processed data at most degree. Utilizing the ability to remove small allowance and the low continuous grinding force, the 5-axis CNC grinding with electroplated cubic boron nitride (CBN) wheel is carried out. Moreover, typical examples are used to demonstrate the effectiveness and superiority of this strategy.

Two-Criterion Optimization of Automatic CNC Grinding Cycles

A new method is proposed for optimizing the automatic cycles for wheel grinding with respect to two criteria: maximum productivity and minimum machining cost. The methoyd is based on structural and parametric changes in the grinding cycle on the basis of optimization by dynamic programming.

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Generalized cutting force model for grinding

In CNC grinding operations different surfaces are processed with various types of grinding. Model of cutting force is necessarily used in cutting modes calculating. However, it's impossible to use partial empirical dependences of cutting force for automating of cutting modes calculation because they do not cover all normative space of grinding conditions and are not intended for use in the calculation of automatic CNC grinding cycles. Therefore analytical wide-range models of cutting forces for different types of grinding are needed, but these models should be designed on the basis of common idea of kinematics and physics of metal removal processes. The article proposes the method of obtaining cutting force models for different grinding types, obtained from a generalized analytical wide-range cutting force model, as particular cases for a given grinding type. Generalized model of cutting force is obtained on the basis of fundamental regularities of mechanics of metal' plastic deformation by wheel grains in a cutting zone, kinematic of cutting process by abrasive grains under conditions of temperature and speed parameters during grinding, functionally related with cutting modes, geometrical parameters of a contact zone between a wheel and a workpiece, structural behaviors of processed material, wheel grains blunting.

Optimization of simplified grinding wheel geometry for the accurate generation of end-mill cutters using the five-axis CNC grinding process

A simple geometric and optimal method is adopted for the five-axis CNC grinding of the end-mill cutters. In this research, initially a simplified parametric profile of the grinding wheel is constructed using line segments and circular arcs. The equation of the wheel swept-surface in five-axis grinding is derived. Then subjected to the flute profile design, the profile parameters of the grinding wheel, its relative location, and orientation with respect to the end-mill cutter are optimized, ensuring a specified normal rake angle. Finally, validation of the newly developed method has been performed using the CAD simulation; two virtually ground flutes are measured and compared with the given specifications. The normal rake angle is related with the radial rake angle by a relationship established in this work. This innovative approach can determine the non-standard grinding wheel that can be economically produced or dressed to accurately grind the end-mill cutters using the five-axis CNC grinding process.

A Practical Method of Modelling and Simulation for Ball End Mill CNC Grinding

The spherical cutting edge on the ball end mill directly affects its cutting performance. This paper presents a practical method for end mill rake/clearance face modelling. The rake face is a developed ruled surface to fulfill the desired normal rake angle. Revolution surface of the bottom curve on the rake face avoids the interference between the wheel with the designed rake face while grinding. An equidistance curve of the cutting edge on the sphere is deduced by the geodesic curve in order to adjust the position of the cutting edge. With this new modelling method as a platform, it is very helpful for model modification and contour error compensation. The measurement results show that the average value of contour error on spherical cutting edge of the machined sample is 0.01mm inspected by the tool measuring instrument. Its validity is verified by good agreement between the results computed and the data measured.

Reliability analysis of cooling system of CNC grinding machine based on FTA analysis

In view of the lack of relevant research on CNC grinders in the field of reliability research of CNC machine tools at present, This research collected reliability data based on 19 MSK series grinder machine tools of a machine tool factory., found out the crucial subsystem which is the most important component to the whole, and analyzed the reliability of the subsystem adopting FTA (Fault Tree Analysis) . Statistical researched on 438 reliability data collected, combining with the actual production situation, the results shows that cooling system is the key to the reliability of the whole grinder machine tool. The 29 minimum cut sets obtained by FTA can be adjusted to improve the reliability of the cooling system, what is more, the reliability of grinder machine tool would be improved as well.

Optimization and Analysis of Grinding Head Components Based on MGK-4080 CNC Grinding Machine

The research of CNC grinding machine system has become an important frontier topic in the field of machinery industry. In this paper, the design and optimization analysis of the grinding head components of MGK-4080 CNC grinding machine are carried out. Therefore, the research of this subject has high scientific research value and economic value, which is of great significance to the development of the subsequent grinding machine parts system of CNC grinding machine.

Modeling of Precision Machining for Crankshaft Follow-up Grinder

In this paper, follow-up grinding of crankshaft is studied and the mathematical model of follow-up grinding motion is established. Taking the double grinding wheel crankshaft follow-up grinder as the research object, the motion errors of the machine tool are obtained by analyzing the motion relations among the moving bodies. Based on the kinematics theory of multi-body system, the kinematics model of the whole machine tool is established. The position matrix of any cutting point is described according to the kinematic chain of “bed-workpiece” and “bed-tool”, and the precise machining model of double grinding wheel follow-up grinding machine tool is established by using the coincidence principle of tool actual trajectory and tool path. The coordinate system of each moving body is established, the transformation matrix between moving bodies is obtained, and the precision machining model of double grinding wheel follow-up crankshaft CNC grinding machine is solved, which lays a foundation for error compensation of the machine.

Fiber laser CNC tangential turing V-shaped concave diamond grinding wheel system based on machine vision technology

In order to achieve high-precision V-shaped concave diamond grinding wheel by laser tangential turing, a high-precision laser-inspecting and tangential turing diamond grinding wheel system was built by utilizing high-pixel camera, double telecentric lenses, backlights, CNC grinding machine, and a fiber laser as the main hardware and adopting digital image processing technology as the processing method. The experimental results showed that the depth error rate of compensation turing was approximately 1/2 that of rough turing, and the width error rate was greatly reduced. After compensation turing, all of the evaluation indexes tended to improve. In particular, the error rate of compensation turing was approximately 1/6 that of rough turing. Under the optimized process parameters, the geometric parameters of the V-shaped concave contour and the error average difference were within 3%. Thus, the proposed approach effectively improves the shape and position error of the turing process. The experimental results showed that the system can detect the geometric profiles and size of the grinding wheel accurately and can obtain high turing precision effectively and quickly.

TEMPERATURE MODELS FOR GRINDING SYSTEM STATE MONITORING

The grinding temperature limits the productivity of this operation and is an important parameter for assessing the state of the grinding system. However, there is no information about the current grinding temperature in the existing computer systems for moni-toring and process diagnostics on CNC grinding machines. This is due to the difficulty of measuring this parameter directly or indi-rectly. In the first case – difficulty with the installation of temperature sensors, in the second – there are no acceptable mathematical models for determining the grinding temperature. The objective of the study is development of a simpler temperature model which is acceptable for the modern grinding with large values of the workpiece velocity relative to the grinding wheel. To reach the study objective a classification of solutions of three-, two-, and one-dimensional differential equations of heat conduction with the same initial and boundary conditions was made to research the grinding temperatures with the help of these solutions under otherwise equal conditions. The conditions of results close agreement of the solutions are established depending on the geometrical configura-tion of the contact zone between the grinding wheel and the workpiece: H / L<1 and H>4, where HandL are half width and half length of the contact zone, respectively. The above three solutions of differential heat conduction equations obtained under boundary conditions of the second kind and were converted to a uniform dimensionless form, in which the dimensionless temperature depends on the coordinate and dimensionless time multiplicity of the Peclet number, which characterizes this time, the dimensionless half and velocity of the moving heat source. A comparative analysis of surface and deep temperatures was performed for the above three solu-tions depending on the Peclet number. The possibility of determining the grinding temperature on modern high-speed CNC machines with a one-dimensional solution with H>4 on the basis of computer subsystems of designing, monitoring and diagnosing of grind-ing operations is shown.

Improving the grinding efficiency of the external camshaft sprocket

A new technique and application program for automating the programming of the operation of grinding the cams of the outer sprocket of the limited slip differential on a CNC grinding machine is presented. The program is based on the created digital model of the grinding process, which allows modeling and determining the main characteristic of the process - MRR - Material Removal Rate. The resulting simulation file, containing an array of cutting force data with reference to the polar angle of the sprocket contour, with the help of another specially developed application program, is used to design the law governing the spindle speed of the workpiece, which provides a certain stabilization of the cutting process. Modeling of grinding with this control shows that if the original MRR variation range of the process is preserved, it is possible to increase the productivity of the operation by at least 1.5 times.

Regeneration of industrial cutting blades made from X39Cr13 steel used in skinning process of Pleuronectidae-family flatfishes

One of the important and still current problems occurring in the fish processing industry is the intensive wear of the cutting surface of industrial cutting blades used to separate the fish raw material. In the paper, the proposes a proprietary solution to the above problem consisting in the regeneration of worn surfaces realized in the process of precise grinding by the use of a prototype 5-axis CNC grinding machine was presented. The obtained machining results were verified, among others on the basis of measurements of values of the cutting edges inclination angles and analysis of values of selected surface roughness parameters. The proposed solution along with the developed methodology can be an interesting alternative to typical ways of renewing the cutting ability of cutting tools in applications from the fish processing industry.

Modeling and identification of the error in eccentric axis follow-up grinding machine

Apply the theory of multi-body system, this paper establishes the follow-up error analysis model of grinding machine, and focuses on the study of its error identification method to improve the accuracy of the eccentric shaft servo grinder, providing a theoretical basis for error compensation of CNC grinding machine. And by using nine-line identification method to identify the all 21 items of geometric errors grinding machine translation system three translational axis of, By using the nine line identification method of the translation system to identify the all 21 items of geometric errors about the three translational axis of the grinding machine. Based on the three indicators, axial runout, radial runout and totating error of the rotating shaft, to arrive at the basic geometric error in the direction of six degrees of freedom of the rotating shaft. Motion model of multibody system error is analyzed, and based on the traditional geometry description method of multibody system, putting forward more practical description method on engineering body motion. The ideal movement of engineering object and the motion model under the condition of error are reasonably integrated and analyzed.