Grinding Head Research Articles

Effects of electrolyte flushing and surface state on electropolishing TB2 titanium alloy

TB2 titanium alloys are widely used in the aerospace industry. A high surface quality is required for the performance and fatigue life of titanium alloy parts. Electropolishing is useful for thin metal plates owing to its good processability and conformability. In this study, electrolyte flushing was proposed for electropolishing a large surface and a NaCl-containing ethylene glycol electrolyte was adopted. Three different mechanical grindings were employed for pretreatment, and the ideal surface quality was obtained with a rubber grinding head. Therefore, in the process of electropolishing a large surface, electrolyte flushing is superior to stirring because its flow field is even and controllable. The effects of the main processing parameters (voltage, flow rate, and process time) on the surface roughness and morphology were studied. Finally, a mirror-like surface with a surface roughness of 10.5 nm was obtained after flushing electropolishing for 30 min under a voltage of 25 V and a flow rate of 0.84 m/s.

Повышение эффективности концевого алмазного абразивного инструмента на металлической связке за счет совершенствования технологии изготовления

Introduction. Difficult-to-machine materials with enhanced physical and mechanical properties are increasingly being used in various industries. Such materials are used in mechanical engineering for the manufacture of parts and assemblies of machines and mechanisms, in the production and processing of food products where increased operational requirements are required. In modern production, along with traditional methods of intensifying technological operations, combined and hybrid processing technologies are used. For the finishing of products, abrasive grinding with a diamond tool is used. One of the problems hindering the wide practical application of this method in industry is the fact that it has a high prime cost caused by the cost of materials used in the manufacture and the laboriousness of the tool shaping process. This leads to the need to develop a new technology for manufacturing diamond tools. The purpose of the work is to increase the efficiency of the end diamond abrasive tool with a metal bond by using carbon steels as a body material, increasing the strength of the connection between the body and the diamond-bearing part, as well as choosing an effective tool manufacturing technology. Research methodology. To gain this task, a technology for manufacturing end diamond abrasive tools is developed and tested. Allowing using the technology of capacitor welding to connect the diamond-bearing part with the shank and use medium-carbon hardened high-quality steels with a hardness of 45-60 HRC as the shank material. The strength of the connection of the body with the working diamond-bearing part of the grinding head samples is determined by tensile testing on a 1958U10 tensile machine with maximum load 100 kN. The quality of the joint is assessed visually by the presence of discontinuities in the joint, as well as by examining the microstructure and measuring the microhardness of the weld and heat-affected zones. The microhardness of the welded joint is measured using an HMV-G21ST semi-automatic microhardness tester (Shimadzu, Japan) at a load of 50 g. Results and discussion. Thus, the results of comparative studies allow us to assert that the strength of the connection between the shank and the working diamond-bearing part according to the proposed technology surpasses similar characteristics of the strength of the connection between the shank and the diamond-bearing layer of grinding heads obtained by the method selected by the prototype. Conclusions. The proposed technology for the manufacture of diamond heads increases the strength of the connection between the body and the diamond-bearing working part, reduces the cost of manufacturing the grinding heads due to the use of hardened medium-carbon steels as the material of the tool body instead of high-speed steel grades, the technology is simplified and the possibility of automating the manufacture of tools appears.

Accuracy analysis in mobile robot machining of large-scale workpiece

• The accuracy analysis for mobile robot machining of a large wind turbine blade has been proposed. • The tool center point (TCP) error index is defined as the distance between the TCP and the designed machining point to evaluate the machining error qualitatively. • The optimal mobile robot machining strategy is proposed based on the accuracy analysis. Mobile robot machining provides more flexible machining mode compared to the robot machining with a fixed base. However, its machining accuracy is frequently questioned. This paper focuses on the accuracy analysis in mobile robot machining. To evaluate the machining error qualitatively, the tool center point (TCP) error index is defined as the distance between the TCP and the designed machining point. The different error sources acting on the TCP error index are enumerated, and the theoretical accuracy analysis is proposed to eliminate the TCP error. The mobile robot machining strategy is then proposed based on the accuracy analysis. To ensure high machining accuracy, the global measurement system locates the position of the workpiece and the mobile platform. The force-controlled grinding head is used to compensate the TCP error. Experimental results show that the TCP error during mobile robot machining is lower than 40 mm, which mainly introduced by the calibration of the workpiece. The force-controlled grinding head can compensate the TCP error and the fluctuation of the grinding force under the control is lower than ±2 N.

Fine module hobs for processing cylindrical involute gears

Aspects of formation of a hobs cutting part for processing of gear wheels are considered. In the traditional manufacture of hobs for processing the rear surfaces of cutting teeth, the process of radial or oblique relieving is used, which due to its dynamic nature associated with reciprocating motions of a grinding head with a grinding wheel installed thereon, makes it difficult to ensure high accuracy of teeth pitch and profile, as well as main hob parameters. These shortcomings are effectively eliminated by using the process of screw relieving to process the lateral rear surfaces of the hob teeth. Execution of a hob teeth profi le in the form of a gear rack enables to obtain a hob for processing gear wheels. A number of formulas are given, by means of which it is reasonably proved that hobs made using the considered principle of formation of teeth back surfaces can have a high class of accuracy — AA or AAA. Calculations showed that the displacement of the hob teeth at two revolutions of the main worm screw with a probability of 0.9973 does not exceed 0.13 μm, which is signifi cantly higher than the requirements of GOST 10331-81 for hobs with AAA accuracy class (not more than 4 μm for hobs with a pitch over 0.5 to 0.9 mm). The considered method of forming the hob rear surfaces in the form of counter right and left multi-turn screw surfaces (screw relieving) allows to obtain hobs not only for machining involute gears, but also other types of cutters, e.g. for machining threads, ratchet wheels and other parts having a regular profile.

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。

Geometric characteristic modeling for flexible contact of sanding wheel–polished complex surface

The blade profile of a milled aeroengine blisk is a spatial free-form surface with significant curvature changes, which seriously restrict the quality uniformity of the polished surface. To investigate the geometric characteristics of the flexible contact of an elastic grinding tool–polished complex surface, a polishing process equipment integrating “CNC machine tool + flexible grinding head + elastic grinding tool” was used in this study. Through an analysis of the geometric theory, a mathematical model for the boundary between the sanding wheel and polished surface in the contact zone, a mathematical model for the compression amount in the contact zone, and a mathematical model for the removal depth were established to conduct simulation and polishing tests. The results show that both the compression amount of the sanding wheel and curvature radius on workpiece surface have remarkable effects on the boundary and removal depth in the contact zone; the feed speed, rotation speed, and particle size of the sanding wheel have no bearing on the boundary in the contact zone, but they can influence the removal depth markedly. The simulation results are basically consistent with the test results, proving that the established models are reliable and applicable to geometric characteristic prediction of the elastic grinding tool–polished complex surface.

Transfer of functional structures from multiple bovine teeth to a multilevel grinding head via a biomimetic approach

It is highly desirable to improve the crushing performance in powder processing. This study presents a bionic multilevel grinding head for a grinder inspired by the natural friction pairs of bovine teeth. The mechanism of adaptive mastication for various teeth in bovine dentition was revealed, and the main functional structures of the incisor and molars were extracted to construct the biomimetic multilevel surface. To optimize bionic structure parameters, a discrete element method was introduced to simulate the crushing process, and surrogate models that respond to the breakage rate and heat production were constructed and solved. Compared with the conventional multilevel grinding head, highly efficient crushing effects were achieved for the bionic type. Furthermore, its efficient crushing mechanism was discussed.

Diagnostic of spindle units on rolling bearings based on measuring of the housing vibrations

The analysis of modern methods of accuracy and technical condition evaluation of spindle units on rolling bearings has been performed. The prospectivity of measurements in the resonant vibrations zones is assessed. To evaluate the accuracy and technical condition of spindle units on rolling bearings at the stages of manufacturing and maintenance, it is proposed to use the previously developed method for indirect measurement of resonance vibrations of the spindle, based on spindle quill vibration measurement of the spindle units with subsequent calculation of spindle vibrations (mandrel installed in the spindle) using theoretical compliance function. Usage of this method in accuracy and diagnosing defects identification in manufacturing and assembly of the spindle units, a theoretical justification of the measurement schemes is given, the dynamic model of the test rig is adapted, and the corresponding research methods are developed. The general experimental part of research methods provides for: determining the first natural frequency of the test rig frame; determination of spindle speeds corresponding to frame resonant vibrations as a result of manifestation of manufacturing and assembling defects of the spindle unit; spindle quill vibrations measurement at these rotational speeds. The general theoretical part of the methods assumes: the calculation of dynamic compliance and the compliance function which connects mandrel and spindle quill subsystems vibrations; mandrel vibration spectra calculation from the experimental vibration spectra of the spindle quill and determination of the relative vibrations amplitudes of the mandrel at the forced vibrations characteristic frequencies. Based on the results, depending on the task, a 3D spectrum of vibrations or a spindle rotation error diagram in a given range of rotation frequencies is calculated. The results of evaluating the accuracy and technical condition of the grinding head at idle and under load are presented.

ANALYSIS OF THE MACHINING SCHEME OF COMPLEX-PROFILES SHELLS OF ROTATION

Modern engineering products have complex geometry with high quality requirements, are made from new materials that is provoked the development and use the mechanisms of parallel structure, which are distinguished by high rigidity characteristics, as well as have wide functional capabilities. The precision problems of machining of complex-profile low-rigid parts, in particular thin-walled pyroceram shell are considered in article. Scheme of machining affect the accuracy and depends on the capabilities of technological equipment. Rationale for scheme of machining a thin-walled casing is presented in article. The accuracy of machining the outer profile of the casing was simulated for last step of diamond grinding. The simulation was performed for a traditional scheme of machining, which is performed for a lathe with an aggregate grinding head and a direct copying system, and for a scheme of machining for equipment that is fitted out with a mechanism with a parallel structure. The model of formation of the machining error is based on using the equations of relative displacement of the technological bases of the workpiece and the contact point of the working surface of the diamond wheel with the workpiece. The model takes into account the static and dynamic characteristics of the technological system and force factors during grinding. The calculations have confirmed that proposed solutions are able to provide the necessary machining precision. Changing the machining scheme of the workpiece and performing such machining on equipment with mechanisms of parallel structures eliminates the basing error, increases the rigidity of the technological system, and provides the possibility of turning the axis of the diamond wheel with the required angle.

An optimization study of polishing efficiency of blisk and its technological parameters.

When applied to blisk blade profile polishing of aero-engines, "five-axis NC + flexible grinding head + elastic grindstone" polishing technological equipment has advantages of high precision, minor interference, favorable adaptivity, etc. In order to improve the polishing quality and polishing efficiency, a mathematical calculation formula of polishing efficiency was established according to the polishing principles of elastic grindstone (sanding wheel). The optimized combination of technological parameters (ω = 6000 r/min, ap = 0.9 mm, vf = 320 mm/min) was obtained through the range method of orthogonal test results with double optimization objectives-surface roughness and polishing efficiency. Based on the relationship between number of polishing times and surface roughness, a technological program was put forward, that is, polishing is firstly conducted using 320# sanding wheel for 6 times and then 400# sanding wheel for 9 times (totally 15 times) under the optimized combination of technological parameters, then surface roughness less 0.4 μm can be achieved. Blade polishing test results indicate that: efficiency-optimized technological parameters can not only significantly shorten polishing time but also acquire qualified blade surface roughness less 0.4 μm, thus verifying reliability of the optimization method and results.

Design and Dynamic Performance Study on Hydrostatic Lubrication System of High-speed Precision Roller Grinding Head

To meet the need of high-speed steel roll grinding, a hydrostatic lubrication system for high-speed precision roller grinding head is designed and the dynamic performance of the system is simulated and analyzed in this study. The hydrostatic lubrication system was designed according to the lubrication characteristics of the eccentric sleeve and thrust bearing of the high-speed precision roller. Then the mathematical models of the main components of the system were established. And according to the schematic diagram of hydrostatic lubrication system, the dynamic performance of the lubrication system at high speed was simulated and tested. The simulation and experiment results show that the lubrication effect of the eccentric sleeve static chambers and thrust bearings is good, and the designed hydrostatic lubrication system is feasible.

Bionic-tribology design of tooth surface of grinding head based on the bovine molar

Abstract This paper presents a new bio-inspired grinding head based on the natural friction pair of bovine molars. According to the morphology analysis and chewing simulation, the infundibulum dentis and dental star were selected as biological coupling elements, and their characteristic parameters were extracted, characterized and optimized for surface structure design of the grinding head. Compared to the commercial grinding head, the bio-inspired grinding head has higher crushing efficiency verified by the experiments on grinding the same food products.

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.

ТЕХНИКО-ЭКОНОМИЧЕСКОЕ ОБОСНОВАНИЕ ЭФФЕКТИВНОСТИ ПРИМЕНЕНИЯ ПЛАНЕТАРНЫХ ШЛИФОВАЛЬНЫХ ГОЛОВОК

The development of aviation technology is based on the introduction of new progressive technologies, the use of new materials, the improvement of technological equipment and tools. Improving aircraft engines often leads to greater use of wear-resistant, heat-resistant, heat-resistant materials based on nickel and titanium, which are characterized by low machinability. Blade processing of such alloys faces many difficulties: increased equipment wear, increased machine setup time for the operation, high cutting forces, increased wear of the cutting tool, increased processing time, etc. All this harms productivity, an increase in production time and a decrease in economic efficiency. The use of the operation of creep feed grinding instead of blade milling operations, pulling, planning and abrasive operations (pre-grinding, final grinding) reduces the time to manufacture parts while maintaining its quality and accuracy. The study of the technical and economic aspect of the proposed technology of creep feed grinding instead of preliminary and final grinding operations is of interest. The paper compares two methods of abrasive machining: traditional grinding and creep feed grinding on the SPD-30B surface grinder from Jotes (Poland) with a planetary grinding head (PGH) installed on its spindle. The study was conducted when grinding the castle part of turbine blades. The removable allowance was 3.8 mm. The processing according to the traditional grinding scheme took place in 10 passes, while the processing time was about three and a half minutes. The processing under the scheme of creep feed grinding with the use of PGH for 4 passes took about a minute of machine time. It should be noted a significant increase in productivity at the first transition when removing an allowance of 3.5 mm in the mode of deep grinding compared to traditional grinding 2.1 times. On the second and third transitions, the performance of both methods is virtually the same.

Investigation of surface topography formation mechanism based on abrasive-workpiece contact rate model in tangential ultrasonic vibration-assisted CBN grinding of ZrO2 ceramics

Ultrasonic vibration-assisted grinding is widely used as a highly efficient processing method for hard-and-brittle materials such as zirconia ceramic materials. Based on the characteristics of ultrasonic vibration assisted intermittent machining, combined with the motion characteristics of the single abrasive particles and adjacent abrasive particles, the abrasive grain-workpiece contact rate model between abrasive particles and workpieces during ultrasonic vibration assisted grinding is proposed. The grinding force, surface quality and the life of the grinding head are directly affected during the machining process. In the ultrasonic vibration assisted grinding process, the non-periodic distribution of the contact and separation between the grinding head and the workpiece is reflected, which increases the complexity of analysis in the ultrasonic vibration assisted grinding process. According to the model, the influence of machining factors (cutting speed) and vibration factors (amplitude, frequency) on the contact rate is analyzed. In addition, a contrast experiment is designed to analyze the surface morphology between ultrasonic vibration assisted grinding and common grinding. And the surface quality is effectively improved by using ultrasonic vibration. Besides, a four-level and four-factor orthogonal experiment is designed. The surface roughness prediction model is established on the basis of the neural network of genetic algorithm, and the validity of the model is verified by the experiment.

The grinding force modeling and experimental study of ZrO2 ceramic materials in ultrasonic vibration assisted grinding

As an advanced structural ceramic, zirconia ceramics are gradually used in the fields of manufacturing, aerospace and other fields with their excellent properties. However, the mechanism of material removal is complex for zirconia ceramics but it is generally accepted that the brittle-and-hard material is removed by plastic removal and brittle removal. In this paper, ultrasonic vibration assisted grinding is used as non-traditional processing to machine the ceramic materials. Firstly, a single abrasive grain scratch test was first carried out on the ZrO2 ceramic materials. It can be obtained through experimental analysis that the removal mode of the zirconia ceramic material is changed with the increase of load. When the applied load is greater than 500 mN, the zirconia ceramic materials are removed by brittle removal. Then, based on analysis of scratch test and kinematics of ultrasonic vibration assisted grinding (UVAG), a grinding force prediction model is developed and the validity of the model is verified by the experiment designed. It can be found that the grinding force is decreased with the increase of spindle speed (n) and amplitude (Aa). And the grinding force is increased with the increase of feed rate (vf) and grinding depth (ap). In addition, compared with the grinding force of the common grinding (CG), the grinding force is significantly reduced in the UVAG. And the surface quality of the workpiece is improved and the wear of the grinding head is reduced in the UVAG by the analysis of experiment.

Experimental studies of the grinding process by planetary grinding head

The object of research is the process of creep feed grinding of parts of aircraft engines with hard-to-machine materials. In the aviation industry from such materials (steel 4Х5МФ1С, ХН53КВМТЮБ, etc.) blades and disks of turbines, segments of nozzle apparatuses, sectors of input guide vanes, plungers, pistons, gears, etc. similar details are made. Blade processing methods are not very effective in creating such parts. Increased wear of technological equipment and tools leads to an increase in temperature in the cutting zone, adversely affects the quality indicators and reduces the life of the product as a whole. Constant sharpening, editing or changing the tool to a new, additional adjustment of the process equipment leads to an increase in the cost of manufacturing parts from difficult-to-work materials. The introduction of creep feed grinding in technological processes allows to avoid the above negative factors. The increase in the technological modes of grinding reduces the processing time, but it becomes a cause of burn in the surface layers and damage to the processed surface. Experimental studies of the process of creep feed grinding are carried out to determine the temperatures in the subsurface layers of the part during its processing and subsequent comparison with the theoretically obtained results of the developed mathematical model. Processing was performed on a surface grinding machine Jotes SPD-30b (Poland). The temperature is measured by the contact method (measuring instrument ОВЕН МВА 8, Russia) and contactless (using a pyrometer СТ 3M, Germany). The results of the experimental temperature values are given in tabular form. According to the research results, it is found that the use of a planetary grinding head for the technology of creep feed grinding of machine-building and aviation parts of difficult-to-process, corrosion-resistant materials leads to a decrease in the power-process parameters. In addition, there is an improvement in the surface cleanliness class (surface roughness Ra is between 1.25-1.8 μm). The results suggest that the technology of creep feed grinding should be introduced into technological processes instead of milling, external pulling and traditional grinding.

Investigation of mechanics and machinability of titanium alloy thin-walled parts by CBN grinding head

A force model of machining TC4 titanium alloy thin-walled part is developed based on the actual geometry and abrasive characteristics of CBN grinding head in this paper. Then, the single factor experiment illustrates that the grinding force increases with the increase of the grinding depth and feed rate, while it decreases with the increase of the spindle speed. And the contrast experiment results show that new improved grinding head is beneficial for reducing the force compared with common grinding head. On the basis of the mechanics analysis, the chatter stability of grinding thin-walled parts is studied based on the modal tests of titanium alloy thin-walled parts and grinding head, and the stability lobe diagrams are finally drawn as well by considering the radial grinding depth. In addition, further research indicates that the surface roughness of vertical side wall surface and surface micro-hardness is determined by several key parameters including spindle speed, feed rate, and cutting depth in grinding process based on analysis of experiments. An optimal combination of these parameters is of great benefit to achieving better surface of the parts.

Mobile System for Restoring the Sealing Surfaces of Pipeline Valves

A single-disk grinding head with simple primary kinematics does not ensure satisfactory machining of the sealing surfaces of pipeline gate valves. New multidisk grinding heads are considered.

Experimental study on the affecting factors of compensating blocks for repairing EDM abrasive electrode

Aiming at the problem of electrode wear during EDM, a method of instantaneous repairing EDM abrasive electrode with compensation block was proposed, taking relative mass wear as research index. The results show that diamond abrasive electrode is processed by intermittent spray cooling at 1mm / min feed rate, and the adhesion layer appears on the surface of abrasive electrode. The experimental results show that the relative wear of the electrode with compensation block is lower than that of the electrode without compensation block by comparing the relative wear value of the electrode with different speed, voltage and duty cycle for the 304 stainless steel processed by EDM abrasive electrode 0.7 times. The method of adding compensation block shows that the electrode grinding head can be compensated online to some extent.