Gear Grinding Research Articles

Digital twin modeling for loaded contact pattern-based grinding of spiral bevel gears

To distinguish with the conventional tooth flank grinding only considering geometric accuracy, an innovative digital twin modeling is proposed for loaded contact pattern based grinding of spiral bevel gears. Where, data-driven grinding simulation, sensitivity analysis strategy, adaptive decision and control are developed. Focusing on loaded contact pattern optimization, numerical loaded tooth contact analysis (NLTCA) considering noncentrosymmetric problem and tooth flank roughness is developed for data-driven relationship establishment. Then, an adaptive data-driven tooth flank grinding decision and control model is established. Where, the universal motion concept (UMC) machine settings is selected as the optimal design variable. It is actually an infinite approximation to the target tooth flank in form of an adaptive control system. Moreover, with point-to-point material removal distribution, the different optimization strategies are proposed for accurate tooth flank grinding. In particular, the overcutting problem on the tooth flank grinding programming is investigated. Finally, Levenberg-Marquardt method is applied to solve the established nonlinear lease square model for the accurate machine tool settings having modification variations. Thus, this accurate data-driven digital twin modeling can achieve loaded contact pattern-based grinding. The provided numerical and test instances can verify the proposed digital twin modeling.

MODERN METHODS OF GEAR MILLING OF HARDENED LARGE-MODULE GEARS

The latest developments of modern methods of high-speed gear milling of large-module cylindrical gears, both for preliminary grinding of teeth and for final blade processing of gears, are considered. For high-speed blade gear processing, promising designs of worm carbide cutters have been developed, manufactured and implemented. The technological regulations of blade gear processing for the operation of each of the design solutions of worm carbide cutters have been developed. The design of a special double-body worm cutter for double-sided cutting has been developed. It is shown that the carbide cutting elements of the milling cutters, which are placed only along the lines of the machine engagement of the tool and the workpiece, make it more economical compared to the known designs of similar tools. The application of the developed technological methods of pre-blade processing of the teeth of hardened wheels with carbide cutters reduces the labor intensity of low-performance gear grinding operations, depending on the wheel module, by 3-4 times by reducing the allowance from 1.5–2.5 mm on the tooth side to 0.3–0.5 mm, and also allows you to ensure the gear processing process is economical by reducing the consumption of carbide plates. The developed technological studies of ensuring the quality of gear processing of large-module cylindrical wheels allow us to solve the scientific and technical problem associated with the production of large-module gears with high-hardness teeth while improving the quality of their manufacture, reducing labor costs and reducing material consumption.

ПОВЫШЕНИЕ ТЕХНОЛОГИЧЕСКИХ ВОЗМОЖНОСТЕЙ МЕТОДА НЕПРЕРЫВНОГО ОБКАТНОГО ЗУБОШЛИФОВАНИЯ

The work purpose consists in the technological capacity updating of the method for cog-wheel continuous run-in gear grinding based on the purpose of efficient modes and characteristics of the worm disk. 
 The investigation methods are based on mathematical modeling and planning experiments. Machining aircraft cylindrical cog-wheels and special samples was carried out on modern NC machines, benches and plants with the use of up-to-date test equipment: coordinate inspection machine KIM R-100 “Klingelnberg”, profile meter MarSurf M300S “Mahr”, optical microscope Axiovert 400MAT “Zeiss”, electronic scanning microscope Tescan Mira3 “Tescan”, micro-hardness gage Micro Met 5104 “Buehler”, X-ray diffractometer Xstress Robot “Stresstech OY”, Barkhausen digital nose analyzer
 Rollscan 350 “StresstechOY”, plant APOON on the well-known and developed techniques. 
 The research results and novelty. Special strategy and cutting modes at the required characteristics of the combined polish-grinding worm allow ensuring gear profile roughness Ra=0.089 mkm keeping high accuracy of a ring gear (gear profile error Fa=1.6mkm) without gear honing thereby increasing productivity. The quality researches of gear surface layer give grounds for the application of the method for aircraft cog wheels.

Prediction and control for local bearing contact-based collaborative grinding of non-orthogonal aerospace spiral bevel gears

It is very different with the recent tooth flank grinding, an innovative collaborative optimization considering both geometric accuracy and local bearing contact evaluations is proposed for non-orthogonal aerospace spiral bevel gears. In particular, its data-driven prediction and adaptive control is developed. Firstly, tooth flank grinding using double helical method is simulated to establish mathematical model of the whole tooth flank including work flank and root fillet. Then, prediction of local bearing contact evaluations including geometric topography, loaded contact pressure and loaded contact deformation is performed by correlating with numerical loaded tooth contact analysis (NLTCA). Where, loaded contact pressure and its distribution considering time-varying meshing characteristics are developed, respectively. Moreover, an adaptive collaborative control model is established by extending the conventional machine tool settings modification only considering geometric accuracy to case that collaborative optimization. In the normal direction, loaded contact deformation of material removal point is predicated in the geometric accuracy control. In tooth flank tangential plane, the material removal points are constrained within the prescribed boundary. Finally, the sensitivity analysis strategy is used to select the optimal design variables, and control mode is solved for accurate machine tool settings. The given numerical instances can verify the proposed method.

Investigation on Precision Finishing of Helical Gears Using Newly Developed Silicon Carbide Mixed Styrene Butadiene Media and Abrasive Flow Finishing Process

The good surface finish of gears is one of the critical parameters which leads to its noise-free operation, efficient power transmission, and longer service life. However, most of the gear manufacturing processes do not produce a good surface finish. Therefore, gears need post-processing to finish their surface. Out of several methods of gear finishing like gear grinding, lapping, and honing, the abrasive flow finishing process offers more flexibility due to its self-deformable abrasive medium which can easily flow across complex internal or external geometry. The present study aims to improve the surface finish of helical gear by abrasive flow finishing (AFF) by experimentally identifying the optimum range of the potential input process parameters. An AFF set up was used for gear finishing by using a medium of styrene-butadiene and soft silicone polymer, Silicon carbide abrasive, and silicone oil as a blending agent. A special fixture was developed comprising of five parts namely spider, mandrel, upper, middle, and bottom cylinder with a circumferential hole, which allows the back and forth movement of AFF medium through the annular volume between fixture and gear. Further, an experimental investigation of process parameters like viscosity, effect of percentage of various components in medium, operating pressure, and helix angle of helical gears have been studied on percentage improvement of surface roughness (Ra) value of the gear. It is found that the concentration of abrasives in media and extrusion pressure were the two most significant parameters that have a maximum effect on the percentage reduction in surface roughness and finishing rate. Results show that the optimum combination of the extrusion pressure and abrasive weight percentage is 38 bar and 40 % that produces best results of around 76 and 69 % improvement in Ra for gear of helix angle 30 degree and 45 degree respectively.

Determination of allowances at continuous running-in grinding of teeth of cylindrical wheels

A computational and analytical method for determining the allowances on the lateral surface of the teeth of cylindrical wheels is developed. Experimental studies carried out on a modern gear grinding machine using a highly porous abrasive wheel made it possible to give recommendations on determining the optimal values of allowances depending on the modulus and pitch circle diameter of cylindrical gear wheels. Keywords: gear grinding, grinding wheel, allowance, dressing, balancing, teeth accuracy alexandr_kalashnikov45@rambler.ru

Determining the actual form diameter of the helical gears according to the results of 3D scanning

The most universal method of measuring machine parts is optical scanning by specialized optical systems. The scanning results are presented as a 3D model of the scanned part based on clouds of obtained points on the real surface of the part elements. As a rule, the model is directly compared with the nominal model of the part by building color maps of deviations of the actual surfaces of the parts from the nominal ones. However, a direct comparison is not effective in the case of a decision of a task of finding explicit indicators of the accuracy of the details. The article presents a method for determining the boundary points of the fillet curve of the tooth leg of cylindrical gears based on the data of the end section of the scanned model of the gear wheel. The results of finding the form diameter of the fillet curve obtained after the operations of gear milling and gear grinding are presented. In contrast to the results of measurements of gears on a gear measuring machine, the value of the diameter of the boundary point is directly located, therefore it is less likely to make an incorrect conclusion based on the analysis of the standard profilogram of tooth profiles. Using this method, you can use optical scanning systems that are more common and cheaper than specialized machines to find the size.

Investigation of Mechanical Loads Distribution for the Process of Generating Gear Grinding

In grinding, interaction between the workpiece material and rotating abrasive tool generates high thermo-mechanical loads in the contact zone. If these loads reach critically high values, workpiece material properties deteriorate. To prevent the material deterioration, several models for thermomechanical analysis of grinding processes have been developed. In these models, the source of heat flux is usually considered as uniform in the temperature distribution calculation. However, it is known that heat flux in grinding is generated from frictional heating as well as plastic deformation during the interaction between workpiece material and each grain from the tool. To consider these factors in a future coupled thermomechanical model specifically for the process of gear generating grinding, an investigation of the mechanical load distribution during interaction between grain and workpiece material considering the process kinematics is first required. This work aims to investigate the influence of process parameters as well as grain shape on the distribution of the mechanical loads along a single-grain in gear generating grinding. For this investigation, an adaptation of a single-grain energy model considering the chip formation mechanisms is proposed. The grinding energy as well as normal force can be determined either supported by measurements or solely based on prediction models.

In‐process evaluation of continuous generating gear grinding for maintaining workpiece quality and acoustic behavior of gear wheels

AbstractHard finishing of gearings such as continuous generating gear grinding is highly essential for manufacturers due to increasing demands on gearboxes regarding quality and economical aspects, especially in the growing field of electric mobility. Here, high requirements on the acoustic behavior and low production cost come into conflict in the last stage of manufacturing gearings in a particular way. Against this background, in‐process evaluation methods for manufacturing processes are developed in order to reduce scrap parts and to exploit the process limits by collecting and processing of sensor signal data and by adapting measures based on reasonable process models. This investigation shows how the condition of abrasive tools and workpiece quality are evaluated by means of process near acoustic emission sensor application and motor current of the grinding spindle in order to adapt shifting and feed movement in generating gear grinding process. A calculation method based on a simulation process model is introduced to characterize relevant vibration frequency bands and the resulting acoustically effective waviness on tooth flanks, depending on workpiece and process parameters. Appropriate adaption of the grinding process for increasing productivity while maintaining workpiece quality is based on the findings of an intelligent in‐process evaluation.

Potentials of Vitrified and Elastic Bonded Fine Grinding Worms in Continuous Generating Gear Grinding

Continuous generating gear grinding with vitrified grinding worms is an established process for the hard finishing of gears for high-performance transmissions. Due to the increasing requirements for gears in terms of power density, the required surface roughness is continuously decreasing. In order to meet the required tooth flank roughness, common manufacturing processes are polish grinding with elastic bonded grinding tools and fine grinding with vitrified grinding tools. The process behavior and potential of the different bonds for producing super fine surfaces in generating gear grinding have not been sufficiently scientifically investigated yet. Therefore, the objective of this report is to evaluate these potentials. Part of the investigations are the generating gear grinding process with elastic bonded, as well as vitrified grinding worms with comparable grit sizes. The potential of the different tool specifications is empirically investigated independent of the grain size, focusing on the influence of the bond. One result of the investigations was that the tooth flank roughness could be reduced to nearly the same values with the polish and the fine grinding tool. Furthermore, a dependence of the roughness on the selected grinding parameters could not be determined. However, it was found out that the profile line after polish grinding is significantly dependent on the process strategy used.

Characterization of vibration in continuous generating grinding and resulting influence on tooth flank topography and gear excitation

Besides harmonic meshing frequencies, excitation behavior of gears is highly affected by micro geometry of tooth surface caused by waviness on gear flank topography. Errors in finishing processes like continuous generating gear grinding are examined to demonstrate their impact on gear flank topography under consideration of characteristic waviness with a simulation model. Results of an experimental investigation on manufactured topography and measured transmission error show well correlation with the model. The pursued analysis of characteristic cutting volume in frequency domain of systematically considered process errors is a reasonable step towards the prediction of process conditions in the manufacturing process.

Physics-based vibration feature for detecting eccentric workpiece/runout faults during continuous generating gear grinding processes

Continuous generating gear grinding is a well-established and widely used process in the industry for large-scale production gears. It offers an economic/efficient process for finishing gears, which shapes the micro-geometry of the gear tooth flank and improves its surface quality. The resulting quality of ground gears depends on several factors, namely the tool performance, the machine stability as well as the correct clamping/positioning of the workpiece. The grinding step is very crucial since it has a direct impact on the operating quality of gears and in particular on the running noise behaviour of the end product. The potential of online vibration-based gear grinding monitoring has been explored and demonstrated in the previous work (Gryllias et al., 2017) as a means of quality control that could lead to the overall reduction of production losses and to the prevention of sending defective parts to customers. Several features which could be used to monitor the grinding processes and to identify a specific type of defects have been proposed & experimentally validated to some extent. The types of faults include (i) high feed rate, (ii) high infeed, (iii) non-flat workpiece, and (iv) eccentric workpiece. However, a further investigation on a new test campaign revealed that none of the features developed in (Gryllias et al., 2017) was robust enough to detect eccentric workpieces during the grinding process. It is worth mentioning here that an eccentric workpiece fault is unlikely to happen, but it is analogous to a runout on the incoming workpiece quality. In this paper, a qualitative model to predict the vibration signature due to eccentric workpieces/runouts is developed and discussed. Based on the qualitative understanding, a novel feature to detect eccentric workpieces/runouts during gear grinding processes based on vibration signals has been developed. The newly developed feature has been validated on real vibration signals captured during the emulation of process malfunctions on an industrial gear grinding machine. In this study, it is shown that the novel feature seems sensitive and robust for detecting workpiece eccentricities/runout errors of about more than 60 µm. It is also shown in this study that the feature is insensitive to other types of gear grinding faults, which is important for diagnostics/root-cause analysis purposes.

COMPLEX-SHAPED PARTS GRINDING TECHNOLOGY INFORMATION ENSURING

A method of computer-aided design and manufacture of complex-shaped parts of machines and implants from difficult-to-machine materials (titanium, cobalt-chromium alloys, zirconium dioxide, etc.) has been developed, based on the principles of building an integrated CAD/CAM/CAE system of computer-aided designing and a hierarchical intelligent numerical control system. It is shown that kinematical mechanisms created over the past several centuries do not allow reproducing with the required accuracy the joints movement of living organisms for their use in biomedical implantation technologies. Therefore, the worn out joints of living organisms are reconstructed by adding complex-shaped parts from these difficult-to-machine materials. Information about the geometric shape of these parts (3D model) at the pre-production stage is obtained using modern methods of computed tomography and magnetic resonance imaging, and at the production stage the actual location of the stock grinding allowance is measured by laser (or tactile) scanning. To reduce the unevenness of the position of the grinding stock allowance, the workpiece of a complex-shaped part before grinding is oriented in the coordinate system of a CNC machine based on the established criterion for minimizing the allowance. An example of such orientation of the gear workpiece is given. This workpiece is measured with a Renishaw tactile probe on the left and right sides of the gear valleys before gear grinding. Both the minimum allowance on the left and right sides of the valleys and the difference between them are determined, and then additionally the gear wheel blank is rotated in the appropriate direction to align these minimum values detected. In turn, the aligned minimum allowances, should be sufficient to compensate for the influence of technological factors from the previous operation and the error in setting the workpiece for this operation. For complex-shaped implants, such an additional orientation is performed, for example, according to algorithms for ensuring the minimax value of the allowance.

Dynamic model identification for CNC machine tool feed drives from in-process signals for virtual process planning

Virtual process planning offers advantages in terms of predicting servo and contouring errors ahead of time, and taking corrective action by modifying the program or CNC parameters. Successful application of virtual process planning requires accurate models that capture the dynamics of feed drives. Identification of such models is typically time consuming.This paper presents a pole search method used in conjunction with least squares (LS) projection technique for identifying virtual machine tool drives. Compared to earlier research published in rapid identification, and the generic system identification method (i.e., a two-stage instrumental variable method), the parameter convergence has been improved significantly. This is achieved by reducing the number of unknown variables solved during LS estimation from eight to four (corresponding to each candidate pole triplet), and by avoiding the use of noisy position measurements and their time derivatives in the LS matrix pseudo-inversion. As a result, virtual feed drive models can be constructed using only in-process gathered data, without interrupting a machine tool's production for dedicated identification tests. Effectiveness of the new method is demonstrated in simulations and experimental case studies on two different machine tools, a gear grinding machine, and a 5-axis machining center. With the new method, servo errors can be predicted during the process planning stage to within 1-2% of closeness of their actual (experimental) values.

Geometric error identification and compensation for rotary worktable of gear profile grinding machines based on single-axis motion measurement and actual inverse kinematic model

Gear profile grinding accuracy is often restricted by geometric errors of the rotary worktable. This paper proposes a novel approach to improve the geometric accuracy of the worktable based on single-axis motion measurement and the actual inverse kinematic model (IKM). The volumetric error model of gear profile grinding machines is first established based on homogeneous transformation matrices (HTMs) and machine kinematic chains, and the actual IKM based compensation method is then proposed to offset the position-dependent geometric errors (PDGEs) of the worktable. It directly gives explicit analytical expressions of compensated motion commands for efficient compensation. Besides, a novel PDGEs identification approach based on single-axis motion measurement with a double ball bar (DBB) is presented for the worktable. This approach has improved identification accuracy and stronger robustness as the interference error of non-targeted axes is avoided. The influence of the installation errors of the workpiece ball on measurement results and the PDGEs on gear grinding errors were discussed. The experiments verified the effectiveness of the identification approach, and the geometric accuracy tests of the worktable validated the compensation method.

An efficient generation grinding method for spur face gear along contact trace using disk CBN wheel

In order to further improve the grinding efficiency of face gear, this paper presents a novel method for grinding face gear along contact trace using disk CBN wheel. Firstly, the grinding principle of face gear is studied, and the tooth surface equations of rack and gear shaper cutter are derived, thus formulating the tooth surface equation of disk CBN wheel. Secondly, considering the structure of the face gear grinding machine tool and the impact of the grinding wheel parameters on the face gear tooth surface, the disk CBN wheel configuration is proposed, and the calculation method of the tool position of the face gear grinding is established. Thirdly, according to the structural characteristics of the grinding wheel, the tooth surface contact trace of the face gear is designed, and the face gear development grinding processing method along the tooth surface contact traces is presented. Finally, a test of grinding spur face gear with disk CBN wheel is carried out on a laboratory-made five-axis face gear processing machine. The test results verified the correctness of the face gear grinding. Compared with the dish wheel for grinding face gear, the grinding method proposed in this paper can further improve the grinding efficiency of face gear. This method will break new ground for the engineering application of the face gear.

Analysis and experimental study of cycloid gear form grinding temperature field

Form grinding is the finishing process of the cycloid gear of RV reducer. In order to avoid the tooth surface burn of the cycloid gear during the grinding process and improve the grinding efficiency, the heat distribution ratio and the convection heat dissipation coefficient during the grinding process are calculated. The computer simulation software ANSYS 17.0 is used to calculate the instantaneous temperature field of the tooth surface during the grinding process of the cycloid gear. The distribution of the instantaneous temperature field of the tooth surface along the axial of the gear is obtained. According to the characteristics of the YK7350B gear grinding machine, the grinding process parameters is reasonably selected, and the grinding experiment is carried out. The metallographic structure of the burned section of the experimental part was observed by the ProgRes C5 metallographic measuring instrument to verify the simulation results. The research is beneficial to predict the temperature field distribution of the tooth surface of the cycloid gear and select the grinding process parameters reasonably.

Grinding Wheel Loading Evaluation by Using Acoustic Emission Signals and Digital Image Processing.

In the manufacturing industry, grinding is used as a major process for machining difficult-to-cut materials. Grinding is the most complicated and precise machining process. For grinding machines, continuous generating gear grinding machines are widely used to machine gears which are essential machine elements. However, due to its complicated process, it is very difficult to design a reliable measurement method to identify the grinding wheel loading phenomena during the grinding process. Therefore, this paper proposes a measurement method to identify the grinding wheel loading phenomenon in the grinding process for continuous generating gear grinding machines. In the proposed approach, an acoustic emission (AE) sensor was embedded to monitor the grinding wheel conditions; an offline digital image processing technique was used to determine the loading areas over the surface of Al2O3 grinding wheels; and surface roughness of the ground workpiece was measured to quantify its machining quality. Then these three data were analyzed to find their correlation. The experimental results have shown that there are two stages of grinding in the grinding process and the proposed measurement method can provide a quantitative grinding wheel loading evaluation from the AE signals online.

Modeling and experiment of grinding wheel axial profiles based on gear hobs

Hobbing is one of the crucial gear manufacturing processes with high precision and high efficiency. In order to improve the accuracy of hobbing and hob relief grinding, more precise grinding wheels are demanded for relief grinding in the production of gear hobs. In this paper, a new and accurate mathematical method for calculating the axial profile of grinding wheel based on the corresponding gear hob to be ground is proposed. Considering that most researches have been conducted to focus on the optimization of hob geometric feature and only can be applied to a specific type of hand of helix and rake angle of gear hobs. The method in this paper can be served as a general algorithm for generating axial profile of grinding wheels on the basis of the spatial envelope theory, the principle of coordinate system transformation, and studies on normal profile of single-tooth. The accuracy of grinding hobs is based on applying the approach in practical manufacturing. Taking two typical different kinds of pre-grinding gear hobs as examples for calculation and experiment, the results of tooth profile errors strengthen the position that the validity and feasibility of this method, it can be employed for gear hob design and grinding processing.

Study on surface generation mechanism and roughness distribution in gear profile grinding

The non-uniform grinding conditions due to the tool and workpiece geometries lead to the complexities of the chip geometry and topography characteristic in gear profile grinding. As a result, the previous surface prediction models that have been extensively studied for surface grinding are not able to reveal the surface generation mechanism of gear profile grinding. In this work, a comprehensive model is presented to calculate the surface topography and the chip geometry considering the non-uniformity of geometric contact and grain-workpiece interaction along the tooth profile. In this process, the geometric conditions are characterized by the radius of local tool circumference and the included angle between the plane of grain rotation and the surface normal. Experimental results show reasonable consistency with numerical simulations that validate the proposed model. Based on the model, the effect of geometric conditions on the texture pattern and roughness distribution is studied to give an in-depth analysis of the process characteristics by comparing the simulated results under actual and ideal conditions. Besides, the optimization method is proposed to obtain a more uniform tooth surface. This work provides new insight into the fundamental understanding of profile grinding of gears and can be utilized to guide the machining process for higher tooth surface integrity.