Workpiece Spindle Research Articles

Improving the transmission error source tracing method for gear hobbing machines

By considering the uncertainness of initial measuring position of encoders and signal sidebands caused by the fault gear pair, this paper presented a new comprehensive harmonic analysis method for the transmission error of gear hobbing machine. Based on that, a test platform was established, in which two circle grating encoders were connected to the hob spindle and workpiece spindle respectively. With the help of this new harmonic analysis method as well as the self-developed test platform, a new improved transmission error fault diagnosis method was developed for the gear hobbing machines. To verify its accountability, a case study was conducted on a YS-type gear hobbing machine. According to the spectrum amplitude comparison and the analysis of harmonic frequency distribution, the fault transmission gear pair was successfully located. This improved transmission error source tracing method was very helpful for quantifying both the manufacturing qualities and assembly qualities of parts and locating potential error source for new gear hobbing machines.

Simulation Based Prediction of Compliance Induced Shape Deviations in Internal Traverse Grinding

Internal traverse grinding (ITG) using electroplated cBN tools in high-speed grinding conditions is a highly efficient manufacturing process for bore machining in a single axial stroke. However, process control is difficult. Due to the axial direction of feed, changes in process normal force and thus radial deflection of the tool and workpiece spindle system, lead to deviations in the workpiece contour along the length of the bore, especially at tool exit. Simulations including this effect could provide a tool to design processes which enhance shape accuracy of components. A geometrical physically-based simulation is herein developed to model the influence of system compliance on the resulting workpiece contour. Realistic tool topographies, obtained from measurements, are combined with an FE-calibrated surrogate model for process forces and with an empirical compliance model. In quasistatic experimental investigations, the spindle deflection is determined in relation to the acting normal forces by using piezoelectric force measuring elements and eddy current sensors. In grinding tests with in-process force measurement technology and followed by measurement of the resulting workpiece contours, the simulation system is validated. The process forces and the resulting characteristic shape deviations are predicted in good qualitative accordance with the experimental results.

Simulation and Experimental Study on the Surface Generation Mechanism of Cu Alloys in Ultra-Precision Diamond Turning.

The surface generation mechanism of the Cu alloys in ultra-precision diamond turning is investigated by both simulation and experimental methods, where the effects of the cutting parameters on the surface characteristics are explored, including the workpiece spindle speed, the cutting depth, the feed rate and the nose radius of the diamond tool. To verify the built model, the cutting experiments are conducted at selected parameters, where the causes of the error between the simulation and the machining results are analyzed, including the effects of the materials microstructure and the diamond tool wear. In addition, the nanometric surface characteristics of the Cu alloys after the diamond turning are identified, including the finer scratching grooves caused by the tool wear, the formation of the surface burs and the adhesion of graphite. The results show that the built model can be basically used to predict the surface topography for the selection of the appropriate machining parameters in the ultra-precision diamond turning process.

Theoretical analysis of the Influence of workpiece spindle vibration displacement on machining accuracy of gear hobbing machine

In order to study the vibration characteristics of the workpiece spindle of a gear hobbing machine, this paper established a mathematical model for the workpiece spindle vibration displacement in the x-axis direction. To verify the reliability of the proposed model, a series of experiments were run on the CNC gear hobbing machine. The relative error between the experimental data and the calculated values was lower than 5 %, which proves that our proposed mathematical model is qualified to be a research tool for the investigation of the variation law of the workpiece spindle. According to the analysis results, the workpiece spindle vibration displacement literally decreases with the increasing order, and the hobbing process with high hob revolution speed and small cutting depth is preferable for gear hobbing accuracy.

Suitability of integrated sensors for the determination of chatter characteristics in a cylindrical grinding machine

Wheel-sided chatter vibration is a limiting factor in terms of productivity and surface finish regarding the application of conventional grinding wheels. Due to the formation of waviness on the grinding wheel during the process, many expensive trueing cycles are necessary. Therefore, a system for chatter detection and elimination for external cylindrical grinding machines was presented in previous work. It was demonstrated that an electromagnetic actuator reduces the generation of the grinding wheel waviness. The control of this actuator requires precise knowledge about frequency, amplitude, and phase of the chatter vibration. This information is extracted from two eddy-current sensors, which measure the workpiece displacement. However, a direct measurement of the workpiece displacement restricts the working area and is inflexible. Hence, this paper explores the qualification of sensors integrated into the grinding machine for extracting the aforementioned information with high accuracy of phase. For this purpose, two acceleration sensors mounted on the workpiece spindle and the tailstock, an acoustic emission (AE) sensor applied to the grinding wheel, and the motor current of the directly driven headstock spindle are considered. To determine the suitability of these sensors, the frequency response function (FRF) for each sensor is calculated under three conditions: no contact between the workpiece and the grinding wheel, the grinding wheel tensed to the workpiece without a grinding process, and during the process. The method for the in-process measurement of the sensor FRFs and the influence of the contact conditions on these FRFs is shown in this paper.

RPM-SYNCHRONOUS GRINDING - Investigation and comparison of surface topography of Synchro-Finish manufactured workpieces

The innovative RPM-Synchronous Grinding process enables highly efficient manufacturing of various geometries in an ordinary plunge grinding process. An oscillation of the infeed axis, which is coupled to the rotary workpiece spindle axis, like in conventional non-circular grinding approaches is not required. This is achieved by using a fixed ratio of grinding wheel- and workpiece speed and also a non-circular grinding wheel geometry. In this first test series, practice-orientated circular steel-workpieces are Synchro-Finish ground with conventional vitrified grinding wheels for finishing applications. The surface topography of the Synchro-Finished parts is evaluated and compared with conventionally ground workpieces.

Non-circular gear continuous generating machining interpolation method and experimental research

Current non-circular gear manufacturing process all use discrete machining method, which generates a large number of small line segments, brings in approximate error, and leads to high-order discontinuity of the whole tool path curve. The tooth surface quality will be decreased significantly due to the vibration of machining tool caused by the discontinuity of machine tool motion trajectory especially in high-speed machining. In addition, the processing speed and efficiency will be limited due to the unsmooth kinematics profile. This paper proposes a non-circular gear completely continuous generating machining interpolation method. The non-circular gear machining electronic gearbox is developed to compute the real-time interpolation point data to guarantee the strict generating motion relationship between the workpiece spindle, feed shaft, and cutter spindle during the gear manufacturing process according to the derived linkage model for non-circular gear hobbing and generate continuous smooth machining trajectory. The proposed interpolation method is implemented on the self-developed CNC system based on the embedded CNC system hardware structure platform and verified experimentally on a gear hobbing machine. A pair of two-order oval non-circular gear is machined, and the roll and application experiments on a kind of gear pumps are done to illustrate the machining performance and provide a high efficiency and precision machining method for non-circular gear.

Mechanics of turn-milling operations

Turn-milling machines, which are capable of carrying out turning and milling operations, are widely used in machining complex parts in one set-up. However, due to the complex kinematics and tool-workpiece interaction, turn milling operations are mainly carried out by relying on costly machining trials and experience. This paper presents the mechanics of turn-milling operations to predict cutting forces, torque and power requirements. Typical turn milling process involves three linear (x,y.z) and two rotary drives of the machine tool. The resulting feed vector is modeled as a function of linear velocities of the drives, and angular speeds of workpiece and tool spindles. The generalized chip thickness distribution is modeled as a function of linear feed drive motions, tool and workpiece spindle rotations. The cutting force predictions are experimentally verified for sample cylindrical and ball end mills. The identification of productive tool and workpiece spindle speeds is demonstrated using chip load limit of the tools and torque-power constraints of the turn milling machine tools.

Simulated and measured surface roughness in high-speed grinding of silicon carbide wafers

In this paper, the primary factors affecting surface quality are studied and a theoretical model is developed for surface generation in grinding silicon carbide (SiC). The model takes into account the geometrical kinematics and tool micro-vibration in the grinding operation. The simulated roughness profiles agree reasonably well with experimental results. Spectrum analysis was used to extract three different frequencies from the machined surface topography in the frequency domain: figure error, micro-vibration of the wheel, and workpiece. The wheel synchronous micro-vibration is found to be the dominant mechanism for surface generation. The pattern of vibration marks is found to be dependent on the feed rate and the ratio of the rotational speed of the grinding wheel and the workpiece. In addition, the phase shift denoted in the fractional part of the speed ratio is inevitably induced in the evolution of surface generation in the grinding, which imposes a remarkable effect on surface quality. For a non-integral speed ratio (1500 RPM for the workpiece spindle), the arithmetical mean height of the surface (Sa) is significantly improved to about 0.108 μm. A medium phase shift (about 0.5) can suppress the scallop height so as to achieve a good surface finish (Sa = 0.091 μm). The results provide important means for improving the surface quality in ultra-precision grinding.

Application of Multiple Regressions to Thermal Error Compensation Technology – Experiment on Workpiece Spindle of Lathe

This study focuses on a type of intelligent machine tool – Thermal Error Compensation Technology. Lathes are used to rotate a cylindrical workpiece against fixed tools. The high speed of rotation and frequent changes to the cutting load can result in heat deformation which will reduce the accuracy of the relative position between the tool and the workpiece, thus reducing machining precision. This study measures lathe temperature and thermal errors of a workpiece spindle. Experimental results are subjected to multiple regression analysis to assess the relationship between the heat source and deformation to produce a three axis thermal error model. Additional items from polynomial, interaction and cyclical series are included in the model. Finally, we choose the best thermal error model based on predictive ability. The resulting model has a standard deviation of the forecast error within 5 μm.

Machine Learning of Cutting Conditions in Drilling Using Artificial Neural Network

Machining has traditionally been one of the major operations within most manufacturing systems and intelligent machining will play an important role in feature manufacturing systems. This paper concerns the machine learning, specifically classification and recognition of cutting conditions in drilling process. Awareness of the cutting conditions can enhance the auto-diagnosis of an intelligent machining system. In this paper, features representing the drilling process are generated from the converted forms of thrust force and torque and extracted with wavelet packet transform (WPT) and then selected by principal component analysis (PCA). Data instances are generated from experiments with different cutting conditions including workpiece material, drill diameter, feed rate, and spindle speed. A feed-forward network trained with back-propagation method (BPNN) is applied to distinguish between the patterns of each cutting condition. The different contributions of features and the recognition results of cutting conditions are discussed.

Flatness Error Analysis Produced by Carbide End Mill Milling Plane Method

Improving the machining precision mechanical manufacturing field is an indispensable chapter topic. In this analysis focuses on the rail straightness, process system stiffness, milling way, cutting layer parameters, tool wear, thermal deformation of the workpiece spindle axis traverse peace pliers jaws of irregularities in the machining precision flatness influence. Milling cutting process parameters of different layers, different milling heat, different deformation of the workpiece, resulting flatness error is different. Different milling methods and different milling force also affect flatness errors. Therefore, the workpiece machining pass these factors need to be considered. And proposed a solution for uneven of flat-nose pliers jaws and surface of workpiece.

Degradation analysis of grinding machine spindle systems based on complexity

In order to monitor the degradation statuses of the spindle systems of machine tool during use, a degradation analysis method based on the complexity is proposed. In this article, the workpiece spindle systems of the grinding machine tool are taken as research object. First, the vibration signals of the workpiece spindle systems in X2 direction are monthly measured from April to October. The complexity values per month of the filtered vibration signals in X2 direction are calculated by Lempel–Ziv algorithm and are used as the index to monitor the degradation statuses of the workpiece spindle systems during 6 months running. The results show that the complexity values of the measured vibration signals from April to October gradually increase, and the status of the workpiece spindle systems of the grinding machine tool has a slight degradation. Finally, in order to verify the validity of the proposed method, the degradation bearing data published by Case Western Reserve University are used to verify the feasibility, and the result shows that the complexity is effective to the degradation analysis of the spindle systems of machine tool.

Experiments and Study of the Static Rigidity of Workpiece Spindle of Direct-Drive Gear Hobbing Machine

Static rigidity of workpeice spindle component is a very important index of the rigidity of derict-drive gear hobbing spindle unit. In this study, the static rigidity of workpiece spindle system were analyzed through a finite element method (EFM) by building geometric models and studying the deformation when radial cutting force was imposed. Experiments on workpiece were carried out with and without the assistance of tailstock center separately to measure the changes of the static rigidity of spindle. The results prove a less change of the static rigidity of spindle when with the assistance of tailstock center, which helps to ensure the accuracy and surface roughness of a workpiece.

Effect of Machining Precision Caused by NC Gear Hobbing Deformation

Research on the effect of main spindle deformation which is caused by hobbing force of gear hobbing machine is an important way to diminish or control the machining tolerance of gear. This paper bases on the structure and technique parameter of some typical large-scale NC gear hobbing machine, and the theory of bend and deformation of beam, a novel equation was proposed in this paper to calculate the hobbing force and deformation by practical hobbing parameter. By calculating and analyzing gear hobbing force and deformation data, we can conclude a change rule between hobbing force and deformation with spindle rotative velocity and hobbing depth. And we can reach a conclusion that we should increase hob rotative velocity and feed in a small hobbing depth in several times, it will diminish cutting force, deformation of hob and workpiece spindle, which will improve the machining precision, efficiency and diminish product scrap ratio. It also prove this research approach has reference value for optimizing gear hobbingmachine structure design, choice of processing technique parameter and machining error prediction and compensation.

Measurement of Machined Surface Temperature in Drilling by Using Fiber-Coupled Pyrometer

In drilling, excessive temperature rise is known to cause various types of thermal damage to the drill and workpiece. This paper presents a novel approach to measure the temperature variation on the machined surface at the bottom of the hole during drilling. A newly developed infrared radiation pyrometer equipped with two optical fibers is used to measure the temperature. One of the optical fibers is inserted through the oil hole of internal coolant carbide drill. It runs through the inside of the machine tool spindle and connects to the other optical fiber at the end of the spindle. Infrared rays radiating from the bottom of the hole during drilling are accepted and transmitted to the pyrometer by the two optical fibers. The workpiece thickness, spindle speed and feed rate are varied as experimental conditions. The temperature increases gradually as drilling progress and increases rapidly near the undersurface of the workpiece, possibly due to the reduced capacity of the workpiece to conduct heat away from the drill point. The temperature rise near the bottom of the workpiece effects on the rapid drill wear.

Friction drilling of cast metals

This study investigates the friction drilling process, a nontraditional hole-making technique, for cast metals. In friction drilling, a rotating conical tool is applied to penetrate work-material and create a bushing in a single step without generating chip. The cast aluminum and magnesium alloys, two materials studied, are brittle compared to the ductile metal workpiece material used in previous friction drilling research. The technical challenge is to generate a cylindrical shaped bushing without significant radial fracture or petal formation. Two ideas of pre-heating the workpiece and high speed friction drilling are proposed. Effects of workpiece temperature, spindle speed, and feed rate on experimentally measured thrust force, torque, and bushing shape were analyzed. The thrust force and torque decreased and the bushing shape was improved with increased workpiece temperature. Varying spindle speed shows mixed results in bushing formation of two different work-materials. The energy, average power, and peak power required for friction drilling were calculated and analyzed to demonstrate quantitatively the benefits of workpiece pre-heating and high spindle speed in friction drilling.

Development of an ultra-precision grinding system for machining optical aspheric components with a large depth—diameter ratio

When grinding a large depth—diameter ratio aspheric part of high precision and high quality, the factors influencing surface roughness and profile accuracy of machined surfaces were theoretically analysed first. Afterwards the authors designed and manufactured the ultra-precision aspheric grinding system. The workpiece spindle, transverse guideway, longitudinal guideway and the grinder spindle are in aerostatic form. Turning accuracy of the workpiece spindle is 0.05 μm, the maximum rotational speed of the grinder is 80 000 r/min and the turning accuracy is 0.1 μm, and the resolution of linear displacement of the transverse and longitudinal guideway is 4.9 nm. The accuracy of the precise adjusting mechanism is 0.1 μm. The discharge principle of the dressing mechanism was developed in order to dress the diamond wheel. The ball-headed wheel has high profile accuracy after dressing. This mechanism solved the problem of on-position dressing of the case iron bonded diamond wheels and reduced the machining errors for aspheric surface components. Finally, grinding experiments for machining aspheric components were carried out. The grinding results indicated that the achieved profile accuracy is 0.3 μm and the surface roughness is less than 0.01 μm.

深穴内面オシレーション研削におけるテーパ形成機構の解明とその改善策の提案

In this paper, the retraction grinding method, in which the grinding wheel head gets rapidly back by very small amount immediately after beginning of spark-out state, is proposed for improving the taper error in the deep hole oscillation internal grinding. Main conclusions obtained are as follows : (1) It is made clear that by the retraction grinding method the taper error of workpiece can remarkably be improved with the fine surface roughness condition. (2) In the retraction grinding the taper generation mechanism is affected just by extending of spark-out grinding time due to a decrease of the residual stock due to the stiffness of the grinding wheel shaft and workpiece spindle. (3) By taking account of the periodic change of the normal grinding force linking to the oscillation movement, the measured taper can sufficiently be predicted.

ENERGY PARTITION FOR GRINDING OF NODULAR CAST IRON WITH VITRIFIED CBN WHEELS

An investigation was undertaken to determine the energy partition to the workpiece for grinding of an automotive nodular cast iron with a vitrified CBN wheel. The energy partition is a critical parameter which is needed for calculating grinding temperatures and predicting the occurrence of thermal damage to the workpiece. Straight surface grinding experiments were conducted over a wide range of removal rates to measure the workpiece temperature response and spindle power. Temperature matching analyses were then applied in order to obtain the energy partition. Values for the energy partition were found to range from 3 to 6% when the temperature at the grinding zone was maintained below the fluid burnout limit. Such low energy partitions indicate cooling of the workpiece by the fluid at the grinding zone. Higher energy partitions up to 60% were obtained by reducing or eliminating the fluid, which also raised the temperature above the burnout limit.