Wheel Spindle Research Articles

Performance Enhancement of Cylindrical Grinding Process with a Portable Diagnostic System

Material removal processes are one among several manufacturing processes that necessitates the enhancement of their precision capability to cater the demanding needs of higher technological innovations. The performance of a material removal process depends on several factors like the precision of the machine tool, process parameters, process consumables and to a certain extent on the skill of the operator. This paper presents an approach to develop a diagnostic system that can enhance the performance of cylindrical grinding process by monitoring vital process signals like grinding power and infeed of axis. The developed diagnostic system comprises of a powercell and LVDT enabling the measurement of power drawn by wheel spindle along with the wheel infeed movement. Using the measured signals, the developed system is used to optimize the grinding cycle parameters in order to enhance the efficiency of the process. The effectiveness of the developed in-process portable diagnostic system is demonstrated with two case studies. The effect of dressing on the performance of the grinding process is explained in one of the case studies using the diagnostic tool. In another industrial case study, the application of diagnostic tool for selecting the grinding cycle and to determine the frequency of dressing is explained.

Loop Stiffness of Grinding Machine Developed for 450 mm Silicon Wafers

Increasing the wafer diameter from φ300 mm to φ450 mm is required to enhance semiconductor devices productivity. A high-stiffness rotary grinding machine equipped with water hydrostatic bearings was developed for a φ450 mm silicon wafer. The grinding machine has an upper structure consisting of a wheel spindle system and a lower structure consisting of a rotary worktable system. The spindle shaft creates both rotary and axial feeding motion. The upper and lower structures are clamped together rigidly by three kinematic couplings. A higher loop stiffness is required for the grinding machine because grinding the larger wafer requires a higher grinding force. This paper investigates the loop stiffness of the developed wafer grinding machine.

大径シリコンウエハ加工用ロータリ研削盤の開発（第１報：水静圧ロータリテーブルの基本特性の検討）

Increasing of Si wafer diameter from φ300 mm to φ450 mm is required to enhance productivity of semiconductor devices. The authors developed a high stiff rotary grinding machine, which consists of a rotary table system and a wheel spindle system. These system are rigidly clamped using three ball screws and kinematic couplings. This paper investigates a basic design and the performances of the rotary table system equipped with constant flow water hydrostatic bearings. A fluid analysis around bearing pad was attempted by using the finite volume method in order to enhance a static stiffness of water hydrostatic thrust bearing. Performances of the developed rotary table was evaluated experimentally and compared with the analyzed value. The measured static stiffness and the numerical analyzed static stiffness ware 1.96 kN/μm and 1.97 kN/μm, respectively under the flow rate of each bearing pads Q=30 mL/min.

Life Cycle Assessment of Process Eco-Innovations in an SME Automotive Supply Network

The aim of the study presented in this article is to assess, from an environmental standpoint, a set of eco-innovations applied to the production process of an automotive component. The eco-innovations were developed by a supply network of small- and medium-sized enterprises (SMEs) in the framework of a project named “Hi-reach”. The component considered is a motorcycle rear wheel spindle. The conventional version is obtained by machining a single forged steel part. The Hi-reach version is indeed manufactured by joining a shaft to a flange; in addition, conventional surface treatments are replaced by a plasma-enhanced chemical vapour deposition (PECVD) treatment and other machining steps are improved. This process was conceived with the aim of maintaining (or enhancing) the technical performance of the spindle and reducing production costs. A Life Cycle Assessment (LCA) was carried out to compare the two scenarios described. Those eco-innovations resulted in significant improvements of the environmental performance of the analysed component, ranging, on average, between 50% and 70% for the impact indicators considered. Our results also highlight the role of SMEs in promoting process eco-innovations and the increasing relevance of LCA as a tool to support decision making in manufacturing.

An investigation into parallel and cross grinding of aspheric surface on monocrystal silicon

Cross and parallel grinding modes are two typical general grinding modes for aspheric surface in vertical wheel spindle grinding system. In this paper, roughness, surface profile, form accuracy, and wheel wear of the ground aspheric surface utilizing the cross and parallel grinding methods are compared and investigated. Firstly, the maximum undeformed chip thickness of aspheric surface was analyzed in the two grinding modes. And then, the precision grinding of monocrystal silicon for aspheric surface and wheel wear experiments was carried out with the same grinding parameters. Experimental results revealed that the cross grinding mode was advantageous over parallel grinding in terms of achieving precision aspheric surface with a roughness (Ra) of 20.1 nm, form accuracy (PV) of 235 nm, and a steady surface. The change of the maximum undeformed chip thickness in grinding process caused the increased surface roughness from the edge to the center. And without considering the influence of the wheel arc profile form error, better form accuracy was obtained by cross grinding. Besides, the wheel wear modes were significantly different in the two grinding modes. This study gives an indication of the strategy to follow to achieve high-quality ground aspheric surfaces on brittle materials.

Effect of grinding wheel spindle vibration on surface roughness and subsurface damage in brittle material grinding

The external interference and vibration can seriously affect the machining errors in brittle materials grinding process. This paper proposes a new model to analyze the relationship between surface roughness (SR) and subsurface damage (SSD) depth on the basis of grinding kinematics analysis and indentation fracture mechanics of brittle materials taking the wheel spindle vibration into account. The basic equations, for example, equations of grain trajectory and penetration depth are derived in new forms. Based on the basic equations above, the existing SR and SSD formulae are modified for further study. The effects of grinding and vibration parameters on SR and SSD are respectively analyzed in detail. Results show that both SR and SSD increase with the increase of table speed and vibration amplitude resulting in bad surface and subsurface quality. On the other hand, both the increasing grinding speed and decreasing vibration frequency can improve the quality of ground surface and subsurface with small SR and SSD. In addition, the increase of initial grinding depth and vibration initial phase increase the depth of SSD but have little effect on SR. The penetration depth and distance between grain's tip and finished surface are the two main factors considered to cause the different effect laws on SR and SSD among these parameters. Experiment is carried out to validate the rationality of proposed model. The effect trends of various grinding parameters on SR obtained by our model consist with measured experimental data. The typical subsurface crack system is clearly revealed through the experimental observation on SSD using SEM. Finally, the relationship between the two is fitted utilizing quadratic polynomial. Results show that the SSD depth is nonlinear monotone increasing with SR and the fitting accuracy is more or less affected by both grinding and vibration parameters.

A novel ball joint wear sensor for low-cost structural health monitoring of off-highway vehicles

Mechatronic agricultural machines and equipment are continuously increasing their complexity and cost. In order to ensure their efficiency and reliability and preserve their value, it is important to actively monitor damaging and wear occurring on critical components. This approach needs the introduction of sensors on the machine, which allow continuous monitoring of the residual life of components. This work presents the development and testing of a wear sensor for a ball joint which can be applied for monitoring and diagnosis in off-highway vehicles, automotive and the industrial fields. Many peculiar features make this sensor innovative and contribute to the advance of the technology in the sector: there are no other active sensors for this specific and safety-critical joint; it has an ultra-low power consumption and can be self-powered through energy harvesting; it implements wireless connectivity; it is simple, small size and low cost. This wear sensor for the ball joint is firstly aimed at monitoring the damage of the ball joint placed between the steering actuator and the wheel spindle, since failure of the joint leads to complete loss of steering action. However, the sensor can be applied to any application involving a safety-critical ball joint (e.g. the front suspension of a vehicle). The present work describes the conceptual design and development of the whole mechatronic sensor, which includes the mechanical joint sensor and the electronic board which manages the system. Validation of the ball joint wear sensor, which was performed on an agricultural tractor through tests on a track, proved the reliability of the proposed solution.

S1310101 450mmシリコンウエハ用ロータリ研削盤の開発 : 切込機構内蔵砥石スピンドルの静剛性および位置決め精度

S1310101 450mmシリコンウエハ用ロータリ研削盤の開発 : 切込機構内蔵砥石スピンドルの静剛性および位置決め精度

Virtual sensors for on-line wheel wear and part roughness measurement in the grinding process.

Grinding is an advanced machining process for the manufacturing of valuable complex and accurate parts for high added value sectors such as aerospace, wind generation, etc. Due to the extremely severe conditions inside grinding machines, critical process variables such as part surface finish or grinding wheel wear cannot be easily and cheaply measured on-line. In this paper a virtual sensor for on-line monitoring of those variables is presented. The sensor is based on the modelling ability of Artificial Neural Networks (ANNs) for stochastic and non-linear processes such as grinding; the selected architecture is the Layer-Recurrent neural network. The sensor makes use of the relation between the variables to be measured and power consumption in the wheel spindle, which can be easily measured. A sensor calibration methodology is presented, and the levels of error that can be expected are discussed. Validation of the new sensor is carried out by comparing the sensor's results with actual measurements carried out in an industrial grinding machine. Results show excellent estimation performance for both wheel wear and surface roughness. In the case of wheel wear, the absolute error is within the range of microns (average value 32 μm). In the case of surface finish, the absolute error is well below Ra 1 μm (average value 0.32 μm). The present approach can be easily generalized to other grinding operations.

A novel method for grooving and re-grooving aluminum oxide grinding wheels

In this paper, a new grinding wheel grooving system is proposed that is able to both groove as well as re-groove a grinding wheel using a single-point diamond dressing tool. The re-grooving capability of the new system is achieved by synchronizing the grinding wheel angular position with the dressing tool translational position. This position synchronization enables the diamond dressing tip to repeatedly engage the grinding wheel at the same angular position around the wheel and then proceed to trace the existing groove pattern along the wheel surface to, for example, refresh a worn groove geometry. Furthermore, the proposed system can be mounted on either a non-CNC or a CNC conventional grinding machine and can groove and re-groove the grinding wheel without the need to remove it from the grinding wheel spindle. The novel wheel grooving system was experimentally validated by creating helically shaped circumferential grooves on the grinding wheel surface. The resulting maximum differences in groove width and depth were found to be 0.015 and 0.013 mm, respectively, for ten consecutively cut grooves. These small discrepancies are believed to be primarily due to the brittle fracture mechanism of the abrasive grits. Furthermore, the new wheel grooving system was shown to be able to create a wide range of different groove patterns on the wheel surface. A wear study was then carried out to compare the performance of both grooved and non-grooved grinding wheels. For the conditions used in this research, the results of this wear study showed that a grooved wheel not only exhibits less wear than a non-grooved wheel but also can remove approximately twice as much workpiece material before failure occurs.

High-Accuracy Calibration of the Wheel Spindle Tilt Angle for Grinding Hydrostatic Seal Rings Used in Reactor Coolant Pumps

The hydrostatic seal rings are one of the most important components used in reactor coolant pumps. They are generally made of hard materials such as silicon nitride, alumina, silicon carbide and tungsten carbide. Meanwhile, the form error should be within the length of one to two helium light bands and the surface roughness should be in the scale of nanometers, which make them difficult to machining. In order to solve this problem, a high accuracy grinding method using a large cup wheel had been proposed and the tilt angle of the cup wheel spindle become a crucial factor affecting the ground form errors. This paper addresses a novel method for high-accuracy calibrating the tilt angle of the cup wheel spindle to fit the extremely shallow taper angle of the seal ring conical surface, and the mathematical model is established incorporating a standard optical flat with a high-accuracy laser displacement sensor. The practicability of this method is verified by grinding a seal ring sample with the outer diameter is 200 mm and the taper angle is 700 μrad. It is found that the taper angle error is only 1.72 μrad and the radical profile error of the conical surface is about 0.22 μm.

Experimental Research on Ultrasonic Torsional Vibration-Assisted Grinding of Hard and Brittle Materials

An experimental study of quartz glass grinding with ultrasonic torsional vibration assistance is presented. The grinding forces and surface roughness are measured. The results show that the grinding force and surface roughness with ultrasonic torsional vibration assistance are much less than those in conventional grinding. The grinding force increases with the feed rate of workpiece and the depth of grinding, and decreases with the speed of wheel spindle. This research indicates that the ultrasonic torsional vibration-assisted grinding can enhance grinding performance and be an effective method for the machining of hard and brittle materials.

C004 Characteristics of thermal displacement of cylindrical grinding machines with rotation of wheel spindle : Influence of thermal displacement of wheel spindle and wheel spindle head

Measurement devices are proposed for the relative thermal displacement between the grinding wheel and the workpiece, and for the thermal displacement of the wheel spindle itself during rotation of the wheel spindle. Then by separating the thermal deformation of the wheel spindle and the wheel spindle head from the relative thermal deformation between the wheel spindle and workpiece, the thermal deformation of the grinding machine is evaluated in detail. The following results are obtained. (1) The grinding wheel spindle and the wheel spindle head cause the thermal displacement in various directions. (2) A percentage of the influence of the wheel spindle and the wheel spindle head in the relative thermal deformation is different depending upon the direction of the thermal displacement.

Research on Dynamic Balance of Grinding Wheel Spindle

In this paper, grinding wheel spindle of high precision CNC is researched. Mathematics - mechanical mode of dynamic balance of grinding wheel is established on the principle of rotor dynamic balance. New method of critical speed of grinding wheel is proposed, and verified by testing the reasonableness. And, dynamic unbalance of grinding wheel spindle of high precision CNC is studied on quality surface. These studies provide theoretical direction for balance speed range and the accurate level.

Effects of bushings characteristics on suspension ball joint travels

In this paper, a short-long arm type front suspension is represented using multi-body dynamics model established with ADAMS®, where the suspension bushings modelled as linear and nonlinear elements, respectively, are integrated with a flexible cradle and other suspension components. A ball joint travel, defined as the angular displacement between the two parts connected with the ball joint, is calculated, where the measured wheel loads and spindle accelerations from a proving ground severe durability test schedule serve as the input data. The ball joints considered in this study include lower ball joints, upper ball joints, outer tierod ball joints, and inner tierod ball joints. The results clearly illustrate that the bushing stiffness and nonlinearity are important for an accurate prediction of ball joint travels and the ball joint travel sensitivities to considered design variables are important for engineers to understand and ensure reliable designs of ball joints.

Development of Measurement Device for Thermal Displacement in Cylindrical Grinding Machines (Study on Measurement Method for Thermal Displacement with Rotation of Wheel Spindle)

Cylindrical grinding machines are typical machine tools for the final finishing process which produce high accurate and value-added products. However the universal method of measurement and evaluation for their thermal displacement has not been established. Therefore, in this study, we propose a measurement and evaluation method for the thermal displacement of the cylindrical grinding machines with rotation of the wheel spindle and make a device on an experimental basis based on the proposition and examine their validity. As the result of this study, it is made clear that the method proposed by us can measure and evaluate effectively and simultaneously 5 thermal displacements of the cylindrical grinding machines, that is, 3 translational deviations and 2 angular deviations.

Electrolytic In-Process Dressing Superfinishing of Spherical Bearings Using Metal—Resin Bond Ultra-Fine CBN Wheels

The use of electrolytic in-process dressing (ELID) superfinishing has been investigated with the aim of substantially improving surface finish on spherical bearing balls as well as reducing process times. Using ELID in a superfinishing configuration is substantially different from the more conventional precision grinding set-up. With this ELID superfinishing system, metal—resin bonded (MRB) wheels containing very small superabrasives (30 to 0.12 μm) were employed. Surface finishes of 2 nm Ra were achieved with a #12 000 wheel, an order of magnitude better than balls produced using the conventional production techniques of barrelling or polishing. Consistently sub-10 nm Ra finishes were achieved with a #2000 wheel. Different ways of using the ELID system, including ELID 1, ELID 2, and ELID 3, were studied to examine how the different types control the cutting condition at the wheel's surface. It is the ability to control easily the cutting condition of superabrasives of this size that allows mirror surface finishes to be efficiently produced. Monitoring of wheel spindle and ELID power usage was found to provide useful information in assessing the wheel condition.

Investigation of Hydrodynamic Pressure in High-speed Precision Grinding

The conventional method of delivering grinding fluid that floods delivery with high supply fluid pressure and nozzle fluid rare to achieve high performance grinding. However, the hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect between the wheel's peripheral surface and the work surface. Indeed, this reduces the depth of cutting and increases grinding wheel spindle deformation and overall grinding resistance, thereby affecting machining accuracy. In this paper, a theoretical hydrodynamic pressure modeling is presented for the flow of coolant through the grinding zone during high-speed precision grinding. The simulated results show that the hydrodynamic pressure was proportional to the velocity of the grinding wheel and inverse proportional to the minimum gap between the wheel and the workpiece. Furthermore, the hydrodynamic pressure peak value was only generated in the minimum clearance region where a higher fluid pressure gradient was observed. It can also be deduced that the hydrodynamic pressure distribution was uniform in the direction of the width of the wheel. However, due to side leakage, the edge of the wheel was an exception to this rule.

Fault diagnosis of cylindrical grinding machine

Based on experiment modal analysis (EMA) and operation modal analysis (OMA), the dynamic characteristics of cylindrical grinding machine were measured and provided a basis for further failure analysis. The influences of grinding parameters on dynamic characteristics were studied by analyzing the diagnostic signals extracted from racing and grinding experiments. The significant frequency of 38 Hz related to grinding wheel spindle speed of 2 307 r/min showed that the wheel spindle system was in a state of imbalance. And wheel rotating frequency of 38.45 Hz in grinding process was close to the first natural frequency of 38 Hz, which resulted in resonance. Moreover, the main excitation at 147 Hz in grinding process together with resonance led to the deterioration of workpiece. Roundness measurement of workpiece shows good agreement with the vibration responses obtained from dynamic experiments. The fault diagnosis method was also applicable to similar machining systems.

Study on the Ultrahigh Speed Grinding of Superhard Materials with Squeeze Film Damping Technology

In order to further improve machining quality of superhard materials, it was presented that adds a squeeze film damper on the wheel spindle of ultrahigh speed grinder as a assistant elastic sustain to attenuate the vibration of the wheel spindle. Work principle of squeeze film damper was analyzed; the squeeze film pressure distribution was researched through simulation and damper parameters effect on damping coefficient was studied. Base on the theory research the damper was designed and experiments was done. Experimental result shows the amplitude of the grinding wheel spindle can be reduced 20% and machining quality of superhard materials can be improved 10%～20%. Research works provides a new method for superhard materials machining.