The double-disc straight-groove (DDSG) grinding method is a new precision machining method for the rolling surface of bearing cylindrical rollers by using a flat grinding disc and a straight-groove ...grinding disc as machining tools. The machining principle of bearing cylindrical rollers based on the DDSG grinding method is experimentally investigated in this study. A circulating grinding platform has been constructed. The grinding test of the cylindrical rollers was performed with W40 white corundum abrasive. Under the experimental conditions of the grinding disc rotation speed of 7.5 rpm, the machining load of 110 N, and the eccentricity of the straight groove of 6 mm, 2000 cylindrical rollers (AISI 52100) were synchronously ground by the DDSG grinding method. The average diameter, surface roughness, and roundness of the ground rollers were investigated. Experimental results show that the material removal rate of the rollers is uniform. After 270 grinding cycles, the average diameter decreased from 5.99082 to 5.94135 mm, with an average material removal rate of 0.183 microns per cycle. The average roundness of ground cylinders reduced from 9.64 to 2.78 μm. The diameter variation decreased significantly from 14.5 to 6.0 μm. The average roughness reduced from 0.258 to 0.137 μm, and the fluctuation range of the roughness decreased from 0.143 to 0.033 μm. Experimental results demonstrate that the DDSG grinding method can improve the bearing cylindrical rollers’ dimensional consistency, roundness, and surface quality.
In this paper, a fast positioning platform (FPP) is proposed, able to meet simultaneously the requirements of large stroke and high frequency response, developed based on a PZT (piezoelectric ...actuator) and a quad-parallel flexible mechanism, for application in precision machining. The FPP is driven by a high-stiffness PZT and guided by a flexible hinge-based mechanism with a quad-parallel flexible hinge. The proposed quad-parallel flexible hinge mechanism can provide excellent planar motion capability with high stiffness and good guiding performance, thus guaranteeing outstanding dynamics characteristics. The mechanical model was established, the input and output characteristics of the FPP were analyzed, and the working range (output displacement and frequency) of the FPP was determined. Based on the mechanical model and the input and output characteristics of the FPP, the design method is described for of the proposed FPP, which is capable of achieving a large stroke while responding at a high frequency. The characteristics of the FPP were investigated using finite element analysis (FEA). Experiments were conducted to examine the performance of the FPP; the natural frequency of the FPP was 1315.6 Hz, while the maximum output displacement and the motion resolution of the FPP in a static state were 53.13 μm and 5 nm, respectively. Step response testing showed that under a step magnitude of 50 μm, the stabilization times for the falling and rising edges of the moving platform were 37 ms and 26 ms, respectively. The tracking errors were about ±1.96 μm and ±0.59 μm when the amplitude and frequency of the signal were 50 μm, 50 Hz and 10 μm, 200 Hz, respectively. The FPP showed excellent performance in terms of fast response and output displacement. The cutting test results indicated that compared with the uncontrolled condition, the values of surface roughness under controlled conditions decreased by 23.9% and 12.7% when the cutting depths were 5 μm and 10 μm, respectively. The developed FPP device has excellent precision machining performance.
Nickel-based superalloys (GH4169) are a typical difficult-to-machine material with poor thermal conductivity and severe work hardening. They are also prone to poor surface quality, severe tool wear, ...and poor machinability, which affect their performance. In this paper, an experimental study of GH4169 ultrasonic elliptical vibratory ultra-precision cutting was carried out. The experimental results show that ultrasonic elliptical vibratory cutting (UEVC) significantly reduces surface roughness and improves surface quality compared to conventional cutting (CC). The effects of cutting parameters such as cutting speed, feed rate, cutting depth, ultrasonic amplitude, and tool nose radius on the surface roughness of GH4169 workpieces were further investigated in UEVC. Based on the analysis of the experimental data, the optimal combination of parameters for GH4169 ultrasonic elliptical vibration ultra-precision cutting was determined: cutting speed of 3 m/min, feed rate of 16 μm/rev, cutting depth of 2 μm, ultrasonic amplitude of Ay = 3.0 μm, Az = 0.8 μm, and a tool nose radius of 0.8 mm. This parameter combination improves the machining quality of GH4169 and provides a valuable reference for the subsequent development of ultrasonic elliptical vibratory cutting for other difficult-to-machine materials.
A novel pure rotary actuator with a double-layer flexible mechanism (RA-DFM), which is driven by a single piezoelectric ceramic in the lower mechanism and generates rotational motion in the upper ...mechanism, is proposed in this paper. The output of piezoelectric ceramic is successively amplified using an enhanced double Scott–Russell mechanism and two lever-type mechanisms to obtain a large rotation range. The static, kinematic and dynamic properties of the RA-DFM are numerically analyzed, and the actual output of the piezoelectric is analyzed considering the input stiffness. The geometric parameters of the RA-DFM are optimized based on the constructed numerical models. Finite element analysis has been implemented to validate the correctness of the theoretical models and further evaluate the output property. The simulation results show the maximal rotation angle of the RA-DFM is 15.14 mrad with 0.44% center drift.
Ultrasonic elliptical vibration-assisted cutting (UEVC) has been successfully applied in the precision and ultra-precision machining of hard and brittle materials due to its advantages of a low ...cutting force and minimal tool wear. This study developed a novel double-excitation ultrasonic elliptic vibration-assisted cutting (D-UEVC) device by coupling ultrasonic vibrations in orthogonal dual paths. A two-degree-of-freedom vibration system of the D-UEVC was modeled, form which the elliptical trajectory of the end under different phase angle φ values was derived. The initial dimensions of the D-UEVC device were obtained through theoretical calculations. Subsequently, with the aid of finite element analysis methods, structural dynamic analysis of the device was conducted to obtain the elliptical vibration trajectory under different phase differences of the excitation source. In order to verify the cutting trajectory and cutting performance of the D-UEVC device, a prototype of the device was developed, and a series of vibration performance tests as well as the Inconel 718 cutting experiment were conducted. The experimental results illustrated that the D-UEVC device can achieve the elliptical vibration trajectory at the tool tip with a resonant frequency of 36.5 KHz. The adjustable elliptical vibration trajectories covered a range of ±4 μm in the axial and radial directions. Compared with the surface roughness Ra = 0.36 μm under the conventional cutting, the surface roughness of Inconel 718 under D-UEVC was Ra = 0.215 μm. Thus, the surface quality can be significant improved by utilizing the D-UEVC device.
The rotational performance of the spindle-bearing system has critical influence upon the geometric shape and surface roughness of the machined parts. The effects of preload and preload method on the ...rotational performance of the spindle-bearing system is explored experimentally to reveal the role of preload and preload method in spindle rotational performances under different speeds. A test rig on which both the rigid preload and elastic preload can be realized, equipped with variable preload spindle-bearing system, is developed. Based on the mechanical model, the relationship of the axial preload and negative axial clearance of the spindle-bearing system is provided. Rotating sensitive radial error motion tests are conducted for evaluating synchronous and asynchronous radial errors of the variable preload spindle-bearing system under different rotating speeds and preload methods. The change regularity of synchronous and asynchronous radial errors with preloads under different rotating speeds are given. The results show that the preload plays an important role on the rotational performance of spindle-bearing system. The rigid preload is more efficient in achieving better rotational performance than elastic preload under the same rotating speed. Furthermore, this article significantly guides the preload designing and assembling of the new spindle-bearing system.
In the field of precision machining, the spindle-rolling bearing (SRB) system is widely used on the machine tool as one of the most fundamental and important components. The rotational error motions ...of the SRB system have significant effects on the machining accuracy (contour accuracy and surface roughness). Over the past decades, much work has been focused on the measurement of spindle balancing and rotational error motions, the vibrations response induced by the nonlinear stiffness and surface waviness of the bearing. However, the formative mechanism of the rotational error motions for the SRB system is not well understood. In this paper, the dynamic model of the SRB system considering the bearing nonlinearity is established. Seeking to reveal the effects of surface waviness of the bearing raceway, unbalance mass and disturbance force on the dynamic rotational error, the modeling method and formative mechanism of the dynamic rotational error for the SRB system is explored both theoretically and experimentally. Then, numerical simulation is performed to analyze the influence of the bearing raceway waviness, unbalance mass and disturbance force on the dynamic rotational error. An experimental setup is established based on a typical SRB system and a series of experiments are carried out. The experimental results are in good agreement with the theoretical and simulation results, which can demonstrate the feasibility and validity of the modeling method. Furthermore, this method can be effectively applied to the design and development phases of an SRB system to improve dynamic rotational accuracy.
Predicting and avoiding the onset of milling chatter are desirable to reduce its harm to machine tools, workpieces, and cutters. This paper presents an updated method to complete the stability ...prediction for the milling process with multiple and distributed time delays. After the dynamic of the combination milling process with variable helix cutter (VHC) and variable spindle speed (VSS) is modeled as linear delay differential equations with multiple and distributed time delays, the presented method is applied to carrying out its stability prediction for the first time. By comparing with the existing researches and time-domain simulations, the effectiveness of the presented method has been validated. The influence and feasibility of the combination process on chatter suppression are explored and investigated for the associated one- and two-degree-of-freedom systems. Results show that the application of the combination process can realize a further suppression of milling chatter in practice. It can result in nearly 2-fold as high as the minimum depth of cut for the traditional milling or VSS milling and about 1.3-fold for VHC milling for some special domain, and can respectively lead to the average increase of stable area by 30.4%, 23.5%, and 1.5% for the adopted simulations. However, consider the contribution, the combination process is actually one process in which VHC plays an absolutely leading role but VSS plays an auxiliary role, in terms of milling stability.
The spindle rotational accuracy is an important indicator to evaluate the characteristic of a machine tool. In this article, an easy-to-use measuring module is proposed based on virtual instrument ...platform. A new method for measuring rotational speed and angular orientation using an adaptive filtering method to processing the target installation eccentricity is proposed, instead of using the encoder. This method can reduce the measuring cost and make the measurement more convenient, without affecting the measuring accuracy. Meanwhile, the selective principle of target installation eccentricity for rotating sensitive direction is investigated by theoretical analysis and numerical simulation. Based on the proposed method, measuring module is developed. National Instruments data acquisition card and capacitive sensors are used to acquire the displacement signals of the spindle rotational error motion. Contrast experiments with the commercial measuring software are performed to validate the feasibility and repeatability of the proposed measuring module. The experimental results demonstrate that the developed measuring module can reach the same precision using less test parameters.
•This study provides EQA design and laboratory performance for Coagulation factors VIII and factors IX assay in China for the first time.•Chromogenic assay is a supplement to accurate determination ...when necessary.•The implementation of the external quality assessment has contributed to facilitate the enhancement of testing quality.
Testing for coagulation factors VIII (FVIII) and IX (FIX) plays significant importance in the diagnostic and treatment of hemophilia A and B. External quality assessment (EQA) scheme aimed to assess the participants’ performance of testing for coagulation factors and identify shortcomings in clinical practice. This study aimed to investigate the performance trends of the participating laboratories in China national external quality assessment Scheme (China NEQAS) for FVIII and FIX over a five-year period (2019–2023).
A total of ten external quality assessment (EQA) rounds were conducted from 2019 to 2023 in the China NEQAS for FVIII and FIX. The distribution of method, reagent and instrument were calculated. The trends of method- specific inter-laboratory coefficient of variation (CV) and pass rates were analyzed over 5 years. The dilutions for coagulation factor testing were also investigated.
All laboratories use one-stage assays to detect FVIII and FIX activity. The inter-laboratory overall CV decreased year by year (10.9 % to 9.3 % for FVIII and 13.5 % to 10.2 % for FIX), and the laboratory pass rate steadily increased (88.0 % to 93.4 % for FVIII and 81.3 % to 92.7 % for FIX). The majority of laboratories employed a single dilution methodology for the assessment of FVIII and FIX activity. The interlaboratory CV was elevated for the Siemens reagent (Actin FSL) during analysis of moderately abnormal FIX concentrations of EQA samples in most batches.
The implementation of the external quality assessment has contributed to facilitate the enhancement of testing quality. Chromogenic assay is a supplement to accurate determination when necessary. Laboratories may choose to perform dilution tests or direct assays to identify the presence of inhibitors, particularly when they are suspected.