机械球磨过程控制技术的研究进展

如何实现对机械球磨过程的控制，扬长避短，加快应用进程是当前发展机械球磨技术的研究热点之一。评述了机械球磨过程控制技术的研究进展，介绍了控制气-固反应的反应球磨技术，控制球磨中焊合-碎裂等基本过程的过程控制剂技术，及其在纳米粉体、氢化物、氮化物及复合材料等制备中的应用。     

基于H∞的铣削加工振动主动控制

本文通过对铣削系统进行受力分析,建立了圆柱螺旋立铣刀的铣削系统动力学模型。在此基础上,针对刀具和工件的相对振动,运用H∞的鲁棒混合灵敏度法,选取了合适的权重函数W1,W2,W3,设计了主动减振控制器。将该控制器加入铣削模型之中,仿真和实验结果证明了该控制方法在铣削颤振抑制方面的有效性和鲁棒性,扩大了稳定铣削区域;同时将针对刀具和工件相对振动的控制效果与只针对刀具或者工件振动的控制效果进行了比较。     

On-line condition monitoring of tool wear in end milling using acoustic emission

The monitoring of tool wear is important in maintaining the quality of workpieces produced. This paper presents a methodology to monitor on-line tool wear in end milling using acoustic emission. It is well known that the root-mean-square (RMS) value of the acoustic emission is directly proportional to the power expended in turning. A mathematical model has been developed to predict the RMS value of the acoustic-emission signal in milling. This mathematical model incorporates the machining parameters as variables. The accuracy of the model has been verified by a series of experiments. The experiments were carried out on a Bridgeport milling machine and data was collected and analysed by using an on-line computer data acquisition system. A comparison of the experimental and theoretical RMS values indicates a very good agreement between them. A control strategy similar to the moving average/moving range charts has been developed for monitoring on-line tool wear. The limits for the control charts were obtained from the theoretical equation of statistical quality control. An observation of the control charts clearly indicates the region of tool failure and the time at which the tool failed. The philosophy behind the use of control charts is based on the ease of implementation and widespread use in industry.     

Multi-sensor inline measurements of crystal size and shape distributions during high shear wet milling of crystal slurries

Size and shape distributions are among critical quality attributes of particulate products and their inline measurement is crucial for monitoring and control of particle manufacturing processes. This requires advanced tools that can estimate particle size and shape distributions from multi-sensor data captured in situ across various processing steps.In this work, we study changes in size and shape distributions, as well as number of particles during high shear wet milling, which is increasingly being employed for size reduction in crystalline slurries in pharmaceutical processing. Saturated suspensions of benzoic acid, paracetamol and metformin hydrochloride were used in this study. We employ our recently developed tools for estimating particle aspect ratio and particle size distributions from chord length distribution (CLD) measurements and imaging. We also compare estimated particle size distributions from CLD and imaging with corresponding estimates from offline instruments.The results show that these tools are capable of quantitatively capturing changes in particle sizes and shape during wet milling inline. This is the first time that such a capability has been reported in the literature. The ability to quantitatively monitor particle size and shape distributions in real time will enable development of more realistic and accurate population balance models of wet milling and crystallisation, and aid more efficient control of crystallisation processes.     

Automated manufacturability assessment of rotational parts by grinding

Automated manufacturability assessment of a given design is a key requirement in realizing complete integration of design (CAD) and manufacturing (CAM). The paper deals with a system developed for automated manufacturability assessment by machining processes. The purpose of this system is to assist designers in their effort to come up with manufacturable parts economising in terms of cost and time. Unlike most of the work done in the past, which concentrates on assessment by primary machining processes such as turning and milling, the present work deals with grinding operation. The present system uses geometric reasoning to extract manufacturing specific information from a part model. It uses a knowledge base consisting of grinding process knowledge and control rules, which are activated by the designer. It also has a provision to account for company-specific manufacturing resources to come up with meaningful assessment for part manufacturability. The use of the proposed system is demonstrated for the assessment of axisymmetric parts to be manufactured by cylindrical and internal grinding processes.     

Prediction on milling distortion for aero-multi-frame parts

Because the multi-frame component of an airplane has thin walls of variable wall thickness, and a high fitting accuracy is required, the prediction of its milling distortion is extremely important. In this study, the finite element model of the milling distortion analysis is established firstly for the multi-frame components, and the prediction analysis of the milling distortion under different milling conditions is carried out, by means of three-dimensional finite element simulation technology. Comparing the simulation results and the measurement ones of the milling distortion, the proposed model is modified and prediction method is proved to be effective. Software system is developed specially for the prediction of the milling distortion for aero-monolithic multi-frame components. By using of the software, a platform structure with 192 frames is analyzed and its milling distortion is predicted successfully.     

Mechanochemical effects on the properties of starting mixtures for PbTiO3 ceramics by using a novel grinding equipment

The effects of milling were studied using a newly developed multi-ring media-type grinding machine on the synthesis processes of PbTiO₃ ceramics from PbO-TiO₂ mixed sols. The temperature of the endothermic and exothermic DTA peaks, corresponding to dehydration and crystallization, decreased with milling time. After milling the mixed sol for 5 min and heating to 823 K, the product was a single-phase PbTiO₃. This suggests rapid homogenization and formation of lead titanate precursors during milling. The effects of milling were revealed to be much less when mixtures of dry and wet powders were used.     

Flank milling model for tool path programming of turbine blisks and compressors

In this paper, a methodology for complex surface machining based on cutting forces prediction is presented. The work is focused on blade finishing operations. The cutting forces model developed can be applied to three axis and five axis milling cases. For three-axis cases, the chip thickness is calculated according to traditional analytical methods. On the contrary, for five-axis cases the chip thickness is obtained from a geometric method developed in the paper. The cutting forces values can be calculated for the complete toolpath, but the presented model can also provide the programmer information about the cutting forces in a single point of the toolpath. The cutting force model is integrated in the CAM software in order to provide an extra tool that helps the programmer to decide which the optimal milling strategy is, based on the minimum cutting forces. In the last section, results of a case study based on impeller and blisk blades flank milling are discussed. Model predicted forces and real measured forces of flank milling operations are compared for model validation. Applying this methodology, cutting forces can be taken into account as a decisive criterion for optimal tool path selection.     

Mill,material, and process parameters – A mechanistic model for the set-up of wet-stirred media milling processes

Stirred media milling is frequently used to generate nanoparticles for industrial applications such as paints, inks, and food or for the life sciences. Each product suspension has different requirements and therefore different material and formulation parameters. The first attempts to set up a new process are experimental in nature, especially the determination of a suitable composition. To adapt a process to the production scale, more experimental work is often needed to determine suitable operation parameters with regard to energy consumption, throughput, and investment cost. The energy consumption is influenced by operation parameters such as the size of the grinding media or the stirrer tip speed, whereas the investment costs are influenced by the mill geometry and size and the type of grinding media used. Therefore, it is challenging to transfer or scale up processes because lab-scale mills are smaller and may have different geometries than production-scale mills. Moreover, it is well known that the lab-scale operation parameters cannot be easily adapted to the production scale. In this study, the stress model developed by Kwade was improved by introducing parameters corresponding to the mill and the material in addition to the process parameters. Using this model, the optimum operating conditions for stirred media milling processes can be determined with a reduced amount of experimental work, even for geometrically unequal mills.     

A cortical bone milling force model based on orthogonal cutting distribution method

In orthopedic surgery, the bone milling force has attracted attention owing to its significant influence on bone cracks and the breaking of tools. It is necessary to build a milling force model to improve the process of bone milling. This paper proposes a cortical bone milling force model based on the orthogonal cutting distribution method (OCDM), explaining the effect of anisotropic bone materials on milling force. According to the model, the bone milling force could be represented by the equivalent effect of a transient cutting force in a rotating period, and the transient milling force could be calculated by the transient milling force coefficients, cutting thickness, and cutting width. Based on the OCDM, the change in transient cutting force coefficients during slotting can be described by using a quadratic polynomial. Subsequently, the force model is updated for robotic bone milling, considering the low stiffness of the robot arm. Next, an experimental platform for robotic bone milling is built to simulate the milling process in clinical operation, and the machining signal is employed to calculate the milling force. Finally, according to the experimental result, the rationality of the force model is verified by the contrast between the measured and predicted forces. The milling force model can satisfy the accuracy requirement for predicting the milling force in the different processing directions, and it could promote the development of force control in orthopedic surgery.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00300-7     

Comparison of Milling Processes: Ball Mill Versus Air Classifying Mill

A study was initiated to compare the milling process and equivalence of mills for milling a fibrous material. In this study, milling processes using either a ball mill (Abbe Model Number 2) or an air classifying mill (Mikro ACM 10) were compared. Samples from both processes were evaluated by appropriate physical and chemical analyses such as particle size, surface area, densities, and potency. The particle size distribution and surface area analysis showed equivalence between the two milling processes. Scanning electron micrographs (SEM) showed that the samples had similar morphology. The potency of samples obtained from either of the milling processes was not affected by differences in the milling processes. In addition, results of milled samples that were subsequently granulated and compressed into tablets showed no difference in assay, content uniformity or disintegration time. Based on these results, it is concluded that the ball mill and the air classifying mill produce material that is equivalent in terms of physical and chemical properties, and therefore the processes of milling are interchangeable.     

Comparison of Milling Processes: Ball Mill Versus Air Classifying Mill

Abstract

A study was initiated to compare the milling process and equivalence of mills for milling a fibrous material. In this study, milling processes using either a ball mill (Abbe Model Number 2) or an air classifying mill (Mikro ACM 10) were compared. Samples from both processes were evaluated by appropriate physical and chemical analyses such as particle size, surface area, densities, and potency. The particle size distribution and surface area analysis showed equivalence between the two milling processes. Scanning electron micrographs (SEM) showed that the samples had similar morphology. The potency of samples obtained from either of the milling processes was not affected by differences in the milling processes. In addition, results of milled samples that were subsequently granulated and compressed into tablets showed no difference in assay, content uniformity or disintegration time. Based on these results, it is concluded that the ball mill and the air classifying mill produce material that is equivalent in terms of physical and chemical properties, and therefore the processes of milling are interchangeable.     

An integrated machine-process-controller model to predict milling surface topography considering vibration suppression

Surface topography is an important factor in evaluating the surface integrity and service performance of milling parts. The dynamic characteristics of the manufacturing system and machining process parameters significantly influence the machining precision and surface quality of the parts, and the vibration control method is applied in high-precision milling to improve the machine quality. In this study, a novel surface topography model based on the dynamic characteristics of the process system, properties of the cutting process, and active vibration control system is theoretically developed and experimentally verified. The dynamic characteristics of the process system consist of the vibration of the machine tool and piezoelectric ceramic clamping system. The dynamic path trajectory influenced by the processing parameters and workpiece-tool parameters belongs to the property of the cutting process, while different algorithms of active vibration control are considered as controller factors. The milling surface topography can be predicted by considering all these factors. A series of experiments were conducted to verify the effectiveness and accuracy of the prediction model, and the results showed a good correlation between the theoretical analysis and the actual milled surfaces.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00386-7     

多齿铣刀侧铣加工多层CFRP铣削力的建模与仿真

由于碳纤维增强树脂基复合材料(CFRP)的层间结合强度较低,进行切削加工时在切削力的作用下容易出现分层和毛刺等质量缺陷。因此,通过对切削力的预测与控制可以有效提高加工质量。采用瞬时刚性力模型对多齿铣刀侧铣多层CFRP材料的加工过程进行铣削力建模与仿真,分析了多齿铣刀特有的几何结构对切削力的影响。试验中保持切削速度恒定,以不同进给速度分别对45°、0°、-45°和90°这4种典型纤维方向的单向CFRP进行侧铣加工,通过测得的切削力数据计算各自的铣削力系数。根据力学矢量叠加原理得到了多向CFRP铣削力系数的简化计算表达式,最后将计算结果代入铣削力模型得到了各时刻的铣削力仿真值。在同样的试验条件下对该多向CFRP进行侧铣加工验证试验,试验结果表明: 该模型能较好地预测铣削力,最大相对误差小于9%,平均相对误差小于5%,可为铣削参数优化和刀具结构优化提供理论基础。     

Modeling of flow and debris ejection in blasting erosion arc machining in end milling mode

Blasting erosion arc machining (BEAM) is a typical arc discharge machining technology that was developed around 2012 to improve the machinability of difficult-to-cut materials. End milling BEAM has been successfully developed and preliminarily applied in industry. However, owing to the high complexity of the flow field and the difficulty of observing debris in the discharge gap, studies of the flow and debris in end milling BEAM are limited. In this study, fluid dynamics simulations and particle tracking are used to investigate the flow characteristics and debris ejection processes in end milling BEAM. Firstly, the end milling BEAM mode is introduced. Then the numerical modeling parameters, geometric models, and simulation methods are presented in detail. Next, the flow distribution and debris ejection are described, analyzed, and discussed. The velocity and pressure distributions of the axial feed and radial feed are observed; the rotation speed and milling depth are found to have almost no effect on the flow velocity magnitude. Further, debris is ejected more rapidly in the radial feed than in the axial feed. The particle kinetic energy tends to increase with increasing milling depth, and smaller particles are more easily expelled from the flushing gap. This study attempts to reveal the flow field properties and debris ejection mechanism of end milling BEAM, which will be helpful in gaining a better understanding of BEAM.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00328-9     

Experimental investigations of ceramic machining using µ-grinding and µ-rotary ultrasonic machining processes: A comparative study

Comparative experimental investigations of µ-grinding and µ-rotary ultrasonic machining (µ-RUM) were made on borosilicate and Zerodur materials to know the efficacy of the processes for micro electro mechanical system (MEMS) application. The electroplated diamond tool of Ø 300 µm for drilling operation and Ø 300 µm to Ø 6 mm for milling operation has been tried in the computer numerical control (CNC) machine with an HSK63 ultrasonic actuator. A suitable interface has been developed to hold the micro tool with the ER11 taper in the existing ER20 collet ultrasonic tool holder. Cutting force, edge-chipping area, and taper in drilling operation; and surface finish, material removal mode, specific energy and un-deformed chip thickness in milling operation were evaluated for both processes under the same material removal rate conditions. The experimental results showed that µ-RUM could perform in a less spindle speed machine as compared to µ-grinding. It was inferred that the maximum and minimum amount of reduction in cutting force, edge chipping, and taper were found to be (49.3%, 10.8%), (87%, 40%), and (95.56%, 4.76%), respectively, in µ-RUM compared to µ-grinding for drilling operation. It was also concluded that surface finish and ductile mode of fracture were higher in µ-RUM compared to µ-grinding for the milling operations. These effects were more pronounced as tool size decreased.     

Extraction of milling know-how from NC programs through reverse engineering

To automate machining process planning, the acquisition and representation of machining knowledge or know-how in a reusable way is needed. The machining know-how is implied in NC programs made by experienced workers. In this paper, the methodology and system for extracting machining know-how in milling operations have been developed. With the system, machining features, operations and their associated cutting conditions (depth of cut, feed rate and spindle speed, etc.) and machining method can be extracted by analysing NC programs in conjunction with the tools used and workpiece blank model. The milling know-how is represented as a collection of these extracted data that can be used in future machining operations. To verify the system, actual NC programs for milling have been analysed and the milling know-how has been extracted successfully.     

Population balance modeling applied to the milling of pharmaceutical extrudate for use in scale-up

This study modeled the particle size distribution (PSD) of pharmaceutical extrudates after milling by developing a so-called time-discrete population balance model (PBM). The PBM, which models size reduction as a series of breakage events, was formulated so that the model parameters separate the effect of material properties and milling process conditions. Because of this novel aspect, the PBM should have excellent predictive capability with specific applications in technology transfer and scale-up. To investigate this application, copovidone extrudate produced by the hot-melt extrusion process was milled using a lab-scale continuous impact mill (Fitz Mill). The effect of impeller speed and classification screen size on PSD of the extrudate was investigated. The PBM with parameters obtained by fitting lab-scale PSD data was then applied to model the PSD of the extrudate following milling by a pilot-scale continuous impact mill (Hosokawa mill). The study found that the parameters determined at the lab-scale can be used to model PSDs at the pilot-scale and may be generally applied to similar classification-type impact mills. Since technology transfer and scale-up can be material and time consuming, this approach may offer significant benefits to the pharmaceutical industry for the development of milling processes.     

Integrated in-process chatter monitoring and automatic suppression with adaptive pitch control in parallel turning

Simultaneous processes such as parallel turning or milling offer great opportunities for more efficient manufacturing because of their higher material removal rates. To maximize their advantages, chatter suppression technologies for simultaneous processes must be developed. In this study, we constructed an automatic chatter suppression system with optimal pitch control for sharedsurface parallel turning with rigid tools and a flexible workpiece, integrating in-process chatter monitoring based on the cutting force estimation. The pitch angle between two tools is tuned adaptively in a position control system in accordance with the chatter frequency at a certain spindle speed, in a similar manner as the design methodology for variable-pitch cutters. The cutting force is estimated without using an additional external sensor by employing a multi-encoder-based disturbance observer. In addition, the chatter frequency is measured during the process by performing a low-computational-load spectrum analysis at a certain frequency range, which makes it possible to calculate the power spectrum density in the control system of the machine tool. Thus, the constructed system for automatic chatter suppression does not require any additional equipment.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0222-0.pdf