Control and process monitoring are key technologies supporting high machining accuracy and efficiency.
This special issue features six papers taking novel approaches to controlling machine and cutting tools and monitoring the machining process. The motion control of machine tools and cutting tools are introduced. A new challenge for monitoring the machining process by referring to NC control servo signals implements a practical proposal. The precise identification of friction at driving elements of machine tool components is an important factor in improving machine tool control motion accuracy.
I would like to express my sincere appreciation to the authors and reviewers whose invaluable efforts have helped make the publication of this manuscript possible.
In order to achieve flexible and autonomous milling operation, a system called Digital Copy Milling (DCM) was developed in our previous studies. Additionally, tool motion control, in which the voxel information of the removal volume voxel model is referred to, is performed in DCM. In this study, a feed speed control function and tool posture control function are integrated with the DCM by referring to the feed speed and tool posture parameters stored in the voxel properties of the removal volume voxel model. It is assumed that these parameters change gradually as a diffusion phenomenon to automatically determine the voxel properties using a diffusion equation. In order to calculate the diffusion equation, the voxel in the removal volume corresponds to a calculation grid of the diffusion equation and not just to the storage of the feed speed and tool posture parameters. For experimental verification, the feed speed and tool posture parameters were automatically determined, and the tool motion was successfully controlled independent of the tool path generation to perform the milling operation.
This paper proposes a method of simulating the effects of the machining center motion errors onto the finished surface. The proposed simulation method consists of the servo delay models of feed drive systems, a geometrical error model of the machine tool, a machined shape simulator, and a renderer. In order to compare the simulated finished surfaces with the machined one, tests consisting of machining spheres are carried out using a ball-end mill. As result, it is proven that the proposed simulation method can adequately simulate the effects of motion errors on the finished surface. In addition, an investigation into the cause of blemishes is carried out. It is also confirmed that the proposed method can be an effective tool in the identification of the causes of blemishes on the surface.
Friction in linear guideways has an influence on the motion accuracy of machine tool drives. As feedback control has a lag to the friction change in reverse motion, a feedforward compensation is generally used in friction models. However, it is difficult to estimate the friction of rolling balls in raceway grooves because it involves both stick and differential slip characteristics. In this paper, a measurement method is presented using an analytical procedure to clarify micro stick and slip factors in rolling friction. In the measurement test, four balls and two raceway grooves are used to measure the friction force under dry and lubricated conditions. The locomotive bristle model is then applied to identify the stick and slip parameters, which are then compared between the various conditions of lubrication.
It has been verified that ultra-precision diamond machining of hardened steel can be realized by applying the elliptical vibration cutting process. This innovative machining technology enables direct machining of steel dies and molds with a single crystal diamond tool and makes the indispensable nickel-plating step in the conventional diamond machining process unnecessary. This not only increases mold tool life, but also reduces the machining cost and cycle time. Therefore, elliptical vibration cutting has been considered as a very promising manufacturing technology for high precision die and mold machining. However, progress in elliptical vibration cutting has been hampered by bottlenecks in machining of large-size steel workpieces owing to the low machining efficiency. This study proposed an efficient machining method, elliptical vibration cutting with a large nose radius single crystal diamond tool. Experimental findings revealed that the proposed machining method had great potential to realize efficient ultra-precision diamond machining of hardened steel. However, it was found that the ploughing phenomenon affected the finished surface quality significantly. To minimize the ploughing effect an analytical model was developed. This model enabled minimization of the ploughing effect by optimizing the machining conditions. Finally, the analytical model was qualitatively validated with a series of plane cutting experiments and the experimental results demonstrated good agreement with the analytical model.
In current practice, the buffing process required to finish the surface of mechanical parts is performed manually by a technical expert as it requires a delicate adjustment of the buffing force. The automation of this process is desirable in an effort to shorten the process time and reduce labor cost. To automate the buffing process, a beneficial process monitoring technique that supervises the buffing tool conditions in real time must be developed. From a practical perspective, an observer technique that does not require additional sensors would be most suitable for monitoring the tool operating condition. The authors propose a technique that estimates the buffing tool stiffness based on a disturbance observer. The validity of the proposed method as a buffing tool condition monitoring technique is verified through numerical simulations and experiments.
A series of high-speed milling tests of Inconel 718 were carried out utilizing SiAlON ceramic tools, and the transitions of the cutting edge geometry and cutting forces were investigated. Through the experimental investigations, it was confirmed that the cutting edge is worn rapidly and a round shape is formed at the initial stage of machining. The radius of the round cutting edge becomes considerably large with respect to the uncut chip thickness, and thus the ploughing process is dominant in ceramic milling like general micro cutting operations. Based on the observed phenomena, a quasi-mechanistic model for cutting force prediction was proposed, where the measured cutting edge geometry and the contact stress distribution at the tool-workpiece interface are taken into account. The estimated cutting force by the proposed model showed a good agreement with the measured one. Minimizing the estimation error in the cutting forces, contact stresses of the cutting edge to the workpiece are identified. Stress field analysis using the estimated contact stresses revealed that the large tensile stress instantaneously generates around the stagnation point. This mechanism may contribute to the generation of the rake face flaking, which determines the end of the tool life.
The dynamic thermoelastic behavior of a sheet glass subjected to single-pulse laser irradiation is clarified using a one-dimensional model. From the equation of motion for this system, a thermoelastic equation was derived and applied in the analysis. For a 0.1-μs pulse duration, the displacement and thermal stress caused by the thermal expansion within the slab show oscillatory wave characteristics. When thermal stress waves are reflected at the free ends of the sheet glass, the polarity of the stress changes. Alternating stress waves of approximately 0.5-MHz frequency appear in the slab. With cracks propagating in the glass as a result of stress, high-cycle fatigue is possible. We confirm that the dynamic behavior generated by single-pulsed laser irradiation features wavelike properties.
The initiation and propagation of cracks generated on a work surface during UltraSonic Machining (USM) were simulated using Smoothed Particle Hydrodynamics (SPH). Different abrasive materials, tool materials, and abrasive sizes were used in this simulation. The distribution and size of the calculated cracks were found to be strongly influenced by different process conditions. According to the simulation results, using tools with a lower yield strength and slurry comprising softer and smaller abrasives decreases the crack size. Experiments were conducted to drill deep blind holes in soda-lime glass by USM and observe the cracks remaining on the machined surfaces. The experimental results agreed well with the simulation results. This work was the first to visualize the crack formation during USM under different process parameters with the SPH method. The results may be very useful for improving the machining performance of the USM process.
The aim of this paper is to design, fabricate and control a novel Linear Magnetic Actuator (LMA) for applications such as active magnetic bearing systems to deal with vibration problems in rotating machines. This LMA actuator contains a moving body named ‘mover’ and three driving parts to drive the mover. Firstly, experiments have been conducted on the LMA to derive its mathematical model in order to investigate the generated electro-magnetic force as well as further research. The modeling result in a comparison with the actual system performance show that the electro-magnetic force varied symmetrically with the mover motion defined by the applied current. Secondly, an advanced trajectory controller named online tuning fuzzy PID controller has been designed for the LMA to improve the working performance. Finally, real-time experiments have been carried out to evaluate the tracking performance of the designed LMA control system. The results prove that the LMA driven by the proposed controller could track the desired trajectories with high accuracy.
As the miniaturization of integrated circuits has progressed, the penetration holes of bonding jigs have become smaller. However, micro drills have a tendency to break when drilling small holes with high aspect ratios. Moreover, to reduce the impact on the environment, there has been a recent trend towards the use of lead-free brass as jig materials, but these are very difficult to drill. In the present study, small holes are drilled in lead-free brass using a micro drill, and the effects of web thinning, the helix angle, and the nick geometry on chip evacuation are investigated. The results indicate that drills with a helix angle of 15◦ have the longest tool life. The formation of a nick on the cutting edge is found to help decrease the thrust force during deep drilling. A drill with a relatively shallow nick perpendicular to the cutting edge have excellent chip discharge performance, and its cutting force is stable. Nick treatment effectively decreases the thrust force at a deep drilling position.
In the apparel, medical and welfare, and nursing care industries, working with cloth items is highly dependent on manual work, so many people have hoped that such work could be automated. However, there are still no established ways for robots to handle cloth. In this paper, a method for acquiring developed shapes is proposed for the purpose of form recognition and classification operations of flat, limp materials. Experiments are performed to acquire developed shapes of materials by actively searching for contours of cloth using a sensor embedded in the finger of a robot.
This paper presents an integral-type adaptive sliding mode controller integrated into a neural network for position-tracking control of a pneumatic muscle actuator testing system. Stability of the closed-loop system is covered by the sliding mode algorithm while both control error and control energy are minimized by the neural network. With only four weight factors in the hidden layer and two weight factors in the output layer, the network provides a very high calculation speed. Then, the approach is successfully verified on a real-time system under different working conditions. By comparing it with a proportional-integral-differential controller on the same system and under the same working conditions, the effectiveness of the designed controller is confirmed.
The mechanism behind the laser ablation of LN is investigated using near infrared pico-second-pulsed laser. A model of the mechanism is developed, deriving the mechanical, thermal, and photonic properties of LN in addition to doing preliminary experiments on laser ablation with controlled laser fluence. β is material removal using the nonthermal process via multi-photon ionization, γ is nonthermal material removal with chipping or cracking produced by generated heat (but at temperatures below the melting point), and δ is material removal using the thermal process with temperatures above the melting point, resulting in resolidification at the surface and the adhesion of once-molten burrs around the processed area. In a process modes map constructed through exhaustive experiments on laser ablation under various irradiation conditions (at specific energy ρ and with number of pulse shots N’), different contributions of ρ and N’ in the machining process are found. In terms of machining quality, desirable conditions in the control of laser irradiations are the use of weaker ρ and increased N’ to keep thermal damage to a minimum and to raise the removal rate.
A new cutting mechanism for the fabrication of micro-scale grooves is presented in this study. Based on the control principle of the nano-cutting mechanism using an Atomic Force Microscope (AFM), in the newly developed system, a single crystal diamond tool is mounted at the free edge of a cantilever beam and is used for the removal of material. During the cutting process, the cantilever undergoes a deformation that is required for the implementation of a machining force feedback control. It was experimentally observed that the use of this mechanism enables to maintain the cutting depth of the micro-grooves constant even if they are fabricated on inclined surfaces; this is achieved by maintaining the normal cutting force constant using a feedback controller. For this experimental system, an optical lever is used to measure the angular deformation at the tip of the cantilever, thus providing a better understanding of total cutting force involved in the machining process.