Workpiece Changes Research Articles

Hybrid prognosis of drill-bits based on direct inspection

Within the paradigm of industry 5.0, manufacturing systems are seeking for human-centred production, where the operator finds high-level supervision tasks. In this context, low-level decision making should be performed by machines themselves. In this paper, a hybrid prognosis algorithm is developed to automatically inspect the cutting edges of drill-bits and to predict their Remaining Useful Life (RUL) and the associated probability density function. The solution relies on the automatic measurement of flank wear through convolutional filtering and edge detection. Prognosis exploits particle filter, which updates multi-layer perceptron with online data, to adaptively predict drill-bits RUL. The solution reduces the experimental preliminary run-to-failures needed for training standard machine learning algorithms, exploiting them in a real-time adaptive scenario, while predicting tool RUL under untested and variable cutting process operations. The algorithm uses direct wear observations, taken during set-up times (e.g., tool changes, workpiece change), thus not interfering with the process.

Effect of workpiece pre-straining on tribological performance of surface coatings in sheet metal forming

The material condition of a workpiece changes as it is formed. Typically, the workpiece hardens and undergoes geometrical and topographical changes. In progressive forming, where workpieces are formed in multiple steps, this means that the workpiece in subsequent steps is different from the as-received material. In this work, strip reduction of an as-received strip and of a pre-strained strip are compared. EN1.4404 stainless steel is pre-strained by bending-under-tension. This leads to changes in the material condition and the surface topography of the strip. Two different coatings are tested in a strip-reduction test to evaluate the effect of these changes to the workpiece state on the tribological performance of the tool coatings. A coating that performed poorly when used to reduce the as-received material exhibited an improved performance when used to reduce the pre-strained material.

Practical Approaches for Acoustic Emission Attenuation Modelling to Enable the Process Monitoring of CFRP Machining

Acoustic emission-based monitoring of the milling process holds the potential to detect undesired damages of fibre-reinforced plastic workpieces, such as delamination or matrix cracking. In addition, abrasive tool wear, tool breakage, or coating failures can be detected. As measurements of the acoustic emission are impacted by attenuation, dispersion, and reflection as it propagates from source to sensor, the waveforms, amplitudes, and frequency content of a wave packet differ depending on the propagation length in the workpiece. Since the distance between acoustic emission sources and a stationary sensor attached to the workpiece changes continually in circumferential milling, the extraction of meaningful information from the raw measurement data is challenging and requires appropriate signal processing and frequency-dependent amplification. In this paper, practical and robust approaches, namely experimentally identified transfer functions and frequency gain parameter tables for attenuation modelling, which in reverse enable the reconstruction of frequency spectra emitted at the acoustic emission source, are presented and discussed. From the results, it is concluded that linear signal processing can largely compensate for the influence of attenuation, dispersion, and reflection on the frequency spectra and can therefore enable acoustic emission based process monitoring.

Comparing surface roughness and tool wear when milling convex surface of hardened steel using different milling strategies

Regarding milling of dies and molds, there are several geometric requirements, and it is absolutely not trivial to machine complex either concave or convex surfaces. Since the contact between tool and workpiece changes all the time, making the components of the milling forces also to change, it is fundamental to find the correct milling strategies which cause the smallest variation of cutting forces (amplitude and sense) in order to obtain the best possible workpiece surface quality. In this work, four different machining strategies for finish milling of D6 tool steel were studied. They were compared in terms of surface roughness, cutting force, and tool wear at the end of tool life. Results show that lower surface roughness was obtained using descending down milling and ascending up milling because the sense of the cutting force components, specially the one that is normal to the machined surface on the most critic region of the workpiece, pulled the workpiece against the tool and the tool against the workpiece. On the other hand, descending up milling and ascending down milling did not present good results because the sense of the force components was responsible for excessive tool bending moving the tool and workpiece apart.

Heat Transfer Coefficient of Zinc Phosphate Coating with Metal Soap during Cold Backward Extrusion

In cold forging, the temperature difference between the workpiece and the tool is small and thus deformation analysis is rarely coupled with thermal analysis. However, the friction coefficient of zinc phosphate coating with metal soap has a large temperature dependence. Consideration of the effects of workpiece and tool temperature change on the friction coefficient is thus expected to improve the analytical accuracy of cold forging. Thermally coupled cold forging analysis requires thermal conductivity, specific heat, heat transfer coefficient between the workpiece and the tool, in addition to the temperature dependence of flow stress and friction coefficient. The heat transfer coefficient between workpieces coated with zinc phosphate with metal soap and tools is investigated in this paper. Cold backward extrusion was performed with a 50% reduction of area, and the temperature history in the punch was measured with a thermocouple. The forging speed was 1, 3, and 10 spm. FEM analysis was performed to simulate the experiment by considering the temperature dependence of flow stress and friction coefficient. The heat transfer coefficient was estimated at 20 kW/(m2•°C) by comparing the experimental result and calibration curves.

The influence of the production type on the choice of the method of obtaining the workpiece

his article describes the systematization of the workpiece types according to the method of production, the scope of their application, the advantages and disadvantages of each method. The authors analyzed and classified the groups of workpieces according to the main characteristics, properties, types of production, etc. The examples of selecting methods for obtaining workpieces of parts "Case", "Nipple" and "Pump case", in which the workpieces are shown in detail and clearly with different production methods, as well as with different production volumes, are given. During the transition from single-unit to mass production, the method of obtaining the workpiece changes dramatically. This affects the entire further strategy of manufacturing the part and the technological process. Selecting the method of workpiece production has a great influence on the time of the preparation of technological equipment (production of stamping tools, models, molds, etc.). In case of an error, the company will incur large losses. Therefore, the technologist, together with the designer, must carefully check the selected workpiece and make sure that it is suitable for this production. The research was carried out at the Department of Machine-Building Technologies, Bauman Moscow State Technical University.

ПАРАМЕТРИЧЕСКАЯ ОПТИМИЗАЦИЯ СРЕДСТВАМИ ANSYS WB КОНСТРУКЦИИИНСТРУМЕНТА ДЛЯ РОТАЦИОННО-ФРИКЦИОННОГО РАСТАЧИВАНИЯ

The authors developed a special design of a rotary friction tool with a self-rotating cup cutter for rotary friction boring of large holes. This paper presents the results of parametric optimization of stressed components of the rotary friction tool by virtual experiments in ANSYS WB. The authors predicted the cutting force components at the worst position of the cup cutter, which was 20 degrees as contact forces in the process of boring a large diameter hole, and built a design model. Using the Johnson-Cook model as the failure criterion for the elements of the mesh, projections of the cutting forces resulting from the hole processing were obtained. The relation between input and output parameters (stresses) is established, optimization criteria are specified, and optimal parameters of the tool stresses components are chosen. It was also found that the averaged values of the force at the initial moment (cutting into the workpiece) change linearly, then becoming practically constant. The idea of parametric optimization consisted in carrying out several virtual experiments, in which the possible range of variation of the basic dimensions was indicated and the optimization criteria were set, the optimal parameters of the tool design were selected from the presented candidates. The optimization method bypasses the design cycle, which is costly and time-consuming due to prototype testing and subsequent refinement.

Research on the influence of the discharge breakdown process on the crater formation during EDM

PurposeThis paper aims to study the breakdown, oscillation and vanishing of the discharge channel and its influence on crater formation with simulation and experimental methods. The experiment results verified the effect of the oscillating characteristics of the discharge channel on the shape of the crater.Design/methodology/approachA mathematical model that considers the magnetohydrodynamics (MHD) and the discharge channel oscillation was established. The micro process of discharging based on magnetic-fluid coupling during electrical discharge machining (EDM) was simulated. The breakdown, oscillation and vanishing stage of the discharge channel were analyzed, and the crater after machining was obtained. Finally, a single-pulse discharge experiment during EDM was conducted to verify the simulation model.FindingsDuring the breakdown of the discharge channel, the electrons move towards the center of the discharge channel. The electrons at the end diverge due to the action of water resistance, making the discharge channel appear wide at both ends and narrow in the middle, showing the pinch effect. Due to the mutual attraction of electrons and positive ions in the channel, the transverse oscillation of the discharge channel is shown on the micro level. Therefore, the position of the discharge point on the workpiece changes. The longitudinal oscillation in the discharge channel causes the molten pool on the workpiece to be ejected due to the changing pressure. The experimental results show that the shape of the crater is similar to that in the simulation, which verifies the correctness of the simulation results and also proves that the crater generated by the single pulse discharge is essentially the result of the interaction between transverse wave and longitudinal wave.Originality/valueIn this paper, the simulation of the discharge breakdown process in EDM was carried out, and a new mathematical model that considers the MHD and the discharge channel oscillation was established. Based on the MHD module, the discharge breakdown, oscillation and vanishing stages were simulated, and the velocity field and pressure field in the discharge area were obtained.

Effects of grinding speeds on the subsurface damage of single crystal silicon based on molecular dynamics simulations

Understanding the damage mechanism of silicon under interfacial shear is vital as it can provide insights for the ultra-precision low damage machining. In this work, the nano-grinding process of single crystal silicon was studied by molecular dynamics (MD) simulations, the damage mechanism of single crystal silicon were analyzed in details under different grinding speeds. The results show that the maximum height of the grinding chip does not always increase with the increase of the grinding speed. When the speed exceeds 150 m/s, more atoms will flow to both sides of the groove. During grinding, the workpiece changes from cubic diamond structure to non-diamond structure and a small amount of hexagonal diamond structure. The Si-II phase was found in the subsurface damage layer. Residual stresses are mainly distributed in the subsurface damage layer (SDL) and do not always show compressive or tensile stresses as the depth increases. This investigation may shed light on the damage mechanism of silicon from an atomic perspective.

Study on staged work hardening mechanism of nickel-based single crystal alloy during atomic and close-to-atomic scale cutting

Nickel based single crystal alloys have excellent properties such as heat resistance, corrosion resistance and creep resistance, which are widely used in aerospace and other national defense fields. Severe work hardening occurs in the process of cutting nickel based single crystal alloy. How to improve the machining quality and grasp the cutting deformation mechanism has become the research focus. In this paper, the effect of work hardening on the surface of workpiece during the atomic and close-to-atomic scale (ACS) cutting process is studied. The model of Si3N4 ceramic tool cutting the nickel based single crystal alloy was established, and the ACS cutting process was simulated by the molecular dynamics method. The existing strain rate conversion model was modified to make it suitable for the process of ACS cutting into nano compression with the same strain rate. The results show that the dislocation density of Ni-based single crystal alloy workpiece changes greatly with the change of cutting distance. According to the change of microstructure in the workpiece, a new staged work hardening mechanism is proposed. The development of work hardening in the cutting process is divided into three stages, and the transition node of each hardening stage is defined. An important sign of the transformation from the first stage to the second stage of work hardening is the occurrence of a large number of dislocation pile-up group, dislocation tangles and the appearance of non-basal slip lines. The distinctive feature of the transformation from the second stage to the third stage of work hardening is that a large number of screw dislocations are cross-slip and the dislocation pile-up group is destroyed. At the same time, the different hardening mechanisms in each stage and the reasons for the change of work hardening mechanism in different stages are summarized. The research content is believed to be helpful to understand the mechanism of significant work hardening effect in nickel-based alloys.

Measurement and analysis of thrust force and torque in friction drilling of difficult-to-machine materials

Thrust force and torque applying in friction drilling contain some important information related to sufficient heat generation which can improve product quality and reduce tool wear. This concern becomes more challengeable when friction drilling is applied on difficult-to-machine materials. In the present study, temperature, thrust force, and torque for friction drilling of difficult-to-machine materials namely AISI304 and Ti-6Al-4V and Inconel718 are measured and analyzed. It contributes to provide an enhanced understanding of how friction in workpiece-tool interface increases the temperature. Subsequently, the sufficient heat generation, the effective thrust force, and torque that are needed to form a proper bushing with optimum features can be predicted. It is found that increasing in number of drilled holes reduces the quality of bushing shape. It is observed that thermal conductivity of workpiece material has significant effect on bushing formation quality. The findings indicate that better bushing formation and longer tool life are obtained from friction drilling of Inconel718. The microstructural changes of workpiece and tool wear are also analyzed and a relationship between them, temperature, thrust force, and torque, is explored. The maximum tool wear is observed on conical region where the process is in critical cycle time and temperature is on peak point.

Comparative investigation of tool wear mechanism and corresponding machined surface characterization in feed-direction ultrasonic vibration assisted milling of Ti–6Al–4V from dynamic view

This paper mainly investigated the wear mechanism of universal coated carbide tools in feed-direction ultrasonic vibration-assisted milling (UVAM) of Ti–6Al–4V alloy through theorical analysis and experimental approaches, where the external ultrasonic vibration excitation was imposed on the workpiece. The rapid intermittent machining features, the generation mechanism of ultrasonic-frequency pulse cutting force and alternating friction, ultrasonic-frequency dynamic impact effect of resonant workpiece and considerable changes in tool trajectory and relative cutting speed in UVAM were analyzed from perspective of tool-workpiece dynamics and kinematics. Due to the ultrasonic-frequency friction between the tool and the workpiece, the minimum quantity lubrication (MQL) with biodegradable cutting fluid was firstly introduced in UVAM to improve the lubrication/cooling performance between tool and workpiece/chips interfaces. Three different machining methods, general milling, feed-direction UVAM and feed-direction UVAM&MQL, were sequentially carried out to comparatively investigate the tool wear mechanism and characterize tool wear and machined surface features. The corresponding machined surface quality including surface topography, surface profile and surface roughness under different tool wear states were presented to evaluate the tool wear condition. The results indicated that the tool wear mechanism in workpiece feed-direction UVAM system was dominated by ultrasonic-frequency dynamic load, where ultrasonic-frequency cutting force, ultrasonic-frequency friction, ultrasonic-frequency vibration impact and cutting inflection points of tool-tip trajectory worked together on the cutting edges. And the tool wear morphology in feed-direction UVAM was mainly characterized by tool-tip fracture, impact crack, friction traces and fatigue crack. The results of machined surfaces indicated that compared with the surfaces obtained in CM and general UVAM, the UVAM&MQL method could significantly improve the finished surface quality, which can also improve the tool wear to a certain extent.

Modeling the techological process of pipe forging without a mandrel

A broaching technique for thick-walled pipes has been investigated. The proposed technique implies the deformation of a hollow workpiece without a mandrel. The procedure has been devised to conduct theoretical studies using FEM. The procedure is aimed at determining the thermal, stressed state and a shape change in the workpiece while forging pipes without the use of a mandrel. The variables applied were the internal diameter of a hollow workpiece, which ranged in the interval of 0.30; 0.55; 0.80. Based on the finite-element modeling, the following was established: the distribution of temperatures and intensity of logarithmic deformations within the volume of a pipe after broaching without the use of a mandrel. The diameter of a pipe’s hole has been determined, which is formed at broaching when applying a given technique. The dependences of intensity of lengthening and thickening of the wall of a pipe have been established. A special indicator was devised to estimate the elongation rate of a pipe. It was determined that increasing the inner diameter increases the lengthening of a pipe and decreases the intensity of the hole forging. The common dependence for the simulated broaching schemes is that the magnitude of elongation of a hollow workpiece changes insignificantly for different degrees of reductions at constant relative sizes of a pipe. It has made it possible to establish a recommended feed in order to increase the elongation of a hollow forging and to decrease the degree of closing a hole. The rational feed shall be (0.05...0.15)D. The results from the finite element modeling were verified by experimental study using lead samples. An experimental modeling procedure has been devised. It was established that at an inside diameter of the workpiece of (0.5...0.6)D one observes a maximum of the wall thickening. It was established that the results for a workpiece shape change, obtained from a theoretical study using FEM, exceeded those acquired experimentally by 9.14 %. The validity of results from theoretical modelling is confirmed by data from experiments on decreasing the internal diameter of the pipe. Difference between the theoretical and experimental results amounts to 9...12 %. The established patterns make it possible to determine the resulting diameter of a pipe’s hole. It was found based on the results from modeling that it is impossible to broach pipe workpieces without a mandrel. This technique extends the possibilities of technological processes aimed at manufacturing pipe workpieces.

Combining translation-invariant wavelet frames and convolutional neural network for intelligent tool wear state identification

On-machine monitoring of tool wear in machining processes has found its importance to reduce equipment downtime and reduce tooling costs. As the tool wears out gradually, the contact state of the cutting edge and the workpiece changes, which has a significant influence on the vibration state of the spindle. The performance of traditional intelligent fault diagnosis methods depend on feature extraction of dynamic signals, which requires expert knowledge and human labor. Recently, deep learning algorithms have been applied widely in machine health monitoring. In this paper, we present a novel intelligent technique for tool wear state recognition using machine spindle vibration signals. The proposed technique combines derived wavelet frames (DWFs) and convolutional neural network (CNN). Constructed based on dual tree wavelets, DWF are equipped with merits of centralized multiresolution and nearly translation-invariance. In this method, DWFs are employed to decompose the original signal into frequency bands of different bandwidths and different center frequencies, which are more pronounced as the tool wears. Further, the reconstructed sub-signals are stacked into a 2-D signal matrix to match the structure of 2-D CNN while retaining more dynamic information. The 2-D convolutional neural network is utilized to automatically recognize features from the multiscale 2-D signal matrix. End-milling experiments were performed on a S45C steel workpiece at different machining parameters. The experiment results of the recognition for tool wear state show the feasibility and effectiveness of the proposed method.

A new method for field dynamic balancing of rigid motorized spindles based on real-time position data of CNC machine tools

In high-speed precision machining, the spindle balance state may be altered by re-clamping of the workpiece or tool changes, as well as a number of other reasons. Therefore, repeating the dynamic balancing process on-site after any changes have been made to the spindle system is of utmost importance. This paper proposes a new method for balancing rigid motorized spindles based on the real-time position data of CNC machine tools with the aim of reducing the costs associated with external balancing instruments and improving the efficiency of the dynamic balancing process. Moreover, the proposed technique can be integrated into CNC controllers and data such as the amplitude and phase angle of spindle can be extracted based on the real-time position of linear axis with the feed direction perpendicular to the spindle axis. The speed of the spindle and the reference position of the correction masses can then be calculated using the index pulse of the spindle measurement system and unbalanced spindle data. The dynamic balancing system was shown to accurately identify sensitive processing speeds of motorized spindles, which is crucial to high-speed high-precision machining. Finally, the feasibility and the stability of the spindle dynamic balancing system were experimentally validated using an LDT500 ultra-precision diamond turning. The roughness of the machined surface was shown to decrease from 25.2 to 5.9 nm and thus, verifies the feasibility of applying spindle dynamic balancing system in practical engineering.

Research on Arc Length Control Technology of Double Closed-loop for Pulsed MIG Welding

This paper presents a pulsed MIG welding arc length control method based on fuzzy control, which can better realize the dynamic control of arc and ensure arc length stability. In this system, a double-closed-loop control scheme is proposed, a variable-parameter PI control method is used, and a two-dimensional fuzzy controller of an arc-length loop is designed. Both the simulation and the experimental results show that when the distance between the welding gun and the workpiece changes, the arc length can reach a new balance and stable state after 9 pulse periods. The arc length control technology of double closed-loop for pulsed MIG welding is verified feasible in this paper.

Idle time selection for wire-arc additive manufacturing: A finite element-based technique

Wire‐arc additive manufacturing is a metal additive manufacturing process that enables the production of large components at a high deposition rate. This process transfers a large amount of heat to the workpiece, requiring the introduction of idle times between the deposition of subsequent layers so that the workpiece cools down. This procedure prevents the workpiece from collapsing and ensures a suitable interpass temperature. The main challenge is the selection of such an idle time capable of ensuring the required interpass temperature, because the cooling rate of the workpiece changes throughout the process, entailing the need for a different idle time between the deposition of subsequent layers to achieve a constant interpass temperature.This paper proposes an innovative approach to schedule the deposition of interlayer idle times for wire‐arc additive manufacturing process. The technique is based on a finite element analysis of the thermal behavior of the workpiece, by solving the heat transfer equations. The simulation data are processed using the developed algorithm to compute specific idle times for the deposition of each layer, thereby ensuring a constant interpass temperature. The effectiveness of the proposed technique is validated by experiments performed on a test case component. The idle times are calculated using the proposed technique, by simulating the process, and used to manufacture the test case. The temperature data measured during the process are compared with the FE simulation results to verify the accuracy of the model. An analysis of the geometry of the manufactured workpiece confirms that the adoption of the idle times obtained by the proposed technique prevents the occurrence of major structural collapses.

Technological capabilities of increasing surface quality of workpieces made of titanium alloy VT22 and stability of surface grinding

Surface grinding of flat workpieces made of alloy VT22 was conducted by the periphery of a highly porous wheel (HPW) from cubic boron nitride CBN30 B107 100 OV K27 КF40 with three processing techniques (ij). They are 10 - cross-feed per stroke, HPW cutting into a workpiece changes alternately from up to down; 12 – cross-feed per double stroke during the up HPW cutting-in at the working stroke; 22 – cross-feed per double stroke during the down HPW cutting-in at the working stroke. With the involvement of artificial neural network models, it was revealed that to improve the quality of surfaces and stability of its formation, grinding should be conducted if ij = 12.

Vibrations of Flat‐End Cutter Entering Workpiece Process: Modeling, Simulations, and Experiments

During all the machining process, the milling cutter has to enter the workpiece either from the boundary or from the machined/unmachined surface, due to the change of machining sequence/cutter or the variation of cutting depth. Unlike the stable cutting process, the contact between cutter and machined workpiece changes significantly in the entering process, resulting in vibration and leaving marks on the machined surface. Aiming at in‐depth understanding the mechanism of this phenomenon, this paper presents a novel time‐domain simulation model to predict the dynamic response of the cutter during the entering process. Two typical entering conditions, including entering from the workpiece boundary and from the machined surface along the cycle path, are modeled based on the dynamic cutting force calculation by considering dynamic undeformed chip thickness created by consequential teeth engagement. Then, it is synthesized with the time‐varying immersion angle and exit angle of cutter teeth in the entering process to simulate the dynamic cutting forces and cutter vibrations. To validate the developed model, eight conditions in boundary entering and six conditions in cycle path entering are carried out by comparing the collected data and the predicted results. Results show that the developed model could precisely predict the dynamic cutting forces and cutter vibration, especially the forces and displacements under the varied cutter‐workpiece contact.

Effect of layered polyurethane elastic cushion on quality of surface part in multi-point forming

Multi-point forming (MPF) is a dieless forming method. The upper and lower dies of MPF are composed of discrete height-adjustable punches. However, defect will be generated as some particular dimples crease on the smooth surface parts. Therefore, the addition of elastic cushion between the sheet metal and multi-point die is needed to improve the forming quality of surface parts. In this paper, we investigate the forming quality changes of workpiece through dividing polyurethane elastic cushion of the same thickness into different layers. Besides, spherical parts are selected as the study objects. The dynamic explicit algorithm is used to simulate the MPF process and static implicit algorithm is used to simulate springback. The results demonstrate that the values of the strain, stress and residual stress are smaller in process of multi-layers than that of one layer, and the distributions of the stress and strain are more uniform. Based on the results, it was also found that the layered polyurethane elastic cushion can effectively improve the quality of forming parts in MPF.