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EN
Measurement of the process force in milling is usually conducted by using piezo-electric dynamometers which are costly and reduce the stiffness of the system. A less invasive alternative is an indirect estimation of cutting forces based on the power of the servo drives. However, a correction of frictional effects from the transmission system is necessary to achieve accurate results. Most machine tools are equipped with ball-screw drives whose friction behavior is highly nonlinear due to dependency on both velocity and position. This study provides a novel approach to consider all frictional and inertial effects in transmission behavior of ball-screw drives by utilizing the well-established generalized MAXWELL slip (GMS) model and combines it with a data-based approach, namely support vector regression (SVR). The approach acquires the internal states of the GMS model and uses them as an additionnal input for the SVR. The model is validated on different experiments conducted on a five-axis machining center and compared to established friction models, as well as a sole SVR. The results show the model to have errors between 7% and 12% over the full working range of the x- and y-axes, respectively, outperforming the benchmark models significantly.
EN
Composite materials are alternative materials to aluminum and titanium alloys. The wide-spread use of this materials makes it necessary to gain insight into the phenomena occurring in machining processes for thin-walled structures. This paper shows the investigation of the machinability of thin-walled composite materials. The study involved milling glass and carbon reinforced plastics using tools dedicated to the processing of this type of material. Their machinability was determined based on the measured feed force, deformation and surface roughness. In addition, surface analysis was performed by SEM. The results showed that the feed had the greatest impact on the feed force, deformation and surface roughness, followed by cutting speed. Lower values of the measured machinability indicators such as the maximum feed force and roughness were obtained for composites with glass fibers. Lower deformations were induced in the machining of composites with carbon fibers. The study also involved conducting a recurrence analysis in order to select the most appropriate quantifications depending on the technological parameters of milling. It was found that the most appropriate indicators related with the technological parameters for both materials were laminarity and averaged diagonal length.
EN
The paper focuses on the problem of selecting the correct tool geometry in high-speed milling of 316L stainless steel. Carbide milling cutters with two configurations of helix angle (40/42 degrees for tool#1 and 35/38 degrees for tool#2) with different cutting edge radiuses rn (i.e. 4 µm, 6 µm, 8 µm, 10 µm and 12 µm) were prepared and their impact on cutting force and roughness were analyzed. The obtained results revealed that the small changes in cutting edge radius rn have a significant effect on both cutting forces and surface roughness. In this context, irrespective to the type of the tool, increasing the cutting edge radius results in further cutting force. However, increasing the cutting edge radius shows different behavior on roughness while using different tool helix angles. For the tool#1, it was found that the surface roughness increases by increasing the cutting edge radius from 6 μm to 12 μm; while in the samples machined by tool #2, increase in cutting edge radius results in reduction of roughness. It was also found that irrespective to the values of cutting edge radius, the cutting force while using tool #1 is slightly less than the tool#2. In addition, the induced milling surface roughness of the samples machined by tool#2 is significantly less than the tool#1 where the mean value of Ra was reduced from 2.55 µm to 0.35 µm
EN
This study emphasizes on the physicochemical and grindability characteristics and work index of an alluvial formed silica dominated ferro-columbite mineral from Rayfield-Jos minefields in Plateau state, Nigeria. Investigations were also carried out in order to determine the mineralogy of the mineral deposits and most essentially the actual energy consumed during comminution and milling of the mineral so as to achieve the liberation size prior to high efficient mineral processing or beneficiation and the extraction of value metals. The distribution of the mineral particles as well as their sizes was determined, with a mineral liberation size fraction range essentially established as -150+90 μm particle sizes. Mass percentage of each size fraction obtained from PSD analysis conducted before and after comminution was also determined, obtaining 80% passing for both the mineral feeds and comminuted products. Berry and Bruce modified Bond’s work index was therefore obtained, and was determined to be within the range of 2.0414 to 2.5667 kWh/ton. Hence, the energy consumed or required to comminute or grind the Fe-columbite mineral to 80% passing is expected to fall within the range of 0.3613 to 0.4543 kWh. Thus, it could be said that a low milling work index as well as moderately low energy is required for comminution and this can be attributed to the mineralogy, mineral source and alluvial formation of the mineral reserve. Therefore, the grindability/PSD result of the mineral sample indicates that its mineralogy is considered a class of moderately soft mineral type in terms of texture with easy grindability.
EN
Variation in cutting forces with cutting parameter selection, tool geometry, and wear status plays an important role for milling process evaluation and modeling. While piezoelectric force measurement is commercially available, it is often considered a precise but expensive method. This paper presents a novel solution for vector-valued cutting force measurement. The table-mounted, flexure-based kinematics provide three degrees of freedom that are used to measure the in-process milling force vector components in the working plane by low-cost optical sensors. Based on analytical models and FEM analysis, an appropriate design was derived. The assembly and testing of the developed dynamometer are presented. A test setup based on a machining center was used for the system evaluation and the data are compared to the forces measured by a commercially available, piezoelectric cutting force dynamometer.
EN
CNC milling machines are frequently used in the manufacturing of mechanical parts in the industry. One of the most important components of milling machines is the cutting tool. Monitoring the cutting tool wear is important for the reliability, continuity, and quality of production. Monitoring the tool and detecting the stage of wear are difficult processes. In this work, the convolutional neural network (CNN), which is a deep learning method in which the features are extracted by an inner process, was performed to detect the wear stages of the milling tool. These stages that define the total lifespan of the tool are known as initial wear (IW), steady-state wear (SSW), and accelerated wear (AW). Short Time Fourier Transform (STFT) was applied to signals, and signal spectrograms were used to train CNN models with different complex architectures. Vibration signals, acoustic emission signals, and motor current signals from The Nasa Ames Milling Dataset were used to obtain the spectrograms. Pre-trained CNNs (GoogleNet, AlexNet, ResNet-50, and EfficientNet-B0) detected the tool wear stage with varying accuracies. It has been seen that the time duration of model training increases as the size of the dataset grows and the network architecture becomes more complex. The recommended method has also been tested on the 2010 PHM Data Challenge Dataset. CNN shows promise for condition monitoring of milling operations and detecting tool wear stage.
EN
The aim of the research is to classify and evaluate the size of deformations appearing during milling of thin-walled elements representing a pocket form made of aluminum alloy AW-7075A. Finishing, which is the purpose of the research, was carried out at the full depth of cut ap = 15 mm, milling the entire height of the wall in one pass. Deformations during machining were correlated with the geometric accuracy of the workpieces after machining. During the tests, deformations were measured with a laser displacement sensor, and the temperature of the samples was measured using a resistance temperature sensor. The tests made it possible to identify deformations occurring during the milling of thin-walled elements. The course of deformation during milling was analyzed, from which the value of deformation caused by milling, the reaction to this deformation and its time were extracted, additionally, permanent distortion of the workpiece was detected. The results show the effect of the ratio of the height to the thickness of the thin-walled element on its geometric accuracy after machining in the form of straightness and flatness of the samples. The test results were compared to the tests carried out on the Ti6Al4V titanium alloy, which confirmed the influence of the material selection on the course of deformations during milling.
EN
Polymer composites are widely used in various fields and industries. This study investigated milling of four different glass and carbon fiber reinforced plastics. First, feed force values were determined in the milling process conducted using tools with polycrystalline diamond inserts, with titanium nitride-coated cemented carbide inserts and with uncoated ground cemented carbide inserts. Machined surfaces were then examined for roughness. Using scanning microscopy (SEM), differences in the surface layer were also determined. Results showed that the lowest force values were obtained in milling of glass fiber reinforced plastics using tools with polycrystalline diamond inserts. The best machining results in terms of roughness were obtained after milling glass fiber reinforced plastics.
9
Content available remote Trendy rozwoju narzędzi w aplikacjach z sektora lotniczego
PL
Produktywność jest jednym z głównych wyzwań w świecie nowych technologii. Dzięki niej koszty wytworzenia danego elementu mogą być mniejsze. Nierzadko to właśnie cena decyduje o możliwości dotarcia produktu do szerszego grona odbiorców. Często niezauważone przez zwykłego konsumenta są technologiczne aspekty, czyli maszyny uzbrojone w odpowiednie narzędzia. A w świecie opanowanym przez szybkość i wydajność to właśnie one stanowią klucz do sukcesu.
EN
In the world of new technologies, the main challenge is productivity. It is reflected in a reduction in the cost of an item, which in turn determines the success of a product. In the world of global marketing, the ultimate price determines the ability to reach a broader group of clients. Somewhere at the end of this puzzle, unnoticed by an ordinary consumer, are technological machines armed with tools. In a world dominated by speed and performance, they are the key to success.
EN
The quality of the geometric structure of a surface is influenced by factors such as the geometry of the cutting tool, the cutting conditions and the displacements in the tool-workpiece system. This paper describes the results of a study to analyse the influence of selected machining factors accompanying the face milling process on the geometric structure of the surface. During the machining tests, relative displacements in the T-W system were recorded, as well as the components of forces and moments of the face milling process for specimens made of grey cast iron. The tests were carried out on an AVIA VMC 800 milling centre, and the accuracy of the machined surface was checked. A Talysurf CCI - Lite Non-contact 3D Profiler, which was equipped with TalyMap Platinum software, was used to measure the geometric structure of the surface.
PL
Na jakość struktury geometrycznej powierzchni wpływają takie czynniki, jak: geometria narzędzia skrawającego, warunki skrawania oraz przemieszczenia w układzie narzędzie-przedmiot obrabiany. W artykule opisano wyniki badań, których celem była analiza wpływu wybranych czynników obróbki towarzyszących procesowi frezowania czołowego na strukturę geometryczną powierzchni. W trakcie prób skrawania rejestrowano przemieszczenia względne w układzie N-P oraz składowe sił i momentów procesu frezowania walcowo-czołowego próbek wykonanych z żeliwa szarego. Próby przeprowadzono na centrum frezarskim AVIA VMC 800. Sprawdzono dokładność wykonania powierzchni poddanej obróbce frezarskiej. Strukturę geometryczną powierzchni zmierzono profilometrem Talysurf CCI - Lite Non-contact 3D Profiler, wyposażonym w oprogramowanie TalyMap Platinum.
EN
A new approach is presented to monitor the average cutting forces that are used for the calculation of the average cutting coefficients through neural networks using available controller signals. The cutting forces and the relevant controller signals are measured using a dynamometer and commercially available software supplied by the controller manufacturer in the calibration stage. Then a neural network is trained, which treats these controller signals as inputs and the cutting forces as the outputs. Finally, the average cutting forces for a new milling operation are predicted using the trained neural network without using a dynamometer. The proposed approach is validated using an experimental study, where a good match between predictions and measured forces is achieved. It is also shown that cutting coefficients can be calibrated and stability lobe diagrams can be generated using this method.
EN
Machining vibrations are an important issue as they occur in all types of machining processes. Due to its negative impact on machining results, this phenomenon is undesirable, and so there have been continuous efforts to find solutions that will minimise it, and thus improve the stability and safety of the machining process. The paper attempts to determine the impact of toolholder type and cutting condition on the vibrations generated while milling an AZ31 magnesium alloy. The tests were performed using the three most common types of toolholders: ER, Shrink Fit and hydraulic. The vibration displacement and acceleration signals were analysed based on parameters such as Peak-to-Peak, Peak, and Root Mean Square. Composite Multiscale Entropy was also applied to check the stability of cutting processes and define the level of signal irregularity. To determine the frequencies of vibrations and to detect chatter vibrations Fast Fourier Transform was performed. This provides information on the stability and enables vibrations to be minimized by avoiding unfavourable cutting conditions.
EN
This work presents the development of a safer processing route for hard metals. Traditional processing of fine particles under organic solvents presents significant explosion risks. The milling under dichloromethane (DCM) reduces the risks associated with fire hazards. After milling and drying, the samples have been sintered in an industrial sintering furnace under a vacuum at 1380°C. The materials’ characterisation has been done by X-ray diffraction, scanning electron microscopy, particle size analysis, optical microscopy, and by magnetic measurements. The present work results reveal the powders’ appropriate properties after milling and drying and the desired biphasic (Co-WC) phases obtained after sintering, thus proving the feasibility of such a route, therefore the diminishing of specific fire hazards.
EN
Purpose: The chip removal from the cutting zone of closed slots (T-shaped, "dovetail", etc.) is relevant since the repeated cutting of the chip with the blades of the tool teeth leads to a decrease in the resource of the cutting tool and processing accuracy. However, theoretical studies of the processes of filling, accumulation, and movement of the chip have not been considered. The purpose of the research is to develop the theoretical foundations of the chip filling and removing processes from profile slots using pneumatic hydrodynamic action of pressure jets of cooling liquid. Design/methodology/approach: Several stages of the analysed process are considered, namely the separation and filling of the space between the cutter teeth with the chip, filling the machined slot with the chip, removing the chip element from the space between the cutter teeth, moving the chip element along the machined slot, moving the chip array along the machined slot, pneumatic hydrodynamic impact. Findings: The complex of mathematical models have been developed to describe the functioning of the chip removal system during the milling of the closed profile slots in this research. The set of the developed models makes it possible to determine the required values of the design and operating parameters of devices that ensure the chip removal from the cutting zone as a result of the use of inertial forces and the application of additional compulsory forces. Research limitations/implications: Theoretical studies were applied for T-shaped slots for milling cutters with diameters from 12.5 mm to 95 mm made of high-speed steel and carbide inserts during steels and cast irons processing. The use of pneumatic hydrodynamic action is limited by the diameters of the nozzle hole from 0.5 mm to 3 mm. Practical implications: The practical significance of the research lies in the ability to control the process of timely chip removal from the cutting zone and to prevent the repeated ingress of the chip under the milling cutter blade. This is achieved by a set of mathematical models that simulate the chip removal process. Research can be applied in production in slots milling, using a liquid not only to cool the cutting zone but also to remove the chip in a timely manner. Originality/value: Theoretical studies previously not carried out for closed profile slots are presented in the research.
EN
The paper presents an overview of high-performance milling techniques of thin-walled elements. Currently, the tendency to simplify semi-finished products is used in aviation. In that case even 95% of semi-finished product mass is converted into chips, hence the increasing interest in such technol-ogies as: High Performance Cutting and High Speed Cutting. The aim of the paper was to research high-performance milling techniques of thin-walled elements in reference to conventional machin-ing. The material was the EN AW-7075 T651 aluminium alloy. A thin-walled pocket structure was designed and manufactured. The aspects related to geometric accuracy, surface quality and cutting time were analysed. On the basis of the obtained results, it was found that in case of geometric accu-racy related to the wall deformation, the greatest deformation was obtained after HPC, while the smallest one after HSC. The difference was over 400% (comparing HPC to HSC). A similar relation-ship was also received for the quality of the machined surface. Analysing the cutting time, the best result was achieved after HPC in reference to HSC and conventional machining. Taking into ac-count all analysed variables, the best solution was a combination of HPC and HSC. Thanks to the use of high-speed machining as a finishing, it is possible to receive high geometric accuracy and quality of the machined surface, while the application of HPC for roughing allows to shorten the cutting time, translating into an increase in the efficiency of the milling process. Conventional ma-chining is slightly less advantageous in terms of geometric accuracy and surface quality and it could possibly be used alternatively with High Speed Cutting, but its weakness is significantly lower effi-ciency compared to high-performance machining.
EN
The paper describes the effect of cutting parameters and tool geometry on the surface quality after machining of an Al/CFRP (aluminium alloy/ Carbon Fibre Reinforced Plastics) sandwich structure. A two-layer sandwich structure made of an EN AW 2024 aluminium alloy and Carbon Fibre Reinforced Plastics (CFRP) was examined. The experiment used the process of peripheral milling. The experiment investigated the effects of cutting speed (vc), feed per blade (fz) and helix angle (λs) on surface quality as defined by differences in the height of materials. It was also analysed how the machining conditions described above affected the values of cutting force components. In the experimental stage of the study, uncoated, double-bit carbide mill cutters with working diameter Dc = 12mm and a variable helix angle (λs = 20˚, λs = 35˚, λs = 45˚) were used. The results have shown that cutting parameters and tool geometry do affect the surface quality and cutting forces after milling of the sandwich structure. The lowest material height difference was achieved when machining with the helix angle λs = 45˚, cutting speed vc = 300m/min and feed per blade fz = 0.08mm/blade. The highest material height difference occurred after machining under the following conditions: vc = 300m/min, fz = 0.08mm/min, λs = 20˚. The minimum cutting force value was obtained for cutting parameters: vc = 80m/min, fz = 0.08mm/blade during milling with the helix angle λs = 45˚. The maximum cutting force was recorded during machining with the helix angle λs = 20˚, cutting speed vc = 400m/min and feed per blade fz = 0.08 mm/blade.
17
EN
Due to the wide application of Carbon Fiber Reinforced Polymer (CFRP) composites in various industries, more and more attention is paid to machining these materials. One of the most popular way of machining composites is the milling. Milling of composite materials (CM) is a difficult technology due to their anisotropic and heterogeneous structure and the fact that the reinforcing fibers have an intense abrasive effect on the tool edge during machining. The appropriate selection of technological cutting parameters as well as the type and geometry of the tool can significantly affect the value of cutting forces during milling and the quality of the surface after machining. The aim of the paper is to assess the influence of used tools (differing in the number of cutting edges) and various technological parameters of surface milling of CFRP composites on the cutting forces occurring during machining and on the surface quality after machining. Cutting forces were measured during the milling process on a special stand produced by Kistler and the roughness measurements and surface structure were analyzed using the Alicona InfiniteFocusG5 3D optical microscope. On the basis of performed research it was found that 14 edge tool gives lower values of Fx and Fy components of the cutting forces comparing to 2 edge tool, which is especially noticeable at higher cutting speed values vc=160 m/min, where the values of Fx and Fy components decreased by about 43% at fz=0.0030 mm/tooth. This tool gives also lower values of the Sa roughness parameter 1.65 µm.
EN
The paper presents the results of measurements of chip temperature in the cutting zone during milling. The main aim of the research was to record and compare the maximum chip temperature in consecutive frames of thermal images. An additional goal may be the influence of changes in technological parameters on the temperature of the chips in the cutting zone. Two grades of magnesium alloys were used for the tests: AZ31 and AZ91HP. The research used a carbide milling cutter with an additional chip breaker, dedicated to effective roughing of light alloys. These tool geometries can assist in the high-performance machining of magnesium alloys by efficiently splitting the chip and consequently reducing friction in the machining zone. This can reduce the cutting area temperature. The results of the research work were showed as exemplary "time" charts, box-plot charts and a summary table, which additionally included an error analysis of the measurement method. On the basis of the tests and measurements performed, it can be concluded that despite the observed chip fragmentation, the obtained temperatures can be defined as the so-called safe milling areas. During the machining tests, the risk of chip ignition during machining was not observed, also the characteristic melting points, which clearly indicates the safety of the milling process of these alloys. It has been observed that with the increase of vc and fz, there was no increase in the maximum temperature of the chip in the cutting area. This situation only occurs when increasing ap.
EN
The paper presents the results of modeling 2D surface roughness parameters in milling by means of an artificial neural network (ANN). The AZ91D magnesium alloy was used. A HSS milling cutter was employed in the research. The main aim of the study was to obtain the lowest possible surface roughness (good quality) using a commonly available HSS cutter. The results of the research work were presented in the form of bar charts, surface charts and graphs depicting the quality of artificial neural networks. The conducted research shows that it is possible to carry out the machining processes that enable obtaining an average surface quality (defined by roughness parameters Ra, Rz, RSm, Rsk). The Ra, Rz, RSm parameters increase along with the machining parameters (fz, ap), as expected. The Rsk parameter takes (in most cases) negative values, which may indicate a surface with more intense friction and indicative of flat-topped distribution. On the other hand, the results of modeling the selected parameters – Ra, Rz, RSm – with the use of artificial neural networks allow concluding that the obtained network models show satisfactory predictive ability (R = 0.99), and thus are an appropriate tool for the prediction of surface roughness parameters.
EN
Subtracting manufacturing technologies have entered that realm of production possibilities which, even a few years ago, could not be directly adapted to direct production conditions. The current machines, i.e. heavy, rigid cutting machines using high spindle speed and high feed speed, allow for manufacturing very thin and relatively long parts for use in the automotive or aerospace industry. In addition, the introduction and implementation of new 70XX aluminium alloys with high strength parameters, as well as monolithic diamond cutting tools for special machining, have had a significant impact on the introduction of high-speed machining (HSM) technologies. The main ad-vantage of the applied manufacturing method is obtaining a very good smoothness and surface roughness, reaching even Sz = 6–10 μm and Sa <3 μm, and about four times faster and more efficient machining compared to conventional machining (for the beam part). Moreover, fixed and repeatable milling process of the HSM method, reduction of operational control, easy assembly of components and increase in the finishing efficiency compared to other methods of plastic processing (forming) are other benefits. The authors present a method using HSM for the manufacturing of aircraft parts, such as the chassis beam at the front of a commuter aircraft. The chassis beam assembly is made of two parts, front and rear, which – through a bolted connection – form a complete element replacing the previous part made using traditional technology, i.e., cavity machining, bending and plastic forming. The implementation of HSM technology eliminates many operations related to the construction of components, assembling the components (riveting) and additional controls during construc-tion and assembly.
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