A new method for 5-axis flank computer numerically controlled (CNC) machining is proposed. A set of tappered ball-end-mill tools (aka conical milling tools) is given as the input and the flank ...milling paths within user-defined tolerance are returned. Thespace of lines that admit tangential motion of an associated truncated cone along a general, doubly curved, free-form surface is explored. These lines serve as discrete positions of conical axes in 3D space. Spline surface fitting is used to generate a ruled surface that represents a single continuous sweep of a rigid conical milling tool. An optimization-based approach is then applied to globally minimize the error between the design surface and the conical envelope. The milling simulations are validated with physical experiments on two benchmark industrial datasets, reducing significantly the execution times while preserving or even reducing the milling error when compared to the state-of-the-art industrial software.
Thin-wall parts are common in the aeronautical sector. However, their machining presents serious challenges such as vibrations and part deflections. To deal with these challenges, different ...approaches have been followed in recent years. This work presents the state of the art of thin-wall light-alloy machining, analyzing the problems related to each type of thin-wall parts, exposing the causes of both instability and deformation through analytical models, summarizing the computational techniques used, and presenting the solutions proposed by different authors from an industrial point of view. Finally, some further research lines are proposed.
Firstly, this work investigates a new design of a conformal cooling channel for injection molding tools containing serial and parallel circuits. Secondly, a hybrid-manufacturing process, combining ...machining and metal powder additive manufacturing, was also evaluated to manufacture molds. Specimens were manufactured by selective laser melting (SLM) using stainless steel (Corrax®) powder, which was deposited on a pre-machined PH13-8Mo stainless steel substrate. The melting zone interface (MZI) between the two materials were assessed. The results showed that the laser-melted and machined surfaces were successfully melted and bonded. Thus, an injection mold was designed and manufactured. A pair of inserts containing the conformal cooling channels were manufactured by the hybrid process and another equivalent pair of inserts containing a conventional cooling system were produced only by machining. Injection molding was carried out alternating the two types of inserts. The results showed that the mold with the conformal cooling channels reduced the warpage of the injected plastic parts by a factor of ~7. The difference in temperature along the insert was reduced by a factor of ~10 and the molding cycle time was around 36% shorter compared with that of the conventional mold. Overall, the proposed hybrid manufacture of the inserts reduced the manufacturing costs and time by 53% and 60%, respectively. The results indicate the benefits of using the proposed conformal cooling design and the hybrid-manufacturing approach, which combines machining with additive manufacturing for injection mold production.
Machine tools are the main production factor for many industrial applications in many important sectors. Recent developments in new motion devices and numerical control have lead to considerable ...technological improvements in machine tools. The use of five-axis machining centers has also spread, resulting in reductions in set-up and lead times. As a consequence, feed rates, cutting speed and chip section increased, whilst accuracy and precision have improved as well. Additionally, new cutting tools have been developed, combining tough substrates, optimal geometries and wear resistant coatings. "Machine Tools for High Performance Machining describes in depth several aspects of machine structures, machine elements and control, and application. The basics, models and functions of each aspect are explained by experts from both academia and industry. Postgraduates, researchers and end users will all find this book an essential reference.
The versatility and potential applications of additive manufacturing have accelerated the development of additive/subtractive hybrid manufacturing methods. LPBF processes are exceptionally efficient ...at producing complex-shaped, thin-walled, hollow, or slender parts; however, finishing machining operations are necessary to ensure part assembly and surface quality. Rapid solidification during LPBF processes generates columnar grain structures in alloys. This is associated with crystalline textures and anisotropy, and therefore, mechanical properties are highly dependent on space directions, thus affecting cutting force and its variability.
In this study, theoretical and experimental analyses examined the effects of LPBF parameters on cutting forces and the anisotropy of alloys. Therefore, an oblique cutting Taylor based model was proposed to quantify the crystallographic effects on the shear strength. For this, the tool geometry, tool position, and laser scanning strategy were considered along with the microstructures, crystallographic textures and grain morphologies of two samples with different layer thicknesses (low-volumetric energy density (VED) and high-VED) using scanning electron microscopy and electron backscatter diffraction. Peripheral milling operations had been performed under 54 experimental conditions to evaluate the interactions between the machining parameters along with the layer thickness and the microstructural characteristics of printed alloys. The analysis revealed a significant interaction between the direction of the plane of the shear band and the grain orientation along the main axis. Three milling configurations were evaluated. The effects of the layer thickness on the evolution of the cutting force were elucidated. Additionally, the low-VED sample exhibited higher anisotropy in the cutting force compared to the high-VED one. The anisotropy in the latter corresponds to a high, dense ring-like texture; however, the crystallographic effect is lower in the low-VED sample. A good correlation between the cutting force fluctuation and the predicted Taylor factor was obtained. Lastly, the grain boundary density was acceptably correlated with the level of cutting force for both the printed cases.
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•Correlation between directional dependency of the measured milling force response and crystallographic effect is quantified.•Tool-test piece relative position and grain refining interaction is evaluated.•Cutting forces are reduced for low volumetric energy density (VED)fabrications (grain refining) when tool axis and grain major axis are parallel.•A correlation between cutting force levels and grain boundary density is observed.
•Iterative design methodology to improve the stiffness of LPBF components considering machining and anisotropy effects.•Young's modulus improvement by evaluating the elastic anisotropy of different ...manufacturing configurations.•Application to case study for finishing of thin-walled bent ducts.
Additive manufacturing of metallic parts has witnessed significant development. The laser powder bed fusion (LPBF) process has emerged as a key process for manufacturing thin-walled components. However, despite the significant advances, post-machining operations are required for the improvement of dimensional and surface quality, specifically in low stiffness components. This study proposed an iterative design methodology for improving the stiffness of such LPBF components. In the first stage, an initial assessment of the machining conditions was performed to obtain a first approach to the relationship between tooth passing, natural, and chatter frequencies. Thereafter, a method to improve Young's modulus was proposed by evaluating the elastic anisotropy of different manufacturing configurations. Furthermore, LPBF lateral stiffeners were included in the workpiece design, thereby converting the final workpiece into a temporary assembly. The proposed methodology was applied in a case study for finishing thin-walled bent ducts and a comparison for surface quality between stiffened and non-stiffened ducts using the proposed methodology was conducted. A significant roughness and cutting force reduction (≈50%) were obtained for the stiffened duct.
Prediction and control of machining distortion is a primary concern when manufacturing monolithic components due to the high scrap and rework costs involved. Bulk residual stresses, which vary from ...blank to blank, are a major factor of machining distortion. Thus, a bulk stress characterization is essential to reduce manufacturing costs linked to machining distortion. This paper proposes a method for bulk stress characterization on aluminium machining blanks, suitable for industrial application given its low requirements on equipment, labour expertise, and computation time. The method couples the effects of bulk residual stresses, machining stresses resulting from cutting loads on the surface and raw geometry of the blanks, and presents no size limitations. Experimental results confirm the capability of the proposed method to measure bulk residual stresses effectively and its practicality for industrial implementation.
Accurate finite element models of mechanical systems are fundamental resources to perform structural analyses at the design stage. However, uncertainties in material properties, boundary conditions, ...or connections give rise to discrepancies between the real and predicted dynamic characteristics. Therefore, it is necessary to improve these models in order to achieve a better fit. This paper presents a systematic three-step procedure to update the finite element (FE) models of machine tools with numerous uncertainties in connections, which integrates statistical, numerical, and experimental techniques. The first step is the gradual application of fractional factorial designs, followed by an analysis of the variance to determine the significant variables that affect each dynamic response. Then, quadratic response surface meta-models, including only significant terms, which relate the design parameters to the modal responses are obtained. Finally, the values of the updated design variables are identified using the previous regression equations and experimental modal data. This work demonstrates that the integrated procedure gives rise to FE models whose dynamic responses closely agree with the experimental measurements, despite the large number of uncertainties, and at an acceptable computational cost.
Machining of titanium alloys such as Ti-6Al-4 V can be very intimidating due to their low thermal conductivity leading to elevated cutting temperatures at the chip-tool interface (ICT). In this ...regard, the self-lubrication effect of coatings like TiSiVN represented by topography, oxidation, and diffusion at the chip-tool interface are crucial. Thus, the present work investigates the latter three mechanisms during dry machining of Ti-6Al-4 V titanium alloy with uncoated and TiSiVN coated Al2O3/SiC whiskers-reinforced ceramic cutting tools. The results reveal that the adhesion height (AH) and O% increases with cutting temperature, showing the dominant influence of cutting temperature on material adhesion and oxidation levels at the ICT. AH increases with increased cutting speed for both coated tools, indicating that the crater depth increment was not so severe for the coated tools. However, a drastic upward surge of crater depth for uncoated and TiSiN coated tools at 125 m/min cutting speed makes the crater edge near the ICT act as a chip breaker and facilitates the chip's bending away from the tool face causing reduction in chip bend angles (BA). Additionally, the TiSiVN coating accounts to a reduction of approximately 23% in AH and 18% in Ti%, and 37% lower oxygen levels at the highest cutting speed when compared to the uncoated tool primarily due to lower cutting temperatures and self-lubricating behavior.
Machining parameters affects the final quality of components made in carbon fiber reinforced plastic (CFRP) composite materials. In this framework, the work here presented aims at studying the right ...combination of cutting speed (vc) and feed rate (vf), for dry drilling of carbon fiber reinforced plastic composite materials, which obtained better results regarding roughness, hole cylindricity, and diameter. A series of experimental tests were carried out under different drilling conditions (vc/vf), monitoring the thrust force (Fz), torque (T), and electric power (EP), to define which one can help more for industrial daily life production. Results validation was carried out using the analysis of variance, in order to relate main machining parameters cutting speed and linear feed, with thrust force, drilling torque, main spindle electric power and hole quality parameters (average roughness, cylindricity and diameter). The conclusions show that thrust force is not proportional to the cutting speed and the best combinations of cutting speed and feed were found out around the average values of tested parameters. Spindle electric power is an interesting element to take into account because it is easy to consider in real production.
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