Subtractive Manufacturing Techniques Research Articles

On morphology and roughness of upskin surfaces in laser powder-bed fusion additive manufacturing – Contouring strategy effects

The surface quality of inclined parts made by Laser powder-bed fusion (L-PBF) additive manufacturing is inferior to those made by conventional formative and subtractive manufacturing techniques. The inherited step edges formed during such layer-by-layer fabrications and partially melted or non-melted particles attached to the newly formed surface are the major causes of poor surface finish of L-PBF parts. This study is a part of a research framework, in which the effects of different contouring strategies and scan parameters on the surface morphology of inclined parts are investigated by both experimental and numerical methods. In particular, the effect of two different contour scan strategies, namely pre-contouring and post-contouring, on the upskin surface roughness of 30⁰ inclined parts is analyzed. The inclined specimens were fabricated with Ti6Al4V powder using an EOS M270 system and the upskin surfaces were measured by a white light interferometer. In addition, a multi-track multi-layer numerical approach using coupled discrete element method and thermo-fluid simulation was also performed to understand the inclined surface formation in L-PBF.The findings show that the pre-contouring strategy with high linear energy density (LED) (0.4 J/mm) results in average surface roughness (Sa) as low as 7.43 µm, whereas the lowest LED (0.05 J/mm) resulted in the highest Sa of 33.74 µm. Larger melt pool dimensions were obtained in the high LED pre-contouring simulations, which indicates a better material fusion resulting in a good surface finish. The numerical simulation showed that the upskin surface roughness is also affected by the raster scan, if the raster scanning LED is higher than that of pre-contour scans. For the post-contouring strategy studied, higher and lower LEDs were used in inner and outer contour scanning, respectively. It is indicated that the inner contour scanning with a high LED reduces the surface roughness because of a larger melt pool size, irrespective of outer contour scanning. The lowest Sa obtained was 8.24 µm for the highest LED inner contour (0.05 J/mm) case and the highest Sa was 19.95 µm, for the parts made with the lowest LED inner contour scan (0.075 J/mm) strategy. The coupled discrete-element and thermo-fluid-based simulations offer insights into the sloped surface formation and the results supported the experimental findings in qualitative manner.

THE EFFECT OF DIFFERENT STAINING SOLUTIONS ON THE COLOR STABILITY OF PERMANENT INDIRECT COMPOSITE RESINS PRODUCED BY ADDITIVE AND SUBTRACTIVE TECHNIQUES

Objective: To investigate the effects of various beverages on the color stability of permanent composite resins produced by additive (AM) or subtractive manufacturing (SM) techniques comparatively. Materials and Methods: Six composite resin materials produced by SM (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and AM (Varseo Smile Crown plus-VSC, Saremco print Crowntech-SPC, Formlabs 3B Permanent Crown-FPC) techniques were selected and soaked in different solutions (artificial saliva, black tea, coffee) for different times (0, 1 and 7 days). L*, a*, b* values of the samples were recorded using a spectrophotometer. The color changes of the samples were determined using the CIELAB formula. In determining the color differences between the test materials, Kruskal-Wallis analysis was used when one-way analysis of variance wasn’t available. Results: Group VE was the least stained group on the 1st and 7th day of artificial saliva solution and the 7th day of coffee solution, while Group CE was the least stained group on the 1st day of coffee solution. In the tea solution, on the 1st and 7th days, there wasn’t difference in the materials' color change (p>0.05). Tea and coffee solutions caused statistically significantly more color change in all test materials than artificial saliva (except Group CE on the 7th day, Group VSC and FPC on the 1st day) (p<0.05). Conclusion: 3D permanent composite resins generally showed more staining than CAD/CAM milled composite resins. Tea and coffee staining solutions changed the color of the materials compared to artificial saliva. As the storage time increased, more color changes were observed.

A model-adaptive compensation algorithm for additive-subtractive hybrid manufacturing

Abstract Additive-subtractive hybrid manufacturing (ASHM) is a manufacturing method that combines additive manufacturing (AM) with subtractive manufacturing (SM) techniques. Given that the surface accuracy of ASHM components primarily relies on numerical control (NC) machining, it is imperative to incorporate model compensation to preserve finishing allowances, thereby obtaining additive manufacturing (AM) models from design models. This paper proposes a model adaptive compensation algorithm capable of dynamically adjusting the design model based on both model characteristics and the AM process. This algorithm not only ensures the retention of suitable finishing allowances but also addresses part size errors arising from the AM process. Comparative analysis against traditional CAD reconstruction methods highlights the algorithm’s superior attributes in terms of accuracy, efficiency, and adaptability when confronted with intricate model compensation scenarios.

Comparison of Tensile Bond Strength of Soft Denture Liner Material on Denture Base Resins

Aim: This study aims to evaluate the tensile bond strength (TBS) of a silicone-based soft denture liner material on denture bases produced via conventional, subtractive, and additive manufacturing techniques and examine the effect of aluminum oxide particle abrasion (APA) on TBS. Material and Methods: A total of 48 cylindrical denture base resin samples were manufactured using three different techniques: conventional, subtractive, and additive manufacturing. The samples were divided into two groups: control and APA. All samples were separated at the center, and the soft liner was applied to the corresponding surfaces. The specimens then underwent TBS testing. Data were analyzed using Two-way ANOVA and Bonferroni post hoc tests. Results: Two-way ANOVA results indicated a significant difference among the denture base resins, while no significant difference was found between the control and APA groups. The highest TBS was observed in the subtractive-manufactured APA group, while the lowest TBS was in the additive-manufactured APA group. Significant differences were found between the subtractive and additive-manufactured groups (p=0.022). Conclusion: This study demonstrates that TBS varies with the DB's manufacturing technique. While APA increased TBS in subtractive manufacturing, it had no statistically significant effect. Further research should explore different soft lining materials and consider in vivo conditions for more comprehensive insights.

Advanced constraint programming formulations for additive manufacturing machine scheduling problems

In comparison with traditional subtractive manufacturing techniques, additive manufacturing (AM) enables fabricating complex parts through a layer-by-layer process. AM makes it possible to produce one-piece and lightweight functional products, which are traditionally made from several parts. This paper introduces constraint programming (CP) models to minimise makespan in single, parallel identical and parallel unrelated AM machine scheduling environments for selective laser melting. Alternative CP formulations are explored to improve efficiency. The proposed CP model significantly benefits from the introduction of interval variables to replace binary assignment variables, and pre-definitions to narrow the search space, resulting in increased search performance. A computational study has been conducted to compare the performance of our proposed CP model with both a mixed-integer programming and a genetic algorithm from existing literature, evaluating improvements made to its search capability. Computational results indicate that the proposed CP model can obtain high-quality solutions in a timely manner even for several large-size instances.

Bridging Nature and Technology: A Perspective on Role of Machine Learning in Bioinspired Ceramics

Nature has long inspired scientific and engineering advancements, particularly in the development of bioinspired ceramics. However, replicating nature's intricate structures through subtractive manufacturing techniques remains a significant challenge due to the limitations of precise and controlled material removal while maintaining structural integrity and complexity. This perspective article explores the transformative potential of machine learning (ML), particularly advancements in generative artificial intelligence (generative adversarial networks, transformer models) and multimodal learning, in accelerating the discovery of high‐performance bioinspired ceramics. ML offers an avenue to optimize material behavior beyond the constraints of traditional experimental methods. Recent advancements have shown ML's effectiveness in predicting mechanical properties and refining material designs, often surpassing conventional approaches. ML excels at identifying complex relationships even with incomplete data during training. The integration of cutting‐edge experimental data, cross‐scale simulations, and ML facilitates high‐fidelity multiscale modeling for predicting intricate phenomena like crack propagation paths in bioinspired ceramic structures. This article emphasizes the significant potential of ML to propel the field of bioinspired ceramics forward, paving the way for the discovery of ceramics with superior and tailored properties.

INNOVATIVE MATERIAL PROCESSING TECHNIQUES IN PRECISION MANUFACTURING: A REVIEW

Precision manufacturing plays a pivotal role in various industries, demanding high accuracy, efficiency, and quality in the production process. The continual pursuit of innovation in material processing techniques is essential to meet evolving demands and challenges. This review explores the latest advancements and innovations in material processing methods within precision manufacturing. The review encompasses a comprehensive analysis of various innovative material processing techniques, including additive manufacturing, subtractive manufacturing, and hybrid approaches. Additive manufacturing, often referred to as 3D printing, has gained significant attention for its capability to produce complex geometries with high precision. The exploration of novel materials, such as metal alloys, polymers, and composites, expands the applicability of additive manufacturing in diverse industrial sectors. Subtractive manufacturing techniques, such as milling, turning, and grinding, are also undergoing transformative advancements to enhance precision and efficiency. Emerging technologies like abrasive waterjet machining, electrical discharge machining (EDM), and laser machining offer improved accuracy and surface finish while enabling the processing of a wide range of materials, including hard-to-machine alloys and composites. Hybrid manufacturing approaches, combining additive and subtractive techniques, are revolutionizing precision manufacturing by leveraging the strengths of both methods. These hybrid systems enable the production of intricate components with high precision, reduced lead times, and minimized material waste, addressing the challenges of traditional manufacturing processes. Furthermore, the review highlights advancements in process monitoring and control technologies, such as in-process sensing, real-time feedback systems, and adaptive control algorithms, facilitating enhanced quality assurance and productivity in precision manufacturing. The integration of advanced computational tools, simulation techniques, and artificial intelligence further augments the optimization and customization capabilities of material processing techniques, driving efficiency and innovation in precision manufacturing. Overall, this review provides valuable insights into the latest developments and trends in innovative material processing techniques, offering a roadmap for future research directions and applications in precision manufacturing industries.
 Keywords: Material, Processing, Techniques, Precision, Manufacturing, Review.

Three-dimensional printing of wood.

Natural wood has served as a foundational material for buildings, furniture, and architectural structures for millennia, typically shaped through subtractive manufacturing techniques. However, this process often generates substantial wood waste, leading to material inefficiency and increased production costs. A potential opportunity arises if complex wood structures can be created through additive processes. Here, we demonstrate an additive-free, water-based ink made of lignin and cellulose, the primary building blocks of natural wood, that can be used to three-dimensional (3D) print architecturally designed wood structures via direct ink writing. The resulting printed structures, after heat treatment, closely resemble the visual, textural, olfactory, and macro-anisotropic properties, including mechanical properties, of natural wood. Our results pave the way for 3D-printed wooden construction with a sustainable pathway to upcycle/recycle natural wood.

Effect of thermocycling on the mechanical properties of permanent composite-based CAD-CAM restorative materials produced by additive and subtractive manufacturing techniques

BackgroundThe aim of the study was to determine and compare the biaxial flexural strength (BFS) and Vickers hardness (VHN) of additive and subtractive manufactured permanent composite-based restorative materials, before and after thermal aging.MethodsA total of 200 specimens were prepared; 100 disc-shaped specimens (diameter 13 × 1.2 mm) for the BFS test and 100 square specimens (14 × 14 × 2 mm) for the VHN test. The specimens were made from various materials: two subtractive composite-based blocks (Cerasmart 270 [CS], Vita Enamic [VE]), two additive composite-based resins used for two different vat polymerization methods (digital light processing [DLP]; Saremco Print Crowntec [SC] and stereolithography [SLA]; Formlabs Permanent Crown Resin [FP]), and one feldspathic glass-matrix ceramic block (Vita Mark II [VM]) as the control group. Specimens of each material were divided into two subgroups: thermal cycled or non-thermal cycled (n = 10). BFS and VHN tests were performed on all groups. Data were analyzed with two-way ANOVA and post hoc Tukey test (α = 0.05).ResultsThe type of restorative material used for the specimen had a statistically significant influence on both BFS and VHN values. However, thermal cycling did not affect the BFS and VHN values. After thermal cycling, the results of the BFS test were ranked from best to worst as follows: CS, FP, SC, VE, then VM. For the VHN values, the order from best to worst was as follows: VM, VE, CS, FP, then SC.Conclusions3D printed and milled composite groups showed higher BFS than feldspathic ceramics. When the VHN results were examined, it was seen that the 3D resin groups had the lowest VHN values. Furthermore, it was observed that the thermal cycle had no effect on BFS or VHN.

Comparison of textured nylon surfaces manufactured by CNC micromachining and 3D printing

Patterned surfaces can be designed and engineered to control friction and wear resistance in various applications. In the present work, a comparative analysis of two contrasting manufacturing processes for surface texturing of polyamide, namely 3D printing by fused filament fabrication (FFF) and CNC micromachining (micro CNC) as additive and subtractive manufacturing techniques respectively was carried out. The analysis included the evaluation of the topography, roughness, mechanical properties, and tribological performance of the texturized surfaces. Both manufacturing routes were suitable for fabricating deterministic surfaces, being the micro CNC method the one that provided better repeatability and surface finishing as well as higher hardness. These factors influenced the tribological behavior of the polyamide when in contact with AISI 304 stainless steel. The effects of size, distribution and height of the texture elements and the manufacturing technique on the Coefficient of Friction (COF) were also discussed.

Electrochemical Additive Manufacturing of Binary and Ternary Alloys at the Mircon Scale by Electrohydrodynamic Redox 3D Printing

The need for miniaturisation throughout many different industries brings classical subtractive manufacturing techniques to their limits. Additive manufacturing is able to overcome these limits which has made it a topic of interest in many scientific fields. This additional geometric freedom becomes increasingly important if feature sizes on the micron- or even nano-scale are desired. Multiple different techniques to fabricate device-grade metals at such length-scales have been reported [1]. As one of these techniques, electrohydrodynamic redox printing (EHD-RP) has shown promise to be a versatile fabrication tool [2, 3, 4] depositing dense, pure metallic structures at high deposition rates.In this contribution, we present our work on additively manufactured alloys. First, we introduce a novel EHD-RP approach using aqueous metal salt electrolytes instead of sacrificial anodes as ion sources. The use of metal salts not only expands the range of manufacturable metals, but also enables the fabrication of metal alloys with precise compositional control without the need for additives or a surplus of the less noble metal. We demonstrate this control by fabricating binary and ternary Cu-Ag, Cu-Zn and Cu-Ag-Zn alloys. The composition of the fabricated alloy exactly mirrors the composition of the aqueous metal salt solutions. These systems were chosen as a representative immiscible and miscible system, in order to study different growth mechanisms. Microstructural analysis of Cu-Ag alloys reveals the formation of a metastable mixed phase. Cu-Ag alloys were successively dealloyed to produce nano-porous Ag structures. The compositional control over the Cu-Ag alloy enables precise control of porosity in the dealloyed structures. These nano-porous Ag structures have also been tested as substrates for surface enhanced Raman spectroscopy.(1) L. Hirt, A. Reiser, R. Spolenak & T. Zambelli, Adv. Mater 2017, 29, 1604211(2) A. Reiser, M. Lindén, P. Rohner, A. Marchand, H. Galinski, A. S. Sologubenko, J. M. Wheeler, R. Zenobi, D. Poulikakos & R. Spolenak, Nat. Comm. 2019, 10, 1853(3) M. Nydegger, A. Pruška, H. Galinski, R. Zenobi, A. Reiser & R. Spolenak, Nanoscale 2022, 14, 17418(4) M. Menétrey, L. Koch, A. Sologubenko, S. Gerstl, R. Spolenak & A. Reiser, Small 2022, 18, 2205302

VASCO: Volume and Surface Co-Decomposition for Hybrid Manufacturing

Additive and subtractive hybrid manufacturing (ASHM) involves the alternating use of additive and subtractive manufacturing techniques, which provides unique advantages for fabricating complex geometries with otherwise inaccessible surfaces. However, a significant challenge lies in ensuring tool accessibility during both fabrication procedures, as the object shape may change dramatically, and different parts of the shape are interdependent. In this study, we propose a computational framework to optimize the planning of additive and subtractive sequences while ensuring tool accessibility. Our goal is to minimize the switching between additive and subtractive processes to achieve efficient fabrication while maintaining product quality. We approach the problem by formulating it as a Volume-And-Surface-CO-decomposition (VASCO) problem. First, we slice volumes into slabs and build a dynamic-directed graph to encode manufacturing constraints, with each node representing a slab and direction reflecting operation order. We introduce a novel geometry property called hybrid-fabricability for a pair of additive and subtractive procedures. Then, we propose a beam-guided top-down block decomposition algorithm to solve the VASCO problem. We apply our solution to a 5-axis hybrid manufacturing platform and evaluate various 3D shapes. Finally, we assess the performance of our approach through both physical and simulated manufacturing evaluations.

Micromechanical Models for FDM 3D-Printed Polymers: A Review.

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling (FDM). This is the most efficient technique for manufacturing physical three-dimensional thermoplastics, such that FDM machines are nowadays the most common. Regardless of the 3D-printing methodology, AM techniques involve layer-by-layer deposition. Generally, this layer-wise process introduces anisotropy into the produced parts. The manufacturing procedure creates parts possessing heterogeneities at the micro (usually up to 1 mm) and meso (mm to cm) length scales, such as voids and pores, whose size, shape, and spatial distribution are mainly influenced by the so-called printing process parameters. Therefore, it is crucial to investigate their influence on the mechanical properties of FDM 3D-printed parts. This review starts with the identification of the printing process parameters that are considered to affect the micromechanical composition of FDM 3D-printed polymers. In what follows, their (negative) influence is attributed to characteristic mechanical properties. The remainder of this work reviews the state of the art in geometrical, numerical, and experimental analyses of FDM-printed parts. Finally, conclusions are drawn for each of the aforementioned analyses in view of microstructural modeling.

Design and additive manufacturing of root analogue dental implants: A comprehensive review

Dental implants are key components in treating dental diseases and correcting dental defects, and they have gained widespread utilisation in various medical operations. However, traditional screw thread implants have been associated with certain drawbacks, including issues such as poor consistency with the alveolar bone and difficulty in customisation. Root analogue implants (RAI) are considered a promising substitute; however, they are not widely applied until now as their geometry design needs more improvements. The utilisation of porous structures, such as triply periodic minimal surfaces, in dental implants can reduce the elastic modulus, increase interconnectivity, and allow for strictly controllable structural characteristics. To achieve optimal initial and long-term stability, it is essential to have a moderate geometry that promotes a proper fit between the dental implants and the natural bone. Different porous and macro-retention structures of RAIs have been investigated due to the above two demands. However, owing to their complex porosity, such structures can only be effectively manufactured using additive manufacturing techniques. Various additive manufacturing technologies have been employed for the fabrication of dental implants and have provided good surface quality and mechanical properties. In vivo tests have demonstrated that their performance is similar to that of commercial implants fabricated using subtractive manufacturing techniques. In this review, we comprehensively examine the design concepts and processes involved in the development of dental implants, along with the application of additive manufacturing methods for their fabrication, while also offering recommendations for the future advancement of dental implant designs.

Surface trueness and precision of interim restorations fabricated by digital light processing and CAD-CAM milling systems

The development of digital dental technologies has enabled clinicians to use additive and subtractive manufacturing techniques to fabricate interim restorations. However, knowledge of the trueness and precision of such restorations fabricated using digital light processing (DLP) and computer-aided design and computer-aided manufacturing (CAD-CAM) methods is limited. The purpose of this in vitro study was to assess and compare the accuracy of interim crowns fabricated using DLP and CAD-CAM methods. A typodont mandibular first molar was prepared for a ceramic crown, and a digital scan (Medit T500) was obtained to design interim crowns by using the CAD software program. The CAD data were designated as the reference data. A total of 20 crowns were fabricated by DLP and CAD-CAM technology. The fabricated interim crowns were further scanned using a laboratory scanner and were superimposed with the CAD data by using a 3-dimensional (3D) point cloud assessing software program (CloudCompare) for the evaluation of trueness and precision. Root mean square values (RMS) were obtained for the evaluation of discrepancies. The Student t test was used to compare data as the Shapiro-Wilk test confirmed the normal distribution. RMS values for the trueness values of the external and intaglio surfaces of the 3D printed and milled interim crown displayed no statistically significant differences (P>.05). Precision for the external surface reported significance (P<.05), whereas that for the intaglio surface reported no significance (P>.05). The accuracy of interim crowns fabricated by using DLP was comparable with that of milled crowns. Both manufacturing systems produced a true reproduction of the CAD. As for precision, the external surface of the DLP interim crown was statistically different from that of the milled group as it relates to the CAD.

Performance and Durability of Non-Stick Coatings Applied to Stainless Steel: Subtractive vs. Additive Manufacturing.

This study compares subtractive manufacturing (SM) and additive manufacturing (AM) techniques in the production of stainless-steel parts with non-stick coatings. While subtractive manufacturing involves the machining of rolled products, additive manufacturing employs the FFF (fused filament fabrication) technique with metal filament and sintering. The applied non-stick coatings are commercially available and are manually sprayed with a spray gun, followed by a curing process. They are an FEP (fluorinated ethylene propylene)-based coating and a sol-gel ceramic coating. Key properties such as surface roughness, water droplet sliding angle, adhesion to the substrate and wear resistance were examined using abrasive blasting techniques. In the additive manufacturing process, a higher roughness of the samples was detected. In terms of sliding angle, variations were observed in the FEP-based coatings and no variations were observed in the ceramic coatings, with a slight increase for FEP in AM. In terms of adhesion to the substrate, the ceramic coatings applied in the additive process showed a superior behavior to that of subtractive manufacturing. On the other hand, FEP coatings showed comparable results for both techniques. In the wear resistance test, ceramic coatings outperformed FEP coatings for both techniques. In summary, additive manufacturing of non-stick coatings on stainless steel showed remarkable advantages in terms of roughness, adhesion and wear resistance compared to the conventional manufacturing approach. These results are of relevance in fields such as medicine, food industry, chemical industry and marine applications.

A Finite Element Analysis on the Effect of Scanning Pattern and Energy on Residual Stress and Deformation in Wire Arc Additive Manufacturing of EH36 Steel.

Wire arc additive manufacturing (WAAM) is a metal additive manufacturing (AM) technique that has a high throughput and has seen a potential interest for replacing currently available subtractive manufacturing techniques. Contrary to other metal AM machines, WAAM rigs can be built using existing welding plants and using welding wire as feedstock, thus, making it a cheap and viable manufacturing technique for a number of industries, such as the maritime industry. However, the effects of AM parameters, such as the scanning pattern and energy, on the residual stress and deformation, are still not completely understood. In this work, a finite element (FE) study has been conducted to understand the influence of different scanning patterns (alternate, in-out, raster and zigzag) and energies on residual stress and warpage. Analyses show that the in-out scanning pattern leads to the highest residual stress, while the zigzag pattern results in the lowest residual stress for all scanning energies considered in this study. Findings in the present study also show that the scanning pattern affects the residual stress and deformation more than does the scanning energy.

Manufacturing Guidelines for W-Band Full-Metal Waveguide Devices: Selecting the most appropriate technology

This article analyzes some of the key aspects of manufacturing techniques for passive components and antennas in the millimeter band, with emphasis on the W band. Even experienced microwave designers might face great technological challenges when upscaling their designs to higher-frequency bands. Thus, several manufacturing technologies are widely analyzed in this work by designing, manufacturing, and measuring different components in the W band. Subtractive manufacturing techniques, such as computer numerical control (CNC) milling and electrical discharge machining (EDM), as well as additive manufacturing techniques, including stereolithography (SLA), direct metal laser sintering (DMLS), and diffusion bonding (DB) are explored. The advantages and disadvantages of these technologies are evaluated using features such as manufacturing tolerances, accuracy, surface roughness, and cost. The purpose is to offer some guidelines for the selection of the most appropriate manufacturing technology in the W band, bearing in mind both the performance of the different manufacturing methods and the particular circuital topologies of the component under development.

Glass Additive and Subtractive Manufacturing of a Fiber Optic Rotary Encoder for Downhole Pressure Sensing

This article presents a fiber optic rotary encoder-based pressure sensor for downhole applications. The rotary encoder, which is composed of an encoding pad and an all-glass optical fiber sensing head, converts the rotation angles of a pressure transducer to digital codes. The optical fiber only serves as the telemetry channel to directly transmit the data in digital format such that the environmental temperature influence and the long-time drift are minimized. The glass additive and subtractive manufacturing (ASM) techniques are used to embed the multichannel optical fibers into a bulk-fused silica glass substrate. Because the fused silica glass shares a similar material property to the optical fiber (e.g., thermal expansion coefficient), the optical fiber sensing head is well sealed and fixed even at an elevated temperature. The picosecond laser blackening technique is used to fabricate the high reflectivity contrast encoding pad with high accuracy. The proposed pressure sensor was manufactured and experimentally verified to have a signal-to-noise ratio (SNR) of 23 dB and a linear pressure response with a root-mean-square error (RMSE) of 0.37. During the 400-h 250 °C long-term stability test, there was no digital code variation. In addition, a mathematical model to study the relationships between the sensor’s performances and design parameters was established. According to the model, a 12-bit encoder (0.02% pressure sensitivity) can be achieved with a radius of 20 mm.

Design, Manufacturing and Acoustic Assessment of Polymer Mouthpieces for Trombones

Brass instruments mouthpieces have been historically built using metal materials, usually brass. With the auge of additive manufacturing technologies new possibilities have arisen, both for testing alternative designs and for using new materials. This work assesses the use of polymers for manufacturing trombone mouthpieces, specifically PLA and Nylon. The acoustical behavior of these two mouthpieces has been compared with the obtained from a third one, built from brass. Both additive and subtractive manufacturing techniques were used, and the whole manufacturing process is described. The mouthpieces were acoustically assessed in an anechoic chamber with the collaboration of a professional performer. The harmonic analysis confirmed that all the manufactured mouthpieces respect the harmonic behavior of the instrument. An energy analysis of the harmonics revealed slight differences between the mouthpieces, which implies differences in the timbre of the instrument. Although these subtle differences would not be acceptable when performing with the instrument in an orchestra, they could be perfectly valid for early learners, personal rehearsals or any kind of alternative performance.