Subtractive Manufacturing Technologies Research Articles

Accuracy, adaptation and margin quality of monolithic zirconia crowns fabricated by 3D printing versus subtractive manufacturing technique: A systematic review and meta-analysis of in vitro studies

ObjectiveThe purpose of this systematic review and meta-analysis was to evaluate the accuracy (trueness and precision), marginal and internal adaptation, and margin quality of zirconia crowns made by additive manufacturing compared to subtractive manufacturing technology. MethodsThe investigation adhered to the PRISMA-ScR guidelines for systematic reviews and was registered at the Prospero database (n°CRD42023452927). Four electronic databases, including PubMed, Scopus, Embase, and Web of Science and manual search was conducted to find relevant studies published until September 2023. In vitro studies that assessed the trueness and precision, marginal and internal adaptation, and margin quality of printed crowns compared to milled ones were included. Studies on crowns over implants, pontics, temporary restorations, laminates, or exclusively experimental materials were excluded. ResultsA total of 9 studies were included in the descriptive reporting and 7 for meta-analysis. The global meta-analysis of the trueness (P<0.74,I2=90 %) and the margin quality (P<0.61,I2=0 %) indicated no significant difference between the root mean square of printed and milled zirconia crowns. The subgroup analysis for the printing system showed a significant effect (P<0.01). The meta-analysis of the crown areas indicated no significant difference in most of the areas, except for the marginal (favoring milled crowns) and axial (favoring printed crowns) areas. For precision and adaptation, both methods showed a clinically acceptable level. ConclusionsAdditive manufacturing technology produces crowns with trueness and margin quality comparable to subtractive manufacturing. Both techniques have demonstrated the ability to produce crowns with precision levels, internal discrepancy, and marginal fit within clinically acceptable limits. Clinical significance3D printing emerges as a promising and potentially applicable alternative method for manufacturing zirconia crowns, as it shows trueness and margin quality comparable to restorations produced by the subtractive method.

3D printers and their use in prosthetic dentistry

In recent years, the use of computer-aided design and computer-aided manufacturing (CAD/CAM) has increased considerably in addition to the traditional methods used in routine. CAD/CAM technology has many advantages. However, despite these advantages, it has a very important disadvantage such as material waste. Today, the technology that overcomes this problem is the additive manufacturing method with three-dimensional printers. This method has recently replaced the traditional subtractive computer-aided design and manufacturing technology in prosthodontics. The use of 3D printers has been increasing in recent years due to its advantages such as ease of production, time saving and material saving, freedom of design, error-free and faster production. It is also predicted that the use of this technology will increase in the future and will be the main method for digital manufacturing. The aim of this review is to evaluate the production methods of 3D printers, the areas of use in prosthodontics, the advantages and disadvantages of 3D production methods, and to review the purposes of use, materials used and developments in prosthodontics.

Fabricating Precise and Smooth Microgroove Structures on Zr-Based Metallic Glass Using Jet-ECM.

Zr-based metallic glasses (MGs) are promising materials for mold manufacturing due to their unique mechanical and chemical properties. However, the high hardness of metallic glasses and their tendency to crystallize at high temperatures make it challenging to fabricate precise and smooth microscale structures on metallic glasses. This limitation hampers the development of metallic glasses as molds. Jet electrochemical machining (jet-ECM) is a non-contact subtractive manufacturing technology that utilizes a high-speed electrolyte to partially remove material from workpieces, making it highly suitable for processing difficult-to-machine materials. Nevertheless, few studies have explored microgroove structures on Zr-based MGs using sodium nitrate electrolytes by jet-ECM. Therefore, this paper advocates the utilization of the jet-ECM technique to fabricate precise and smooth microgroove structures using a sodium nitrate electrolyte. The electrochemical characteristics were studied in sodium nitrate solution. Then, the effects of the applied voltages and nozzle travel rates on machining performance were investigated. Finally, micro-helical and micro-S structures with high geometric dimensional consistency and low surface roughness were successfully fabricated, with widths and depths measuring 433.7 ± 2.4 µm and 101.4 ± 1.6 µm, respectively. Their surface roughness was determined to be 0.118 ± 0.002 µm. Compared to non-aqueous-based methods for jet-ECM of Zr-based MGs, the depth of the microgrooves was increased from 20 μm to 101 μm. Furthermore, the processed microstructures had no uneven edges in the peripheral areas and no visible flow marks on the bottom.

Hot isostatic pressing as an alternative thermo-mechanical treatment for metallic full-arch implant-supported frameworks obtained by additive and subtractive manufacturing technology: Vertical and horizontal fit, screw removal torque, and stress analysis.

To assess vertical and horizontal fit, screw removal torque, and stress analysis (considered biomechanical aspects) of full-arch implant frameworks manufactured in Ti-6Al-4V through milling, and additive manufacturing Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM), and the effect of the thermo-mechanical treatment Hot Isostatic Pressing (HIP) as a post-treatment after manufacturing. Maxillary full-arch implant frameworks were made by milling, DMLS, and EBM. The biomechanical assessments were screw removal torque, strain-gauge analyses, and vertical and horizontal marginal fits. The vertical fit was assessed by the single-screw test and with all screws tightened. All frameworks were submitted to a standardized HIP cycle (920°C, 1000bar pressure, 2h), and the tests were repeated (α = 0.05). At the initial time, milled frameworks presented higher screw removal torque values, and DMLS and EBM frameworks presented lower levels of strain. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally, higher fit values were found for milled frameworks, followed by DMLS and EBM. After HIP, milling and EBM frameworks presented higher screw removal torque values; the lowest strain values were found for EBM. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally no differences were found. DMLS and EBM full-arch frameworks presented adequate values of screw removal torque, strain, and marginal fit, although the worst values of marginal fit were found for EBM frameworks. The HIP cycle enhanced the screw removal torque of milled and EBM frameworks and reduced the strain values of milled frameworks. The HIP represents a reliable post-treatment for Ti-6Al-4V dental prostheses produced by milling and EBM technologies.

Fabrication Trueness, Intaglio Surface Adaptation, and Marginal Integrity of Resin-Based Onlay Restorations Fabricated by Additive and Subtractive Manufacturing.

To evaluate the fabrication trueness, intaglio surface adaptation, and marginal integrity of resin-based onlay restorations made via additive manufacturing (AM) or subtractive manufacturing (SM). An onlay restoration was designed (DentalCAD Galway 3.0) and saved as an STL file to generate a design STL file (DO-STL). Using this design, 45 onlays were fabricated either with AM (3D-printed resin for definitive [AM-D; Tera Harz TC-80DP] and interim [AM-I; Freeprint temp] restorations) or SM (composite resin, Tetric CAD) technologies. Onlays were scanned with an intraoral scanner (CEREC Primescan SW 5.2), and the scans were saved as test STL files (TO-STLs). For trueness evaluation, TO-STLs were superimposed over the DO-STL, and root mean square (RMS) values of overall and intaglio surfaces were measured (Geomagic Control X). For the intaglio surface adaptation and marginal integrity, a triple-scan protocol was performed. Kolmogorov-Smirnov, one-way ANOVA, and post-hoc Tukey honestly significant difference tests were used to analyze data (α = .05). RMS values of intaglio and overall surfaces, intaglio adaptation, and marginal integrity varied among test groups (P < .001). AM-D had the greatest overall surface RMS (P < .001), while SM had the greatest intaglio surface RMS (P < .001). SM had the highest average distance deviations for intaglio surface adaptation and marginal integrity, whereas AM-D had the lowest (P < .001). AM-D onlays showed lower overall trueness than AM-I onlays and SM definitive onlays. However, AM-D onlays presented high intaglio surface trueness, intaglio surface adaptation, and marginal integrity.

316L Stainless Steel Thin-Walled Parts Hybrid-Layered Manufacturing Process Study.

Additive manufacturing technology overcomes the limitations imposed by traditional manufacturing techniques, such as fixtures, tools, and molds, thereby enabling a high degree of design freedom for parts and attracting significant attention. Combined with subtractive manufacturing technology, additive and subtractive hybrid manufacturing (ASHM) has the potential to enhance surface quality and machining accuracy. This paper proposes a method for simulating the additive and subtractive manufacturing process, enabling accurate deformation prediction during processing. The relationship between stress distribution and thermal stress deformation of thin-walled 316L stainless steel parts prepared by Laser Metal Deposition (LMD) was investigated using linear scanning with a laser displacement sensor and finite element simulation. The changes in stress and deformation of these thin-walled parts after milling were also examined. Firstly, 316L stainless steel box-shaped thin-walled parts were fabricated using additive manufacturing, and the profile information was measured using a Micro Laser Displacement Sensor. Then, finite element software was employed to simulate the stress and deformation of the box-shaped thin-walled part during the additive manufacturing process. The experiments mentioned were conducted to validate the finite element model. Finally, based on the simulation of the box-shaped part, a simulation prediction was made for the box-shaped thin-walled parts produced by two-stage additive and subtractive manufacturing. The results show that the deformation tendency of outward twisting and expanding occurs in the additive process to the box-shaped thin-walled part, and the deformation increases gradually with the increase of the height. Meanwhile, the milling process is significant for improving the surface quality and dimensional accuracy of the additive parts. The research process and results of the thesis have laid the foundation for further research on the influence of subtractive process parameters on the surface quality of 316L stainless steel additive parts and subsequent additive and subtractive hybrid manufacturing of complex parts.

Microstructural and surface analysis of NiTi TPMS lattice sections fabricated by laser powder bed fusion

Due to their high ductility and superior strength, the machining of NiTi shape memory alloys using conventional subtractive manufacturing technologies poses significant challenges. However, additive manufacturing (AM) offers a viable solution by circumventing the limitations of machinability through the elimination of tooling, thereby enabling the production of NiTi structures with previously unachievable intricacy. This study focuses on the fabrication of base layers of architected triply periodic minimal surface (TPMS) lattices using laser powder bed fusion (LPBF) and explores primitive and gyroid topologies. The investigation involves a comprehensive analysis and discussion of the influence of geometric properties and process parameters on the microstructural characteristics and the distribution of solid phases within the samples. Notably, the study reveals a substantial impact of process parameters and structural topology on the microstructural features. Additionally, notable observations are made concerning nickel evaporation, as well as the formation of oxide- and titanium-rich phases in relation to their distance from the base plate. Investigating intricate TPMS geometries in NiTi alloys in conjunction with varying laser process parameters represents a relatively new and unexplored area of research. These geometries may offer unique structural and functional properties that can potentially lead to innovative applications and advancements in various fields.

Mechanical properties of additively manufactured zirconia with alumina air abrasion surface treatment

This study aimed to evaluate the mechanical properties of zirconia fabricated using additive manufacturing technology and compare them to those of zirconia fabricated using subtractive manufacturing technology. Sixty disc-shaped specimens were fabricated for the additive (n = 30) and subtractive manufacturing groups (n = 30), and each group was divided into two subgroups according to their air-abrasion surface treatment: control (n = 15) and air-abrasion groups (n = 15). Mechanical properties including the flexural strength (FS), Vickers hardness, and surface roughness were determined, and the values were analyzed by one-way ANOVA and Tukey’s post hoc test (α = 0.05). X-ray diffraction and scanning electron microscopy were used for phase analysis and surface topography evaluation, respectively. The SMA group exhibited the highest FS (1144.97 ± 168.1 MPa), followed by the SMC (944.58 ± 141.38 MPa), AMA (905.02 ± 111.38 MPa), and AMC groups (763.55 ± 68.69 MPa). The Weibull distribution showed the highest scale value (1213.55 MPa) in the SMA group, with the highest shape value in the AMA group (11.69). A monoclinic peak was not detected in both the AMC and SMC groups, but after air abrasion, the monoclinic phase content ({mathrm{X}}_{mathrm{m}}) reached 9% in the AMA group, exceeding that in the SMA group (7%). The AM groups exhibited statistically lower FS values than those of the SM groups under the same surface treatment (p < 0.05). Air-abrasion surface treatment increased the monoclinic phase content and FS (p < 0.05) in both the additive and subtractive groups, while it increased the surface roughness (p < 0.05) only in the additive group and did not affect the Vickers hardness in either group. For zirconia manufactured using additive technology, the mechanical properties are comparable to those of zirconia manufactured using subtractive technology.

Rapid Prototyping of 3D Printed, High Aspect Ratio, Low Noise Amplifier for Active Handheld Sensor Devices

In this paper, we report the use of additive manufacturing methods to fabricate a high aspect ratio, low noise amplifier (LNA) for a handheld active sensor device operating at up to 1 GHz. The new form factor LNA incorporates a modification of a square-shaped commercial off-the-shelf (COTS) LNA into a 5:1 aspect ratio device without a loss in RF performance. For rapid prototyping, we employ both subtractive and additive manufacturing technologies, such as milling, extrusion-based syringe printing, and aerosol jet printing techniques to fabricate both small form factor and high aspect ratio devices. The 5:1 aspect ratio LNA demonstrated a 20% smaller form factor, a gain of 25 dB, and an NF less than 3 dB over an operating frequency range up to 1 GHz, comparable to the COTS LNA. Design, simulation, and experimental results are given to highlight the advantages of 3D printed hybrid electronic technology over the conventional PCB fabrication method for rapid prototyping of RF electronic devices.

Optimal Process Planning for Hybrid Additive and Subtractive Manufacturing

AbstractHybrid manufacturing technology has enabled manufacturers to combine advantages of mainly subtractive and additive manufacturing technologies. A single machine supports producing products with complex geometry, at high quality, and with a high degree of automation. To benefit from these advantages, decisions taken in the process planning stage of such a sophisticated manufacturing system should be optimized. The objective of this paper is to determine the optimal process plan considering both the engineering and manufacturing aspects of the hybrid technology. A comprehensive process planning model is proposed. The model specifies the optimal sequence of additive and subtractive features that minimizes the production cycle time. In addition, the model sets the optimal part orientations such that the time needed for building support structures, performing post-processing and inspection operations, changing cutting tools and printing nozzles, and unclamping the part is minimized. The model is comprehensive as it considers productive and non-productive times, precedence, technological, quality, and manufacturing restrictions imposed on hybrid manufacturing systems. The proposed model is nonlinear; due to this nonlinearity, the model is intractable. A linearization scheme is applied to formulate an equivalent linear model that is solvable to optimality by commercial solvers. Case studies on test and industrial parts are provided to evaluate the computational performance of the proposed model. Integrating the proposed model in hybrid manufacturing (HM) systems ensures adopting the HM technology in its optimal direction. HM technology is an enabler of establishing a smart manufacturing system which is one of the pillars of Industry 4.0.

The process planning for additive and subtractive hybrid manufacturing of powder bed fusion (PBF) process

Additive and subtractive hybrid manufacturing (ASHM) technology has attracted extensive attention in industry and academia because of its vast design freedom and surface accuracy. The powder bed fusion (PBF) process has high forming accuracy, the ASHM of PBF process is more suitable for integrated precision manufacturing of components with complex internal structures. However, existing process planning for ASHM are not suitable for the ASHM of PBF process because of the limitation by the powder bed. This research work focused on planning the process for the ASHM of the PBF process, while dividing it into three stages. Firstly, a model adaptive compensation algorithm is proposed to retain the finish machining allowance. Then, considering tool accessibility and constraint of the powder bed, the compensation model is decomposed into several sub-models and the hybrid manufacturing of sub-models in the sequence of construction. Finally, some unprocessed parts of the internal structure could be re-process after removing the parts from the powder bed. Combined with experiments and examples, this hybrid manufacturing process planning can provide technical support for the integrated precision manufacturing of components with a complex internal structure based on the ASHM of the PBF process.

Emerging applications of 5D and 6D printing in the food industry

3D and 4D printing are well-established additive manufacturing techniques in the food sector. However, there are several challenges associated with 3D/4D technique that needs to be addressed. 3D printing technique prints structures in a flat shape with less mechanical strength. It requires additional support material to print structures in most complex shaped geometry such as curved surfaces. The 4D printing method requires additional stimuli to change the morphology of the printed geometry. These challenges can be overcome by using the 5D printing technique where the product gets printed using three movements and two rotational axes without the use of additional support material. In this regard, this paper presents the perspective on using the 5D/6D printing technique in the food sector. 5D printing technique can be used for developing very complex-shaped confectionary items, and curved snack products. It could be advantageous if used in the printing of food packaging materials such as curved-shaped boxes and tableware items (cups, bowls). Furthermore, 6D printing can also be applied in the food sector, resulting in the development of stronger objects with higher responses to external stimuli. • Limited information is known about 5D/6D printing of food. • 5D printing is a hybrid (subtractive and additive manufacturing) technology. • 5D printing can be used for printing curved structures. • 5D/6D printing has promising scope for applications in the food sector.

What is the economic feasibility of manufacturing a metal-metal- polymer composite part compared to other technologies?

ABSTRACT The purpose of the article is to analyse the manufacturing factors that affect the cost of manufacturing a part. Nowadays the cost of equipment used for metal 3D printing, as well as metal powders, are still very expensive. The cost of additive manufacturing of metal parts is mainly dependent on the volume of printing, therefore, reducing the volume of printing can lead to a significant reduction in the cost of manufacturing the part. Manufacturing of a metal shell, the cavity of which is filled with a cheap metal polymer, can be an excellent alternative to an all-metal part. The article provides a method for calculating the cost of manufacturing a lever part using various technologies: subtractive, additive, and composite part manufacturing technology. According to the calculated data, the dependence of the cost of manufacturing a part on piece time has been built, which can be interpreted as the amount of machining. The constructed linear dependence can give an idea of the effectiveness of the application of a particular technology for obtaining a part. In addition, non-economic factors affecting the possibility of using various technological processes for manufacturing a part are described.

ОЦЕНКА ЭКОНОМИЧЕСКОЙ ЭФФЕКТИВНОСТИ ТЕХНОЛОГИИ ИЗГОТОВЛЕНИЯ КОМПОЗИТНЫХ МЕТАЛЛ-МЕТАЛЛОПОЛИМЕРНЫХ ДЕТАЛЕЙ В СРАВНЕНИИ С АДДИТИВНОЙ И СУБТРАКТИВНОЙ ТЕХНОЛОГИЯМИ

The development of additive manufacturing leads to the emergence of new 3D printing technologies, new materials for 3D printing and a gradual reduction in the cost of production. Nowadays, the cost of equipment used for metal and metal powders 3D printing are still very expensive. This factor makes the production technologies unavailable for the civil engineering industry in the manufacture of functional parts. The cost of additive manufacturing of metal parts is mainly dependent on the volume of printing. Reducing the print volume can lead to a significant reduction in the cost of manufacturing the part. Fabrication of a metal shell, the cavity of which is filled with a cheap metal polymer, can be an excellent alternative to an all-metal part. Such a metal-metal-polymer composite part can have sufficient strength and significantly lower cost. However, there are no dependencies today to understand the economic efficiency of using a particular production technology. The article provides a method for calculating the cost of manufacturing a lever part using various technologies: subtractive, additive and composite part manufacturing technology. According to the calculated data, the dependence of the cost of manufacturing a part on piece time is built. It can be interpreted as the amount of machining. The constructed linear dependence can give an idea of the effectiveness of the application of a particular technology for obtaining a part. In addition, non-economic factors affecting the possibility of using various technological processes for manufacturing a part are described. Together, the presented data allow the technologist to comprehensively assess the possibility of effective application of a particular production technology and make an appropriate informed decision.

Comparison of the Accuracy between Denture Bases Produced by Subtractive and Additive Manufacturing Methods: A Pilot Study

Today, two different types of CAD-CAM fabrication methods for complete denture bases are available besides the conventional protocols: a subtractive milling process from a prepolymerized block of polymethylmethacrylate and an additive manufacturing process that built the denture base using a light-cured liquid in a VAT-polymerization process. The aim of this study was to evaluate and to compare the accuracy and precision of denture prosthetic bases made with subtractive and additive manufacturing technologies and to compare them with a denture base with the conventional method in muffle. From the results obtained, 3D printing dentures show a statistically significant higher accuracy than milled prosthetic bases. Milled prosthetic bases have similar accuracy than conventional fabricated dentures.

Additive and subtractive manufacturing of gold micro/nanostructures by using laser trapping and ablation

Gold micro/nanostructures were additively manufactured by using laser trapping of gold nanoparticles in an aqueous solution. Gold wire composed of sintered compacted nanoparticles with spatial resolution of 470 nm was fabricated. Influence factors for wire fabrications were also studied systematically. In order to investigate the fabrication capacity of this technology for three-dimensional structures, several microstructures were fabricated. A new additive and subtractive hybrid manufacturing technology by using laser trapping and ablation was proposed and realized to further improve the spatial resolution of the fabricated structures. A gold microring with line width of 37 nm was fabricated through precisely controlling fabrication parameters. This hybrid manufacturing technology has great application prospects in the fabrication of high spatial resolution nanostructures.

Multiple platforms design and product family process planning for combined additive and subtractive manufacturing

Industry 4.0 promotes the utilization of new exponential technologies such as additive manufacturing in responding to different manufacturing challenges. Among these, the integration of additive and subtractive manufacturing technologies can play an important role and be a game changer in manufacturing products. In addition, using product platforms improves the efficiency and responsiveness of manufacturing systems and is considered an enabler of mass customization. In this paper, a model to design multiple platforms that can be customized using additive and subtractive manufacturing to manufacture a product family cost-effectively is proposed. The developed model is used to determine the optimal number of product platforms, each platform design (i.e. its features set), the assignment of each platform to various product variants, and the macro process plans for customizing the platforms while minimizing the overall product family manufacturing cost.The multiple additive/subtractive platforms and their process plans are determined by considering not only the commonality between the product variants but also their various manufacturing cost elements and the customer demand of each variant. The design of multiple product family platforms and their process plans is NP-hard problem. A genetic algorithm-based model is developed to reduce the computational complexity and find optimal or near optimal solution. Two case studies are used to illustrate the developed multiple platform model. The model results were compared with a single platform model in literature and the results demonstrate the multiple platform model superiority in manufacturing product families in lower cost. The use of the developed model enables manufacturing product families cost efficiently and allows manufacturers to manage diversity in products and market demands.

Influence of depositing sequence and materials on interfacial characteristics and mechanical properties of laminated composites

Laminated composites offer customizable properties based on applications manufactured in one operation by hybrid additive and subtractive manufacturing (HASM) technology. Such manufacturing options are fascinating, since joining two metallic materials is challenging, especially if they are two dissimilar metals without significant defects. Laminated composites were fabricated by transforming the additive manufacturing system and subtractive milling to keep the interface of the directed energy deposition smooth and clear. The microhardness, phase, oxidation, elemental content and microstructural evolution of the interface with different laminated composites were examined. The flexural strength and tensile strength of the laminated composites were measured through a three-point bending test and tensile test at room temperature. The experimental results suggest that the laminated composites had better performances than single materials of identical size. Different deposition sequences led to diverse interfacial microstructures and mechanical properties. The overall performance of laminated composites of Inconel 718 (IN718) deposited on 316L stainless steel (SS316L) was better than that of the other deposition sequence. New substances produced on the interface of SS316L and 1040 steel (1040) laminated composites obviously improved the microhardness, tensile strength and bending strength.

Shape Optimization of a Wooden Baseball Bat Using Parametric Modeling and Genetic Algorithms

Baseball is a popular and very lucrative bat-and-ball sport that uses a wooden bat to score runs. We hypothesize that new design features for baseball bats will emerge from their shape optimization using parametric modeling and genetic algorithms. We converge the location of two points on bats made from maple (Acer sp.) and ash (Fraxinus sp.) wood that are associated with increased velocity of a ball rebounding off a bat: vibrational nodal points and the center of percussion (COP). Our modeling and optimization approach was able to reduce the distance between the nodal points and COP from 166.0 mm to 52.1 mm. This change was similar in both wood species and resulted from changes to the geometry of the bat, specifically shifting of the mass of the bat toward the center of the barrel and removing mass from the very end of the barrel. We conclude that the combination of parametric finite element modeling and optimization using genetic algorithms is a powerful tool for exploring virtual designs for baseball bats that are based on performance criteria and suggest that our designs could be realized in practice using subtractive manufacturing technology.

Geometry and tool motion planning for curvature adapted CNC machining

CNC machining is the leading subtractive manufacturing technology. Although it is in use since decades, it is far from fully solved and still a rich source for challenging problems in geometric computing. We demonstrate this at hand of 5-axis machining of freeform surfaces, where the degrees of freedom in selecting and moving the cutting tool allow one to adapt the tool motion optimally to the surface to be produced. We aim at a high-quality surface finish, thereby reducing the need for hard-to-control post-machining processes such as grinding and polishing. Our work is based on a careful geometric analysis of curvature-adapted machining via so-called second order line contact between tool and target surface. On the geometric side, this leads to a new continuous transition between "dual" classical results in surface theory concerning osculating circles of surface curves and osculating cones of tangentially circumscribed developable surfaces. Practically, it serves as an effective basis for tool motion planning. Unlike previous approaches to curvature-adapted machining, we solve locally optimal tool positioning and motion planning within a single optimization framework and achieve curvature adaptation even for convex surfaces. This is possible with a toroidal cutter that contains a negatively curved cutting area. The effectiveness of our approach is verified at hand of digital models, simulations and machined parts, including a comparison to results generated with commercial software.