Parametric shape optimization for combined additive–subtractive manufacturing

The final publication is available at Springer via http://dx.doi.org/10.1007/s11837-019-03886-xIn industrial practice, additive manufacturing (AM) processes are often followed by post-processing operations such as heat treatment, subtractive machining, milling, etc., to achieve the desired surface quality and dimensional accuracy. Hence, a given part must be 3D-printed with extra material to enable this finishing phase. This combined additive/subtractive technique can be optimized to reduce manufacturing costs by saving printing time and reducing material and energy usage. In this work, a numerical methodology based on parametric shape optimization is proposed for optimizing the thickness of the extra material, allowing for minimal machining operations while ensuring the finishing requirements. Moreover, the proposed approach is complemented by a novel algorithm for generating inner structures to reduce the part distortion and its weight. The computational effort induced by classical constrained optimization methods is alleviated by replacing both the objective and constraint functions by their sparse grid surrogates. Numerical results showcase the effectiveness of the proposed approach.Peer ReviewedPostprint (published version

Automated process planning for metal hybrid additive and subtractive manufacturing

The manufacturing industry is currently evolving from mass production to mass customization and ultimately towards mass personalization. Direct Digital Manufacturing (DDM) is deemed as a key to the future of manufacturing, and Hybrid Additive and Subtractive Manufacturing (Hybrid AM/SM) can be a path to realize it. While Hybrid AM/SM equipment are being developed, automated process planning for them is far from being integrated. Enabling automated process planning for Hybrid AM/SM will bring the integrationof AM and SM to an unprecedented level. This research problem spans multiple aspects of Computer Aided Design (CAD), Computer Aided Process Planning (CAPP) and Computer Aided Manufacturing (CAM). This presentation introduces several proposed methods for AM/SM automated process planning, including an out-of-envelope method, Design-for-Hybrid systems and future integration modes for Hybrid AM/SM. The results of this work will enable integration of the extraordinary geometric capabilities of Additive Manufacturing with the precision of subtractive methods

Dynamic lifecycle cost modeling for adaptable design optimization of additively remanufactured aeroengine components

Additive manufacturing (AM) is being used increasingly for repair and remanufacturing of aeroengine components. This enables the consideration of a design margin approach to satisfy changing requirements, in which component lifespan can be optimized for different lifecycle scenarios. This paradigm requires lifecycle cost (LCC) modeling; however, the LCC models available in the literature consider mostly the manufacturing of a component, not its repair or remanufacturing. There is thus a need for an LCC model that can consider AM for repair/remanufacturing to quantify corresponding costs and benefits. This paper presents a dynamic LCC model that estimates cumulative costs over the in-service phase and a nested design optimization problem formulation that determines the optimal component lifespan range to minimize overall cost while maximizing performance. The developed methodology is demonstrated by means of an aeroengine turbine rear structure

Parametric Analysis of Particle Spreading with Discrete Element Method

The spreading of metallic powder on the printing platform is vital in most additive manufacturing methods, including direct laser sintering. Several processing parameters such as particle size, inter-particle friction, blade speed, and blade gap size affect the spreading process and, therefore, the final product quality. The objective of this study is to parametrically analyze the particle flow behavior and the effect of the aforementioned parameters on the spreading process using the discrete element method (DEM). To effectively address the vast parameter space within computational constraints, novel parameter sweep algorithms based on low discrepancy sequence (LDS) are utilized in conjunction with parallel computing. Based on the parametric analysis, optimal material properties and machine setup are proposed for a higher quality spreading. Modeling suggests that lower friction, smaller particle size, lower blade speed, and a gap of two times the particle diameter result in a higher quality spreading process. In addition, a twoparameter Weibull distribution is adopted to investigate the influence of particle size distribution. The result suggests that smaller particles with a narrower distribution produce a higher-quality flow, with a proper selection of gap. Finally, parallel computing, in conjunction with the LDS parameter sweep algorithm, effectively shrinks the parameter space and improves the overall computational efficiency

Digital unique component manufacturing through direct and indirect additive manufacturing

The objective of this study is to define an optimum additive manufacturing process which incorporates not only low volume production and short delivery time but also missing, or defective documentation of the industrial components. This inevitably requires the integration of digitization through reverse engineering and state of the art direct and indirect additive manufacturing methods as these are built upon the fundamentals of lead time and cost efficiency which complement business potentials. The work was commissioned by Outotec (Finland) Oy and Aalto University. The data of exemplary components was provided by Outotec (Finland) Oy. The digitization measures and the ISO/ASTM standard additive manufacturing methods were explored and an integrated screening and design process was developed. Cost and lead time analyses were performed in correspondence to exemplary components and their relative business advantages against conventional manufacturing methods were discovered. In addition, performance of two exemplary components was evaluated via additive manufacturing enabled optimization studies. In order to validate and verify the suitability of the manufactured materials according to the predefined standards of Outotec (Finland) Oy, corrosion tests and tensile tests were performed. As a result of this thesis, an additive manufacturing integrated screening algorithm and design process is developed through which costs and lead times of 15 industrial components are evaluated and are utilized for good advantage. In addition, design for additive manufacturing is used to enhance the performance of two industrial components and prototypes are manufactured in order to provide proof of concept. Finally, it is discovered that additively manufactured Stainless Steel 316L is not as corrosion resistant compared to wrought alloys of EN 1.4404 and EN 1.4432 in very aggressive corrosion environments and it has an ultimate tensile strength of approximately 595 MPa with 13% anisotropy in favour of horizontal print orientation. Whereas, additively manufactured Titanium Ti64 is corrosion resistant with respect to its bulk material with an ultimate tensile strength of approximately 1100 MPa containing 5% anisotropy in favour of horizontal print orientation. Overall, this study provided a fundamental workflow for implementation of industrial additive manufacturing for higher production efficiency

Computer aided process planning for multi-axis CNC machining using feature free polygonal CAD models

This dissertation provides new methods for the general area of Computer Aided Process Planning, often referred to as CAPP. It specifically focuses on 3 challenging problems in the area of multi-axis CNC machining process using feature free polygonal CAD models. The first research problem involves a new method for the rapid machining of Multi-Surface Parts. These types of parts typically have different requirements for each surface, for example, surface finish, accuracy, or functionality. The CAPP algorithms developed for this problem ensure the complete rapid machining of multi surface parts by providing better setup orientations to machine each surface. The second research problem is related to a new method for discrete multi-axis CNC machining of part models using feature free polygonal CAD models. This problem specifically considers a generic 3-axis CNC machining process for which CAPP algorithms are developed. These algorithms allow the rapid machining of a wide variety of parts with higher geometric accuracy by enabling access to visible surfaces through the choice of appropriate machine tool configurations (i.e. number of axes). The third research problem addresses challenges with geometric singularities that can occur when 2D slice models are used in process planning. The conversion from CAD to slice model results in the loss of model surface information, the consequence of which could be suboptimal or incorrect process planning. The algorithms developed here facilitate transfer of complete surface geometry information from CAD to slice models. The work of this dissertation will aid in developing the next generation of CAPP tools and result in lower cost and more accurately machined components

Design and fabrication of conformal cooling channels in molds:Review and progress updates

Conformal cooling (CC) channels are a series of cooling channels that are equidistant from the mold cavity surfaces. CC systems show great promise to substitute conventional straight-drilled cooling systems as the former can provide more uniform and efficient cooling effects and thus improve the production quality and efficiency significantly. Although the design and manufacturing of CC systems are getting increasing attention, a comprehensive and systematic classification, comparison, and evaluation are still missing. The design, manufacturing, and applications of CC channels are reviewed and evaluated systematically and comprehensively in this review paper. To achieve a uniform and rapid cooling, some key design parameters of CC channels related to shape, size, and location of the channel have to be calculated and chosen carefully taking into account the cooling performance, mechanical strength, and coolant pressure drop. CC layouts are classified into eight types. The basic type, more complex types, and hybrid straight-drilled-CC molds are suitable for simply-shaped parts, complex-shaped parts, and locally complex parts, respectively. By using CC channels, the cycle time can be reduced up to 70%, and the shape deviations can be improved significantly. Epoxy casting and L-PBF show the best applicability to Al-epoxy molds and metal molds, respectively, because of the high forming flexibility and fidelity. Meanwhile, LPD has an exclusive advantage to fabricate multi-materials molds although it cannot print overhang regions directly. Hybrid L-PBF/CNC milling pointed out the future direction for the fabrication of high dimensional-accuracy CC molds, although there is still a long way to reduce the cost and raise efficiency. CC molds are expected to substitute straight-drilled cooling molds in the future, as it can significantly improve part quality, raise production rate and reduce production cost. In addition to this, the use of CC channels can be expanded to some advanced products that require high-performance self-cooling, such as gas turbine engines, photoinjectors and gears, improving working conditions and extending lifetime

Force-Driven Weave Patterns for Shell Structures in Architectural Design

The use of lightweight carbon fiber reinforced polymers (CFRP) in the discipline of architecture opens new possibilities for the construction of architectural components. CFRP has been explored mainly in engineering fields, such as aeronautics, automotive, ballistic and marine engineering. CFRP has also been explored in the discipline of architecture in the construction of shell structures because of its high strength-to-weight ratio and low-cost. There is, however, limited research on how structural analysis can be used to inform weave patterns for shell structures using CFRP. Further, previous research in the field has not performed physical structural tests to validate which force driven weave patterns perform best. This thesis addresses this gap by contributing a methodology for the creation of CFRP weave patterns from structural analysis and their validation through physical testing. Specifically, this thesis addresses three main problems: Firstly, understanding and analyzing the structural behavior of a shell structure through computation; Secondly, the creation of a weaving pattern of carbon fiber optimized for structural performance; the third part seeks to translate the digital model into fabricated prototypes. The results of this research show that force-flow derived patterns perform best. Consequently, force-flow is the information we should implement to create a more efficient force-driven weave pattern in shell structures. Adviser: David Newto