Shifting value stream patterns along the product lifecycle with digital twins

The concept of digital twins promises high potentials for product design, manufacturing, user experience and recycling. Thus, digital twins have received increasing interest in academia and industry. However, the actual benefits of digital twins remain in many cases unclear. This article aims to summarize selected recent developments in this field and demonstrate use cases from different phases of the product lifecycle. For that purpose, examples from the design, manufacturing, use and recycling phase are presented. In a subsequent discussion, ideas for new value stream patterns using digital twins are envisioned and research questions are derive

Tool Path Planning and Optimization for Five-Axis Flat-End Milling Considering Machine Kinematics (Het plannen en optimaliseren van gereedschapsbanen voor het 5-assig frezen met behulp van vingerfrezen, rekening houdend met de kinematica van de machine)

Although flat-end multi-axis milling has been proven to be more efficient than ball-end machining for more than twenty years, dedicated tool path generation and planning algorithms have been seriously suffering from insufficient intelligence because they originate from ball-end algorithms and do not consider issues attributed to the flat-end shape of tools. This research work describes the development and implementation of new algorithms designed for tool path planning and generation aiming taking machine kinematics into account. The developed components are founded on prototype software that can handle STL geometry for robust computation of tool path tracks and interference-free tool postures. This STL kernel was also extended with support of facet machining status to enable machining simulation. In addition to the kernel, three different components were developed to facilitate optimization of tool inclination, material removal simulation, and tool path planning. First, two tool path optimization methods were elaborated to perform minimization of machine tool rotations in reasonable computation time. Second, a novel material removal simulation based on accurate estimation of swept sections has been introduced. Third, tool path planning algorithms integrating the developed material removal simulation allow efficient tool path generation with reduced machining strip overlaps and dynamic step-over between adjacent tool path tracks. This integration has also given an opportunity to introduce two strategies. First strategy implements the cutting plane approach to slice STL surfaces and generate zig-zag-like tool paths with intelligent selection of tool path tracks directions. Second strategy generates contour-like tool paths, going inwards from a workpiece outside, resulting in machined surfaces with predictable scallop height. This research highlighted and resolved several flaws in existing algorithms. First, estimations of machining strip widths derived from a single posture are almost surely incorrect in a case of five-axis machining. Therefore, a new approach taking several postures into account has been developed and implemented. Second, regardless of the dramatic influence of machine tool kinematics and CNC behavior onto the actual shape of a machined surface, machine tool characteristics are not considered by the existing material removal simulation algorithms. Thus, in this research, tool motion has been interpolated in machine coordinates. The developed methods can be smoothly integrated with themselves and other CAM software. Eventually, these methods are believed to assist CAM programmers in generating efficient tool paths in an automated manner.nrpages: 158status: publishe

Five-axis milling tool path generation with dynamic step-over calculation based

This paper describes the development of a five-axis tool path generation algorithm for the machining of complex shaped parts using flat-end tools. In order to reduce the machining time and to ensure optimal quality, the step-over is optimized in each tool contact point. This step-over calculation is obtained through the integration of a newly developed algorithm for material removal simulation. The latter is performed by calculating swept volumes which represent tool motions interpolated according to the machine kinematics. The developed algorithm has been implemented for contour like (spiral) strategies and validated through the machining of an industrial example. 2012 CIRP.status: publishe

Development of a Five-Axis Tool Path Generation Algorithm Minimizing Machine Axes Movements

This paper describes the development and validation of a multi-axis tool path generation algorithm which incorporates the kinematics and dynamics information of the machine tool. In this research, the optimization is only performed for the rotary axes as these axes are most often discovered as a bottleneck in the kinematic chain. The algorithm first calculates admissible tool inclinations in every tool contact point, followed by a mapping of these admissible tool orientations to machine axes values. All these information is then represented in a graph. The algorithm, based on dynamic programming, finds a shortest path in this graph through minimization of a cost function without violating velocity and acceleration constraints of the machine. The developed algorithm has been validated by the machining of a complex shaped surface, having concave and convex areas.status: publishe

Adaptive Ortho-Planar Toolpath Planning for Five-Axis Milling Considering Tool Swept Volumes

In this paper, a novel approach for five-axis toolpath planning taking tool swept volumes and machining performance into account has been introduced. The toolpath generation is based on cutting planes slicing a meshed surface to provide toolpath tracks on the surface. The cutting planes can be orthogonal to each other, and positions of these planes are computed consequently so that a next iteration considers regions machined at the previous iterations. The developed algorithm alternates between several candidate tracks to ensure that a track with the best performance, which may be formulated variously, is selected. Each candidate track is computed to result in a tool swept volume that completely removes stock material between the toolpath track and the boundary of the un-machined region. Several planning strategies can be applied in order to obtain a machined surface with scallop height not exceeding a given value.status: publishe

Computing of the actual shape of removed material for five-axis flat-end milling

This paper describes an algorithm that predicts the shape of material removed by a flat-end milling tool, and this may be used to compute machining strip width and scallop height at different positions of the tool path track. The algorithm computes swept sections, profiles which are swept by a moving tool bottom by passing through given planes. The technique is applicable for finish and semi-finish multi-axis milling strategies that use flat-end tools. For these strategies, the algorithm complexity can be reduced from computation of the 3D envelope of swept volumes to computation of plane-circle intersections. A new adaptive derivative-free method to sample tool motion provides robust means to generate intermediate tool positions. The step length is constrained by and dependent on different geometrical measures. At each point of a tool path, in the plane perpendicular to the cutting direction, the bottom profile of the swept section is an estimate of the profile of material left. By calculating the distance between part geometry and the computed profile of removed material, machining strip width and a scallop profile can be derived. These results can be used by tool path generation and validation routines to accurately determine the step-over between tool path tracks and surface quality.status: publishe

Optimization of a five-axis tool path taking into account machine kinematics

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Graph-based optimization of five-axis machine tool movements by varying tool orientation

There is a relatively vast class of tool path optimization methods that minimize cost functions depending on a whole tool path. In these methods, cost functions are usually limited to convex function because the used optimization approaches cannot either handle nonsmooth functions or perform with an acceptable computational time. This paper describes a developed optimization method that finds a sequence of tool orientations that can minimize various cost functions including displacement of machine rotary axes. Every posture, tool feasible orientation can be represented in discrete fashion as nodes of a directed graph in which the edge weights denote an objective. Shortest paths are sought iteratively by applying Dijkstraâ s algorithms and narrowing intervals of feasible tool orientations around the previous solution. The developed algorithm is a derivative-free optimization method working in a linear time.status: publishe

Manufacturing education and research at K.U.Leuven using a Mori Seiki NL2000Y/500 mill-turn centre

High level education and research in machine tools, production systems and processes is crucial to safeguard the future of our manufacturing industries. Today, education and research in these areas should be made more attractive in order to increase the intake of young people into university. Modern labs with advanced and high level production/manufacturing equipment are essential to reach these goals. This paper describes a brief overview of on-going research/education activities performed on a Mori Seiki NL2000Y/500 mill-turn centre, made available to the K.U.Leuven by the Machine Tools Technologies Research Foundation (MTTRF). Educational activities include lab sessions on multi-task machining, study of machine tools and the use of the machine by students within project assignments. The development of systems and strategies for the machining of ceramic materials, energy based optimization of machining strategies and high level modeling of machine tools are research topics performed on the available machine and are described as well.status: publishe

Tool path generation functionality and ultrasonic assisted machining of ceramic components using multi-axis machine tools

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