Optimal layer setup generation in layered manufacturing with a given error constraint

This paper introduces a new tolerance-based method to generate the optimum layer setup required to build layered manufacturing (LM) end-user parts for maximized efficiency. To achieve this, the deviation between the final polished LM part geometry and the original design model is formulated and controlled. Minimum build time is then realized through optimization of the thickness and position of each layer with respect to the design and final polished part geometry in order to minimize the number of layers to be used. Current LM layer setup methods target the intermediate or raw layered model, generated directly by an LM machine. By not considering the complete LM build process as well as the final polished part geometry, the involved layer setup problem cannot be correctly formulated and solved. Overly conservative layer thickness is then chosen, causing more layers than necessary to be used and greatly compromised efficiency. To achieve maximized efficiency, this work proposed a method based on error compensation and minimization. It has been applied to solving for the optimum layer setup necessary to allow the final polished physical part to meet the user-specified tolerance limit for the design model. Case studies have been performed and the results have validated that the presented method is able to minimize the number of layers for constructing an LM part while controlling the maximum error for tolerance conformance.     

Feature extraction and volume decomposition for orthogonal layered manufacturing

Robust and efficient process planning techniques play an important role in CAD/CAM integration. These techniques need to be developed for each type of manufacturing processes owing to the unique characteristics of each of these processes. In this paper, we describe feature extraction techniques that can be applied to layered manufacturing (LM). The aim is to improve the LM process efficiency by considering the specific feature information of the model, which is normally neglected by previous researches. A feature-based LM system has been developed using these techniques. Based on the proposed orthogonal LM system, features extracted from the geometric analysis are defined in the LM domain, and the algorithm for process planning and volume decomposition based on the specific LM features is proposed and implemented.     

Signature analysis and defect detection in layered manufacturing of ceramic sensors and actuators

This paper presents the concept of a process signature for the use of online signature analysis and defect detection in the layered manufacturing (LM) of ceramic sensors and actuators. To achieve the high quality of parts built by the fused deposition of ceramics (FDC), an online process-monitoring system is implemented to detect the processing defects. Using a process signature extracted from the image of a layer captured by the monitoring system, an ideal image is created that is then compared to the original image to detect and identify the defects. Some results of signature analysis and defect detection for single-material and multi-material parts are also presented.Received: 22 July 1999, Accepted: 21 October 2001, Published online: 29 October 2003 Correspondence to: Mohsen A. JafariThis work was supported by the Office of Naval Research under grant # N-0014-96-1-1175. Ref. US Patent # S-5738817, April 14, 1998.     

An optimal algorithm for the boundary of a cell in a union of rays

In this paper we study a cell of the subdivision induced by a union ofn half-lines (or rays) in the plane. We present two results. The first one is a novel proof of theO(n) bound on the number of edges of the boundary of such a cell, which is essentially of methodological interest. The second is an algorithm for constructing the boundary of any cell, which runs in optimal (n logn) time. A by-product of our results are the notions of skeleton and of skeletal order, which may be of interest in their own right.This work was partly supported by CEE ESPRIT Project P-940, by the Ecole Normale Supérieure, Paris, and by NSF Grant ECS-84-10902.This work was done in part while this author was visiting the Ecole Normale Supérieure, Paris, France.     

Low cost integration of additive and subtractive processes for hybrid layered manufacturing

While CNC machining (subtractive method) is the only option when it comes to high quality components, it demands greater human intervention to generate the CNC programs, making it a slow and costly route. On the other hand, Rapid Prototyping (additive method) is able to convert the design into the physical objects without any human intervention. But its total automation comes with compromises in the qualities of geometry and material. A hybrid layered manufacturing process presented here combines the best features of both these approaches. In this process the near-net shape of the object is first built using weld-deposition; the near-net shape is then finish machined subsequently. Time and cost saving of this process can be attributed to reduction in NC programming effort and elimination of rough machining. It is envisioned as a low cost retrofitment to any existing CNC machine for making metallic objects without disturbing its original functionalities. Near-net shape building and finish machining happening at the same station is the unique feature of this process. A customized software generates the NC program for near-net shape building. The intricate details of integrating arc welding unit with a CNC milling machine are presented in this paper.     

Progress towards an international standard for data transfer in rapid prototyping and layered manufacturing

This paper discusses the informational requirements of rapid prototyping and layered manufacturing (RPLM). The study is motivated by the recent decision to embark on the development of a new Application Protocol for the international standard ISO 10303, specifically to handle layered manufacturing information.

The most common industrial use of RPLM today is for rapid prototyping, but a wider view of it as a flexible fabrication technology is taken here, to allow for future developments. Its use in building functional metallic parts under computer control has already been demonstrated, and commercial RPLM machines for building production parts are already being marketed.

The paper includes a survey of current and proposed data formats for communication between the various stages of the RPLM process. In comparing them, particular attention is given to the issue of extensibility to meet future needs. In this last respect, special emphasis is given to materials-related and other non-geometric information needed for fabricating multi-material objects and objects with graded material properties.     

Parallel merging: algorithm and implementation results

An efficient parallel algorithm for merging two sorted lists is presented. The algorithm is based on a novel partitioning algorithm that splits the two lists among the processors, in a way that ensures load balance during the merge. The partitioning algorithm can itself be efficiently parallelized, allowing the solution to scale with increased numbers of processors. A shared memory multiprocessor is assumed. The time complexity for partitioning and merging is O(N/p + log N), where p is the number of processors and N is the total number of elements in the two lists. Implementation results on a twenty node Sequent Symmetry multiprocessor are also presented.     

Drivers, barriers and critical success factors for ERPII implementation in supply chains: A critical analysis

This paper reviews existing literature to determine the drivers of and barriers to Enterprise Resource Planning II (ERPII) implementation. The ERPII literature is then extended through interviews with potential players in ERPII implementations to identify the critical success factors (CSFs) or preconditions required for successful implementation throughout supply chains. These interviews were conducted with leading ERP vendors/consultants and organisations involved in the entire supply chain to gather evidence on the success, or lack thereof, of ERPII implementations. The results were compared and contrasted to existing literature on ERPII, collaborative networks, and the extended enterprise. We found more barriers to than drivers of successful ERPII implementation. This leads prospective implementers to have a pessimistic forecast for ERPII implementation success. Our research reveals that main reason for this negativity is a general lack of understanding and appreciation of the capabilities of the extended enterprise network. Second, the research presents two sets of CSFs: CSFs which apply to traditional ERP and carry forward to apply to ERPII, and CSFs that are tailored to the new needs for successful ERPII implementations. Finally, the research questions the suitability of ERPII in today’s modern business environment, and suggests that technology may have overtaken management’s capabilities to capture the full benefits of such an advanced enterprise system. Future trends in ERPII development are also considered in an attempt to find the next phase in the enterprise system life cycle. Beyond ERPII, the research suggests that infrastructure such as large-scale business intelligence (BI) systems must be heavily incorporated into modern enterprise systems to fully understand how information flows throughout an organisation and to make sense of that information.     

Design and planning problems in flexible manufacturing systems: a critical review

This review paper describes the state-of-the-art research on flexible manufacturing systems (FMS) design and planning issues. The emphasis is on presenting research results coming out of the current FMS literature that help the FMS manager in setting up a highly efficient manufacturing system. In addition to that, it discusses relevant research contributions after 1986, that were not part of any of the previous survey papers on operations research models for FMSs. Also, applications of combinatorial optimization approaches to FMS planning problems are adequately exposed in the paper.     

Voronoi tessellation of points with integer coordinates: Time-efficient implementation and online edge-list generation

The Voronoi tessellation in the plane can be computed in a particularly time-efficient manner for generators with integer coordinates, such as typically acquired from a raster image. The Voronoi tessellation is constructed line by line during a single scan of the input image, simultaneously generating an edge-list data structure (DCEL) suitable for postprocessing by graph traversal algorithms. In contrast to the generic case, it can be shown that the topology of the grid permits the algorithm to run faster on complex scenes. Consequently, in Computer Vision applications, the computation of the Voronoi tessellation represents an attractive alternative to raster-based techniques in terms of both computational complexity and quality of data structures.     

Systematic literature review on augmented reality in smart manufacturing: Collaboration between human and computational intelligence

Smart manufacturing offers a high level of adaptability and autonomy to meet the ever-increasing demands of product mass customization. Although digitalization has been used on the shop floor of modern factory for decades, some manufacturing operations remain manual and humans can perform these better than machines. Under such circumstances, a feasible solution is to have human operators collaborate with computational intelligence (CI) in real time through augmented reality (AR). This study conducts a systematic review of the recent literature on AR applications developed for smart manufacturing. A classification framework consisting of four facets, namely interaction device, manufacturing operation, functional approach, and intelligence source, is proposed to analyze the related studies. The analysis shows how AR has been used to facilitate various manufacturing operations with intelligence. Important findings are derived from a viewpoint different from that of the previous reviews on this subject. The perspective here is on how AR can work as a collaboration interface between human and CI. The outcome of this work is expected to provide guidelines for implementing AR assisted functions with practical applications in smart manufacturing in the near future.     

Capturing crossings: Convex hulls of segment and plane intersections

We give a simple O(nlogn) algorithm to compute the convex hull of the (possibly Θ(n²)) intersection points in an arrangement of n line segments in the plane. We also show an arrangement of dn hyperplanes in d-dimensions whose arrangement has Θ(nd−1) intersection points on the convex hull.     

面向企业制造过程的信息集成研究与实现

为了发挥MES系统在网络化制造环境中的实用价值,必须保证MES能够与企业管理系统进行信息集成及共享,并且能够解决异构系统中所遇到的知识表达、存储与获取问题。以沈阳透平机械股份有限公司生产车间为系统开发背景,针对信息管理系统中的信息孤岛现象,与企业现有网络结构结合,设计开发出MES^NEU.net v1.0系统。通过对实际问题的解决应用,实现了MES在协同制造中与企业信息系统的集成应用。     

Cloud-based design and manufacturing: A new paradigm in digital manufacturing and design innovation

Cloud-based design manufacturing (CBDM) refers to a service-oriented networked product development model in which service consumers are enabled to configure, select, and utilize customized product realization resources and services ranging from computer-aided engineering software to reconfigurable manufacturing systems. An ongoing debate on CBDM in the research community revolves around several aspects such as definitions, key characteristics, computing architectures, communication and collaboration processes, crowdsourcing processes, information and communication infrastructure, programming models, data storage, and new business models pertaining to CBDM. One question, in particular, has often been raised: is cloud-based design and manufacturing actually a new paradigm, or is it just “old wine in new bottles”? To answer this question, we discuss and compare the existing definitions for CBDM, identify the essential characteristics of CBDM, define a systematic requirements checklist that an idealized CBDM system should satisfy, and compare CBDM to other relevant but more traditional collaborative design and distributed manufacturing systems such as web- and agent-based design and manufacturing systems. To justify the conclusion that CBDM can be considered as a new paradigm that is anticipated to drive digital manufacturing and design innovation, we present the development of a smart delivery drone as an idealized CBDM example scenario and propose a corresponding CBDM system architecture that incorporates CBDM-based design processes, integrated manufacturing services, information and supply chain management in a holistic sense.     

Approximation and inapproximability results for maximum clique of disc graphs in high dimensions

We prove algorithmic and hardness results for the problem of finding the largest set of a fixed diameter in the Euclidean space. In particular, we prove that if A^∗ is the largest subset of diameter r of n points in the Euclidean space, then for every ε>0 there exists a polynomial time algorithm that outputs a set B of size at least |A^∗| and of diameter at most . On the hardness side, roughly speaking, we show that unless P=NP for every ε>0 it is not possible to guarantee the diameter for B even if the algorithm is allowed to output a set of size .     

Hybrid learning-based digital twin for manufacturing process: Modeling framework and implementation

Digital twin (DT) and artificial intelligence (AI) technologies are powerful enablers for Industry 4.0 toward sustainable resilient manufacturing. Digital twins of machine tools and machining processes combine advanced digital techniques and production domain knowledge, facilitate the enhancement of agility, traceability, and resilience of production systems, and help machine tool builders achieve a paradigm shift from one-time products provision to on-going service delivery. However, the adaptability and accuracy of digital twins at the shopfloor level are restricted by heterogeneous data sources, modeling precision as well as uncertainties from dynamical industrial environments. This article proposes a novel modeling framework to address these inadequacies by in-depth integrating AI techniques and machine tool expertise using aggregated data along the product development process. A data processing procedure is constructed to contextualize metadata sources from the design, planning, manufacturing, and quality stages and link them into a digital thread. On this consistent data basis, a modeling pipeline is presented to incorporate production and machine tool prior knowledge into AI development pipeline, while considering the multi-fidelity nature of data sources in dynamic industrial circumstances. In terms of implementation, we first introduce our existing work for building digital twins of machine tool and manufacturing process. Within this infrastructure, we developed a hybrid learning-based digital twin for manufacturing process following proposed modeling framework and tested it in an external industrial project exemplarily for real-time workpiece quality monitoring. The result indicates that the proposed hybrid learning-based digital twin enables learning uncertainties of the interaction of machine tools and machining processes in real industrial environments, thus allows estimating and enhancing the modeling reliability, depending on the data quality and accessibility. Prospectively, it also contributes to the reparametrization of model parameters and to the adaptive process control.     

Effective human utilization in an original equipment manufacturing (OEM) industry by the implementation of agile manufacturing: A POLCA approach

Agile manufacturing (AM) has been recognized as an international strategy for improving industrial competitiveness. Agility refers to the ability of an organization to adapt to changes within its environment and to utilize them for earning profit and constituting a major item of expense for any organization, having a palpable effect on its profitability. Manpower utilization is considered as one of the important attributes affecting the organization's ability to be agile. In other words, an effective manpower utilization in any agile environment can reduce the workload and enhance the profitability of any organization. The efficiency of any agile organization lies in improved production, through the utilization of a smaller workforce without impacting on its work‐life balance. Thus, this research is focused on ensuring minimum manpower utilization on the machine shop floor of an Original Equipment Manufacturing (OEM) industry by implementing the Paired‐cell Overlapping Loops of Card with Authorization (POLCA) approach. Effective manpower utilization is an important aspect requiring focus in all areas relating to manufacture. However, POLCA, despite being a powerful and multiapplicative tool for AM, has still not been used by researchers for effective manpower utilization. This article takes initiative in this area.     

Implementation of self-managed teams in manufacturing: More of a marathon than a sprint

During the past decade teamwork in manufacturing, as in other sectors, has become the organisational form of choice. In contrast to earlier manifestations such as autonomous workgroups some 30 years earlier, this appears to have been largely for business and production reasons rather than being directly aimed at improving the quality of work life. Taken from part of a larger study of teamworking in several different manufacturing companies this paper draws upon a retrospective analysis of cases of self-managed team implementation in UK manufacturing. Examples of good and bad practice and consequent guidance have been identified where the weight of evidence gives confidence in their general applicability. A basis for benchmarking is provided, related to preparation, implementation and maintenance of self-managed teams in manufacturing. Key gaps identified are for tools to assist in early functional analysis, leadership decisions and boundary setting, and appropriate team performance measurement and reward systems.     

Voronoi diagrams of moving points in the plane and of lines in space: tight bounds for simple configurations

The combinatorial complexities of (1) the Voronoi diagram of moving points in 2D and (2) the Voronoi diagram of lines in 3D, both under the Euclidean metric, continues to challenge geometers because of the open gap between the Ω(n²) lower bound and the O(n3+?) upper bound. Each of these two combinatorial problems has a closely related problem involving Minkowski sums: (1′) the complexity of a Minkowski sum of a planar disk with a set of lines in 3D and (2′) the complexity of a Minkowski sum of a sphere with a set of lines in 3D. These Minkowski sums can be considered “cross-sections” of the corresponding Voronoi diagrams. Of the four complexity problems mentioned, problems (1′) and (2′) have recently been shown to have a nearly tight bound: both complexities are O(n2+?) with lower bound Ω(n²).In this paper, we determine the combinatorial complexities of these four problems for some very simple input configurations. In particular, we study point configurations with just two degrees of freedom (DOFs), exploring both the Voronoi diagrams and the corresponding Minkowski sums. We consider the traditional versions of these problems to have 4 DOFs. We show that even for these simple configurations the combinatorial complexities have upper bounds of either O(n²) or O(n2+?) and lower bounds of Ω(n²).