Designing heterogeneous porous tissue scaffolds for additive manufacturing processes

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer, which represents the geometric internal feature or the spine. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. To avoid the twisting of the internal channels, reorientation and relaxation techniques are introduced to establish the point matching of ruling lines. An optimization algorithm is developed to construct sub-regions from these ruling lines. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the subregions peripherally into pore cells and consecutive iso-porosity curves are generated using the isopoints from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. A continuous zig-zag pattern deposition path crossing through the medial region is used for the initial layer and a biarc fitted isoporosity curve is generated for the consecutive layer with C-1 continuity. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive manufacturing processes

Dynamic Facility Layout for Cellular and Reconfigurable Manufacturing using Dynamic Programming and Multi-Objective Metaheuristics

The facility layout problem is one of the most classical yet influential problems in the planning of production systems. A well-designed layout minimizes the material handling costs (MHC), personnel flow distances, work in process, and improves the performance of these systems in terms of operating costs and time. Because of this importance, facility layout has a rich literature in industrial engineering and operations research. Facility layout problems (FLPs) are generally concerned with positioning a set of facilities to satisfy some criteria or objectives under certain constraints. Traditional FLPs try to put facilities with the high material flow as close as possible to minimize the MHC. In static facility layout problems (SFLP), the product demands and mixes are considered deterministic parameters with constant values. The material flow between facilities is fixed over the planning horizon. However, in today’s market, manufacturing systems are constantly facing changes in product demands and mixes. These changes make it necessary to change the layout from one period to the other to be adapted to the changes. Consequently, there is a need for dynamic approaches of FLP that aim to generate layouts with high adaptation concerning changes in product demand and mix. This thesis focuses on studying the layout problems, with an emphasis on the changing environment of manufacturing systems. Despite the fact that designing layouts within the dynamic environment context is more realistic, the SFLP is observed to have been remained worthy to be analyzed. Hence, a math-heuristic approach is developed to solve an SFLP. To this aim, first, the facilities are grouped into many possible vertical clusters, second, the best combination of the generated clusters to be in the final layout are selected by solving a linear programming model, and finally, the selected clusters are sequenced within the shop floor. Although the presented math-heuristic approach is effective in solving SFLP, applying approaches to cope with the changing manufacturing environment is required. One of the most well-known approaches to deal with the changing manufacturing environment is the dynamic facility layout problem (DFLP). DFLP suits reconfigurable manufacturing systems since their machinery and material handling devices are reconfigurable to encounter the new necessities for the variations of product mix and demand. In DFLP, the planning horizon is divided into some periods. The goal is to find a layout for each period to minimize the total MHC for all periods and the total rearrangement costs between the periods. Dynamic programming (DP) has been known as one of the effective methods to optimize DFLP. In the DP method, all the possible layouts for every single period are generated and given to DP as its state-space. However, by increasing the number of facilities, it is impossible to give all the possible layouts to DP and only a restricted number of layouts should be fed to DP. This leads to ignoring some layouts and losing the optimality; to deal with this difficulty, an improved DP approach is proposed. It uses a hybrid metaheuristic algorithm to select the initial layouts for DP that lead to the best solution of DP for DFLP. The proposed approach includes two phases. In the first phase, a large set of layouts are generated through a heuristic method. In the second phase, a genetic algorithm (GA) is applied to search for the best subset of layouts to be given to DP. DP, improved by starting with the most promising initial layouts, is applied to find the multi-period layout. Finally, a tabu search algorithm is utilized for further improvement of the solution obtained by improved DP. Computational experiments show that improved DP provides more efficient solutions than DP approaches in the literature. The improved DP can efficiently solve DFLP and find the best layout for each period considering both material handling and layout rearrangement costs. However, rearrangement costs may include some unpredictable costs concerning interruption in production or moving of facilities. Therefore, in some cases, managerial decisions tend to avoid any rearrangements. To this aim, a semi-robust approach is developed to optimize an FLP in a cellular manufacturing system (CMS). In this approach, the pick-up/drop-off (P/D) points of the cells are changed to adapt the layout with changes in product demand and mix. This approach suits more a cellular flexible manufacturing system or a conventional system. A multi-objective nonlinear mixed-integer programming model is proposed to simultaneously search for the optimum number of cells, optimum allocation of facilities to cells, optimum intra- and inter-cellular layout design, and the optimum locations of the P/D points of the cells in each period. A modified non-dominated sorting genetic algorithm (MNSGA-II) enhanced by an improved non-dominated sorting strategy and a modified dynamic crowding distance procedure is used to find Pareto-optimal solutions. The computational experiments are carried out to show the effectiveness of the proposed MNSGA-II against other popular metaheuristic algorithms

Porous composite with negative thermal expansion obtained by photopolymer additive manufacturing

Additive manufacturing (AM) could be a novel method of fabricating composite and porous materials having various effective performances based on mechanisms of their internal geometries. Materials fabricated by AM could rapidly be used in industrial application since they could easily be embedded in the target part employing the same AM process used for the bulk material. Furthermore, multi-material AM has greater potential than usual single-material AM in producing materials with effective properties. Negative thermal expansion is a representative effective material property realized by designing a composite made of two materials with different coefficients of thermal expansion. In this study, we developed a porous composite having planar negative thermal expansion by employing multi-material photopolymer AM. After measurement of the physical properties of bulk photopolymers, the internal geometry was designed by topology optimization, which is the most effective structural optimization in terms of both minimizing thermal stress and maximizing stiffness. The designed structure was converted to a three-dimensional STL model, which is a native digital format of AM, and assembled as a test piece. The thermal expansions of the specimens were measured using a laser scanning dilatometer. The test pieces clearly showed negative thermal expansion around room temperature.Comment: 11 pages, 4 figure

Cell Production System Design: A Literature Review

Purpose In a cell production system, a number of machines that differ in function are housed in the same cell. The task of these cells is to complete operations on similar parts that are in the same group. Determining the family of machine parts and cells is one of the major design problems of production cells. Cell production system design methods include clustering, graph theory, artificial intelligence, meta-heuristic, simulation, mathematical programming. This article discusses the operation of methods and research in the field of cell production system design. Methodology: To examine these methods, from 187 articles published in this field by authoritative scientific sources, based on the year of publication and the number of restrictions considered and close to reality, which are searched using the keywords of these restrictions and among them articles Various aspects of production and design problems, such as considering machine costs and cell size and process routing, have been selected simultaneously. Findings: Finally, the distribution diagram of the use of these methods and the limitations considered by their researchers, shows the use and efficiency of each of these methods. By examining them, more efficient and efficient design fields of this type of production system can be identified. Originality/Value: In this article, the literature on cell production system from 1972 to 2021 has been reviewed

Detailed design of product oriented manufacturing systems

This paper describes a procedure for the detailed and repetitive design of manufacturing systems within an approach of constantly fitting production system configuration to the varying production needs of products and, therefore, designing Product Oriented Manufacturing Systems – POMS. The detailed design procedure depart from a set of conceptual manufacturing cell configurations and develops from there, through conceptual cell and workstation instantiation, with basis on available methods, the required manufacturing system and control mechanisms for a product or a family of similar products.Fundação para a Ciência e a Tecnologia (FCT

Analysis, Design, and Implementation of a training center for variable-speed drive assembly production : Case ABB Oy

In manufacturing constant developments in production, processes, and layouts are required to respond towards increased production volume, quality, and customer requirements while meeting production targets and objectives. The case company of this thesis is ABB Ltd Drives Manufacturing Unit, which specializes in variable-speed drive production. ABB has recognized the need for re-designing a new and effective training center that supports One-piece flow assembly production since the old model is based on a cell production method. The training center is used for the training and integration of the company's new and experienced assemblers. The aim of the research is to analyze the current training concept, design a new technical solution, and create a detailed implementation plan. Thus, the following research questions were developed: RQ1: How to develop and re-design a training center that supports the assembler for One-piece flow method production of variable-speed drives? RQ2: How to design and create the best possible layout and solution to guarantee safety, flexibility, ergonomics, clear flow, and the maximum utilization of space? RQ3: How to implement a training center that does not disrupt the main production lines and makes that way operations more efficient? To achieve the objectives, the waste, bottlenecks, and issues of the current design were first identified by observing the training process and organizing focus groups and workshops with the production line and logistics (customer), and with the project team. Work-time studies were also conducted to solve the flow, outputs, cycle time, and waste time of the current process. These data collection methods aided in identifying potential improvement opportunities for the new design. The layout design process was committed by utilizing Lean principles and the Systematic layout planning procedure. AutoCAD was used to create and map various layout structures, options, and alternatives. The design process required the tendering of two layout location options, which were solved using the quantitative multiple attribute decision-making method, Weighted decision matrix (WDM), with voting based on the scoring of various criteria and features. The result was a Flexible 6-phase U-model one-piece flow training center that allows assemblers to be trained in both one-piece flow and cell production methods. The new design's scope of work was delivered to the supplier, numerous negotiations were held to achieve the best final solution, and the new training center was ordered. In the end, a detailed implementation plan with an estimated schedule was created and a future action list was established. The new design fulfils the objectives and eliminates all issues, waste, and bottlenecks while also ensuring safety, ergonomics, flexibility, a clear flow, and a high-quality training process. With the new design, the efficiency, quality, and output of training and production operations will improve.Teollisuuden alalla tuotantojärjestelmiä, prosesseja ja layouteja on jatkuvasti kehitettävä sekä modifioitava reagoidakseen kasvaneisiin tuotantomääriin sekä laatu- ja asiakasvaatimuksiin ja saavuttaakseen asetetut tuotantotavoitteet ja päämäärät. Tämän opinnäytetyön toimeksiantaja on ABB Oy Drives Manufacturing -yksikkö, joka on erikoistunut taajuusmuuttajatuotantoon. Toimeksiantaja on tunnistanut tarpeen uuden ja tehokkaamman koulutuslinjan suunnitteluun One-piece flow malliseen taajuusmuuttajien kokoonpanotuotantoon, sillä vanha tuotantomalli perustuu solutuotantomenetelmään. Koulutuslinjaa käytetään niin uusien kuten jo talossa olevien vanhojen kokoonpanoasentajien koulutukseen ja integrointiin. Tutkimuksen tavoitteena on analysoida nykyinen koulutuskonsepti, suunnitella uusi tekninen ratkaisu ja laatia yksityiskohtainen implementointisuunnitelma. Tavoitteiden saavuttamista varten on kehitetty seuraavat kolme tutkimuskysymystä: RQ1: Kuinka kehittää ja suunnitella koulutuslinja, joka tukee asentajia One-piece flow malliseen kokoonpanotuotantoon? RQ2: Miten suunnitella ja luoda paras mahdollinen layout ja ratkaisu, joka takaa turvallisuuden, joustavuuden, ergonomian, selkeän virtauksen ja maksimaalisen tilankäytön? RQ3: Kuinka implementoida koulutuslinja, joka ei häiritse päätuotantolinjoja ja tehostaa siten operaatioiden tehokkuutta? Saavuttaakseen tavoitteet, nykyisen koulutuskonseptin aiheuttamat pullonkaulat, ongelmat ja hukka tunnistettiin ensin havainnoimalla koulutusprosessia ja järjestämällä haastatteluja sekä työpajoja tuotantolinjan ja logistiikan (asiakkaan) sekä projektiryhmän kanssa. Nykyisen prosessin virtauksen, ulostulon, tahti -ja hukka-ajan selvittämiseksi suoritettiin myös työaikatutkimuksia. Nämä tiedonkeruumenetelmät auttoivat kehitysmahdollisuuksien tunnistamisessa uutta ratkaisua varten. Layout suunnitteluprosessi toteutettiin Lean-periaatteita ja systemaattista layout suunnittelua käyttäen. AutoCAD layout suunnittelusovellusta käytettiin erilaisien asettelurakenteiden ja vaihtoehtojen luomiseen sekä kartoittamiseen. Suunnitteluprosessi edellytti kahden layout-sijaintivaihtoehdon kilpailuttamista. Lopputulos ratkaistiin äänestämällä kvantitatiivisen päätöksentekomatriisin (WDM) avulla, joka perustui eri kriteerien ja ominaisuuksien pisteytykseen. Tulokseksi saatiin joustava 6-vaiheinen U-mallinen One-piece flow koulutuslinja, jonka avulla asentajia voidaan kouluttaa sekä One-piece flow että solutuotantomallisesti. Uuden koulutuslinjan työn laajuus -dokumentti toimitettiin toimittajalle sekä lukuisia neuvotteluja käytiin parhaan loppuratkaisun saavuttamiseksi, jonka jälkeen uusi koulutuslinja tilattiin. Lopuksi koostettiin yksityiskohtainen implementointisuunnitelma arvioituineen aikatauluineen ja laadittiin toimenpidelista tulevaisuutta varten. Uusi ratkaisu täyttää asetetut tavoitteet ja eliminoi kaikki ongelmat, hukat ja pullonkaulat sekä takaa turvallisuuden, ergonomian, joustavuuden, selkeän virtauksen ja laadukkaan koulutusprosessin. Uuden ratkaisun myötä koulutuksen ja operaatioiden tehokkuus, laatu ja tuottavuus paranevat

Group technology: amalgamation with design of organisational structures

Group technology has been studied extensively from an ‘industrial engineering’ perspective (layout, scheduling, workflow, etc.), but less often from an organisational design viewpoint. To study this implication of group technology, the approach of applied systems theory for the design of organisational structures was used as framework for analysis in three empirical cases. To increase the reliability of findings from the analysis of these three empirical cases, five more cases were drawn from archival search. Cluster analysis and product flow analysis were the methods used for forming groups of machines and employees in manufacturing cells, whereas the coding of parts was not employed to this end. Furthermore, the results indicate that the implementation of group technology generally meets shifts in performance requirements caused by competitive pressures, particularly flexibility and responsiveness, albeit the companies considered group technology only when under pressure of ‘poor’ business performance. However, group technology is not always a solution to challenges that companies experience; one empirical case shows that defunctionalisation and scheduling with virtual groups was more beneficial. Nevertheless, when the introduction of group technology is feasible, it also allows firms to consider delegating responsibility for production planning and scheduling to lower levels in the hierarchy and semi-autonomous groups as an alternative to ‘complex’ software applications (a socio-technical approach). Whereas the current study sheds light on the relationship between group technology and design of organisational structures, further research is necessary into the design of these structures and their relationship to group technology

Quadrature Phase Shift Keying (QPSK) Modulator Design using Multi-Port Network in Multilayer Microstrip-Slot Technology for Wireless Communication Applications

The design of the quadrature phase shift keying (QPSK) modulator by using a multi-port network is proposed in this article for the use in wireless communication applications. The multi-port network is in the form of multilayer microstrip-slot technology. This multi-port network is composed of three 3-dB rectangular-shaped directional couplers with virtual stubs and an equal power division divider with in-phase characteristic. The design is performed by applying a full-wave electromagnetic simulation software, CST Microwave Studio (CST MWS). Keysight’s Advanced Design System (ADS) is applied in analyzing and evaluating the QPSK constellation of the proposed modulator. This comparatively small size of proposed design has been fabricated, and its wideband performance of 2 to 6 GHz is verified

Layout Planning with Isles: A Genetic Approach

Plant layout problems involve distributing different resources or departments in a given plant and achieving maximum efficiency for the services or goods being made or offered. To this end, plants are designed to optimize production flow from the first stage (i.e. as raw material) to finish product. However, optimization which is generally expressed either in terms of minimization (for example, of material handling costs) or of maximization (for example, the number of desired adjacencies in a qualitative chart) is not always feasible when real problems or real sizes are being handled. The level of complexity may turn out considerable as the number of parameters, restrictions and other variables considered in the study become larger. This kind of problem has been formulated, from a mathematical view point as a static quadratic assignment problem. However, the number of problems that are usceptible to being solved by optimization methods is very limited. Some alternatives have been called from the field of graph-theory, direct method algorithms, construction algorithms (such as CORELAP), and improvement algorithms (such as CRAFT). In this thesis work, an attempt is made to develop the algorithm for solving layout problem with real-life restriction like aisles, used in factories for the easy transfer of materials from one section to the other, using Genetic Algorithm