Modeling and Verification of Error Propagation in Integrated Additive/Subtractive Multi-Directional Direct Manufacturing

Integrated additive-subtractive manufacturing, when applied in the framework of SolidFreeform-Fabrication (SFF) allows the fabrication of functional parts on single platform, directly from its computer model. Reduction in process complexity and total processing steps is ensured by multi-directional material deposition and machining. However, due to shift in the datum location in reorientation steps and sequential addition of material in the form of layers, the CAD process intent is not exactly replicated. This leads to inclusion of dimensional errors. Machining in order to eliminate the errors as frequent as layer deposition is highly expensive and can be avoided by estimation of errors and varying process parameters, and/or performing machining after a set of layers are deposited. This paper proposes a state space model for modeling the error propagation due to linear as well as angular variation in the datum. The model is based on identification of possible sources of error, mechanism of error inclusion and influence of process parameters. An experiment performed to determine parameters of error modeling has been reported.Mechanical Engineerin

Mechanism for Determination of G-factors for Solid Freeform Fabrication Techniques Based on Large Heat Input

A major class of Solid Freeform Fabrication (SFF) methods for metal deposition are based on large heat input. The geometry and microstructural properties of the deposition depend primarily on the heat input and the subsequent distribution at the substrate. On one hand the insufficient heat may lead to the inadequate melting of the metal, on the other hand overheating and heat accumulation leads to the overmelting, resulting in the deformation of the build up geometry. The heat distribution is governed by the available heat sink . For a better control of the process, the estimation of heat sinks and the subsequent control of the energy input allows a better control of the process. A parameter G-factor that estimates the heat sink based on the local geometry of a part has been introduced. The estimation of G-factor is based on the simulation and the experimental results. Also a mechanism to determine the G-factor for various substrate geometries has been introduced.Mechanical Engineerin

An Investigation of Gas-Powder Flow in Laser-Based Direct Metal Deposition

Laser-Based Direct Metal Deposition (LBDMD) is a blown-powder laser deposition process which can produce fully-dense and metallurgicaly sound parts by a layered manufacturing method. Since a deposition head equipped with discontinuous radially symmetric nozzles has the potential to be tilted without influence of the gravity on the powder stream shape, it can be used for multi-axis deposition. The shape of the gas-powder stream with respect to the shape of laser beam and the size of the molten pool, have a large influence on the size and shape of the buildup. They determine the geometrical accuracy and the surface quality of the buildup. This paper examines gas-powder flow from radially symmetric nozzles using computational fluid dynamics method. For verification purpose the powder flow was investigated by a visualization method and powder concentration distribution was analyzed using image processing technique. The obtained results are in good agreement with numerical model.Mechanical Engineerin

Thermo-structural Finite Element Analysis of Direct Laser Metal Deposited Thin-Walled Structures

Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which particles are injected. During fabrication, a complex thermal history is experienced in different regions of the build, depending on the process parameters and part geometry. The thermal history induces residual stress accumulation in the buildup, which is the main cause of cracking during the fabrication. The management of residual stress and the resulting distortion is a critical factor for the success of the process. A thermostructural finite element model (FEM) of the process is developed, and the analysis reveals different patterns of residual stress in the thin-walled structures depending on the deposition strategy and the geometry of the structures. The residual stress patterns obtained from finite element analysis (FEA) are in good agreement with the experimental results.Mechanical Engineerin

Mirror-Curves and Knot Mosaics

Inspired by the paper on quantum knots and knot mosaics [23] and grid diagrams (or arc presentations), used extensively in the computations of Heegaard-Floer knot homology [2,3,7,24], we construct the more concise representation of knot mosaics and grid diagrams via mirror-curves. Tame knot theory is equivalent to knot mosaics [23], mirror-curves, and grid diagrams [3,7,22,24]. Hence, we introduce codes for mirror-curves treated as knot or link diagrams placed in rectangular square grids, suitable for software implementation. We provide tables of minimal mirror-curve codes for knots and links obtained from rectangular grids of size 3x3 and px2 (p<5), and describe an efficient algorithm for computing the Kauffman bracket and L-polynomials [18,19,20] directly from mirror-curve representations

Ternary Hopf algebras

In this paper we introduce the notion of a ternary Hopf algebra and prove that it can be embedded into a universal enveloping Hopf algebra

n -ary comodules over n -ary (co)algebras

In the paper we study connections between (co)modules over n-ary and binary (co)algebras

Strateški okviri EU za održivi razvoj industrije i mogućnosti našeg usklađivanja

U radu su analizirani strateški okviri EU u planiranju održivog razvoja industrije i mogućnost našeg prilagođavanja. Cilj analize je pokušaj iznalaženja prihvatljivih načina formulisanja osnova i mogućnosti harmonizacije planiranja održivog razvoja industrije u Srbiji u odnosu na evropske strateške okvire postavljene Lisabonskom agendom, Perspektivama evropskog prostornog razvoja ka uravnoteženom i održivom razvoju teritorije EU (ESDP) i mogućnost uvođenja Direktive EU o integralnoj kontroli zagađivanja u industriji (Directive IPPC) i Direktive EU o proceni strateških efekata planova i programa na životnu sredinu (tzv. SEA-strateška procena uticaja). U radu se izučavaju strateški okviri, pristupi i ciljevi održivog razvoja industrije u EU i predlaže prilagođavanje Srbije u periodu tranzicije ka tržišnom privređivanju. U razmatranje su uključene prednosti i nedostaci za primenu pristupa planiranja održivog razvoja u periodu tranzicije u Srbiji, i predlaže se formulisanje nove održive industrijske politike koja bi trebalo da sadrži kombinovane elemente tržišnih i envajronmentalnih mehanizama i način implementacije (standardi, indikatori set raznih politika, instrumenata, mera i dr). U radu su dati predlozi za okvire strategijskog planiranja teritorijalnog razvoja industrije