Kongens Lyngby, Denmark
Kongens Lyngby, Denmark

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Hansen K.S.,IPU Technology Development | Olsen F.O.,IPU Technology Development | Kristiansen M.,University of Aalborg | Madsen O.,University of Aalborg
Journal of Laser Applications | Year: 2015

The introduction of high-power single mode fiber lasers has given deeper and narrower welds than previously seen using lasers. In some cases, the weld becomes too narrow and must be expanded to fit the geometrical shape of a given welding task. Instead of using only one beam, it was suggested to split the beam into multiple spots placed in a prespecified pattern. In this way, the dimensions of the weld pool could be controlled. In this work, the spots are placed on a row perpendicular to the welding direction. This provided the ability to control the final weld face by controlling the width and depth of penetration independent of each other with minimum heat input. An examination was conducted on how the weld cross section is influenced by spot distance, number of spots, power, and focus. It is shown that a weld seam can be widened in steps by using multiple spots, and the depth can be controlled independently from the width by adjusting the laser power. It is possible to produce a rectangular like cross section of the weld by choosing correct design parameters. For a pattern with multiple spots on a row, equal depth of penetration in the weld bead is reached if the edge spots have 5%-10% more power than the center spots. Basic rules for design of spot patterns are given for a configuration with a single mode laser and spot diameter of Ø85 μm. The ability to bridge gaps is increased in multispot welding compared to multiple single passes. The technique shows promising results in welding parts which resembles the conditions of a real production regarding robustness and tolerances. © 2015 Laser Institute of America.

Hansen K.S.,IPU Technology Development | Kristiansen M.,University of Aalborg | Olsen F.O.,IPU Technology Development
Physics Procedia | Year: 2014

The introduction of high power single mode fiber lasers has given deeper and narrower laser welds than seen previously. In some cases the weld becomes too narrow and must be expanded to fit the geometrical shape of a given weld task. It was suggested that instead of using only one beam, the beam was split into multiple beams placed in a pre-specified pattern. In this way the dimensions of the weld pool could be controlled. This gave the ability to control the final weld face width and penetration depth independently of each other with minimum heat input. Practical implementation of splitting a beam into a beam pattern with a diffractive optical element (DOE) is presented with results on splitting a beam from a single mode fiber laser into either three or seven individual beams on a row. Basic design rules for controlling the weld pool dimensions are developed. Results show that it is possible to control weldpool in size. © 2014 The Authors. Published by Elsevier B.V.

Kristiansen M.,University of Aalborg | Villumsen S.,University of Aalborg | Olsen F.O.,IPU Technology Development
Physics Procedia | Year: 2015

Remote fusion cutting (RFC) is an interesting industrial process compared to traditional laser cutting. It is because traditional laser cutting is limiting travel speed and accessibility due to the required positioning of the cutting head just above the workpiece for providing a cutting gas pressure. For RFC this pressure is created by the vapor, which is formed when the laser beam evaporates the cut material. The drawback of RFC compared to traditional laser cutting is a worse cut quality, wide cut kerf and a slower travel speed. The contribution of this paper is an experimental investigation, which determined the process window for RFC in stainless steel with a single mode fiber laser. The process variables: travel speed, focus position, power and sheet thickness were investigated. Based on the results of the experiments and process knowledge the aim of this work was to determine and describe the most important driving mechanisms for understanding and modelling the RFC process. The purpose is to deepen the understanding of the mechanisms in the process and find the factors, which can improve the performance and also determine the limitations. The validation results show that the developed model of the RFC process gives a similar process window as the experimental results for the tested parameters and variation of travel speed and focus position. © 2015 The Authors.

Hovgaard T.G.,Danfoss A/S | Larsen L.F.S.,Danfoss A/S | Skovrup M.J.,IPU Technology Development | Jorgensen J.B.,Technical University of Denmark
2011 International Symposium on Advanced Control of Industrial Processes, ADCONIP 2011 | Year: 2011

Refrigeration systems consume a substantial amount of energy. Taking for instance supermarket refrigeration systems as an example they can account for up to 50-80% of the total energy consumption in the supermarket. Due to the thermal capacity made up by the refrigerated goods in the system there is a possibility for optimizing the power consumption by utilizing load shifting strategies. This paper describes the dynamics and the modeling of a vapor compression refrigeration system needed for sufficiently realistic estimation of the power consumption and its minimization. This leads to a non-convex function with possibly multiple extrema. Such a function can not directly be optimized by standard methods and a qualitative analysis of the system's constraints is presented. The description of power consumption contains nonlinear terms which are approximated by linear functions in the control variables and the error by doing so is investigated. Finally a minimization procedure for the presented problem is suggested. © 2011 Zhejiang University.

Hovgaard T.G.,Danfoss A/S | Hovgaard T.G.,Vestas Inc. | Hovgaard T.G.,Technical University of Denmark | Larsen L.F.S.,Danfoss A/S | And 3 more authors.
Canadian Journal of Chemical Engineering | Year: 2012

Supermarket refrigeration consumes substantial amounts of energy. However, due to the thermal capacity of the refrigerated goods, parts of the cooling capacity delivered can be shifted in time without deteriorating the food quality. In this study, we develop a realistic model for the energy consumption in super market refrigeration systems. This model is used in a Nonlinear Model Predictive Controller (NMPC) to minimise the energy used by operation of a supermarket refrigeration system. The model is non-convex and we develop a computational efficient algorithm tailored to this problem that is somewhat more efficient than general purpose optimisation algorithms for NMPC and still near to optimal. Since the non-convex cost function has multiple extrema, standard methods for optimisation cannot be directly applied. A qualitative analysis of the system's constraints is presented and a unique minimum within the feasible region is identified. Following that finding we propose a tailored minimisation procedure that utilises the nature of the feasible region such that the minimisation can be separated into two linear programs; one for each of the control variables. These subproblems are simple to solve but some iterations might have to be performed in order to comply with the maximum capacity constraint. Finally, a nonlinear solver is used for a small example without separating the optimisation problem, and the results are compared to the outcome of our proposed minimisation procedure for the same conceptual example. The tailored approach is somewhat faster than the general optimisation method and the solutions obtained are almost identical. © 2012 Canadian Society for Chemical Engineering.

Mahshid R.,Technical University of Denmark | Hansen H.No.,Technical University of Denmark | Arentoft M.,IPU Technology Development
CIRP Annals - Manufacturing Technology | Year: 2014

Multi-step micro bulk forming is characterized by complex processes and high precision requirements. In particular the demands regarding handling accuracy between different forming steps are of the order of a few μm. The paper introduces a methodology for the analysis and characterization of this transfer system on component level and system level. Laser interferometry is used in combination with analytical models to predict the positioning ability of the actuator in a static as well as dynamic mode. In combination with an analysis of the grippers, a full description of the transfer precision inside the forming press is obtained. © 2014 CIRP.

Hovgaard T.G.,Vestas Inc. | Larsen L.F.S.,Vestas Inc. | Skovrup M.J.,IPU Technology Development | Jorgensen J.B.,Technical University of Denmark
Proceedings of the IEEE International Conference on Control Applications | Year: 2012

We consider two important challenges that arise when thermal energy is to be stored in foodstuffs. We have previously introduced economic optimizing MPC schemes that both reduce operating costs and offer flexible power consumption in a future Smart Grid. The goal is to utilize the thermal capacity of refrigerated goods in a supermarket to shift the load of the system in time without deteriorating the quality of the foodstuffs. The analyses in this paper go before closing any control loops. In the first part, we introduce and validate a new model with which we can estimate the actual temperatures of refrigerated goods from available air temperature measurements. This is based on data obtained from a dedicated experiment. Since limits are specified for food temperatures, the estimate is essential for full exploitation of the thermal potential. Secondly, the thermal properties, shapes and sizes of different foodstuffs make them behave differently when exposed to changes in air temperature. We present a novel analysis based on Biot and Fourier numbers for the different foodstuffs. This provides a valuable tool for determining how different items can be utilized in load-shifting schemes on different timescales and for estimating maximum energy storage time. The results are shown for a large range of parameters, and with specific calculations for selected foodstuff items. © 2012 IEEE.

De Chiffre L.,Technical University of Denmark | Carli L.,Technical University of Denmark | Eriksen R.S.,IPU Technology Development
CIRP Annals - Manufacturing Technology | Year: 2011

A novel artefact for calibration of the height in 3D microscopy is presented. The artefact comprises three steps having a common vertical axis, which allows z-coordinate calibration at different magnifications without requiring repositioning. The artefact is suitable for transferring traceability to 3D techniques at the micrometer and nanometer scale, e.g. 3D SEM, confocal microscopes etc. Two different series of samples were fabricated using EDM with three steps of 2-5-7 μm, and 20-50-70 μm, respectively, from a 3 mm diameter carbide wire. The artefact steps were calibrated on a stylus instrument according to ISO 5436 and measured on 3D microscopes. © 2011 CIRP.

Tang P.T.,IPU Technology Development
Micro and Nanosystems | Year: 2011

Electroforming is a surprisingly versatile process which is being utilised for production of a number of very different metallic products. The two main reasons for the exploitation of electroforming are the remarkable replication accuracy and the ability to grow seamless metallic products. In this paper the most important types of electroforming processes are discussed, along with the expected properties of the deposits and the challenges associated with selected applications. A special attention will be given to the utilisation of electroforming in the FlexPAET project. © 2011 Bentham Science Publishers.

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