3-d-printing with steel: additive manufacturing of connection … · 2020-05-21 · keywords:...

IABSE Symposium 2019 Guimarães Towards a Resilient Built Environment - Risk and Asset Management March 27-29, 2019, Guimarães, Portugal

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3-D-Printing with Steel: Additive Manufacturing of Connection Elements and Beam Reinforcements

Jörg Lange, Thilo Feucht Technical University Darmstadt, Institute for Steel Structures and Materials Mechanics, Darmstadt, Germany

Contacting author: [email protected]

Abstract Automated steel construction manufacturing with robots is no longer just a dream of the future but a reality. The Institute for Steel Structures and Materials Mechanics of the Technical University (TU) of Darmstadt/Germany has two welding robots. These robots are being used to assess various application for Additive Manufacturing. For the construction of steel, Wire + Arc Additive Manufacturing (WAAM) is suitable, which is similar to Gas-Shielded Metal Arc Welding. The wire electrode serves as printing material. With this method we can produce components in layers and achieve deposition rates of 5 kg/h. The components studied in this research project are connection elements such as simply supported girder connections and head plates and reinforcing elements such as stiffeners and beam reinforcements. In this paper topology-optimized structures are presented, which can be printed with the WAAM directly on steel beams.

Keywords: Additive Manufacturing, WAAM, steel constructions, stiffeners, head plates,

1. Introduction / Additive Manufacturing

The topics of 3-D Printing and Additive Manufacturing (AM) are currently very much discussed. The technologies of these processes are progressing rapidly. The printing materials are diverse and also the printing of steel is now easily possible. In Additive Manufacturing, a component is created by adding material, as opposed to milling, which removes material from a body. Selective Laser Melting (SLM) and Selective Laser Sintering (SLS) exist for the Additive Manufacturing of steel [1]. A further method is Laser Metal Deposition (LMD), in which a metal powder is applied to a local molten pool generated by the laser [2]. All these methods are of high accuracy, but also associated with high equipment costs.

For steel construction, Wire + Arc Additive Manufacturing (WAAM), which is similar to Gas Shielded Metal Arc Welding (GMAW), is suitable [3]. The wire electrode serves as printing material. With this method, it is possible to produce large components in layers (see Figure 1) and achieve deposition rates of up to 5 kg/h [4].

Additive Manufacturing in general and the welding process WAAM in particular make it possible to use the material in a targeted manner. Structures can be freely modelled and get almost any shape. Unlike conventional steel construction, economical production hardly limits the form of construction. The customary trade-offs between a cost-effective production and material saving can be omitted. Material only needs to be placed where it is necessary. It therefore makes sense to determine these structures by means of a topology optimization.

IABSE Symposium 2019 Guimarães: Towards a Resilient Built Environment - Risk and Asset Management March 27-29, 2019, Guimarães, Portugal

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Figure 1. Additive manufactured structure (height

13.5 cm)

2. Topology Optimization As part of the structural optimization, the topology optimization is suitable for "cutting out" unstressed areas of solid components and thus increasing the effectiveness (in kN/kg). The topology optimization pursues the lightweight construction approach of material-saving. The objective is to guide a load from load introduction point to support. For exampleplates are disintegrated into truss structures and thus the structure adapted to the flow of force [6]. In principle a severe reduction of material is desired while the rigidity and the load-bearing capacity stay as large as possible. This approach leads to an optimisation problem and guarantees economic added value, since the resource steel is used only at the statically necessary places. In AM however material savings lead mainly to less manufacturing time because less material has to be applied.

3. Possible Applications This research project concentrates on connection elements whose mass is low compared to the entire structure and which can be "printed" using automated welding robots. Some examples are

shown, which are examined at the Institute for Steel Structures and Materials Mechanics of TU Darmstadt.

3.1 Beam Hook

Connections of beams to columns are often designed as flag plate or with double angles (see Figure 2). With Additive Manufacturing it is possible to place the beam on a topology-optimized hook by using bolts (see Figure 3). The hook can be welded directly onto the column during fabrication. Erection is simplified by eliminating the need for a bolted connection.

Figure 2. Double angle connection

Figure 3. Beam hook (animated)


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3.2 Stiffeners

Stiffeners are often used for better load transfer into an I-profile and to prevent the flange from bending or buckling. Figure 4 compares a conventional stiffener (left) with the topology-optimized stiffener (right) to be produced additively. In traditional production, unloaded areas would not be removed, as this would require additional effort and the waste would not be usable.

Figure 4. Stiffener in H-Beam

3.3 Head Plate / T-Stub

In the case of rigid connections with head plates moment and tensile force are transmitted with a height offset, since the screw connection is not at flange height (see Figure 5).

Figure 5. Head Plate / T-stub (conventional)

Figure 6. Head Plate / T-stub (topology-optimized)

The tensile force is transmitted from the flange to the bolt by bending the head plate. The geometry of the head plate can be changed by optimization in such a way that the effectiveness increases and less material has to be used (see Figure 6).

3.4 Beam Reinforcements

In the design of beams, in most cases the stress analysis according to first order theory in the middle of the field or the stability analysis (lateral torsional buckling) is decisive. The beam profile is chosen the same over its entire length and is therefore only fully utilised at the decisive point. A staggering of the beam profile is not economical due to the complex manufacturing process. Reinforcements with sheet metal or even arch stiffeners, which prevent warping and thus torsional bending, are also unusual due to the manufacturing effort. With the aid of Additive Manufacturing, reinforcements can be automatically welded directly onto beams using robots and thus smaller nominal heights can be selected for profile dimensioning.

4. Implementation within the context of automated manufacturing

In fully automated manufacturing systems, steel beams are automatically provided with connection elements (e.g. head plates, stiffeners). The elements are scanned, delivered by handling robots and fixed to the steel girder with the help of welding robots (see Figure 7) [7].


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Figure 7. Zeman Steel Beam Assembler (SBA)

In addition, the connection elements can be applied directly to the steel beam with the aid of Additive Manufacturing. This simplifies the production chain of the connection elements: steel plates for stiffeners, head plates, etc. are not needed any more. This reduces material handling, transport and storage. There is no more waste, which would otherwise have to be stored or disposed of. Instead of a handling robot and a welding robot, two welding robots can additively produce at the same time.

5. Influences on geometry and material properties

For conventional and commercially available 3-D printers, parameter sets exist that allow almost any geometry to be printed without the need for any investigations. Slicer programs divide a 3-D body into paths, which the print head travels at a corresponding speed and applies the material in such a way that the planned structure is created. For the WAAM, various parameter investigations already exist, which are very widely scattered with regard to material (steel, aluminum, titanium, alloys) and production equipment (power source, robotics), but they cannot be applied in any case. Especially the required parameters for this particular research project are very complicated due to the complex multilayer geometries. It is therefore inevitable to gain knowledge of further parameters. This becomes clear when one looks at

the many influences that affect the geometry and the material properties.

5.1 Input parameters

x Wire electrode x Wire diameter x Shielding gas x Gas flow rate x Geometry of the gas nozzle x Welding System

5.2 Process parameters

x Current x Voltage x Wire feed speed x Welding process regulation (normal, pulse,

CMT) x Travel speed

5.3 Thermal boundary conditions

x Interpass temperature x Temperature history / temperature cycles x Cooling

5.4 Geometric boundary conditions

x Orientation of the nozzle (neutral, dragging, piercing)

x Welding position (trough position, rising, falling)

x Contact tip to work distance x Weld seam beginning, weld seam centre,

weld seam end

6. Previous investigations Several preliminary tests have already been carried out at the TU Darmstadt.

6.1 Equipment

x 2 x Comau Robots Smart NM 16-3 x Fronius CMT Advanced System x Fronius TransPuls Synergic 5000 x Wire: G3Si1 x Gas: M21


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6.2 First results

First tests have shown that structures can be produced linearly on steel beams. A topologically optimized beam hook was produced on an I-beam without any noticeable welding distortions (see Figure 8).

Figure 8. Beam Hook (additive manufactured with

milled hole)

In a further investigation, full stiffeners were welded onto an I-beam (see Figure 9). Despite recognisable welding distortions, destructive compression tests showed that the bearing loads of the additive manufactured stiffeners were at the same level as those of conventionally manufactured stiffeners (see Figure 10).

Figure 9. Full stiffener in I-beam (additive

manufactured)

Figure 10. Full stiffeners in I-beam (conventionally

manufactured)

7. Conclusions Additive Manufacturing makes new structures possible, because the constraints of conventional manufacturing no longer exist. More complex and topology-optimized constructions can thus be realized. In this paper, some completely new structures of connection elements and beam reinforcements are presented.

At the TU Darmstadt these new structures are numerically developed with the help of topology optimization and capacity load calculation. In the next step, the elements are additively manufactured and tested. A great challenge here is the finding of suitable process parameters. The parameters such as the settings on the welding machine (current, voltage, wire feed speed, etc.) and on the robot (travel speed) influence the geometry and the material properties very much.

Another advantage of Additive Manufacturing lies in the improved production logistics. The connection elements can be applied directly to the steel beam. This simplifies the production chain of the connection elements: steel plates for stiffeners, head plates, etc. are not needed any more. This reduces material handling, transport and storage.


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8. References [1] Schmidt, T. Potentialbewertung generativer

Fertigungsverfahren für Leichtbauteile, Hamburg: Springer Vieweg; 2016.

[2] Gebhardt, A. Additive Fertigungsverfahren – Additive Manufacturing und 3D-Drucken für Prototyping – Tooling – Produktion. München; 2016

[3] Sequeira Almeida, P. M. Process control and development in wire and arc additive manufacturing, Dissertation, Cranfield University, 2012. Available from http://dspace.lib.cranfield.ac.uk/handle/1826/7845, [Accessed 27th October 2017]

[4] Hartke, M., Günther, K., Bergmann, J. P. Untersuchung zur geregelten, energiereduzierten Kurzlichtbogentechnik als generatives Fertigungsverfahren, DVS Bericht, Band 306: 98-102; 2014.

[5] Ali, Y., Steinerstauch, D., Günther, K., Henckell, P., Bergman, J.P. Additive Fertigung von 3D-Verbundstrukturen mittels MSG-Schweißen, DVS Bericht, Band 327: 75-80; 2016.

[6] Harzheim, L. Strukturoptimierung: Grundlagen und Anwendungen, Haan-Gruiten: Europa-Lehrmittel; 2014.

[7] Fischer, R. Eine Untersuchung zur roboterbasierten Baugruppenfertigung im Stahlbau, Dissertation TU Darmstadt; 2014

3-d-printing with steel: additive manufacturing of connection … · 2020-05-21 · keywords:...

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