Method of Welding and Spinning Combination for ... - Science Direct

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ScienceDirect Materials Today: Proceedings 2S (2015) S162 – S168

Conference MEFORM 2015, Light Metals – Forming Technologies and Further Processing

Method of welding and spinning combination for complex aluminium alloys lightweight components V. Vovka, *, R. Hoffmannb, A. Yasenc a Otto-von-Guericke-Universität Magdeburg, PSF 4120, 39016 Magdeburg Germany awab Umformtechnik und Präzisionsmechanik GmbH, Am neuen Teich 6, 39387 Oschersleben Germany c Vorrichtungsbau Giggel GmbH, Am Iserfeld 1, D-39359 Bösdorf Germany

b

Abstract A technology for a fast, flexible and low cost production of aluminium parts was developed for small quantity down to prototypes. Those parts are pre-defined by measures and material properties. The first effects from the welding and flow forming were theoretical analysed by FEM-Simulations. The achieved surface compaction from the flow forming has a high residual compressive stress especially in weld seam area, which increases the durability for load cycles, corrosion and abrasion. It saves additional steps in the manufacturing of an aluminium precise pipe, like the pre-processing of the aluminium sheet, flattening and post-processing of the weld seam. © 2014 The Authors. Published by Elsevier Ltd.

© 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Selection and peer-review under responsibility of the Conference Committee of Conference MEFORM 2015, Light Metals – (http://creativecommons.org/licenses/by-nc-nd/3.0/). of is thean Conference Committee Conference MEFORM 2015, Light Metals – Forming Selection peer-review under open access articleofunder the CC BY-NC-ND license Formingand Technologies and responsibility Further. This Technologies and Further

(http://creativecommons.org/licenses/by-nc-nd/3.0/).

Keywords: spinnin;, welding; aluminium alloys; lightweight components

1. Introduction Essential requirements of automotive industry and aerospace industries dealt with reducing of weight, increasing of lifetime and performances as well as further optimization of power consumption can be realized through innovative

* Corresponding author. Tel.: +49-391-671-2357; fax: 49-391-671-2370. E-mail address: [email protected]

2214-7853 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Conference Committee of Conference MEFORM 2015, Light Metals – Forming Technologies and Further doi:10.1016/j.matpr.2015.05.006

V. Vovk et al. / Materials Today: Proceedings 2S (2015) S162 – S168

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developments only. The substitution of steel by composite fibre materials and aluminium alloys becomes more and more important. Design, static and optical aspects of mainly closed profiles with no apparent joints (weld seams) are the basis for innovative design and engineering ideas. At present the range of profiles is very limited by dimensions and special materials (e.g. high-strength aluminium alloys). The reasons for this dealt with the manufacturing costs of welded Al-pipes / profiles, thermal impact on weld stresses and geometrical tolerances. Economically, these pipes can be produced in large quantities only. The market of semi-finished confronts to automotive industry development. This industrial sector is characterized by individualized and variable constructions, new designs, ever shorter times between development and prototype manufacture, often small numbers or only small series and permanent reduction of production, material and tooling costs. The original combined method "Welding & flow forming" provides new opportunities for lightweight concepts and the design of light alloy semi-finished products. 2. Background Due to demands of lightweight construction, automotive and electrical industries or specialty engineering demand for aluminium profiles (especially pipes) increases. These profiles are often needed for small series due to the increasing model diversification and variety of parts. These profiles, which are often reshaped, require high-precision output forms (tube or hollow sections) with tight tolerances, e.g. in the wall thickness. Suppliers of such precision profiles x x x

provide a limited "standard range" both with regard to material, as well as dimensions and geometry, can provide no less than minimum amount (usually > 20 t) and charge a high price for precision profiles.

A number of high-alloy aluminium alloys are only offered as metal sheets or coil, and exclude "ready" profile shape, because the relatively low demand for this modern construction materials, mass production (as it is e.g. for extrusion condition). Due the research project has been developed and tested a viable technology, economically enables precision profiles from high alloyed aluminium alloys with excellent low tolerances and residual stresses for small quantity requirements. As an alternative to extrusion (expensive tools and equipment, unfeasible economically for small quantities) the flow turning was used. The spinning was a final operation to a finished component, and unknown as an intermediate operation for the production of semi-finished products (precision profiles). 3. Principle of procedure As part of a cooperation project Otto-von-Guericke-University Magdeburg together with industry partners GIGGEL GmbH and awab GmbH, have developed a new method combining welding + over spinning (Fig. 1) for the production of rotationally symmetrical precision profiles and tested in practice.

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Welding

Rolling

Spinning

Cutting

Einflussfaktoren Infl uence fa ctors

• •Prozessparameter Process parameters • •Werkzeuge Tools

Fig. 1. Process principle

Based on these findings, a method was developed, allowing quick and inexpensively manufacturing of rotationally symmetrical aluminium components according to market demand. The following main points should be considered: x

x

The problem with welded Al-tubes is the seam area where the thermal joining processes, from the local heat supply results internal stresses, changes in the microstructures to form and dimensional tolerances and to modify the surface qualities. For this reason, the laser and friction stir welding are used as a joining method, since in these welding processes there are significantly lower heat supply into the material. Spinning as a rotatory forming process requires a flat semi-finished surfaces inside the spinning mandrel and the outside of the spinning rollers. During the spinning the length of the semi-finished product is increased, i.e. the material 'flows' in the longitudinal direction. This expansion also includes the area of the weld seam. It was investigated to what extent the introduced by the welding process tensions can be reduced by spinning again and what influence the spinning on the strength of the weld seams occurs (cracking, breakage).

The manufacturing of precision profiles (e.g. pipe sections) as task-related alternative to commercial profiles of high-strength aluminium alloys by flow turning failed so far: x x x x x

on the requirements relating to the ductility of the base material, which no longer is often sufficient by previous manufacturing steps (hardening). Because of the high degree of deformation during flow turning but is sufficient material ductility a prerequisite at the low ductility of the weld seam itself and the weld seam area to necessary for subsequent forming operations of the required rest-ductility-reserves in the finished semifinished (after spinning) to the high residual stresses by previous technologies, which require extensive pre-and post-treatment (heat treatment) to process-related relatively strong weld beads with longitudinally welded profiles, the flow turning in difficult or even impossible.

The above described problems are not more manageable especially in modern high-strength aluminium alloys with a very limited formability. As a part of the research project, a welding method for the longitudinal seam welding of rolled Al-sheet-blanks has been developed with the following premises: x x x x

lowest possible heat supply minimum and defined in their geometry weld beads sufficient strength of the joint to allow a subsequent spinning without flaws defined low welding residual stresses, which do not require a post-processing


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Development of a flow forming process and special tools allows the precision profiles with extremely low tolerances and ductility reserves to manufacture. Although previous work steps such as cutting, rolling and welding significantly adversely affect the ductility already are reserves of rest ductility for further deformations are available through the new technological regime even after spinning. The specific features of depression require minimal weld beads and a homogeneous ductile microstructure in the weld seam area. Conventional weld beads, which can be reached at minimum, are represented in Fig. 2. Required for the subsequent spinning, the weld beads (geometry and dimension) are shown in Fig. 3. Spinning roller

0,5-1,0 mm

Sheet 0,1 mm Fig. 2. Conventional weld geometry - not suitable for the following spinning.

Spinning roller

≤0,5 mm

0,1 mm

Sheet

Spinning mandrel

Fig. 3. Required bead geometry for the succession process spinning (ideal contour)

This special form of weld bead was achieved by welding gap defined, appropriate pre-processing of the abutting edges and sheet rolling with a narrow tolerance clash of bending edges for the so-called narrow gap welding. A homogeneous and ductile microstructure in the weld area is achieved x x

by minimal heat input used in high-power fibre laser welding [1] and by welding without filler material with low shrinkage.

In addition to the special weld bead geometry the welding residual stresses continues to play a crucial role. Welding residual stresses significantly influence on the dynamic and static behaviour of welded components [2]. The stresses occurring during welding are specifically modified in the following flow forming that can be dispensed with a heat treatment of the welded semi-finished products. Because of their low ductility, high-strength aluminium alloys are rarely formed by spinning. The only known example is the spinning cast or forged aluminium semi-finished products for car wheel rims. Despite the hardening by cutting, rolling and welding and thereby further reduced ductility, precision-profile (-pipe) was achieved by flow turning with high degrees of deformation. On the basis of FEM-calculations, a suitable technology is developed with

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special tools (suitable angle spinning, spinning forces interpretation of the spinning rollers made of ceramic or other suitable special material, designing a suitable spinning mandrel ...). The spinning with degrees of deformation of up to 50% and more has essential requirements to the weld seams, which transforms as a homogeneous material without burst and tear. It is noted that the weld seam after spinning has a rather "distorted" contour. To minimize the effect of "the twist", process parameters are optimized and specialized tools used with driven spinning rollers. 4. Theoretical studies The first effects achieved during welding and spinning were theoretically investigated by FEM simulation. For the calculation models and the software modules (Fig. 4.) were developed and tested. For the simulation calculation, the FE-software ABAQUS is used. The tools are modelled as analytical rigid body. The influence of inhomogeneity in the region of the weld on the results of the FEM calculation is judged based on the local deformation rate [3] over the cross-section of the joint of the welded pipes.

Fig. 4. FEM simulation for pipe stretching

The feasibility of this method was demonstrated by the virtual studies. During the forming the longitudinal welded tube is compressed to the diameter of the mandrel and stretched in the length. Based on used array of spinning rollers simulation results based the amount of deformation clearly shows flow of material, fibre orientation, rotation of the weld seam and the formation of the typical bead in the deformation region. Elemental responsible for the quality of the semi-finished product produced are the geometry imaging spinning mandrel and spinning roller. 5. Experimental Results of the performed experimental studies with a modular tool for method of combined welding + spinning are presented here. Test die was mounted to a vertical spinning machine from the company WF, it has two independently CNC slide rests (Fig. 5).


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Pusher

Preform

Spinning roller

Spinning mandrel

Fig. 5. Working space of the spinning machine

Electric drives in the machine provides a variation of the main spindle speed 150 rpm - 1300 rpm, it makes possible the realization of a wide range of deformation rates. The sample clamping in spinning tool was conducted with a newly developed clamping device. The spinning tools are water-cooled and require no water supply. The aluminium alloy AA5754 was used as the base material for the semi-finished product in the process combination. The 2.5 mm thick along the welded cylinder with a diameter of 180mm is provided with a welded-in bottom (Fig. 6).

Weld seam

Fig. 6. Output cylinder of AA5754 with a bottom

For the experiments on multi-stage forming the welded splice plates are used (Fig. 7). Weld seam

Fig. 7. Deep drawing experiments with shock-welded plates

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6. Discussion and summary x x x x x

x

x

x x x

A combined welding process routes for the manufacture of precision profiles in Al-alloys in small estates are presented. It results in significant differences between individual good weld able and easily formable Al-alloys. Particularly noteworthy is the high forming the shock-welded without filler metal Al sheets, which could be found in cold untreated state. Achieved high deformations offer great advantages in the design of welded Alcomponents. When welding aluminium alloys, but in particular for high-strength Al-alloys without the addition of materials results in a significant shrinkage and a high level of residual stresses and thereby a risk of cracking. If there is insufficient ductility, especially in the field of conventional weld, the flow turning is only partially or not at all feasible, because the local formability is exhausted. One way for this to find a solution based on model calculations interpretation of spinning tools and process parameters that allow realizing a defined pressure-train-load during flow turning and defined pressure-residual stresses in the weld area is The welding board’s preparation is already realizing during the cutting process (bevel and assignment of the abutting edges). Dimensions of the blank must be extremely precise and the abutting edges are deliberately positioned (rolling direction) so that after rolling with specially profiled tool (e.g. cambered), it is a uniform low welding gap with defined geometry arises. This is problematic because of the small sheet thickness (low stiffness) and the necessary provisional test tools (i.e. without complex devices for fixing). When flow turning of the welded hollow section, e.g. a pipe section, beginning of the longitudinal seam is always problematic, since cracks, etc. in the control arise during the engagement of the spinning rollers. Here, a solution has been found to avoid a special geometry of the spinning rollers and adapted technological parameters (e.g. entry curve for spinning rollers) with a possible defect at the beginning of the weld beginning. The conventional resulting weld beads are an obstacle during the spinning process - a "burnishing" generates high local hardening. The resulting bead has to be minimized so that the welding process can be carried out; a sufficient filling of the joint is achieved, and can be carried out subsequent spinning. Since aluminium alloys have a strong tendency for welding, special measures must be taken for the active parts. This problem was solved by a nitriding or chrome plating of the active parts, testing of ceramic spinning rollers and through theoretical and practical studies on the use of a suitable lubricant. The achieved surface compaction during the manufacturing process brings a high compressive residual stress, which is also reflected in terms of the lifetime when the load changes very noticeably advantageous.

The original method of combination provides fundamentally new possibilities for the design of precision components. A joint test of the research results with corresponding test suites with awab [4] and GIGGEL [5] has demonstrated the favourable conditions regarded to time, quality and reproducibility. Acknowledgements This publication is based on researches of ZIM-cooperation project KF2292027RU2 and cooperation project “REDAL” 1204/00020-23, which is funded by AiF Projekt GmbH Federal Ministry of Economics and Technology (BMWi) and Investment Bank Sachsen-Anhalt respectively. References [1] 3. Internationaler Workshop „Faserlaser“, Dresden, 2007 [2] K. Schneider, Ingenieur-Werkstoffe 8 (1999) pp. 40. [3] Vovk, V.; V. Vovk, A., DGM, 2006, 251-257. [4] awab Umformtechnik und Präzisionsmechanik GmbH, Firmenprospekt, 2014 [5] Vorrichtungsbau GIGGEL GmbH, Firmenprospekt, 2014