Lasersvetsning : En genomförbarhetsstudie av stora rotationssymmetriska komponenter med varierande materialsorter
Sammanfattning: A big problem with welding is that it is hard to predict how a high heat canaffect different materials. The effects that can appear is shape changes in thematerial and brittle structures. The brittle structures will affect the strengthof the material and if the shape changes are big, the fatigue strength of thecomponents will be limited. A new gear box is under development at VolvoConstruction Equipment. This thesis was created because there currently is alack of documentation and tests in this field. The purpose of the thesis is tocheck if there is any changes to the welded components in the gear box and howthese changes can be avoided.Before the thesis, the company had made test components in a smaller scale.This was made because it is more cost effective and the components are easierto handle in the laser welding station. The prototypes that will go in to the gearbox will be 150-200 percent bigger than the test components.The methods used in this thesis is to investigate if there is support in recentresearch, investigate if here is any practical solution that can be applied directlyand to see if there is a simulation that can be used in the future. During thethesis work there were tensile tests, hardness measurements and microscopicexaminations made to the test components. This was made in order to controlthe strength in the welded parts, assess the risk of cracks and idenftify thestructure of the materials. There were also a comparision made with the articlesthat are welded today at Volvo. In addition to this, a simulation was made byan extern company. This simulation was used in a comparions with the weldedcomponents. These three methods will be validated against each other. Methodsthat are developed for welding most often regards only arc welding and can notbe applied for laser welding. This regards both cooling times and cracking risks.There is an ISO EN-standard to assess pores and cracks, but these often lackclarity.Five of six welded components from the gear box has been investigated in thisthesis. These components has three different materials; low carbon steel, mediumcarbon steel and high carbon steel. The components can be made of two or threewelded parts and depending on which component it is, it has varies mixtures oflow, medium, or high carbon steel.The result shows that very small shape changes occur in the welding componentsregardless of which material they are made in. The low and medium carbon steelsare close to the same hardness as materials that are being welded today andthe tensile tests shows that the geometry can be more limiting than the weldingitself. This gives the low carbon steels good conditions to work. The high carbonsteels contain a lot of pores and cracks and it should be investigated closer ifthey need pre- and post heating. The simulation shows good results and a fullsize prototype test should be executed now. A recommendation for future workis to make a fatigue strength test.
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