Welding Procedure for High-Strength Steel S960QL

New technologies for obtaining fine-grained steels have a significant impact on changes in processing and forming processes, which requires constant adaptation of individual work phases, machinery and technology. Obtaining permission to use materials for standardised and non-standardised areas often represents a major difficulty, which ultimately affects preparation, production, supervision and control, and most of all the agreed delivery deadlines or contractually bound delivery dates. Based on positive test results of the sample in the technological laboratory, precise instructions are prepared for operators, requiring training on proper handling of available materials in production. Selected procedures and clear work instructions, consistent with individual customer requirements, standard recommendations and data sheets, must be available to operators and have a direct impact on product quality.

Solution and Method

New technologies for obtaining fine-grained steels have a significant impact on changes in processing and forming processes, which requires constant adaptation of individual work phases, machinery and technology. Obtaining permission to use materials for standardised and non-standardised areas often represents a major difficulty, which ultimately affects preparation, production, supervision and control, and most of all the agreed delivery deadlines or contractually bound delivery dates. Like all metallic materials, these steels are also sensitive to the energy input in the fusion welding process described in the thesis due to their structural composition. The particular sensitivity to temperature influence of these materials requires a special approach to documentation preparation and the execution of forming and joining tests before commencing production of specific objects.

Results

Based on positive test results of the sample in the technological laboratory, precise instructions are prepared for operators, requiring training on proper handling of available materials in production. Selected procedures and clear work instructions, consistent with individual customer requirements, standard recommendations and data sheets, must be available to operators and have a direct impact on product quality. Knowledge of the cooling time concept between 800 and 500 °C, setting welding parameters, marking and traceability of completed work phases, knowledge of weld quality assessment, maintenance of machines and tools, use of measuring instruments, reading and observing technological and technical documentation, and maintaining technological discipline is of key importance on the part of operators, which also affects quality and required work completion deadlines.

The diploma thesis established that in the case of using high-strength fine-grained steel, economic savings are achieved due to: At the same time, the diploma thesis established that the use of fine-grained high-strength thinner materials in certain cases does not satisfy requirements due to the rigidity of positions under various loads and the permissibility of standards for designing weldments. Based on the hypotheses written above, S960QL steel is suitable for use in areas requiring weight reduction, appearance improvement, increased reach and load capacity of individual types of cranes.

According to the results of the technological laboratory, for S960QL steel the MAG welding procedure is the most economical compared to other welding procedures. To ensure improvement of individual work execution phases in production, cooperation between the design office and production technology is of great importance. Thus, this year at Palfinger d.o.o., a system of such cooperation was also introduced. When the design department prepares a concept or modification of a crane or components, the documentation is forwarded to production technology for review of manufacturing feasibility.

Production technology adds improvement suggestions, which the design office later implements. Only in this way can the design office prepare final documentation for the execution of prototype products. The decision to produce the diploma thesis was primarily influenced by the problem of manufacturing the steel structure of an already existing type of crane with a working platform and the customer's requirement to increase the scope of the working area and reduce the overall weight of the crane due to installation on a lorry with permitted lower loads.

In accordance with the prepared technical documentation or drawings, a change in the quality and dimensions of the installation material is required. Due to this, it was necessary to change the entire production process and prepare new technological documentation for welding procedure approval. After preparing the technological documentation for work execution and commencing production of the sample weldment, it turned out that the decision to switch to higher quality material and thus reduce the thickness of the installation material used in the weldment, despite weight reduction, was unjustified, as unacceptable deformations occurred in the welding process itself.

Likewise, due to excessively high costs of implementing the production procedure for such components in relation to annual demand quantities, it is not cost-effective. Due to the above, the decision was made to maintain the established forming and welding process. Despite the results obtained, however, obtaining welding process approval for high-quality fine-grained steel designated S960QL contributed to the company gaining permission to increase the range of installation material selection to materials with the mentioned high mechanical properties.

• lower own weight of the weldment,
• lower costs of base material procurement,
• shorter time and reduced costs of material processing,
• energy savings for preparing weldment positions,
• reduced costs of filler material due to weld volume,
• time and cost savings of the welding itself.