Determining and Ensuring Weld Quality in the Production of the Main Boom of a Truck-Mounted Crane

In the diploma thesis, the author sought to illustrate, through a concrete example of weld joint execution, the seriousness of determining and ensuring quality in the process itself, as well as the appropriate selection of materials and other segments of the process, such as the weld joint. Because in today's world the quality of the final product is very important, and strong competition does not allow settling for a grade of good, the company Palfinger strives at every step of the work process to ensure only the highest possible quality. Nevertheless, we must not forget the specificity of the welding procedure, which, despite all standards, can alter the desired result of examinations and tests to which the final products or welds are ultimately subjected. Examinations, however, confirm or refute the expected quality of the welding process with concrete values.

Solution and Method

In the diploma thesis, the author sought to illustrate, through a concrete example of weld joint execution, the seriousness of determining and ensuring quality in the process itself, as well as the appropriate selection of materials and other segments of the process, such as the weld joint. Because in today's world the quality of the final product is very important, and strong competition does not allow settling for a grade of good, the company Palfinger strives at every step of the work process to ensure only the highest possible quality. Thus, each segment of this process is defined by a standard, which contributes to an additional increase in the quality of individual segments and thereby of the final product.

Results

Nevertheless, we must not forget the specificity of the welding procedure, which, despite all standards, can alter the desired result of examinations and tests to which the final products or welds are ultimately subjected. Examinations, however, confirm or refute the expected quality of the welding process with concrete values. Thus, these results can subsequently be used to improve the process reliability of the welding procedure, which is also the purpose of this diploma thesis. Because there is no perfect weld, there is always room for improvement, to which precisely such data contribute. Non-destructive examinations, such as visual, penetrant and radiographic examination of the first, that is, the HV-weld, showed us that the weld joint is within the permissible limits or acceptable for quality class B.

Destructive examinations (tensile, bending and toughness tests, as well as hardness measurement) showed us that the values of the tested HV-weld in the listed tests, except for the toughness test, are outside the permissible limits. The cause of these values was shown to us in more detail by the metallographic examination, where a defect in the weld was visible – lack of fusion. Because lack of fusion is a common occurrence in weld joints for various reasons, in the case in question we assume that this occurrence arose due to the shape of the weld joint or the associated incorrect heat dissipation. Non-destructive examinations of the second tested V-weld likewise showed an acceptable result without deviations. Destructive examinations, primarily tensile, bending and hardness tests of the second specimen, showed significantly better values than with the previous HV-weld. ** The finding of the macroscopic examination also showed that the weld is without macroscopically visible defects.** The toughness test was likewise without peculiarities.

The results of the examinations thus showed us that the values of the tensile test were below the permissible limit, the values of the bending test were negative, and the hardness measurements were too high, therefore the results are unacceptable. The metallographic examination of the tested specimen also showed a defect in the weld joint, which additionally confirmed our presumed questionability of the choice of HV-weld as the right choice for the construction in question. ** The values of the tensile test, which were 724 N/mm² for the first specimen and 763 N/mm² for the second specimen,** indicated that there is a defect in the weld joint.

The required values of the completed tensile test for the selected material S690QL according to standard SIST EN 10025-6:2005+A1:2009 are between 770 and 940 N/mm². The bending test also indicated a defect in the root of the weld joint, because the fracture occurred during the test across the face of the weld. Likewise, the excessively high hardness value, which exceeded the limit of 450 HV, indicates hardening in the weld. Thus, the findings of the metallographic examination of the tested specimen are crucial for defining the type of defect, which showed an all too common welding defect – lack of fusion in the weld joint.

Because of this, based on the type of selected weld joint and the consequent defect, it was determined that there is incorrect heat dissipation during the welding process. Given all the established facts, the key recommendation to avoid potential defects or to ensure process reliability is to change the HV-weld to a V-weld, whereby we ensure better heat dissipation and thereby avoid a potential defect and thus ensure a higher-quality weld joint.