Problem:
In the test runs, the welded forks of a forklift truck were subjected to a pressure-swelling Stress test to determine the changing recording and Sell of loads. During this test, a fault occurred in the area of welds zu cracking.
Findings:
After the cracks opened, the depth of material bonding in the welds (load-bearing cross-section) is visible. In all samples it was found that in large parts of the cross-section of the weld there was no complete material bond. This led to a significant weakening of the weld joint.
Fatigue fracture and fracture mechanism:
The fracture surfaces of the samples showed typical characteristics of a fatigue fracture on how they through oscillating strip and secondary cracks In addition, in some areas of the fracture surfaces broken combs recognizable, which points to a ductile fracture In the unconnected areas no clear fracture structure was visible, while in the only slightly connected areas a significant amount of spherical enamel structures could be recognized.
Metallographic analysis:
The metallographic micrographs through the welds confirmed the macroscopic findings. The material binding in the I-welds between C-profiles war irregular and in some areas much lower than the thickness of the C-profile. This inadequate weld bond led to increased tensions in the area of the weld and promoted crack formation.
Root cause analysis:
The inadequate material connection in the welds can be attributed to several potential causes:
- Insufficient weld filling:
The 3 mm gap between the C-profiles may not have been filled sufficiently with material, which indicates a insufficient welding wire supply In some areas there was material in the gap, but the Transportation to the base material inadequate. - Too little heat input:
The insufficient material bonding indicates a too little heat input during the welding process, which leads to a suboptimal Fusion of the welding materials. This was particularly observed in the areas with incomplete or low bonding.
Recommendations:
It is recommended that welding process to optimize in order to ensure sufficient material connection between C-profile sections This can be achieved by more precise control of the heat input and the welding wire supply A possible alternative would be to use a multi-layer V-seamto strengthen the weld and improve material binding to achieve.
Conclusion:
The cause of the cracking in the welded forks is the insufficient material bonding in the weld seams, which was promoted by insufficient heat input and insufficient filling of the gap between the C-profiles. optimization of the welding process is required to strength to improve the connection and the cracking to prevent.