Weld Penetration Defects and Streamlining of Measurement and Inspection

The welds (weld beads and penetration) that join these base materials, while also being metallic material, include filler materials (such as welding rods and welding wires) that have been melted and solidified.
In typical arc welding, for example, metal structures continuously change not only in the weld metal but also in the parts of the base materials affected by the welding heat. Along with this change, the mechanical properties of the metal materials also change continuously. On the other hand, reinforcement, which is formed on the weld bead surface, has discontinuities. Discontinuity concentration leads to mechanical property deviation, thereby causing fractures due to stress concentration.

In strength design of metal products, materials are generally selected by assuming the load to be applied to the products and determining the load to be applied to each metallic material. Also, loads applied to welds of each material need be taken into account in strength design, thus setting a standard for welding quality that must achieved.
Therefore, it is important to inspect the welding quality on the basis of strength design by measuring, for example, the throat thickness (or throat cross section, the size of the weld bead cross section after welding), the leg length, and the penetration depth. The quality of welds can be evaluated through macroscopic measurement of cross sections after welding.

The penetration depth is closely related to the joining strength. Any penetration defects on welds, such as inappropriate relationships between the penetration depth and base material, will greatly affect the quality and strength of welding. With butt welding as an example, the following describes typical penetration defects.

Different grooves also cause different patterns of penetration, leading to differences in the strength of welds.

Full penetration welding is a welding method in which the groove of the base material to be joined is united and embedded with molten joining materials (filler rod and welding wire), as with butt welding.
It can be said that full penetration welds are highly reliable in strength design as they have the same proof stress as the base material. On the other hand, they require high welding quality. Particular attention is required at the ends of welds to prevent defects such as undercut welds. It is also important to control and adjust reinforcement because stress concentrates on excessive reinforcement, causing cracking or other such problems.

The cross sections of welds sometimes make judgment and measurement difficult due to the low contrast of weld boundaries both for the penetration and the base material. Hence, these boundaries cannot be observed clearly with a conventional microscope.
The VHX Series 4K Digital Microscope can capture edges clearly with high-resolution 4K images. Even for the cross sections of lap fillet welding, whose boundary between weld metal and base material is hard to distinguish, it is now possible to quickly and distinctively observe clear boundary edges, differences in metal structures, and defective areas.
These observations eliminate confusion in conventional dimensional measurement of penetration and reduce work hours while improving inspection accuracy.

Dimensional measurement of weld cross sections is an important inspection related to strength and quality. However, with a conventional stereoscopic microscope, it is difficult to judge measurement points due to low contrast between the base material and the beads. Also, visual matching with memory and manual entry of the obtained values are required, resulting in the problems of human error and complicated operation.
With 4K high-resolution images on its monitor that can clearly represent weld boundaries, the VHX Series 4K Digital Microscope enables 2D dimensional measurement of items such as leg length, throat depth, and penetration depth through the easy operation of simply clicking the point to measure. You can complete even high-accuracy, submicron-order measurements easily and in a short time, thereby achieving significant work hour reductions.
Also, the latest automatic edge detection function prevents variations in measurement points between operators. Furthermore, a wide variety of inspection needs are satisfied thanks to the function that enables users to repeat dimensional measurements by selecting measured and saved data from an album.

Weld beads have continuous uneven shapes. If there are (discontinuous) defects on the bead surface such as insufficient reinforcement, overlap, undercut, pits, and cracking, the intended mechanical properties cannot be obtained and fractures may occur. Conventional microscopes, however, cannot bring the entire uneven bead surface into focus and cannot provide the height information required for evaluation of items such as reinforcement.
The VHX Series 4K Digital Microscope enables fully focused viewing and 3D dimensional measurement for targets that have uneven surfaces. Additionally, by displaying the 3D shape of weld beads, you can not only inspect the shape freely from various angles, but also measure the profile of any cross section. Because shapes and roughness can be analyzed, you can also inspect spatters, cracks, and similar issues on the base material surface around weld beads.

Conventionally, operators have had to deal with not only complicated measurement and inspection, but also the large workload that report creation entails.
The VHX Series 4K Digital Microscope is equipped with a report function. You can also install Excel on the VHX Series, just like a PC. Setting up templates in advance makes it possible to instantly enter not only magnified images, with the dimensions included, but also measured values and pass/fail judgments. These templates dramatically reduce the effort and man-hours required for report creation.