# Effect of Augmented Reality Support on Quality Inspection of Welded Structures
## 3 Materials and Methods
### Experiment Design  
This research works with two factors: one is the medium to support quality inspection (AR-enabled or paper-based), and the second factor is the level of user experience. In the AR variant, the instructions were displayed by the HHD variant, i.e., through visualisations on portable devices. The products to be inspected were divided into two sets. Each set contained a total of five types of products in five pieces each; thus, each set consisted of a total of twenty-five items for inspection. These products were chosen so that the dimensions would allow for relatively easy handling during the inspection tasks. Due to the nature of the inspection operations, there is not as much emphasis on the freedom of both hands as, e.g., in assembly operations, during which both hands need to be free to move, and HHD is therefore more limiting. The products were chosen so that they are relatively easy to handle on the inspection board and do not require the use of other auxiliary equipment, such as a crane, to move them. These parts ranged in size from 300 to 800 mm and weighed between 2 and 7 kg. The weldments consisted of 5-17 welded components. As part of the experiment, a check on parts welded using the MIG method (metal inert gas) was performed to verify the following points:  
* All components are selected correctly and none are missing;
* All components are placed in the correct positions;
* All welds are placed in the correct positions in the correct number, size, length, spacing, and quality. The basic shape of each part is formed by a sheet metal plate with bends from a bending press. Components such as welding nuts, pins, or bosses of various lengths and diameters with different holes or threads are then welded onto this base sheet. In addition to these components, other sheet metal components can be welded to the base sheet. The parts for both sets were chosen to present the same challenge to the inspectors. In addition to being very similar in design, the parts in both sets were chosen so that each set required an inspection of the same number of total points. The detailed drawings of the parts tested are subject to confidentiality and cannot be published in full. An illustrative example is therefore provided to show the complexity of the parts in experiment. For simplicity, only basic drawing views and dimensions (all in mm) are shown in Figure 4; they are not complete production drawings. Based on interviews with quality managers, these parts involve relatively complex inspection tasks. Their inspection often requires going through several levels of drawings and BOMs, navigating multiple sheets of very similar drawings, and correctly interpreting auxiliary drawing details and sections. Some parts are very similar to each other, and it is common in the manufacturing process for small batches of several types of such very similar products to be rotated during a shift. This is why mistakes are made when a welder, for example, selects a pin with the wrong length, omits a welding nut, or welds it in the wrong position. It can happen that the welder chooses an incorrect weld layout that does not correspond to the drawing documentation or omits a weld. Often, this type of error does not occur in the entire production batch but occurs due to inattention only partially in the batch. It is therefore challenging for inspectors to reliably detect this type of error, to maintain maximum attention during the inspection of the entire batch, and to perform the inspection in the shortest possible time so that the value stream of the production process is not interrupted. By the observation and analysis of the internally captured defect records, the following defects were randomly placed in the control set:  
* Missing welding component;
* Component welded in the incorrect position;
* Nut welded from the opposite side;
* Missing weld;
* Incorrectly spaced welds. In the whole set of 25 products, 20 pieces were completely correct (80%) and 5 pieces (20%) had one of the above errors.