The Subjective Judgement of Weld Quality and its Effect on Production Cost
Paper i proceeding, 2013
The focus is often on new material, improving weld methods or in-creased automation when cutting production costs within the welding industry. However, the way the quality inspection is conducted can as well cause not negli-gible production costs.
Visual inspection is a common way to examine certain quality properties of welds. The performance of the visual inspection have been analyzed using attrib-ute agreement analysis where experienced auditors evaluated welded parts visual-ly for certain defects in a predefined order. The result showed a visual inspection system not capable of auditing parts the same way. The auditors evaluated differ-ently, not only between the appraisers, but also within by assessing the same part several times contrarily.
Another test was performed were personnel from different functions within the company visually evaluated the quality of test samples. This test also showed a vast variation in the subjective evaluation. The evaluated quality score varied throughout the whole scale from “good” to “need to be repaired.”
An incapable inspection can have a severe effect on the production costs. If a defect product finds its way to the customer, without being detected in the inspec-tion, the consequences can of course be immense. If defect free products are eval-uated as defect, this creates waste in the form of unnecessary repairs and process changes. An even larger amount of waste, however not as visible, lies within the area of unused capacity and process improvements that are not executed due to improper evaluation. An example from the evaluation tests shows a possible cost reduction of up to as much as 24% for a sample that was approved by part of the appraisers.
The solution is not necessarily to automate the inspection but rather to define the actual information needed and the demands made on the evaluation method.
type II error
attribute agreement analysis
type I error