CQI-15: What Is a Welding Quality System?
The welding process is a special process (operation). After a part is welded, the intrinsic quality characteristics of its welded joint—such as penetration depth and mechanical properties—cannot be fully detected without damage. Whether the quality is good or bad can only be discovered by the customer during use. Clearly, the welding process carries higher risk than ordinary processes! This is first reflected in the undetectability of its failure modes!
Since this cannot be known through post-weld inspection, how can the quality of welded products be ensured? The vast majority of people would answer: monitor the factors of the welding process!
That answer is correct, but it contains an obvious "leap"!
Which factors should be monitored? What is the standard range for each factor? What methods and frequencies should be used for monitoring? Where do these requirements come from? And there are quite a lot of these influencing factors! For example, for a mechanical performance indicator in arc welding, the influencing factors can number more than a dozen—current, voltage, welding speed, gas flow rate, and so on—and there are interactions among them, some of which are difficult to control (such as fit-up gap and arc length)!
Therefore, before monitoring the process, we need to first determine the characteristic items and standards to be monitored, as well as the control methods and frequencies, and the workflow when out-of-control conditions and problems occur. This work is called process planning, and it is what we must do first; only then can control (monitoring) be implemented in formal production.
For the welding process, the quality assurance model shown in Figure 1 exists:
The above is the planning at the welding process (level). In the automotive industry, ideal process planning includes the steps shown in Figure 2:
Figure 2 shows welding process planning based on design requirements, but the factors that determine welding quality have a much broader source!
Consider this: if there are fatal problems in the design—manufacturability or weldability issues—for example, the designed structural space is too limited to allow welding, materials with very poor weldability and low plasticity are used, or the structure has densely intersecting welds, these are very difficult to satisfy from welding process measures alone!
Therefore, we should first review the manufacturability of the design, i.e., DFM, where the M should include welding. This requires clearly including a DFM step in the design and development process, and defining welding-related review points within the M.
If the intention is to use materials and structures for which no mature welding process exists anywhere in the industry, or if the evaluation of product profit and price does not take into account that the materials used will also require post-weld heat treatment during welding, then no matter what is done later, it will be difficult to ensure the expected quality level and profit level!
Therefore, the project feasibility assessment should include welding-related review points.
The above two examples show that welding quality should be considered at the entire project (level), including project planning (before project initiation), product design (manufacturability DFM), and welding process planning.
A critical question is: from project feasibility study and design manufacturability study to welding process planning, who should do this? Who will execute and be responsible for the various planned requirements in the future? For example: training and qualification management of welding personnel, handling of anomalies during monitoring, welding problem solving, rework/repair, etc.
Of course, it should be people proficient in welding professional knowledge/skills! Not merely people proficient in these planning tools (such as PFMEA)!
We define the responsibility for planning, as well as the responsibility for process control and welding problem solving after formal production, in documented form. This work is the planning of management responsibility (level)!
In summary, the planning results at the process level, the project level, and the management responsibility level constitute a quality system. For the welding process, it is called a welding quality system. These three levels of planning all have clear requirements in the CQI-15 standard.
For processes where quality is difficult to ensure through post-event inspection, quality must be ensured by a quality system!
Many people focus on visible, tangible things—such as equipment, materials, and products—while belittling abstract things such as systems and planning! What is more, for the setting of welding parameters, they rely entirely on the welding equipment supplier for commissioning; when the product changes in the future, they neither adjust them nor know how to adjust them!
Ultimately, this is a matter of mindset!