The vast majority of laser welding "process development" work has obvious shortcomings, often stopping only after the sample appearance is qualified. However, true process certification has strict requirements and must rely on data to prove that, on mass-produced equipment, operated by frontline operators, the process can continuously and stably produce qualified workpieces in the face of full range fluctuations in incoming materials. The completion nodes of these two are very different, and once confused, it will become the most costly mistake in laser process engineering. For example, in some practical production, mistakenly believing that the appearance of the sample is qualified is equivalent to passing the process certification, resulting in extremely low product yield during subsequent mass production, causing huge economic losses.

We must clarify the difference between process development and process certification. Process development focuses on the initial production and appearance adjustment of samples, while process certification places more emphasis on stability and reliability in actual mass production environments. Only through strict process certification can the quality of products be ensured in large-scale production. If this important link is ignored, companies may face problems such as unstable product quality and increased customer complaints, which can affect their reputation and market competitiveness. Therefore, it is crucial to have a correct understanding and complete the certification of laser welding processes.

Before debugging the laser, the primary issue is not to consider what process parameters should be selected, but to clarify the criteria for determining qualified welds, testing methods, and the thresholds for qualified/unqualified. Before the formal trial welding, multiple indicators need to be clearly defined in writing. For example, the depth of fusion has minimum and maximum requirements, with the lower limit being to ensure welding strength and the upper limit being to prevent weld penetration; The width tolerance of the weld bead is usually ± X% of the nominal size, which is determined by the joint structure. In addition, there are also indicators such as pore limit, number of splashing particles, mechanical properties, resistance value, and pollutant control that need to be clarified. The determination of these indicators plays a crucial role in subsequent process certification, as they are important criteria for measuring the qualification of welds.

The determination of acceptance criteria is a rigorous process, which is jointly determined by design engineers and customer specification documents, rather than being limited by the capabilities of laser equipment. It is strictly prohibited to relax product specification requirements in reverse based on the level of craftsmanship. Because if the standards are relaxed arbitrarily, it may lead to problems in the actual use of the product. For example, in the scenario of new energy vehicle battery modules, if the standards for pollutant control are relaxed, it may affect the performance and safety of the battery. Therefore, it is necessary to strictly follow scientific and reasonable standards to clarify the acceptance conditions and ensure the accuracy and reliability of process certification.

In laser welding process certification, the comprehensive characterization of incoming material characteristics is often overlooked by most certification projects, but this is actually one of the key factors for subsequent mass production yield. We need to test actual mass-produced materials, not ideal standard samples. The surface condition of incoming materials, assembly fit gaps, and batch differences can all have a significant impact on the welding process. The oxide layer, coating, oil impurities, etc. in the surface state can change the material's absorption rate of 1070nm laser, so the actual incoming material state in the workshop must be taken as the standard. The assembly fitting gap also needs to be measured for the gap distribution under the mass production fixture. If there is a difference between the drawing requirements and the actual production, certification must be completed according to the limit gap. In terms of batch differences, if the material grade, thickness tolerance, and surface treatment process change with the supplier's batch, the fluctuation extreme value needs to be taken for certification in order to verify the stability of the mass production process.

Parameter screening experiments (DOE experimental design) are also an important step. We need to sort out all controllable process parameters, such as laser power, welding speed, focal position, beam oscillation amplitude and frequency (if any), protective gas flow rate, etc. Then, a screening type orthogonal experiment is conducted, which can efficiently traverse parameter intervals without the need for full combination testing. During the experiment, it is necessary to collect and test data against the various indicators set in the first step. The output of the experiment is to distinguish parameters and trends with significant impact, eliminate irrelevant parameters, and focus on optimizing key variables. For example, in the copper welding scene, laser power, travel speed, and focal position are the core influencing factors, while the amplitude of beam oscillation has a prominent impact on the width of the weld bead. By selecting reasonable parameters, the efficiency and accuracy of process certification can be improved.

After determining the key parameters, it is very important to survey the complete process window. The process window refers to the parameter range that simultaneously meets all the acceptance criteria of the first step. If the budget is sufficient, response surface methodology (RSM) can be used to map the process window; The minimum requirement is to test the boundary samples of the testing window and confirm that the failure is smooth and controllable when the parameters reach the critical value, rather than sudden serious defects within the standard process interval. We need to document the standard process parameters (window center interval) and critical boundary parameters (acceptable limit values) in writing. The width of the process window is an important achievement of certification work, and the allowable range of key parameter fluctuations less than ± 5% represents a narrow window, which requires extremely high equipment control accuracy and incoming material consistency; A spacious window can accommodate various fluctuations in mass production.

Robustness validation is to ensure the stability of the process under fluctuations in mass production. We set the parameters at the center of the process window and manually reproduce all real fluctuating operating conditions during mass production for testing. These operating conditions include material limit conditions, such as the thinnest/thickest specification of the plate, and the tempering state of both soft and hard materials; Maximum clearance condition during assembly; Thermal accumulation test, comparing the situation of the first piece after starting the shift with 100 pieces of continuous welding, to determine whether parameter adjustment is needed; And multi machine compatibility testing to determine whether standard parameters can be directly reused. If the robustness test fails, it indicates that the process window is too narrow, and it is necessary to return to the fourth step to widen the window or tighten the incoming material admission standards to ensure the reliability of the process in actual production.

In laser welding process certification, non-destructive testing verification is an essential step. We need to prepare sufficient samples according to statistical requirements to verify the mass production yield with the target defect rate and confidence level. According to the Poisson distribution, for example, when the target defect rate is 0.1% and the confidence level is 95%, approximately 3000 defect free samples are required; When the target defect rate is 1% and the confidence level is 95%, approximately 300 defect free samples are required. Corresponding samples and testing budget need to be reserved before certification is initiated. Destructive detection is the process of cutting weld sections at fixed intervals and measuring penetration depth, weld bead width, porosity, etc. using a calibrated image analyzer; Non destructive testing uses X-ray to detect internal pores according to specifications, and visually inspects the appearance against standards. Copper bars and pole products also require additional resistance testing. All samples must be bound with a unique number, associated with corresponding laser parameters and incoming batch, and traceable throughout the process. A complete traceability record is the core basis for the certification results to have contractual validity.

The handover and control plan for mass production is the final step of process certification. We need to prepare a complete process control document, clarify the parameters that need to be monitored for mass production, the frequency of testing, the parameter threshold for triggering shutdown and re inspection, and perform calibration items before starting each shift. At the same time, it is necessary to establish process capability indicators, such as automotive grade welding processes, with a minimum requirement of Cpk ≥ 1.33 for penetration depth and weld bead width. The data is taken from the sixth step validation sample, rather than a small number of samples under ideal conditions. Training operators is also important, as it involves training them on the underlying logic of the process, rather than just memorizing parameter values. In addition, it is necessary to clarify the triggering conditions for re certification. In the event of changes such as material supplier replacement, equipment overhaul, tooling wear, and process parameter deviation, which level of certification needs to be re conducted to ensure the stability of the mass production process and product quality.

In the industry, the most common simplification operation is to skip the first three steps, that is, to omit the development of acceptance standards, characterization of incoming material characteristics, and parameter DOE screening, and directly repeat the trial welding until the appearance is qualified, and then determine that the process has passed certification. However, this approach carries significant risks. Due to the unknown process window, various fluctuations during mass production can easily exceed the qualified range, resulting in lower than expected yield. Moreover, without basic reference data, once a fault occurs, it is impossible to locate the cause of the fault. For example, on some production lines, due to the use of this shortcut, quality problems frequently occur during mass production, but the root cause of the problem cannot be found, wasting a lot of time and resources.

Although a complete copper welding seven step certification process takes 4-8 weeks, it can save months of on-site production debugging time and eliminate the problem of end product failure caused by incomplete process certification. By summarizing the core of the seven step process, we can clearly see the core outputs and common errors of each step. If you are setting up a laser welding process for the first time, or if your existing "certified process" continues to have poor production, you can apply this process to troubleshoot each step step step by step. The step where the deviation occurs is the root cause of the problem. If you need to apply it to specific scenarios such as copper bars, flat wire motor card terminals, structural aluminum materials, ultra-thin stainless steel, etc., you can leave a message in the comment section or consult directly to better complete the certification work of laser welding technology.