2. Materials and Methods
The analyzed CO
2 laser micro-perforation process technology is presented in
Figure 1.
Material preparation: The materials used for airbags include robust technical textiles such as nylon or polyester, which are treated for high tear and wear resistance. The airbag material must be securely fixed on a work platform to prevent movement during perforation, ensuring precision perforations.
Laser configuration: The CO2 laser used for the micro-perforation of airbag materials operates at a wavelength of 10.6 μm. This wavelength is effective for absorption by technical textile materials. The laser power varies depending on the thickness of the material and the perforation specifications, with typical powers ranging from a few watts to hundreds of watts.
Laser beam focusing: The optical system focuses the laser beam using lenses or mirrors to concentrate the beam into a small point. The size of the focused point determines the diameter of the micro-perforation, and the precise adjustment of the focus is essential to ensure high-quality perforations in airbag materials.
Control and movement: A computer controls the movement of the laser and the perforation pattern, allowing the precise programming of the size, shape and distribution of the perforations. The movement system, which may include stepper motors or servomotors, ensures the precise movement of the laser or the platform holding the material, essential in achieving uniform perforations in the complex airbag materials.
Micro-perforation process: The laser beam is emitted and absorbed by the material, causing the rapid evaporation of a small portion of the material and creating a perforation. In airbag materials, the perforations must be precise to ensure the proper and safe deployment of the airbag during an impact. Lasers can operate continuously or in pulses, with short, high-intensity pulses often preferred to minimize the heat-affected zone (HAZ) and increase the perforation precision.
Cooling and inspection: After perforation, the airbag material may need time to cool, especially if the process generates significant heat. Quality inspection is essential, with the perforated material being checked to ensure the size and uniformity of the perforations. Optical instruments or high-resolution cameras are often used for this inspection, thus guaranteeing compliance with the strict standards of the automotive industry.
Important parameters in the micro-perforation process for airbags: The laser power is crucial to ensure precise and uniform perforations in the technical textile materials of airbags. The power must be sufficient to vaporize the material but not so high as to degrade the edges of the perforation or cause excessive material damage.
The pulse duration affects the precision of the perforations. Short pulses produce precise perforations and minimize the heat-affected zone (HAZ), essential to maintaining the structural integrity of the airbag material.
The movement speed of the laser affects the size and shape of the perforations. High speeds can produce smaller, shallower perforations, while slower speeds allow deeper penetration and larger perforations.
Beam focusing determines the size of the focused point, and precise focusing produces smaller, more precise perforations. The stability of the focus is crucial to ensuring uniform perforations across the entire airbag material.
The material type influences the absorption of the laser. The technical textile materials used in airbags have specific absorption rates for the CO2 laser wavelength, and materials with high absorption require less power for perforation. The thermal properties of the material, such as the thermal conductivity and heat capacity, influence the heat dispersion and the size of the HAZ. The following materials and technology were utilized for the laser micro-perforation process.
Synthetic leather: The synthetic leather parts used in this study were selected to represent common materials utilized in the automotive component manufacturing industry for airbag production (
Figure 2). The sample size was 50 parts for each analyzed parameter: the laser power and material thickness. For the factorial analysis, 950 samples were considered. The material used consisted of synthetic leather produced from polyvinyl chloride (PVC) with a nominal thickness of 1.2 mm. This was laminated with a spacer fabric with a nominal thickness of 2.99 mm, with a specified tolerance of ±0.3 mm.
Laser process: The micro-perforation process was conducted using a high-precision laser system, enabling precise control of the perforation parameters, such as the power and operating speed (
Figure 3).
The main components of the machine setup for laser micro-perforation include a CO2 laser, mirrors, a laser beam and a gas nozzle. The most important parameters of the laser micro-perforation process are the focus, laser power (P1, P2), impulses, robot speed (ms) and tolerance of material deviation.
The laser utilized in the conducted experiments operated in pulsed mode, exhibiting a pulse duration of 200 femtoseconds (fs) and a repetition frequency of 2 kilohertz (KHz). This configuration facilitated precise control over the laser’s output, providing high-intensity pulses conducive to experimental investigations.
The analysis stages consisted of testing based on the following.
Material characterization: Preliminary tests were conducted to characterize the material properties, including the thickness, texture and temperature resistance, before commencing the micro-perforation process.
Laser parameter setting: Critical parameters of the laser process, including the power, frequency and beam traversal speed, were optimized to ensure efficient and uniform material perforation.
Real-time monitoring and control: During the micro-perforation process, monitoring and control systems were implemented to detect and rectify any deviations in the operating parameters, thereby maintaining the quality and consistency of the perforations.
2.1. Methodology
The investigative approach adopted herein involved a meticulously planned and executed series of experiments, orchestrated with precision to closely examine the intricacies of airbag cutout laser processing. The methodology was designed to simulate real-world production scenarios, ensuring that the findings were applicable and relevant to industrial practices. Airbag cutouts, a critical component in automotive safety systems, underwent laser processing precisely 24 h after adhesive application, mimicking the timeline encountered in actual manufacturing settings. However, the key aspect of this investigation lies in the identification of a significant challenge: the inadvertent use of left-hand drive (LHD) parameters for right-hand drive (RHD) components during laser processing. This systemic inconsistency has far-reaching implications, potentially compromising the quality and reliability of airbag cutouts, which are vital for passenger safety. The manifestation of nonconforming (NOK) outcomes during subsequent pull testing procedures underscored the urgency of addressing this issue, prompting a comprehensive examination of the underlying causal factors.
2.2. Laser Processing Investigation
The airbag cutout laser processing investigation detailed in this report represents a meticulous endeavor aimed at comprehensively understanding and rectifying the discrepancies encountered during the manufacturing process. With automotive safety as a paramount concern, the study meticulously delves into the nuanced intricacies surrounding the application of LHD and RHD parameters in laser processing techniques. The optimization of production methodologies within the automotive safety industry is not merely a matter of efficiency but a critical aspect in ensuring passenger safety and regulatory compliance. This investigation, therefore, serves as a critical work in the quest for excellence in automotive safety standards. Through rigorous experimentation and analysis, the study aims not only to identify areas of improvement but also to pave the way for innovative solutions that elevate the standards of airbag cutout manufacturing processes.
2.3. Experimental Design and Setup
The experimental design was meticulously crafted to ensure robustness and reliability in data collection. Airbag cutouts, sourced from diverse production batches, were carefully selected to capture the variability inherent in real-world manufacturing processes. Prior to laser processing, the cutouts underwent stringent quality control checks to ensure uniformity and consistency across samples. Adhesive application was carried out using state-of-the-art equipment, adhering to industry best practices to minimize variability. The laser processing parameters, including the power, intensity and speed, were systematically varied to evaluate their impacts on the processing outcomes. Additionally, environmental conditions such as the temperature and humidity were closely monitored and controlled to minimize external influences on the experimental results.
2.4. Collection and Statistical Analysis
Data collection during the experimental phase was conducted with meticulous attention to detail, employing advanced instrumentation and data logging techniques to capture a comprehensive range of process parameters.
The inferential analyses of the recorded experimental data were performed using the Minitab v17 software (Minitab LLC, State College, PA, USA). Considering a 95% confidence interval (CI) and a significance level of α = 0.05, the normal distribution of the experimental data was qualitatively and quantitatively validated by applying the Anderson–Darling (AD) goodness of fit [
18,
19]. An analysis of means (ANOM) chat [
20] for a normal distribution was computed for different laser power levels (P1 and P2). We used an analysis of means for normal data and a two-way design to identify any significant interactions and main effects. The experiments were designed (DOE) [
21,
22] based on the process’ particularities by choosing the main control factors that affected the micro-perforation characteristics, applying a full factorial design.
3. Statistical Analysis of Experimental Data
3.1. Goodness-of-Fit Test of Experimental Data
The pull test results and material thickness were statistically analyzed with a 95% confidence interval (CI) and significance level of α = 0.05. The homogeneity of the experimental data was tested by assessing the goodness of fit with a probability plot (
Figure 4 and
Figure 5). Additionally, the quantitative assessment was performed with a hypothesis test, such as the Anderson–Darling normality test.
The results of the goodness-of-fit normality test are synthetically presented in
Table 1. A parametric distribution analysis was considered in order to estimate the statistical parameters of the pull test and material thickness (
Table 2).
Visually comparing the probability plots depicted in
Figure 4 and
Figure 5, it can be concluded that the experimental data complied with a normal distribution. The points roughly follow the straight line, all of the points are within the lower and upper confidence boundaries, and the
p-value is over 0.05.
The estimated mean of the pull test data is 209.5 (95% confidence intervals of 155.31 and 263.64), the standard deviation is 112.4 (95% confidence intervals of 84.91 and 166.18), and the median is 210 (95% confidence intervals of 127.28 and 292.72). Using a significance level of α = 0.05, the Anderson–Darling normality test indicates that the pull test data follow a normal distribution.
In the case of the material thickness, the mean is 3.003 (95% confidence intervals of 2.951 and 3.054), the standard deviation is 0.107 (95% confidence intervals of 0.081 and 0.159), and the median is 2.99 (95% confidence intervals of 2.958 and 3.074). Moreover, it can be underlined that the estimated value of the Anderson–Darling statistic is 0.192.
The overall inferential analysis concludes that the pull test results and material thickness are from a normally distributed population.
3.2. Analysis of the Main Factors in the Laser Micro-Perforation Process
The assessment of the main influencing factors on the micro-perforation laser process is based on the analysis of means chart (ANOM) for a normal distribution. An experiment was performed to assess the effects of the most important factors: the level I laser power (P1), the level II laser power (P2), the pull test results and the material thicknesses. The ANOM results are illustrated in
Figure 6 and
Figure 7.
In the case of first level of the laser power (P1), the pull test results indicate that the lower delimitation limit is 172.4 N and the upper limit is 246.7 N, with a mean of 209.5 N (
Figure 6) and standard deviation of 74.2 N. Tested parts that had recorded values below the lower limit value were declared scrap.
The normal analysis of means chart for the P2 laser power (
Figure 7) showed a lower delimitation limit of 161 N, an upper delimitation limit of 257.9 N and a mean of 209.5 N (
Figure 3) with a standard deviation of 96.9 N.
The computed delimitation limits allow us to take appropriate measures to optimize the laser process. The indicated direction is to optimize the two laser powers, P1 and P2, to ensure the process’ stability.
The comparative analysis of the two laser powers emphasizes that the optimal level should be set around 0.25 W to ensure a material rupture force during testing. Additionally, quality limits can be easily determined from the comparative analysis: power of 0.20 W—beyond tolerance threshold; power of 0.21–0.24 W—within accepted limits; power > 0.25 W—higher precision, efficiency and stability (covers and removes material defects).
In order to highlight the interaction between the pull test results, laser power and material thickness and its effect on the micro-perforation process, a factorial analysis was designed (
Figure 8 and
Figure 9). The magnitude and the importance of the effects were determined by applying the Pareto chart of the effects (
Figure 10).
The interaction plot indicates that the material with the highest thickness depends on the P1 laser power, while the material with the lowest thickness depends on the P2 laser power. The difference between the P1 and P2 powers is given by the number of pulses. Specifically, a laser power fraction of 5–25% from the nominal laser power has a negative influence on the results of the pull test, while, for a laser power greater than 25%, the tested parts in the pull test are compliant.
In conjunction with an analysis of variance and design of experiments, we examined the differences among the level means for the three analyzed factors. The P1 and P2 laser powers appear to affect the pull test results compared to an overall mean of 209.5 N. A main effect is present because the different levels of the studied laser powers factors affect the response differently. Additionally, the graph for the material thickness shows that there is no main effect present.
The absolute effect values compared to the reference line show that the laser powers are statistically significant (
Figure 10). Moreover, the standardized effects of the micro-perforation factors show a significant effect of the P2 (90%) and P1 (77%) laser powers.
4. Results and Discussion
4.1. Results and Summary
Nonconforming results (
Figure 11): The statistical analyses revealed deviations from the established acceptance criteria during pull testing, indicative of underlying inconsistencies within the manufacturing process.
Post-pull-test values: Subsequent evaluations of the post-pull test revealed values within the predefined intervention thresholds, underscoring the need for further investigation to address the root causes.
Further action: This section delineates the ensuing steps, including additional testing protocols and proposed remedial measures aimed at rectifying the identified discrepancies and optimizing the manufacturing practices (
Figure 12).
4.2. Proposed Measures and Next Steps
Laser processing with adhesive application on Bluemelt machine: Noteworthy consistency was observed within the specified tolerance limits, affirming the efficacy of this approach and providing valuable insights for future process refinements.
Cross-testing RHD parts on LHD nest: The validation experiments yielded pull test results consistent with the acceptance criteria, highlighting the potential interchangeability of the manufacturing parameters and informing standardized practices.
New batch of material preparation: The rigorous assessment of the material batch’s impact on the pull test tolerances can inform future manufacturing practices and enhance the process’ predictability and repeatability.
Adhesive application and laser: The granular examination of the variances after adhesive application and laser processing can identify process optimization opportunities and minimize variability.
4.3. Detailed Analysis
Pull test influences: The in-depth analysis revealed the significant influences of the adhesive application techniques and spacer dimensions, necessitating meticulous control and calibration of the process parameters. The laser power needs to be set and optimized for both the P1 and P2 powers to ensure the coverage of defects from the previous process.
Parameter adjustments: The dynamic nature of the spacer thickness underscored the imperative for frequent iterations and standardization efforts to ensure consistent laser processing outcomes.
Continued research: The ongoing exploration of alternative laser processing scenarios, including variations in adhesive application techniques, is necessary to comprehensively delineate the process dynamics and inform iterative enhancements.
Glue application influence: The differential outcomes observed based on the adhesive application methodologies underscored the need for systematic evaluation and refinement to optimize the process parameters and ensure uniformity across adhesive types.
4.4. Proposed Enhancements
Spacer dimension standardization: The implementation of stringent protocols to standardize the spacer dimensions, minimizing the need for frequent parameter adjustments and enhancing the process’ stability and predictability.
Laser line optimization: The precision calibration of the laser line positioning to ensure seamless alignment with the spacer fabric, facilitating consistent pull test results and mitigating variability.
Refinement of glue application: The systematic evaluation of the adhesive application methodologies to ascertain the optimal parameters conducive to uniform outcomes across different adhesive types and enhance the process’ repeatability.
Contingency planning: The development of robust contingency plans to preemptively address potential machine-related issues, safeguarding the production continuity and efficiency.
Noise parameter adjustment: The fine-tuning of the noise parameters to optimize the process’ stability and minimize adverse effects on the pull test outcomes, enhancing the overall process’ reliability and repeatability.
4.5. Discussion
The investigation results indicate several significant findings and implications in the context of previous studies and working hypotheses. The detailed analysis of the airbag cutout laser process revealed substantial discrepancies in the application of LHD and RHD parameters, aligning with the initial working hypotheses. Additionally, other influences on the process, such as the adhesive application techniques and spacer dimensions, were identified.
Interpreting these results in the context of previous studies suggests that a more rigorous and systematic approach is needed to ensure consistency and reliability in the airbag cutout laser process. Compared to previous research, which has indicated similar challenges in laser processing for automotive applications, this investigation adds a new perspective by identifying and documenting detailed issues related to the incorrect use of the LHD and RHD parameters.
The implications of these findings are extensive and could significantly impact the production process across the automotive industry. Optimizing the airbag cutout laser process could lead to significant improvements in the quality and reliability of automotive safety components, thereby reducing the risk of failure and enhancing passenger safety.
Regarding future research directions, this investigation opens the door to several further studies. These include more detailed research into the influence of various process parameters on the final outcomes, exploring alternative adhesive application methods and assessing the impact of introducing new or improved technologies into airbag cutout laser processing.
These future research directions can contribute to the ongoing development of knowledge and practices in laser processing in the automotive industry and provide innovative solutions to improve the production processes and product quality.
Moreover, it is essential to consider the broader implications of autonomous vehicles beyond the manufacturing process. The widespread adoption of autonomous driving technologies has the potential to revolutionize urban mobility, reduce traffic congestion and minimize environmental impacts. By leveraging AI-driven autonomous vehicles, cities can reimagine transportation systems, optimize infrastructure utilization and enhance the overall quality of life for residents.
Furthermore, the ethical and societal implications of autonomous vehicles must be carefully examined. Issues such as liability, privacy and job displacement require thoughtful consideration and proactive measures to mitigate the potential risks and ensure equitable outcomes. Collaborative efforts between policymakers, industry stakeholders and the research community are essential to addressing these challenges and fostering public trust in autonomous driving technologies.