- Written by: Fu Shufeng, Zhu Hongping, Nie XiaoJun, Liu Jiemin
Guangqi Honda Automotive Co., Ltd.
Summary: To ensure the stability and quality of the automotive parts coating supply chain, from the import of coating materials from suppliers to the stable supply for mass production, research was conducted on process quality control, and corresponding measures were taken to control the quality of automotive parts coating, which significantly increased the production efficiency of coating suppliers and effectively provided stable supply and reliable quality of the parts for vehicle assembly.
Keywords: - Automotive parts- Electroplating coating- Coating line certification- Process control
Research on the Quality Control Process of Automobile Parts Coating
FU Shufeng, ZHU Hongping, NIE Xiaojun, LIU Jiemin
GAC Honda Automobile Co., Ltd., Guangzhou, Guangdong, 510700, China
Abstract: To ensure the stability and quality of the automotive coating parts supply chain, the entire process quality control from the introduction of coating suppliers to mass production and stable supply was studied, and corresponding measures were taken to control the automotive coating quality. This significantly improves the production efficiency of coating suppliers and effectively provides stable supply and quality reliability for loading parts.
Keywords: automotive parts; electrocoating; coating line approval; process control
0. Introduction
Coating is a major measure for enhancing the corrosion resistance and extending the service life of automotive products. Currently, the coating of automotive parts mainly includes electrodeposition coating and spraying. Electrodeposition coating, which has advantages in terms of environmental protection, safety, cost, and corrosion resistance, accounts for over 95% of the market. Electrodeposition coating involves immersing the coated object in a liquid containing charged coating particles, where the coated object adsorbs and deposits coating particles through a direct current between the coated object and the cathode. There are two types of electrodeposition coating: anodic and cathodic. The most widely used type is cathodic.[1]The quality of electrophoretic coating depends heavily on the pretreatment process. In the automotive industry, phosphate treatment is currently the most widely used and technologically mature pretreatment method. In recent years, relatively environmentally friendly methods such as silane treatment and zircon treatment have also been used by a few complete vehicle manufacturers or component suppliers. However, due to factors such as corrosion resistance, cost, efficiency, and technological maturity, their application range is far less than phosphate treatment. Phosphate film generated by phosphate treatment has porosity, allowing coatings to penetrate these voids, creating a "bond effect", significantly improving the adhesion of the coating. Furthermore, the phosphate film transforms the metal surface from a good conductor to a poor conductor, thereby inhibiting the formation of microbatteries on the metal surface, effectively hindering the corrosion of the coating, and can significantly improve the corrosion resistance of the coating. Additionally, phosphate treatment equipment is simple to operate, has low cost, and high production efficiency.[1]"Therefore, this study focuses on the quality control process for coating applications that have undergone phosphate treatment and cathodic electrodeposition. The "coating" referred to in the following descriptions refers to coatings that have undergone phosphate treatment and cathodic electrodeposition. Due to differences in coating supplier's process technology capabilities and quality assurance capabilities, even though coating and coating process technology development has been very mature, different coating suppliers have varying process technology capabilities, quality control experience, and even some coating suppliers rely entirely on coating manufacturers for technical guidance. Furthermore, the scope is broad. When there are quality issues with the coating of components, it is typically a batch-level problem. once installed in the vehicle, the impact is widespread, making traceability and replacement work difficult and costly. Finally, the impact is significant. If the coating quality is substandard, rust can occur during the vehicle's lifespan. In addition, the accelerated corrosion caused by environmental factors will further accelerate the rust, not only affecting the vehicle's appearance but also potentially impacting the vehicle's functionality and, in severe cases, leading to critical components failing due to corrosion, posing a safety hazard. Therefore, as a vehicle manufacturer, it is essential to implement comprehensive quality control measures for component coating."
1 Automotive Parts Coating Quality Control System
Since its establishment, the company has placed a high priority on quality management, strictly adhering to the "three no" principle: no acceptance, no production, and no leakage. It also consistently upholds the philosophy that "good quality is not inspected, but manufactured." based on the unique characteristics of the coating production process, the company has developed a strategy for controlling the quality of automotive parts coating, and has formed a team to conduct research and practice on this strategy. This has resulted in the establishment of a quality control system for automotive parts coating, which covers all aspects from the acceptance and commissioning of new coating lines to the ongoing supervision and management of quality stability after mass production, as well as the comprehensive enhancement of the quality assurance capabilities of supplied products.
1.1 Acceptance of New Coating Line
1.1.1 Establishing the Quality Control Process for Coating Application
To ensure a standardized and efficient workflow, and to guarantee effective results, establishing a rational workflow is a primary task. The coating quality control process is illustrated in Figure 1.
1.1.2 Requirements for Accredited Coating Line A00
Typically, the electroplating coating process involves approximately 19 steps, including surface inspection of metal parts and inspection before shipment, with several critical steps. The electroplating coating process flow is shown in Figure 2, with the key steps highlighted within the dashed box.
The complex characteristics of coating production processes determine the high difficulty in obtaining coating line recognition. Firstly, the recognition of coating lines requires specialized expertise, demanding that personnel have a good understanding of coatings, coating principles, quality management systems, and environmental, occupational, health, and safety management systems. They must also be familiar with controlling production process parameters, the impact of various parameters on coating performance, and the detection and testing of phosphate crystals, as well as the ability to assess the feasibility of various special situations. Secondly, the scope is broad, requiring the verification and confirmation of more than ten production processes across pharmaceutical plants, laboratories, and production sites. Therefore, to standardize work and ensure the transfer of experience, establishing the "A00" requirements for coating line recognition is crucial. To achieve this, through years of study and research, and leveraging the experience gained from promoting the recognition of domestic components, quality management, supplier management, and the onboarding of new suppliers, the key processes and critical process parameters were identified, resulting in the complete "A00" requirements for coating line recognition, covering the procurement and storage of pharmaceuticals/coatings, coating production, quality inspection of liquids/coatings, and handling of anomalies, encompassing nearly 200 recognition points (due to company confidentiality requirements, the A00 requirements cannot be displayed here).
1.1.3 On-site validation and verification of coating lines
After the initial preparation work is complete, a thorough on-site validation and verification process is conducted for the supplier's coating line. This involves a detailed assessment across five factors: personnel, equipment, materials, methods, and environment, specifically focusing on the procurement/storage of pharmaceuticals/coatings, coating production, quality control of pharmaceutical/coating products, and handling of anomalies. Key areas of focus include: ① Verification of the origin and frequency of pharmaceutical/coating procurement, ensuring that storage and retrieval conditions comply with the characteristics of the products and environmental health requirements, and adherence to the "first-in, first-out" principle during use, along with proper record-keeping; ② Verification of the reasonableness and adherence to standard operating procedures (SOPs) for the production process, including the implementation of daily production controls, such as regular checks for blockage in spray systems, monitoring of liquid parameters, and adherence to the rules and records for adding agents, as well as effective monitoring of furnace temperature; ③ Verification of the suitability of detection methods and conditions for liquid samples, ensuring the reliability of detection results, and the reasonableness of sampling frequency, sample selection, and the scope of testing; ④ Procedures for handling anomalies discovered during the production process or quality control, ensuring the reasonableness of the handling process and traceability, etc.
The quality and performance of the parts are the most direct indicators of whether the production process parameters are set appropriately. Therefore, in addition to on-site verification, relevant performance tests are conducted on parts produced under standard conditions and parts produced under extreme conditions, including tests for the quality of phosphate coatings and the appearance, film thickness, hardness, adhesion, corrosion resistance, and pollution resistance of the finished products after coating. To ensure the representativeness of the test results, samples are typically selected using a grid sampling method, as shown in Figure 3.
1.2 Supervision and management after coating line approval
Due to the complexity of painting processes, numerous factors affecting coating quality, and significant influence from human factors, coupled with varying hardware conditions and personnel skill levels among suppliers, ensuring the stability of component painting quality presents a considerable challenge. Therefore, vehicle manufacturers need to establish a reasonable monitoring and management system and effectively implement quality process supervision.
1.2.1 Establishment of Supervision and Management Mechanism
By integrating the production technology, quality assurance capabilities, and past performance records of coating suppliers, suppliers will be categorized to form a dynamic management pyramid model. Corresponding management measures will be implemented for each category, establishing a standardized management mechanism, as illustrated in Figure 4.
1.2.2 Implementation of Supervision and Management
Following the implementation of a supervisory and management mechanism, appropriate supervisory and management measures are taken for approved coating suppliers, depending on the category and requirements of the products supplied by the vehicle manufacturers. Periodic on-site quality assurance surveys (QAV) are the preferred method for supervisory and management, as they are effective, cost-efficient, and allow for continuous monitoring of supplier production management, timely identification of issues, and prompt corrective actions. Additionally, these surveys can be used to enhance the skills and knowledge of management personnel and to provide targeted training and guidance to suppliers, improving their technical skills and quality assurance capabilities. This ensures the reliable quality of supplied products.When conducting new product coating trials on newly imported coating lines, it is essential to perform on-site verification to confirm the coating process and testing procedures throughout the entire production process. This includes conducting sampling tests to ensure that suppliers strictly control the production and testing processes, thereby enhancing the reliability of the supplied products.
2. Enhancing the quality assurance capabilities and quality management awareness of coating suppliers.
based on on-site surveys and verification of past supply quality records from multiple suppliers, it has been confirmed that suppliers frequently experience poor quality or defective products, fail on-site quality control tests, and engage in falsifying inspection reports or test results. This is ultimately due to limited supplier capabilities, inadequate implementation of standardized management, and high production costs. While daily supervision of the entire assembly plant can effectively reduce the outflow of defective products, this is a superficial solution that is also costly. To fundamentally solve the stability and continuous supply of automotive component coating quality, it is essential to specifically train and provide technical guidance to coating suppliers, comprehensively enhance their technical capabilities, quality assurance capabilities, and quality management awareness, and help them establish a comprehensive coating quality assurance system. This will enable them to continuously improve their self-sufficiency and transition from passive to proactive quality assurance, ultimately making self-sufficiency the norm.
2.1 Enhancing Technical Competence and Quality Awareness
For coating production processes that are complex, involve multiple steps, require high levels of expertise, and have relatively low levels of automation, the quality of the coating depends not only on the equipment but also significantly on the technical skills, quality management capabilities, and overall competence of the personnel involved. Therefore, it is essential to first enhance the technical skills and quality awareness of coating suppliers' personnel.[2]"In addition to internal training provided by suppliers, it is recommended that experienced quality and technical personnel from vehicle manufacturers or paint manufacturers periodically conduct specialized training for coating suppliers on coating, painting processes, relevant coating/painting testing/experimentation, and quality management. This training will enable coating supplier personnel to understand the impact of various concentrations, pH levels, temperatures, durations, and voltage values on coating quality, and to gradually improve their technical and quality management skills. For on-site quality personnel, it is essential to possess the ability to handle and assess anomalies, and to establish a KNOWLEDGE database to gradually optimize production processes, improve quality, and reduce costs. Furthermore, it is necessary to enhance the quality awareness of personnel in all positions and to ensure that they operate strictly according to established standards. only personnel who have successfully passed the job competency assessment are authorized to perform their duties independently."
2.2 Ensuring the Quality Assurance System for Coating Application
Establish a comprehensive and well-established coating quality assurance system to standardize and regulate coating production, which is the fundamental basis for ensuring the quality of coated parts. Firstly, for coating suppliers with limited experience, provide guidance to validate extreme process parameters to establish a reasonable range for process parameter control. Secondly, based on the relationship between liquid consumption rate and production capacity, calculate and set appropriate sampling frequencies and dosing rules for the liquid. Thirdly, define appropriate part quality inspection items and frequencies, and standardize sampling rules and testing methods, to guide daily representative pre-treatment of phosphate film quality (phosphate film appearance, crystal size, and film quality) and finished product quality (film thickness, hardness, adhesion, corrosion resistance, etc.), enabling a comprehensive understanding of product quality and timely identification of defects, along with appropriate measures. These items should be managed according to standards to form a complete coating quality assurance system. The main standardized documents in the system include: "Process Quality Management Table," "Coating Equipment Daily Inspection Table," "Operating Standards," "Daily Liquid Testing and Additive Specification," "Coating Performance Testing Standard," "Inspection Results," and "Past Defect Prevention Management Table," and continuously improve production processes and testing methods to improve efficiency and reduce costs under the condition of quality assurance. Finally, due to the specific nature of coating production, quality defects typically occur in batches. once defective products enter the assembly plant, the impact is widespread, and tracing the source of defects is a costly and labor-intensive process. Therefore, it is necessary to control the outflow of defective products from the source. The inspection and traceability of supplier products must be standardized to comprehensively improve the coating quality assurance capabilities of suppliers.
3. Conclusion
Practical experience has demonstrated that implementing the above measures to control the quality of automotive component coating effectively improves the production efficiency and pass rate of coating suppliers, effectively controls the outflow of defective products, and significantly reduces the costs associated with corrective actions, outsourcing coating, and outsourcing testing. Furthermore, it reduces the risk of unstable component quality and supply disruptions, ensuring that the entire vehicle enters the market without defects and establishes a positive brand image. Additionally, the technical and testing capabilities of suppliers are effectively enhanced.
In recent years, the electrification and automation of the automotive industry have led to rapid development, and the rapid development and application of artificial intelligence have also disrupted people's understanding of traditional automobiles. Voice control and autonomous driving will gradually free up the hands of drivers and passengers, and many new materials and production technologies have also emerged. However, no matter how new technologies and equipment develop and evolve, it is highly likely that automotive component coating processes will remain an essential and indispensable process in the automotive industry for a long period. As the level of vehicle intelligence increases, the quality requirements for basic parts also increase. Coating components as important structural components not only affect the vehicle's appearance but also its durability. As a vehicle manufacturer, it is essential to lead all suppliers and promote comprehensive safe production and scientific production concepts. It is also important to require quality management personnel, production management personnel, and on-site operating personnel to fully establish a strong quality awareness.[2], strictly adhere to the "three no principles", and continuously improve, constantly enhance production process and testing technology capabilities, in order to comprehensively improve the quality assurance capabilities of suppliers, jointly improve coating quality, and provide safe, reliable and trustworthy products toWide user base.
References:
[1] Wang Haiqing, Li Li, Zhuang Guangshan. Coating and Coating Technology. Beijing: Chemical Industry Press, 2012.
[2]Feng Li. Automotive Parts Coating Management [J]. Electroplating and Coating, 2010, 29(5):68-70.
FENG L. Management of automotive parts coating [J]. Electroplating& finishing, 2010, 29(5):68-70.
This article is reprinted from "Dynamic and Overview" in September 2022.