On Quality Control of Automotive Coating

On Quality Control of Automotive Coating

- Changzhou Anjia Coating Equipment Co.,Ltd

product design

Quality is designed, not manufactured, indicating the importance of the design process for product quality. So to improve the quality of painting, we should study the quality of products from the product design stage. By studying the pass-ability, work-ability, corrosion resistance, and sealing of the white body structure in product design, the coating quality can be greatly improved.

1.1 Passing ability of white body

The body structure is complex, and the body structures of different car models vary greatly. This requires confirmation of the pass-ability of the new car model on existing painting equipment, mainly including the load-bearing capacity of lifting equipment and transportation chains, the handling ability of components, and the installation of painting fixtures on the body.

1.2 Work-ability of White Body

The research on the effectiveness of the interior/exterior panels of the white body mainly includes predicting the areas where paint flow marks or insufficient paint may occur, dividing the areas for automatic and manual spraying, evaluating the spraying and masking performance of black paint, analyzing non adhesive areas, and evaluating the convenience of the glue (wax) gun.

1.3 Corrosion resistance of the vehicle body

The research on the corrosion resistance of car bodies mainly includes confirming the positions and sizes of electrophoretic power holes, pre-treatment electrophoretic drainage holes, exhaust holes, and anti-corrosion wax holes, the methods and discharge times to prevent water accumulation on the bottom plate, and the wax spraying areas and sizes.

1.4 Vehicle body sealing

The research on vehicle body sealing mainly includes the process of spraying (injecting) glue, confirmation of working space (checking interference), analysis of water leakage in areas where glue cannot be injected, and sealing analysis of connection parts, joint parts, and groove parts of vehicle body panels.

2. Selection of Coating Materials

2.1 Recognition of new materials

Before bulk supply, all paint materials must undergo comprehensive approval tests, including raw material indicators, construction performance indicators, film-forming performance indicators, and compatibility with other materials. The recognition projects of phosphating materials mainly include the performance of phosphating films and the matching of phosphating films with electrophoretic primers

Performance. The recognition projects of electrophoretic paint mainly include the performance of the original paint, tank liquid parameters and performance, paint film performance, and compatibility with the phosphating layer and intermediate/topcoat. The development of intermediate/topcoat requires recognition of the performance and paint application performance of the original paint, as well as the appearance, mechanical properties, chemical resistance, corrosion resistance, water resistance, aging resistance, and temperature change resistance of the paint film.

2.2 Batch Supply Acceptance

Conduct supply batch acceptance for all painting materials used in production (pre-treatment chemicals, paint, PVC, wax, etc.), strictly follow material quality standards and production process tests, focus on checking raw material indicators and construction performance indicators, and ensure that unqualified materials are not put into production.

2.3 Monitoring during material use

To better control the quality of painting, it is not only necessary to have qualified painting materials, but also to effectively monitor the painting materials during use. The production process is mainly monitored through the following methods:

⑴ Key parameter monitoring for pre-treatment and electrophoresis production line: By conducting two laboratory tests on each tank liquid, especially the key processes of phosphating and electrophoresis, twice a shift, the various parameters of the tank liquid are ensured to be stable and within the range required by the process, thereby ensuring that the vehicle body is within the range required by the pre-treatment and electrophoresis processes

The performance of the paint film meets the required indicators.

⑵ On site tank liquid collection and laboratory swimming plate test: Take tank liquid from the site once a week for testing in the laboratory to ensure that the various properties of the tank liquid meet the standard requirements.

⑶ Production line hanging samples (pre-treatment, electrophoresis, PVC), laboratory testing performance: Through hanging plate tests on the production line, various properties of phosphating film and electrophoretic paint film are tested to ensure that each layer of paint film meets the performance requirements. Regularly go to the workshop to collect painted parts and conduct performance tests in the laboratory to monitor the quality level of the vehicle's painting.

(4) Paint film performance testing: Randomly collect a certain amount of car bodies every day, with at least one electrophoretic car body, one intermediate coated car body, and one topcoat each, to test the appearance, drying, film thickness, adhesion, and other paint film properties of the paint film. And measure the NAP value of the appearance level of the paint and prepare a weekly paint quality report for analysis. Collect the main quality issues in the production process through the above experiments, analyze and rectify them in a timely manner, promote the resolution of coating quality problems, and thereby improve coating quality.

3. Quality control of painting production process

In order to better control the production quality of the painting workshop, a series of quality control indicators have been developed as KPI indicators for monitoring quality, such as paint body straightness rate, PVC straightness rate, paint AUDIT, NAP value, primer polishing point, intermediate coating polishing point, topcoat polishing point, paint deduction point in vehicle AUDIT, etc. These indicators have been quantified; To ensure the smooth implementation of the above quality indicators, the painting workshop has established a good indicator guarantee system from several aspects such as personnel, machinery, materials, methods, environment, and process monitoring.

(1) Human aspect: New employees should have quality awareness before entering the factory

Training to develop a certain level of quality awareness before starting work; During the production process, various training programs such as "mentoring apprentices", "substitute class teacher teaching month", and "workshop director teaching week" are carried out to enhance the quality concept of employees and make them pay more attention to the quality in their hands; Conduct training on commonly used methods for solving quality problems, such as "QC activity methods", "8D problem solving methods", and "error prevention technology applications", to enable employees to better grasp the methods of handling quality problems; Through methods such as "going out and inviting in", employees are trained and learned on the five quality manuals, quality system audits, specialized quality tools, and other excellent quality improvement methods of the company.

In terms of equipment: "If you want to do a good job, you must first sharpen your tools." Good equipment is the prerequisite for ensuring good quality. In the production of sedans, there are many equipment for the painting process, and it is necessary to create a "Equipment Operation and Maintenance Operation Guide" for each equipment. Through regular lubrication and maintenance of the equipment, the normal operation of the equipment is ensured, thereby ensuring the quality of the painting.

In terms of materials: Most painting processes require contact with chemicals, such as pre-treatment, electrophoresis, PVC, wax spraying, paint transportation, and post-treatment. Therefore, the amount of chemicals added can directly affect the stability of the tank liquid. Monitoring the amount of various chemicals added is particularly important for controlling the quality of painting. There are many types of chemicals and feeding frequencies used in pre-treatment and electrophoresis, such as degreasers, surface conditioners, phosphating additives, phosphating accelerators, electrophoretic resins, electrophoretic pastes, electrophoretic solvents, etc. In response to this situation, the coating workshop and material suppliers adopt a "single vehicle calculation" approach, which means that all parameters that need to be controlled and the types and quantities of feeding are completed by the chemical supplier, The painting workshop only undertakes the task of adding materials, which not only saves manpower in the painting workshop, but also effectively controls the quality of pre-treatment and electrophoresis.

In the process of adding and changing materials for PVC glue, the PVC glue conveying system is the most important equipment. In order to ensure sufficient glue amount in the glue barrel, an alarm device needs to be added to the glue conveying system. A trigger switch is added at one end of the hydraulic rod of the glue conveying pump, and an alarm light is installed at the PVC workstation to achieve automatic monitoring through the flashing of the alarm light

For the paint transportation and mixing system, real-time monitoring of parameters such as the number of strokes of the circulation pump, paint transportation, reflux pressure, and paint temperature is first used; Secondly, carry out TPM (Total Production Maintenance) maintenance on the paint mixing system to ensure the normal operation of the equipment; Once again, it is necessary to regularly monitor the temperature and humidity, ventilation conditions, and air cleanliness of the paint transportation and mixing system environment.

In terms of law: Process documents are the foundation and basis of painting operations, so in order to control painting quality, it is necessary to implement specialized management of process documents. The system personnel in the painting workshop are responsible for uploading, controlling, and archiving all process documents to ensure the integrity of the process documents and to ensure that employees have a basis for their operations; And confirm various important parameters of painting every year through experimental methods, in order to achieve continuous improvement of painting process parameters; To ensure that employees follow the document requirements, a three-level process discipline inspection is implemented for painting, which includes company level, factory level, and workshop level process discipline inspections.

In terms of environment: A good painting environment is a prerequisite for achieving excellent paint film quality. Therefore, in order to obtain a good paint film, it is necessary to strictly control the "four degrees" of painting (cleanliness, lighting, temperature, humidity).

① Cleanliness: Firstly, it is necessary to control the entry and exit of personnel in the painting workshop, especially in the painting room. Personnel entering the painting room must blow dust; Secondly, it is necessary to use laser particle counters to measure the cleanliness of areas with high cleanliness requirements such as paint spraying rooms, drying ovens, and clean rooms; Confirm the air balance of each section in the paint spraying room on a third regular basis, check whether the air filtration system is normal and effective, and replace the filter cotton regularly according to the actual production situation; Finally, it is necessary to regularly clean and lubricate various transportation chains, oil receiving trays, paint spraying rooms, drying ovens, and other equipment to ensure that they do not shed iron shavings or dirt.

② Illuminance: The illuminance standards for each workstation in the workshop are formulated by the process engineer and regularly measured and monitored; The lighting system in the workshop is the responsibility of a dedicated person, so that lighting damage can be repaired in a timely manner.

③ Temperature and humidity: The temperature and humidity of the paint spraying room are one of the key parameters to ensure a good paint film. Monitoring of the temperature and humidity of the paint spraying room needs to be carried out from the following aspects: the air conditioning system in the paint spraying room needs to have temperature and humidity rise and fall devices, and equipment personnel should regularly inspect the air conditioning equipment to ensure that the temperature and humidity in winter and summer meet production needs; In addition, it is necessary to monitor and record temperature and humidity. Technicians and coating technicians should take corresponding measures in a timely manner based on changes in temperature and humidity, such as adjusting temperature and humidity or adjusting paint construction parameters.

Process monitoring

There are three methods to improve the manufacturing quality of products: pre prevention, in-process control, and post inspection. Pre prevention is the prediction before an event occurs, which may not be detailed enough; After inspection, the incident has already occurred and the response is slow; In process control is the most effective way to improve manufacturing quality.

The projects monitored through process monitoring in the painting workshop include:

① Monitoring of drying performance and adhesion of electrophoresis, intermediate coating, and topcoat: timely reflecting the basic performance of each layer of paint film and the operation status of the drying oven;

② Monitoring of electrophoretic, intermediate, and topcoat film thickness: timely reflect whether the construction parameters and methods of each main process meet the requirements;

③ PVC coating monitoring: timely reflect the quality of the coating and whether the thickness of the bottom plate spray meets the requirements;

④ Electrophoresis, intermediate coating, and topcoat polishing point monitoring: timely reflect whether the environment and coating condition of the painting workshop are qualified.

4. Quality Information Communication

Effective communication and transmission of quality issues are prerequisites for solving quality problems. In order to ensure that relevant responsible units or individuals can timely obtain and understand quality information, the painting workshop has adopted the following methods.

⑴ Determine the quality information transmission process

The current quality transfer process diagram of the painting workshop is shown in Figure 1.

picture

⑵ Utilize various conference platforms for communication

The daily morning/evening meetings not only serve to summarize today and plan for tomorrow, but also serve as an important way for relevant units and personnel to obtain quality information. AUDIT in English means "review, verification", and the AUDIT of the vehicle body refers to using the customer's most critical perspective to review issues with the vehicle body. The painting workshop conducts AUDIT audits on painted car bodies every day, aiming to identify quality issues during the process and resolve them in a timely manner. At the same time, relevant leaders will participate in the AUDIT review meeting, playing an important role in promoting and resolving issues.

⑶ Establish a reasonable performance evaluation mechanism

A reasonable and effective performance evaluation mechanism can form effective competition among quality personnel to promote the rapid resolution of quality issues.

5 Conclusion

The quality of painting involves multiple aspects such as personnel, machinery, materials, methods, environment, and measurement. The above is the experience summarized through long-term on-site work, hoping to provide some reference for quality control on painting sites.

- Changzhou Anjia Coating Equipment Co.,Ltd  Dec.7,2023