One of the most challenging issues in automotive surface coating manufacturing is how to ensure the polymer coating quality developed on the vehicle surface. In production, vehicle bodies, before entering each baking oven, are covered by a thin layer of wet film of waterborne or solvent-borne paint on the panel surface. When a vehicle body travels in the oven, its panels are heated, which leads to the corsslinking reaction between the precursor polymer chains and crosslinkers within the polymer coating film. Within a pre-set operational period, the curing process should be accomplished and the surface coating is expected to achieve a desired coating quality in terms of its corsslinking network structures.[1], [2] However, due to a variety of disturbances on both the polymer curing process and the polymer coating product in operation, the final coating quality of the vehicle surface film is always a challenge in industry.

In this paper, both the polymer curing process and the polymer coating product are deeply analyzed and carefully modeled. [1]-[3] The reference models of the process and the product are also introduced to compensate the model uncertainty due to the lack of sufficient knowledge and information about the curing process and more critically the coating product. With the model set developed, an internal model control (IMC) based integrated process and product control (IPPC) methodology is introduced for the control of both the polymer coating curing process and coating quality. By this methodology, the control system design is capable of realizing simultaneous dynamic control of both the operational performance of the curing process and the manufacturing quality of the coating product.

The proposed IMC-IPPC design methodology is featured by the following advantages. First, the control of the polymer coating corsslinking quality can be ensured through all-time, on-aim proactive quality control (QC). This allows prediction of potential quality problems and derive early actions to prevent the occurrence of certain types of quality problems in the earliest manufacturing steps. Second, the energy supplied to the curing process can be balanced with the coating film temperature and the polymer crosslinking conversion rate, which can make the process operation much more efficient. Third, the process constraints on the curing hot air temperature can be practically imposed in controller design. Thus, the integrated control scheme can be more realistically implemented in real applications.

The introduced IMC-IPPC design methodology has been successfully tested with industrial problems. It has shown that although there exist a number of model inaccuracies for both the polymer curing process and the polymer coating product, and although the automotive polymer coating curing system experiences various disturbances, the crosslinking quality of the polymer product can be effectively controlled to achieve a desired conversion rate, and the polymer curing process performance has been fully acceptable as well with a high efficiency of the process control energy, and a satisfaction of the hot air temperature constraints. The introduced methodology is general enough for application in many other types of polymeric coating manufacturing processes.

Reference: [1] Lou HH, Huang YL. Integrated Modeling and Simulation for Improved Reactive Drying of Clear Coat. Ind Eng Chem Res. 2000;38:500–507.

[2] Dickie RA, Bauer DR, Ward SM, Wagner DA. Modeling Paint and Adhesive Cure in Automotive Applications. Prog Org Coat. 1997;31:209–216.

[3] Xiao J, Huang YL, Qian Y, Lou HH. Integrated product and process control of single-input-single-output systems. AIChE J. 2007; 53: 891-901.