With the development of the domestic passenger car industry, more and more mechanical spraying has replaced manual work. In this trend, the proportion of robotic spray is also increasing. For example, the 6-cup or 9-cup system that was originally used in body painting has also been replaced by robotic spray. Robotic exterior coatings are also heavily sprayed with robots, such as robots used in more than half of the production of domestic car bumper coatings. Robotic spraying not only maintains the adaptation of manual spray to complex shapes, but also accuracy and repeatability. This article will discuss various factors affecting the final coating thickness during robot construction, and provide some ideas for the control adjustment of the membrane during production.
The significance of film thickness control
For coating applications, film thickness is the most important controlling factor in the coating process, and its significance is:
(1) Prevention of coating defects due to improper film thickness. According to experience, more than half of the appearance defects of coatings in on-site production are caused by improper control of the film thickness of the paint. Some common coating defects such as sag, thin paint, and undercoat color are directly related to the loss of control of film thickness control, and some defects are also indirectly related to this. For example, if the first layer of the adhesive layer coated with the bumper is not thick enough, the adhesion of the entire coating will decrease, and the conductivity of the primer will be reduced when the film thickness of the primer is not required, which will cause the first road. When the paint is electrostatically sprayed, the transfer rate of the paint is lowered, which eventually leads to insufficient paint.
(2) Help adjust the appearance indicators. Common paint film appearance indicators such as gloss, color difference, orange peel, DOI, etc. need to be based on film thickness control. The above indicators are obviously affected by the film thickness, especially the thickness of the topcoat film. Therefore, it is necessary to use the film thickness as the most important control factor in the overall coating quality control.
(3) Control of costs. In addition to the quality cost of film thickness control on the quality of the coating, about half of the main cost of painting is occupied by the coating. Precise film thickness control not only contributes to the stability of the coating quality, but also contributes to the saving of the coating. Statistics show that when spraying with the same equipment, whether the film thickness is accurately controlled is more than 25%. At present, the robots used in China mainly include Japanese Iwata or Mitsubishi robots. These devices are introduced earlier and have poor control precision. The new coating lines generally use ABB, FANUC, MOTOMAN, DURR and other multi-axis robots. Discussion based on ABB robots
Factors Affecting Film Thickness In robotic spray application, the coating film thickness can be calculated as follows:
Dry film thickness = (flow rate × paint volume solid content × paint transfer rate) / (gun speed × spray width) (1) Flow rate, that is, the volume of paint flowing out of the gun nozzle per unit time during spraying. In robotic spraying, this data is determined directly in the BRUSH (brush) parameter table. In some old-fashioned robotic sprays, flow control did not establish contact with the robotic system and it was not possible to change the flow at any time in the middle of a spray program. Most of the new robot's flow control system is directly controlled by the robot's IPS system, making flow control more accurate and convenient. For example, in the flow control of ABB robot spraying, there are two types according to whether the flow control is closed or not.
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