Automatic online monitoring to reduce scrap rate by 35%

In the past, the surface quality of lenses was only inspected at the end of the production cycle. However, a new approach now allows for checking the finish of lenses during an earlier stage of manufacturing, significantly reducing the scrap rate by up to 35%. This shift in quality control not only improves efficiency but also helps minimize waste and unnecessary costs. Traditionally, quality checks in many industries are conducted at the final stage of production. If errors occur in previous steps, they may go undetected until after lengthy processing or even after the product is completed. This leads to increased costs, delays, and wasted resources. These issues often result from higher energy consumption, additional material use, unnecessary machine time, and equipment wear. The cost impact varies depending on the type of manufacturing process, but it typically involves a combination of these factors. By implementing automatic quality identification between key processing stages, manufacturers can detect problematic products early, which helps reduce additional costs. This is especially beneficial when subsequent processes are time-consuming or expensive. Inspecting semi-finished products offers significant advantages, as it allows for predicting the success rate of later stages and making timely adjustments. The same principle applies to lens production. Plastic lenses have become increasingly popular, now accounting for about 85% of the market. They are cheaper to produce, offer optical properties comparable to mineral lenses, and are lighter and more durable, making them a preferred choice for many customers. During the production of plastic lenses, quality checks are usually performed after the workpiece has undergone grinding and shaping. A complex polishing process follows, which determines the optical quality of the lens surface. If the polishing does not meet the required standards, the defective workpiece must be removed from the production line, and the entire process must be restartedâ€”this is both time-consuming and costly. If the quality of the grinding tool deteriorates due to wear, continuous inspection of the lens surface can help identify this issue before it affects the final product. This proactive approach minimizes the risk of poor surface quality and reduces waste. As diamond tools are used over time, their performance gradually declines, leading to more machining marks and lower surface quality. Figure 2 illustrates the difference in surface quality caused by varying tool conditions. Since the lifespan of grinding tools is unpredictable, it has been difficult to anticipate when the tool quality will fall below acceptable levels. Traditionally, quality checks were performed only after polishing, which meant that any defects were detected too late to prevent further processing. To address this challenge, Deggendorf University of Technology developed an optical measurement system designed to inspect the surface finish of plastic lenses directly during the production process. As shown in Figure 1, the system uses two perpendicular positioning axes and a confocal sensor from Micro-Epsilon to measure surface roughness in real-time. This allows for continuous monitoring of tool quality and ensures that any decline in surface finish is detected early. The system is designed to work seamlessly with the grinding equipment, ensuring that the measuring cycle aligns with the production rhythm. Within just a few seconds, the system can identify areas where defects may have occurred, preventing the polishing process from being applied to substandard lenses. In traditional lens production, quality checks are performed after several processing steps, including one hour of grinding. By the time a toolâ€™s quality is noticed, up to 60 lenses may already have been affected. Using the new measuring system, tools can be replaced in time to avoid such losses, and parts with occasional surface defects can be removed before entering the next stage. This method not only reduces waste and cost but can also be adapted for other similar manufacturing processes. Beijing Furui Hengchuang Technology Co., Ltd. is one of the companies exploring the integration of this technology into its production lines to enhance efficiency and quality control.

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