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 process. However, a new approach now allows for checking the finish of lenses during an earlier stage of manufacturing, reducing the scrap rate by up to 35%. This shift in quality control not only improves efficiency but also significantly lowers production costs. Traditionally, quality inspections in many industries are conducted at the final stage of production. If errors occur in earlier steps, they may go undetected until the product is nearly complete, leading to costly rework or waste. This can result in increased expenses related to energy, materials, equipment downtime, and machine wear. These inefficiencies often delay delivery times and reduce overall profitability. By implementing automatic quality checks between key processing stages, manufacturers can identify defective products early on, preventing unnecessary post-processing. This is especially beneficial when subsequent steps are time-consuming or expensive. Inspecting semi-finished products not only helps reduce waste but also provides valuable insights into the success rate of upcoming production phases. The same principle applies to lens manufacturing. Plastic lenses have largely replaced mineral lenses due to their lower cost, comparable optical performance, and superior durability. With a market share of around 85%, plastic lenses offer significant advantages in weight and resistance to breakage, making them a preferred choice for many customers. During the production of plastic lenses, quality checks are typically performed after high-value processing steps. After grinding and shaping, a complex polishing process determines the optical properties of the lens surface. If the polished surface does not meet the required standards, the workpiece is removed from the production line, and the entire process must be restarted. This is both time-consuming and costly, as reworking defective parts is not always feasible. If tool wear leads to a decline in surface quality, continuous inspection of the lens surface can help detect issues before the tool becomes completely ineffective. This proactive approach minimizes the risk of producing substandard lenses and reduces material waste. One of the main challenges in lens manufacturing is the gradual wear of diamond tools used in the grinding process. As these tools degrade, they leave visible marks on the lens surface, affecting its optical quality. Without regular monitoring, it's difficult to predict when a tool needs replacement, leading to potential quality issues that are only detected after polishing. To address this, Deggendorf University of Technology developed an optical measurement system that inspects the surface finish of plastic lenses directly during the production process. This system enables real-time monitoring of tool quality, allowing for timely replacements when surface finish falls below acceptable limits. The system consists of two perpendicular positioning axes and a confocal distance sensor. After grinding, the lens is positioned under the sensor, and the surface roughness is measured along a specific section. The data collected helps determine whether the tool is still in good condition or needs to be replaced. This technology has been successfully integrated into the production line, ensuring that any defects are identified before the polishing stage. By matching the measuring cycle with the grinding process, the system operates efficiently without disrupting the workflow. As a result, unnecessary processing on flawed lenses is avoided, and production costs are significantly reduced. With this innovative approach, manufacturers can achieve greater precision, reduce waste, and improve overall productivity. The system is not only beneficial for lens production but can also be applied to similar manufacturing processes across various industries.

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