Q: How does inspection/defect detection offer better quality control?
A: Inspection/detection techniques and processes offer manufacturers an effective way to control the quality of their products, while reducing product waste or give-away and increasing productivity. From the standpoint of non-contact measurement, today’s inspection techniques involve the use of laser encoders to accurately measure product length and speed during production. The precise measurement of these dimensions directly affects quality control in several ways during the production process.
For example, the accurate length measurement of incoming product ensures manufactures have received the exact amount of material to meet their flexible packaging production needs. During production, the precise measurement of product length and speed enables manufactures to accurately control various processes, such as the differential speed of two converging materials during lamination processes, cut-to-length operations of packaging materials, product positioning for printing and coating applications, and continuous length at the slitter/rewinder.
Q: Any generic pointers on how to troubleshoot this step?
A: If the manufacturer is using mechanical contact encoders like tachometers and wheel encoders to perform indirect product length and speed measurements, it’s a good idea to employ a non-contact measurement technique such as a laser encoder to measure products directly. Contact wheel encoder systems by their very nature have several fundamental flaws that make them prone to measurement errors. These include:
• The amount of slippage or jitter between the wheel and the measurement surfaces
• Day-to-day wear of the contact wheel, causing the radius to change
• Build-up of product material, debris, or other material between the wheel and product
In general, most contact wheel encoder systems provide a length and speed error of 0.5 percent or higher; greater than 1.0 percent error is common. Laser-based, non-contact measurement provides +/-0.05 percent accuracy with +/-0.02 percent repeatability.
Q: What should one look for when inspecting a film for defects? Are there instances when a defect detection machine detects something that is miniscule enough to allow it to pass through approval?
A: Depending on the process or application, manufacturers should look for any signs that their product is deviating from production requirements designed to meet customer quality expectations. For instance, does the product have surface damage (i.e., scratched or marred) from the use of mechanical contact encoders? Is the product being stretched to the desired mil thickness specification needed for the flexible packaging? Or, is the proper amount of coating being applied evenly or to the exact layer thickness as specified by production requirements? Are two or more products being joined and sealed properly during the lamination process? Are there any bubbles, wrinkles, unevenly joined materials, material excess or other imperfections in the laminated product? Has the product been cut to the exact length requirements for next-step production needs? Or, has the correct amount of product been accumulated on the rewind roll to ensure the end user receives the exact quantity for the next step in the process or for ultimate customer delivery.
In some instances, slight defects may not be that important for meeting general end results. In many cases, less than desired quality results can have a direct and costly impact on rework, productivity, and materials.
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