Molding machine inspects plastic parts

Small electronic components that combine tiny metal and plastic parts have typically been manufactured and assembled on a loose-parts basis.

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Small electronic components that combine tiny metal and plastic parts have typically been manufactured and assembled on a loose-parts basis. Now, that inefficiency is giving way to fully automated processes such as reel-to-reel molding.

Although the completed parts give the appearance of being plastic parts with metal inserts, the plastic is actually molded over the part. Molded parts are then delivered to the customer on the take-up reel and placed directly in automated production equipment for hands-off operations that add more components, install covers, or form electrical leads. However, if the reel contains stamped parts that are bent or crushed, the parts may damage the mold as the press closes, resulting in expensive repairs and downtime. Parts may also be incorrectly molded or damaged as they exit the mold.

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Spectrum Plastics, a manufacturer of continuous reel-to-reel moldings, uses vision systems from PPT Vision to inspect each molded part before and after manufacture.
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"Rates of up to 960 parts/min can occur as the strip is indexed. Some applications require two cameras to inspect the in-feed and two cameras for the payout. For complete inspection and protection, 24 images per second are required," says Kieran Coleman, a process engineer with Spectrum Plastics (Ansonia, CT). This company is a specialized manufacturer of continuous reel-to-reel moldings of thermoplastic parts for the electronics, medical, telecommunications, and automotive markets.

Spectrum Plastics is currently using 26 Passport or Scout vision systems supplied by PPT Vision (Minneapolis, MN) to inspect its reel-to-reel, insert-molded products. Each Passport or Scout vision system consists of multiple cameras and lights that capture the image of each part both prior to and after the molding process. High-speed strobe lighting is used to stop the motion of the strip as each individual part passes under the camera during the index cycle. The vision system then processes the image to inspect and measure each part for malformed inserts and misalignment.

When a nonconforming part is found, the vision system sends a signal through a discrete input/output connection to a programmable logic controller that stops the molding press and flashes a tower alarm lamp. The image of the nonconforming part is locked on the vision system's control panel with a red border around it. The vision system records and displays the problem for future analysis and process improvement. The technician examines the defective part, cuts it out, reconnects the loose ends of the strip, and continues running the production line.

"We customize each inspection station and provide consistency for technicians by maintaining the same look and feel of each control panel," says Coleman. Pass/fail, gauge-result, failure-analysis, and mean-time-between-failure information can be gathered and saved on a hard disk or sent over a serial or network connection to allow real-time or delayed process monitoring and control.

All the process and inspection information is collected and stored at each molding press and is also available for central processing and analysis over the inspection network. In addition to quick-turnaround reel-to-reel applications, Spectrum Plastics operates seven days a week, handling multicavity molds to meet production requirements. To accommodate more than one type of part, the technician downloads a new inspection file to the machine-vision system during part changeover.

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