Assembly in Action: Plastic Molder Uses Vision
Founded in 1967, Spectrum specializes in close-tolerance molding, insert molding and continuous reel-to-reel moldings. The moldings are used on metal and plastic carriers of precision thermoplastic parts for the electronics, medical, telecommunications and automotive industries. The company operates 64 presses, and parts are shipped worldwide.
Part of the company¿s commitment to quality is to implement the latest technologies into its production processes. Therefore, Spectrum employs high-speed machine vision systems to ensure that only the highest quality products are shipped to its customers. As an additional benefit, this 100 percent inspection has also reduced mold damage and machine downtime.
The reel-to-reel precision molding process begins with a reel of stamped parts on a continuous strip. This strip is fed into the molding process. For example, the mold closes, and a thermoplastic resin is injected into the mold around each of the stamped parts. After a few minutes, to allow the plastic to harden, the mold is opened, and the completed parts are ejected and indexed out for the next cycle.
Problems can occur before, during and after the molding press. If the reel contains any stamped parts that are bent or crushed, they may damage the mold as the press closes. This damage can result in expensive repairs and downtime. Parts also may be incorrectly molded or damaged as they exit the mold. "Rates of up to 960 parts per minute can occur as the strip is indexed. Some applications require two cameras to inspect the infeed and two cameras for the payout. High-speed vision inspection systems are needed, because we require 24 images per second for complete inspection and protection," explains Kieran Coleman, process engineer.
Spectrum currently has 26 Passport and Scout vision systems supplied by PPT Vision Inc. (Eden Prairie, MN). These systems perform 100 percent inspection of its reel-to-reel insert-molded products. Each system consists of multiple cameras and lights to capture the image of each part prior to and after the molding process. High-speed strobe lighting freezes 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, misalignment, short shots, flash and other part features.
When a nonconforming part is found, the vision system sends a signal through discreet I/O to the line programmable logic controller. The controller then stops the press and flashes a tower light to signal the operator that there is a problem. The image of the nonconforming part is locked on the vision system¿s operator control panel with a red border around it. The system records and displays exactly what the problem was for future analysis and process improvement. The operator examines the defective part, cuts it out, reconnects the loose ends of the strip and continues running. "By maintaining the same look and feel of each operator control panel, we are able to easily customize each inspection station while providing consistency for the technician. The icon-based programming makes it easy," says Coleman.
Pass or fail, gauge results, failure analysis, statistical process control, mean time between failures, and other data or images can be gathered and saved on a hard disk. It can also be sent over a serial or network connection to allow real-time or delayed process monitoring and control. Even though all the process and inspection information is collected and stored at each press, it is available for central processing and analysis via the network.
In addition to quick-turnaround reel-to-reel applications, Spectrum handles multicavity molds to accommodate production requirements for its customers. Due to volume requirements, flexibility is necessary.
The vision systems easily accommodate more than one type of part being manufactured on a line by quickly loading a new inspection file during part changeover. "I like the flexibility of the new digital systems. If we need additional cameras or strobes, we just add them as plug-and-play items," says Coleman. "Things are always changing. We have received speed, flexibility and ease-of-use from vision inspection."
"We are very pleased with the benefits we have achieved by using vision systems. But more importantly, our customers have seen the benefits and appreciate the quality of the products we provide," says Dziubina.
For more information on vision systems, call 952-996-9500, visit www.pptvision.com.