Vision Molds Inspection Capability

May 1, 2003
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"We must provide the highest quality product to our customers. This has been our goal since day one," says Pierre Dziubina, president of Spectrum Plastics (Ansonia, CT).

Dziubina is a stickler for quality, and it shows in every aspect of the company's operations. As part of Spectrum's commitment to quality, the company aggressively uses the latest technologies. Spectrum employs high-speed machine vision systems to ensure the shipment of only the highest quality product to their customers. It allows them to perform 100% inspection and to reduce machine downtime and damage to molds.

Founded in 1967, Spectrum specializes in close-tolerance molding, insert molding, and continuous reel-to-reel moldings on metal or plastic carriers of precision thermoplastic parts for the electronics, medical, telecommunications and automotive markets. They operate 64 presses and ship parts worldwide.

The reel process
The reel-to-reel precision molding process begins with a reel of stamped parts on a continuous strip being fed into the molding press. The mold closes and a thermoplastic resin is injected into the mold around each of the stamped parts. After a few seconds 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 or 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 resulting in expensive repairs and downtime. Parts may also be incorrectly molded or damaged as they exit the mold.

"Part rates of up to 960 parts per minute can occur as the strip is indexed," says Kieran Coleman, Spectrum's process engineer in charge of vision. "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." Before purchasing its first vision inspection system in 1992 from PPT Vision Inc. (Minneapolis), the company did visual checks to the reel. Unfortunately, intermittent problems were not caught by the company, but sometimes by the customer.

Spectrum currently has 26 vision systems that perform 100% inspection on critical reel-to-reel, insert-molded products. Each of the PPT Passport or Scout systems consists of multiple cameras and lights to capture the image of each part both prior to and after the molding process. High-speed strobe lighting is needed to "freeze" 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.

Continuous feed
Spectrum Plastics runs continuous strip feed molding that provides the customer with no interruption in the product flow. The inspection department could have pulled a sample to test in the lab for confirmation of compliance to the customers print specifications, but this would defeat the advantage of strip feed. Spectrum can now check parts without creating splices or stopping the process. With the inline system, the company performs go/no go gaging and visual inspection on every part molded.

The vision system also saves Spectrum money in scrap. By detecting a defect immediately upon occurrence, the molding process is stopped before scrap is made. Prior to this the "end of reel" inspection, a defect was found and a complete reel of discrepant product may have been made.

When a nonconforming part is found, the vision system sends a signal through discreet I/O to the line PLC, which 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, and the system records and displays exactly what the problem is 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. "We are able to easily customize each inspection station while also providing consistency for the technicians by maintaining the same look and feel of each operator control panel. The icon-based programming makes it easy," says Coleman.

In addition, pass/fail, gage results, failure analysis, SPC, MTBF and other data or images 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.

Dziubina concludes, "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 product we provide."

BENEFITS
Vision allows the company to do 100% inspection of critical products.
Vision inspection can capture the required 24 images per second the company needs for complete inspection.
When a nonconforming part is found, the vision system sends a signal, which stops the press and alerts operators.
Pass/fail, gage results, failure analysis, statistical process control and other data can be gathered for real-time or future analysis.
The vision system processes the image to inspect and measure each part for malformed inserts, misalignment, short shots, flash and other part features.

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