Vision System Prevents Injectiona Molding Tool Damage and Improves Part Quality
At TNT Plastic Molding, located in California, USA, when an injection molding operation is completed, pins on the movable side of the mold push the part out of the mold. Occasionally, however, a part sticks in the mold. In the past, the operator was responsible for checking the mold after each cycle to ensure the part was removed. Sometimes, the operator did not notice that the part had not been ejected—and the typical result was $14,000 in damage to the mold.
TNT Plastic Molding has overcome this problem by using a mold monitoring system developed by A.S.K. Technologies, that inspects the mold before it closes to be sure that the part has been ejected. The mold monitoring utilizes the Cognex In-Sight® vision system, which was trained in minutes simply by taking images of the mold in the proper condition without a part. The vision system now checks the mold for the presence of the part on every cycle, eliminating the risk of damage to the mold. The mold monitoring system has also improved quality by enabling the press to run in automatic mode, which increases cycle time consistency.
TNT Plastic Molding’s 55,000 square foot facility in California is equipped with 28 molding machines ranging from 55-ton to 610-ton capacity. The company has ISO 9001 and AS 9100 certification. Its mold-making capabilities range from single-cavity prototypes, multi-cavity, and hot runner, to three-plate and automatic unscrewing production molds. TNT also has a mold-making facility in China that it uses to fabricate tools for price sensitive programs.
Difficult manual inspection challenge
Injection molding machines can run in either semi-automatic or automatic mode. In the past it was necessary to run a 300-ton JSW press in semi-automatic mode because of the danger of damage to the mold if a part was not ejected. The operator had to open the safety guard door around the mold after every cycle to check that the part had been ejected into a drop chute leading to a conveyor. During a typical eight-hour shift, the operator inspected the mold approximately 640 times. Not only was there great potential for human error due to fatigue, variable inspection times caused dimensional variations in the parts.
It was not uncommon for the operator to accidentally cycle the press even though the part had not been ejected from the mold, which would result in damage. It would take up to three weeks to repair the costly mold, resulting in substantial lost revenues for the company.
Taking human error out of the equation
“We were interested in taking human error out of the equation in order to improve quality and reduce costs,” said Murray Anderson, Director of Sales and Marketing for TNT Molding. “We had noticed that the performance of vision systems designed for injection molding had improved at the same time their cost was being reduced. We selected A.S.K. Technologies’ mold monitoring system because their system is very easy to program for a wide range of mold monitoring applications including insert molding, short shots, part presence or absence, runner presence or absence and before and after shot inspections. The flexibility of the system also enables many other possible applications. We were also very impressed with the cost of the mold monitoring system which, at about $10,000, is less than the cost of a single accident caused by failure of the part to eject.”
“We designed our mold monitoring system to meet the requirements of the injection molding industry: reliability, ease-of-use and low cost,” said Mike Askin, President of A.S.K. Technologies. “A critical requirement was to find a vision system that could easily be configured to handle a wide range of mold monitoring tasks. The vision system also needed to be small in order to fit into the often crowded press environment. The Cognex In-Sight vision system meets all of our requirements. Its small size and flexible mounting capability makes it easy to fit into nearly any press application. The system is very easy to program with a library of 22 vision tools. We used inspection tools to simply capture images of the mold with the part properly ejected. These images are used to train the vision system. Then if the part remains in the mold or any other problem occurs, the vision system reliably detects the problem.”
“We had worked with another vision company and made suggestions as to how their product could be improved but no changes were ever made,” Askin said. “When we started working with Cognex we discovered they were much more responsive. Cognex made changes to their In-Sight system that made it better for molding applications. In particular, they increased the flexibility of their interface, making it easier for us to develop our mold monitoring system.”
Simple setup and programming
A.S.K. Technologies used the In-Sight Software Development Kit to develop a user interface for the new mold monitoring system with a simple point and click setup. The interface makes it easy for the user to configure the vision system for new applications or molding machines. The user can specify a tolerance that determines the vision system’s rejection standards. Up to 16 configurable windows can be activated or deactivated by the user. “We worked with the Cognex engineering department to develop a very user friendly interface that accesses Cognex’s standard vision tools,” Askin said.
It took just 10 minutes to develop the program for the JSW press. After the setup was complete, the job was saved onto the camera and PC for backup and future reference. The operator simply turns the camera on and waits for it to boot, then starts the PC to power up the mold monitoring system. The camera automatically loads the program specified by the user and puts it online. The pattern-find function is able to locate the area that needs inspection from anywhere in the field of view so the program can consistently detect the presence or absence of the part despite the fact that the two sides of the mold might be in different positions.
Eliminating mold damage and improving quality
“We easily set up A.S.K.’s mold monitoring system to confirm that the part has been ejected from the mold,” Anderson said. “We then ran a series of tests that confirmed that the mold monitoring system is able to consistently identify the absence of a part in the mold and shut down the press. This system has eliminated damage to the mold and associated lost production. It also made it possible to reconfigure the machine for full automatic operation. Quality has also been improved because the cycle time is consistent which means the hold time, cool time and shrink time are now the same for every cycle. By eliminating variation from the operation—such as temperature fluctuations—it is now possible to hold the part to tighter tolerances.”
Another important advantage: there is no need for a manual check of the mold: this has allowed the operator time for other tasks. Previously, the press operator could only handle a single machine, but now has time to handle two machines, substantially reducing labor costs. Despite handling the two machines, the operator has more time than before for inspecting the parts, which has helped to improve quality. “We are also very pleased with the flexibility of the system,” Anderson said. It has run flawlessly on this operation for several months. We are confident that we can easily program it to run on different molding operations as required.”
“The minute a tool closes on a part or insert there’s a strong probability that damage is going to occur,” Askin concluded. “TNT Plastic Molding’s success with the mold monitoring system is indicative of what we have seen with many other customers that were having problems due to stuck parts, failed ejection, short shots, failed insert loading or other problems that usually resulted in a damaged tool. The mold monitoring system is compact and can be installed and interfaced on almost any injection molding machine. It inspects the mold before it closes for part presence, part absence, insert loading, etc. It stops the press from even beginning to close and prevents a cycle from taking place until the mold is cleared of any problems. This saves a considerable amount of repair cost and downtime. Users have also seen improvements in quality and productivity by moving from a semi-automatic to an automatic press cycle.”
