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TNT Plastic Molding has used a monitoring system developed by Ask Technologies and Cognex to prevent damage to its injection-moulding tools.

At TNT Plastic Molding – located in California, the US – when an injection-moulding operation is completed, pins on the movable side of the mould push the part out of the mould.

Occasionally, however, a part sticks in the mould.

In the past, the operator was responsible for checking the mould after each cycle to ensure the part was removed.

Sometimes the operator did not notice that the part had not been ejected, with the typical result being USD14,000 (GBP8,643) damage to the mould.

TNT Plastic Molding has used a mould-monitoring system developed by Ask Technologies to overcome this problem.

The system inspects the mould before it closes to be sure the part has been ejected.

The mould monitor utilises the Cognex In-Sight vision system, which was trained in minutes by simply taking images of the mould in the proper condition without a part.

The vision system now checks the mould on every cycle for the presence of the part, eliminating the risk of damage.

The mould-monitoring system has also improved quality by enabling the press to run in automatic mode, which increases the consistency of cycle time.

TNT Plastic Molding’s 55,000ft2 facility in California is equipped with 28 moulding machines, ranging from 55 to 610-ton capacity.

The company has ISO 9001 and AS 9100 certification.

Its mould-making capabilities range from single-cavity prototypes, multi-cavity and hot runner, to three-plate and automatic unscrewing production moulds.

TNT also has a mould-making facility in China that it uses to fabricate tools for price-sensitive programmes.

Injection moulding 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 mould if a part was not ejected.

The operator had to open the safety guard door around the mould 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 mould 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 mould, which would result in damage.

It would take up to three weeks to repair the costly mould, resulting in substantial lost revenues for the company.

Murray Anderson, director of sales and marketing for TNT Molding, said: ‘We had noticed that the performance of vision systems designed for injection moulding had improved at the same time their cost was being reduced.

‘We selected Ask Technologies’ mould-monitoring system because its system is easy to program for a wide range of mould-monitoring applications, including insert moulding, 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 applications.

‘We were also very impressed with the cost of the mould-monitoring system, which, at about USD10,000, is less than the cost of a single accident caused by failure of the part to eject,’ Anderson finished.

Mike Askin, president of Ask Technologies, said: ‘We designed our mould-monitoring system to meet the requirements of the injection-moulding industry: reliability, ease-of-use and low cost.

‘A critical requirement was to find a vision system that could easily be configured to handle a range of mould-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 mould with the part properly ejected.

‘These images are used to train the vision system.

‘Then if the part remains in the mould 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 its product could be improved but no changes were ever made.

‘When we started working with Cognex we discovered it was much more responsive.

‘Cognex made changes to its In-Sight system that made it better for moulding applications.

‘In particular, it increased the flexibility of the interface, making it easier for us to develop our mould-monitoring system,’ Askin added.

Ask Technologies used the In-Sight Software Development Kit to develop a user interface with a simple point-and-click setup for the new mould-monitoring system.

The interface makes it easy for the user to configure the vision system for new applications or moulding 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 user-friendly interface that accesses Cognex’s standard vision tools,’ Askin continued.

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 mould-monitoring system.

The camera automatically loads the program specified by the user and puts it online.

The pattern-find function can 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 mould may be in different positions.

Anderson added: ‘We easily set up Ask’s mould-monitoring system to confirm that the part has been ejected from the mould.

‘We then ran a series of tests that confirmed that the mould-monitoring system is able to consistently identify the absence of a part in the mould and shut down the press.

‘This system has eliminated damage to the mould 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,’ Anderson said.

Another important advantage is that there is no need for a manual check of the mould, giving the operator time to carry out other tasks.

Previously the press operator could only handle a single machine, but now has time to handle two machines, substantially reducing labour 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.

‘It has run flawlessly on this operation for several months.

‘We are confident that we can easily program it to run on different moulding operations as required,’ Anderson concluded.

Askin finished by saying: ‘The minute a tool closes on a part or insert, there’s a strong probability that damage is going to occur.

‘TNT Plastic Molding’s success with the mould-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 mould-monitoring system is compact and can be installed and interfaced on almost any injection-moulding machine.

‘It inspects the mould before it closes for part presence, part absence or insert loading.

‘It stops the press from even beginning to close and prevents a cycle from taking place until the mould 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,’ he said.

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