Cartesian Robots

“The mastery of chemistry has to go hand in hand with the process of mechanical engineering,” Dr Bayer, inventor of polyurethane, the world’s first two component polymeric system.

There are countless two-part reactive chemical systems that are essential to a vast number of manufacturing processes. These range from performance critical gluing and sealing on vehicle production lines to civil engineering projects. Such processes rely on the ratio content of the two-part adhesive system, which typically ranges from 1:1 to 10:1 by weight, being completely accurate. Imagine an airplane where the tail assembly bonded composite structure delaminates and fails and one can begin to see why accurate two-part mixing is truly mission critical.

As a result, TM Robotics, AMT and Failsafe Metering have worked together to develop a groundbreaking method of using robots to dispense 100% accurately mixed two-part reactive chemicals.

The work was conducted in Failsafe Metering’s R&D lab in Kettering. It uses a Shibuara Cartesian linear actuator supplied by TM Robotics as the robot ‘guinea pig’. AMT provided its integration expertise to ensure that the robot operates to its full potential.

The process developed by Failsafe Metering, is based on the fundamental properties of a liquid under pressureIn this case, the two reactive liquid parts of a reactive adhesive system are subjected to high pressure, thus, becoming hydraulic, and producing a maximum density per unit volume. Each liquid part can then be uniformly divided into two precise, volumetric units in the specified ratio relative to each other (usually 1:1 to 10:1, by weight) and prior to being electronically checked for accuracy. This is where the biggest distinction between this system and a conventional two-part reactive chemical mixing system lies. In most processes, the manual taking of random weight checks of the two outputs, prior to the mixer is the only way to check the theoretical ratio of each liquid in the mix. For example, and with conventional machines, if resin is used when manufacturing a car, the only real way to check for the correct ratiocontent of that glue, would be to take, say, the bumper off a car and to test the glue itself!  Even if this were possible, the test result would only referto the glue content on that specific bumper and not the entire production run.  By using the Failsafe Metering system, all the glue is checked for ratio before it is applied, dot-by-dot.

After checking, the adhesive components are rapidly fired forward towards, and combined within, a dispensing head, from which the output forms a shot or flow. The qualification of this metering process is based on an electronic signal, which is generated when each dot is tested for the correct volumeThese high-speed signals are sent to a meter, which will shut down the system if the mix is incorrect and, thus, preventing it from reaching the point of application. At present, the entire system is correct to two decimal points. For example, if you require a mixture of one part to fifty and you actually have 1/49.99 the process is stopped.

At this point, the correct adhesive mix is pumped through to a‘static’ mixer, which dispenses the glue smoothly onto the product. This process is already being used on vehicle spoilers and in several different kinds of vehicle door sealing systems.

If the process is stopped, any mix already in process will still be perfectly mixed. There is no possibility for contamination whatsoever because it is checked before it gets the dispensing head. In a regular system the adhesive quality is not known and the adhesive would not be checked until the product was complete.

Laurie Penn, managing director of Failsafe Metering, had the idea for this new system while toying with a replica revolver. One evening, as he spun the barrel of the gun it occurred to him that, instead of sending a constant flow of liquid through the ‘barrel’ of a mixing system, he could ‘machine gun’ that liquid through. The result would be a series of discrete ‘dots’, which could each be measured and checked for volumetric accuracy.

“Using conventional methods it is perfectly possible for a product to make it all the way down the production line with no adhesive on it at all. It could be, literally, held together by its component parts,” said Penn. “This would not be possible with our system. When companies come to us talking about quality assurance standards such as ‘Six Sigma’ and asking for failure rates of, no more than, 3.4 defect parts per million, I ask why such a high failure rate? With Failsafe Metering there need not be any failures.”

“Automation, by itself, only increases the efficiency of a process,” said Nigel Smith, managing director of TM Robotics. “It doesn’t mean that the product being manufactured is of any higher quality. Unless the raw materials or quality assurance process is improved, a line of glue will always be a line of glue, with all the faults inherent in that. However, Failsafe Metering’s process actually allows the end product to be improved. When combined with the innovation delivered by automation this represents a formidable proposition.”


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