Robotics

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Robotics automation is being introduced in many coatings shops in their gun manipulation. Simple gun manipulation systems such as mechanical “Up / Down” units to simple robotic systems to very sophisticated robotic systems are all finding place in thermal spray shops worldwide. In addition to reducing operator fatigue quite evident in manual operations, use of robotics in automation allows to achieve one more step towards thermalsprayedcoatings repeatability. By the use of robotics , the thermal spray gun travel velocity can be controlled consistently as well as spray distance can be maintained consistently even on complicated part geometries. In more sophisticated robotics controlled thermal spray coating systems, where the “Powder ON” and “Powder OFF” controls, turntable rotation checks, rpms as wells as “Feed Rate Controls” are automated and integrated with the robotics program, there is further progress towards coating repeatability by reducing the variables involved in the application of thermal spray coatings.

An important but frequently overlooked aspect in thermal spray shops using robotic systems is the programming finesse and capabilities of the robot programmer. Sure, the robot itself could be quite sophisticated with multiple axes capabilities and so on, but what about the human being that is doing the robot programming ? Thermal spray shops that simply employ the services of a robotics software engineer are liable to gain nearly not as much as thermal spray companies that involve a seasoned thermal spray engineer who “knows” the coating process to learn the ins and outs of robotics and have him do the programming. Conversely, if the person starting out in the robotic thermal spray cell is simply trained only in software, then he should be trained in the thermal spray process as well in order to get the most out of the automated spray cell.

In light of the aforementioned point, I would like to give a real world example dealing ONLY with thermal spray gun movement using robotic systems. I was once involved with a thermal spray coating company that was coating the same family of parts with the same plasma spray coating material for years by manual hand spray technique. Later, they introduced automation in that plasma spray booth by way of a simple pneumatic “UP / DOWN” traverse. Things looked up – because they were getting consistent coatings without operator skill dependance and at the same time reducing operator fatigue. The company was making all kinds of profits and they wanted to step up to the modern world and so invested in a fairly sophisticated robotic system. They had always been very good at collecting data and logging it well – they had years of data – all kinds of data ( more about data analysis in a future post ). They found suddenly that the plasma spray powder usage in that booth had gone up since they had installed this expensive robot. That is when I was asked to step in. What was happening was that they had a programmed “Gun Light Point” where the gun would be lit, powder turned ON, stabilized and then move to the part, finish coating the part and then move back to the “Gun Light Point” and then powder turned OFF and the gun turned OFF. This point in space was quite a distance away from the part; whereas the old UP / DOWN machine stopped right above the part. This may not sound like much, but remember they coated the same part family hundreds of times a day and then day after day – ( ever wonder where those high volume thermal spray jobs are nowadays ? – don’t worry they are still there – you just need to look harder :-) ) The five additional seconds the robot arm was moving TO the part at the start phase and AWAY from the part at the end phase was enough to make a difference in the powder usage data. So I moved it right above and to the right of the part with a very quick move.

There are other kinds of tricks that the programmer can do to save on thermal spray powders by the use of robotics. For example, many times the thermal spray gun will move at an “UP - Angle” during the upward traverse and with a “DOWN - Angle” during the downward traverse. Well, when the gun switches the angle of travel, you need to code the robotic program as an arc whose center point is calculated as being away from the the robotic arm end point by [ the gun length and any extensions to it PLUS the spray distance] . This will allow for a very quick but smooth gun angle change, so that very little thermal spray powder is wasted not to mention the savings in time during the angle changeover. I instituted this procedure on ALL part families where gun angles changed at the end of the traverse. ( a note here: the thermal spray gun traverse could be up/down or side/to/side – doesn’t matter – the arc can be described either way. )

Of course, simple things like how much of idle spray the gun is performing, how far of an overshoot is handled, etc are simple enough to observe and rectify. Remember, robotics must be properly programmed and used so that the goal is to reduce operator fatigue, produce consistent thermal spray coatings and conserve on thermal spray powders. Then the investment will pay off.