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Process Cleaning Magazine
© 2012
AMT-The Association For Manufacturing Technology
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Technological advances and reduced costs have brought robotic cleaning systems to the forefront for a variety of cleaning applications.
Robots are often used during the stripping of ceramic coatings that are thermally applied to jet engine and gas turbine components. The robot can precisely control a high pressure water jet to remove the coatings.
Other applications where robots are gaining popularity include deburring and washing of machined components and shell and core removal of investment castings.
Waterjet cleaning systems from KMT Robotic Solutions can be customized to meet the customer’s needs, accommodating a variety of part sizes and shapes.
Robotic cleaning systems have been in production for about 20 years, but for much of this time, their use was relatively limited. Slowly but surely, this trend is changing as robotic technology advances, total system costs decline, and accumulated process knowledge expands, allowing robotics to penetrate new cleaning opportunities.
Robotic Thermal Spray Stripping
One of the first uses of robots in cleaning was for stripping ceramic coatings that are thermally applied to jet engine and gas turbine components. To provide both protection and increased life, a ceramic coating is applied to the high wear engine components. These coatings are applied with a thermal spray process to assure a tight bond with the parent material. However, over time these coatings wear and must be reapplied.
This process is handled at dedicated depots that completely refurbish jet engine and gas turbine components after a specified number of hours of use. The first step is to completely remove any ceramic material remaining from the factory or the last refurbishment before reapplying the ceramic coating. Paint, glue, rubber coatings, oxides and other deposits are also removed in preparation for the reapplication of the ceramic coating. Automated stripping systems robotically remove the remaining coating using high pressure water. The robot’s ability to precisely control the water blast path, including location, stand off, tool orientation and water pressure, is the key to success.
Because of the demanding requirements of aircraft and power generation customers, the robotic stripping process leaves no room for error. Traditionally, this need for precision was addressed by a tedious and time consuming process of programming thousands of points and then verifying the extremely complex stripping paths. Further complicating this effort is the need to coordinate the robot path and cleaning parameters with a turn table that must rotate larger components during the cleaning operation.
Thanks to the recent advances in robot accuracy and off-line programming, this effort has been significantly reduced. Robot accuracies over the workable range of a stripping system are down to 1 mm or less. This technology, combined with advances in off-line programming, has greatly reduced the amount of time required to teach and verify robot paths. So refurbishment depots purchasing new stripping systems can operate their systems at reduced costs and expect a greater return on investment compared with earlier systems.
The relatively high cost of the parts being stripped and the precision required by the stripping process boosts the case for robotic stripping systems versus chemical baths, shot blasting or other alternatives when removing thermal spray. But such precision is not required in many other cleaning processes, which, until recently, has played a role in limiting the more widespread adoption of robotic cleaning.
Investment Casting Shell and Core Removal
One industry application that is now beginning to benefit from the advances in robotic cleaning is the shell and core removal of investment cast parts. In addition to aircraft engine components, investment casting is widespread in the medical orthopedics, automotive, machinery and electrical equipment markets. A ceramic shell that is used to mold investment cast parts must be removed after the metal cools and before the parts can be processed further. This process can be challenging considering that investment casting is commonly used for more intricate parts with cavities and other hard-to-clean areas.
The state of the investment casting shell and core removal mirrors the state of the robotic stripping market when it first started. Alternate technologies such as water blast booths, shot blasting, chemical leaching or vibratory/knock out systems have been traditionally used to remove the shell and core material from investment cast parts, but each of these alternatives has certain limitations. These limitations include having to deal with the high disposal cost and environmental impact of chemical leaching agents or shot blast material, the high energy and water usage of manual or automated water blast systems, and the risk of part damage associated with vibratory or knock out systems. In many cases customers use a combination of these systems, adding to the cost and cycle time to clean parts.
As with thermal spray robotic stripping systems, robotic shell and core removal systems benefit from a robot’s ability to precisely control the water blast path and associated process parameters required to remove the shell and core material. By properly controlling the stand off, water jet orientation and water pressure, robots are able to consistently and effectively break off and clear away the shell material. The key is to have a clear line of sight (no hidden areas) and sufficient process repeatability so that the robot can direct the jet to all required areas to knock off and clear away the shell or core material.
The opportunity to address the concerns of legacy systems is large, but there are still challenges to implementing robotic shell and core removal systems. The first (and probably the biggest) challenge is breaking the mindset that cleaning can only be handled by traditional cleaning methods. Going from a mechanical knock out and leaching or shot blast combination, which is one of the most common approaches to a robotic cleaning system, can appear to be a big leap. Even a jump from a hard automation water blast system can appear daunting. But when comparing the relatively high per-part costs to dispose of chemicals or waste shot material and to cover water and energy usage, labor, and long cycle times, the per-part savings offered by a robotic shell and core removal system can be surprising.
Early adopters have already begun to implement robotic shell and core removal systems with great success. One investment caster in Europe has reduced per part running costs by 80% by eliminating chemical leaching and the associated high disposal costs. As with other markets, companies in shell and core removal are quickly realizing the advantages of robotics and are beginning to implement these systems. With more than 150 investment casters in the U.S. and hundreds more throughout the world, the market for robotic shell and core removal could far exceed that of the thermal spray stripping market.
Robotic Deburring and Washing
Perhaps the biggest opportunity for robotic cleaning is deburring and washing of machined components. Just like stripping and shell removal, legacy washing systems have been the prevalent solution for washing and deburring of machined metal components. These systems typically apply large volumes of lower pressure water to parts on transfer lines, sometimes heated and sometimes with chemical agents. The legacy hard automation systems get the job done, but use a large amount of water, energy and associated costs. They also typically require a relatively large amount of floor space and cycle time to process a required volume of parts. Robotic cleaning systems use less water at higher pressure without heating or special agents. Just as with stripping or shell removal, the robots direct the water blast stream, precisely controlling the path, orientation, stand off and dwell time. In some cases the robot orients the part over a fixed nozzle and in some cases the robot orients the nozzle over the part. One advantage of the robot manipulating the part is that it also takes care of the extra material handling step of loading and unloading the part.
In many cases, these machined components are going into automotive, machinery, aircraft or other assemblies; assuring a high level of cleanliness is imperative. The early adopters who have converted to robotic cleaning technology have found that these cleaning systems provide a more consistent level of cleanliness than their legacy hard automation systems. In many cases, these customers have been able to eliminate costly chemical cleaning agents and greatly reduce their water and energy consumption.
Future Opportunities
The total market for cleaning systems is quite big, and robots have barely scratched the surface. There is no doubt that new markets will continue to open up, and additional cleaning technologies will find opportunities with robots. The following economic drivers are too strong to not eventually open up new opportunities.
• Lower water and energy usage
• Higher, more consistent levels of cleanliness
• Reduced cycle time
• Run batch size of 1
• Chemical and waste disposal
• Safer, simpler jobs for workers
• Reduced damage to parts
• Reduced equipment footprint
Any plant considering robotics as an alternative for its cleaning process should first find an experienced robotic system integrator or other automation partner. Even if requirements don’t exactly match what is commercially available, an experienced integrator can work to find the best approach to meet those requirements within any budget constraints.
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