Thermal Spray Operation Sheets

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Most thermal spray coatings facilities generate operation sheets to provide instructions for thermal spray masking, plasma and HVOF operators, deburring, inspection criteria and such. These operation sheets that range from simple one page write-ups to very elaborate ones for complex aerospace geometries form the basis for continued reproducible thermal spray processing for the same part when it is received repeatedly as well as forming the basis for a history of how a specific part was processed, should questions arise in the future regarding thermal spray coating quality. Now, one of the biggest complaints that I have heard from thermal spray process engineering teams is that their operation sheets that they have spent hours and hours developing are never read by the operators. I am sure that makes them feel bad. On a lighter note, it is like producing a movie that no one wants to see. On a serious note, this is a problem that many thermal spray shops everywhere face. And put simply, how do you ensure that operators READ the thermal spray operation sheets when performing their tasks? This post is geared towards addressing this very issue.

Operators not reading the process sheets is actually a pretty serious issue and it is the thermal spray quality department who needs to be actively involved in solving it. First of all, there are two basic kinds of operation sheets that can be developed and frankly, I have seen both of them used in service and both seem to have failed to force reading of these sheets. The first kind is the elaborate instruction sheet. Such operation sheets describe in detail, every single step, including basic safety data, precautions, quality requirements, specification requirements and such. These sheets end up running twenty to twenty five pages long for EVERY single part. The second kind is the succinct operation sheets that refer to sets of standard operating procedures as much as possible to reduce redundant instructions. These SOPs, as the standard operating procedures are usually nicknamed, are usually separately maintained and kept outside the realm of the mainstream operation sheet and the operator is asked to refer to these SOPs if he or she has standard questions pertaining to that operation. For example, there might be a SOP designated for grit blasting processing, that will entail how to mix or blend two different grit sizes, how often to use a grit media before changing, how to measure surface roughness after grit blast and so on. Then the main operation sheet will simply specify grit size or blend, pressure and stand off distance together with angle of grit blast.

In either case, if the operator does not read the instructions and goes by “experience” or “gut feeling”, part quality may get seriously affected. Now, the first thing that the quality department needs to do is to insist that operators read the sheets, by conducting operator training. I know, you are probably saying to yourself, that is like asking your kid to not eat candy But that is the first step. The second step is that each traveler that the operator signs off, must have a sign off area for EACH OPERATION, indicating that the corresponding instruction has been read by the operator. This forces the operator to state in a legal manner that he or she DID read the instructions. Signing off on a traveler is a legal act and operators generally do not want to do anything that violates law. The quality department also needs to impress upon the operators that if they sign off stating that they read the instructions and then the part gets processed incorrectly, then they are now liable for having committed two errors and not one and the appropriate actions need to be taken firmly and decisively.

After all, what is the point in writing all of these instructions if no one is going to read them?

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Anonymous said...

So informative and well explained. I am a grad student working on Plasma spray process. I am very thankful to you providing such useful information.

Monaliza Legarto said...

Plasma Spray is a Thermal Spraying Process that uses an arc as a heat source that ionizes an inert gas to melt a coating material which is finally propelled onto the substrate.