Thermal Spray Incoming Inspection Dilemma

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Thermal spray coatings quality control functions obviously involve inspection procedures that include incoming, in-process as well as final inspection. The common thermal spray coatings inspection procedures involve metallurgical lab testing, dimensional testing and visual inspection.Visual inspection in most prominent thermal spray coatings facilites takes place in three distinct locations, namely incoming, inprocess and final. In this post, we will limit ourselves only to incoming visual inspection. Incoming visual inspection comprises of inspecting parts for nicks, dents and other damage to the required thermal spray coating area. For example, knife edge seals that are employed in aircraft engines generally get coated with thermal spray abrasive coating combinations of nickel-aluminum followed by aluminum oxide generally by plasma spray techniques. If the knife edge surfaces configurations come in damaged, then there is no point in thermal spraying the parts. Hence incoming visual inspection plays an important role in ensuring that the parts coming in prior to any thermal spray work being performed on them are okay from a visual standpoint. Note that we are not dealing with any dimensional discrepancies at present. Most quality control manuals and instructions usually spell out the procedure for incoming visual inspection whether surfaces shall be examined with the naked eye or under specified magnifications. However, what most quality control manuals and instructions do not specifically address is what happens if the incoming visual inspection reveals that some area that is NOT a required thermal spray coating required location exhibits characteristics of concern. What is the inspector to do then. Obviously, the answer would be to get his supervisor. Okay. But what does the supervisor or QC manager do then. Obviously, the answer would be to contact the customer and let him make the decision as to what to do. However, that is not the end of all problems. If the inspector finds something potentially troubling with any area of the part prior to thermal spray in the incoming inspection department, obviously he or she is to raise a red flag. But then the burning question becomes how much of his time should he spend looking at areas that he is not required to look. This does not seem like a big deal when dealing with small quantities like a few compressor cases to inspect. But imagine doing a one hundred percent visual incoming inspection on a thousand air nozzles or two thousand compressor blades EVERY day. Now all of a sudden, the question of where does the inspector draw the line of where his responsibilities for inspecting to enable subsequent thermal spray operations ends and where his bigger responsibilities for overall part integrity ends, becomes a subject of great debate. Additionally, where does the QC manager draw the line when specifying this limit of responsibility in his quality control manual which then becomes the guideline to follow by everyone in the organization including the incoming visual inspector. This is especially important for thermal spray shops that deal with aircraft or medical components where part liabilities run very high. From a legal liability stand-point, it now becomes extremely important during auditing of ones quality control manual that this set of instructions be very clearly specified and be customer concurrence be clearly obtained. This will avoid a lot of problems later.