Drilling Processes Inspection

The efficiency of gas turbines is limited by the maximum allowable turbine inlet temperature (TIT). The TIT may be increased by cooling of the blades and vanes of the high pressure turbine. Cooling channels can be casted into the components or may be drilled afterwards. Non-conventional processes like EDM, ECD or Laser are used for drilling. Radiographic examination of the drilled components is part of the inspection procedure. Traditional X-Ray film technique has been used. The consumable costs, the waste disposal and the limited capacity of the two film units lead to the decision to investigate the alternative of Real-Time X-Ray. 

Process capability is shop specific. Each shop needs its own process capability database of its own before process planning can be done automatically. Collecting and analyzing capability data can be tedious. Some of these data can be collected through inspection, such as from the control charts. Others require experiments on the machines. Most of the processes that remove material quickly, such as milling, drilling, and turning, create poorer surface finish and accuracy. 

A routing sheet for the BOM example above is given below in Table 9.2. The path that the part is to follow is given in the left hand column. In this example there are five operations needed. The first and second operations occur at work center 100. The estimated time needed for both set-up and processing is given. The first step is to unpack the component and the second is to clean and inspect it. The third operation is to put 3 of the parts into a jig and to weld them together. The fourth operation is to inspect the component again. The fifth operation is to drill 3 holes. 

A quality control operation is performed after the components are cut and fused. The replacement of faulty components is more convenient at this stage as it does not affect the previously finished cutting process, or the forthcoming sewing process. AH the cut components are inspected and the following quality parameters are controlled fabric quality the conformity of the size and shape of cut components to their pattern pieces the quality of notches and drill marks. 

After the manual cutting process, the quality of notches and drill marks is inspected. Their placement is compared with the corresponding marks in the pattern pieces. If inaccurately placed notches or drill marks are found during inspection, the components are taken out of the bundles and sent to be recut. After automated cutting the control of notches and drill marks is not performed as the process ensures high cutting precision. 

The point of a postdrilling inspection process is that if one takes the time on a regular basis, to examine materials and drill bits after drilling, many driUing problems would be solved before they get out of hand. 

I was involved in looking at how an oil pipeline had internal corrosion and unexpectedly failed, leaking crude oil onto an environmentally sensitive area. The economics of oil drilling had changed, and the producer started injecting more and more seawater into old wells to get as much oil out of the well as possible. This is a common practice for mature wells. The problem was that no one had sufficiently studied the implications and understood that maintenance and inspection frequencies had to be increased to account for the much more corrosive operating environment from so much seawater added to the process. 

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