Documenting the Measuring Process

Statistical quality control (SQC) has been in use since the 1930s, when it was performed with paper, pencil, and maybe a slide rule.  As such, it was originally somewhat time consuming, and it required a fairly high level of care and understanding on the part of its practitioners.  SQC got a big boost in the 1970s and '80s, when electronic gages, data loggers, and PCs began to proliferate.  Suddenly, untrained line inspectors could easily perform the necessary calculations, without really understanding the process.

Many instructors using SQC as part of the measuring process insisted that inspectors and machine operators should learn to do SQC manually before they plug in their data loggers. This was under the general principle that people who understand what they're doing tend to do a better job.  This is a totally understandable concept – until of course, the production manager gets involved.

Machinist today are often very skilled and highly trained users of complex and powerful machine tools. These machine tools are far more powerful and complex than they were a generation ago. In many cases, they can be more brain than brawn, and the users are often part CNC programmer as well as a production machinist. It can be a stretch to try and train these same skilled machinist to also be quality control inspectors and SPC [JC1] analysts. Their skill and job is to produce parts and as quickly as possible and ensure that the parts coming off their machines are good.  The focus is production – and when the process is running well, the goal is that quality is built in.

However. it is important in a many industries to have verification that the process is under control and to verify that the parts coming off the machine are within the design tolerances. Thus, these machinists will be required to do some inspection to verify their process. Any final part inspection should therefore be easy and fast for the machinist, not taking time from production, requiring little added skills or processes. In effect, the inspection of the part needs to be simple and when documenting the results, the data collection has to be not only transparent to the user, but it also reliable and accurate.

As data collection techniques have advanced over the years, more steps are being implemented in the process—and sometimes even into the gaging equipment—to ensure that the data being collected is correct. By putting into the hands of the operator, gaging that allows for ease of use as well as easy and reliable data collection will go a long way into being easily implemented.

One of the first steps in implanting transparent data collection to the machinist was the effort to make the tools as simple as possible for the user. For example, you don’t want to train a machinist to be a surface finish inspector.  Rather, the goal is to design surface finish tools to be as simple to use as possible with automatic sensing of set up parameters and simple one button operation. And one does not want the user doing complex set up alignments that take up production time or potentially damage sensitive equipment. Special featuring can help ease the actual measuring process and really become that one button operation.

The same goes with many of the hand tools today. With the integration of wireless data transmission, the act of collecting data for documentation or SPC[JC2]   is just as simple as measuring the part. No add on boxes or cables to get hooked or tangle during the process. Ease of use makes it simple for the user.

Most SPC/SQC programs have features built in that collect and record the data to the files for process control or documentation. They inherently will also record the date and time, to the second that the measurement was made. But there is one bit of this information during this measurement process that is often overlooked and, in the end, it could be one of the most important. 

The missing link often is the recording of the information about the device making the measurement. In most processes the measurement data is recorded, as is the date and time the measurement was made – but rarely is the instrument that made the measurement is tracked with the stored data.

Certainly most facilities have a gage tracking system that identifies the gage making the measurement and its calibration status. But very rarely is this information tracked as part of the part specific measuring process. This seems like a critical piece of information. There are new standards being set that will require not only the measurements and the time it was collected to be recorded , but a gage serial number identifier will also be required to complete the data.  In an effort to meet this demand, gages are starting to include the ability to send out a unique gage identifier with the measurement data.

Now the data collection and documentation process is complete – the quality analyst is satisfied because they have the complete story of the part dimension – the measurement data, when it was take and by what measuring device, with the unique identifier of the measuring device tagged..

The gaging data is compete and it is traceable.