Submicron Measurement at the Point of Manufacture
Universal measuring machines can help qualify parts as they are made.
We all are aware of the challenges we face in trying to manufacture today’s ever more technical products. New levels of manufacturing are also making the requirements for precision measurement more and more profound. The current shift is toward submicron measurement, and not just in the measurement center. Now we need that level of precision as close to the point of manufacture as possible.
The simple fact is, when your shop has ultra-high-precision machining centers and grinders that cost hundreds of thousands of dollars and are being run by highly skilled machinists, it is a very costly exercise to take a part off the machine, bring it to the lab, wait for it and a gage block stack to normalize to ambient temperature, and then make a measurement. In the meantime, the machine sits idle. It can’t be broken down to run another part because it’s dedicated to the part it is in the process of making. Idle machines mean lost productivity.
Fortunately, submicron measurement on the shop floor is more feasible in today’s ultra-high-precision shop, because the investment for it has already been made. Before that multiple-hundred-thousand-dollar machine was put in place, there had to have been a substantial investment made in creating the controlled environment necessary for such a machine to meet its performance expectations. Environmental conditions affect the manufacturing process the same way they affect dimensional measurements. Eliminating temperature variations in the environment is the basis for starting to manufacture to submicrons. This goes beyond ensuring the room temperature is controlled; it even extends to controlling the effects of motors and coolant in the machine.
Since you’ve already made this investment in a controlled environment, you probably have the foundation for bringing a universal measuring machine to the point of manufacture. A universal measuring machine is a stationary instrument that has its own standard (a high-precision scale) built in and is designed to make submicron measurements. This means it is robust and stable enough for submicron measurement, and is designed to eliminate the effects of Abbé error. Many grades of universal measuring machines are available, including those with measuring capabilities of 0.5 to 0.01 micron or better for gage block, and master-setting ring or disc measurement. In most cases, the manufacturing environment for machining is not stringent enough for such lab-grade measuring machines, but there is certainly a class of measuring machine available to meet the performance requirements for your particular precision-manufacturing operation.
The first task then is to research and select the universal measuring machine that best fits the expected manufacturing capability. This means not only matching it in terms of precision, but bettering it by a factor of at least five.
Then, just as you made the evaluation of where to put the manufacturing machine for best performance and environmental control, the same should be done for the universal measuring machine. A careful study must be made to identify potential hot and cold spots, as any quick temperature change is going to be read by the measuring machine—universal measuring machines are not only designed to measure dimensions very accurately, they are also great indicators of temperature.
This means you also must understand the airflow and convection patterns in your production area. What happens when the doors open and close, and even what type of lighting is in the room? Then there is the issue of vibration. Will there be a lot of foot traffic going by? Are there coolant motors or other machines in close proximity? As I mentioned earlier, the same environmental conditions that affect the machine will also affect the universal measurement machine—but even more so. This may require a table with side walls around the machine to help control drafts or even a four-sided enclosure to prevent sudden temperature changes. The good news is that these are relatively easy measures that make big increases in performance.
Once you are set up and the machining process is good, and you have developed a process to monitor your measurements so that they closely relate to those you achieve in your measurement center, you’re still not done. Another issue sneaks up before you know it. With machining going on, there is apt to be coolant mist in the air, even with the best air control system. Even when the machine is being changed over to another part or being cleaned, contamination can become airborne and find its way to the universal measuring machine. Thus, it is critical that the gage and its tools are wiped down every night, and sometimes even between measurements.
Submicron machining is the way of the future, and the challenges will only become greater. Today’s universal measuring machines are up to the challenge and can help you qualify parts as they are made. Just remember that it’s important to apply the same environmental consideration and controls to both manufacturing machines and measuring machines.
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