Air gauging is not what it used to be. It can provide a reliable, highly accurate production measurement system when optical and contact gauging are impractical due to heat, coolant, swarf, and other by-products of manufacturing. Typical air gauge system pressures range from as low as 22psi (low pressure) all the way up to 42psi (high pressure). Using a pressurized air circuit means parts can be introduced in a non-clean state while still allowing accurate repeatable measurement results. This is possible because as the part is being introduced into the air tooling, air bleeding from the measurement jets “blows” all the contaminants away from the measurement surface. If the part is exceptionally dirty, complementary “cleaning” jets can be manufactured into the air tooling for additional pre-measurement blow-off. An additional factor to take into consideration is the inherent difference between low pressure systems (22psi) and high pressure systems (42psi). Low pressure systems require constant air flow (high consumption),Are incapable of being turned off between measurements without losing accuracy, have slower response times, and have smaller measurement ranges. High pressure systems on the other hand, have quite an edge over their low pressure counterparts specifically because of their high pressure state. Higher pressures allow much greater measurement ranges (300µm compared to 200µm), more effective parts cleaning, faster measurement acquisition (up to 4X), and the system can be shut off between measurements without loss of accuracy thereby reducing air consumption while still delivering accurate results. While air gauging in general is much more application specific than say a CMM, one of its core strengths is the interchangeability, or adjustability, of different components for a greater range of flexibility. A good example of this would be connecting rod systems. Using a simple length adjustment block, the center-to-center distance between the pin and crank diameters can be modified, allowing a much greater range of sizes to Be measured. Combine this with interchangeable air tooling and you get a highly flexible machine capable of measuring a wide range of part sizes. Capable of measuring inner diameters as small as 0.8mm (difficult using any other technique), air tooling can be custom-manufactured using single, multiple, or annular air jets to cover the full range of dimensional and geometric measurement characteristics such as: I.D., O.D., average, match, height, edge location, taper, length, width, max, min, class, cylindricity, out of round, symmetry, barrel shape, hour class shape, and perpendicularity. Also, unlike contact gauging which requires fragile “flex fingers” to measure small bore diameters, air tooling has no moving parts thereby circumventing this limitation. With no moving parts, and using simplified designs with wear resistant materials (carbine, TCIN coating, etc), air gauging tooling is typically long-life and can reduce maintenance costs. Resolution and repeatability depend on the style and quality of the manufactured tooling, the type of air jets (round or rectangular), the style and quality of the airto- electronic converters, as-well-as the measured value. Resolutions of 0.01µm are achievable using basic off the shelf equipment. Capable of repeatability =0.1µm (very difficult to achieve through contact style gauging), air gauging consistently proves itself an accurate and robust form of metrology.
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