How to Use Probing (Surface Mapping) in High Speed Machining

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Probe_Edge_Finding
CNC Probe locates the centers of holes and bosses and performs edge finding for quick part referencing.

Probing is one of the features available on DATRON high speed milling machines that earn our German engineers the greatest accolades.  But many machinists coming from traditional backgrounds using conventional CNC equipment are not certain how to employ this function in their applications and are unaware of the ultimate benefits of surface mapping and 3D probing. A CNC probe is an instrument that can measure a material’s surface by contact. The measurements can be used to ensure uniform depth of milling and engraving.

In a perfect world, the material blanks that we receive from vendors would be perfectly flat – a starting point that would help to guarantee that our finished milled parts will be characterized by uniformity. In reality, this just isn’t the case.  For example, two pieces of ½ inch 6061 aluminum from a single vendor could vary in actual depth from one another. There could even be a variance of depth from one end of the blank to the other, or multiple peaks and valleys over the entire surface of the sheet. With some applications, a variance of thousandths or microns may not make a difference to the manufacturer. But for many manufacturers producing parts for aerospace, electronics and medical, tight tolerance is required and accuracy is critical to their success. So the premise for surface mapping in CNC milling is that a machining center with an integrated probe can take measurements at various intervals or locations (custom matrices) across the surface of the material blank, feed that data into the control software and adjust the milling program accordingly to maintain an even depth of cut regardless of the blank’s innate surface variance.  This is all done dynamically, before the milling even begins which helps to minimize waste and maintain part uniformity. But not all parts are flat and therefore they don’t begin with a flat work piece like sheet material.  These parts may begin with rounded blanks like bar stock.  In the case of firearm manufacturing, gun companies often have to machine on rounded parts like steel gun barrels, or curved parts like gun receivers made of metals such as steel and aluminum.

CNC Probe integrated on DATRON high-speed milling machines for surface scanning, part position referencing, accuracy and part uniformity.
The DATRON CNC Probe for surface mapping detects and compensates for irregular material surfaces.

An example of this would be engraving serial numbers, which is a process that is regulated by the ATF (Alcohol, Tabaco and Firearms) because they mandate that serial numbers are engraved at a particular depth (currently 0.003”) to make it harder for them to be honed off for use in criminal activity.

For milling or engraving on rounded surfaces, a probe like DATRON’s Z-Correction Probe is required and in many cases a rotary axis is also necessary. To machine round stock or engrave on round work-pieces, the 4th axis provides the necessary flexibility. The 4th axis integrates virtually seamlessly with the CNC machining control. The 4th axis can be used to substitute either the X or the Y axis, and can be dynamically switched under program control. The 4th and 5th axis together provide the flexibility needed for the most complex work-pieces. The 5th axis is used to independently rotate the 4th axis, each axis independently and dynamically controlled by the appropriate machining program. As a result, machining at an angle on a round part is easily accomplished.

But, there are still more great uses for an integrated CNC probe.  Take part identification or part location for example. Part identification is when the probe takes measurements to determine which blank has been set up so that it can automatically run the appropriate milling program. This strategy is often used by manufacturers who have a variety of similar but different parts to produce.  Again, using firearm manufacturing as an example, 1911 hanguns often have similar size and shape but come in a variety of different calibers – from 9mm, 45 mm etc.  So, if the manufacturer uses a milling machine with integrated probing for part identification, even if the machine operator places the wrong blank in the machine, the machine can be programed to run the program appropriate for that particular part.  This eliminates waste, and in this heavily regulated industry that eliminates headaches as well.

In terms of part location, a machine such as the DATRON M8Cube with integrated probing and the 3D Probe Extension can probe features unique to a particular part to determine the exact position and placement of that part on the machining table. This includes finding centers of holes and bosses, edge finding and pre-measuring blanks before the machining starts. The 3D-Probe extension enables the Z-Correction Probe to function in three dimensions. Intuitive programming allows machining programs to adjust themselves to the particular work-piece on the machining bed. Material variations in X, Y, and Z can be compensated dynamically to maintain part quality and uniformity. For further quality control, work pieces can be checked after machining almost like a built in CMM (Coordinate Measuring Machine). Finally, don’t tell your competitors, but, certain parts can even be probed for the purpose of reverse engineering.

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steve.carter@datron.com'

About the Author

Steve Carter is the Brand Manager at DATRON Dynamics and has been with the company for 11 years. His writing on high-speed machining has been published in trade magazines such as Aerospace Design & Manufacturing, Modern Applications News, Manufacturing Engineering and Tooling & Production.

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