A Digital Approach to Machining Better Parts
Sponsored ContentWith advanced integration of CAD/CAM, CNC and probing technology, this digital manufacturing expert demonstrates a better process for making complex airfoils without the need for special fixturing.
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SIXDIGMA is a Cincinnati based company that specializes in advanced integration of CAD/CAM and CNC systems to solve complex machining problems. Their team consists of some of the top talents in design, manufacturing and process development. They also work closely with the CAD/CAM and CNC units of Siemens Digital Industries to provide machining solutions that utilize that company’s formidable digital manufacturing capabilities to develop more efficient and higher quality processes.
SIXDIGMA Founder, Edwin Gasparraj, recently published a video demonstration on how they combined three digital technologies to machine a complex airfoil. It includes:
- Advanced toolpath technologies in CAM to significantly improve surface finish.
- Complex 5-axis probing to accurately locate the part without special fixturing.
- Closed-loop adaptive machining to validate workpiece surfaces and automatically modify individual toolpaths to machine to very high tolerances.
Airfoil machined on a Grob 350 5-axis universal machining center with a Siemens 840D CNC.
All of these capabilities were demonstrated with the airfoil machined on a Grob 350 5-axis universal machining center with a Siemens 840D control. Probing was executed with a BLUM DIGILOG scanning probe, and all part programing was done with Siemens NX CAM software.
The excerpts below provide a brief overview of the technology behind each step. Or, watch the full 12-minute demonstration.
Excellent Finish Begins With the Part Program
Advanced CAM systems are vital to achieving the desired finish in complex parts. Tight tolerances that machinists often need to meet, combined with complex features of an airfoil make it exceedingly difficult to program a toolpath that achieves the desired tolerance with conventional NC programming technologies. Advanced CAM systems are often capable of providing these toolpaths with considerably less effort from the NC programmer and machine operator.
Path smoothing options in advanced CNC machines today deliver much better surface finishes right out of the box. However, small discontinuities in 3D surface geometries can sometimes cause axis reversals that will mar the surface finish of the part.
It's better to avoid axis reversals in a continuous toolpath wherever possible, but they can be very difficult to predict and identify. Siemens 840D control can to that with an onboard trace diagnostics for each axis. And it can monitor a variety of machine parameters using this trace function.
NX CAM has a vast array of tool axis and projection options, allowing you to generate any toolpath and tool axes to correct issues identified by Siemens 840D. Additionally, the integrated G-code-driven simulation in NX CAM enables an accurate digital validation that eliminates any possible errors on the machine, which is critical for complex parts like airfoils. As shown in the video demonstration, in the case of this airfoil part the result is a smooth surface that requires no further manual polishing. The tolerance of the part is maintained well under one thousandths of an inch.
Locating Complex Part Surfaces Automatically
Airfoil machining requires very accurate positioning of surface locations on the part. That would typically require a complex fixture to locate the six- point datum nest of the part. Instead, with SIXDIGMA’s method, the part is placed in a simple vise, probed, and the location data is processed by the CNC. The SIXDIGMA’s software then computes a new alignment and mathematically assigns the alignment to the fixture offset of the part.
After the initial alignment routine is run individual surface points can still be off by 0.060” or more, so the part is probed again to fine-tune measurements and readjust workpiece offsets. After this second probing cycle, actual part surfaces can be established within a few microns which enables extremely accurate machining measured in “tenths” of an inch as well as superior surface finish.
Because of the perfect alignment in all six degrees of freedom, SIXDIGMA is able to demonstrate re-machining 0.001” off an already machined airfoil. Being able to exactly locate the part has many applications such as airfoil repair, being able to correct coatings and being able to machine the datum surfaces of ECM cast or forged parts. This is also very useful in centering 3D printed parts inside the intended volume and machine its datum surfaces.
Closed-Loop Adaptive Machining
Another issue that can impact accuracy are variations in the surface geometry from part to part. That means it may be necessary to correct individual toolpaths within the part program because the variation may only be present is certain areas of any given workpiece.
BLUM’s Digilog scanning probe is used here to discover the variations, and the is data is fed back to the Sinumerik 840D control. Toolpaths can now be corrected down to the individual X-Y-Z coordinate points to compensate. So while there may be geometry variations from part to part, there will still be extremely high consistency and accuracy after each part is machined.
With accurate machine tools, and by bringing together Siemens’ CAM, post processor, G-code-driven simulation, and CNC controllers, SIXDIGMA can maintain very tight tolerances even on large parts. The digitally connected solution enables the company to maintain less than 0.0001” tolerance on a part that's a few inches long and less than 0.001” tolerance even on parts up to three feet long.
This accuracy is very much enabled by the amount of data being collected and the speed at which this data is processed behind the scenes. Moreover, the close integration between Siemens’ NX CAM software and Sinumerik 840D control allows SIXDIGMA to generate complex toolpaths and produce excellent surface finish on tight tolerance parts.
