How to Improve Accuracy and Precision in CNC Machining
Precision in processing is the most critical attribute of any technological equipment, particularly in the work at hand – a CNC machine tool. We define processing precision as the degree to which the parameters of the manufactured part align to their nominal values. As you are probably aware, enhancing the accuracy of manufacturing components extends the life of machines and equipment. We frequently associate machining center accuracy and precision with the machine’s movements. That is, the machine’s accuracy is a built-in feature. Specific machines are more precise than others, just as certain machines have a longer journey than others. This is a partially accurate statement. The CNC machining center accuracy, however, is also a component of a system. The machine is configured and operated in a specific manner. It exists in an environment that is subject to change in terms of temperature, among other variables. Additionally, the machine is a system in and of itself—composed of moving components that interact dynamically. All of these effects contribute to the CNC machining precision and thus must be considered.
This article explicitly covers some crucial points in optimizing CNC machining accuracy and precision. For instance, how well is your machining center leveled? How is the spindle tram faring? Take a look at these steps next on how to increase the accuracy and precision of your CNC machining center.
1. Recognize the spindle in CNC machining
Do you adjust the tool offset in response to variations in spindle speed?
Users of machining centers are less inclined to adjust tool offsets in this manner; instead, they treat the tooltip placement as static. However, it takes little reflection to realize the folly in this. Different spindle speeds result in varying temperatures and centrifugal forces inside that spindle. The spindle responds to some extent to these alterations. As a result, a natural first step toward tighter tolerances is familiarizing oneself with the spindle’s behavior.
A straightforward method to accomplish this is to experiment with changing the tooltip position. This information can be obtained by measuring a gauge pin in the spindle at various rpm values. After then, tool offsets can be corrected for varying speeds.
2. Suppress chatter
Chatter can be decreased by increasing the rigidity of the setup and tooling. Additionally, chatter can be eliminated by determining a spindle speed at which the rate of cutting edge hits is in phase with the system’s inherent frequency.
While diagnostic tools are available for determining the harmonic spindle speeds of specific milling runs, these optimal speeds can also be determined through test cutting. Not only does achieving a quieter cut increase the machine’s precision for smooth surfaces and sensitive details, but it also enables the machine to remove more metal.
3. Assess the process rather than component
Inspections are typically conducted after work has been completed, implying that the gauge essentially polices the process. An approach is, to begin with, measurement—gauging the process rather than the component. In other words, identify potential mistakes in the process and eliminate them before starting the precision CNC machining services. To be sure, there could be other sources of these errors. A three-axis machining center has twenty-one degrees of freedom or twenty-one possible points of error. That is prior to the addition of tooling and work-holding. Nonetheless, the number of possible sources of inaccuracy is minimal. Both mechanical and probable user error sources can be discovered and addressed, and repaired sequentially. Simply recognizing that a process can be improved in this manner is frequently a vital first step toward establishing a method that requires less post-process gauging.
4. Conduct an inspection with a reference
Is it possible for a machining center equipped with a measurement probe to perform self-inspection? The answer appears to be “no,” because any thermal anomaly introduced during the processing pass would impair the machine’s measurement capability. Nonetheless, some users of machining centers overcome this constraint.
A tried-and-true method for accomplishing this in CNC machining services is to incorporate a known reference item within the machining zone. Suppose the calibrated reference item is constructed of the same material as the machined part and similar geometry. In that case, the reference object can be used to capture any measurement mistake. The error would be the difference between the known and measured values of a reference dimension. This discrepancy can then be utilized as a correction factor to update and correct the machine’s measurement of a similar size to the genuine part.
By doing so, the machine may inspect its work. Perhaps more importantly, this allows the machine to adjust its location and maintain precision during a production cycle where part and machine position errors might otherwise creep in.