Precision Metal Milling : Several Crucial Points You Must Know

Precision Metal Milling : Several Crucial Points You Must Know

For prototype and end-use components, precision constitutes a highly significant aspect in metalworking. Accuracy implies obtaining a part that appears and feels precisely as you have designed it, without any errors that might impact the mechanical functionality.
Thanks to the emergence of CNC machine tools, metalworking has now achieved a higher level of precision than ever before. Mechanics can utilize the computer to program the cutting tool's trajectory down to the micrometer. Inaccuracies resulting from human errors are almost eliminated. As long as the CNC machine is configured correctly, it is supposed to cut metal parts with high precision.
However, numerous factors influence the precision of metal processing. Machine quality, material selection, and even room temperature can all play a role.
This article discusses the details of precision metalworking and elaborates on the concepts of precision, accuracy, and tolerance.

What is machining accuracy?
Although "precision" and "accuracy" seem to be synonyms, they have distinct meanings in the field of processing. Hence, it is crucial to comprehend the implications of these different terms.
In the context of metalworking, accuracy refers to the extent to which a machine can align with the measured values stipulated in the design.
If the machine can precisely cut the exact position specified in the design, then it demonstrates a high degree of accuracy.
If it occasionally misses the target but hits the right spot on average, we can still assert that it has a relatively high degree of accuracy.
However, the key point is that a superior CNC machine will not merely be average...
What is machining repeatability or machining accuracy?
Machining accuracy pertains to the similarity of measured values among multiple attempts or multiple copies of a component.
In other words, if a machine precisely hits the same point in 100 copies of a component, it possesses high accuracy.
This is distinct from precision because precision is not particularly concerned with whether the "point" is the same as stipulated in the design! A machine can be highly precise even if it consistently cuts 3 mm to the left of the intended mark.
Evidently, it is significant to have both accuracy and precision.
Accuracy implies reaching the coordinates specified in the design, while precision indicates consistently hitting them on multiple units.

What are machining tolerances

In machining, tolerance refers to the cutting

The deviation between the values. Therefore, it is related to precision, but it is a value specified by the customer, not a property of the machine itself.

If the customer requires a feature of the part to be very consistent across the units, they will specify strict tolerances on that feature to allow for minimal deviations. In practice, this means that machines must be operated more slowly and carefully.

If looser tolerances are specified - for example on non-mechanical features - machining can be carried out more quickly.

Although the tolerances are defined by the customer, the machine usually specifies its standard tolerances

And the lowest possible tolerance.

What contributes to the accuracy of CNC machines?

The accuracy of a CNC machine depends on several factors, some of which are determined by the manufacturer of the CNC machine, and some of which can be controlled by the mechanic.

In order to achieve accurate metal machining, the following factors must be considered:

Machine quality: Sophisticated machines with high-quality components will usually produce more accurate parts than low-quality machines.

Machine condition: CNC machines contain countless components, so proper maintenance is crucial to keeping them accurate.

Tool condition: Passivation and worn tools that show signs of back tool face wear, crescent wear, etc., can reduce the accuracy of CNC machines, so they must be kept in good condition. Dull tools also increase the cutting temperature, which is another factor that reduces accuracy.

On-board inspection: Feedback tools such as on-board probes can tell the mechanic whether the machine is cutting accurately during operation. These tools can also be used to correct any deviations in real time, improving accuracy.

Temperature and humidity: The working environment will affect the machining accuracy. Although the machine is capable of cutting parts in warm conditions, thermal consistency must be maintained to avoid deviation.

Calibration: The machine should be calibrated regularly to maintain accuracy.

( Claire@proto-mold.com ).