Improving Machine Inspection Speed And Accuracy
If you are a machinery inspector, you are always looking for new ways to increase your speed and accuracy
. Here are some ways in which you can accomplish this, while keeping the quality of your work at an all-time high.
On-machine inspection using probing technology is gaining popularity, because it delivers shorter cycle Arial, and increases quality and productivity. Driving the growth of on-machine inspection is the shift to flexible machining and automated processing, which helps manufacturers meet the shorter lead times and tighter accuracy specifications the market expects.
Facilitating these shifts are advances in probe technology, improved machine repeatability, and sophisticated computer-aided design and manufacturing software. Traditionally, part verification has been performed offline with a coordinate measuring machine (CMM).
Moving the part offline requires additional setups and part handling, making it a time-consuming process. Inspecting the part with a probe while it is still on the machine tool reduces these nonvalue-added activities.
However, this type of inspection must take into account positioning errors that occur during machining, and are likely to be repeated during the inspection process, because the part is measured on the machine on which it was made.
Laser vector measurement can help resolve these volumetric positioning errors and improve the accuracy of on-machine inspection. Integrated equipment and software can make on-machine inspection a viable process.
Because gage accuracy requires a 4-to-1 ratio, machine-measuring accuracy must be four times more accurate than the specified part accuracy, according to a National Institute of Standards and Technology standard that replaces the previous 10-to-1 ratio requirement. This new technique for volumetric calibration and compensation helps ensure machine tool accuracy.
Computer software uses the measured volumetric positioning errors to generate a lookup correction table to list what errors need to be compensated for, and allows the on-machine measurement software to volumetrically compensate for the machine positioning errors. Additionally, a machine tool operator with minimal or no training can use the technique.
In 2 to 4 hours, a machine operator can measure and compensate volumetric errors for a working volume of about 1-cubic meter. Without the technique, this process can take as long as 16 hours.
The basic concept of the laser vector measurement technique is that the laser beam direction, which is the measurement direction, is not parallel to the motion of the linear axis. Therefore, the measured displacement errors are sensitive to the errors both parallel and perpendicular to the direction of the linear axis.
For example, the measured linear errors are the vector sum of errors projected to the direction of the laser beam, such as the displacement errors that are parallel to the linear axis, the vertical straightness errors that are perpendicular to the linear axis, the horizontal straightness errors that are perpendicular to the linear axis and the vertical straightness error direction. By collecting data with the laser beam pointing in three different diagonal directions, nine different types of errors including linear, pitch, yaw, roll, and square-ness are identified.
Because the errors of each axis of motion are the vector sum of the three perpendicular error components, this measurement is called a vector measurement technique. In conventional body diagonal measurement, the displacement is a straight line along the body diagonal, enabling a laser interferometer to calculate the measurement.
For the vector measurement described here, the displacements are along the X axis, then along the Y axis and then along the Z axis. The trajectory of the target or the retroreflector is not parallel to the diagonal direction.
The deviations from the body diagonal are proportional to the size of the increment. A conventional laser interferometer is unable to make these measurements without being out of alignment, even with an increment of a few millimeters.
A laser Doppler displacement meter, using a single aperture laser head and a flat-mirror as the target, can tolerate large lateral deviation because any lateral movement or movement perpendicular to the normal direction of the flat-mirror will not displace the laser beam, therefore maintaining the alignment. After three movements, the flat-mirror target moves back to the center of the diagonal again, so the size of the flat-mirror only has to be larger than the largest increment.
The flat-mirror target is mounted on the machine spindle and it is perpendicular to the laser beam direction. In a conventional body diagonal measurement, all three axes move simultaneously along a body diagonal and data is collected at each preset increment.
With the vector measurement, all three axes move in sequence along a body diagonal and data is collected after each axis is moved. Therefore, data is collected three times, and errors caused by axis movement are separated.
As you can see, there are ways to speed up your work, while keeping the accuracy you need. Research more methods today to ensure your job is done perfectly.
by: Tom Selwick
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