TACKLING THE TOUGH TRAITS OF TUBES
By Dave Gilmore
Another technique measures the adjoining corner positions at the beginning of the radii once again using the capacitive height sensing device and the nozzle. The result is a hole or feature that is positioned correctly on each face, as designed.
Another calculation that may be performed during a measurement cycle can correct for twist in the tube. Measurements of two points on the surface that you are about to cut can be made across the breadth of the face. The height difference between the two is recognized and the tube is rotated to compensate; adjusting so it becomes truly horizontal at that location.
It is important to remember that both bow and twist in the tube is rarely uniform and repeated measurements are often necessary. Although these calculations take precious time they typically account for only a few seconds per measurement set. However, if the tube is of very poor quality, many measurement cycles may be needed.
WELD SEAM SENSING
One would expect there to be greater consistency in weld seam positioning on tubing, yet this is not the case. Tube manufacturers are free to position the seam wherever their customer wants it, resulting in apparent inconsistencies.
Luckily, most laser tube cutting systems today have the ability to detect weld seams and quickly reposition the tube. This ensures holes and other cut features are positioned on the tube so as to avoid deformities later when the tube is formed or bent. Positioning the weld seam is also helpful for fabricators looking to hide the weld and minimize its visibility for cosmetic reasons, such as in manufacturing of furniture or display cases.
Most tube laser processing systems offer optical sensing cameras that detect contrast in color where the weld seam is located. Though this works for most tube, the sensors can only identify fairly sharp contrast or visible welds. The more difficult it is to see, the more difficult it will be to detect. Other types of detection for weld seams, such as magnetic and eddy-current detection, may be available for integration but are often cost prohibitive or difficult to implement.
TIGHT TOLERANCES: REMEMBER “YOU GET WHAT YOU PAY FOR!”
When visiting customers I often see the materials operators are given to be processed. Even when the designer specified tolerances within a few thousandths, the tubing they intend to use is of poor quality. I have seen tubes with inconsistent sidewalls: convex, concave or a combination of both. Or corner radii that are double the size on one corner compared to the others.
Often, I have seen tubes that have been stored such that severe bowing results or rusted from being stored outside for weeks (lasers are not fond of rust by the way!). And everyone expects finished part accuracy. As a general rule, if the tolerances for the assembly are tight, better quality tube should be used.
Until tubing becomes more consistent in their construction and it is stored and shipped properly to minimize deformation, realize that tube cutting laser systems are often the best technology to correct these real world challenges. By working with customers and educating their designers on the possibilities lasers afford, new “smart” tube designs can be easily created. Cost saving assembly simplifications can be easily achieved so that processing tube no longer is a frustration but simply a wise manufacturing solution.
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About the Author: Dave Gilmore is an applications engineer at TRUMPF Inc., 111 Hyde Road, Farmington Industrial Park, Farmington, CT 06032, 860-255-6046, Fax: 860-255-6421, email@example.com, www.us.trumpf.com.