This application was to cut a progressive spiral in a 316L stainless steel tube that was to be used as a catheter.

DLI participated in this project from the R&D/prototyping phase and into production at the rate of 2000 parts/month. The tubes were 1215 +/- 1mm long with an outer diameter of .73mm and a wall thickness of .075mm. A spiral was cut into the last 31.416mm of the tube. The angle of the spiral changed three times (four angles total) during the cut. The kerf width was .11mm +.03/-.00mm. The locational tolerance on each section of the spiral was +/- .05mm. Please see the photos below.

Parts were cut using a pulsed Nd:YAG laser system with an X-Y linear motor motion system coupled with a direct drive rotary axis. A 50mm focal length was used and the beam diameter was 25µm.

There were several major challenges. The first was programming the motion system to allow for the smooth transition from one spiral angle to the next. This needed to be a generic program that allowed us to vary both the length and angle of each spiral section as the customer wanted to be able to try different designs during the R&D phase. The laser spot size was smaller than the required kerf. This meant that the spiral had to be cut twice with the appropriate offset between the two spirals that resulted in the required final kerf.

A Directed Light application engineer wrote this program using the G-code recognized by our Anorad CNC 2000 controller. Several proprietary algorithms were developed for this program that allows DLI to cut not only progressive spirals, but any shape on the surface of a tube.

The second was supporting the part during the cutting process. This is a long, very flexible tube, and we were cutting a spring on the end of it. It was imperative that the end of the part not move out of alignment in either the radial or axial direction as it was being cut.

This challenge had a two-fold solution. First, the cutting sequence of the two spirals was investigated to see which provided the most stability. Experiments demonstrated that cutting the first spiral from the end into the body of the tube, offsetting the beam at this point, and cutting the second spiral from the body back to the end provided the most cut stability. We also left 5mm on the end of the tube to add to the stiffness. The final operation was to cut this piece off while cutting the tube to length.

The second part of the solution was the tooling used to support the part during the cut. A V-block was used with a width and depth selected so that when in the groove, the top of the tube was even with the top of the V-block. A ring was attached to the nozzle assembly with a pad that rode on top of the V-block. This pad not prevents the tube from escaping the V-block, but is also designed to set the required height of the cutting nozzle from the top of the tube. Please see the diagram below:

The third major challenge was to cut through the tube wall without creating any burn marks on the inside of the wall opposite the cut. This was accomplished by using a beam expansion of 8X into a 50mm diameter focusing lens with a focal length of 50mm. This gave us both a small spot size and a very small depth of focus. The beam focus was adjusted so that it just cuts through the wall of the tube without marking the opposite wall.