Direct Part Marking on Stainless Steel with CO2 Lasers

Many large manufacturers as well as the Department of Defense now specify direct part marking (DPM) of components and even sub-components so that each piece has a unique identity that is a permanent part of the component. Although there are many methods for marking parts, the best solution for high-throughput manufacturing is laser marking. Laser marking is the most versatile DPM method when it comes to creating permanent marks (marks not affected by normal wear and tear or harsh chemical solvents) that contain data unique to each individual piece speeding by on a conveyor. Despite misconceptions that CO2 lasers are only effective at marking organic or plastic materials, past Applications Newsletters have highlighted many successful marking applications on mild and stainless steel, tool steel, and even titanium. This article highlights one method of using a CO2 laser to directly mark machined stainless steel housings.

Our mark setup consisted of a Firestar t100 laser, FH Flyer marking head, and a copy of our WinMark Pro laser marking software. The Flyer head was fitted with a 125 mm high-power lens that provides a 180-micron (0.007”) spot with a 3 mm (0.118”) depth of focus. The mark consisted of three lines of text for a total of 24 characters. We used a filled TrueType® font, Times New Roman, at a Text Height of 3 mm (0.12”) and also set the Text Outline Filled property to Yes.

The permanent, high-contrast text on this
machined stainless steel component was
directly marked with a Synrad sealed CO2
laser using 87 watts of power at a speed
of 1 inch per second.

This alignment fixture was cut from a sheet of
0.062” thick Delrin using 100 watts of power at
a speed of 200 inches per minute with 20 PSI
of nitrogen assist gas.

Cutting Fired Alumina Ceramic

Alumina, a compound formed from metallic (aluminum metal) and non-metallic (oxygen) elements, is the most common of the structural ceramics—finding widespread use in fields ranging from aerospace to manufacturing. Alumina’s hardness allows it to perform well as an abrasive or as a bearing; its corrosion-resistance makes a perfect lining for refractory vessels or for implantation into the human body; and its material characteristics make it a great thermal or electrical insulator.

The physical properties that give high-hardness ceramics their unique qualities also increase the difficulty of processing them into useful shapes. In particular, alumina’s brittleness and low thermal coefficient of expansion pose a significant challenge to traditional cutting methods. These two challenges however, highlight the areas where CO2 lasers provide distinct advantages over mechanical cutting methods—the laser’s localized heating effect prevents thermal stressing of the ceramic and the non-contact processing prevents fracturing of the alumina. Non-contact laser processing also eliminates maintenance downtime associated with cutting tool replacement.

Depending on the material thickness or end process, you can cut fired alumina directly by through-cutting, or you can cut it indirectly in a two-part process called scribing—drilling a row of blind holes—and then cleaving along the scribed line. When scribing fired alumina, the laser is set at a predetermined power level and externally-gated so that the chosen power level, pulse frequency, and pulse width create a series of drilled holes as shown in the first photo. These holes should extend through 30% to 50% of the material thickness with a spacing between holes of one to two times the hole diameter.

This cross-sectional photograph shows a series
of scribed holes in a fired alumina substrate
after cleaving along the scribe line.







We through-cut this 0.025” thick piece of fired ceramic using 200 watts at a speed of 15 inches
per minute with 60 PSI of air assist. The cut
edge is clean and shows no signs of dross
or underside burring.

The second photo illustrates the result of through-cutting a piece of fired alumina. In this process, the laser is operated conventionally at a specific pulse width modulated (PWM) duty cycle to obtain the desired output power. In this example, we cut a section of 0.64-mm (0.025”) thick fired alumina using 200 watts of power at a speed of 0.4 meters per minute (15 inches/min). To create this clean cut with no dross attachment or underside burring, we setup our beam delivery with a 63.5 mm (2.5”) focusing lens (100 micron spot size with a 0.8 mm depth of focus) and delivered 4.1 bars (60 PSI) of air assist coaxially with the beam through the nozzle.