Newsletter 161: Marking Delrin Cases, Degating Acrylic Buttons, Marking Stainless Steel

SYNRAD, INC. - http://www.synrad.com
Thursday, May 03, 2007
Issue 161


Marking Polyoxymethylene (Delrin) Cases	Degating Acrylic Keypad Buttons	Marking Stainless Steel

SYNRAD's sealed CO2 lasers are used in a variety of industrial processes including cutting, welding, drilling, and marking. This news brief showcases some of the interesting materials and products that are processed daily by Synrad's line of CO2 lasers and marking heads.

Marking Polyoxymethylene (Delrin) Cases

Polyoxymethylene, also known as acetal resin and sold under the trade name Delrin®, is easily molded to form a variety of products. In this example, the injection-molded Delrin is shaped to encase a Light Emitting Diode (LED). The marking requirement for these cases is to lase a four-digit code, readable under a microscope, to aid product traceability. This is a relatively easy task as CO2 lasers produce a nicely engraved mark on most plastics; however, because the customer uses a swatch of green ink to mark the cathode (negative side) of each LED case, we were able to obtain highly contrasting text marks that are readable by the naked eye.

What makes this application special is that a very small character height of only 0.51 mm (0.020”) is required in order to fit the four-digit text string onto the 2.7 mm (0.108") wide LED body. To accomplish this task, we setup a 48 Series 10 W sealed CO2 laser and an FH Series marking head fitted with an 80 mm focusing lens. The 80 mm lens provides a 116-micron (0.005”) spot size with a 0.8 mm (0.032”) depth of focus.

This 0.020” high, easily readable text string
was marked using 6 watts of power at a speed
of 15 inches per second in a cycle time of 60 milliseconds per part.

Using our WinMark Pro laser marking software, we choose one of WinMark Pro’s built-in stroke fonts and created a four-digit text object. Text Height was set to 0.51 mm (0.02”) with 0.38 mm (0.015”) of Extra Character Spacing. We set Power, duty cycle percentage, to a value that corresponds to 6 watts, Velocity to 381 millimeters per second (15 in/sec), and Resolution to 750. Cycle time for this very small mark is a fast 60 milliseconds (0.060 seconds).

Although the 0.020” high characters are just legible without the aid of a loupe or magnifier (and easily readable under magnification), this text size is about the minimum obtainable with an 80 mm lens. As a rule, minimum text height should be approximately four to seven times the spot size of the lens. This ratio ensures that the beam diameter isn’t large enough that it fills the space between the strokes that form each individual character.

Degating Acrylic Keypad Buttons

Traditional injection molding processes create parts that are attached to a gate or sprue in the mold. The sprue is removed, ideally at or near the injection mold, so excess material can be reground, remelted, and reused. This process is performed using knives—either manually or robotically— punch presses, pneumatic cutters, or lasers. There are several important benefits to using lasers: first, the laser can be reprogrammed quickly and easily to degate new products or redesigned parts; and two, laser degating is a thermal process that tends to produce smooth edges versus mechanical methods that may leave a sharp edge at the trim point. With lasers, beam delivery to the part surface is accomplished using fixed or flying optics, by moving the laser, by moving the part, or by galvanometer beam steering.

In this application test, 1.21-mm thick (0.048”) keypad buttons were cleanly degated using a SYNRAD sealed CO2 laser and FH Series marking head for beam delivery. The FH head was equipped with a 200 mm lens that creates a 290-micron (0.011”) diameter spot with a 5 mm (0.196”) depth of focus. Using our WinMark Pro laser marking software, we drew a circle matching the radius of the keypad buttons and then modified Arc Start and Arc End properties to create an arc of the correct length and orientation to trim each button away from the molded runner/gate assembly.

For each Arc object, we set a Power, duty cycle percentage, equivalent to 50 watts and set a degating Velocity of 203 millimeters per second (8 inches/sec). Based on a cycle time of 80 milliseconds (0.080 sec) per cut, the overall time required to trim each individual button (2 cuts total) is 160 milliseconds.

This keypad button was trimmed from the
molding sprue using 50 watts of power at
a cut speed of 8 inches per second in a
cycle time of 0.080 seconds per cut.

This photograph shows an array of keypad
buttons on sprues as they look when ejected
from the molding machine. Also shown is an individual button that has been laser degated.

Marking Stainless Steel

This stainless steel demonstration piece illustrates the versatility of CO2 laser marking using our WinMark Pro laser marking software. By combining a Synrad laser, an FH Series marking head, and WinMark Pro software, you can create any number of text, graphic, and 1D or 2D barcodes. This particular sample file combines 2D Data Matrix codes, imported EPS graphics, a CAD drawing, stroke text, and filled TrueType® text.

The large 2D Data Matrix code measures only 10 mm (0.394”) square, yet it contains 125 characters. This 9-mil code (where each individual cell measures 0.009” square) was marked using 110 watts at a Velocity of 381 millimeters per second (15 inches per second or IPS). We set the 2D Barcode Bitmap property to No and 2D Barcode Circle Radius to 75%. The small 2D code is a 7-mil code using the same mark parameters. Both 2D codes meet the Unique Identification requirement calling for an overall AIM (Association for Automatic Identification and Mobility Standard) grade of “B” or better.

All the 2D codes, text, and graphic images on
this 3.375" x 2.125" stainless steel coupon were marked with 110 watts of power from a SYNRAD
CO2 laser in a cycle time of 29.81 seconds.

The Washington state outline, an encapsulated postscript (EPS) file, and the interlocking gears, an AutoCAD® drawing interchange (DXF) file, were imported into WinMark Pro, then positioned and resized. Both graphics were marked using 110 watts at a Velocity of 15 IPS. Resolution was set to 750 for the state outline and to 300 for the gears.

The stroke text in the center of the larger gear was created in WinMark Pro with a Text Height of 1.5 mm (0.0591”) and a Text Radius of 4.0 mm (0.575”). These text objects were marked with 110 watts at a Velocity of 15 IPS. All other stroke text was marked with 110 watts of power at a Velocity of 5 IPS and a Resolution value of 750.

The filled TrueType text objects, created using Times New Roman and Arial fonts, were marked with 110 watts at 10 IPS using a Resolution of 300. WinMark Pro is able to mark any TrueType font that is loaded into your computer’s Fonts folder. TrueType fonts can be filled (raster marked) or simply outlined (vector marked) and can also be italicized or bolded.

Using the parameters described above, the large 125-character 2D code marked in 2.69 seconds; the smaller 26-character 2D code marked in 0.64 seconds. Overall cycle time for the entire image – text, barcodes, and graphic images was 29.81 seconds.

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Synrad, Inc.

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Mukilteo, WA 98275

Tel: 1-425-349-3500

Fax: 1-425-349-3667

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