Cutting Plastic Co2 Laser with Fixed Beam Systems
In previous articles, we have discussed Co2 automation cutting plastic, with galvo based beam delivery systems. Sometimes it is necessary or preferred to cut plastic with a fixed beam system.
The use of fixed beam laser delivery over galvo based beam delivery can be driven by several different factors:
- Laser beam spot size – Sometimes to effectively cut plastic a smaller laser spot size is required with a fixed beam systems. A smaller spot size is more efficient by eliminating burning, charging, melted appearance, and raised rounded shoulders.
- Smaller beam spot sizes-With galvo lasers, the energy is concentrated in a spot (actual physical size of the beam on the product) ranging for 200µm to 1000µm.
- Fixed beam Systems– On the other hand, fixed beams can produce spot sizes as small as 25µm, which obviously then is a much smaller area into which the power is concentrated.
- As an example, assume you have a 100w Co2 series, the energy density of 100 watts in an area of 25µm is much greater than the energy density of 100 watts in an area of 200µm. The greater energy density allows the laser to more quickly and successful cut the products and produce a cleaner more acceptable appearance on the product.
- Air Assist – Some plastics, when cut, require air assist. This was used regarding a recently WLSC applications lab process discussed below. Air assist creates a cleaner, faster, more acceptable cut, by blowing away and preventing reforming of melted material. As well as cooling the product being cut. In some cases, the air assist can be nitrogen, instead of compressed air. The nitrogen has the effect of removing oxygen from the cutting area and can reduce or completely eliminate burning and charring of the cut products. Air assist can be used a various PSI levels with differing results and some experimentation in the applications lab might be necessary to achieve the best results.
- Cutting area—Galvo series and flying mirror systems are limited in size or area that can be cut. Automaton can eliminate that issue by coupling Co2 systems with x-y tables, walking beams, and assembly belts so that the cutting area can be increased to virtually any size.
Cutting Plastic Co2 Laser WLSC Applications Lab Report
Discussed in this lab application report is a recent WLSC customer application of Co2 Automation Cutting Plastic, specifically 0.125” thick HDPE. For this application it was necessary to use 150 watts of power with a fixed beam. Experiments were conducted with air assist levels, as well as masking and cutting the HDPE without masks and without air. Successful results were achieved and are detailed below. HDPE (high-density polyethylene) is a thermoplastic, meaning that it melts rather than thermally
decomposes when exposed to heat. This is beneficial because it can be cut easily, without discoloration or charring. The main challenge, when cutting HDPE, is that the molten and vaporized material produced when cutting can redeposit or flow away from the cut to create uneven cut edges. Initial tests with standard coaxial air assist showed that masking the surface helped prevent this by allowing the flowed/redeposit material to be removed along with the mask.
Cutting Plastic Co2 Laser Initial Testing
Cutting test were conducted with 150w of power 2.0” focus distance and .005” spot size. The cuts below were done with one pass and two passes respectively. The heat transfer into the HDPE was too great and an extremely melty appearance in the result. While cutting does successfully take place, the edge quality and surrounding area melt are most likely not acceptable results.
For the next test pictured below, the HDPE was masked in this case with a tape (the mask could also be a permanent metal mask attached to fixtures holding the parts). The cutting results were much better as the edge quality is significantly improved. The material melt and reflow is contained on the mask and when the mask is removed a clean edge appears.
Cutting Plastic Co2 Laser with Fixed Beam Setup
Pictured below is the physical set up for the cutting, with 150 watts of Co2 power delivered via a fixed beam delivery and 3.0” focus distance and spot size of 0.10.”
Cutting Plastic Co2 Laser Results with Air Assist
While use of mask resulted in acceptable edge quality, (the secondary manufacturing process) or step involved in mask removal, is not desirable from a cost and cycle time consideration. An alternative to tape masks that can be permanent are pieces thin metal. These can be included in the fixture of nest area, where the parts are placed before cutting. However, this also involves potential extra costs and complications related to placement of the parts. Subsequent tests demonstrated that high pressure coaxial air assisted performed much better than standard or lower pressure air assist, by ejecting the material down and away from the cut before it can cool and redeposit. The standard air pressure was measured at —16 psi at the cone, while the high pressure air was measured —40 psi. It is possible that even higher air pressures could be used to make the cut process even cleaner. Much of the material blown down and away from the cut was deposited on the cutting table. Results of these tests are just below. Standard air assist without mask achieved good results. High pressure air assist without mask achieved excellent results, virtually eliminating all charring and burning of the HDPE and providing an excellent edge finish.
Cutting Plastic Co2 Laser and Automation Settings
The process settings that were used for each sample are listed in Table 1. In order to test High Pressure Coaxial Air Assist, it was necessary to use a 3.0 lens. The 2.0 focal length was too short to allow for Carriage clearance due to the shape of the high pressure air accessory (see Figure 1). With the 3.0 lens,
Adequate clearance was achieved, although the lower energy density (due to a larger spot size) required a slower translation speed to achieve a full cut.
Cutting Plastic Co2 Laser Automaton Conclusion
WLSC believes laser cutting plastic with Co2 automation with HDPE had successful results. This can be repeatability achieved in production environment cutting the 0.12” thick HDPE to desired shape in 4 to 5 seconds per part, when fixed beam 3.0” focus distance and 0.10” spot size coupled with air assist at 40 PSI [or higher] is used in the laser automation.
Cutting Plastic Co2 Laser and Worldwide Laser Service Corporation
Our mission is to reduce manufacturing costs, protect consumers and products, and provide an eco-friendly green manufacturing environment through the use of automation and integrated systems. For 32 years, since our founding in 1986, WLSC has assisted our end users with the design, building, installation, and maintenance of cutting systems using both galvo and fixed beam delivery systems. WLSC has extensive experience in cutting plastic with Co2 automation. We have an extensive library and knowledge base of applications such as the one discussed in this article. WLSC provides automation with platforms of Co2, Fiber/YAG, UV in the 266nm & 355nm wavelength, and green in the 532nm wavelength. WLSC has manufacturing facility and main offices located in Gilbert AZ 85233, we look forward to working on your laser cutting and/or marking process.