There are two impacts of oxygen on 3D printing. In the case of Powder Bed / Laser 3D printing using materials like copper, oxygen in the material can form bubbles in the part. In the case of Stereolithography (SLA) printing, oxygen can inhibit curing at the surface.
Types of 3D Printers
There are three basic types of 3D printers:
Fused Deposition Modeling or FDM printers. These use filaments of thermoplastic material on a roll that are heated and layered on top of the print bed to build up a desired part. The part is built from bottom to top. FDM printers tend to be the least expensive and easiest to use, but cannot provide the detail created by SLA printers.
Stereolithography or SLA printers use UV light from lasers or digital light processing (DLP) projectors to harden liquid resin in a process known as curing. In an SLA printer the part is built from top to bottom as it is “pulled” up from a tray of liquid resin. The advantage of SLA printers are their ability to produce parts with extreme detail at relatively high speed. Their disadvantage is higher material costs. While SLA printers typically cost more than FDM printers, they are quickly coming down in price.
Powder Bed Printing uses granules of material (typically metal) that are melted by a laser. As each pooled layer of molten metal is created, the another layer is deposited on top of it. Powder bed printing is typically the most expensive, but can produce metal objects at a fraction of the cost of normal machining.
The majority of light-curing adhesives in 3D printing are acrylic-based. The challenge is oxygen inhibition, i.e. oxygen reacting with the surface layer of the product as it cures. Oxygen inhibition can result in the surface of the adhesive or coating feeling “sticky” after curing.
Because oxygen inhibition is caused by cures conducted in open air, there are several solutions that have been explored:
- Increasing the cure temperature
- Changing the type of material or the wavelength of the light
- Introducing a physical barrier between the part and the air
- Curing the part in a low-oxygen, closed environment
Powder Bed / Laser 3D printing
For 3D metal printing, a bed of metal powder is swept across by a laser that makes “pools” of material that fuse. Subsequent layers are combined building up until the part is completed. In order to make a quality part, the intensity of the laser, the cooling time, the humidity and the quality of the metal powder must all be maintained. But in addition, any oxygen in the system can result in bubbles or loss of structural integrity in the finished part. This results in not only defective parts, but hours lost to production defects.
For this reason, Powder bed printers may rely on the use of argon or nitrogen as a shielding gas to limit the oxygen present at the intersection of the laser and the powder. Even in a sealed printing chamber, the operator can never insure all the oxygen is removed before printing begins.
One solution to this problem is the TecPen Weld Purge Monitor. This hand-held purge monitor verifies the number of oxygen molecules in the shield gas is effectively zero parts per million before printing begins.
Used in combination with a shield gas in an enclosed printing area the TecPen has the capability of decreasing not only oxygen, but the time and money lost to rejected parts printing.
Controlling the amount of oxygen during 3D printing can have other benefits. For example, a team of engineers from the University of Colorado Boulder found that by regulating the amount of oxygen during a cure in an SLA 3D printer they could control a part’s rigidity. This has potential benefits for bio-medical applications, where body parts need both structural stability and flexibility.