One of our clients needed to monitor oxygen levels for a 3D metal printing project, and GasLab had the opportunity help. The project was to verify low oxygen levels during powder bed 3D printing of metal components.
Powder Bed 3D Printing
Powder bed laser 3D printing is known by several names including:
- Selective Laser Melting (SLM)
- Selective Laser Sintering (SLS)
- Direct Metal Laser Sintering (DMLS)
- Electron Beam Melting (EBM)
The difference is the type of metal, the addition of nylon or other materials to the metal, and the source of the heat to melt it.
Each type of powder bed 3D printing is accomplished by moving a laser (or electron beam for EDM) across a flat layer of fine metal powder in a sealed chamber. When the laser is turned on it heats the powder to create a small “melt pool” of molten metal. The size and placement of the melt pool are controlled by a computer aided design (CAD) program. After a layer of metal is added to the part from the bottom up, a new layer of metal powder is added. The process is repeated until a metal part is built up inside the chamber.
This 2 minute video shows a small-scale SLM system in action.
Beyond rapid application prototyping, the primary benefit of 3D printing metal parts is that they don't create scrap metal. This is especially important where exotic metals like Titanium are used.
For example, the aircraft industry has been a leader in the use of 3D printing of metal components to prototype and manufacturer parts for their planes.
Oxygen and 3D Powder Bed Printing
In order to create high-quality parts, the machine operator has many variables to work with. In addition to verifying the accuracy of the laser, humidity, heat and gas levels inside the chamber must be constantly monitored.
Monitoring the oxygen level is especially important. Since many different metals react with oxygen when heated, in order to create precise parts the chamber is sealed and the air inside replaced with nitrogen or argon.
Large Scale 3D Metal Printing
While controlling the oxygen level inside a sealed chamber for a small part can be done with a single oxygen sensor, how do you control the oxygen level inside a chamber the size of a bus?
Large metal components for cars or aircraft can take over 30 hours to print can now be made using 3D printing technology. To maintain a low oxygen level, nitrogen or argon is constantly pumped into the chamber.
A single air leak or a failing gas pump can result in a part worth thousands of dollars to be ruined, only to be discovered after the long printing process is complete.
Monitoring the Oxygen Level
Our client decided that the solution to monitoring oxygen levels could best be accomplished by spacing oxygen sensors in the top, middle and bottom of the chamber at both the entrance and exit of the chamber. The idea was that the door seals would be the most likely place for a leak to occur.
After discussion, we decided the LuminOX LOX-O2 Oxygen sensor and a 10,000 hour Thomas Micro Pump would be the best solution. The sensor is stable, accurate, and sends a UART digital output that is more accurate than an analog signal. The micro pump is rated to work continuously over 1.5 years. When accounting for tooling downtime, the components will provide years of reliable service.
In order to connect the sensors, the client wired them into an assembly that included the sensor, the pump, inlet and outlet tubes, power and I2C outputs. I2C allowed the sensors to be daisy-chained along an 80 foot path to the control panel. They then added alarms to the system to notify workers if any of the sensors detected < 0.3% oxygen in the system.
While designing the system, the client also used a LuminOX sensor outside the chamber as a control and to monitor the oxygen level in the room as a safety precaution for the workers in the building.
According to the client, “the O2 sensors have been invaluable. I have set up alarm trigger emails and texts to the service guys to run to the office and check the hardware out if the values fall below a set threshold.”
3D metal printing has the ability to transform the manufacturing process. GasLab was excited to be part of this project as well as the many similar projects we’ve worked on for other clients.
Image by Olivier Cleynen, CC BY-SA 3.0, via Wikimedia Commons
