Will the powder removal process damage metal 3D printed parts?

一, The rationale and need for the powder removal process
Metal 3D printing technologies like SLM and EBM build items by melting metal powder one layer at a time. After printing, the parts are buried in the powder that hasn't melted yet. If these leftover powders aren't completely cleaned up, they could cause a lot of problems:
Structural hazard: Powder obstruction in cooling channels or internal flow channels, which can stop heat from escaping and potentially cause structural disasters;
Performance loss: Powder residue changes the roughness of items' surfaces, which lowers their corrosion resistance and fatigue strength.
Powder shedding can cause problems or mission failure in the fields of medical implants or aircraft.
So, removing the powder is not just a cleaning procedure; it is also an important component of making sure the parts work properly.
二, Problems and dangers of damage that come up during the powder removal process
Taking off the powder is very important, but the process itself is hard, and if done wrong, it could damage the parts.
1. Cleaning complicated structures is hard
Powder tends to attach to metal 3D printed objects in places like thin walls, inner recesses, and holes that cross each other. For instance, a certain kind of liquid oxygen/kerosene engine injection head has hundreds of staggered injection holes. At one point, the residual powder rate of cleaning with normal airflow and vibration can be as high as 8%. If you clean it too hard, the thin wall can bend or the pore might break because of too much mechanical strain.
2. The properties of the powder and how well they work with the procedure
variable metal powders have very variable particle sizes, flowability, and adherence. For instance, titanium alloy powder has small particles and is very reactive, so it can react with the surface of parts. Nickel-based alloy powder, on the other hand, is quite hard and can scratch the surface while cleaning with vibration. The danger of harm will go up a lot if the wrong powder removal method (such airflow, vibration, ultrasound, etc.) is used based on the powder's properties.
3. Drawbacks of doing things by hand
Cleaning large or precise pieces by hand is not very effective and hard to do well. For instance, big structural parts in the aerospace sector have both small and big internal pipes. If you shake or vibrate them by hand, they could move or put too much stress on one area, which could cause cracks. Also, if operators don't use the right protective gear, they could breathe in metal powder while doing the work, which is bad for their health.
三, Steps taken in the industry to stop and control damage
The industry has come up with a number of standardised and smart methods to lower the danger of damage during the powder removal procedure.
1. Design optimisation: Make it easier to clean from the start
Design for clearability: Include cleaning needs in the design phase, including making the angles of the channel outlets better and the layouts of the exhaust holes bigger so that powder may flow naturally. By changing the design parameters, the powder residue rate in a case study of an engine injection head was brought down to less than 1%.
Improving the support structure: Make support structures in the suspended sections that are easy to take off so that cleaning doesn't touch the parts as much. For instance, Desktop Metal uses separable ceramic support technology to keep the support and the parts from sticking together during the sintering process.
2. New ways of doing things: Make cleaning faster and more accurate
System for cleaning powder automatically: The TCB-100 system from Zhejiang Tuobo cleans huge sections of powder quickly and easily by using a combination of 360-degree three-dimensional rotation, vibration, and high-pressure airflow. This cuts down on the need for people to do the work. This technique can save cleaning time by 90% and lower the chance of damaging parts.
Ultrasonic and Inert Gas Shock: For precision items, low-frequency ultrasonic vibration and inert gas shock can get rid of a very little amount of leftover powder without hurting the surface. For instance, while making orthopaedic implants, the ultrasonic cleaning frequency needs to be adjusted exactly to the size of the powder particles to avoid too much bubble impact force.
3. Detection and feedback: a closed-loop system for cleaning quality
CT detection technology: After cleaning, industrial CT scans the insides of the parts to find any powder residue or structural problems. Through a CT feedback mechanism, a certain aerospace company has raised the clearing pass rate from 70% to 99%.
Building up a database: Set up a database with information on different materials, geometric factors, and cleaning techniques so that any future production can follow the same guidelines. For instance, Liantai Technology has made a cleaning process parameter package for SLM technology that works with materials like titanium alloy and aluminium alloy.