How to avoid machining deformation of metal 3D printed parts?

一, Design phase: Topology optimization using stress simulation
1. Simulating the distribution of stress and rebuilding the structure
A company that makes turbine blades for the aerospace industry used Simufact Additive software to run a thermal mechanical coupling simulation. They observed that typical designs show stress concentration in the blade root transition zone. Changing the right angle transition to a rounded corner transition with a 5mm radius and filling the area that doesn't bear stress with a lattice structure lowered the stress peak from 420MPa to 280MPa and the printing deformation by 62%. This scenario shows that topology optimization based on simulation can find high-stress spots ahead of time and make the stress distribution even by changing the structure.
2. Smart design of structures that sustain
Empirical formulas are used in traditional support design, which can easily cause heat to build up in one area. Manga Technology's VoxelDance Engineering software uses scanning deformation compensation technology to automatically create support structures that fit the shapes of the parts. This method improves the density of the support distribution while printing artificial joint handles in a medical device company. It cuts the depth of surface damage caused by removing support after sintering from 0.3mm to 0.05mm and cuts the amount of support material needed by 30%.
3. Building a model for pre-deformation compensation
For aviation hydraulic valve bodies that need to be accurate to within ± 0.02mm, Platinum Technology Company uses a closed-loop process called "printing scanning compensation." In this process, the original model is printed with 316L stainless steel, and the ATOS Triple Scan 3D scanner gets the actual deformation data. This data is then used to make a reverse pre-deformation model in Magics software. After two rounds of correction, the parts' essential dimensional tolerance went from ± 0.15mm to ± 0.03mm, which is what aviation standards need.
二,Process stage: Collaborative control of multiple parameters
1. Changing the settings of the laser on the fly
The Huashu High Tech FS200M equipment dynamically changed the laser power and scanning speed while printing the combustion chamber of a certain engine by keeping an eye on the temperature field of the molten pool in real time. In the 3mm wall thickness area, the 800W/1200mm/s parameter was used, and in the 0.8mm wall thickness area, the 600W/800mm/s parameter was used. This partition parameter adjustment cuts down on heat input in thin-walled sections by 40% and residual stress by 55%. It also fixes the sintering deformation problem in the 0.5mm cantilever structure.
2. Improving the procedure of laying down powder
The EOS M 400-4 equipment uses adaptive powder spreading technology to deal with the effect of powder layer thickness on deformation. It keeps the layer thickness at 40 μ m in the support region and changes it dynamically to 25 μ m in the free-form surface area. Test data demonstrates that this approach cuts the interlayer misalignment of thin-walled parts from 0.12mm to 0.03mm and raises the surface roughness Ra value from 12.5 μ m to 6.3 μ m.
3. Control of the atmosphere via inert gas
The Platinum BLT-S800 device keeps the air and humidity levels very low (less than 10% RH and 50ppm) while printing titanium alloy orthopedic implants. This is done using a closed-loop control system. Experiments that compare different environments have showed that this one can lower the powder oxidation rate from 0.8% to 0.15%. This solves the problem of oxide films making it hard for layers to connect and makes parts 18% stronger.
三,The post-processing stage is when defects are fixed and performance is improved.
1. Hot isostatic pressing (HIP) densification treatment
A particular aviation engine business employed QIH-15L hot isostatic pressing equipment to work on Inconel 718 high-temperature alloy parts. Keeping the parts at 1200 ℃/150MPa for 4 hours made them denser (from 99.2% to 99.98%) and less porous (from 0.3% to 0.002%). The processed parts' fatigue life is three times longer, and the microcrack flaws that formed during the sintering process are completely gone.
2. Process of gradient heat treatment
For 316L stainless steel hydraulic valve bodies, make a three-step heat treatment process: stress relief annealing at 550 °C for 2 hours, solution treatment at 1050 °C for 1 hour, and aging treatment at 480 °C for 4 hours. This procedure makes the parts harder, going from 180HV to 280HV, and lowers the residual stress, going from 320MPa to 80MPa. This fixes the problem of dimensional rebound after machining.
3. Technology for removing intelligent support
On the DMG MORI LASERTEC 65 3D equipment, a five axis linkage machining center is used for support removal: the cutting force is monitored in real time through the Force Control system, and the feed rate is automatically adjusted. Tests have demonstrated that this technology makes it 40% easier to remove support, and it keeps the depth of surface damage to within 0.02mm, which is what aviation parts need to stay intact.