How do you design for DMLS to avoid common defects and failures such as cracks, porosity, and delamination?

1 What are the causes of DMLS defects and failures?

DMLS involves high temperatures, rapid cooling, and thermal stresses that can result in defects or failures. Improper scanning strategy, inadequate support structures, or unsuitable material properties can all contribute to these issues. For instance, the laser beam must be scanned at a specific speed and pattern to ensure uniform heating and cooling of the metal powder. Additionally, the printed parts need support structures to prevent warping or curling. Finally, the metal powder should be of high purity and have a uniform particle size for optimal melting behavior and mechanical properties.

2 How to design for DMLS to avoid cracks?

Cracks are one of the most serious defects that can occur in DMLS parts, compromising the strength, durability, and functionality of the parts. Cracks can form during or after the printing process due to thermal stress, oxidation, or fatigue. To avoid them, select a suitable metal material with high ductility, low coefficient of thermal expansion, and good resistance to cracking such as stainless steel, titanium, or aluminum alloys. Additionally, avoid sharp corners, thin walls, or large cross-sections that can create stress concentrations or rapid cooling. Instead, use fillets, chamfers, or hollow structures to reduce stress and improve heat dissipation. Furthermore, use a proper scanning strategy that minimizes the temperature gradient and the residual stress in the printed parts. For example, use a chessboard or a stripe pattern instead of a spiral or a contour pattern. Finally, apply post-processing techniques such as heat treatment, hot isostatic pressing, or stress relief to relieve the residual stress and improve the microstructure and properties of the printed parts.

3 How to design for DMLS to avoid porosity?

Porosity is a common defect that can detrimentally impact the quality and accuracy of DMLS parts. This occurs when voids or air pockets are present in the printed parts, which can reduce the density, strength, and corrosion resistance of the parts. Porosity can be caused by incomplete melting, gas entrapment, or powder contamination. To avoid porosity, you should use a high-quality metal powder with a high sphericity, narrow particle size distribution, and low moisture content. Additionally, the laser power and speed must be adjusted according to material properties, layer thickness, and part geometry in order to ensure full melting and good bonding of the metal powder. Lastly, a proper gas flow and pressure must be used to remove excess gas and prevent entrapment in the printed parts; this should be optimized according to type of gas, nozzle design, and chamber temperature.

4 How to design for DMLS to avoid delamination?

Delamination is a defect that can occur in DMLS parts, which refers to the separation or peeling of the printed layers, compromising the integrity and the appearance of the parts. This can be caused by poor adhesion, thermal stress, or mechanical stress. To avoid delamination, you should choose a compatible metal material with a similar melting point and thermal conductivity as the base plate. Additionally, large overhangs, gaps, or holes should be avoided as they create weak points or discontinuities in the printed layers. Instead, use support structures, bridges, or infills for a good contact and smooth transition between layers. Lastly, use a proper cooling strategy that controls the temperature and cooling rate of the printed parts in order to prevent overheating and cracking. For example, use a controlled cooling or preheating technique to reduce thermal stress.

5 How to test and evaluate DMLS parts?

After printing and post-processing, you should test and evaluate your DMLS parts to ensure they meet your specifications and requirements. Visual inspection is a great way to check for any visible defects or flaws in your printed parts, such as cracks, porosity, delamination, distortion, or surface roughness. Additionally, you can use a caliper, a micrometer, or a coordinate measuring machine to measure the dimensions and the tolerances of your printed parts. Furthermore, mechanical testing with a tensile tester, a hardness tester, or a fatigue tester can measure the mechanical properties and the performance of your printed parts. It is recommended to test your parts under different loads, temperatures, or cycles to evaluate their strength, ductility, or durability.