What are the best methods to measure and improve the surface roughness of DMLS parts?

1 What is surface roughness and why does it matter?

Surface roughness is the measure of the deviations or irregularities on the surface of a part. It is usually expressed by the arithmetic average of the absolute values of the height variations (Ra) or the root mean square of the height variations (Rq). Surface roughness can affect the friction, wear, corrosion, fatigue, and aesthetics of a part. For DMLS parts, surface roughness can also influence the heat transfer, the bonding strength, the accuracy, and the post-processing requirements.

2 How to measure surface roughness of DMLS parts?

Different methods exist to measure the surface roughness of DMLS parts, depending on the part geometry, the desired accuracy, and the available equipment. Contact profilometry, which uses a stylus that moves along the surface and records the height variations, is accurate and reliable; however, it may damage the surface or miss some features. Optical profilometry utilizes a light source and a camera to capture the surface profile, is non-contact and fast; however, it can be affected by reflectivity, curvature, or roughness of the surface. Scanning electron microscopy (SEM) is very precise and detailed but requires a vacuum chamber and sample preparation; it uses an electron beam and a detector to generate a high-resolution image of the surface.

3 How to improve surface roughness of DMLS parts?

There are different ways to improve the surface roughness of DMLS parts, such as optimizing process parameters or applying post-processing techniques. Factors like laser power, scan speed, hatch distance, and layer thickness can affect the surface roughness during the DMLS process. For instance, higher laser power can increase the melting and densification of the powder for smoother surfaces, but too high laser power can cause overheating or cracking. Machining, polishing, and shot peening are post-processing techniques that can improve the surface roughness of DMLS parts. Machining involves removing material with a cutting tool or grinding wheel, while polishing uses abrasives, chemicals, or lasers to improve the appearance and performance of the part. Lastly, shot peening bombards the surface with small particles at high velocity to reduce roughness and improve fatigue resistance. However, these post-processing techniques can also introduce stress, deformation, or damage.

4 How to choose the best method for your project?

The best method to measure and improve the surface roughness of DMLS parts depends on your project goals, specifications, and constraints. When choosing the best method, you should consider the function and application of the part, such as its role in the environment and its interaction with other components. Additionally, take into account the budget and time frame of the project, as different methods may have different costs and durations. Moreover, assess the availability and compatibility of the method, such as its limitations and challenges with regards to part geometry, material, and properties.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?