The role of wet blasting in the post-processing of AM parts

30 May, 2023

What is wet blasting?

From the family of shot blasting postprocessing technologies, wet blasting is what it is called when water and abrasives media work together and is particularly well suited for the finishing of delicate, precision-produced parts. The process is characterised as being dust free, can use very fine abrasives, uses very low volumes of abrasives due to the protective water layer, and minimises the risk of embedding (especially for soft metals). It also produces what is perhaps the most important AM post-processed part characteristic, superior surface finish.

Wet blasting typically sees a mix of between 10-40% abrasive media to water. The slurry is pumped to the blast gun and then accelerated to a high velocity using compressed air through a blast gun nozzle that is directed at the part. The blast media impact on the work piece creates the desired effect, be that cleaning, surface smoothing, coating preparation, cosmetic surface texturing, or peening.

The process removes powder and supports (from some plastic AM parts), and enhances surface finish in one, and the use of different media can either promote cosmetic or functional surface finish. Wet blasting machines can easily be integrated into an automated production line, or used as an isolated stand alone technology.

Advantages of wet blasting

Wet blasting has benefits for the characteristics of the work piece itself, but also for the processing environment. The over-riding advantage is it gentleness, but also the process produces no dust, which prevents electro-static issues and therefore removes the need to consider ATEX regulations concerning explosive atmospheres. There is also no media impingement using wet blasting, an ever present problem with dry blasting where media particles can embed in the work piece surface compromising surface integrity.

Dry blasting generates significant heat during post processing which when combined with high impact energy of the media on the work piece can lead to warping and bending of delicate parts. Wet blasting by contrast is a cooler gentler process that is especially suited to the post processing of fragile thin-walled parts and components.

When it comes to powder removal on AM parts (even in hard to reach internal channels and features) wet blasting immediately washes away anything that is adhering to the work piece

In terms of surface finish, wet blasting promotes smoother finishes while being more precise, consistent, and repeatable. Finishes are fine and uniform, with low surface roughness of 100µm Ra being easily attainable. From a cosmetic surface finish perspective wet blasting creates a smooth matte effect, and the less abrasive nature of process and lack of warping and bending allows for the attainment of much tighter tolerances.

A key advantage is the versatility of the process, as blast intensities and media concentrations can be easily adjusted to accommodate different materials and the different geometric structures to eliminate damage to part form and function. It is usually preferable to source wet blasting equipment form suppliers that have the knowledge and experience to advise on the numerous technical features that combine in a wet blasting process to ensure that you achieve precise and repeatable result on a wide variety of work pieces.