Ceramic Grinding Media Advancements for Optimized 3D-Printed Part Finishing

The 3D-printed part finishing now achievable with next generation ceramic grinding media matches keeps up with the technological heights of additive manufacturing. Complex 3D printed parts can be created with additive manufacturing processes like metal sintering, electron beam printing and laser sintering. These 3D printed parts are used in applications ranging from aerospace to implantable medical devices.

The potential applications of additive manufacturing technologies are poised to increase as they gain acceptance and commercial viability. The global additive manufacturing industry is expected to reach 7.3 billion dollars by the year 2016, and 21.2 billion dollars by the year 2020.

Typically, 3D printed parts are produced using materials like polymers, metals and ceramics. Although metals are suitable for making both large and small 3D printed parts, their surface roughness remains a challenge for additive manufacturers. The roughness levels of 3D printed metal parts can be as high as 500 to 900 Ra before finishing. After finishing, the roughness ranges between 32 and 40 Ra, which is still quite high. Moreover, the ultra-hard nature of some metals increases the difficulty of the finishing process.

In addition to these challenges, the finishing technologies have not yet caught up with the advancements in 3D printing. As a result, engineers reveling in the speed and flexibility of ultra-high-tech additive manufacturing process are forced to work with primitive finishing process that use buffing, wire wheels and grinding to achieve the specified surface finish.

The advanced ceramic grinding media used by Washington Mills Ceramic Materials Corp not only avoids the use of such primitive and time consuming finishing processes, but also provides numerous benefits for additive manufacturers. Modern ceramic formulations are often combined with robust material removal methods that have lower attrition rates for achieving faster finishing cycles in 3D part printing, as well as extended life of media.

Best of Both Worlds

The level of abrasive aggressiveness required for ceramic grinding media varies from very low to very high. However, it should be remembered that very high aggression levels result in very high media attrition levels, and vice versa.

Modern additive manufacturers prefer using highly aggressive ceramic grinding media in order to minimize the manufacturing time. As ceramic media is a consumable item, the high media attrition associated with conventional aggressive formulas results in higher consumption of media, higher wear and tear of equipment, and significant load on the waste water systems for disposing the sludge resulting from high attrition.

However, in applications that require ultra-fast cycle times, high attrition levels are not significant. The use of new ceramic grinding media formulas in other applications results in highly efficient removal of metal without high loss rates. For instance, the roughness of a 6/4 titanium sample was brought down from 900 Ra to 200 Ra within two hours, with a media loss of 22.8%, by using a highly aggressive ceramic grinding formula.

The new formulation was used on the same material, and a finish of less than 100 Ra, and a media loss of 11.2%, was achieved within two hours. The grinding media option based on the new formula lasts twice as long as conventional aggressive products, and also reduces the finishing time substantially. Although the new formula is costly, the benefits of using it quickly cover up the additional cost.

Finding the Ideal Solution

It is critical for additive manufacturers to choose the right ceramic grinding media formulation from the various options available for 3D printing applications. Additive manufacturers can test their 3D printed parts using the different ceramic grinding media options available at the Parts Finishing Lab at Washington Mills. A high-energy centrifugal disc finishing machine is installed at the lab, which can accommodate parts of varying thickness, from 0.25 - 1". A spinning bowl capable of rotating at speeds of 235 rpm is present at the bottom of the machine.

The spinning bowl generates a centrifugal force for driving the ceramic grinding media and part upward. Once the part and the media reach an apex, they fall back into the center of the vortex. Now, the part is accelerated up through the media. This goes on until the required finish is achieved.

The centrifugal disc machine is constructed such that the media and the part can be accessed easily. Unlike the centrifugal barrel layout, where the chamber is closed, the centrifugal disc machine is open; enabling easy and fast access to the 3D printed parts so that the parts finishing lab can record the results throughout the testing.

Samples of the 3D printed parts, along with a part that has been already finished as per the specifications, can be sent to the lab by the additive manufacturer. Once they receive the sample, lab technicians will quiz the manufacturer about the components of the product, specific alloys, initial roughness level and the expected outcome.

Armed with this information, the appropriate starting point for the ceramic grinding media will be ascertained. The part can be removed from the centrifugal disc machine at specific intervals during the test run to assess the surface finish and reflectivity.

Parts like the bearing surface may only need to attain a particular Ra, while others like titanium stiletto heels may need reflectivity or shine in addition to the surface finish. The lab technicians will work on these specific requirements during the test run.

A comprehensive report including details on the ceramic grinding media that is used and the details of the results at each interval will be provided by the lab to the additive manufacturer. The additive manufacturer can use this data to decide on the ceramic grinding formulation that works best for his application, and also assess the time for which the parts need to be machined to achieve the desired finish.

Making the Dream a Reality

In the past, many ideas could not be pursued to completion due to limited processing capabilities. With the advent of 3D printing, that is changing, and additive manufacturers are trying to turn their ideas into products. Moreover, advanced formulations of ceramic grinding media are enabling improved finishes on 3D printed parts.

This information has been sourced, reviewed and adapted from materials provided by Washington Mills.

For more information on this source, please visit Washington Mills.

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