Mass finishing has come a long way since its “invention” in the 1950’s. It evolved from a somewhat crude method for the mechanical deburring of mass-produced simple metal parts to a sophisticated surface refinement technology for complex work pieces made from metal, plastic, and even wood. Today’s mass finishing applications range from straightforward deburring, over-precise edge radiusing, surface cleaning and smoothing, up to high gloss polishing. Mass finishing also plays a dominant role in the post processing of 3D printed components. This became possible through groundbreaking new equipment concepts. But, for the undeniably great success of this surface finishing technology, the creation of innovative grinding & polishing media and sophisticated chemical compounds was of equal importance. In this article, we are looking for some of the latest media and compound developments, which not only improve the finishing results but also save costs.
Around 70 years ago, the deburring media used in mass finishing machines consisted of random-shaped river pebbles, lava rock or slag, a material used in the production of steel. Crushed grinding disks and wheels also served as processing media. At that time, no special compounds existed, and the first users of the newly born mechanical surface finishing technology simply used water mixed with petroleum. The water helped to cool down the process, and the petroleum provided a certain degree of corrosion protection.Since then mass finishing underwent a rapid technological development.
A game changer: geometrically shaped finishing media and special compounds
It is not surprising that the finishing results were inconsistent and rather poor, owing to the poor and highly erratic media quality and unavailability of suitable compounds. One big problem was that the grinding material got easily lodged in the work pieces, and certain surface areas like undercuts, holes, tight corners, etc. could not be reached.
Therefore, the development of geometrically shaped media in different sizes was a real breakthrough. The shape and size of the media could now be precisely adapted to the work pieces, and along with the creation of special chemical compounds, the mass finishing processes became more stable. Above all the new media and compounds could now be perfectly matched to the respective finishing tasks, be it deburring, edge radiusing, surface smoothing, polishing, de-greasing/de-oiling, corrosion protection, etc.
Since then numerous media and compound innovations have permitted the mass finishing technology to handle surface refinement tasks that were considered impossible just a few years ago. For example, high density porcelain media combined with sophisticated grinding & polishing pastes are used for smoothing and polishing a wide array of components such as turbine blades in jet engines, medical instruments, door handles, knifes, the rollers in roller bearings, etc. In the field of orthopedic implants, novel plastic media help to place a perfect pre-polish finish on artificial knees and hips. Or tiny ceramic and plastic media – with edge lengths of less than 1 mm – allow the mechanical surface finishing of very small work pieces such as the components in high-end mechanical wrist watches. More recently, specially developed compounds allow the cleaning and recycling of the process water in mass finishing operations with centrifuges.
The finishing challenges today
In today’s manufacturing environment, the shape of many components in products like automobiles, machinery, airplanes, consumer goods, etc., is increasingly becoming more complex. Moreover, the customers demand higher-quality surface finishes, zero-defect production and finishing operations that are simple and easy to handle.
For mass finishing, this means, among other requirements, that no media get lodged in the finished work pieces, that the finishing process causes no excessive foaming, that the risk of bacterial contamination of the process water is minimized, that the drying of the finished work pieces does not generate excessive amounts of dust and, not to forget, that the entire process can be automated.
In addition, there are demands for a non-hazardous, safe working environment and environmental sustainability. Last but not least, cost pressures demand lower costs for surface finishing operations.
Innovative media and compound solutions to meet these demands
Below are some examples of recent media and compound developments that help to cope with today’s finishing challenges:
Multi-shape ceramic media
The constant “rubbing” of the media against the work pieces in mass finishing operations causes the media to become smaller and lose its initial shape. Especially in the case of geometrically complex components, the diminished media size not only results in poorer finishes but also increases the risk of “undersized” media getting lodged (wedged) in the work pieces. Since they would severely disrupt automated downstream manufacturing operations, such lodgings must be prevented at all costs.
The new multi-shape ceramic media was specifically developed for such critical applications. With rounded areas on all sides, this unique media maintains its extraordinary shape even after extended use, and minimizes the risk of lodging. This makes the multi-shape media the ideal tool for finishing complex work pieces with difficult-to-reach internal surface sections, tight corners, notches and slits. Such work pieces can be intricate stampings, housings or deep-drawn components.
Compared to traditional products, the multi-shape media offers additional advantages. For example, it maintains its original shape, even after extended use, and can be used for a longer time, therefore. The new product also creates a faster and more dynamic motion of the media/work piece mix, resulting in up to 10% shorter cycle times. These technical features result in higher productivity and lower operating costs.
Non-foaming plastic media
The use of plastic media in mass finishing operations frequently causes extensive foaming. Foam is problematic because, acting as a buffer between the media and work pieces, it reduces the grinding performance and unnecessarily increases the cycle times. Excessive foaming can even destabilize the entire finishing process. Moreover, the foam contaminates the surface of the finished work pieces since it contains metal and media fines. In the past, the foaming problem had to be controlled by injecting special defoaming compounds into the finishing process. But, apart from the fact that these compounds are expensive, they also made the process water cleaning operation more costly.
A solution to this problem is an innovative plastic media that no longer produces such unwanted foam. With the new media, the finishing processes have not only become more stable, but the desired surface finishes are achieved in shorter cycle times. This, combined with lower compound usage and a longer usable life of the media, results in considerable cost savings.
Because of the disruptive foaming effect of the plastic media, many users of the mass finishing technology had been using ceramic processing media in the past, even though it was not the best option. The new non-foaming plastic media presents a great opportunity to these users to optimize their surface finishing operations.
Long-life compounds for process water recycling
Cleaning and recycling of the process water with centrifuges has pretty much become the standard for mass finishing operations. But a big headache is that the process water becomes contaminated and must, therefore, be frequently replaced with fresh water and compound, which not only disrupting the mass finishing operation but also being expensive.
Recently, a supplier introduced revolutionary long-life compounds that practically double the time period during which the process water can be used before it must be exchanged. But the long-life compounds offer additional benefits: the addition of biocides to the process water for getting rid of unwanted bacteria is no longer necessary.
Overall, the long-life compounds cut the water and compound consumption in half, eliminate the need for biocides, reduce the costs for waste disposal and significantly lower the personnel costs for process water management. This adds up to cost savings as well over 50%, compared to traditional compounds.
Dust-free drying of finished work pieces with drying media
Most mass finishing processes require the addition of water and compound. Therefore, the finished work pieces must undergo a drying operation. A common drying method is to embed the work pieces in a heated organic drying medium consisting of crushed corn “ears,” generally known as corn cob. An advantage of the organic drying medium is that it does not leave any water spots, but it produces dust, which settles on the work piece surface and can cause problems with subsequent manufacturing operations. In addition, the generated dust also pollutes the immediate environment of the mass finishing operation.
This entire dust problem has been eliminated with the anti-dust additive, a liquid that is sprayed into the organic drying medium. The additive, dispensed in small quantities, more or less completely suppresses the formation of dust. The finished work pieces coming out of the drier are completely dust-free. Likewise, no dust pollutes the environment.
Since the anti-dust additive is purely organic and complies with prevailing food standards, it also represents a significant contribution towards a cleaner environment. The additive can be sprayed by hand or dosed automatically with a special dosing system.
Automation – a driver for the development of new media and compounds
The above examples are just a few of many innovative products. It is safe to assume that the pace for developing new mass finishing consumables will accelerate. One obvious reason is the demand for automation. Automated finishing operations not only relieve labor shortages, but also eliminate the unpredictability of human skills/shortcomings and improve the quality and consistency of the finishing results. The new media and compounds must allow the running of such automated processes without the need for any human intervention.
For instance, not too long ago the pastes for the KeramoFinish polishing process had to be dispensed manually, which was time-consuming, frequently produced poor polishing results and was costly. By making them pumpable, the pastes can now be administered by special pumps, thus allowing the automation of the entire process.
We can look forward to many more of such innovative mass finishing consumables.
Contributing Editor MFN and
Rösler Oberflächentechnik GmbH