Vibratory Deburring Machines: Tips for Choosing the Right Tumbling Media
Vibratory tumblers, or vibratory deburring machines, are extremely useful tools that can help speed up deburring and finishing operations. Available in different sizes, these bowl-looking machines are designed to remove material from pockets, recesses, and bores on delicate parts by shaking and stirring together the abrasive media in the bowl and the unfinished parts.
In simple terms, all you have to do to get your parts deburred and finished with a vibratory tumbler is place them in the tub, activate the vibrations and wait until your parts come out clean, deburred and ready to ship. Seems easy, right? It is. But, before getting started with your mass deburring operations in a vibratory tumbler, there’s one important decision to make: the type of tumbling media to use.
What is Tumbling Media?
Tumbling media is the term used to define any type of abrasive material that will fill the vibratory tumbler’s bowl. They come in multiple shapes, sizes and materials and serve different purposes, such as keeping the parts separate, burnishing surfaces, deburring and polishing. The selection of media depends on multiple factors such as the part characteristics and the type of finishing operations needed.
Selecting the Right Size
The main factors affecting the choice of the media size are the size of the part and its features. Larger parts typically call for larger media due to their ability to give rapid cuts and leave coarse surfaces. Smaller parts, on the other hand, are usually deburred and polished using small media to avoid damage and obtain a finer finish. The features of a part, however, play an important role in the selection of the size as well. Wrong sized media, for example, could end up lodging in the holes of the part, affecting the final results. As a rule of thumb, to prevent lodging in the part, media should be a minimum of 70% the size of the hole or slot. This avoids two pieces getting stuck side by side in a hole.
Selecting the Right Shape
Stars, pyramids, cones, wedges, spheres, cylinders, and ovals are just some of the shapes available. As they do for size selection, the part’s features, such as holes and slots, affect the media shape selection. Cones, angle stars and pyramids, for example, are best for reaching into an area as they prevent the media from becoming lodged. Angle cut cylinders are best for passing through holes.
Media materials have different characteristics. Some of them work better for finishing while others are recommended for removing unwanted machining edges. The type of metal is also an important factor to consider as some abrasives are more effective on hard metals while others work better on soft materials.
Here’s an overview of the main abrasive materials and their uses:
Plastic media are commonly used on soft metals, such as aluminum, brass or copper. They produce a very smooth finish but have little or no shine. Tetrahedrons or cones are generally recommended for parts with holes while triangles are good for corners and flats.
Steel media are commonly used for heavy deburring, shining, polishing and burnishing metal, plastic or ceramic parts. If steel media are used to deburr plastic parts, a second polishing step might be required as plastic parts have high abrasion resistance resulting in a matte finish.
Better suited for hard metals and operations where heavy cutting is needed, ceramic media are also the first choice when working with heavy parts. Plastic parts also go well with ceramic media as they require tough abrasive action.
Porcelain media have no abrasive power in it, therefore it’s used only to polish materials. They are usually white in color and is generally available in spheres and cylinder shapes. Spheres are usually best for polishing soft metals like aluminum while cylindrical pins work best on hard materials like steel.
Organic media include a wide selection of organic materials such as walnut shells, coconut shells, and corn cob. Each material has different purposes and characteristics. Walnut and coconut shells are usually recommended for light to medium deburring operations while corn cob works particularly well in cleaning operations thanks to its ability to absorb surface oils. Organic media are safer for the environment, biodegradable, durable and reusable.
Wet Tumbling Compounds
Although not frequently used, wet compounds can be mixed with tumbling media to protect the parts from corrosion and rust to maximize deburring action.
Choose Your Media Wisely
As you’ve probably figured out, choosing the right media is not an easy decision. A lot of variables need to be factored into the equation and, as for many other operations within a job shop, requires process trial and error to perfect.