Mass Finishing Basics (Part 3)

Vibratory tumblers come in all different shapes and sizes. Bowl style vibes include both round bowl and oval-bowl shapes. Tub style systems look kind of like bathtubs. In general, vibes are produced in sizes as small as 1-2 gallons up to 150 gallons (and much larger). Both systems force the tumbling media and parts to vibrate and rotate around the vibe.

Tub style vibes force the parts (and media) to vibrate and rotate around the center axis of the tub. This creates a similar sliding and rolling action to a barrel tumbler but adds the additional vibratory energy working against the parts resulting in shorter cycle times. Since tub style vibes can be very long in length and diameter extremely large large parts can be tumbled.

Bowl vibes add circular movement around the bowl in addition to the typical tumbling and vibrating. Since the entire load is moving around the bowl, this system allows the option for a separating screen (either above or below the load) to automatically remove the parts from the media. Unlike tub style systems, bowl vibes can only process parts smaller than the bowl channel width.

Getting Aggressive with Tumbling

Barrel tumbling is a time tested method to deburr, polish and create a desired surface finish. Vibratory tumbling is a new (well...newer) technology that also works great and has replaced barrel tumbling for deburring and surface finishing for lots of reasons. The aggressiveness of a vibe is largely limited by the tumbling media being used.

Welcome back - barrel tumbling. Extremely aggressive processes can be achieved in barrel tumblers. Rough cut, laser cut, parts with lots of slag and scale, heavily rusted parts can be tumbled successfully part-on-part in a barrel tumbler. The weight of each part acting on the others creates an environment in the barrel that will clean these parts in a way that a vibe never could. Adding a grit to the process will add to the cutting action.

Sure, it's a loud process. It can even be a little dirty. But the results speak for themselves.

Mass Finishing Basics (Part 1)

There are two basic types of mass finishing - barrel tumbling and vibratory tumbling. Each of these mass finishing methods have pros and cons. There are also a number of sub-varieties which we will discuss in future posts.

Barrel tumbling might be more familiar if described as rock tumbling. Inside the tumbler the parts and media are lifted by the corners of the barrel and allowed to bump, scrape and slide against each other. The media used will depend on whether you are trying to deburr or polish your parts. Barrel tumbling is also good for part-on-part tumbling (another future post - so many posts and so little time). While typically used wet, barrel tumbling can also be a dry tumbling process. The big down side to barrel tumbling is the loading and unloading of parts.

Vibratory tumbling is a little different. Similar to barrel tumbling the parts and media are sliding against each but in more of a 'filing' motion. The tumbling action is occuring in 100% of the load with a vibe versus only 20-30% of the load in a barrel tumbler. This allows a vibrator (you know what I mean) to typically offer shorter cycle times. Vibratory tumbling can abrade and smooth a surface with minimal affect on the edges while barrel tumbling loves to round the edges. Vibratory tumblers can offer very simple and even automatic separation of parts and media.

Generally, barrel tumbling is good for durable parts that require heavy deburring or high polishing and for processes that use a lot of weight (i.e., tumbling with steel media). Vibratory tumbling is great for general purpose deburring, surface finishing and for easy loading/un-loading of parts.

Deburring Aluminum Tube

A client asked us for a process that would remove the burrs from an aluminum part consisting of an assembled tube within a tube. The part was made by inserting one tube into another and then bonding the assembly together. The outer tube was 4 inches larger in diameter than the inner tube. Holes were then drilled through both tubes of the assembly. The holes could only be drilled after assembling the two tubes together due to the critical tolerances involved. There were a total of about one hundred holes in each part. The challenge was to remove the burrs from the inner as well as the outer surfaces of both tubes.

The problem was solved by attaching the part to the vibratory tub in a fixed position so that it would move along with the tub, but still be able to rotate on its axis. By clamping the part down and forcing it to vibrate with the tub, the amount of energy transmitted to the part was greatly increased.

A deburring, ball-shaped Precision Ceramic Media was used to minimize the chance of having media get stuck inside the part. The tub was slightly under-loaded with media to increase the flow rate through the holes and to aid in rotating the part. The compound flow rate was kept at eight gallons per hour. A mild acid cleaning compound (Kramco 1030) was used to speed up the cutting rate and maintain good color on the aluminum.

Due to the elevated cutting energy, the part was completely deburred with a 0.005 edge break in a cycle time of ten to fifteen minutes in a tub-type three cubic foot capacity vibratory machine. The inner tube was deburred thoroughly, exhibiting a 0.003 edge break. The parts were originally being deburred by hand, which took over three hours per part. The vibratory finishing system developed not only dramatically reduced the cost of finishing the parts, but also produced a more consistent part than when finished by hand.