The Vibratory Finishing 101: A Layman’s Guide

Vibratory finishing is an industrial process where materials get a finished look.

The ultimate material finishing goals can vary: better wear resistance, electrical conductivity, brightness, corrosion resistance, paintability, bond to rubber, chemical resistance, harness, and so on.

Vibratory finishing techniques are popular, cost-effective, and less labor-intensive.

Applications of vibratory finishing

Vibratory finishing is a mechanical/chemical process usually done on a large scale. And vibratory finishing machines are universally acclaimed mass finishing machines which came to use for a wide range of workpieces and surface finishing objectives.

The vibratory processes are typically utilized on metallic components that have undergone previous machining operations, but they can be used for non-metallics as well.

Parts Drilling before vibratory finishing
Parts Drilling before vibratory finishing

Sometimes, vibratory finishing may be used just for simple cleaning as they’re great at removing grease and dirt from components after machining.

Where a vibratory finishing machine usually ranks is while deburring and creating isotropic surface finishes on, for example, a burr left over from a drilling process. Burrs are highly undesirable in industries and being able to remove them using an automated process — such as the vibratory finishing — is highly advantageous.

A well-tuned process can actually get your component a highly desirable high-gloss finish.

More applications range from intensive deburring and edge radiusing all the way to mirror image polishing. In other words, from aggressive grinding to pre-plate surface finishes. Descaling, reducing the edges, polishing, and rust removal are some of the other applications of the vibratory finishing process.

A great everyday example where vibratory finishing really helps is your cutlery: knife, fork, and spoon. It is awful just to imagine eating with a rough-surfaced spoon. The solution? Your metal cutlery undergoes smoothening with the help of vibratory finishing.

Cutlery vibratory polishing
Cutlery vibratory polishing

The process

The components that require finishing are called workpieces. To achieve the finish, they are mixed with a media in a bowl that vibrates. The process is simple: the media aids in getting the desired finish of the workpieces.

Sometimes, there may be a supply line that will actually add a compound to your media. The compound is typically water and detergent, or water and degreaser. Also, you can add in rust inhibitors, or some additional polishing compound as well.

Media as a crucial agent for material finishing

The media functions as an abrasive agent to remove unwanted material from the parts. It also acts as a cushioning for rapidly moving parts by serving as a carrier for compounds such as water. Choosing the right media accounts for right mass finishing.

The workpieces determine the shape, size, and performance characteristics of the media that must be selected for the job. Water and compound are essential ingredients, not only for cleaning and passivating, but also pickling of the workpieces. They also help maintain the abrasiveness of the media.

A variety of media are used in the industry. Depending on the workpieces, steel, ceramic, and plastic are the usual media used in vibratory finishing. Sometimes, you have to choose the media by trial and error method. The finishing machine provider can also help.

For example, ceramic media is used for general finishing, steel media is used for finishing metal parts, plastic, and even organic media (walnut shells and corn cob) when required. Mixed pellets of media are also common such as stones, river stones, and tiles.

The next step is to choose the right shape and size of the media as this prevents workpieces from lodging and helps in easy separation. Usually, the media sizes are significantly smaller than workpieces. This way, finished material separation is easy. If workpieces are much smaller than media, inverse separation can be a bit of a hassle. Bigger size media are cheaper, cut faster, and will have a longer life, but will leave your bowl rougher. Striking a balance between media size and bowl longevity is essential.

The vibration & finishing

Typically, the bowl of a vibratory finishing machine sits on springs, with a motor on the underside. The vibratory finishing process involves basic kinematics (motion of objects) and components in the system. The components include a bowl that ranges in size from that of a third of a meter to over a meter depending on your application. To the underside of the container, we have a motor which has an offset mass attached to it. The bowl sits on reasonably stiff springs.

In a deburring process, when the motor is turned on, it takes on this steady-state flow trajectory and then the workpieces are entrained within this. Because of the relative motion between the media and the workpieces, the deburring happens on the surfaces of workpieces. To be precise, the oscillating movement of the processing bowl created by the vibratory drive system causes constant rubbing between the workpieces and the media. This leads to the removal of material, especially from the workpiece edges.

In a smoothing or cleaning process, the bowl is subjected to the following kinematics: as soon as you turn on the motor, because of the offset mass present at the bottom, it sets up vibrations within the bowl. The bowl induces the media to go into a steady-state flow pattern, and the workpieces become entrained within the media. The relative motion between them is what actually removes material and gives you the desired isotropic surface finish.

The characteristic vibratory motion of the processing bowl is controlled by the quantity and setting of the imbalance weights on the vibratory motor. Pushing and holding a dedicated button changes the motors rotational direction. When the button is released, the rotational direction of the motor changes back allowing the mix of media.

The vibratory motor speed is controllable, and it ranges anywhere between 900 and 3600 cycles per minute. The maximum extent of vibration is called amplitude and it ranges from 0 to 5 mm.

In a highly automated industrial environment, workpieces made from carbon steel can be separated from the media with a magnetic belt separator in a batch-type operation. Workpieces are picked up by the magnetic separator and passed over a demagnetizing zone integrated into the belt before they are transferred to the next manufacturing step for finishing applications.

The process runs in an open tub and allows you to easily observe if the required finish has been obtained. You can run this process anywhere from half an hour to overnight to get the finish.

Types of vibratory finishing equipment

  1. VB(A) vibratory finishing machine: Used in high polishing processes.
  2. VB(B) vibratory finishing machine: Simplest machine construction and economical to use with the bowl straight-wall design.
  3. VBS(B) vibratory finishing machine: Suitable for finishing thousands of smaller parts with a deck outlet that separates batch-processed finished parts into the next equipment in an automated industry.
  4. VBS(A) vibratory finishing machine: The bowl has a curved-wall design that provides shorter processing time and better performance than straight-wall design.
  5. Vibratory dryer: This is used along with vibratory finishing machine where workpieces fall directly into the dryer.

Choosing vibratory finishing equipment

It is highly recommended that you purchase equipment that not only suits your needs but also from someone who meets all statutory industry standards. Customization plays a crucial role. You should look out for usual customization options such as soundproof cover for noise reduction in vibratory production, input pump for constant compound feed-in into the vibratory bowl, separation flap for media and workpieces’ separation, and installed- on-floor control box and hang-on-wall control box.

Sometimes, when electronic parts are involved, choosing an expensive and intricate machine may not be the best option. Mass finishing is a simple process, and the machine needs to be as simple as possible to avoid malfunctioning.

Look out for equipment that is ISO or CE certified. The supplier should also provide documentation for every part.

Running vibratory finishing equipment

3 phase electricity: 380V, 460V or 480V is best for running vibratory finishing equipment because it is safe and grounded. First-time users are advised to take help of expert electricians.

Conclusion

Vibratory finishing is a simple process but needs thorough understanding. Many considerations come into play. A personal investigation into vibratory finishing equipment can save a lot of time and resources in your journey down the line.