Vibratory finishing is now the most popular type of mass finishing process. In some case, people will think vibratory finishing equals mass finishing. There is still another process use centrifugal barrel machines, centrifugal disc finishing machines, and rotary barrel machines. Some special process will be done in some special surface finishing machines.
The process vibratory finishing is carried on in a vibratory bowl or a vibratory tub for parts surface deburring, polishing, smoothing, cleaning, descaling, rust removal, radiusing and so on.
The first vibratory finishing machine is tub-type which introduced in 1957. Five years later, in 1962, the bowl-type vibratory finishing machine is invented and commercialized.
1. Major process in vibratory finishing:
Deburring has the widest application in the vibratory finishing process. Usually, people use a mild compound with a PH around 7.0 and a general performance ceramic media to deburr. Mild steel stamping parts deburr with ceramic media in 30-60 min. And Aluminum die casting parts to deburr with plastic media in 1-2 hours.
In the deburring process, compound cleans off machining oil or lubricant in the same time cycle. This leaves a neat surface for assembling and handling.
The burnishing process usually done with steel ball but also can be done with zirconia ball. Steel media including ball shape and ballcone shape are most popular. When ball shape steel media can offer better polishing performance, ballcone shape steel media never remove burrs but hammer down the burrs and leave a dull edge.
In burnishing process, cleaning media before the process is critical to performance. A dull media always results in dull metal finishing. As a result, keep tumbling media shining and glossy is essential.
Compound selection is another important factor to determine ball burnishing quality. There are several different burnishing compounds which formulate according to different material: stainless steel, aluminum, zinc, and copper.
The ball burnishing process carried out usually in curved wall vibratory finishing machine or tub vibratory machine. In curved wall design machine, tumbling media rotate in cross-section area. This achieves maximum surface contact between parts and media and acquires optimal tumbling performance. The ball burnishing process time usually takes 20-30 minutes to get a brilliant surface.
Parts surface properties change with different media processing. Cutting marks from machining and wheel grinding process almost every components manufacturers come up with. Ceramic media offer an economical way to give the metal surface a pre-painting finishing.
For soft metal materials like aluminum, copper, and zamak3, plastic media is selected to get a superior pre-plating finish.
In some application, you can matt finish surface with ceramic media with increased surface roughness. This property is required in friction pad in the automotive industry.
1.4 Cleaning and degreasing
When cleaning oily and greasy parts, vibratory finishing machine is a good choice. In the cleaning process, we want to run it in a pass-through mode. So we save time and give more output.
The larger machine diameter, longer time parts stay in the machine and better cleaning parts there will be.
The best media for cleaning process is porcelain media and steel tumbling media because they have almost no wearing. The media not leave wear debris which contaminates and leave on parts surface. Besides, media will not reduce in size (which is costly for you) and risk lodging in parts.
However, cleaning compound is the main contributor. Compound type selection, dosing rate, and concentration are the key factors related to performance. This process requires a strong acidic compound to clear off fatty and oily substance from the metal surface.
Even though the hot solution can reduce degreasing and cleaning time, we will use cold water. A hot solution will soften PU lining and result in premature wear.
1.5 Rust Removal
parts process in high temperature (laser cutting/plasma cutting/welding) leave oxidation layer on the surface. However, the oxides and corrodes adhere to metal surface always result in paint chips and poor plating quality.
As a result, the vibratory finishing process is necessary to remove the oxide layer and make the metal surface smooth before the next procedure.
The rust layer usually is thick. Also corrosion surface sticks tightly on the metal base material. To remove these materials, ceramic media with strong cutting power is used. In some case, a strong cutting compound is used to reduce processing time. Hydrochloric acid and sulfuric acid or their mixtures are used in some special applications for oxide removal.
Radiusing also called edge rounding or edge breaking. It is the process to make parts edge round and smooth. This property required for most metal components with direct contact with users.
The round edge can protect user and operator from likely injuries. Besides, it also makes easier for labors to handles and smoother parts on parts workflow.
In the vibratory finishing process, edge rounding process usually comes together with deburring and surface material removal.
2. Key Element in Vibratory Finishing
The parts size decided the type of vibratory finishing machine that can be used. Small parts like pins and tabs usually made with huge production volume every day. You don’t want to pick 10,000 pieces of parts one by one out of machine once they are ready. As a result, the vibratory bowl finishing machine is preferred in the situation.
Larger parts like transmission gear parts would be faster to take out by hand.
If the parts size is even larger like the ceramic coated exhaust pipe, most vibratory bowl channel cannot accommodate. Then you need to consider a vibratory tub.
2.2.1 VB(A) Vibratory Finishing Machine:
The curved wall design vibratory finishing machine is popular for an excellent cascade of media and parts flow. This makes shorter cycle time of the process and saves cost in the high polishing process.
One of the major applications for the curved wall vibratory machine is the ball burnishing process. When burnishing with stainless steel tumbling media, vibrator motor power updated to support increase loading weight.
Some small parts or lightweight parts (for example aluminum die casting parts) tend to float at the outer surface with standard vibratory machines. With the increased tumbling performance, these parts have excellent movement with media mass.
2.2.2 VB(B) Vibratory Finishing Machine:
The standard vibratory finishing machine without internal separation deck is the simplest machine type. If you have no special requirement on parts, you can use this economic model to get started.
Straight wall vibratory finishing machines widely suit for most medium size parts deburring and cleaning.
2.2.3 VBS(B) Vibratory Finishing Machine:
When you process hundreds or even thousands of parts each load, taking out parts piece by piece with the hand is time-consuming. Then you need a vibratory machine with separation deck integrated into the machine. When parts are ready, the lever at the right side of machine pulled down then the mass moves onto separation screen.
Media with smaller size go through the screen and parts with larger size keep up over the screen. After the final parts come out, you can close the level shutter and continue with next batch processing.
2.2.4 VBS(A) Vibratory Finishing Machines:
Curved wall design vibratory finishing machines are an excellent improvement based on straight wall design. They offer better tumbling performance with a shorter processing time.
However, machine chamber width is narrower compared with straight wall design. Bigger components not easy to make a complete turnover. In addition, fewer media and parts mass can be put in the machine.
2.2.5 Vibratory Dryer:
Vibratory dryers have mostly the same design with vibratory finishing machines. Practically there are two types of vibratory dryers: one with PU lining and another without.
The one without PU design is most popular among workshops for simple design and maintenance free. There are 6 sets of heating elements installed beneath the vibratory bowl.
Usually, parts come out of vibratory finishing machine fall straightway into the vibratory dryer. Then parts run one circle in vibratory dryer tunnel and come out.
Because corn cob is lightweight material, especially for the small size and grounded corn cob. A PVC cover is necessary to prevent corn cob dust flying.
However, if parts have blind holes, vibratory dryers not recommend. Because corn cob stuck into parts slots or holes is hard to take it out.
2.3 Tumbling Media
2.3.1 Media type
For general deburring of a hard metal material, ceramic media with brown aluminum oxide abrasive (corundum) is frequently used.
An experienced engineer selects case hardened stainless steel tumbling media for ball burnishing process. Plastic media usually choose for aluminum and zinc die casting parts smoothing and deburring.
2.3.2 Media shape and size
After you select the right media type, the next step is to choose the right media size and shape. Right media size and shape is important to prevent parts from lodging and easy for separation.
Firstly we choose the shape of media, the media shape not easy to lodge on parts even after a long time of running. Secondly, we choose the size of the media. Media size should be significantly smaller than parts. As a result, vibratory finishing machines can easily make a separation in the screen. If parts are much smaller than media then you can make the inverse separation.
Compared with small size media, big size media is cheaper, longer life, and cut faster. However, big size media leave rougher surface compared with small media. So you can choose the bigger media that not affect your surface quality.
2.3.3 Media to parts ratio
The final step is to decide media to parts mixture ratio. To maximize your output, you always want to put extra pieces in your vibratory bowl. However, too many parts in a vibratory bowl result in parts on parts impingement. So here we make some idea regarding media to parts ratio:
1:1 Media and parts are mixed in equal capacity. The small amount of media will make parts on parts hit and scratch a lot. This can work out when the surface mark is not a problem.
3:1 The average ratio use in the vibratory finishing process. However, with vibratory finishing machine with internal separation, you need to have a higher ratio of 4:1.
8:1 8 times and higher media to parts ratio suggest for delicate parts. This mixing ratio also used in vibratory polishing and burnishing process.
2.4 Compound and Water
The correct choice of the compound is very important to get optimal finishing result. The most grinding compound can be used. Today most compounds are formulated in liquid form.
3. A step by step guide for the vibratory finishing process
3.1 Check your parts and decide machine volume
Make the estimation of how many parts you need to run every day, how much time to finish them, the parts to media ratio. With the information above you will know the right size and model of vibratory finishing machine for your job.
You have 2000 pieces of the zamak3 belt buckle to deliver to your customer every day.
Each day you have 10 working hours in your workshop.
From sample testing you know vibratory smoothing process takes 1.5 hours with plastic media.
It will take 30 minutes for parts loading and unloading.
Now we can calculate we need a machine can hold up to 400 zamak3 buckles a day.
To prevent parts scratch and hit, media to parts volume ratio is 3:1
After that, you measure 400 pieces belt buck stacking volume as 50L
The real volume for the machine is 200L
However, in vibratory finishing machines, we only use about 70% of total capacity. This means machine total capacity 200÷70%=285L
You know you need a 300L (or 10 cubic feet) vibratory finishing machine.
3.2 Find a suitable but not expensive machine
The most expensive machines not always the best choice. Keep machine simple as possible. The more complicated the machine, more likely it will go malfunction somewhere, especially for the electronic device.
We don’t install automatic oil lubrication system in the vibratory motor. This adds on the cost and complexity of the machine. We would rather prefer a manual gun which lubricates once a month with 2-3 strokes.
If you can do with vibratory finishing machines without internal separation, then buy a machine without it.
The machine installation is important before you start to use the machine. Vibratory finishing machines structure is simple and ready to go. If you have experience for the job, you can do it by yourself following our vibratory finishing machine installation guide.
If you are first time user of vibratory finishing machines, better to find an electrician close to your location.
3.3 Make installation and get it run
If you can choose electricity, go with 3 phase electricity, for example, 380V, 460 V or 480 V. A single-phase voltage 220V will greatly increase your amperage flow. Besides, 3 phase electricity is safer because it usually grounded.
After confirming with compound performance, you need also take a look at compound concentration because it is one of the important factors for your operational cost. A compound with high concentration and mixing ratio will save you lots of money; even their price is higher with the same package.
If you can buy a compound in tons, the cost of the compound will be greatly reduced and freight reduced as well.
However, if the machine does not work in the right condition, just make a call to the man where your machine purchase from. You can call your media supplier, your compound supplier. Life is short so we do everything right in a simple way.