In many ways, the tumbling process for metal finishing is an art, as it makes metal components and other smaller workpieces look more appealing. But just like with other finishing methods, it’s not just about making parts look pretty. There are numerous practical reasons manufacturers use a metal tumbling process. For metal, such finishing also gives components greater resistance to both friction and wear, while also augmenting their durability. A better understanding of how the tumbling process for metal works will help manufacturers decide whether it or another finishing process should be used for their specific application.
Understanding the Tumbling Process for Metal
In a nutshell, the tumbling process is a method for collectively finishing smaller components and workpieces. Depending on the exact technique used, how rough the parts are after fabrication and the number requiring finishing, this mass tumbling process for metals can take anywhere from a few minutes to as long as 24 hours. The various metal parts that can be finished via the tumbling process include titanium, stainless steel, copper, bronze, brass and aluminum. A key aspect of the tumbling process for metal involves placing parts within a barrel or other container, where they’re mixed with abrasive media. The barrel is then rotated, which in turn causes the media to polish the components within it en masse.
The intensity of these actions depends upon:
- Barrel or container diameter
- Compounds mixed into media and what amount
- Duration of process
- How much water is used (if any)
- Number of components processed
- The rotational speed of the barrel or container
- Type and amount of media used
A key element for this finishing method often involves water, though a dry tumbling process for metal is sometimes used instead for certain applications. In addition to water, media and compounds are also added in the wet tumbling process. For metal deburring or polishing, water reduces the friction that occurs between the media and components. Water also acts as a cleanser to remove contaminants like dirt or grease that build up on parts during fabrication.
Media will often contain abrasive pastes that assist with this finishing process. Components, media and abrasive compounds are put into the tumbling machine’s barrel, where their surfaces are ground down, polished and otherwise made smooth via friction. Treatments also depend on the material undergoing the tumbling process. For harder metals, for example, the type of media and abrasive pastes will differ from those used on softer materials. The level of friction created from mechanical tumbling action is based on the amount and nature of the media used.
Media Used in Metal Tumbling Processes
Various media can be used in the tumbling process. For metals finished via tumbling techniques, primarily ceramics, natural plastics like wood chips, steels and synthetic plastics are used, with each media having certain advantages. This media also comes in different sizes and shapes, from plastic or ceramic chips used for cutting to needles or steel shot used for burnishing. Carbon steel, high-density ceramics, hardwoods and plastics can all be used in the tumbling process for metal parts.
Carbon Steel
Used to burnish and polish metals, carbon steel media creates considerable pressure that results in a very shiny finish. Introducing carbon steel as a media in the tumbling process truncates finishing times, while also improving components’ resistance to wear. Carbon steel media also hardens component working surfaces.
Other benefits of carbon steel in the tumbling process for metal parts include:
- Bulk density is extremely high
- Can process multiple sizes and shapes
- Cycle times shortened
- Dimensions of components are maintained
- Media lasts longer
- Short Cycle Times
Using carbon steel media in the tumbling process for metal components results in increased wear resistance and improved performance, while also decreasing metal porosity.
High-Density & Other Ceramics
While regular ceramics can be used in the tumbling process for metal parts, high-density ceramic media results in a better overall polish, less residue, reduced processing times and speedier deburring, regardless of the type of tumbling equipment used.
Other benefits of high-density ceramics in the tumbling process for metal parts include:
- Allows increased throughput of components
- Enables more intricate finishing
- Fracture-resistant
- Highly durable media
- Media comes in a wide variety of sizes
- Quicker cutting actions
- Results in less residue and wastewater
Ceramic media is generally used in the tumbling process for harder metals, along with applications that require heavy cutting.
Hardwoods
Sometimes used in a dry tumbling process for metals, hardwood chips are employed in conjunction with abrasive finishing creams. Though well-suited for plastic parts, it can achieve mirrorlike finishes for metal components, while also providing a durable polish.
Other benefits of hardwoods in the tumbling process for metal parts include:
- Cushions components during tumbling
- Media is lighter weight, so it works well for delicate components
- No need for water
- Provides consistent finishes
- Used for a variety of tumbling systems
Ceramic media for tumbling metal is used to do light deburring and create very polished finishes on such items as eyeglass frames.
Synthetic Plastics
Often synthetic plastics are used as media in the tumbling process for metals like aluminum or alloys like brass, which are softer. Used for burnishing and polishing as well as both standard and precision deburring, plastic media is also used for finishing components that feature threaded holes. Conically shaped plastic media is used most frequently in the tumbling process. For metals, this shape allows media to last significantly longer, as cones don’t lose their original shape as they wear.
Other benefits of plastics in the tumbling process for metal parts include:
- 30 percent lighter than ceramic tumbling media
- Available in various sizes and shapes
- Doesn’t make parts shiny or otherwise discolored
- Eliminates lines from machining
- Enables shorter cycling times
- Provides parts with smooth surface finishes
Prior to an anodizing treatment, the tumbling process for metal often uses plastic media. The variety of shapes available also makes plastic particularly suitable for certain applications. For example, triangles work well for flats and corners, whereas components with holes often use media shaped like tetrahedrons or cones.
Advantages of the Tumbling Process for Metal
Regardless of the exact type of tumbling process used, precision finishing can be achieved in a relatively short period via tumbling. The process for metals can take between a few hours to mere minutes. It’s generally speedier than other finishing techniques, providing precise and reliable finishing consistently. The tumbling process for metal is also particularly effective at clearing drill holes, eliminating sharp edges and smoothing surfaces.
Advantages of using a tumbling process for metal finishing include:
- Automation: Unlike manual or other finishing processes, the tumbling process for metals doesn’t require monitoring to produce large quantities of finished components.
- Cost-effectiveness: Today’s tumbling machines offer a very affordable means of finishing parts; with their ability to process multiple components simultaneously, allowing manufacturers to enhance durability and lifespan quickly and efficiently.
- Gentleness: While the tumbling process for metal uses high levels of friction to deburr and clean components, this finishing technique is comparatively gentle, maintaining the shape and integrity of parts made from more sensitive materials with complex geometries.
- Lower maintenance: Modern tumbling machines are known for their uptime, needing very little maintenance or cleaning in comparison to other finishing methods.
- Mass-finishing: Capable of finishing numerous workpieces all at once, the tumbling process for metals saves considerable time and, in turn, money.
- Uniformity: With any metal components, consistency is key to ensuring their tolerances so products work as they should; along with ensuring more uniform mechanical properties, the tumbling process for metals ensures better aesthetics, luster and evenness of surfaces.
- Versatility: Machines used in the tumbling process for metal, particularly vibratory machines, can be customized to meet specific manufacturing requirements, while also being able to polish a wide range of metals and alloys, including titanium, stainless and other steels, nickel, copper, bronze, brass and aluminum.
Barrel and other tumbling processes for metal also allow more sophisticated techniques to be used, which can increase the toughness and strength of components.
Different Types of Metal Tumbling Processes
Various types of tumbling processes can be used to finish metal parts and other workpieces. However, two of the more commonly used tumbling processes for metal are vibratory and high-energy tumbling.
Vibratory Tumbling
Though some vibratory tumbling techniques don’t use water, which is known as dry tumbling, wet tumbling processes are far more common since they result in cleaner finishes on metal parts. The wet vibratory tumbling process for metals is also more sustainable as the water can be reused. With the dry process, the media is normally nonabrasive or synthetic to produce less dust. Additionally, dry processes are more expensive, another reason why it’s less used.
With wet vibratory tumbling, water and abrasive media are combined in a vibrating bowl or tub. The machine to which the bowl or machine is attached vibrates rapidly, causing the media and parts to collide within the water. While this process cleans and descales surfaces, it also can be used to prepare components for further surface treatments. Whether wet or dry, the vibratory tumbling process for metals is a tried and tested technique used for many decades that polishes and smooths the parts’ surfaces.
High Energy Tumbling
Known also as centrifugal barrel finishing, the high-energy tumbling process for metal parts features a barrel positioned on the end of an arm that rotates to produce considerable centrifugal force within the barrel, speeding the process exponentially. Typically, when time is limited manufacturers will prefer a high-energy tumbling process. For metal components finished via this technique, water and abrasive media are put into a barrel, which is then sealed. Barrels are then put on a carousel, which spins to create a centrifugal force as the parrels move in one direction and spin in the other.
Within this suspension of abrasive media and water, component surfaces are smoothed out quickly. How fast depends on the type of material out of which the parts and media are made, along with the tumbling machine’s speed. For many applications, a high-energy tumbling process for metal components proves to be the most economical. However, though this metal tumbling process offers greater efficiency and speed than other tumbling methods, it can cause damage to more fragile components.
RP Abrasives for Metal Tumbling Finishes & More
RP Abrasives offers finishing services for manufacturers, including vibratory and high-energy tumbling processes for metal. Providing quick turnaround times, our company is ISO 9001:2015 certified, ITAR registered and RoHS and RoHS2 compliant. Our eco-friendly facility provides finishing services for customers throughout North America. To learn more about what RP abrasives can do for you, contact us at (603) 335–2132 or request a quote online