ABRASIVES IN 3D PRINTING: FINISHING TECHNIQUES FOR METAL COMPONENTS

Although post-processing is optional for many uses of metal 3D printed parts, a wide range of finishing choices are available for those that are.

While binder jet parts have material qualities that are on par with or better than their conventionally made equivalents, several significant differences exist.

In comparison to parts that are cut, machined, or turned, 3D-printed metal products will have substantially increased surface roughness, visible build layers, and sharp edges or burrs.

GREEN SANDING

Green sanding is a fantastic way to minimize the visibility of printed layer lines and other surface irregularities, particularly in extrusion-based printing techniques. It is used after producing parts, while a polymer binder binds the metal powder together. 

Layer lines and other minor defects can be easily smoothed out with a basic Scotch Brite pad because the green sections have a consistency similar to that of a crayon. Sandpaper can be used more vigorously, and a detailed razor can sharpen edges.

Green components are easier to work with than sintered metal parts, but because of their soft consistency, caution must be exercised to avoid damaging them. 

On the other hand, green sanding has several significant advantages. The surface finish of items that have been green sanded is usually three to five times finer than that of unsanded parts. Depending on the application, sanded parts can result in a ten-fold reduction in the time needed to post-process final metal parts.

MEDIA BLASTING

To wear down the surface and create a consistent matte or shiny finish, media blasting uses compressed air to force a blast media, such as alumina, stainless steel shot, or glass beads, against the part. 

Media blasting is a quick and easy way to remove discoloration or blend in surface scratches and tool marks without affecting the items' dimensional correctness. It just takes a few minutes to complete.

Varying the air pressure can also alter the blasting process's level of aggression. At lower pressures, a part's surface can be colored, and at higher pressures, when glass beads or steel shots are used, the surface can even be deburred.

TUMBLE FINISHING

"Tumble finishing" describes operations in which parts are only mechanically polished using low-energy, random-motion machines, media, and abrasives. 

Tumble finishing works best on parts with relatively basic geometries; however, it can be applied to big and small parts. When used in more intricate geometries, tumble finishing may produce uneven finishes.

PIN FINISHING

Pin finishing, a tumble finishing, is perfect for processing smaller parts at a minimal cost. 

Strong magnets push metallic components and media in a circular direction. The agitation and movement of the media and parts against each other deburr parts.

VIBRATORY FINISHING

Vibratory finishing is a batch-finishing technique usually used on many relatively tiny components. It entails placing parts in a vibratory tumbler tub filled with different-shaped abrasive media. 

The parts are burnished, cleaned, and brightened as a result of the media rubbing against them due to the tub's vibratory action, which also removes burrs. The technique can be wet or dry, gentle or forceful, depending on the application and abrasive medium composition.

The operation is usually carried out in an open tub so operators can readily see when the required finish has been reached.

HIGH ENERGY FINISHING

High-energy finishing is a mass finishing process with removal rates up to ten times faster than vibratory finishing, allowing for the quick finishing of tiny parts. 

Centrifugal disc systems, centrifugal barrel systems, and drag finishers—which significantly shorten finishing times by utilizing centrifugal force and mechanical advantage—are standard methods for high-energy finishing.

High-energy finishing is typically used in applications that require quick, high-volume throughput and situations where material removal from parts is required, such as burnishing, cleaning, deburring, radiusing, or blending.

ISOTROPIC SUPERFINISHING

Isotropic superfinishing, exclusive to REM Surface Engineering, combines chemical and mechanical finishing to give metal components a mirror-like sheen. 

The procedure first employs a chemical solution to create a self-assembled monolayer or simply a soft metal layer on a part's surface. After removing that layer, the pieces have very little roughness, waviness, or sharp micro-notches and are incredibly smooth. This is achieved with a relatively light vibratory finishing cycle.

The method has many benefits over conventional, abrasive-only methods. 

This procedure creates mirror-like finishes faster than other methods. It can also finish more intricate internal features and tiny through-holes while maintaining a uniform finish on more complex geometries.

The process's superior ability to preserve part geometry over conventional finishing techniques, especially for features like gear teeth, may be the most significant advantage.

ABRASIVE FLOW MACHINING

Abrasive flow machining is an internal surface finishing method involving forcing a viscous solution packed with abrasives into a workpiece. It can be used to remove burrs, polish surfaces, produce radii, and even remove material from parts. 

Abrasive flow machining, commonly employed in the mold, tool, die-making automotive, and aerospace industries, uses a hydraulic ram to push the media through the part.

This force forms an abrasive material "file" or "slug" that precisely fits the item, making it the perfect method for interior surfaces, slots, holes, cavities, and other hard-to-reach places for other grinding or polishing techniques. 

ELECTROPLATING AND ELECTROPOLISHING

While finishing items using electroplating and electropolishing require electricity, they do so in distinct ways. 

In electroplating, a negatively charged portion is drawn into contact with positively charged metal ions dissolved in solution by means of current, creating a thin coating that covers the entire part. Wear and corrosion resistance, electrical conductivity, malleability, solderability, and aesthetic concerns are frequent uses for electroplating.

Electropolishing, frequently called electroplating in reverse, removes material from objects using electric current. 

The method significantly improves surface smoothness, minimizes surface roughness, and levels micro-peaks and valleys, making it the perfect choice for polishing objects with irregular shapes.

MACHINING, GRINDING, AND ELECTRICAL DISCHARGE MACHINING

To guarantee that parts match crucial dimensions and finish standards, machining, grinding, and electrical discharge machining (EDM) are among the most often employed finishing techniques for metal parts. 

Even though they have advantages like quick material removal, exact tolerances, and superb surface finishes, they also have drawbacks like labor costs, equipment accessibility, and the requirement for special jigs and fixtures.

WIRE BRUSHING

Wire brushing is one of the least expensive methods of polishing metal and 3D-printed items in small quantities. It involves using portable power brushes or wire wheels mounted on a drill or grinder to remove surface flaws and burrs.

POLISHING AND BUFFING

Polishing and buffing are two different procedures despite their similarities. Polishing, the most forceful of the two use an abrasive that is adhered to the work wheel. Polishing begins with a rough abrasive, as low as 60 or 80 grits when dealing with an unfinished component. Up until the required finish is reached, progressively finer grits are used in each successive phase.

In contrast, buffing is less forceful and results in a smoother, brighter surface by applying a loose abrasive to a work wheel.

Polishing and buffing compounds are applied to electric drills or high-speed polishing machines to provide a mirror-like finish.

CONCLUSION

Metal 3D printing offers a wide range of finishing possibilities. It enables customers to construct components with extremely complicated geometries that would be challenging, if not impossible, to create using conventional processes. 

There are countless options for printed items' final appearance, feel, and functionality since almost all finishing and post-processing techniques available for conventionally manufactured parts may be applied to 3D-printed parts.

Even while various finishing alternatives have well-known trade-offs, such as part specifications, capital needs, and per-part prices, in some circumstances, the advantages of 3D printing may outweigh those drawbacks.