3D Printed Parts

An interesting thread about deflashing and surface finishing 3D printed parts has been started on the ShopTalk Forum. As this 3D manufacturing process becomes more popular and mainstream, surface finishing using both barrel tumbling and vibratory tumbling will continue to be an issue. Please provide any comments and experience you have either on The Finished Part Blog here or on the Forum.

Dry Tumble Deflashing

Molded plastic parts often have flashing or excess material that needs to removed from the edges of the part (see part on left of picture). This can be accomplished in a variety of ways including a wet process using vibratory and barrel tumbling with an abrasive media (i.e., Plastic Media) or with an abrasive blasting process to blast the flash off the edges.

If the part is a hard plastic with a relatively simple geometry and the surface finish needs to be maintained, tumbling the part with a polishing media is ideal. The mass of a polishing media will knock the flash off the edges and will not change the surface finish since it is a non-abrasive media.

The part on the right was barrel tumbled with a KP Ceramic Angle Cut Cylinder that was small enough to pass through the ID of the part. These results were obtained in only 15 minutes. The parts were retrieved from the process clean, dry and ready for the next step in the production process.

Plastic vs Ceramic Media

Selecting the proper media can be as much an art as a science. A clear understanding of all the finishing requirements is necessary. Considering the needed edge rounding, surface finishing, cycle time, metal type and many other factors are critical.

Notice the very heavy flashing on this aluminum part (far left in picture) left over from the machining process. This 'raw' part also had some machining marks on the surface that needed to be removed. The easy solution to finishing this part is to throw it in a vibratory tumbler with some Ceramic Media (see part on right) to remove the flashing and surface marks. Alternatively, Plastic Media will take a little longer to deflash the part but will result in a smoother surface finish and less edge rounding (see middle part).

For this project, the objective was to get a smooth surface finish with slightly rounded edges in order prepare the part for a painting process. Ceramic Media was the best selection in this case due to the shorter cycle time, increased edge rounding and 'rougher' surface finish.

Polishing Delrin, Nylon and Teflon

Here is a link to a terrific exchange on our ShopTalk Forum about removing machine marks, deflashing and then polishing delrin, nylon and teflon.

Some good practical vibratory tumbling advice.

Deflashing Polypropylene Plastic

The objective is to remove flashing, sharp edges, machining marks and rough surfaces from a polypropylene plastic part. This material is often used to make molded products such as orthotics. This process is required for preparation before further processing such as painting and coating.



The part on the left shows the sharp edges and machining marks that need to be removed. This was accomplished (see part on right) by vibratory tumbling the part in a Ceramic Media for 2 hours. The resulting smooth, matte finish is ready for painting or application of any type of required finish.

The part below shows how aggressive vibratory tumbling can be. The part on the left is a raw part that is dramatically 'worn down' by an aggressive ceramic media after 4 hours.

Thermoplastic Polishing

Before

This small polyamide, thermoplastic resin, hardened part had a rough surface finish as well as flashing that needed to be removed. The challenge in deflashing and polishing plastic parts is to choose a media that will be aggressive enough to remove enough material to create a smooth finish without scratching or etching the surface too much so that the part can be polished successfully.

After

A two-step process was used to first de-flash the part and then polish the surface. The first step involved vibratory tumbling with a Precision Ceramic Fast Cutting Sphere to remove the flash and smooth the surface. This shape and bond (formulation) of media provided good cutting action (deflashing and edge rounding) but not the rough, 'tumbled' finish normally associated with angular shaped media. The part was then polished with a Precision Ceramic Polishing Sphere. Again, this shape provided the best polishing action and left the part with a near-mirror surface.

Deflashing Fiberglass

Heavy flashing on edges

This molded fiberglass part has heavy flashing on the edges that needs to be removed more efficiently than a hand sanding or scraping operation. In addition, a dry process is preferred (in this situation) so the customer does not need to take the extra step of drying the part prior to further processing.

No flashing after vibratory tumbling

A dry tumbling process using Hardwood Peg Media and Dry Abrasive Cream successfully removed the flashing and produced a smooth, rounded edge. In this type of process, the compound is 'coated' to the Pegs and tumbles against the part to abrade away the flashing. If necessary (but not required in this situation), different dry tumbling compounds can be used to polish the part or even produce a high gloss finish.

Deflashing Plastic Parts

Molded plastics often contain flashing that needs to be removed. While there are many methods ranging from a sharp knife to cryogenic deflashing, vibratory tumbling is an effective and cost efficient method.

Flash sticking above edge
Flashing removed - smooth edge, matte finish


The part was vibratory tumbled with Ceramic Media for only 30 minutes. A non-abrasive tumbling compound solution was used to keep the process lubricated and clean. Even after this short cycle time, the flashing was completely removed and the edge was smooth. The surface had matte, tumbled finish. At a 30 minute cycle time the general purpose media should be able to be re-used for 250 or more batches to spread the operating cost over many parts.

Choosing Tumbling Media for Deburring, Deflashing or Polishing

Choosing the proper tumbling media (vibratory tumbling or barrel tumbling) for any deburring, deflashing or polishing application requires balancing the aggressiveness of the operation with the surface finish specifications. As long as a rough, tumbled appearance is acceptable a more aggressive media can be used to remove burrs and 'smooth' a surface resulting in a shorter cycle time . If the surface finish is important (i.e., for anodizing or thin-coat plating), a less aggressive media and longer cycle time is necessary. Often a multi-step process is used with progressively less aggressive media to achieve a deburred and smooth part or even polished part.

Generally, Ceramic Media are used on harder metals like steel or titanium. Plastic or Synthetic Media are better for softer metals like aluminum, brass and copper. Within each type of media, a variety of formulations (or bonds) are available from ultra aggressive to general purpose to polishing.

Deflashing Composite Wood

This customer molds a variety of glass filled plastic and wood composite items. The process creates significant flash on the edges that needs to be removed. The current process involves hand sanding that is time consuming, labor intensive and does not result in an even finish across the entire surface area of the part.

Since these parts cannot get wet (due to swelling and potential damage) the parts were vibratory tumbled with a fast cutting (KSF) Ceramic Angle Cut Cylinder Media with no water and no compound. The cycle time required to get a smooth, slightly rounded edge with a uniform surface finish across the entire part was only 30 minutes.

Tumbling with Abrasive Grit

Tumbling parts to achieve a deburred, deflashed or rounded edge is a common process. Both vibratory and barrel tumblers are used for this purpose. Choosing the proper media type is critical to achieving the desired finish.

Most applications require the use a preformed tumbling media. These media contain abrasives that are released into the tumbling process to remove the burr, etc. The (relatively) large mass of the media assists in this process by acting as a sanding block of sorts on the edge and surface of the part. After this abrasive process, parts can be tumbling in other media (including grits) to achieve a smoother or polished surface finish.

Tumbling parts simply with an abrasive grit such as Aluminum Oxide, Silicon Carbide or Walnut Shell does not typically achieve the deburring, deflashing or edge rounding required. While the grit may be very sharp, hard and abrasive, there is very little force acting against the edge of the part. The surface finish will probably be affected (roughening, smoothing or even polishing) but the edges will be left mostly untouched.

There are some exceptions to this 'rule' (see this post) but generally preformed tumbling media is superior to grit media for deburring, deflashing and edge rounding.