Nip microburrs in the bud

If you have ever heard the saying, “the only things certain in life are death and taxes,” you know there is truth in those words. But it is obvious that the person who coined that phrase was not a machinist – otherwise the adage would have included burrs.

Every machined part will have burrs, it’s a fact. While some industries and parts have a larger tolerance for what is acceptable, machined parts are never 100% burr free after turning, milling, drilling or grinding. It is the nature of what we do.

For the vast majority of parts, the burrs can be removed, when necessary, by filing, scraping, sanding and other similar methods. In other cases, a machined chamfer, fillet or radius will provide an adequate edge with no further treatment. Minor imperfections that remain usually go unnoticed and the customers are content.

Then there are those parts that have very precise geometry, fine finish surfaces or the user cannot risk a microscopic chip coming free and contaminating a system. These types of parts usually have very stringent geometric requirements and fine features. Deburring processes for these types of parts must preserve the fine geometries and guarantee that microscopic burrs are removed so there is no possibility of contamination.

Removing burrs from small parts while they are in the machine is the best option. Adding small chamfers or fillets is by far the most common method to remove or prevent burrs. For high volume parts a special insert or tool geometry might be a good choice. It is common to see special drills and reamers with inserts included to break the edge of a hole.

When a cutting tool cannot be used there are numerous abrasive brushes on the market designed to be used inside the machine. Brushing is an effective method of deburring so long as the burs are not heavy. Brushing is also low risk as the abrasive action is not aggressive and there is little chance of changing the part geometry.

Burs (small cutting tools) are most often used with pneumatic tools for hand deburring, but I have seen creative programmers and machinists mount them in machines. Burs are a great choice in both scenarios because they come in an almost endless variety of shapes and sizes. Because they are typically small and the cutting action is much like that of a file they can be used on very small details. When applied with a machine they can be used on very delicate parts with precision. The only drawback is they often require very high RPM to cut effectively, so using them in a machine can pose some challenges.

When deburring inside the machine is not possible, or hand deburring is not practical, then other processes must be considered.

Vibratory finishing or deburring is a good, well-proven alternative. Vibratory machines vary in size from very small to very large but function in the same manner. Parts are submerged in an abrasive media with a soapy solution and vibrated at high frequency. The abrasive media essentially abrades sharp edges – which removes burrs – and burnishes the edges. The soapy solution rinses and lubricates the parts and media. When removed the parts are clean and burr free.

Abrasive media comes in very large shapes and very small shapes. The media is also manufactured from different materials like ceramic, stainless steel and plastics. Vibratory finishing, when applicable, is an economical way to treat delicate parts. Machines and media are inexpensive, and the process is semi-automated. Like brushing, it is also low risk as the process is not aggressive and fine geometry is easily preserved. However, reaching internal features is very challenging and when the wrong media is used it can become stuck in holes, groves and similar features. This is a significant drawback if there is a large variation in part size and shape.

When cutting and abrading methods like those discussed above are ineffective or cannot be applied, then chemical deburring is probably the last option.

Electropolishing is a good example of a chemical deburring process that is common in industry today. Parts are submerged in an acid bath of sulfuric or phosphoric acid and an electrical charge is applied to the part that enhances the reduction reaction. As the current flows from the part to the solution (anode and cathode) it removes microscopic amounts of material. Small sharp edges and protrusions, like burrs, are subject to more aggressive action than larger smoother surfaces resulting in a smoothing effect. (Note: My description is a very general and simple summation of a complex electrochemical process.)

Of course, there are other chemical processes but, in general, they all work in a similar manner. All offer significant benefits over cutting and abrading. Chemical deburring is very precise, which is critical for protecting small parts and fine details. It enhances the overall appearance of the part while improving corrosion resistance. Chemical deburring, because it relies on a chemical solution, can be applied to internal features and other areas that are inaccessible to cutting and abrading methods. Aside from the purchase of special equipment, it is inexpensive.

So, what is the best method to deburr small parts and fine part geometry? It depends on the application and the requirements. However, ensuring the machining process produces minimal burrs and the burrs are light and fragile is the first step. Second, it is always preferable to remove burrs in the machining process, especially when that process is highly automated. When the burrs must be removed after the machining process, then methods like those discussed earlier are effective – but chemical deburring is the most precise and beneficial option available.