Abrasive filament brush Deburring
Deburring removes residual material left as a result of part processing through stamping, grinding, fine blanking, etc. The process of deburring typically accounts for a large portion of the overall manufacturing cost, but ineffective deburring can lead to part failure, injuries, or system damage. Part material and geometry, burr location(s) and severity, production rate and other variables get factored in when determining the most effective and efficient means to deburr a part. Matching the strength of one of the many deburring process technologies available with the many part and production variables will yield the most effective and efficient process. This article specifically addresses the unique qualities of an Abrasive Filament Brush as a tool to be employed by an automated system to effectively eliminate burrs in high-volume manufacturing applications.
Abrasive nylon filaments are produced by co-extruding heat stabilized nylon and abrasive grains (e.g. silicon carbide, ceramic, etc.) into a monofilament. The result is a homogeneous, flexible structure containing up to 40% abrasive by weight. In the brush manufacturing process, filament diameter, style (crimped or straight), abrasive grit size, type and loading percentage can all be varied.
The advantages of abrasive filaments over traditional wire brushes are their flexibility, durability, self sharpening feature and the limit of their aggressiveness. Abrasive filament is typically applied where a surface contamination, sharp edge, or burr needs to be removed without negatively impacting the critical geometry or structure of the work piece. Simply stated, abrasive filament is selective and controlled in its abrasive action. Unlike a wire brush, where the sharp tips, rotating at high speed will knock/cut a burr off, abrasive filament brushes work at slower speeds. This allows the side of the filaments to strike and drag against an edge, acting like many flexible files. As the nylon begins to wear away, new abrasive particles are continually exposed. The filament is thus self sharpening as it wears.
Abrasive filament brushes are not considered material removal tools. In general, abrasive filament brushes are used in applications where a part is precision ground, cut, or machined and the burrs created by the process need to be removed without further damaging or altering the part geometry. The force of the filament is expended on the targeted edge, with little abrasive action occurring on other part features. Because the filaments are flexible and compliant, they can work on parts with complex geometries. Common applications for abrasive filament brushes are the end deburring of saw cut aluminum extrusions, surface deburring of double disc ground steel parts, precision ground powdered metal parts, fineblanked parts,machined aluminum automotive wheels, honing of carbide inserts and tools as well as various other machined parts.
An abrasive filament brush should be thought of as an engineered tool. For a successful application, the brush maker needs to analyze the specifics of the part to be deburred and then select/design a brush to maximize effectiveness and efficiency. With the proper brush designed, the next challenge is how to present the part to the brush.
As described, abrasive filaments are flexible and are thus compliant and forgiving in application. They are relatively easy to apply to get desired results in the short term, but much more difficult to apply effectively and efficiently in the long term. Builders of machinery to apply abrasive filament brushes tend to believe that their forgiving nature means that machine design tolerances are not that critical. Conversely, for the performance typically demanded the smallest misalignment or inaccuracy in machine design will be greatly magnified in performance. Design oversight or error will result is an out of spec edge break on the part and/or decreased brush life.
To maximize the performance of an abrasive filament, the machine must apply the part to the brush in a manner that allows the filaments to strike the desired edge at a perpendicular angle. As this perpendicularity is reduced, abrasive action (deburring) marginalizes. Filaments dragging parallel to an edge have little to no effect on burrs or surface finish. Applying a radial style brush (figure 1) results in the filaments wiping in a single (typically downward) direction. Since the filaments need to strike, and drag against the desired edge, effective presentation method of the burred surface is limited. For flat parts, a disc brush provides a more efficient presentation format. A disc brush (figure 2) can provide 360 degree wiping action if employed properly by the machine builder. In designing a machine to apply disc brushes, the builder must consider how to present the part to the brush so that each surface receives proper filament impact. Often, the most effective and efficient way to accomplish this is to independently rotate a group of brushes in a planetary manner.
A planetary brushing head (figure 3) makes achieving a uniform and consistent edge radius possible. The pictured head utilizes 3 x 10” diameter disc brushes. Through use of this design, more than 200” of abrasive surface area is acting on the part. Providing variable brush rotational speed and direction, independent of the turret (head) rotational speed and direction, offers the ability to fine tune the process for each specific application or part. With abrasive filaments continually moving in multiple directions throughout the head, parts being conveyed through benefit from a uniform amount of abrasive action from all possible directions. This result of the planetary action yields the consistent edge radius demanded on today’s precision parts.
Planetary head based deburring systems are commonly used for processing flat surfaces that have been precisely ground, lapped, or machined. Ferrous parts are often “fixtured” magnetically as they are being brushed. Parts are loaded on to a continuously moving conveyor which has a magnetic platen under the belt. The advantage of this system is that it will accept any ferrous metal part without the need for unique tooling, securing each part in place while being deburred. A demagnetizer is typically incorporated into the exit conveyor to remove any residual gauss from the part.
Production rates with planetary head systems are variable. Part type, burr severity, and desired edge break will impact the speed at which they can be processed. Adding additional planetary heads will increase productivity. With multiple heads, conveyor belt speeds up to 60 feet per minute are possible.
A competent deburring machine builder will have an applications laboratory to test your parts. Through this, they will demonstrate the finish provided by abrasive filament brushes and show how different filament and grit combinations will alter edge break. This testing will also determine the optimal machine design necessary to meet productivity and quality requirements.
Abrasive filament brushes have the ability to selectively deburr desired surfaces without dimensionally changing the part. Applied on an automated system engineered for your application they provide an effective, efficient, and safe means for deburring parts.