Automated deburring with nylon abrasive filament brushes generates a payback measured in quality and productivity gains

By John Sockman
Market Manager-Engineered Solutions, Weiler Corp., Cresco, PA

During the 1990s manufacturers spent billions of dollars automating and improving machining processes. In most cases, these investments were made to reduce direct labor content and improve part quality. In this new environment, high-tolerance parts are produced at speeds that were unimaginable a decade ago.

While quantum leaps were made in machining, the ancillary process of deburring received relatively little attention. Trying to improve deburring seemed ludicrous when machining processes were more critical to controlling part geometry and consumed considerably more direct labor.

It is common to see precision-machined components deburred with hand files and power-tool-driven abrasive products. The shortcomings of manual deburring result from the fact that edges and surfaces define the interaction between parts and their environment.

While existing machining methods can quickly produce a part that is dimensionally perfect, poor deburring methods add expensive direct labor and create part inconsistencies, which can result in scrap or performance problems with the part.

Implementing automated deburring solutions with nylon abrasive brushes can eliminate the technology gap between deburring and machining processes. In many cases, implementation is quick and easy and generates immediate payback that can be measured in productivity and quality gains.

Reasons for automating

Recently, manufacturers have focused on improving deburring processes with the following motivations:

* Reduce direct labor content: Secondary deburring operations add incremental direct and indirect labor costs to the finished product. Reducing these inputs can offer significant financial justification for automated deburring. Further justification is created by the difficulty of attracting and retaining competent manufacturing personnel for manual deburring positions that can be perceived as dirty and demeaning.

* Reduce scrap, rework and part variation: Variation is at the heart of manufacturing process instability. While the consistency of parts coming from machining processes can be very high, anything can happen to a part it is deburred manually. Since manual deburring is at the end of the manufacturing process, it can be extremely expensive. Scrapping a raw casting due to dimensional problems is not nearly as costly as scrapping a machined part that has been subjected to "Friday afternoon deburring."

* Eliminate MSDs: Muscular-Skeletal-Disorders (MSD) such as Carpal Tunnel Syndrome have become mainstream issues in the manufacturing community. OSHA (Occupational Safety and Health Administration) and Congress have threatened legislation targeting repetitive motion disorders like those created by manual deburring. Nylon abrasive brushes are commonly selected for automated deburring processes for a number of reasons.

* The capital requirement is low. In-machine deburring using CNC machining centers to remove burrs at the end of the machining process is the least expensive automated deburring method. For the cost of a brush and some programming time, a user can institute an automated deburring process in a few hours.

* Part dimensions are not changed. Nylon abrasive filament brushes are compliant deburring tools which offer selective aggression focused toward part edges. Although the filaments in a nylon abrasive brush act aggressively when applied to an edge, their aggression diminishes on flat surfaces. As a result, they refine surface finishes without measurably changing part dimensions, making them preferable to many aggressive abrasive products.

The selective cutting action of nylon abrasive brushes is due to their pressure sensitivity. When a filament is filing across an edge, the cutting pressure is high due to the small contact area. However, the pressure drops dramatically when the same filament begins to move across a flat surface. Hence, a brush which is used to produce a 0.015´´ radius can also be used to reduce the surface finish to less then 20 microinches Ra.

* Surface finishes are improved. In most applications. Nylon abrasive brushes reduce the surface finish produced by machining processes. As the nylon filaments move across a surface, they file away the asperity peaks in the surface profile. For parts requiring lubrication this is beneficial because the improvement in surface finish does not necessitate a reduction in the ability of the surface to hold lubricant.

* Implementation in CNC machines is easy. Typically, nylon abrasive brushes can be implemented in CNC equipment by copying existing machining programs and making slight changes. For example, the toolpath for a disc brush is very similar to the toolpath for a face mill. The major differences are parameters: spindle speed, feedrate and depth of interference (analogous to depth of cut). In some operations, it is also necessary to take two passes across the part with opposite directions of brush rotation.

* Unlike cutting tools, nylon abrasive brushes do not require exact positioning. The conformability of the brushes makes them extremely forgiving. Typically, positioning within 0.020´´ of the ideal location will produce acceptable results. Although this window of acceptability varies with brush size and application, most operating windows are large and do not require significant programming time to achieve.

* Brush deburring works well in single part flow cells. Many deburring technologies involve batch and queue processes which extend manufacturing leadtimes and increase work in process. In contrast, brush deburring is frequently combined with upstream processes to reduce overall process complexity and cost.

* Finish parts are tracked. Automated deburring with brushes is frequently ac-complished using equipment linked with upstream pro-cesses in single part flow cells. This creates single point accountability for the combined process and encourages overall optimization of quality and productivity.

If the machining and deburring operations are viewed as stand-alone processes, the natural tendency is to optimize them individually. While this approach can produce positive results, it rarely creates an optimal overall system, especially because optimized machining can create additional costs and quality issues which may not be measured. Combining processes allows accountability for productivity and quality at one point in the organization.

* Energy requirement is low. The energy calamity affecting the West Coast recently is causing many manufacturing managers to consider energy issues in the decision-making process. When energy costs are taken into account, brush deburring looks especially attractive relative to competitive deburring technologies.

Application tips

Unlike conventional abrasive products, when using nylon abrasive brushes, faster is not better. Speed causes many deleterious effects in brush performance. First, the nylon carrier is heat sensitive and can be softened or melted by the heat which accompanies excessive speed. Secondly, speed causes the filaments to bounce off the workpiece instead of wiping and filing across the part edges and surfaces. This causes diminished aggressiveness. To prevent these problems, nylon abrasive brushes should be operated at surface speeds below 3,500 sfm. In most applications 2,500 sfm is a good starting point.

When selecting the size of brush to use, a good rule of thumb is to use the largest brush which is practically possible. Generally, large diameter brushes offer better production stability, lower consumable-cost-per-part and shorter cycle times.

Small bore deburring poses its own special requirements for brush selection. While brushes can be effective tools for bore cleaning and removing light burrs within holes, bores that are less than 1.5" in diameter are difficult to debur with brushes. In contrast, bores that are larger than 1.5" can frequently be deburred quite successfully with gangs of nylon abrasive wheel brushes.