Abstract:
Nylon abrasive filament (NAF) brushes solve many deburring, edge radiusing and finishing of complex extruded part shapes. Their compliancy and filamentary nature accommodate part contours and prevent damage to value added components. These brushes can be used either on manual/off-hand set-ups like bench/ pedestal grinders, drill presses or on  automated set-ups like CNCs, robots and other automated workstations. However, the compliant, forgiving nature of these brushes and make them ideal candidates for CNCs, robotic and other automated work stations. These brushes replace tedious hand operations such as filing/picking, provide consistent quality, improve productivity, shorten cycle times, improve part finishes, generate precise edge radii, and lower finishing costs. This paper discusses guidelines to engineering deburring and finishing solutions using NAF brushes by providing a thorough understanding of the NAF brushes and the brushing process. 


1. Introduction to Nylon Abrasive Filaments:

Nylon abrasive filament (NAF) brushes have been providing deburring solutions for many complex part shapes. These tools evolved over the past decade to cope with the increasingly stringent requirements of state-of-the-art manufacturing. Shorter cycle times, tighter part tolerances, improved part finishes, precise edge radii and lower deburring costs are easily achieved by employing NAF brushes in CNCs, robots and other automated deburring set-ups.

NAF brushes are made of heat stabilized nylon filaments impregnated with abrasive grain, as shown in Figure 1. Working like flexible files, they conform to part contours, wiping and filing across part edges and surfaces. This action deburrs, edge blends and surface finishes parts. 

Filament configurations available are round crimped, round straight or rectangular. Rectangular filaments, having a larger cross section, are stiffer than round filaments, and, therefore, are more aggressive. They also provide greater abrasive contact with the work surface, as shown in Figure 2.




Figure 1: 
Enlarged View of Nylon Filaments
Impregnated with Abrasive Grain



Figure 2:
An Illustration of Nature of Contact of Various
Filament Configurations with Work Surface

Nylon, an ideal material for a brush filament, has excellent toughness and fatigue properties as well as moisture, abrasion and chemical resistance compared to other polymers [1]. Also, its good memory (ability to return to its original position after being deformed) lends itself to brushing. Nylons used in the production of nylon abrasive filaments are Type 6, Type 66 and Type 612. Of these, Type 612 offers the most heat resistance and is preferred in industrial applications. Normal percentage of abrasive grit weight to total filament weight is 20-40%. 

Abrasive grits commonly used in nylon filaments are silicon carbide and aluminum oxide. Silicon carbide has excellent hardness, toughness and sharpness, and is cost-effective for use in nylon filaments. The silicon carbide used in these filaments has less than 0.1% iron oxide and no free iron. Therefore, filaments with silicon carbide can be used on non-ferrous metals, such as aluminum, without a chance of corrosion from iron contamination [1]. Because aluminum oxide is tougher than silicon carbide, it is less likely to fracture, and is used for finishing softer metals. It is also used when risk of carbon contamination raises concern in 'hi-tech' applications, especially in the aircraft, aerospace and bio-medical fields.

Abrasive grits in round filaments generally range in size from 46 to 600; grit sizes available in rectangular filaments vary from 80 to 320. These grit sizes represent the mesh (sieve) number used in abrasive particle separation. Smaller grit numbers relate to coarser (larger) grit particles. In round filaments, grit size decides filament diameter (coarser the grit, larger the filament diameter) as shown in Table 1. Rectangular filaments, regardless of grit size, are offered in .045" X .090" (~1.1 mm X 2.3 mm); although other rectangular filament sizes are available.


Table 1: Typical Nylon Abrasive Filament Diameters and Grit Sizes

* Grit Size corresponds to the mesh number used in abrasive particle separation

Although grit sizes range from coarse (46) to fine (600), NAF brushes are not high material removal tools like grinding wheels or coated abrasive products. They only remove very 'small' amounts of material, changing surface characteristics and improving micro finish. Figure 3 shows relative material removal (and surface finishing capabilities) of NAF brushes as compared to grinding and coated abrasive products. As shown, grinding and coated abrasive products can be high material removal tools, but NAF brushes, metallic wire brushes and non-woven abrasive products are surface finishing tools. The manner in which abrasives are held in the above products governs their material removal and surface finishing capabilities. 

For instance, under a specific condition, an 80 grit coated abrasive belt and an 80 grit rectangular NAF wheel brush were run on a mirror finished surface (4 µin or .1 µm Ra) to compare their finishes. The belt made deeper scratches and removed larger amounts of material compared to the NAF brush. On measuring the finish, it was found that the belt generated a 100 µin. or 2.54 µm, (Ra) finish. The NAF brush, even with aggressive rectangular filaments, only produced a 30 µin. or .76 µm (Ra) finish. 




Figure 3:
A Chart Showing Relative Material Removal (Surface Finishing)
Capabilities of Various Material Removal/Surface Finishing Products
(Source: Anonymous)


2. NAF Brush Configurations: 

Nylon abrasive filaments are used in various brush configurations such as wheel, disc, cup, end and tube as shown in Figure 4. They are used on automated equipment such as CNCs, robots and other specially designed automated set-ups. They are also used on manual and semi-automated equipment such as air and electric portable tools, bench/pedestal grinders, buffing and polishing lathes, drill presses and milling machines. These brush configurations are used to process different part geometries under various operating conditions as illustrated in application case studies later in the paper.



Figure 4: 
Different Configurations of Nylon Abrasive
Filament (NAF) Brushes: a) Wheel b) Disc c) Cup d) Tube e) End


3. Benefits of a NAF Brushing Process:

The NAF brushing process offers several benefits to the end-user: 

During use, sharp new abrasive grains are constantly being exposed as nylon wears against the work surface. This provides consistent brushing action throughout the brush life.
These brushes accommodate various part contours due to their compliance and filamentary nature.
Their compliance accommodates for small errors in part positioning and slight variations in part or burr sizes, making them good candidates for robotic and automated workstations [2]. 
Unlike rigid tools, their compliance also prevents damage to value added components, and hence minimizes/eliminates scrapping of components. 
They lend themselves to automation, thereby making deburring and edge radiusing processes less labor intensive and time consuming. 
Due to automation, medical conditions such as carpal tunnel and tendonitis can be prevented.
Under normal operating conditions, no coolant is required; therefore, no wastes are produced, leading to a clean and dry working environment. 
Dedicated equipment is not needed, as they can be used on CNCs, robots and automated workstations. 
They allow machining and deburring/finishing operations in a single set-up, thereby eliminating the need for additional part handling or refixturing.
NAF brushing processes do not require part preparation or post cleaning, as may be required by some contemporary methods. 
They cost-effectively replace tedious manual methods, non-woven abrasives, mass media finishing, buffs and compounds, abrasive flow/jet machining, air blasting, and thermal and electro-chemical deburring methods. Table 2 discusses some limitations of the contemporary methods that can be alleviated by using NAF brushes.

Table 2: Limitations of contemporary methods of deburring and edge 
radiusing that can be overcome using NAF brushes.

4. Engineering a Deburring Solution using NAF Brushes: 

Effective deburring solutions can be engineered by controlling the brush and process parameters (see Figure 5) that affect brush aggression and performance. Below are some guidelines to customize these parameters to suit your specific application. 


4.A. Brush Parameters: 
Tips on selecting brush parameters for effective deburring are discussed below:

4.A.1. Filament Configuration: 
Use round filaments when: 
-  reduced aggression is required; especially when processing softer 
   metals such as aluminum and brass
- added brush conformability is desired to accommodate contours in a 
   part. Proper selection of filament diameters can allow the filaments to 
   reach burrs in tight, inaccessible areas, such as burrs on the sawcut ends 
   of a aluminum heat sink. This means the smaller diameter filaments offers 
   better reach into tight, inaccessible areas better than larger filaments. 
   Also, be informed that smaller diameter filaments, although provides better 
   reach, have smaller abrasive particle size, thus reduces brushing aggression. 
   The exception to this rule, is 120 grit which is offered both in .040” and 
  .022” diameter. For applications requiring to reach into tight, inaccessible 
  areas without sacrificing aggression, .022” diameter filament with 120 grit 
  is recommended. Also, to get into tight, inaccessible areas, round straight 
  filaments are more effective than round crimped filaments. Round crimped 
  filaments with 180grit round crimped filament would be a good starting 
  point for deburring aluminum extrusions. The 180 grit is aggressive enough 
  for the soft aluminum while providing a good finish. 

Use rectangular filaments for maximizing aggression, and when brush conformability to parts is not an issue. Using rectangular filaments with 80 grit abrasive grains will provide the most aggressive brushing to enhance productivity.

4.A.2. Grit Size: 
Use 80 grit for all applications except when:
-  reduced aggression is required; especially when processing delicate parts 
   and softer metals such as aluminum and brass. 
-  generating minimal edge breaks
-  producing a desired surface finish
-  smaller filament cross-section offered in other round filament grit sizes are more suitable to get into the edges of small holes/slots and other features on the part.




4.A.3. Abrasive Type: 
Use silicon carbide for all general applications. 
Use aluminum oxide only in cases where silicon carbide causes part discoloration or raises contamination concerns on certain non-ferrous applications. 

4.A.4. Brush Diameter and Trim Length: 
Brush diameter depends on the size and shape of the work piece, and process/equipment constraints. Some constraints include available spindle speeds, maximum brush diameter that can be used due to machine guard clearance or space limitation between brush face and work surface, etc. 

Wheel brush diameters are sometimes chosen based on the trim lengths. Generally larger diameter wheel brushes have longer trim lengths. Longer trim length is required to adapt to contoured parts and for parts requiring greater wiping and filing action. In many cases, each wheel brush diameter is available with various trim lengths to create different degrees of conformabilites and brushing characteristics. Disc brushes, however, are offered with a standard trim length unless customized to suit a specific application.

4.B. Process Parameters: 
Tips on selecting process parameters for effective deburring are discussed below:

4.B.1. Depth of Interference (DOI): 
DOI is analogous to depth of cut in machining. It depends on:
trim length - longer trim can accommodate greater DOI
spindle speed - slower spindle speeds [RPM] can allow greater DOI
part geometry - contoured parts require greater DOI to allow filaments 
   to adapt to contours and wipe and file across all edges and surfaces

4.B.2. Spindle Speed (RPM): 
Spindle speed depends on brush diameter, DOI and part geometry. Spindle speed, along with brush diameter, dictates surface speed (SFM). Usually, NAF brushes are operated at surface speeds below 3500 SFM (17.8 m/sec) to prevent overheating and smearing of the nylon onto the work surface. However, higher surface speeds can be accommodated by using coolants. Tables 3a & 3b show suggested spindle speed (RPM) ranges for various wheel and disc brush diameters. 

Table 3a: Suggested Spindle Speed Ranges for Wheel Brushes

Table 3b: Suggested Spindle Speed Ranges for Disc Brushes

Suggested spindle speed for tube brush is not to exceed 2000 RPM. 
Spindle speed for an end brush is not to exceed 10,000 RPM. 

When selecting spindle speeds from the above tables, 
1. using a higher spindle speed in the range will improve brush aggression 
2. using a lower spindle speed in the range will enhance brush conformability

Spindle speed, influenced by DOI, is generally decreased with increase in DOI. This ensures that the spindle speed and DOI combination allow filaments to conform smoothly to part contours. Such a combination insures that filaments are not hitting the part and bouncing off its surfaces, but are wiping and filing across its surfaces and edges. This brushing action also contributes toward longer brush life. Therefore, contoured surfaces are processed at slower speeds and greater DOI than flat surfaces. 

4.B.3. Feed Rate: 
Feed rate is determined by the amount of deburring, edge radiusing or surface finishing required, as well as type of material being processed. It is generally application specific. Slower feeds result in greater brushing action. 

4.B.4. Coolants: 
NAF brushes can be run dry; however, certain deburring conditions such as higher speeds and greater DOI combinations can create excess heat buildup, causing the nylon filaments to melt and smear on the work surface. To overcome smearing, coolants are recommended. Coolants are also recommended when working with CNCs and other automated setups to flush the burrs/metal particles and worn abrasive grit away from the precision machine components such as bearings, guides and slideways. The worn abrasive particles and metal chips in the coolants can then be trapped and removed by using a good filtration system with at least a 50 micron filter. This will minimize machine wear and tear, keep machines running clean, and keep airborne particles to a minimum. Coolants used are generally water-based.

4.B.5. Other Process Considerations:
Number of brush stations required: Once the brush and other process parameters are customized to provide maximum aggression, actual cycle time required to deburr a part can be established. If this cycle time does not meet the desired production rate, multiple brush stations may have to be set up. 

Brush path and rotation direction: For effective deburring, path and rotation of the brush(es) with respect to the part shape, burr location and burr orientation also need consideration. 

5. Case Histories:

Some applications using NAF brushes are discussed in the following case histories. The abrasive grit used in all the case histories was silicon carbide. provides more case histories on applications specifically involving aluminum extrusions. Appendix A *** provides more case histories of NAF brush applications. The case histories in the Appendix, although does not pertain to aluminum extrusions, is included to enhance the readers’ understanding of the brushing mechanics and provoke ideas that could be applied or adopted when developing deburring/ finishing processes for aluminum extrusions. 

5. Various Applications Involving Deburring and Finishing of Aluminum Extrusions

Deburring various shapes of aluminum extrusions as seen in Figure 6. Alternate methods are to use hand files, wire brushes and sanding discs, depending on part shapes.

NAF brushes in various configurations (wheel, disc, tube and end) are very conducive to deburring various extruded shapes. Normally, brushes with 180 grit crimped filaments are chosen. The 180 grit crimped filaments provide adequate aggression on a soft metal like aluminum without sacrificing part finish. Their compliance and filamentary nature adapt to various shapes without damaging/ changing part shapes. When deburring saw cut ends of extrusions, either a wheel or a disc brush is selected depending on the equipment available, and level of automation desired. Tube brushes and small diameter wheel brushes are chosen to deburr/finish inside diameters, while end brushes are selected to deburr/ finish hard-to-reach areas and tight corners. Figures 6-16 show a number of deburring/ finishing applications using different brush configurations.


Figure 6: Various Shapes of Aluminum Extrusions


Figure 7: Deburring of Aluminum Extruded Shapes
(left extrusion in each photo shows the extrusion before
deburring and the right extrusion in each photo shows
extrusion after deburring 

Figure 8a: Saw Cut End Before Deburring 


Figure 8b:
Saw Cut End Being Deburred Using a Disc Brush 




Figure 9: Deburring Heat Sinks Off-hand on
A Pedestal Grinder Using A Wheel Brush

Figure 11:
Generating An Esthetic Finish Before Anodization



Figure 12:
Deburring the Slots on the Inside Diameter using Tube Brushes





Figure 13: Deburring Machining Edges
Using Banded End Brushes (bands on the brushes
regulate the filaments for easy brush entry into the hole)


Figure 14: Deburring Around Drilled Holes,
in the Recessed Area of an Extrusion Using an End Brush










Figure 15: Removing the Extrusion Marks and
Producing an Uniform Finish on the Inside Diameter
of an Extruded Part Using a Stack of Wheel Brushes





Figure 16: Esthetic Finishing of Extruded
Tube Using a Stack of Wheel Brushes


6. Conclusion:

NAF brushes are excellent solutions for deburring and finishing operations. They replace tedious manual operations, provide consistency, and improve productivity. These tools adapt to part contours, prevent damage to value-added parts, lend themselves to automation, and provide an environmentally safe process. 


References:

1. Watts, J.H., "Abrasive Monofilaments - Factors that Affect Brush Tool 
    Performance", SME Deburring and Surface Conditioning Conference, 
    MR89-112, San Diego, CA, February 13-16, 1989.

2. Dawson, B.L., and Hennies R.C., "Robotic Long String Brush 
    Deburring System, SME Robots and Vision Conference, MR88-297, 
    Detroit, MI, June 6-9, 1988.

3. Vaccari J.A., (Ed.) "Aluminum Engine Heads Deburred Automatically", 
    American Machinist, pp 45-47, December 1993.

4. Hettes, F.J., "Brush with Success", Cutting Tool Engineering, pp 39-42, 
    June 1992.

5. Dawson B. L., "Automated Surface Finishing", Aerospace Engineering, 
    pp 25-28, August 1989.

6. Anonymous, "Nylon Brushes Feature Composite Hubs", Modern 
    Application News, pp 26-27, June 1992.


Appendix A: Application Case Histories 

Case History A: Automotive Cam Shafts
Problem: Deburr and radius edges of lobes and journals, remove heat scale, 
and provide surface finish below 20 µin. or 0.5 µm (Ra). 


a) Automotive Cam Shaft Being Processed Under NAF Wheel Brushes


b) Processed (left) and Unprocessed (right) Portions of a Cam Shaft 


Case History B: Aluminum Engine Heads 
Problem: Deburr all edges on intake and exhaust valve faces,
front and rear block faces, combustion face and cover rail of
the cylinder heads on a production basis on a multi-station
deburring workstation.


a) Deburring Exhaust Valve Face (in foreground)
and One Half of the Cover Rail (in rear)


b) Deburring Other Half of the Cover Rail (in foreground)
and Intake Valve Face (in rear)


c) Deburring Block Faces (only one face shown)


d) Deburring Combustion Face
(Photos: Courtesy of ACME Manufacturing)

Case History C: Steel Transmission Part
Problem: Deburr and radius inner and outer
edges of the housing using wheel brushes.


a) Before Deburring


b) After Deburring

Case History D: Auto. Transmission Valve Body 
Problem: Deburr and break the edges on the transmission valve body. 
Approximately 50,000 of these parts are produced each year.


Auto Transmission Valve Body Being
Deburred Under a NAF Disc Brush


Before Deburring


After Deburring

Case History E: Automobile Wheel Rim 
Problem: Deburring the machining burrs on
the inside of automobile wheel rims


Automated Machine for Deburring 
Automobile Wheel Rims Using Cup Brushes


Close-up and Cut-away View of a Wheel Rim Being Deburred by 
NAF Cup Brushes (Photo courtesy of Hautau Specialty Machines, Inc.)

Case History F: Aluminum Aircraft Parts [4,5]
Problem: Deburring and radiusing parts ranging from bulk heads 
to spars and formers using large diameter wheel brushes on a robotic
workstation. Some parts range up to 4' (1.2 m) wide X 7' (2.1 m) long.


An Aluminum Aircraft Part Being Deburred by a Robotic Workstation 
Using NAF Brushes (Photo courtesy of Cincinnati Milacron)


Case History G: Steel Compressor Plates
Problem: Deburr and edge radius compressor plates after surface grinding.


Steel Compressor Plate


Steel Compressor Plate Being Deburred by an Automated Machine with
NAF Disc Brushes (Photos courtesy of Hautau Specialty Machines, Inc.

Case History H: Turbine Blades
Problem: Deburr and generate a generous edge radii 
(.005” - .030”) on the turbine blades


Before Deburring


After Deburring