On-Machine Deburring With Abrasive Nylon Filament Brushes

On-Machine Deburring with Abrasive Nylon Filament Brushes - A Case Study

Frank J. Hettes, Vice President, Research & Development
fhettes@weilercorp.com
Weiler Corporation
Executive Summary:
A European manufacturer of rotary screw air compressors wanted to replace hand deburring with an automated method. The materials to be deburred were high grade cast iron and alloy steel. The hand deburring operation was very dirty, and some parts were damaged. The unique requirements were:
The castings were painted before machining and the deburring operation could not remove the paint. The deburring operation could not produce a large edge break that could create a leakage path in the compressors.
The manufacturer also wanted to refine the surface finish of the rotor bores during the deburring process. The manufacturer decided to use abrasive nylon filament brushes in various configurations to replace hand deburring. To date, brushes have been used to replace the hand deburring operation for one size air compressor. The size chosen was the smallest, highest volume casting. Using brushes has reduced the deburring time by approximately 75%.
Introduction:
A European manufacturer of rotary screw air compressors developed a high level of automation in their factory. The last operation to be automated was deburring the machined parts (see Figure 1). The manufacturer wanted to eliminate the hand deburring operation because:
The operation created a lot of dirt The operation caused inconsistent results The parts were damaged by operator error The operation required excessive time
Figure 1: Deburring workbench - note variety
of tools required and amount of dirt created
The manufacturer decided to automate the deburring operation by using abrasive nylon filament brushes operated on the machine tool where the parts were machined. The special requirements were:
The pre-painted castings could not have the paint damaged The edge radius created by the deburring process had to be controlled The surface finish in the rotor bores required refinement
Scope
Workpiece:
Ten different sizes of air compressors are being manufactured. The rotor housings are manufactured from high-grade cast iron and are pre-painted before machining. The rotors are made of alloy steel. Figure 2 shows partially assembled compressor units with the main housing and rotors. Approximately 10,000 units per year are made in all sizes combined. The smallest size compressor is the highest volume at approximately 4,000+ units per year. Due to the high volume, it was decided to automate the smallest size housing first.
Product Selected:
Four sets of housing parts consisting of 3 castings are mounted on a tombstone fixture. Figure 3 shows the fixture with 4 sets of compressor housings. Each housing consists of the main center section with 2 end plates. The time to machine the 4 sets is approximately 2 hours, 10 minutes. Using 3 different configurations of nylon abrasive filament brush tools, the 4 sets of parts are deburred in approximately 5 minutes after the machining cycle is complete. The operation of the brushes is part of the program. The brushes are simply treated as another type of cutting tool.

Figure 2: Completed compressor units

Figure 3: Machining fixture
Figure 4 shows a disc-style brush. This style brush is used to deburr the flat surfaces of the end housing and the center housing. Two sizes of disc brush are used. No attempt to automatically compensate for wear has been made yet.
Figure 4: Disc brush mounted in tool changer
The inside diameters of the rotor bores are finished and deburred using nylon abrasive filament wheel brushes (see Figure 5). The brushes are programmed to interpolate the bore ID, similar to a boring operation. The sides of the brushes are used to deburr the bottom of the bores also.
Figure 5: Wheel brushes mounted in the tool spindle

There are several areas where the fixture precludes the use of the disc brushes. In those areas, nylon abrasive filament end brushes are used (see Figure 6).
Figure 6: 44mm trim end brush
Results:
The rotor housings have been successfully deburred on the CNC machine where the machining is done. Figure 7 shows a housing that has been machined and not deburred. Burrs can be seen at the edge of the rotor bores and the outside housing edge. Figure 8 shows the same part after brush finishing and deburring. A uniform, burr-free edge radius is formed at all corners that have burrs created during the machining process. The rotor bores have had the surface finish reduced from approximately 64 Ra to approximately 32 Ra and the burrs have been removed from the line formed by the junction of the bores. The bottoms of the bores are also completely deburred. Figure 9 shows another typical surface that is deburred in the process. This surface shows a significant number of small holes. These holes are all deburred along with the outside edge of the casting. All deburring is accomplished without disturbing the paint that has been applied before machining. The assembled compressor shows no evidence of any work being done near the painted surfaces. The dirt problems, damaged parts and inconsistent results caused by hand deburring have been eliminated. The deburring time has been reduced from 5 - 7 minutes for each set of housing parts to 5 minutes for 4 sets of housing parts. In addition, the need for a skilled deburring operator has been eliminated.
Figure 7: Machined housing - not deburred

Figure 8: Finished and deburred housing
Figure 9: Opposite end of machined and deburred housing
Future Work:
The finishing and deburring of the rotors is now being worked on. The other 9 sizes of compressor units will be automated.