To All:
This is a direct copy of a thread I recently made in alt.machines.cnc. I thought it would be interesting to many in here. It's from an article in Modern Machines Shop Online. Some excerpts from the long MMSO article follow:
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http://tinyurl.com/rax7gk
Mechanical surface finishing, also known as mass finishing or vibratory finishing, is a technology that has been around for more than 6 decades. Its applications range from burr removal, putting a radius on sharp edges, and degreasing and de-rusting/de-scaling of metal parts all the way to high-gloss polishing of metal components. This technology is generally associated with vibratory tumblers, centrifugal barrels or centrifugal disk machines.
In recent years, “drag finishing” has become a popular alternative for surface finishing of high value and somewhat delicate metal components. Like pushing a plow through the soil and, thus, polishing its blade, in drag finishing systems the parts mounted to a carousel—that in turn is equipped with multiple workstations—are “dragged” through a circular work bowl filled with grinding or polishing media.
Pressure and Speed
Mass finishing is all about pressure and speed. The higher the pressure exerted by the media on the parts, and the faster the media “rubs” on the parts, the faster the desired finishing results can be achieved. In this respect, drag finishing is standing out above other finishing methods: Because of the high speed at which the parts are dragged through the media and the high pressure generated, drag finishing works 40 times faster compared with vibratory systems and about 4 to 5 times faster than high energy systems.
No Part-on-Part Contact
The outstanding characteristic of drag finishing is that the parts are individually mounted onto the workstations of the carousel.
Compared with conventional mass finishing systems where the parts are free-floating in the media, in drag finishing systems, the parts—being individually attached to the workstations—can never touch during the finishing process. This prevents part-on-part contact and, therefore, nicking or marring of the finish.
To individually mount the parts to the workstations requires special parts fixtures. Frequently, the design of these parts fixtures poses an engineering challenge. But the payoff is worth the effort because it produces consistent and totally repeatable surface finishes without the danger of the parts ever touching and, therefore, possibly nicking each other.
Aggressive Deburring to High-Gloss Polish
The applications for drag finishing range from aggressive deburring and edge breaking all the way to high gloss polish of a range of parts. Here are a few examples of successful drag finishing applications:
Grinding and polishing of stainless steel boat propellers: These are castings that undergo a drag grinding process in one machine followed by a polishing step in a second drag finisher.
Surface smoothing and polishing of turbine blades after machining and shot peening: This application reduces the surface roughness from Ra = 70 to Ra < 10 (1.8 micrometers to < 0.25 micrometers).
Grinding and polishing of medical implants such as artificial knees, hip stems, ankles, and so on.
Whenever a manufacturer produces high value parts with a complex geometry, and these parts require a first-class surface finish (be it strictly functional or decorative), drag finishing is certainly a surface finishing technology worth considering.
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--
BottleBob
http://home.earthlink.net/~bottlbob
This is a direct copy of a thread I recently made in alt.machines.cnc. I thought it would be interesting to many in here. It's from an article in Modern Machines Shop Online. Some excerpts from the long MMSO article follow:
================================================================
http://tinyurl.com/rax7gk
Mechanical surface finishing, also known as mass finishing or vibratory finishing, is a technology that has been around for more than 6 decades. Its applications range from burr removal, putting a radius on sharp edges, and degreasing and de-rusting/de-scaling of metal parts all the way to high-gloss polishing of metal components. This technology is generally associated with vibratory tumblers, centrifugal barrels or centrifugal disk machines.
In recent years, “drag finishing” has become a popular alternative for surface finishing of high value and somewhat delicate metal components. Like pushing a plow through the soil and, thus, polishing its blade, in drag finishing systems the parts mounted to a carousel—that in turn is equipped with multiple workstations—are “dragged” through a circular work bowl filled with grinding or polishing media.
Pressure and Speed
Mass finishing is all about pressure and speed. The higher the pressure exerted by the media on the parts, and the faster the media “rubs” on the parts, the faster the desired finishing results can be achieved. In this respect, drag finishing is standing out above other finishing methods: Because of the high speed at which the parts are dragged through the media and the high pressure generated, drag finishing works 40 times faster compared with vibratory systems and about 4 to 5 times faster than high energy systems.
No Part-on-Part Contact
The outstanding characteristic of drag finishing is that the parts are individually mounted onto the workstations of the carousel.
Compared with conventional mass finishing systems where the parts are free-floating in the media, in drag finishing systems, the parts—being individually attached to the workstations—can never touch during the finishing process. This prevents part-on-part contact and, therefore, nicking or marring of the finish.
To individually mount the parts to the workstations requires special parts fixtures. Frequently, the design of these parts fixtures poses an engineering challenge. But the payoff is worth the effort because it produces consistent and totally repeatable surface finishes without the danger of the parts ever touching and, therefore, possibly nicking each other.
Aggressive Deburring to High-Gloss Polish
The applications for drag finishing range from aggressive deburring and edge breaking all the way to high gloss polish of a range of parts. Here are a few examples of successful drag finishing applications:
Grinding and polishing of stainless steel boat propellers: These are castings that undergo a drag grinding process in one machine followed by a polishing step in a second drag finisher.
Surface smoothing and polishing of turbine blades after machining and shot peening: This application reduces the surface roughness from Ra = 70 to Ra < 10 (1.8 micrometers to < 0.25 micrometers).
Grinding and polishing of medical implants such as artificial knees, hip stems, ankles, and so on.
Whenever a manufacturer produces high value parts with a complex geometry, and these parts require a first-class surface finish (be it strictly functional or decorative), drag finishing is certainly a surface finishing technology worth considering.
================================================================
--
BottleBob
http://home.earthlink.net/~bottlbob
