(Interview by Ray Chalmers) Dave Davidson has surface finishing in his DNA. His manufacturing beginnings trace to the 1970s working in a longstanding family business that manufactured wooden shoe pegs used for tumble-polishing small plastic items using steam-era machinery.
To get a leg up on the technology, Mr. Davidson, who remains active as a consultant in the industry, joined the Society of Manufacturing Engineers’ Burr, Edge and Surface Technology Division. With the help of SME mentors, he developed a line of abrasive and polishing products as well as new mass finishing processes for barrel, vibratory and centrifugal finishing systems. He is a master at problem-solving customer challenges.
That includes gear-making. Depending on the particular application, Mr. Davidson describes three mass-finishing methodologies for producing surface finishes on gears that contribute to improved performance and extended service life. They are:
Centrifugal Barrel Finishing
This high-energy method is a mechanically accelerated means for producing edge contour and isotropic micro-finishes on gears. This method is used by a variety of gear manufacturers and high-performance racing teams to improve the surface finish and endurance of gear sets. It is also capable of producing low micro-inch finishes to improve load-bearing qualities of mating surfaces and to develop beneficial compressive stress and cold-hardening properties useful to highly stressed parts. A sequence of processes (analogous to roughing, finishing and polishing) is often used to develop highly finished surfaces. The high centrifugal forces and speed of this process achieve high-level surface finishes in short cycle times.
One user, Mr. Davidson recalls, pulled racing transmissions after each event for centrifugal finishing, only to find afterward that gear sets were lasting an entire season.
By this definition, all mass finishing methods could be said to be isotropic in nature. The process outlined above, however, has been optimized to consistently produce gear surface finishes that will improve overall operational performance and extend service life.
Turbo-Finish or Turbo-Abrasive Machining
“Once you’ve got abrasive particles impinging the part at that level of force, you’re creating a shot-peening effect without creating shot-peening surfaces,” Mr. Davidson says.
Admittedly, TAM investment is more on the capital equipment level, but users can create edge contours and other surface finishes very rapidly—with 60- to 120-second cycles in many cases—and machines can accommodate large gears in the 48-inch diameter range that would make vibratory or centrifugal finishing inefficient, if not impossible.
- Reduced friction
- Increased part durability
- Improved corrosion resistance
- Reduced wear
- Reduced lubrication requirements and cost
- Improved oil retention
- Reduced contact and bending fatigue
- Improved pitting resistance
- Reduced vibration and noise attenuation
- Reduced applied torque requirements
- Improved surface finish uniformity (part-to-part, feature-to-feature, and lot-to-lot)
- High-quality, micro-finished surfaces
Reduced Friction Benefits
- Increased fuel economy
- Reduced contact fatigue
- Increased power density
- Lower operating temperature
- Extended mean time between maintenance overhauls
- Reduced maintenance costs
- Eliminated break-in
- Extended component life
- Reduced metal debris
- Reduced part failures
- Minimized overheating
Many gears and gear sets in a variety of industries remain subject to fatigue, fracture and wear, Mr. Davidson says. “Such parts can gain substantial improvements in life and performance, from alterations to their overall surface texture. Improvements in overall smoothness, load-bearing ratio, surface profile skewness and isotropicity can, in many instances, improve life and performance and cut operational costs dramatically. Manufacturers that have not subjected their parts to an analysis to determine the potential benefits of this kind of processing may be making parts that are not all that they can be.”