I���ve learned from limited testing and some published data.
Before starting, let me point out that metal removal in
mass fnishing machines can be compared to fling an
edge with a hand fle. More pressure gives faster cutting,
longer strokes are advantageous, and fling faster back
and forth will get the job done more quickly. It stands to
reason that longer strokes and faster action with more
pressure will be the quickest. Hand fling enables you to
independently vary any action. Not so in mass fnishing.
The earliest test data I saw was by 3M Co. in the 1960s,
titled ���Vibratory Finishing. Effects of Signifcant Variables.��� (My incomplete copy does not contain the publishing date or copyright information. If anyone has the
complete booklet, I would appreciate a copy for my reference.) This is one of few published studies that address
your question. I supplement it with tests I���ve conducted
and with conversations with others in the business.
The 3M study measured the effect of 1) compound fow
rates; 2) load depth; 3) media abrasiveness; 4) media
density; 5) vibratory frequency at 1,500, 1,800 and 2,100
rpm; 6) media size; 7) part loading; 8) fxtured parts
versus loose parts; and 9) compound lubricity. When you
consider all the variables they attempted to measure, you
realize it was impractical to make measurements when
only one factor was changed in each test series. For example, when you change the density of the media, you necessarily reduce the amplitude unless making offsetting
changes to the eccentric weights. The same is true when
you change the load depth or frequency. The 3M study
concluded that higher amplitude increases cutting more
effectively than higher frequency. It also showed that load
depth and compound fow rates affect the cutting rate.
Because bowl machines can obtain higher amplitudes
and still have a smooth rolling action, it is my experience that bowl machines can be set to outperform tub
machines when cutting rate and part integrity are the
criteria. The apples-to-apples comparisons are skewed by
several factors, including differing bowl depths.
OK, machine manufacturers, let���s hear from you on
this subject.
A Note FRoM PRoducts FiNishiNg:
Sadly, this is Steve Marcus��� last column. We thank him
sincerely for many years of insightful, timely answers and
wish him luck in his next chapter.
Starting with our April issue, Pat Wenino will be our
new Mechanical Finishing Clinic writer. Pat is a 30-year
fnishing veteran, owner of Minnesota-based MC Finishing and author of several books on the mechanical fnishing process, including the recently released Metal and
Composite Finishing: Introductory to Mechanical Finishing.
Welcome Pat to the team with your mass and mechanical fnishing questions by emailing him at massfnishing@
pfonline.com. n
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