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By Mark Cranna, American Saw & Mfg. Company
But not at the expense of reducing cutting
speed, cut quality or tooth life. Excessive vibration during
interrupted cuts on structural steel, tubing and nested bundles is
at the heart of a variety of problems in the fabrication process.
Noise from vibration can go way beyond annoying, and become an operator
safety issue. Too much disturbance during the cut has a direct impact
on cycle time and cost when a less than satisfactory surface finish
is the result. And, instability in the process makes premature tool
wear unavoidable.
Recently, engineers at American Saw took on the challenge of isolating
the sources of energy and energy flow paths during the bandsaw cutting
process, in an effort to hone in on a solution for reducing or eliminating
vibration and noise. They not only identified parameters that impact
the magnitude and tendency for excessive vibration, but also developed
a new tooth design that minimizes harmonics during the cutting to
reduce noise levels.
The Research
The first step in isolating the noise components of the cutting
system was to develop a measuring scheme and to assemble the necessary
equipment for taking measurements. In order to analyze the sources
of noise, omni-directional microphones were set up in front of and
behind the cut zone to identify noise frequencies. In addition, accelerometers
were mounted to the horizontal carbide guides on the inlet and exit
side to pick up vibration of the blade normal to the cutting direction,
and on the workpiece itself to determine its contribution to the
overall sound intensity levels. Experiments were done using different
structural materials, blades and cutting conditions. All of the readings
were collected and analyzed by a frequency spectrum analyzer. After
adjustments were made to the data to ensure an accurate analysis,
a “snapshot” was taken of cutting noise/vibration, and sound pressure
(dBA) was plotted as a function of frequency (Hz).
Top Ten Findings
- For any given bandsaw machine configuration, there is an
inherent stiffness and rigidity associated with the machine and
system components. While these factors are typically fixed, one
critical component in affecting the overall magnitude of blade
frequency vibration is proper damping of the blade through the
guide system.
- The tendency for chatter is directly proportional to the
machinability of the material (typically a function of material
shear strength and hardness).
- When material cross-sections differ depending upon orientation
to the blade, minimizing the length of the cut reduces the tendency
for chatter.
- Lowering band speed in combination with heavy chip loads
typically has the greatest effect on reducing overall cutting
noise. Unfortunately, some tooling may not be adequately designed
to handle the increased cutting forces on each tooth.
- Within the practical operating range, guide spacing and band
tension do not have a significant influence on the 1000 – 1200
Hz peak frequency region.
- Most of sound energy propagates from the lateral movement
of the blade itself — not the machine or workpiece.
- Worn blades exhibit “self-excited high frequency” chatter
that can only be eliminated through resharpening of the cutting
edge, if possible.
- As set magnitude is increased, the tendency for blade instability
and regenerative chatter increase.
- Blade lateral damping mechanisms reduce noise levels.
- Blades with highly varied tooth pitch distances and loading
patterns tend to exhibit less noise and vibration.
Typically, some sawing parameters that would reduce noise level
are not viable options for fabricators, due to machine, workpiece
or productivity constraints. Blade parameters, on the other hand,
can be designed to include features that counteract forced vibration
and self-excited regenerative chatter. The engineers postulated that
a blade designed for minimizing harmonics during cutting to reduce
noise levels must sufficiently randomize the tooth loading patterns
in both magnitude and location in order to dampen the system.
Introducing Lenox Rx®+
Unveiled earlier this year, this specialty blade directs maximum
energy into cutting structural steel and very little energy into
vibration and noise. It allows for high feed rates and resists tooth
strippage common to violent, interrupted cutting applications. And,
it’s available in extra heavy set to avoid blade pinching. Design
features incorporate all that current research has to offer:
A resilient bi-metal M-42 tooth tip,
made of 8% cobalt high speed steel alloy with the addition of
vanadium and molybdenum, which performs best in applications
requiring high heat and wear resistance.
A unique Rx®+ Isophonic™ tooth geometry,
highlighted by:
- Extended pitch patterns with maximum tooth spacing variation
to distribute sound energy over a broad spectrum.
- Extended set patterns with optimized combinations of
both tooth height and set magnitude variation that minimize
lateral vibration, providing a system damping effect.
- Optimized cutting channels that allow for better penetration
and reduced vibration when cutting larger cross sections,
such as I-beam materials.
An enhanced rake tooth profile,
giving the blade the tooth strength needed to power through interrupted
cuts and eliminate tooth strippage. Added tooth width also provides
stiffness for consistent tooth set levels and resistance to set
collapse. This stable cutting edge thus decreases the tendency
for regenerative self-excited chatter through the blade’s break-in
period. In addition, the clearance face protrusion of this design
helps guide and redirect the chip off the rake face, minimizing
chip welding in the tooth tip region.
Conclusion
Noise and vibration are unavoidable when cutting structural steel,
I-beam, angle iron, channel iron, tubing, pipe, wide flange beams
and nested bundles. Anyone who has experienced excessive noise and
vibration firsthand, however, knows only too well the safety and
profitability issues associated with this problem. Lenox Rx®+ minimizes
harmonics during cutting to reduce noise levels, and dramatically
improves cutting performance on structurals. That means there is
no sacrificing cutting speed, cut quality or tooth life to get the
vibration and noise to stop!
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