|
Safety
Always wear proper
safety equipment: Safety footwear, snug fitting clothing, safety goggles,
hearing and head protection, and proper respiratory equipment. Always use
blade guards provided on machines. Do not remove these safety devices.
They are for your protection.
Before Using
Make sure that the
arrow on wheel point in the same direction as shaft rotation. Best
performance and life will result. Before performing any cutting
operations, let the tool run for a few seconds without load. If blade
wobbles, vibration or unusual noise occurs, stop the tool immediately.
Inspect blade for damage or incorrect mounting.
BLADE
DRESSING
Dressing is the process of
sharpening diamond particles in diamond bond matrix in order for the
diamond particles to freely penetrate into the material, minimize loads,
and provide good cut quality. Another reason for dressing blades is to
clean a loaded blade from debris that is filling the pores between the
abrasive particles. Cutting into the dressing plate creates mechanical and
thermal stress and thus produces clean surface.
It is important for the diamonds
to be well protruded and exposed in order to easily penetrate into the
material being cut. Wafering/sectioning blades that are poorly dressing
will tend to push the material, creating high loads, high cutting
temperature/heat and poor cut quality. This can also cause blade breakage.
Resin bond wafering/sectioning
blades have a soft binder and in most cases will require minimum dressing,
if any at all. Resin bond wafering/sectioning blade are typically dressed
in the material being cut. This is why they are frequently called “self
dressing blades”.
Nickel bond and metal bond blades
have much harder binder and much more aggressive dressing is needed in
order to achieve the above mentioned goals. Nickel bond wafering/sectioning
blades require dressing.
RECOMMENDED DRESSING PROCESS
Dressing procedures are
established by end user and based on experience and the application
concerned. There is not one common method that applies to all
applications.
Dressing stick used to dress the
blade should be same or similar diamond grit/mesh size as the wafering
blade being dressed. Many sectioning saws are equipped with automatic
dressing chuck that allows the user at push of a button to forward the
dressing stock slowly into the rotating blade as it is sectioning a
sample. This insures the blade is continuously dressed as it cuts through
the sample. This process is highly recommended specially for cutting soft
and gummy samples/materials such as plastic mounted resins that typically
tend to smear or gum up the blade.
For best results we recommend that
the dressing stock used matches the dimensions of the sample as closely as
possible. When sectioning ultra hard and dense materials such as silicon
nitride, it is a good idea to implement a secondary dressing process.
Dressing the blade before starting to cut the sample. Doing so will
re-sharpen the diamond particles, so they are working at their maximum
level of efficiency from the very beginning. This can be accomplished by
by making five cuts through the dressing stick, so that that the dressing
stick covers the diamond section. Make sure coolant is turned on and
working during this process.
When
and how often should I dress my diamond wafering blade?
There
are no specific recommendations or guidelines on when or how often
wafering blade should be dressed. The sectioning saw operator should use
their best judgment in determining when and how to dress the blade being
used. A good rule of thum to remember: when you notice cutting rate/speed
is significantly slower than when the blade was first used is a good sign
the blade you are using needs to be dressed. Eventually all diamond
wafering blades will need to be dressed, regardless of the material being
cut. The amount of dressing a blade will require will depend on the
material hardness, density, porosity being cut, as well as material
diameter and shape/geometry. Dressing will re-sharpen and re-expose the
diamond crystals/particles in the blade bond matrix, as well as unload the
blade from material debris covering the diamond section surface. When
cutting very soft and gummy materials such as plastics and some epoxy
filled composites, the blade will have to be dressed more frequently than
when cutting ceramics and other ultra had and brittle materials.
At
same time when cutting large diameter materials where the wafering blade
is taken almost to its maximum cutting capacity. For example cutting 1”
(25.4mm) of material with 5” wafering blade the blade should be dressed
continuously during its operation. Dong so will help prevent “build
up” edge on the blade and keep the blade from binding up.
Continuously
dressing sintered (metal bond) and resin bond wafering blades will not in
any way reduce the life of the blade. Dressing is will most likely
increase the life of the blade, avoid possible blade damage/wreckage, and
optimize your sectioning operation.
COOLING
Coolant
should always be used to cool and lubricate the blade. Coolant
supply position and pressure is critical to minimize chipping, and
maintain consistent and acceptable cut quality. Most frequent source for
diamond wafering blade damage and material deformation coolant not
affectively reaching the cutting zone.
Coolant serves many functions in
wafering/sectioning operation:
·
Cools blade diamond section and material being cut
·
Provides lubrication to minimize friction between blade and
material
·
Washes out and removes powder residue and swarf from cutting
process
It has been found
that generous flow of coolant increases
diamond blade efficiency, improves surface finish and reduces heat
build-up and material cracks and deformation associated with overheating.
Coolant must be applied in the proper place or it will not cool the blade
or material being worked on properly. Coolant should always be directed so
that the full flow is at the point of contact between blade and material,
facing the same direction as rotation of the blade. The amount of
coolant used should increase with the hardness of the material being cut. If
you see sparks, there is insufficient coolant reaching the cutting zone or
its simply ineffective.
Determine the type
of coolant you are planning to use. Most frequently used coolant for
sectioning operation are water soluable based coolant and mineral oil.
Mineral oil is typically used for sectioning hard metals, where water
soluable coolant is preferred on remaining family of materials.
Plain water
evaporates at 212 F. Often temperature in your cutting zone
reaches as much as 500 degrees F. Often water evaporates, before it has a
chance of affectively cooling the wafering blade and sample being
sectioned. Resulting in shorter Blade Life, Material Damage or micro
cracks associated with overheating.
Water soluble
coolant will greatly benefit your sectioning operation reducing
sample/material thermal stress, edge damage, and internal cracking,
assuring long-term integrity of material being sectioned. Water soluble
coolant acts both as coolant and lubricant. Lubrication provided by the
coolant reduces the friction between the wafering blade and material /
sample. The coolant prevents the sample from sticking to the blade and
will improve cut quality and minimize material deformation.
Plain water is not
recommended for sectioning operation. However If you must use water as a
coolant, check with the blade manufacturer on what type of water
recommended for your blade. City water with 90 psi or running water is
usually used for cutting. For some applications, you may want to use an
additive with your coolant. If you decide to go this route, you will need
a circulating system and the right ratio between your additive and
coolant.
COOLANT SUPPLY TO CUTTING ZONE
However when cutting ultra hard
& brittle materials the coolant flow direction and position will play
a major role in determining blade life and performance.
Dual nozzle configuration is best
suited to supply adequate amount of coolant at point of contact between
blade and material. This type of coolant delivery configuration provides
many advantages over other coolant supply methods to cutting zone. Coolant
should be pointed at blade point of contact and leading edge of blade. The
dual nozzle system provides two separate streams of coolant into cutting
zone at angle of cutting edge of the blade. Each stream will cool one side
of the blade. The nozzles should be as close as possible to the point
where the blade enters the material/sample. Coolant flow should blast with
high velocity into the kerf to improve removing debris. wide kerfs an
premature blade water is a result of improper coolant amount or flow
applied at cutting zone. By correctly position the coolant stream in front
of the blade, the coolant will flow on top of the material. In addition,
coolant will be drawn into the kef
When cutting softer
material/samples direction of cutting is not of ultimate importance.
However, when cutting hard and brittle materials that are hard to section,
this quiet different. The blade should enter into the material “cutting
down”. As the blade penetrates the surface of the material, chips
removed by diamond particles become smaller the deeper the blade
penetrates. This cutting direction is most optimal to provide best cut
quality and minimize material deformation.
COOLANT MAINTENANCE &
OPTIMIZATION
Coolant is one of the most
overlooked variables in the sectioning process. Effective and proper use
of coolant and recalculating coolant system will pay off in terms of
improved surface finish quality, increased blade life and more consistent
cutting results. Coolant does more than just cool the blade and material,
it other more important roles include: lubrication, flush away swarf
particles. For most affective use of coolant the quality of water being
used, coolant concentration, and maintenance of the coolant tank makes a
difference. Different geographic areas have different water harnesses.
Water containing less than six grains of dissolved minerals per gallon is
considered soft water, water containing more then seventeen grains per
gallon is considered hard. The best coolant water to use in a coolant
system is chemically pure water, which is free of all dissolved solids.
Chemically pure water and reverse osmosis. Reverse osmosis is the method
most recommended by coolant manufacturers, however not always available.
Deionized water offers much improvement over available city water.
Water
in the tank can evaporate and remaining water can become harder. Hard
water affects coolant capabilities in many ways decreased capability to
the rust inhibitor, increased foaming, formation of a sticky residue, and
increased bacteria counts. Coolant concentration should be controlled and
maintained to ensure |
|
that the coolant is being used at
optimum efficiency. Too little coolant in the tank will lead to corrosion
and rancidity, while too high of a concentration can also cause foaming.
Maintenance of the re-circulating tank is also critical to coolant
performance. Cleaning he tank is a dirty job, but if done often enough and
thoroughly, it can increase the performance of your sectioning saw.
Keeping he coolant tank clean will ensure that you are getting the most
form your coolant, keeping corrosion and bacterial growth a bay while
providing the necessary coolant, lubrication and protection of your blades
and material.
RECIRCULATING COOLANT SYSTEMS
Recirculating systems in the past
have been used very infrequently in most laboratory environments. Today
the increasing variety of work and materials sectioned by materials
research and sample preparation labs are making this overlooked aspect and
requirement for many applications.
Recalculating coolant systems,
require filtering to remove the swarf particles created during cutting
process. These coolants systems typically use either cartridge,
centrifugal, or cascade. Which process to use will depend on your
application. Excessive amount of swarf particles mixed in coolant will
slow heat transfer of coolant and may cause surface damage to material
being cut. Coolant system must be constantly controlled and monitored in
order to insure process consistency
Coolant temperature will also have
an affect on blade life and cut quality. Typically coolant temperatures of
50 degrees F (10 degrees Celsius) will provide best results. White coolant
temperatures above 80 degrees F (27 C) should be avoided. Refrigeration of
the coolant system can be
used with most coolant systems and will provide best results.
SAMPLE CLEANING
Sectioned samples should be
cleaned with sap and water or alcohol after sectioning. An ultrasonic bath
is an excellent tool for speeding up this process and removing entrapped
debris or fluids. To speed up this process, you can also place the samples
in oven for several minutes. This will relieve the material sample of any
remaining fluid from its pores.
SAMPLE / MATERIAL CLAMPING /
FIXTURING
Properly
securing the material in place is one of the first and most important
steps in sectioning process. The function of the chuck/holidng fixture to
keep the sample/material firmly in place, preventing it from moving.
Various sample chucks/holding fixtures are available for large variety of
sectioning saws to accommodate all types of material shapes and
geometries. Its very important to use the right mounting media for your
specific sample. Which chuck to use for your application will depend on
the beginning sample/material dimensions, desired cut depth, and material
properties (hardness, brittleness, shape/geometry). Some challenges of
sample chuck mounting/fixturing is occasional chipping at bottom of the
cut. The problem is the back side of
material does not have firm
support at cutting area, therefore creating higher chipping rate when
blade exits the cut.
Holding
Sample/material Firmly in Place
The sample should not move while
being sectioned. Movement of sample can damage material or blade. As well
as any possibility of obtaining planar section. At the same time the
sample must not be over tightened. Doing so may possibly damage the chuck
or sample. Some of the more brittle materials such in the glass and
refractory families can fracture if over tightened in chuck. Where the
harder and more denser materials such as silicon carbide may cause dents
in the chuck if excessive force is applied. Dents or nicks in the chuck
will affect samples sectioned in same chuck causing damage and possible
cracks.
Chuck Padding
Padding can help prevent damage of
material/sample hold inside chuck and the chuck itself. Padding serves
many functions including: protecting material/chuck, protecting sample
chuck, avoids sample shifting when pressure is being applied, buffers from
damaged/nicked areas of the chuck.
CHUCK
POSITIONING / ALIGNMENT
The sample chuck should be
securely attached to the load arm. For most applications this is done on
the right hand side of the load arm. Longer samples can be amounted on the
left hand side of the load arm in order to provide extra clearance and
minimize the possibility of sample coming in contact with the saw hood.
Improper mounting of the chuck or sample can cause damage to both
sample/material and wafering blade.
Positioning of the sample and its
angle where it comes in contact with cutting blade can play an important
role on cut quality and material deformation. As well as affect the time
it takes to cut/section. For best results position/align the sample so
that the smallest section/angle comes in contact the blade first. Doing so
will insure the sample/material is cut faster than if the widest dimension
of the material/sample comes in contact with blade.
This is especially critical for
materials/samples with different compositions and properties. For example
coated specimens should be positioned so that the coated side is cut
first. The helps avoid excessive damage to the coating which has different
material properties than remaining part of material.
Sample/materials should be aligned
with blade in a way so that sample chuck does not tough the blade support
flanges. During your sectioning operation if you find the sample chuck is
toughing blade flanges. The chuck should be attached to different position
on the saw load arm. Depending on the design and configuration of your
saw, this may not be always feasible. Another alternative to resolving
this issue is reposition the sample in chuck to the point where there is
proper clearance between chuck and blade flange.
EPOXY SAMPLE MOUNTING
Very small and difficult to
clamp/fixture samples can be filled with epoxy to allow for easier
holding/clamping while being sectioned.
BLADE MOUNTING
Flanges
Proper blade
mounting in a flange set in acceptable condition is key to any successful
wafering/sectioning operation. Flanges are desined to add addition support
and stability to both sides of the blade. Flanges prevent the wafering
blade from warping, blade wreckage, slanting cuts, damage to
material/sample and much more. Flange Diameter to use would be based on
blade diameter and thickness used, material diameter/dimensions (desired
exposure ration). Flange diameter affects directional stability of the
diamond wafering blade. As a general rule of thumb, the largest possible
flange diameter should always to be used.. Flanges shold provide
sufficient clearence for sample so the cut may be completed without any
interruption. For thinner and
smaller diameter wafering blades, recommended flange size is ¾ of the
Outside Diameter of the wafering blade. Often extending right up to the
diamond section. For larger and thicker blades the recommended flange
diameter is approximately 1/3 the diameter of the blade. Flanges
must be free of rust and dirt. Your blade should turn perfectly true after
flange nut is tightened. Carriage alignment must be accurate for deeper
cuts to prevent blade bending.
Any small scratch or nick in
flange edge can cause improper blade mounting. This can lead to slanted
cuts, blades wobbling and wider cuts, more chipping, or even possible
blade breakage.
OPTIMIZING
SECTIONING PARAMETERS
When it comes to optimizing your
sectioning operation. Two most important variables besides the wafering
blade itself is spindle speed and load / feed rate. These two parameters
will typically take presence over all others.
SPINDLE SPEED / RPM’S
Optimal Speeds/RPM's will vary
depending on the OD (Outside Diameter) of the blade, application, material
to be cut, and equipment used. Using optimal RPM’s for your application
will help increase blade life and reduce blade wreckage. Different
material have different requirements for cutting speed. Material hardness,
density, and spindle sped will affect both spindle speed and therefore cut
quality.
Low
spindle RPM’s will cause the blade to wear faster to maintain better cut
quality. Causing softer wafering/sectioning action, where each diamond
particles grind out larger portion of material. Higher spindle RPM’s
will do the opposite. Each diamond particle will grinds away a small
portion of material, creating harder cutting action. A good rule of thum
to remember: for soft, abrasive materials, RPM should increase. For hard,
dense materials, RPM should decrease.
LOAD / FEED RATE
Load Amount / Feed rate should be
determined by your desired cut quality, material hardness, density,
geometry, and thickness. The load to be applied to sample should be
function of your desired cut quality and speed. Typically most loads for
sectioning saws used today are between 10 to 1,000 grams.
Since goal of majority of
metallographic, material research, sample preperation, and failure
analysis operations is to introduce most minimal amount of sample/material
deformation and preserve true material micro structure. The load arm
should feed sample/material slowly into blade so the blade does not lead
off. Excessive pressure can cause wafering blade to bend, warp, and part
of diamond section to fracture. Excessive pressure can also cause unwanted
material burning, smearing, cracks, and deformation.
Best practice to follow would be
to start by applying light to medium pressure. Gradually feeding load arm
into rotating blade, until it begins t cut at its own speed. If you can
see dark “burn” marks around the diamond section, the cutting speed
you are using is too fast or you are applying too much pressure. Load/Feed
rate should never be so great that blade slows down. For this reason great
care and caution should be taken when increasing amount of load/weight
applied to the sample. When cutting completely through a sample/material
and the cut is near completion, reduce slightly the load/pressure on your
blade considerably. Doing so will reduce chipping sample/material as you
exit the cut.
|
