Production managers and manufacturing engineers choose circular carbide saw systems when they need the sawing method with the highest productivity.  Without a doubt, circular sawblades equipped with carbide teeth are the most productive tool for high production metal sawing, but if you are replacing your blades too often, high productivity will quickly be negated by the high cost of tooling and the lengthy changeover time.

Carbide saw blades are optimal tools, but they are not cheap.  Carbide is an extremely hard material, and it cuts through softer material with ease.  But the downside to carbide is that it is very brittle and easy to damage. To reach the highest productivity at the lowest cost-per-cut, avoid these 13 factors that will destroy your saw blades.

1) Mishandling the Carbide Tipped Circular Saw Blades

It happens way too often, carbide blades are shipped, stored, and handled recklessly.  A slight fracture in the carbide tooth may go unnoticed until the blade fails well before the expected tool life.  Whenever a single tooth is damaged in shipping and handling an overload is placed on the next tooth causing it to wear faster.  This domino effect dramatically reduces the life of the blade and causes the operator to question both the quality of the tool and the quality of the machine.

Many cases of blade failure can be avoided altogether if blades are simply handled with more care.  Make sure you are taking these precautions:

• Cover the carbide teeth in plastic or rubber casings and store them in soft plastic or wood racks. (fig.1a)
• Store the blades in racks made of soft material. (fig. 1b)
• Do not place, roll, or drag the blade across the shop floor under any circumstances
• Be careful when mounting the blade not to knock the teeth against the machine.

Fig. 1a Carbide teeth protection

Fig. 1b. Proper blade storage.

2) Failing to Securely Mount the Saw Blade to the Drive Hub

Rigidity is paramount in carbide sawing, because carbide is very brittle.  Vibration is often introduced by failing to properly secure the saw blade to the drive hub. You’ll notice fretting corrosion when the blade body is not properly secured against the clamping disc. This is caused by friction in the micro movements and you will know when this has occurred as it appears as a rust-colored dust.

Locate the blade on the pilot diameter of the drive hub; Make sure the teeth point in the cut direction and rotate the blade opposite to the cut direction until the holes in the blade touch the drive pins or screws fig.2.  This will assure that the blade will not slip on the drive hub when it engages the material. Tighten the screws of the clamp disc to the specified torque.

 
Fig. 2. Rotate the blade in the opposite direction
to the cut rotation to contact drive pins or screws

3) Improper Clamping and Orientation of the Workpiece as the Circular Saw Blade Moves Through the Cut

The clamping of the bar can be challenging. If the material has a high hardness, serrations might not bite into the material very well, so for round material, v-clamps offer a more secure clamping method. In case you use some irregular cross-section (profiles) make sure the webs (or the thin portion of the material) are not flexing and also that the cross section is not changing too much throughout the cut.

 
Fig.3a. Typical and correct rail clamping to cut through a large section

Fig.3b. Wrong position of rail will cut a large portion with one tooth only

4) Using The Wrong Speed and Feed During the Sawing Cycle

It’s important to find the balance between the circumferential speed that the blade is rotating and the feed rate that the blade is being pushed into the material.  Higher cutting speed measured in Surface Feet per Minute (SFM) or (meter/min) wear the carbide tips faster when the tooth impacts the material at a faster rate.

It is better to slow down the cutting speed and take a deeper cut (or higher chip load) to extend the life of the blade without lowering productivity.

5) Torsional Vibration of the Circular Saw Blade

Torsional vibration is the enemy of carbide tips.  Torsional vibration causes the carbide tooth to impact the material at varying speeds due to the compliance of the gear train which acts like a spring. The shock from the accelerated impact can cause the brittle carbide tooth to break. Lost motion due to backlash causes most of these problems and therefore only precision anti-backlash ground gears should be used for the gear train. Engineers design machinery to be as stiff and as rigid as possible, but not all carbide saws are created equal.  Getting the most out of your blade means choosing a rigid machine backlash free and with low compliance. 

6)  Lateral Vibration of the Circular Saw Blade

Lateral vibration can cause torsional vibration and vice versa.  As the saw blade vibrates from side to side, it cuts a wider slot which can overload the gear train, increasing the wind-up.  The teeth will fluctuate more and spring into the cut.  Sawing machines using circular carbide tipped blades are designed with stabilizing and dampening mechanisms that prevent lateral vibration.  However, different manufacturers have different methods with varying effectiveness for stabilizing and dampening.

Make sure the stabilizers and dampeners are adjusted to the specifications provided by the manufacturer. If mounted to lose they will not help much because the blade can vibrate with larger amplitudes. If set too tight they will create substantial heat which will result in losing the tension of the saw blade and causes more vibrations. (see article “Effect and Prevention of vibration in carbide sawing”)

Fig.4. Blade stabilization system (AMSAW patent) with brush assembly

7)  Resonance Within Blade and Machine

Resonance occurs when the exciting frequency of the saw blade matches the natural frequency of the machine.  Resonance can be completely destructive to blade life because it amplifies the vibrations. Machine tool designers go to great lengths to avoid resonance during the design and build process.  If you fear that vibration may be caused by resonance, try making a slight adjustment to the RPM. This may make enough of a difference between the exciting frequency of the blade and of the natural frequency of the machine to eliminate resonance.

The following diagram shows a single mass oscillator with damping as a parameter. On thex-axisyou can see the ratio between the exciting frequency and the natural frequency and the y-axis represents the amplification of the amplitude if a system is excited by a force. (D=Damping, V1=Amplification factor, η=Frequency ratio)

 
Fig. 5. Oscillation and damping effect.

8)  Overloading the Sawing Machine

If the gears in a machine are overloaded, the wind up of the gear train will increase and it may cause torsional vibration.  If the maximum horsepower capacity of the machine is too low to handle tougher materials, it can put too much strain on the gear train causing the gears to wind up and spring the teeth into the material.  This hammering effect can destroy the brittle carbide teeth of a saw blade.  If you’re going to switch your stock size or begin cutting more challenging materials, be sure your machine has enough horsepower to handle the change or you may decrease your tool life.

9)  Poor Separation of the Saw Blade from the Metal Stock

When sawing metal with a circular saw blade, the width of the slot and the kerf of the saw blade have about the same dimension. That being said, before you retract the blade, the material on both sides of the blade must be retracted to avoid rubbing the teeth on the cut surfaces as the blade exits the cut.  Rubbing the carbide tips will create wear and reduce tool life. In cases where the material can’t be retracted on one side, the blade carrying spindle can be designed to shift and clear the blade.

10) Failing to Clean the Chips from the Carbide Teeth

The tool life is negatively affected when the carbide teeth have to cut also through loose chips which might stick to the teeth.  Usually, all carbide saws have a wire brush which can clean the teeth and the gullets from jamming or sticking.  The brush is rotated by the blade rotation when it engages the teeth gullets to clear the chips.  Some saws also have a power brush which is rotated by an electric or air motor.  Powered brushes have more of an effect to clear sticking chips from the cutting edge of the teeth. (See Fig. 4)

11) Hot Chips Welding to the Carbide Tips

Sawing regular steel does not require coolant when using carbide teeth.  The heat is mainly collected in the chips and thrown by the fast rotating saw blade onto the chip conveyor.

However, with some high chrome nickel alloy steel, the heat created by the cutting process is so high that the chips will weld to the cutting edge.  A light lubricant mist can help to prevent this.  The amount of spray is so little that the moisture vaporizes from the chips and the chips actually appear to be completely dry and can be discarded with minimum environmental effort.

12)  Improper Blade Tooth Spacing

Be sure to use the right tooth spacing for your saw blade and material combination (cross section and size). As a rule of thumb, you should have not more than 6 teeth in the cut. For only a few cuts, it might be OK to use a saw blade suboptimal tooth spacing, but over longer production runs, when changing the material size, you should consider a different blade with proper tooth spacing.

Fig. 6 a. Proper teeth spacing allowing more teeth in the cut for better blade stabilization

Fig. 6 b. Wrong teeth spacing will cause more vibrations

13)  Poor Saw Blade Manufacturing

If the previous issues cannot solve or improve your tool life problem, the problem may be the blade itself.  Carbide saw blades may look like simple tools, but the process of manufacturing them properly is quite complex. The blade will not reach the expected tool life if the blade body is not properly tensioned or if the precision ground carbide teeth are out of tolerance.  Fig. 7 shows a typical runout and tension screenshot for a saw blade.

 
Fig. 7. A typical runout and tension screenshot for a saw blade.

Occasionally, your carbide saw blade supplier can change the carbide grade or the steel quality of the blade body and you might face problems without knowing the reason. If you suspect the blade itself to be the problem, try changing suppliers and see if you can achieve a better blade with longer tool life.

by Willy Goellner & Christian Mayrhofer – Advanced Machine & Engineering/AMSAW

If you’re not getting the tool life you expected from your saw blade and you need help troubleshooting the problem,  read the proper articles published on Sawing Academy and contact one of our production sawing experts:

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