In 1926, Krupp, a German company, developed carbide, a very hard mixture of sintered carbides of various heavy metals, especially tungsten carbide, used for cutting edges and dies. This new material revolutionized metal-removal or “chip-cutting” in manufacturing. In the 1950s, carbide was used in all machining processes except for sawing. Ref. Wikipedia, “Cemented Carbide History.”
In 1942, German scientists further developed carbide into cermet. After World War II, American universities developed this material further and began to market it as a cutting material for machine tools under the brand name Cermet. Ref. Wikipedia, “Cermet” history.
In the 1930’s, sawing non-ferrous material, such as aluminum, brass, plastic and wood with carbide tipped circular saw blades began. However, attempts to cut ferrous material with carbide tips failed because the existing saws lacked the speed, rigidity, and innovation required to transfer high force with low vibration. These attributes are all necessary for carbide sawing. Also, the existing tooth geometry with positive cutting angles caused cracking of the carbide tips which were harder and consequently, more brittle than the high-speed steel (HSS) circular blades. Ref. Wikipedia, “High Speed Steel (HSS)”.
Circular Carbide Tipped Saw Blade Development
The blade body is made from rolled chrome, nickel, tungsten alloy steel, heat treated to about 40-45HRC. The carbide tips are silver soldered, sometimes with a copper shim to dampen the impact when the carbide tooth hits the material. The first carbide tooth geometry was similar to the already available geometry used to non-ferrous material sawing. The cutting faces had 10°-20° positive angles which had to be modified and drastically reduced to 5° positive angle, when used on steel on an Ingersoll plate saw. The tool life was poor, only about 5,000 square inches.
Between 1963 and 1969, professor Pahlitzsch and engineers Arno Willemeit and Horst Doepcke at the University of Braunschweig, developed a new carbide tip geometry with a negative cutting angle and a pair of teeth splitting the chip into three parts. With this development in tip geometry using 15° to 20° negative cutting angles, which reduces the sharp cutting edges, it became also economical to saw alloy steel billets. “Das Trennen von Stählen mit Schnellarbeitsstahl- und hartmetallbestückten Kreissägeblättern”
From 1972 to 1976 for his dissertation, Horst Doepcke, a scientific assistant at the Institute for Machine Tools and Manufacturing Engineering at the University of Braunschweig, developed a specific carbide cutting geometry for tubes which had every tooth splitting each chip into two. “Sägen von Rohren mit hartmetallbestückten Kreissägeblättern”
In 1984, Speedcut Inc. of Rockford, Illinois developed and patented another type of carbide tooth geometry by the name of, "Notch Grind" US patent Aug. 7, 1984, Number 4,463,645. This was used for steel billets and it would split the chip with one staggered groove per tooth. With the incorporation of this “Notch Grind” technology, saws became faster than with the Braunschweig geometry, but required more power. For several years after, various companies have been developing carbide saw blades with exchangeable carbide tips. These saw blades, so far, have not been proven economical for cutting steel and are used so far only in special cases.
Thin Kerf Disposable Carbide Tipped Saw Blades
The first carbide tipped circular saw blades had relatively thick blade blanks, up to .500” (12mm) thickness to be stiff enough to withstand the torsional and lateral vibration during the cutting process and get acceptable tool life. With improved technology, the blade body thickness was reduced which also lowered the cost. Another breakthrough in carbide tooth technology was the development of coating the carbide tips with a very hard (up to 95 HRC) material such as titanium nitride, titanium carbide, titanium aluminum nitride, or a combination of these materials. The coating also has a lubrication effect and the cutting edge cuts through the metal at lower temperature and horse power. The coating also prevents the chips from sticking to the cutting surface, avoiding buildup of material at the cutting edge. The result is a much higher tool life. Because of the hard coating, such blades cannot be economically re-sharpened. However, the much higher tool life and the thinner blades reduced the manufacturing cost and it is now economical for smaller blade diameters to use the blade only once and be disposed of thereafter. With the thinner Kerf, less material is wasted during the cutting process using less power and carbide saws using disposable blades now can compete better with band saws.
The name carbide saw came from the tool, a circular saw blade, with silver soldered carbide tips. It competed with and just about replaced, solid or segmental HSS blades, because carbide is much harder than HSS. Before HSS saws were developed, abrasive, friction or hot saws were used and are still manufactured for certain applications. These processes create heat and are therefore called hot saws. However, HSS blades use coolant and the cut surfaces don’t get hot, thus called cold saws. With the unique geometry of the teeth of carbide circular saws, the heat, developed by the cutting process is transferred into the chips and carried away with the chips. The cut surfaces stay cool. Therefore, carbide saws were also called cold saws. Other names include cold cut saws, cold circular saws, cold cut off saws, circular cold saws, or just carbide saws.
In 1963, the American Company, Ingersoll Milling Machine Co. in Rockford, Illinois, developed the first carbide plate saw that was used to cut steel plates with carbide tipped circular saw blades. The positive cutting angle of the teeth minimized the life of the tool, but the savings from not annealing the torch cut strips, with subsequent milling to size justified the higher tool cost.
In 1969, Advanced Machine & Engineering Co. (AME) of Rockford, Illinois developed the first Billet Saw which used carbide tipped saw blades incorporating the "Braunschweig geometry" to saw alloy steel. AME began to build these machines for the company Metalcut Inc., another Rockford based company. The machine was sold on the global market under the name Metalcut 12 and was exhibited at trade shows in Milan, Italy and Chicago. Its cutting efficiency was eight times faster than band saws and four times faster than HSS circular cold saws and revolutionized the production sawing market.
In 1970 the US government defense department learned of the development of the new saw concept. Chamberlain Manufacturing Corporation, contracted by Frankford Arsenal conducted an evaluation of this concept using the name of the inventor and called it the Goellner carbide billet saw. Chamberlain issued a comprehensive technical report on May, 29 1970. The report concluded that the new sawing concept was superior to the conventional band sawing, cold sawing and other billet severing methods in numerous objectives. Proclaimed advantages included faster cutting speeds, long blade life and improved quality of cutoff interfaces.
In 1971 another evaluation was conducted on the new standard Metalcut 12 billet saw and the result, phase 2, was issued on August 25, 1971.
Types of Carbide Saws
1969 Metalcut 10 Prototype Carbide Saw
1970 Standard Metalcut 12 Horizontal Slide Saw
Saws with Horizontal Slides
Horizontal slide saws are probably the most commonly used type of carbide saw. With this design the saw blade is mounted on the gearbox spindle, which slides on horizontal ways and enters horizontally into the billet.
In 1969, the first prototype horizontal carbide billet saw to saw alloy steel was developed by AME and built for Metalcut Inc. A year later, the standard Metalcut 12 billet saw was on the market. For the first time, Hennig telescopic steel way covers and steel aprons were used to protect the vital components of the saw from high velocity flying chips that are difficult to control.
Ohler Double Column Vertical Saw
with Round Ways
AMSAW-Vertical Slide Layer Machine
Saws with Vertical Slides
The saw blade for this type of saw enters vertically into the material. These saws are often used as layer saws, whereby a horizontal layer of multitude tubes, profiles, or bars can be simultaneously cut.
In 1974, the first carbide saw with a vertical slide was developed by Arno Willemeit, the co-inventor of the Braunschweig tooth geometry. It was produced by the company Ohler in Remscheid, Germany. Framag, an Austrian company later took over the production of this type of machine and also built it as a layer saw. Ohler had previously built vertical HSS saws with double round ways and converted them later also into carbide saws.
Carbide Saws with Inclined Slides
Carbide saws with inclined ways are used for cutting railroad rails, because the saw blade enters optimally into the rail profile, but are also used to cut steel billets.
Pivot saws were originally used as HSS saws for cutting small profiles and tubes. In the later 1970s these saws began to be used for larger steel profiles on construction projects (Kaltenbach).
1973 Metalcut III dual pivot saw
In 1973, Metalcut developed the first high-efficiency carbide pivot saw for 75 mm (3 inches) bars, where the center of rotation of the gearbox was mounted to the floor plate. This saw cuts on both sides of the pivot axis, one bar each, and was more productive as a result.
In 1976, the company Carbide Cutoff Inc. (CCI) in Rockford, IL developed a larger production carbide saw of this kind, in order to be able to compete against the horizontal slide saw from Metalcut Inc. This machine successfully cut billets up to 8 inches (200 mm) in diameter.
1990 large Metalcut 24” pivot bar cutoff saw
Larger type pivot saws were also used by Metalcut Inc., as either layer saws or billet saws which cut billet-diameters of up to 600 mm (24 inches). The pivot is located above the machine bed and the saw blade enters vertically in an arch-shaped manner into the material, but does not have a closed force loop arrangement.
1994 AMSAW 200
In 1994, AME developed a cost-effective pivot saw with the brand name AMSAW 200 for the US market.
In 2011, AME developed a high-efficiency carbide saw where the pivot axis of the gearbox is fixed on the lower end of the machine bed, for cutting 350 mm (14 inch) billets. The forces are contained in a closed loop design resulting in an extremely rigid machine. In this machine the chip flow is also improved, as the chips are thrown directly onto the chip conveyor. Similar smaller models, AMSAW 180 and AMSAW 125 were developed thereafter.
Special Models for Carbide Saws
In 1963, Ingersoll Milling Machine Co. Rockford, Illinois developed a plate saw which cut plates made of high carbon steel using carbide tipped saw blades. The horizontal ways were mounted on a beam above the plate.
Later, the Oliver Machinery Co. of Detroit, Michigan developed a less expensive plate saw where the gearbox slid underneath the plate on a machine bed and cut the plate from below.
This version however, was harder to maintain.
Railroad Rail Saws
AMSAW 300-R Rail Saw
Rail Saw for field repair service
In 1973, Metalcut developed the first carbide rail saw which was later produced by other companies including Wagner.
In 1999, AME built a special model of a carbide saw for mitercutting railroad rails for frogs and switches.
In 2005, AME developed an economical rail saw under the brand name AMSAW 300-R, which is still widely used in the USA and other countries.
In 2011, AME develops a special model which is integrated as a double saw on a railroad car and used for repair work of railroad tracks in the field. It replaced abrasive saws which had been used before. These abrasive saws were guilty of causing forest fires due the hot chips and sparks.
Cutting up through a layer of channels.
In 1974, Metalcut developed two layer saws which cut the ends of up to six "C" profiles. The profiles approached the saws horizontally, in layers. The first saw cut the front ends, the second the rear ones, whereby the latter was movable on tracks to cut different lengths of profiles. These machines were built as pivot saws and cut from the bottom up through the profiles.
In 1976, this pivot saw was also used for cutting tubes in layers.
Later, AMSAW Wagner and Framag developed similar saws with a vertical design.
Carbide Hot Saws
In 2008, AME developed a carbide hot saw which cuts off the ends on hot-forged railcar axles used on cars for the railroad industry.
Carbide Ring Saws
Thick-walled rings are hot-rolled and often have to be cut in random thicknesses. MFL Liezen, of Austria, developed such a saw which cut these rings from the inner diameter. AME also developed a simplified special ring cut off saw, however it cuts the rings from the outside.
Carbide Block Saws
In 2013 AME developed a special Block Saw, sawing sections out off large 3 ton steel billets to reduce milling time. The fixture automatically pivots to mill on (3) sides.
With swivel fixture
Carbide Saws to Saw Copper
In 1986, Metalcut received an order to develop a special carbide saw to cut pure copper billets. However, the preliminary tests showed that copper could not be cut with carbide tipped saw blades using steel cutting geometry and the cutting faces had to be changed to positive cutting angles. This machine was still in operations in 2016.
Carbide Saws to Saw Aluminum
Metalcut XII-P Aluminum Pivot Saw
Aluminum sawing using carbide tipped circular saw blades requires positive angle carbide tip geometry.
In 1988 Metalcut developed a very complex automatic sawing system to cut bars up to 350”(mm). This fully automatic system was unique at that time and was still in operation in 2016.
General Design of Carbide Saws
Carbide saws with ways, horizontal, vertical or tilted slide arrangement, consist of a welded base made of solid steel plates which are sufficiently ribbed and often filled with vibration dampening material. This base absorbs the occurring forces and dampens vibrations. Case-hardened ways are bolted on the base where the gearbox slides. With pivot saws, the heavy preloaded bearings are commonly bolted near the base plate to increase rigidity.
It commonly consists of two hydraulic clamping cylinders which clamp the material on both sides of the saw blade horizontally, vertically, or angularly. In order to improve the life of the saw blade, the material is separated from the blade on both sides before the saw blade is retracted from the cut.
The slide is guided by taper gibs with a minimum play, or when using hydraulically operated gibs, can be preloaded to eliminate play, in order to obtain the necessary rigidity. Recently, preloaded linear ways have also been used. Experts still debate, if preloaded box ways with low friction plastic lining are better vibration dampening than preloaded, hardened linear ways with hardened balls or rollers with minimum damping effect. The gearbox can be integral of the slide or bolted to the slide as one assembly.
The feed system consists of either a hydraulic cylinder or a ball screw with a gear reducer, powered by a servo motor.
Most of the time, low backlash case-hardened gears mounted in preloaded ball-or-taper-roller bearings are used. Depending on the size of the saw blades, a maximum of five gear sets with a gear reduction of up to 40:1 can be used. Variable speed motors of up to 150 KW drive the gearbox directly or via timing or "V" belts. Many saws have the blade mounting flange integrated within the spindle. This is less expensive, but requires expensive maintenance when the blade mounting surfaces wear. However, some more innovative saws have removable drive hubs which are mounted rigidly, and can be easily replaced. Some saws also use flywheels on the input shaft of the gearbox to smooth the fluctuating torque.
Saw Blade Mounting
The saw blade must be firmly mounted to the driveshaft in order to transmit the massive amount of torque without vibration. A larger blade flange usually reduces the blade vibration, but requires a bigger blade diameter. In order to reduce the blade costs, several producers use smaller flanges in combination with blade stabilizers and can thereby reduce the tool costs.
In general, there are two different types of measuring systems:
- Measurement with gripper tongs: The billet is clamped with gripper tongs which slide on ways and are operated by a ball screw- servo motor combination.
- Measurement with measuring stops: The billets are driven via roller conveyor toward an adjustable stop. This stop can be accurately positioned by a ball screw servo mechanism and usually incorporates a shock absorber to dampen the impact. This method is used for longer cut pieces.
Automatic production saws are mostly CNC operated using Programmable Logic Controller (PLC). Touch Screen panels are usually arranged for the operators.
A smaller diameter saw blade is less expensive and requires less torque to drive. A thinner saw blade is wasting less material and needs less energy to turn. Therefore, it is desired to use smaller diameter drive hubs for blade mounting and thinner blades to be able to saw larger diameter material with smaller diameter saw blades. These criteria however weaken the lateral stiffness of the blade and the blade may vibrate more due to the large diameter / blade thickness ratio.
The backlash of the gears, especially the spindle gear set, is also critical. The ratio between an 1800 mm (70”) diameter blade and the approximate 250 mm (10”) pitch diameter of the spindle gear is about 7/1. Thus, a tooth play of 0.025 mm (.001”) results in a 0.18 mm (.007”) lost motion on the tooth of the blade.
This large amount of lost motion backlash added to the torsional windup of the gear train, when a tooth enters the cut and relaxes when it exits, induces torsional vibration and must be reduced to a minimum by using anti-backlash mechanisms, by grinding the gear sets to an absolute minimum play, or by using brakes to eliminate the backlash and minimize the effect of compliance int he gear train.
open loop force flow
When a circular carbide-tipped saw blade enters or exits the material, only one tooth is cutting. The fluctuation of the load, when the tooth enters and exits the cut, induces vibrations and requires a very stiff gear box and machine.
A pivot saw has the highest degree of stiffness, because the forces are arranged in a closed loop (fig.1). If we assume that the base of such a saw is very rigid, the force will flow from the pivot of the gearbox to the ball screw feed system in a closed loop, whereby the cutting force engages in the middle, approximately, between rotation point and ball screw. This arrangement substantially reduces the lost motion and compliance in the feed system. Furthermore, the ball screw drive which forces the blade into the cut is bolted to the fixture frame which again is clamped to the billet and gives this arrangement additional rigidity.
Saws with horizontal or tilted slides have an open loop force flow (fig.2) and maintain any lost motion and compliance of the feed system
A circular saw blade is torsional very stiff but axially (laterally to the plane) very weak. If the exiting frequency of an external pulsing force is nearly the same as the natural frequency of the blade, resonance will occur and the blade will laterally vibrate. This external pulse force can be the impact of the carbide tooth when it enters the material or another pulsing cause. Ref. article “Effect and Prevention of Vibration in Carbide Sawing”
In a carbide saw, the most critical component subject to torsional and lateral vibration of the saw blade is the gearbox, commonly called the head. The basic understanding of this effect is outlined in the article “Measuring Compliance - The Weakness in Your Carbide Saw”. When the blade tooth first contacts the material, the reaction force 'winds up' the gear train. First the backlash is removed and then the additional loading will increase the torsional displacement. If there is any backlash in the feed mechanism, it will also act the same way as the powertrain backlash.
The saw blade and its mounting shaft have relatively little inertia. During the time the backlash is being removed, the blade tooth momentarily pauses in its rotation while the motor continues at its full speed. When the backlash is eliminated, the blade comes up to speed almost instantly. The speed may momentarily be even higher if the compliance is high and the cutting tooth 'springs' forward. If this happens when the tooth exits the material, the backlash will open up again and the process repeats until some teeth will stay in the cut. This exciting frequency measured in Hz could become critical when its frequency matches a natural frequency of the system to result in resonance. “Resonance – the destructive force behind carbide saw breakdowns”. As more teeth are engaged, the torque of the gear train will increase but the fluctuating load is only caused by one tooth engaging and disengaging the cut. This fluctuation of the wind-up of the gear train is very damaging to the carbide teeth and reduces the tool life.
The best way to reduce torsional vibration is by using a kind of disk brake directly on the blade, close to the outer diameter. Because of the large brake radius, the brake moment is much greater. The brake prevents or at least reduces the torque fluctuation induced by the entering and exiting of a carbide tooth at the beginning and the end of the cut. The heat created by the braking however, is a problem and must be reduced to prevent the blade body of losing the proper tension. The brake can also be applied on the end of the drive shaft and the heat will not affect the blade tension. But the diameter of a brake at the drive shaft is quite limited and the braking force is much smaller.
Another way to reduce vibration is by making the machine heavy. This lowers the natural frequency. The natural frequency of the saw blade is generally higher therefore, the spread between the induced force frequency and the natural frequency of the machine structure is larger and resonance can be avoided. However, the cost of heavier machines are higher and experienced machine tool designers will find other means to reduce vibrations.
Since carbide saw blades are circular disks, they are tangential the stiffest elements of the powertrain in the direction of the feed, but very unstable perpendicular-laterally to the feed direction. Due to the thin blade body the blades must be stabilized to minimize the side vibration amplitudes. When the first experiments with carbide saws were made, a development engineer of AME stabilized the blade by using a broomstick which he pushed against the vibrating blade, minimizing the vibrations. From this experience a blade stabilizer was developed using two plastic coated ball bearings mounted on eccentric shafts and supported by a welded bracket to the gearbox. “Minimizing The Damaging Effect of Vibration and Resonance with Stabilizers and Dampers”. Horst Doepcke, who saw this method during experiments carried out by Metalcut, also describes them in his dissertation “Sägen von Rohren mit hartmetallbestückten Kreissägeblättern”. Further Amsaw developments lead to segment stabilizers, whereby on both sides of the blade adjustable plastic-lined plates dampens and stabilizes the blade vibrations. Other manufacturers later used hardened steel plates as “vibration dampeners”. These erroneously labeled vibration dampeners did not however dampen the oscillations, but merely minimized the amplitudes. Mr. Doepke describes this function in detail in his dissertation. Recently AME has developed a pair of front stabilizers for its AMSAW machines arranged close to the point at which the blade enters the material. These stabilizers hydraulically extend, when the carbide teeth have moved past the stabilizer button before cutting and stabilize the blade when it enters the cut, which also help to guide the blade into the cut to improve the accuracy. Other forms of stabilizers are listed in German in the VDI Verlag Nr. 1999 by Dipl.-Ing. Rainer Liebrecht. This report especially addresses the effect of vibration on saw blades.
Damping dissipates mechanical energy, in this case vibration energy into heat. This can be done by either electro mechanical (Eddy Current) hydraulically or mechanical brakes, as also outlined under “Torsional Vibrations” in the above chapter. New developments and breakthroughs are still expected in this field.
Closed loop vertical slide saws are the stiffest, but also the most expensive machines. They require less space than horizontal or angular-slide saws, but it is also more difficult to control the horizontal chip flow. They are also more expensive and difficult to service.
Horizontal and incline slide type saws must be built heavier to maintain the same stiffness as vertical or pivot saws because of the open loop force flow. The chip flow is downward and therefore better to control than vertical saws.
Horizontal cutting pivot saws are the most cost-efficient machines. They require less parts and floor space and have favorable downward chip control. The closed-loop system reduces compliance and hence can be built lighter while maintaining a high amount of stiffness.
- Cemented Carbide
- Das Trennen von Stählen mit schnellarbeitsstahl- und hartmetallbestückten Kreissägeblättern
- Sägen von Rohren mit hartmetallbestückten Kreissägeblättern
- (US Patent Aug. 7, 1984, Number 4,463,645) Archived June 10, 2015, at the Wayback Machine
- AMSAW by AME - pioneers in carbide sawing
- contract DAAA25-70-C-0353 “Investigation of New Sawing Concept” PDF #1
- contract DAAA25-70-C-0353 “Production Evaluation of New Sawing Concept” PDF #2
- Werkzeugmaschinen Konstruktion und Berechnung (p. 487-488)
- Effect and Prevention of Vibration in Carbide Sawing
- Measuring Compliance- The Weakness in Your Carbide Saw
- Resonance- The destructive force behind carbide saw breaks
- Minimizing the damaging effect of vibration and resonance with stabilizers and dampers
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