Carbide saw
Carbide saws are machine tools for sawing , the saw teeth of which are made of carbide , so that hard materials can also be sawed.
Development history
In 1926, Krupp developed the hard metal Widia (derived from Wie Diamant) and revolutionized metal-cutting production. This new material found its way into all machining processes with the exception of sawing in the 1950s. In 1942, German researchers developed an oxide- based ceramic material that was further developed by American universities after the Second World War and marketed, among other things, as a cutting material for machine tools under the trademark Cermet .
Circular saws fitted with carbide were already used in the 1930s for sawing non-ferrous metals, plastic and wood. In tests with iron and steel, the existing machines turned out to be too slow and not sufficiently rigid to transfer the higher forces. In addition, the tooth geometries were designed for high-speed steel (HSS) and could not be used for the hard and brittle hard metal alloys in order to achieve an economical tool life. New cutting shapes and fast rotating, robust machines for sawing and grinding hard metal teeth therefore had to be developed. In 1963 Ingersoll Milling Machine Co , Rockford, Illinois, USA developed the first carbide panel saw that cuts steel plates with carbide-tipped circular saw blades. The cutting angle of the teeth is positive and therefore the service life is short.
The term “carbide saw” is derived from the tool, a circular saw blade with hard-soldered carbide teeth. This competed with saw blades made of high-speed steel (HSS) and replaced them over time, since carbide is significantly harder than HSS and therefore shows less wear. Before the introduction of HSS saws, abrasive cutting or hot saws were used, which are still used for specific purposes. The sawing process generates heat, hence the name hot saw. In contrast, HSS saws use a coolant, which means that the surfaces do not get hot. They are therefore called cold saws. With carbide saws you generally do not need coolant, but the cutting surfaces remain cool. For this reason, carbide saws are also classified as cold saws. Another possible name is a cold circular saw.
1963–1969, the Technical University Carolo-Wilhelmina zu Braunschweig, chaired by Gotthold Pahlitzsch and the research engineers Arno Willemeit and Horst Döpcke, developed a new carbide tooth geometry with negative cutting angles and a tooth pair that divides the chip into three parts. With this geometry, it is possible to saw alloy steel bars economically. In 1969, Advanced Machine & Engineering Co. (AME) in Rockford, Illinois, USA developed the first billet saw using carbide-tipped circular saw blades with the “Braunschweiger Geometry”, and built them for the Rockford-based company Metalcut Inc. The machine was developed under the Name Metalcut 12 sold on the world market and exhibited in Milan and Chicago. With its outstanding cutting performance, around eight times faster than band saws , four times faster than high-speed steel cold saws, it revolutionizes the saw market. 1972–1976, Horst Döpcke, scientific assistant at the Institute for Machine Tools and Manufacturing Technology at the Technical University of Braunschweig, developed a carbide cutting geometry for pipes for his dissertation, which divides the chip on each tooth in two. In 1984 Speedcut Inc. Rockford , Illinois, USA developed a hard metal tooth geometry “Notch Grind” for bars, which divides the chip with an offset groove per tooth and which therefore saws much faster than the Braunschweig geometry. Circular saws tipped with cermet are entering the market and are competing with carbide due to their longer service life.
For some years now, companies have been trying to develop circular saws with replaceable hard metal teeth. For reasons of cost, however, these circular saws have not yet caught on for steel.
Types of carbide saws
Sawing with horizontal slide guide
These saws are arguably the most common types of carbide saws. With this type of construction, the saw blade enters the bar in the gear box, sliding horizontally on horizontal guides. In 1969 the first horizontal carbide saw was developed by the company Advanced Machine & Engineering Co. (AME) in Rockford, IL, USA and built for the company Metalcut Inc. For the first time, telescopic steel covers and steel aprons from Hennig GmbH were used to protect critical parts of the saw from chips that are difficult to control due to the high peripheral speed.
Sawing with vertical slide guide
In this type, the saw blade enters the material vertically. These saws are often used as layer saws, whereby several tubes, profiles or bars are sawed at once in a horizontal position.
In 1974 the first carbide saw with vertical flat guides was designed by Arno Williemeit , the co-developer of the Braunschweig tooth geometry, and built by the Ohler company in Remscheid. This machine type was later taken over by FRAMAG , Austria and also built as a layer saw . Ohler had previously built vertical HSS saws with double round guides and later converted them for carbide saws.
Saws with inclined guides
These are also built, but are more expensive than saws with horizontal slide guides and are advantageously used for cutting railroad tracks because the saw blade penetrates the rail profile evenly. In 1970 Chamberlain's development department made tests for the US government with the prototype of the newly developed Metalcut billet saw. The company presented these results to Frankford Arsenal, an officer in charge of the US armed forces, as a final engineering report in book form with the title "Phase I Investigation of new sawing concept". The report was very detailed and shows the advantages of a carbide bar saw. This saw was named "Goellner Saw" after its inventor. In 1971, further tests were carried out under phase II with the new Metalcut 12 series machine.
Swivel saws
Swivel saws were originally used as HSS circular saws to cut smaller cross-sections of steel, profiles or pipes. Later larger profiles were also cut for steel construction ( Kaltenbach , Lörrach). In 1973, Metalcut developed the first high-performance swivel saw for a material thickness of 75 mm, with the pivot point of the gear box attached to the base plate. This saw cuts a bar on either side of the swivel axis and is therefore more productive. In 1976 the company developed Carbide Cutoff Inc . Rockford, IL bought a major manufacturing carbide saw of its kind to compete against Metalcut Inc. This machine cuts billets up to 8.0 inches (250 mm) and has performed excellently. This type of saw is also built by Metalcut Inc. as a layer saw or billet saws up to a diameter of 600 mm. The swivel bearing is located above the machine bed and the saw blade enters the material in a vertical arc, but has no closed force flow. In 1994, AME (Advanced Machine & Engineering, Rockford IL, USA) developed an inexpensive swivel saw under the trademark AMSAW 200 for the US market. From 2011 the same company produced a high-performance carbide saw for cutting 350 mm bars according to the swivel principle, with the swivel axis of the gear box being attached to the lower part of the machine bed. The power flow is a closed circuit and the machine becomes extremely stiff. Chip flow is also improved because the chips are thrown directly onto the chip conveyor.
Special designs
Panel saws
In 1963, Ingersoll Milling Machine Co., Rockford, Illinois, USA, developed a saw that sawed plates made of high-strength carbon steel with carbide-tipped circular saw blades. The horizontal slide guide is mounted on a beam above the plate. Oliver Machinery Co., Detroit, Michigan, USA later developed a panel saw in which the gear box slides beneath the panel on a machine bed while sawing the panel from below.
Rail saws
In 1973, Metalcut developed the first hard metal rail saw, which was later also built by Gustav-Wagner-Maschinenfabrik GmbH (Reutlingen) and other companies. In 1997 AME produced a cheaper rail saw under the name AMSAW, which is widely used in the USA. In 1999 AME built a special version of a hard metal saw that saws railway rails for signal boxes at an angle.
In 2011, AME developed a special version that is integrated as a double saw in a railroad car and is used in the USA for rail repairs. Cut-off saws previously used caused forest fires due to the hot chips and were replaced with these AMSAW cold saws.
Layer saws
In 1974 Metalcut developed two layer saws that cut the ends of up to 6 “C” profiles. The profiles are fed to the saws in a horizontal position. The first saw cuts off the front ends, the second cuts off the rear ends, whereby this, movable on rails, can cut different lengths. These machines are built as swivel saws and saw from bottom to top through the profiles. From 1976 this saw was also used for sawing pipes in layers. Later, Wagner and Framag built similar saws with a vertical slide design. In 1977 Metalcut developed a swivel saw, which was sold at a lower price.
Carbide special machines
In 2008 AME developed a special carbide machine for cutting hot-forged axles. The material was sawn at a temperature of approx. 430 degrees Celsius.
Carbide ring saws
Thick-walled rings have recently been rolled warm and often have to be sawn into slices. MFL Liezen manufactured such a saw that saws these rings from the inside diameter. AME Rockford, IL, USA also offers a saw of this type, but it cuts the rings from the outside.
general structure
Tungsten carbide saws with slide guides (horizontal, vertical or inclined guide arrangement) consist of a welded frame made of sturdy steel plates, sufficiently ribbed and often filled with damping masses that absorb the forces and dampen vibrations that occur. Hardened guides are attached to this frame, on which the gear box slides with as little play as possible.
The slide with gear box is guided almost free of play by V-ledges or hydraulically operated guide ledges in order to achieve the required rigidity. Lately, play-free linear guides have also been used. Experts are still arguing about whether hardened guides on which slides with plastic coverings and hydraulically pre-tensioned strips dampen better than force-transmitting linear guides. There hardened balls or rolling elements roll on guide elements.
Feed
The feed drive consists either of a hydraulic cylinder or, better, of a recirculating ball screw that is driven by a servomotor via a reduction gear.
Gear box
In most cases, hardened gear wheels with low backlash are used, which are mounted in tapered roller bearings. Depending on the size of the saw blades, up to five gear stages can be used, which result in a ratio of around 40: 1. Infinitely variable motors up to 175 kW drive the gearbox directly or via V-belt or toothed belt. A flywheel is often attached to the entry shaft to compensate for torque fluctuations when entering and exiting the teeth.
Jig
This generally consists of two hydraulically operated clamping elements that clamp the material horizontally, vertically or in a combination of both variants on both sides of the saw blade. In order to improve the service life of the saw blade, the material is often moved away from the blade on both sides before the saw blade is pulled out of the cut, in order to prevent the hard metal teeth from rubbing the cut surfaces and thereby reducing the service life of the blade.
Saw blade attachment
The saw blade must be connected to the drive shaft in a stable manner in order to transmit the large torques without vibrations. A larger blade flange usually reduces blade vibration , but requires larger blade diameters. These tend to vibrate more easily. To reduce the higher blade cost, some manufacturers use smaller flanges in combination with blade stabilizers, thereby reducing tooling costs because smaller blade diameters can be used.
Leaf stabilizers
Because of their plate shape, circular saw blades are the stiffest tool element of the drive train radially in the feed direction, but they are extremely unstable transversely to the feed direction due to the small blade thickness. They must therefore be stabilized in order to reduce the formation of rotating plate vibrations. During the first attempts with carbide circular saws, a development engineer from the Advanced Machine & Engineering Company in Rockford calmed the blade by pressing a broomstick against the blade, which was used to interfere with the vibrations. This is how the so-called "Broom Stick Method" and the leaf stabilizer with rollers came about. These eccentrically adjustable double rollers with a plastic covering were attached to a stable console on the gear box and calmed the blade. Horst Döpcke, who saw this method in Metalcut experiments, also recorded it in his dissertation “Sawing pipes with carbide-tipped circular saw blades”. Later developments by the Advanced Machine & Engineering Company led to segment stabilizers, with sliding plates adjustable on both sides of the blade reducing the blade amplitudes. Compressed air enriched with oil is pressed between the plates. This reduced the friction due to its lubricating effect and when it exits, the expansion of the air cools the blade due to the Joule-Thomson effect. Other mechanical engineers later use similar sliding elements as dampers. However, these erroneously designated damper elements did not dampen the vibrations, but merely prevented the formation of amplitudes. Döpcke described this function in detail in his dissertation.
In 2013, AME developed two front stabilizers for its AMSAWS, which are stationary in the cutting area of the saw blade. Since the hard metal teeth are generally wider than the steel blade, these actuators must be hydraulically actuable. The adjustment of the stabilizers on both sides takes place as soon as the material enters the material, and this not only reduces the blade amplitudes, but also the risk of the saw blades running off. Other forms of stabilizers are explained in the progress report VDI series 2 No. 199. This deals in-depth with the behavior of saw blades.
Measuring device
Two types of measuring devices are generally used:
- 1. Measurement with grippers
The bar is clamped with gripping pliers, which slide on a guide and is controlled by a ball screw-servomotor combination.
- 2. Measurement with measurement stop
The bars are moved against a damped measuring stop on a roller conveyor. This method is mostly used for longer sections. In both cases, the measurement takes place automatically via the servo motor integrated encoder and the connected PLC control.
control
Automatic production saws are usually controlled by PLC . This allows automatic processes to be controlled as required.
Construction features
Saw blade diameter
Smaller saw blades are cheaper and require lower drive torques. Thinner blades have less material waste and therefore need less cutting force. Attempts are therefore made to keep the blade diameter as small as possible by making the diameter of the blade holder and clamping disc as small as possible in order to saw a larger material cross-section with a smaller saw blade diameter. However, the smaller diameter of the blade holder weakens the axial stiffness of the blade. It is therefore the task of a saw machine developer to find the best ratio or to reduce the resulting vibrations by using suitable blade stabilizers.
Backlash in the gear box
The backlash, especially that of the drive spindle, is also critical. For example, if a 1800 mm diameter saw blade is driven by a gear wheel about 250 mm, the ratio is about 7: 1. A tooth play of 0.025 mm increases the play on the hard metal tooth to 0.18 mm and also has a detrimental effect on the service life of the blade. Attempts are therefore made to reduce the backlash by means of special design measures or to grind the tooth flanks to a minimum.
Machine stiffness
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Only one tooth is in engagement when the blade is cut and exited. Extreme torque fluctuations occur when the gearbox is loaded when the tooth enters and is relieved when it exits. Horizontal cutting swivel saws have the highest degree of rigidity. The power flow goes in a closed circuit from the console through the highly preloaded ball roller bearings of the pivot axis via the gear box and the feed gear of the ball screw through the workpiece, with the cutting force acting roughly in the middle between the pivot point and the feed gear (see scheme 1). Any remaining flexibility of the feed gear is significantly reduced on the saw spindle and therefore increases the overall rigidity of the machine. The feed gear is articulated to the device, this device is supported with a high clamping force on the material, so the closed force flow is supported even further. Saws with horizontal or inclined guides do not have a closed power flow (Scheme 2) and must therefore be built correspondingly more rigidly and more costly.
Differences between different types of saws
Saws with vertical slide guidance and closed power flow are the stiffest, but also the most expensive saws. They take up less space than saws with horizontal or inclined guides, but the horizontal chip flow is more difficult to handle. Saws with horizontal or inclined guides must be built heavier to achieve the same rigidity. You need more space, but the chip flow is cheaper. However, horizontally cutting swivel saws are the most cost effective saws. They require fewer parts, require less space and have a favorable chip flow. Due to the closed flow of forces and the reduction in the remaining flexibility, these saws can be built lighter and therefore more cost-effective while maintaining the same rigidity.
Web links
Individual evidence
- ↑ USA Patent Aug. 7, 1984, Number 4,463,645
- ↑ Manfred Weck: Machine tools 2 - construction and calculation . 8th edition. Springer-Verlag, 2006, ISBN 978-3-540-30438-8 ( limited preview in the Google book search).
- ↑ H. Döpke. Sawing pipes with carbide-tipped circular saw blades. 1976.
- ↑ http://www.bam-portal.de/showDetail.html?id=%22/bam/library/bsz/swb/022017852%22 ( page no longer available , search in web archives ) Info: The link was automatically saved as marked defective. Please check the link according to the instructions and then remove this notice.
