Knowledge of high-speed steel
High-speed steel is a kind of high-alloy steel containing a large amount of carbon (C), tungsten (W), molybdenum (Mo), chromium (Cr), vanadium (V) and other elements, which has high thermal hardness after heat treatment. When the cutting temperature is up to 600 °C or more, the hardness still does not drop significantly. Powder high-speed steel molds can be divided into ordinary powder high-speed steel molds and high-performance high-speed steel according to chemical composition, and can be divided into melting high-speed steel and powder metallurgy high-speed steel according to the manufacturing process. The domestic manufacturing process is: smelting, and the foreign manufacturing process is: powder metallurgy.
1. Ordinary high-speed steel
High-speed steel is the main material for manufacturing tools with complex shapes and difficult grinding, and ordinary high-speed steel can meet general needs. There are two kinds of common ordinary high-speed steel, tungsten high-speed steel and tungsten-molybdenum-based high-speed steel, and 90% of the current market is tungsten-molybdenum-based high-speed steel.
(1) Tungsten high-speed steel
The typical grade is w18Cr4V, the heat treatment hardness can reach 63-66HRC, the bending strength can reach 3500MPa, the grindability is good, but the toughness is poor, fragile and easy to burst.
(2) Tungsten molybdenum high-speed steel
The typical grade is W6Mo5Cr4V2 (American grade M2, commonly known as W6 in China), which replaces tungsten high-speed steel, and has a series of advantages such as uniform distribution of carbides, high wear resistance and low cost. The hardness of heat treatment is the same as above, the flexural strength reaches 4700MPa, and the toughness and thermoplasticity are 50% higher than w18Cr4V. Commonly used in the manufacture of various tools, such as drills, taps, milling cutters, reamers, broaches, gear tools, etc., can meet the requirements of processing general engineering materials, but its decarburization sensitivity is slightly stronger.
(3) Another grade of ordinary high-speed steel is W9Mo3Cr4V (no international grade, commonly known as W9 in China), which is a new variety developed in China in recent years. The strength and thermoplasticity are slightly higher than W6Mo5Cr4V2, the hardness is HRC63-64, which is compatible with toughness, easy to roll, forge, wide range of heat treatment processes, small decarburization sensitivity, and lower cost. The proportion of these three grades of ordinary high-speed steel in the Chinese market is: W18Cr4V, 16.5%; W6Mo5Cr4V2, 69%; W9Mo3Cr4V,11%。
(4) Another grade of ordinary high-speed steel is W5Mo2Cr4V (no international grade, commonly known as W5 in China), which is a new variety developed in 2006. The strength and thermoplasticity are slightly lower than W9Mo3Cr4V, the hardness is HRC62-63, which is compatible with toughness, easy to roll, forge, wide range of heat treatment process, small decarburization sensitivity, and lower cost
The above three grades of saw blades are recommended to use tensile resistance (500N/mm2), such as: iron aluminum copper, etc.
2. High-performance high-speed steel
High-performance high-speed steel has better hardness and thermal hardness, which is a new variety developed by changing the chemical composition of high-speed steel and improving performance. It has higher hardness, thermal hardness, cutting temperature of 650 degrees Celsius, hardness can still be maintained above 60HRC, durability of ordinary high-speed steel 1.5-3 times, suitable for the manufacture of high-temperature alloys, stainless steel, titanium alloys, high-strength steel and other difficult to machine materials of the tool. There are four main varieties, namely high carbon high-speed steel, high vanadium high-speed steel, cobalt-containing high-speed steel and aluminum high-speed steel.
(1) Aluminum-containing high-speed steel
The grade has W6Mo5Cr4V2 (no international grade, commonly known as W6+ aluminum in China), because of the aluminum content of 1.5%, the wear resistance is greatly improved, but the subsequent wearability is worse. The use and development of aluminum-containing high-speed steel will have a greater market space.
As above, aluminum-containing high-speed steel saw blades are recommended to use cutting tensile resistance (800N/mm2), e.g. iron aluminum copper/stainless steel.
(2) Cobalt-containing high-speed steel
a. The grade is W6Mo5Cr4VCo5 (American grade M35, commonly known as W6+ cobalt in China). Cobalt can promote carbides to dissolve more in the matrix when quenched and heated, and use high matrix hardness to improve wear resistance. This high-speed steel hardness, thermal hardness, wear resistance and abrasionability are very good, heat treatment hardness up to 65-67HRC.
As mentioned above, the cobalt-containing high-speed steel saw blade is recommended to use cutting tensile resistance (800N/mm2__1200N/mm2), such as: stainless steel/45# steel, etc
b. The grade is W2Mo9Cr4VCo8 (Us grade M42). Its characteristics are: the vanadium content is not high (1%), the cobalt content is high (8%), cobalt can promote the carbide to dissolve more in the matrix when quenching and heating, and use the high matrix hardness to improve wear resistance. This high-speed steel has good hardness, thermal hardness, wear resistance and wearability. The heat treatment hardness can reach 67-70HRC, but there are also special heat treatment methods to obtain 67-68HRC hardness, so that its cutting performance (especially intermittent cutting) is improved and the impact toughness is improved.
Cobalt high-speed steel can be made into a variety of tools, for cutting difficult-to-machine materials the effect is very good, and because its grinding high-speed steel is a high-alloy steel containing a large amount of carbon (C), tungsten (W), molybdenum (Mo), chromium (Cr), vanadium (V) and other elements, heat treatment has high thermal hardness. When the cutting temperature is as high as 600 ° C or more, the hardness is still not significantly reduced, and the cutting speed of the tool manufactured with it can reach more than 60 meters per minute, which gets its name. High-speed steel can be divided into ordinary high-speed steel and high-performance high-speed steel according to chemical composition, and can be divided into melted high-speed steel and powder metallurgy high-speed steel according to the manufacturing process.
Cobalt-containing high-speed steel saw blades are recommended to use cutting tensile resistance above (1200N/mm2).
High-speed steel saw blade toothing and grinding technology:
First, the choice of tooth shape
The commonly used tooth types of high-speed steel saw blades are: A type, B type, AW type, BW type, HZ type, CB type, VT type, etc., which are suitable for different application environments, among these several tooth types, the most commonly used is BW type.
Type A is mainly used for slotting, but also for sawing stainless steel workpieces.
Type B is mainly used for sawing ultra-thin pipes or sawing non-ferrous materials.
BW tooth type is commonly known as the left and right teeth, that each tooth has a 1/3 chamfer, mainly used for thin-walled pipe sawing.
HZ tooth type is commonly known as high and low teeth, that is, the serration is a high and a low, the chamfer of each side of the high tooth is 1/3, the low tooth is not chamfered, and it is generally used for the sawing of thick-walled pipes (wall thickness of more than 3.5mm) or solid rods.
CB tooth type (CHIP BREAKER) is also used for thin-walled pipe sawing, characterized by sawn pipe workpiece end face flat, no notch, this tooth type in stainless steel thin-walled pipe sawing applications also have great advantages. The disadvantage is that a special slotting machine is required, and the grinding cost is higher.
VT tooth type is a tooth change, and with the saw blade of the tooth change principle, the advantage of this tooth type is that it can reduce vibration, the disadvantage is that grinding is too troublesome, basically not used in practical applications.
Second, the choice of the number of teeth
According to the experience of Europeans, it is best to have 3.5 teeth working on the workpiece at a time point, and in general, the calculation of the number of teeth of solid rods can be calculated using the following simple formula (the calculation of the number of teeth is more complicated, and many factors need to be considered, for reference only):
Pitch = diameter / 3.5
Number of teeth = blade diameter * 3.14 / pitch
Note: The number of teeth in China is generally a multiple of 20, and the number is not an integer after the formula is calculated, and can be nearly rounded to a multiple of 20.
The number of teeth in the pipe can also be applied to this principle, but the pipe also takes into account the wall thickness. Other factors such as equipment, in general, the number of teeth of the saw blade when sawing pipes can be calculated with reference to the following formula:
The longest cutting motion length of the serration (i.e. the longest chip) = the root number [(diameter - wall thickness) * wall thickness] * 2
Pitch = maximum cutting motion length of the serration / 3.5
When sawing thin-walled tubes, if the clearance of the machine is too large, it is necessary to increase the number of teeth to reduce the impact of vibration on the life of the saw blade.
Theoretically, if the cross-sectional area of the sawdust cut down by each tooth exceeds 20% to 25% of the sawtooth chip groove (different according to the line speed), it will cause the chip removal difficulties of the saw blade, so when selecting the number of teeth, the chip discharge problem should be fully considered.
The area of the chip carrier = n (1/4 pitch) 2
Cross-sectional area of sawdust = maximum cutting movement length of the sawtooth * amount of tool feed per tooth
Third, the linear speed
Linear velocity is a very important indicator in metal processing, and linear velocity has a crucial determinant of the service life of the tool. General metalworking manuals have some data on the speed of the processing line that can be used as a reference.
In the sawing industry, the most commonly encountered problem is the sawing of stainless steel materials, and a lower line speed should be used when processing stainless steel, such as 201 and 202 materials, and the line speed should not be higher than 30 m / min.
The calculation formula of the processing line speed of the saw blade is as follows:
Linear speed = blade diameter * 3.14 * RPM (spindle speed of the machine)
At present, the pipe cutting machine on the market is generally high in line speed, mainly for ferrous metal material sawing. The 325SA and RPM of the front and machinery are adjusted to 22, and the effect of sawing stainless steel material is good.
Fourth, cut off the time
According to the different processing materials, the amount of each tooth of the saw blade is generally 0.02 ~ 0.05mm. This is an empirical value, if the saw machine power is large enough, and there is a chip removal device, the amount of knife feed can be larger, and vice versa. The general carbon steel material is 0.04mm.
To measure the reasonable cut-off time of the workpiece, it is necessary to prepare a stopwatch, and the test time is in the range from when the sawtooth touches the surface of the workpiece to the time when the sawtooth leaves the workpiece.
A reasonable cut-off time can be calculated according to the following formula:
Feed per second = RPM * number of teeth * per tooth feed / 60
Reasonable cut-off time (round workpiece) = workpiece diameter / feed per second
5. Others
When sawing the square pipe, try to let the saw blade enter the knife from the corner of the pipe, and the blade enters the knife from the surface and the knife from the angle, and the life of the saw blade can be more than 3 times.
High-speed steel saw blade is not heat-resistant, it is best to take cooling measures when using, the use of 5% concentration of emulsion effect is better, some processes can not use water cooling, nor can use lubricating oil, then the use of cold air engine effect is certainly not as good as emulsion.
When sawing thick-walled pipes, solid rods, stainless steel materials, it is best to install a wire brush on the sawing machine, the cost of installing a wire brush is not high, but the effect is very good.
High-speed steel saw blades are prone to tooth collapse or rupture countermeasures:
In the process of cutting various types of pipes by high-speed saw blades, there are many conditions caused by not paying attention to details.
(1) Material: Sometimes the problem is in the material being cut. Some suppliers on the market cut corners in the production of materials, resulting in too many impurities in the cut material, so when the saw blade encounters these impurity particles, the superhard saw blade may crack or make a loud noise, and the cut surface will be uneven. The softer high-speed saw blade will not break, but the cutting result will be skewed, because the blade will be turned when it comes into contact with the particles. Or some materials themselves may not be too hard, but the elements added to the production process and the process used may cause the tool to be difficult to cut, resulting in the cutting edge cracking or blunting. (2) Saw blade: the saw blade is not properly arranged under pressure deformation, the serration blunt is not grinded, the deflection degree is poor, the number of teeth is improperly selected, and the serration grinding is not good. In short, the quality of the saw blades is not good. (3) Cutting machine: the state of the fixture, the installation of the saw blade is incorrect, the speed of the saw blade is not correct, the feed speed is not suitable, the cutting oil is selected, and the error between the saw blade and the cutting machine will affect each other. Some customers complained that the cutting results were skewed, and through our observation of the results on the spot, the feeding rack was not fixed, and the workers often accidentally bumped and crooked when transporting materials. After the cut material feeding rack is crooked, of course, the cut material must be crooked. There are also customers who complain that circular saw blades are often broken and cannot be solved, and when we arrived at the scene, we found that the mechanical design book has pointed out that when cutting longer materials, there must be a fixed table to make the cut section not shake. However, the customer is still the same as when cutting the short material, so the saw blade is broken by the shaking of the cut material. There are also customers whose machines are not level corrected when they are installed, so the machine is fundamentally crooked. (4) The use of counterfeit machine: the use of poor quality metal circular saw machine, although the price is very cheap but not enough steel in the production process, thereby causing cutting vibration, so that there is a gap between the blade and the blade, the blade will produce shaking when cutting, and eventually affect the cutting performance of the saw blade. (5) Manual machine operator: When using the manual machine, the user's experience is more important, the user can feel the strength of the knife and the sharpness of the saw blade, it is easier to judge whether the saw blade can be used again! Pneumatic or hydraulic models require the user to use the saw blade more carefully, and in the cutting workpiece, it is not possible to blindly cut on the grounds of experience. Because each blade cannot be the same when cutting the workpiece, the life of the sawtooth is also within a general range. When starting and stopping cutting, do not enter the tool too quickly, otherwise it may cause tooth breakage and damage. When the sawtooth has appeared relatively blunt to continue to use the phenomenon of teeth pulling, tooth breaking, etc., serious will appear saw blade body cracking, burst phenomenon! When using the saw blade, the following must be noted: (1) It must be determined that the cut material has been indeed fixed. (2) The cutting conditions should be set according to the material to be cut. (3) When installing the saw blade, the scrap of the fixture part must be cleaned, and then pay attention to the direction of rotation to fix the saw blade. (4) When starting and stopping cutting, do not enter the knife too fast, otherwise it may cause tooth breakage and damage. (5) Make full use of cutting oil. (Hope to cooperate with the cut material to select cutting oil) (6) Discarded circular saw blade cutting machine and the general circular saw blade cutting machine is different, you must choose the correct saw blade, can not be mixed!
In addition, high-speed steel saw blades have problems in heat treatment or during raw material blank processing. (1) When the raw material blank is processed, there is a little slag doped into it, which affects the quality of the finished product, so that the crystal of the saw blade itself is faulted and the block or fracture phenomenon occurs. (2) The time selection of the saw blade when tempering and annealing during heat treatment is inappropriate, so that the hardness of the saw blade exceeds the specified range standard, such as: the hardness of the W9 high-speed steel saw blade itself after heat treatment cannot exceed 65 degrees, once it is beyond the range. When in use, it will be easy to have cracked teeth, fractures and other phenomena, and serious risk phenomena such as explosion will occur.