Ceramic tools are ideal for machining hardened steels, heat resistant alloys or superalloys. Operators often mistakenly use carbide machining, they need to solve this "hard alloy complex", and then consider the special requirements of ceramic tool processing: select the appropriate blade shape and machine tool, tool bar and according to the processing material The rigidity of the fixture.
High temperatures are the main enemy of carbide machining, so most operators will reduce the cutting speed and increase the feed rate, which will further reduce the spindle speed when the situation is not good. However, this most suitable machining method for cemented carbide is precisely the biggest contraindication in the processing of ceramic tools, because most of the problems encountered in the machining of ceramic tools are caused by insufficient cutting speed and excessive feed rate.
High temperatures have a different effect on ceramics than hard alloys. The material being cut during the cutting process is pushed away from the sheared area on the rake face of the tool, and the heat of cutting also accumulates in this area. As the cutting speed increases, the heat generated by the shearing zone cannot be carried away by the waste in a short time, thereby forming a high temperature and producing a softening effect.
The melting point of cemented carbide is about 1199 ° C, and the high temperature can easily cause deformation and damage of the base of the cemented carbide insert. Therefore, reducing the cutting speed often guarantees a reasonable life of the cemented carbide insert. The melting point of ceramic materials is as high as 1999 ° C, so the high temperature generated in high-speed processing is beneficial to ceramic blades. The most suitable cutting speed of ceramic inserts is much higher than that of cemented carbide inserts. The high temperature effect generated by high-speed cutting softens the material to be processed, which greatly reduces the resistance during cutting. Therefore, the same cutting effect can be easily achieved by selecting a ceramic insert that is more fragile than a cemented carbide insert under the same conditions. Ceramic cutting tools can sometimes be used to increase material removal rates from hundreds of feet per minute to thousands of feet per minute.
A suitable combination of cutting speed and feed rate creates an ideal environment for the ceramic insert in the shear zone. But lowering the spindle speed can cause the tool to spark - causing blade and tool failure.
The material, coating or non-coating of ceramic inserts is based on a silicon nitride or alumina substrate. Silicon nitride mother-based ceramic tools generally have good toughness and are suitable for turning and milling roughing of malleable cast iron, ductile iron and other difficult-to-machine cast irons and high-hardness alloys. In addition to being very suitable for processing cast iron, the silicon nitride-based ceramic tool is also suitable for processing steel materials with hardness lower than HRC65. It can be applied to turning rolls and high temperature because of the low speed and the inability to use whisker-reinforced ceramics. Alloy processing. In the car and milling process of cast iron, the surface line speed of 1524m / min can get the most economical tool life.
The alumina-based ceramics have good wear resistance and moderate hardness. They are the most economical ceramic tool materials, but should be avoided in the processing of intermittent, bumper articles copied in Chinese ceramic mesh or high hardness materials. . Alumina-based ceramics are mostly used for semi-finishing and finishing of gray cast iron. The high compressive strength of this material makes it ideal for boring of cast iron. However, alumina-based ceramics have poor thermal shock resistance and are therefore not suitable for use in processing.
A new type of reinforced alumina mother-based ceramic containing silicon carbide (SiC) single crystal or whisker has high melting point, high strength and good chemical stability, abrasion resistance and thermal shock resistance. Whisker improves ceramic material The breaking strength.
Whisker-enhanced ceramic moons rarely experience catastrophic momentary rupture or destruction like traditional cemented carbide blades. Typically, whisker-reinforced ceramic blades are only gradually worn out in a predictable damage mode.
Whisker-reinforced ceramics are stronger than other ceramic materials and are well suited for processing superalloys and similar materials such as hardened steel, high hardness cast iron, plasma sprayed and welded surface finishes. If the high-nickel alloy is processed by whisker-enhanced ceramics, the interface temperature can reach 982 °C, and the material removal rate can reach more than 10 times that of the cemented carbide tool. The high strength of whisker-reinforced ceramics makes them ideal for interrupted turning, milling and die/die machining.
Due to their good thermal shock resistance, whisker-reinforced ceramic tools can be used for dry, wet or intermittent cooling without fear of chipping or hot cracking.
Coated whisker-reinforced ceramics are ideal for continuous semi-finishing and finishing and similar mild and medium-strength processing that require long tool life. Coated ceramic tools have a lifespan that is three times that of uncoated ceramic tools, but are not suitable for machining in harsh conditions such as milling and interrupted cutting.
It is not recommended to use ceramic tools for the processing of titanium. The burning point of titanium is very low, and the high temperature is inevitable in the processing of ceramic tools, which is easy to cause fire.
The rigidity of the shank is as important as the rigidity of the machine tool. In high-volume environments, ceramic blades must be clamped to specialized shanks that avoid micro-movement of the blades. In the long overhanging, the rigidity of the shank is particularly important. Large overhangs make it easier to make a slight deflection of the shank during high-speed cutting, which can cause vibration and damage the ceramic tool. Therefore, the overhang of the ceramic blade should be shortened as much as possible, because the force generated when the arbor is deflected will increase with the length of the overhang, that is, if the other conditions are the same, the overhang of the shank is doubled. The deflection of the shank will increase to 8 times that of the previous one.
Boring shanks usually have a larger aspect ratio than external burrs, so it is reasonable to use heavy metal and carbide boring bars. In general, a nickel-based alloy can be machined with a steel boring tool with a 3x aspect ratio or a heavy metal boring tool with a 5x aspect ratio (such as a heavy metal anti-vibration arbor) and a 7x aspect ratio carbide. Knife.
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