PCBN tool cutting hardened steel material
Problems we often encounter when machining hardened steel materials:
1. The hardness of hardened steel is very high, and the processing efficiency is low.
2. Many tools are difficult to withstand intermittent machining of high hardness materials.
3. It is difficult to achieve the mirror surface quality, and many require grinding to achieve.
When machining hardened steel we often encounter the following problems:
▶ Hardened steel has high hardness (above HRC50), high strength and almost no plasticity.
▶ The resistance is very large when cutting, which is easy to cause tool chipping.
▶ The thermal conductivity is poor, which will accumulate cutting heat. The cutting heat is more than 50% higher than that when cutting ordinary steel.
▶ It is not easy to produce cutting tumor, and it is easy to obtain lower surface roughness during cutting. In the case of intermittent machining, the blade is required to take into account both hardness and toughness.
The most special feature of PCBN tool is that it has very good red hardness. When cutting hardened steel, a lot of heat will be generated at the tip of the tool.
On the one hand, the workpiece material will be softened, and on the other hand, because the PCBN tool has good red hardness, the increase in temperature will make the hardness gap between the PCBN tool and the workpiece larger, and the cutting performance will be better. At the same time reduce PCBN tool wear.
Classification of hardened steel
Hardened steel is a steel with a martensitic structure formed by quenching and a hardness of 50 or more.
The main categories are:
● Carburized steel: the carbon content is 0.1%~0.25%. Parts are generally used after carburizing, quenching, and low temperature tempering.
Mainly used in: parts with high surface hardness and wear resistance, but the core of the workpiece has good toughness
For example, gearbox gears, piston pins, and some measuring tools of automobile tractors.
Because of the low internal carbon content, few carbides are formed after quenching.
The tool will suffer a lot of chemical wear when cutting hardened carburized steel, so it is necessary to select PCBN tools with better heat resistance and chemical wear resistance for processing.
● Tool steel and bearing steel
The carbon content is relatively high, generally above 6%. There are many carbides formed after quenching.
The abrasive wear on the tool during cutting is very serious.
When choosing a PCBN tool, not only chemical wear resistance, but also particle wear resistance should be considered.
PCBN tool material performance characteristics
1. High hardness and wear resistance
HV3000~5000 is 3~5 times that of cemented carbide, and has extremely high wear resistance.
2. High heat resistance
1000~1500℃. The heat resistance is twice as high as that of diamond, and it is the highest heat resistance among the current tool materials. Therefore, it can be used for high-speed cutting of superalloys and hardened steels.
3. Good red hardness
At 800 °C, the hardness is also higher than that of ceramic and cemented carbide tools at room temperature.
4. High chemical stability
It has good anti-oxidation properties and will not oxidize at 1000 °C. There is no chemical reaction with iron-based materials at 1200~1300 ° C.
Therefore, it is very suitable for processing iron-based metal materials and their alloys.
5. Low friction coefficient
0.1~0.3. It is much smaller than 0.4~0.6 of cemented carbide.
When cutting, the cutting force and cutting heat can be reduced, and the built-up edge is not easily generated.
▲ When the CBN content increases, it is generally dominated by metal binders. Such as aluminum, tungsten, so the mechanical wear resistance, impact resistance is good.
▲ When the CBN content is reduced, it is generally dominated by ceramic binders. Such as nitrogen aluminum titanium, titanium carbide, so chemical wear resistance, red hardness is good.
▲ The smaller the particle size of CBN, the better the surface quality and the better edge toughness.
▲ The larger the particle size, the better the impact resistance but the worse the surface quality.
PCBN tools come in several different forms:
Solder Tab: made of composite sheet. The cutting edge is of good quality and the machining precision is high. Suitable for finishing hardened steel, cast iron and other iron-based metal materials. The structure design of the cutter is also more flexible.
Integral: better impact resistance, which can fill the occasions of semi-finishing and rough-finishing that cannot be used by solder-tab PCBN tools.
PCBN is very suitable for machining hardened steel, powder metallurgy, cast iron, superalloy and other materials.
When machining hardened steel, it can replace the grinding wheel to realize the replacement of grinding by turning and milling. Efficiency is 4 to 10 times the original.
More convenient when changing tools. It does not occupy space and has high processing efficiency. Compared with traditional carbide coated tools, the processing life of PCBN tools can be increased several times to dozens of times.
Cooling is not suitable for PCBN tool processing, so it will be more environmentally friendly and less expensive.
And the energy consumption during use is low, which is only about 20% of that during grinding.
Coated CBN inserts and CBN inserts with grooves
The purpose of development of coated PCBN inserts:
Combining high performance coatings with PCBN inserts provides thermal insulation, reduces flank wear and reduces chemical reactions.
Inhibit crater wear on rake face, inhibit edge chipping, increase edge toughness, and prevent micro-chipping of PCBN tools.
CBN inserts with grooves:
Cut the chips so that the chips are not entangled. Protects the workpiece surface and reduces machining interruptions due to chip jams.
Control the outflow direction of chips and maintain the accuracy of the machined surface.
Reduce cutting resistance and extend tool life.
Case study
Raceway Bearing Machining
Reducer gear machining
