Superhard tool and its application in hard turning
1) many of our customers struggle with what materials to choose for the battery Spring, which is a good choice for cold plate, manganese steel, brass, and phosphor bronze. Which of these materials to choose depends on the battery`s plastic shell structure and the value of the product and the environment in which it is used. Like this common battery sheet is generally used cold nickel plating on the line, nickel plating after a good effect, cost is also very low. If your product uses the environment to be very humid that also may consider does with the brass material, this will cost many times high. (2) the ordinary cold plate nickel-plated Daxin hardware spring can pass through salt spray for 72 hours without rusting after being sealed with oil. Such spring-loaded battery springs are usually made of manganese steel (65M) or phosphor bronze. Some customers may think that stainless steel will be more elastic, but you don`t take into account that stainless steel is tin-free, meaning you can`t solder it or it`s difficult to solder it. In fact, the material of manganese steel after heat treatment elastic and stainless steel is similar. For Phosphor bronze material is also commonly used in this type of products, elastic or good, not rust, low resistance, easy to weld, but the cost of phosphor bronze is higher. Battery spring, divided into positive battery spring, negative battery spring, positive and negative battery spring Nantong Safe Yawl Import &Export Co.,Ltd , https://www.ntsyspring.com
Superhard tool and its selection
The materials used in superhard tools and their tool structure and geometric parameters are the basic elements for hard turning. Therefore, how to choose superhard tool materials and design reasonable tool structure and geometric parameters is very important for stable hard turning.
1, super hard tool material and its selection
Coated cemented carbide
Coating one or more layers of TiN, TiCN, TiAlN and Al3O2 with good wear resistance on a hard tough carbide tool. The thickness of the coating is 2~18μm. The coating usually has a specific ratio of the tool base and the workpiece material. The much lower heat transfer coefficient weakens the thermal action of the tool base; on the other hand, it can effectively improve the friction and adhesion of the cutting process and reduce the generation of cutting heat.
The coating can be divided into physical vapor deposition (PVD) and chemical vapor deposition (CVD) according to the production method. The PVD coating (2~6μm) mainly includes TiN, TiCN, TiAlN, etc., and its composition is continuously increasing, such as TiZrN. The highest pressures of TiN and TiC coatings can reach 3580MPa and 3775MPa respectively. The TiAlN coating can not obtain accurate compressive stress values ​​due to the lack of reliable elastic modulus data. The results of high-speed cutting experiments show that TiAlN has the best performance. Figure 1 shows the hardness of the three coatings as a function of temperature. The hardness is highest at room temperature. When the temperature exceeds [Y; the hardness of the TiAlN coating is higher than that of the TiCN and TiN coatings. Figure 2 shows the tool life of the Ni-based superalloy Inconel178 with two cutting speeds v1=193.5m/min and v2=380m/min. The experimental results show that the cutting performance of TiCN and TiAlN coatings is significantly better than that of TiN coating.
Although PVD coatings show many advantages, some coatings such as Al2O3 and diamond tend to employ CVD coating technology. Al2O3 is a highly heat and oxidation resistant coating that isolates the knife from the heat generated by the cutting. Through CVD coating technology, it is also possible to combine the advantages of various coatings to achieve the best cutting results and meet the needs of cutting. E.g. TiN has low friction characteristics, which can reduce the loss of coating structure. TiCN can reduce the wear of the flank, TiC coating has high hardness, and Al2O3 coating has excellent heat insulation effect.
Compared with cemented carbide tools, coated carbide tools have greatly improved in strength, hardness and wear resistance. Turning workpieces with hardness of HRC45~55, low-cost coated carbide can achieve high-speed turning. In recent years, some manufacturers have applied methods such as improved coating materials to greatly improve the performance of coated tools. Some manufacturers in the United States and Japan use Swiss AlTiN coating materials and new coating patented technology to produce coated blades with hardness up to HV4500~4900, which can cut die steel with hardness HRC47~58 at 498.56m/min. When the turning temperature is as high as 1500~1600°C, the hardness is not reduced and it is not oxidized. The blade life is 4 times that of the general coated blade, and the cost is only 30%, and the adhesion is good.
Ceramic material
With the continuous improvement of its composition and pressing process, especially the advancement of nanotechnology, ceramic tool materials have made it possible to toughen ceramic tools. In the near future, ceramics may cause cutting after high-speed steel and hard alloy. The third revolution. Ceramic cutters have high hardness (HRA91~95), high strength (bending strength of 750~1000MPa), good wear resistance, good chemical stability, good anti-adhesion performance, low friction coefficient and low price. Not only that, ceramic tools also have a very high temperature hardness, the hardness reached HR80 at 1200 °C.
In normal cutting, the ceramic tool has extremely high durability and can be cut 2~5 times faster than cemented carbide. It is especially suitable for high hardness material processing, finishing and high speed machining. It can cut all kinds of hardened steel and hardened cast iron with hardness up to HRC65. Wait. Commonly used are: alumina-based ceramics, silicon nitride-based ceramics, cermets and whisker toughened ceramics.
Alumina-based ceramic tools have higher red hardness than hard alloys. The cutting edges generally do not undergo plastic deformation under high-speed cutting conditions, but their strength and toughness are very low. In order to improve their toughness and improve impact resistance, they are usually ZrO or a mixture of TiC and TiN is added, and another method is to add pure metal or silicon carbide whiskers. In addition to high red hardness, silicon nitride-based ceramics also have good toughness. Compared with alumina-based ceramics, it has the disadvantage of high temperature diffusion during processing of steel and aggravation of tool wear. Silicon nitride-based ceramics are mainly used. Intermittent turning of gray cast iron and milling of grey cast iron.
Cermet is a carbide-based material in which TiC is the main hard phase (0.5~2μm). They are combined by Co or Ti binder, which is a tool similar to cemented carbide, but it It has low affinity, good friction and good wear resistance. It can withstand higher cutting temperatures than conventional cemented carbides, but lacks the impact resistance of cemented carbide, toughness during strong cutting, and strength at low speed and high feed. In recent years, through a large number of research, improvement and adoption of new production processes, the flexural strength and toughness have been greatly improved, such as the new cermet NX2525 developed by Mitsubishi Metal Corporation of Japan and the cermet blade developed by Sweden Sandvik Company. The new CT series and coated cermet blade series have a grain structure diameter of less than 1μm, and the flexural strength and wear resistance are much higher than ordinary cermets, which greatly expands the application range.
Cubic boron nitride (CBN)
CBN hardness and wear resistance
Second only to diamond, it has excellent high temperature hardness. Compared with ceramics, its heat resistance and chemical stability are slightly worse, but impact strength and crush resistance are better. It is widely used in the machining of hardened steel (HRC ≥ 50), pearlitic gray cast iron, chilled cast iron and high temperature alloys, and its cutting speed can be increased by an order of magnitude compared with cemented carbide tools.
The composite polycrystalline cubic boron nitride (PCBN) with high CBN content has high hardness, good wear resistance, high compressive strength and good impact toughness. Its shortcomings are poor thermal stability and low chemical inertness. It is suitable for heat resistant alloys. Machining of cast iron and iron-based sintered metals. The PCBN tool has a low CBN particle content and uses ceramic as a binder. Its hardness is low, but it compensates for the poor thermal stability and low chemical inertness of the former material. It is suitable for the cutting of hardened steel.
When cutting grey cast iron and hardened steel, ceramic tools or CBN tools can be selected. For this purpose, cost-effective and processing quality analysis should be performed to determine which one to choose. Figure 3 shows the wear of the knives in the gray cast iron of Al2O3, Si3N4 and CBN tools. As shown in Figure 3, the cutting performance of PCBN tool materials is better than that of Al2O3 and Si3N4. However, in the dry cutting of hardened steel, the cost of Al2O3 ceramics is lower than that of PCBN materials. Ceramic knives have good thermochemical stability, but not as good as the toughness and hardness of PCBN tools. Ceramic tools are a good choice when the cutting hardness is below HRC60 and when the feed is small. PCBN tools are suitable for cutting workpieces with hardness higher than HRC60, especially for automated machining and high precision machining. In addition, the residual surface stress of the workpiece after cutting the PCBN tool is relatively stable compared to the ceramic tool under the same flank wear.
The use of PCBN tools for dry-cut hardened steel should also follow the following principle: Select a large depth of cut as far as possible under the rigidity of the machine tool, so that the heat generated in the cutting zone softens the metal in the front of the blade, which can effectively reduce the wear of the PCBN tool. In the case of small depth of cut, the PCBN tool should also be considered to have poor thermal conductivity, so that the heat in the cutting zone can not be diffused. The shearing zone can also produce a significant metal softening effect and reduce the wear of the cutting edge.
2, the blade structure and geometric parameters of the superhard tool
Proper determination of blade shape and geometry parameters is critical to maximizing tool cutting performance. In terms of tool strength, the blade tip strengths of various blade shapes are from high to low: circular, 100° diamond, square, 80° diamond, triangle, 55° diamond, 35° diamond. After the blade material is selected, the blade shape with the highest possible strength should be used. Hard turning inserts should also choose the largest possible tool nose arc radius, roughing with a circular and large tool nose arc radius, and the radius of the tool nose arc during finishing is about 0.8μm.
Hardened steel chips are red and soft ribbons, brittle, easy to break, non-bonded, hardened steel cutting surface quality, generally no built-up edge, but large cutting force, especially radial cutting force It is larger than the main cutting force, so the tool should adopt a negative rake angle (go ≥ -5 °) and a large relief angle (ao = 10 ° ~ 15 °). The lead angle depends on the rigidity of the machine. It is generally 45°~60° to reduce workpiece and tool flutter.
Superhard tool cutting parameters and requirements for process systems
1, the choice of cutting parameters
The higher the hardness of the workpiece material, the smaller the cutting speed should be. The suitable cutting speed range for hard turning precision machining using super-hard tools is 80-200 m/min, and the common range is 10-150 m/min. For high-hardness materials with large depth of cut or strong intermittent cutting, the cutting speed should be kept at 80-100 m. /min. In general, the depth of cut is between 0.1 and 0.3 mm.
For workpieces with low surface roughness, a small depth of cut can be selected, but it should not be too small and suitable. The feed rate can usually be selected between 0.05 and 0.25 mm/r, depending on the surface roughness value and productivity requirements. When the surface roughness Ra is 0.3 to 0.4 μm, hard turning with a superhard tool is much more economical than grinding.
2, the requirements of the process system
In addition to the selection of reasonable tools, hard turning with superhard tools has no special requirements for lathes or turning centers. If the lathe or turning center is rigid enough, the required precision and surface roughness can be obtained when machining soft workpieces. Can be used for hard cutting. In order to ensure smooth and continuous turning operations, the usual method is to use rigid clamping devices and medium rake angle cutters. If the workpiece can be positioned, supported and rotated under the action of cutting force, the existing equipment can be hard-turned with super-hard tools.
Application of superhard tools in hard turning
Hard turning with super-hard tools, this technology has gained enormous economic and social benefits after more than ten years of development and application. The following is an example of roll processing and other industries to illustrate the promotion and application of super-hard tools in production.
Roll processing industry
Many large-scale roller enterprises in China have used super-hard tools to carry out rough, rough and refined cars for various types of rolls such as chilled cast iron and hardened steel. All of them have achieved good benefits. 7 Average improvement of processing efficiency by 2 to 6 times, saving processing Working hours and electricity are 50% to 80%. For example, when the Wuhan Iron and Steel Company Rolling Mill has a chilled cast iron roll with a hardness of HS60-80, the cutting speed is increased by 3 times, and one roll per car saves electricity and labor costs by more than 400 yuan. The cost is nearly one hundred yuan and has achieved huge economic benefits. For example, when our school uses FD22 cermet cutter to turn the 86CrMoV7 hardened steel roll of HRC58~63 (Vc=60m/min, f=0.2mm/r, ap=0.8mm), the single-blade continuous cutting roll path reaches 15000m (tool tip) The maximum width of the flank wear band VBmax=0.2mm) satisfies the requirements of the car.
Industrial pump processing industry
At present, 70% to 80% of domestic pulp pump production plants have adopted superhard tools. The slurry pump is widely used in mining, electric power and other industries. It is an urgently needed product at home and abroad. Its sheath and shield are Cr15Mo3 high-hard iron castings of HRC63~67. In the past, it was difficult to turn this material because of various tools, so it was necessary to use a process of annealing, softening, and then quenching. After adopting the super-hard tool, the hardening process is successfully realized, and the two processes of annealing and quenching are eliminated, saving a lot of man-hours and electric power.
Automotive processing industry
In the machining of crankshafts, camshafts and drive shafts in the industries of automobiles and tractors, the processing of cutting tools, measuring tools and equipment maintenance often encounter the processing problems of hardened workpieces. For example, in a locomotive and vehicle factory in China, the inner ring of the bearing needs to be processed in the maintenance of the equipment. The hardness of the inner ring of the bearing (material GCr15 steel) is HRC60, the diameter of the inner ring is f285mm, and the grinding process is used, and the grinding allowance is uneven. It takes 2 hours to grind it; first, it uses an ultra-hard tool and it is processed into an inner ring in only 45 minutes.
Conclusion
After years of research and exploration, China has made great progress in superhard tools, but the application of superhard tools in production is still not extensive. The main reasons are as follows: Manufacturers and operators have insufficient understanding of the effect of hard turning with superhard tools. It is generally believed that hard materials can only be ground; the cost of tools is considered too high. The initial tool cost for hard turning is higher than that of ordinary carbide tools (such as PCBN is more than ten times more expensive than ordinary carbide), but the cost of each part is lower than that of grinding, and the benefits are lower than ordinary. Cemented carbide is much better; there is not enough research on the mechanism of superhard tool processing; the specification of superhard tool processing is not enough to guide production practice.
Therefore, in addition to in-depth study of the processing mechanism of super-hard tools, it is necessary to strengthen the training of super-hard tool processing knowledge, successful experience demonstration and strict operation specifications, so that this efficient and clean processing method is more applied to production practice.