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The new PCBN grades, which are continuously developed according to actual processing requirements, and the deepening of the understanding of the mechanism and performance of PCBN materials, are driving the application range of PCBN tools. Today, PCBN tools have been successfully used for turning, drilling and milling of hardened steel, cast iron, superalloys and high-hard surface layers. Development status of new grades and application technologies of PCBN inserts
In recent years, the newly developed PCBN grade CBN grain content has formed a relatively complete product grade series from low (50% to 60%) to high (80% or higher), based on the cutting of different CBN content. Technology has also made remarkable progress. In general, PCBN insert grades with higher CBN content (more than 80%) are used to process powder alloy (P/M) materials and cast iron; PCBN insert grades with lower CBN content are more suitable for continuous cutting of hardened steel. In hard machining, low-level PCBN grades are generally superior to high-content PCBN grades in tool size retention and machined surface finish. The newly developed KBN510 and KBN525 PCBN inserts from Kyocera Industrial Ceramics belong to the lower CBN grade and are suitable for the cutting of hardened steel. The characteristics of these two grades are that the CBN grains in the material are uniform in size and evenly distributed, which improves the toughness of the insert and is more resistant to impact and interrupted cutting. Another new PCBN grade developed by the company has a high CBN content and is mainly suitable for the cutting of cast iron.
Although standard PCBN inserts are familiar black uncoated blades, the use of various coated PCBN inserts is increasing. In the cutting process, the PCBN blade coating helps the operator to monitor the wear of the tool tip, which can improve the tool life and increase the cutting speed when processing certain workpiece materials, especially in the hard cutting process, TiAlN coating can Effectively extend the life of PCBN blades.
The PCBN blade coating mainly uses the PVD process because the high temperature of the CVD coating process easily causes the PCBN composite sheet to peel off from the substrate, and also affects the quality of the blade. TiN coatings improve the lubricity, heat dissipation and chip fluency of PCBN inserts. In addition, the gold-tone TiN coating makes it easy for the operator to identify the worn cutting edge, so that it can be handled with care to avoid deterioration of the machining process, so that more cutting edges can be used for machining, saving tool costs.
Another technological advancement of PCBN tools is that the overall PCBN inserts are gradually replacing the carbide inserts that weld PCBN tips in certain processing areas. Although the overall PCBN inserts are more expensive than welded PCBN inserts, they still have a good price/performance ratio due to the longer blade life and the higher number of workpieces per blade. The use of integral PCBN inserts requires mastering of multiple cutting edges (4-blade, 6-blade or 8-blade) machining techniques to maximize the performance benefits of the overall PCBN insert by reducing the cost per cutting.
Several integral PCBN insert grades developed by Seco-Carboloy (including the general grade CBN200 for machining grey cast iron) enable roughing of hardened steel and hardened powdered alloy (P/M) materials. These integral PCBN inserts feature locating pin holes for easy positioning of the insert on the tool holder or cutter body.
With the development of PCBN tool cutting technology, the optimized design of PCBN blade geometry has begun to play an increasingly important role in improving the cutting efficiency of PCBN tools. The hardness of the PCBN composite sheet is extremely high, making the formation of the PCBN tip geometry quite difficult. Several PCBN insert grades developed by Kyocera form an optimized BB chipbreaker on a cemented carbide substrate that supports brazed PCBN composites. This chipbreaker allows for better crimping and cutting of chips. The edge can improve the chip control ability of the tool. When processing certain workpiece materials (such as surface hardened materials with a gradient of hardness, the material will gradually become soft or become sticky as the cutting progresses), which is beneficial to improve the workpiece. Surface finish. The BB chipbreaker has three different groove types, and the groove type depends on the size of the PCBN composite on the blade tip.
Hard turning is a major application area for PCBN tools in the future. Hard turning usually refers to turning that has a workpiece hardness higher than HRC45. In the automotive industry, the application of hard turning finishing is increasing and is expected to become an alternative to grinding. Hard turning can be used as the final finishing step for many workpieces. Although for some workpieces with high precision requirements (such as bearing parts), secondary finishing is required after hard turning, but if grinding is used, secondary finishing is also required. In contrast, lathes operate at a lower cost than grinders, and the cost of hard turning tools is much lower than grinding, resulting in better processing economics. Engineers are increasingly considering the use of PCBN tools for single-point machining of hardened parts. However, grinding still has its place, although single-point cutting can achieve good micro-smallness, but it still leaves a knife mark on the surface of the workpiece.
The rigidity of process systems such as machine tools, fixtures, and tools is critical to the success of hard turning operations. In addition, details such as tool overhang, tip overhang, and workpiece clamping methods can have a large impact on the machining results. Another special problem with hard turning is the chatter, which is usually caused by the resonance of the process system and must be removed.
In the automotive industry, PCBN tools are used more and more in milling, such as face milling of cast iron gearboxes. In addition, in the mold manufacturing industry, PCBN milling has also been widely used. The PCBN tool is used to finish the roughened and hardened mold, and a very good surface finish is obtained, and the tool life is also significantly improved. Since most of the cutting allowance is cut in roughing before the hardening of the mold, the maximum depth of cut for semi-finishing is 1 to 1.5 mm, and the amount of depth of cut for finishing is smaller. The minimum workpiece hardness for PCBN milling is approximately HRC 54 to 56. In general, the harder the workpiece material, the longer the life of the PCBN tool.
Whether using PCBN inserts or carbide inserts, high-speed cutting can reduce or even eliminate the original finishing process. PCBN milling requires high rigidity and clamping reliability of the machine tool to ensure that machining vibration and chattering are minimized. In order to ensure reliable clamping of the tool, it is recommended to use HSK chucks or other tool systems that can simultaneously clamp the tool to the end face and the taper surface of the spindle. In order to reduce machining vibration and chatter, it is also necessary to ensure that the clamping of the workpiece is firm and reliable. In addition, the integral PCBN insert with locating holes also improves the positioning accuracy and reliability of the insert on the body. New PCBN tool introduction The following are some of the more representative PCBN tool new products recently introduced by some tool manufacturers: (1) Emuge Corp. CBN end mill
It is said that the end mill can be used for rough milling with a service life up to 50 times that of cemented carbide milling cutters. It can process hardened steel, cast steel, nickel-based and cobalt-based alloys with hardness up to HRC66. Milling cutter types include ball end mills, toroidal end mills and flat end mills with a blade size of 4 to 12 mm. (2) Sumitomo Electric Carbide's BN700 grade PCBN blade
BN700 is a high CBN content insert grade with extremely high cutting edge hardness and excellent wear resistance. It is mainly used for processing cast iron and powder metallurgy alloy materials. The insert uses a multi-tip structure with multiple cutting edges for easy indexing. The precision grinding inserts are extremely dimensionally accurate, and the user can select the blade with a scraping edge, a passivation edge or a blade that is not prepared for the cutting edge. 3) Valenite Turning Tool System from Valenite Inc.
The tooling system combines PCBN insert material with advanced toolholder technology for high performance roughing and finishing of hardened steel (HRC45-62). The PCBN insert features a multi-tip structure and a VPC225 coating. The cutting edge combines a T-land and a slightly passivated preparation technique. This range of tools offers approximately 110 blade types, sizes and geometries. 4) Two types of PCBN inserts from Iscar Metals
These two PCBN inserts are used to machine hardened steel and cast iron, respectively. Among them, IB55 grade is very suitable for semi-finishing and finishing of hardened steel (including under interrupted cutting conditions); IB85 grade is used for processing gray cast iron, cast iron and heat resistant alloy with hardness higher than HRC45. Both inserts feature a single-tip construction with cutting edges and reverse passivation. (5) Kennedy Inc.'s coated PCBN blade
It is said that when processing hardened materials, the coated PCBN inserts can be doubled in processing life compared to uncoated inserts. The KB9640 grade is a high-content PCBN insert with CVD Al2O3 for roughing and semi-finishing of hardened steel and cast iron. The inserts are round, square, triangular and 80°, 55° and 35° diamonds. Blades, etc. The KB5625 grade is made of PVD TiAlN coating for the finishing of hardened steel, suitable for medium to heavy duty interrupted cutting. (6) WCB30, 50 grade PCBN insert from Walter USA This insert is a non-coated PCBN grade for turning and milling of cast iron and hard materials. Car blades use negative geometry (ANSI, ISO C, D, S, T and W) or positive geometry (C, D and T). Milling inserts include CPR button inserts for profile milling, ball end inserts for finishing and octagonal inserts with a single cutting edge. (7) ExoCarb Max PCBN end mill from OSG Tap & Die Inc.
This ball end mill is mainly used for finishing milling of hardened steel (HRC 50 ~ 65). The blade's unique arc radius design increases blade rigidity and tool life and provides a high surface finish for the workpiece, reducing subsequent finishing operations. The milling cutter has a radius tolerance of 5 μm and its nose shape allows the cutter to be cut with the center of the ball. OSG also manufactures tool nose radius PCBN end mills in single, double and 4-slot configurations. (8) Seco-Carboloy's Secomax PCBN100 blade
The insert is said to be the first integral PCBN grade for hardened steel finishing and the first use of a locating pin hole structure. The blade is made of fine-grained, low-content (50%) PCBN, suitable for light continuous cutting or medium-sized interrupted cutting of hardened steel, hard surface alloy and sintered steel, and can be inserted and milled by the full cutting edge length of the insert. This blade can be used with standard M, P and D tool holders. For a variety of cutting operations (such as finishing of hardened steel), W-type and T-shaped insert shapes are used, and the cutting edge adopts standard preparation method and scraping edge type. (9) PCBN grade series of Mitsubishi Materials USA Corp.
The range includes a wide range of coated and uncoated PCBN insert grades for high speed machining of cast iron, hardened steel and powder metallurgy materials. For example, MB8025 grade inserts for continuous or interrupted cutting of hardened steel are manufactured using an advanced sintering process that improves the chip's resistance to chipping and wear. The PCBN tip is welded directly to the insert base, improving bonding. strength. This range includes a variety of different blade shapes and cutting edge preparation methods (including scraping edge). (10) CBN brand series of Kyocera Industrial Ceramics
KBN10B grades are used for the finishing of hard and heat-treated steels with a depth of cut of 0.5 mm; KBN25B grades are used for the processing of hardened steels with submicron CBN grains and binders that improve toughness and chemical stability; KBN65B The grade is used for high-speed cutting of cast iron, which can significantly improve tool life; KBN900 grade is a whole PCBN insert with PVD coating for roughing of hardened materials and processing of high-speed cast iron. The company will also introduce new brands KBN510 and KBN525 in the near future.
Development and application of new grades of PCBN inserts
Since the first time that material scientists have synthesized polycrystalline cubic boron nitride (PCBN) using a synthetic synthetic diamond-like process, the application of PCBN tools in machining has become more widespread. The hardness of PCBN materials is second only to diamond, but unlike diamond tools, PCBN tools can be used to cut iron alloys, even hardened steels with hardness higher than HRC60.