Solutions for cutting difficult-to-machine materials
-PCD and CBN tools
Polycrystalline diamond (PCD) tools and cubic boron nitride (CBN) tools provide solutions to the cutting problems of difficult-to-machine materials. The machining challenges of these two advanced concept tools in cutting tool materials are well known. Different designs of CBN tools are used for continuous or intermittent cutting of hardened ferrous metals, as well as for cutting welded metals and composite metals. PCD tools are widely used for milling non-ferrous metals, composite materials, plastics and super alloys that are extremely difficult to machine.
Choosing the right tool material depends on the comprehensive consideration of the following factors: the hardness of the metal or the type of material; the nature of the cutting process (continuous cutting, light load or heavy load interrupted cutting) and the processing technology used (such as single point Turning or milling). Some other machining processes (such as drilling, reaming and cutting) can also benefit from the correct application of tool technology.
The PCD composite sheet is produced by sintering diamond particles with a metal-based binder under high temperature and high pressure. German DiaCut cuts the PCD tip by laser to form a 3D chip breaker and welds it to a cemented carbide or steel substrate to form a PCD tool. This tool is used for high-speed processing of non-ferrous metals (such as aluminum) and highly abrasive synthetic materials and plastics. Especially effective, it solves the most annoying chip breaking problem when customers process this kind of material.
DiaCut PCD insert with three-dimensional chip breaker ↑
Sandvik Coromant has set the goal of continuing to develop CBN and metal cutting tools with diamond tips, thanks to the acquisition of Diamond Innovations (DI) and its parent company Sandvik Tooling Group (Sandvik Tooling Group). ). Rick Askin, President of Sandvik America, explained that the acquisition is to consider combining DI's expertise in the CBN and PCD fields with Sandvik Coromant's expertise and research results in the field of cemented carbide tools and material interfaces. Get up and develop new tools
DI company is a well-known pioneer company that develops synthetic diamonds for industrial use. Synthetic diamond is the basic material for the production of PCD and CBN products. In addition to metal cutting tools, synthetic diamonds can also be used in grinding, rock drilling, metal drawing dies, polishing and other applications that require superhard materials.
Askin explained that from a cutting point of view, about 95% of tools that use PCD or CBN tips as cutting edges are based on cemented carbide. There are many properties that affect the performance of the tool, on the one hand, the performance of PCD or CBN, on the other hand, the performance of cemented carbide, and the performance of the interface between PCD and cemented carbide. This gives us a huge opportunity to develop diamond tools using our expertise in cemented carbide, diamond technology, and controlling the interface between diamond and cemented carbide.
Sandvik Coromant’s material grade development expert Doug Evans said, “With the rapid development of the aviation industry and the energy industry, the requirements for materials have changed the way we develop, innovate and manage more than 25,000 products. The ability to control the process (from the production of polycrystalline diamond and CBN materials to the processing of the final product) allows us to provide users with products with truly improved performance."
DI's products cover a wide range of applications, including:
① Boron nitride CBN used for grinding hardened tool steel, die steel, alloy steel and nickel-based and cobalt-based super alloys;
②BZN composite blade blanks and blades for processing ferrous metals (including pearlitic cast iron, inconel, hardened steel, powder metal, surface hardened alloy and super alloy);
③Used for finishing aluminum, plastics, precious metals, green ceramics, graphite and graphite composite materials, as well as for intermittent cutting of ceramics, rough machining of metal matrix composite cemented carbide (MMC), and cutting difficult-to-machine materials (such as glass fiber, MMC) And wood laminate materials) of various grades of Compax diamond blanks (PCD).
As the TiroWave series PCD and CVD tools developed by CIMtek Group have introduced a three-dimensional chip breaker and a neat and straight cutting edge, the use of lasers to process tools with diamond tips has gained a new use. Brian Nowicki, a partner of CIMtek Group, said that using laser cutting, one of four chip breakers can be processed on the blade. This series of chip breakers are suitable for machining from finishing to heavy roughing. By optimizing the chip breaker, the chips can be divided into 6-9 kinds of chip shapes that are usually obtained when processing steel, and even when processing the most difficult aluminum, controllable fine chips can be obtained.
It is said that when processing aluminum alloy, the life of TiroWave series PCD tools can be increased by 10 times compared with conventional tools, and the tools are very suitable for processing magnesium alloys, all ferrous metals, composite materials, reinforced plastics and abrasive binders. material.
Using seven-axis laser processing technology, Tiro Tool in Innsbruck, Austria can also produce CVD thick film diamond tools. CVD thick film diamond can be cut to shape and welded on the tip like a PCD tip. The difference is that the diamond purity of CVD thick film is 99.9%, while the diamond purity of PCD is 90%. The thickness of CVD diamond film can reach 1-2mm, and it is a whole piece of material, which can be made into the required tool shape. It is said that the hardness of this new CVD diamond material is almost 50% higher than that of PCD, so it can only be processed with Tiro's laser technology. Processing verification results in Europe show that the life of CVD thick film diamond tools can be increased by 7 times compared with PCD tools. The tool was introduced to the United States at the IMTS exhibition, and the scope of application is turning, drilling, reaming and countersinking tools, including those required for the aerospace industry to process composite materials.
Due to the use of laser processing, TiroWave tools can obtain a more regular and neat surface. Whether used for roughing or finishing, they can obtain a higher surface finish and prevent the cutting material from sticking to the cutting edge. TiroWave can provide ANSI and ISO standard tools, including 80°, 55°, 35° blades, square blades, triangle blades and round blades. This technology is also suitable for drills, end mills and indexable face milling cutters.
The hard materials identified by Iscar include hardened steel and chilled cast iron with a hardness range of HRC55-68. These materials are typical materials commonly used in the production of bearings and processing molds in the automotive industry.
The difficulty of machining hard materials varies, depending on the hardness and the depth of the hardened layer (when machining surface hardened materials), and the microstructure of the workpiece material. Successful machining comes from the good combination of the rigidity and geometry of the workpiece with the rigidity of the machine tool and its vibration damping characteristics.
Iscar's advanced tool materials cover a variety of processing areas, such as the use of CBN, ceramics and sub-micron particle matrix (usually coated with special coatings) to perform various intermittent cutting (milling, cutting and drilling) of hard materials ) And continuous cutting (turning and threading). The use of various tool geometries and chipbreakers has become an inevitable way to improve the quality of the machined surface, extend the life of the tool and increase productivity.
Iscar believes that, based on processing experience, if the hardness of ferrous metal materials is in the range of HRC55-68, and the depth of the hardened layer is greater than the depth of the material to be removed, CBN tools are the best choice.
Iscar can provide 5 CBN grades to meet a wide range of processing needs, including:
① Grades with high CBN content (IB90 and IB85): Recommended for high-speed cutting of cast iron and interrupted cutting (or roughing) of hardened steel. There is a balance between tool hardness and wear rate (toughness and ability to withstand the impact load caused by interrupted cutting).
② Grades with low CBN content (IB55 and IB50): more suitable for semi-finishing and finishing. The shape of the blade edge determines the surface quality that can be achieved within the limits of the rigidity of the machine tool and the workpiece. For example, the blade can be designed to weld the CBN tip on the ISO standard blade. The blade can be divided into triangle, diamond, square and round. It can also use Iscar's GRIP blade.
Due to many factors, both PCD and CBN tools are more expensive. This fact requires careful analysis when considering some machining options. When designing unattended high-volume processing (especially in the automotive industry that requires long tool life and short downtime), PCD and CBN tools are usually good choices.
Chris Wills, a product expert at Mitsubishi Materials USA, explained that the "virtual tool report" developed by the company can be used to evaluate the cost efficiency of any blade (not just CBN blades). It is mainly used to help users evaluate the value of any kind of blade, and is especially useful when evaluating the value of CBN blades in reducing actual processing costs (it is more important than the initial cost of the blade).
Wills said the company is comparing and evaluating the machining cost of CBN tools compared to ceramic or cemented carbide tools. Processing ranges from high-temperature alloys to high-hard metals, including continuous and (or) interrupted cutting of cast iron parts and an increasing number of powder metallurgy parts in the automotive industry. For the processing of steel parts, new chip breakers are required, especially under automated processing conditions (such as bar conveying devices and gantry feeding systems), surface defects caused by chips may damage the quality of parts .
Sumitomo Electric Cemented Carbide has expanded its BNC series of PCBN tool grades for high-speed machining of alloy steel with a hardness higher than HRC45, as well as for machining cast iron and special materials. The company's four ceramic coating grades use three cutting edge treatments.
Rich Maton of Sumitomo Corporation pointed out that although CBN is a relatively mature tool material, coating, cutting edge preparation and chip breaker are all very important for the processing and application of PCBN tools. Typical turning processing of auto parts includes axles, rings, pinions, various drive shafts, bearing caps and similar parts. Other processing objects include cylinder blocks, cylinder heads and molds.
BNC300 is a new brand launched by Sumitomo, which combines PCBN substrate with golden TiAlN ceramic coating, which can extend tool life when turning hardened steel continuously and intermittently. In order to increase strength, all tool tips are individually welded. Maton said that the preparation of the cutting edge is particularly critical for the processing of PCBN tools. We have added three different cutting edge preparation methods (light, standard, and heavy), depending on the selected BNC tool series.
The coverage of the BNC series of tools ranges from the high wear-resistant grade BNC100 for finishing and light interrupted cutting to the high-resistance chipping grade BNC300 for finishing (which can be used for both continuous cutting and interrupted cutting). BNC200 grade is recommended for medium-speed machining of carburized induction hardened bearing steel; while BNC160 grade is developed for special processing requiring low surface roughness (0.406µm). Sumitomo has also introduced a PCD tool with excellent wear resistance and toughness-Sumidia DA 1000. This grade uses NF type composite sheet. Compared with the previous PCD composite sheet, its cutting length is the same, but the thickness is only half. DA 1000 will only provide economical tool tip (PCD composite sheet is thinner). As an economical tool, it can be used for processing non-ferrous parts in the medical, aviation, agricultural and automotive industries.
The ValEDGE hard material turning system provided by Valenite for processing steel and alloys with a hardness range of HRC45-62 includes a full range of CBN and ceramic inserts. The company's application engineer Darrell Johnson recommends specific cutting edge preparation based on processing conditions. "Because of the different processing conditions, it is necessary to perform different cutting edge preparation tests on tools with the same brand and parameters to observe whether it can increase tool life, reduce crescent formation and even improve chip breaking performance (although it is possible to improve chip breaking performance Little sex)". The CBN tip welding tools provided by the company have slightly passivated the cutting edge. Among them, there are 0.13mm×15°T-shaped inserts for light-load cutting and reduced cutting force, and 0.13mm for conventional machining. ×25° blade.
According to Jason Lindsey of Lach Diamond, the processing of composite materials with PCD tools has become the fastest-growing and most challenging processing technology just like processing aluminum alloys. Such as carbon fiber, graphite, green ceramics, glass fiber, and more difficult to process materials (such as Kevlar fiber), all pose challenges to precision processing.
Lach provides 5 types of peripheral milling end mills with patented designs for the burr-free cutting of composite materials. The company’s Z-type end mill is a corncob milling cutter used for peripheral rough milling. It is characterized by the distribution of all PCD tips, and its cutting angle changes throughout the entire process to the end tooth. This tool is suitable for plunge milling and non-plunging milling.
Lach's diamond composite chip integral face milling cutter and right-angle milling cutter are used for face milling of aluminum alloy. The cutter can be installed on the machining center without excessive adjustment. The PCD diamond tip is welded to the steel tool body. There are internal cooling holes between each tooth. The outer circle of the tooth is on the same cutting plane after fine grinding. One of the key elements for processing with PCD tools It has a sharp cutting edge. According to Robert Sullivan, material manager of Ingersoll Tool Company, the basic method to achieve this is to use electrical discharge machining (EDM), brazing and grinding. PCD tools are very effective for mass processing of aluminum alloy parts (such as automobile engine gaskets or transmission case covers). This type of processing is mainly concerned with the economics of processing, so it is necessary to consider tool change and related downtime. Ingersoll face milling cutters have a diameter range of 76-381mm and are used for machining engine cylinder heads, gearbox bodies, and machining graphite electrodes for electrical discharge machining.
Walter (Walter) American company produces both PCD tools and CBN tools. Matthias Goetze of the company said that the advantages of CBN tools in hard turning include longer tool life, lower unit cost, and reduced downtime. About 90% of the company's PCD tools are non-standard special tools, and about 80% of CBN tools are standard tools.
Walter has developed chipbreakers for PCD tools for the automotive industry (especially for the processing of low-silicon aluminum alloy workpieces) to better control chips when processing automotive parts (such as ABS housing) and aerospace parts. The company also offers two different PCD tools, one for processing aluminum alloys with silicon content less than 12%, and the other for processing aluminum alloys with silicon content greater than 12%. In 2008, Walter also established a tool resharpening and refurbishment service center at the Waukesha plant in the United States to support its users' PCD tool tip replacement and resharpening.
Emuge offers an extended series of superhard end mills with PCD and CBN cutting edges. It is said that the tool life of this end mill is more than 50 times longer than that of traditional cemented carbide end mills when processing various materials. The machinable materials include highly abrasive non-ferrous materials, such as graphite, high silicon aluminum alloy, and fiber. Reinforced synthetic materials, copper alloys, etc. The characteristic of this tool is the use of internal cooling design to remove dust and chips. The PCD and CBN end mills of Emok adopt the commonly used ball head, torus and flat head designs, with sizes ranging from 4mm to 12mm.
Seco Tool Company believes that milling is a processing method with harsh processing conditions, often involving a lot of interrupted cutting. Therefore, the PCBN grades for milling must be reasonably selected. Typical machining includes milling gray cast iron (such as automobile engine cylinder blocks, cylinder heads, boxes, etc.) and certain tool steels. Seco’s principle for choosing PCBN milling tools is: The main properties of PCBN inserts—toughness, wear resistance and thermal hardness—depend on the grain size, CBN content and bonding agent. The main difference between turning inserts and milling inserts is the grain size. In order to improve toughness, PCBN inserts used for milling should generally have a smaller grain size. At the same time, the grain size, CBN content and binder must be balanced to maintain good wear resistance and thermal hardness of the blade.
Seco Tool Company believes that milling is a processing method with harsh processing conditions, often involving a lot of interrupted cutting. Therefore, the PCBN grades for milling must be reasonably selected. Typical machining includes milling gray cast iron (such as automobile engine cylinder blocks, cylinder heads, boxes, etc.) and certain tool steels. Seco’s principle for choosing PCBN milling tools is: The main properties of PCBN inserts—toughness, wear resistance and thermal hardness—depend on the grain size, CBN content and bonding agent. The main difference between turning inserts and milling inserts is the grain size. In order to improve toughness, PCBN inserts used for milling should generally have a smaller grain size. At the same time, the grain size, CBN content and binder must be balanced to maintain good wear resistance and thermal hardness of the blade.
Seco's milling inserts can be used in many face milling cutters and shoulder milling cutters specially designed for PCBN. These negative angle milling cutters use integral PCBN inserts with a diameter of 63.5-203mm. Square and round inserts are used for face milling cutters, while triangular inserts are used for shoulder milling cutters. For those machining where the tool pressure must be kept low and negative-angle inserts cannot be used, Seco also has positive-angle milling cutters with integral or full-face positive-angle inserts. Only one side of these blades can be used. By using nearly integral inserts, the number of cutting edges per insert can be maximized. When the integral PCBN round insert is used for face milling finishing, at least 15 cutting edges can be used for cutting on each side.
In square shoulder or similar square shoulder milling, integral triangular or square inserts can be used, and the available cutting edges for each insert are 6 and 8 respectively. Three basic requirements should be followed:
① Dry cutting is always used when PCBN blades are used for milling, because PCBN is a brittle material. When the blades are cut in and out, the use of coolant will cause thermal cracks in PCBN blades.
② Always use conventional milling methods, so that when the blade cuts in, the impact load on the blade can be reduced, thereby minimizing the risk of cutting edge chipping.
③ Compared with turning, the cutting speed can be increased by 10%-50% to compensate for the effect of interrupted cutting.
