Superhard material tool for machining
Superhard material tools currently mainly include single crystal diamond tools, polycrystalline diamond (PCD) tools, chemical vapor deposition (CVD) diamond tools, polycrystalline cubic boron nitride (PCBN) tools, etc. [1]. It is not only the ideal tool for processing high-hardness materials, but also replaces ordinary cutters with super-hard material tools for cutting, which can realize high-speed and high-efficiency machining of cast and forged blanks and/or finish roughing and finishing in one time. Superhard material tools are perfectly suited for high speed, precision and automated machining. Especially in the case of car grinding, milling and grinding, it is suitable for precision grinding of forming, profiling and sizing, and the grinding quality is significantly improved, and the grinding efficiency is increased several times or even dozens of times. It not only prevents defects such as surface burns, micro-cracks, gaps, and excessively deteriorated layers, but also improves work efficiency, reduces consumption and grinding costs. It has the advantages of high efficiency, low consumption, strong adaptability and short manufacturing cycle. At present, it has been widely used in machining of automobiles, motorcycles, aviation, mining, electronics, glass and other industries.
1. Application in machining 1.1 Application in turning machining 1.1.1 Turning steel parts When machining hardened steel, superhard material tools can be worn by car. Since the depth of cutting is ten times higher than grinding, the efficiency can be increased by more than 4 times, and the processing cost is reduced to 1/5.
The hardened steel with a PCBN tool with a hardness higher than 45HRC has the best effect, and the cutting speed is generally 80-120m/min. The cutting speed of high hardness workpieces should be low, such as workpieces with a hardness of 70HRC, and the cutting speed should be 60~80m/min. The cutting depth of the finishing car is 0.1-0.3mm, the feeding amount is 0.05-0.025mm/r, the surface roughness of the processing is Ra0.3-0.6μm, and the dimensional accuracy is 0.013mm. If a rigid CNC lathe is used, and the rigidity of the PCBN tool is good and the cutting edge is sharp, the surface roughness of the finished car can reach Ra0.3μm and the dimensional accuracy is 0.01mm, which can reach the level of CNC grinding machine processing.
A factory originally used the grinding process to process pinion gears, which can only process 100 pieces in one class; now it uses PCBN tool turning, the cutting parameters are: v=60～120mm/min, f≤0.12mm/r, ap≤0.1mm, one The class can process 400 pinions. In addition, the processing costs allocated to each gear have also decreased.
For example, using PCBN tool to process carburized and quenched 20CrMnTi automotive gearbox synchronizer fork (HRC58～62), cutting speed V=150mm/min, feed ƒ=0.1mm/r, ap=0.2～0.3mm, cutter The cutting stroke reached 9.58km [2]. After the car is milled, the efficiency is increased by more than 4 times, and the processing cost is reduced to 1/3 to 1/2 of the original grinding process.
Hembrug of the Netherlands uses PCBN tools for hardened EN21 bearing steel (HRC62) on the Mikroturn CNC series of super-precision lathes, Y.Kevin Chou and Chris J. Evans of the National Institute of Standards and Technology to process AISI M50 steel with Sumitomo BN series PCBN tools. (HRC 62 ~ 64), British DeBeers industrial diamond company MAFleming on the Delta Turn40 lathe using AMBORITE DBN45 tool turning EN31 bearing steel, etc., have achieved nano-cutting.
Examples of superhard material tooling steel parts are the use of the CK7820 CNC lathe of the Great Wall Machine Tool Plant to process the two-axis 20CrMnTiHA3 multi-slot spline cutting groove (HRc58-63) in the heavy-duty vehicle transmission, and the processing of mining machinery using the 1A616 machine tool. No. Φ48h6 drive shaft (HRc42～45)[3], using the PCBN tool to accurately turn GCr15 hardened bearing steel workpieces (30HRc, 40HRc, 50HRc, 60HRc and 64HRc) on the CA6140 lathe with stepless speed change.
Specially ground PCBN tools are used on ultra-precision lathes with a cutting depth of 15 to 20 μm and a feed rate of 0.608 μm/r. The surface finish of the machined surface can reach Rmax = 0.0254 μm. Cutting stainless steel on a general precision CNC lathe can achieve surface roughness within Rmax = 0.2 μm.
1.1.2 When turning hard iron for turning cast iron parts, as long as the hardness reaches the medium hardness level (HRc 45), the tool with super hard material will achieve good processing results, which is very suitable for high-speed processing on large-scale production lines, and is obtained in the automotive industry. widely used.
The exhaust valve seat on the engine cylinder head is made of copper and molybdenum high chromium alloy cast iron (HRC44). The processing methods generally include milling and car. Most of them are on the automatic line, and processed together with the hinge hole of the hinge, v= 71.6m / min, ƒ = 26.5mm / min, ap = 1.0mm, using PCBN overall blade processing, the average durability is 1,200 valve seat, processing surface roughness Ra0.4μm, cone surface swing ≤ 0.05mm, tool life High and stable quality.
In the automobile engine production line, the cylinder hole finishing of the gray cast iron cylinder requires high dimensional accuracy, small surface roughness and good stability of the cylinder bore; the cutting speed is high due to the fast processing cycle of the production line (usually V≥500m/min) The tool life is long (the number of machining holes is ≥1000), and the blade life of multiple stations such as chamfering, sluice, coarse and fine boring should meet the durability requirements. High-speed cutting and high-stability machining of engine cylinder bore can be realized by PCBN tool; the typical cutting parameters are: V=500m/min, f=0.2～0.4mm/r, ap=0.2～0.7mm; machining surface roughness Ra≤1.6μm, tool life>1,000 pieces.
Boron-containing cast iron cylinder liner is processed by PCBN tool. Cutting parameters: V=200m/min, f=0.1mm/r, ap=0.2～1mm, machining surface roughness Ra≤1.6μm, precision IT6, between two sharpening With a tool life of >100 pieces, it can achieve "car grinding". Due to the dry cutting, the environmental pollution of the cutting fluid and the grinding wheel dust is avoided, and the chips can be recycled and reused, which meets the requirements of clean production [4].
Cutting the gray cast iron brake disc with PCBN tool, the cutting speed is generally 700 ~ 2,000m / min, such as Shanghai General Motors Co., Ltd. using Seco tool company PCBN 300 type blade, cutting speed can reach 2,000m / min.
1.1.3 Turning alloy workpieces Using PCD tools to cut aluminum alloy wheels, the cutting speed can be V=500~1000m/min, Æ’0.05~0.5mm/r, ap is generally 0.5mm~3mm.
The PCBN tool turns high cobalt chromium molybdenum corrosion resistant alloy with a cutting speed of 160m/min, which is 8 times that of cemented carbide tools.
Generally, an aluminum alloy containing less than 10% silicon can be cut with a cemented carbide tool. However, if the silicon content exceeds 10%, only PCD can be used. Currently, the silicon content of high-silicon aluminum alloys is above 12%, and some have exceeded 18%, so non-PCD such as turning high-silicon aluminum alloy automobile engine pistons is a [5].
Turning powder superalloy FGH95 also uses PCBN inserts.
1.1.4 Turning other materials Alumina ceramic density 3.9g/cm3, hardness HV2100～2300, bending strength 300MPa, compressive strength 300MPa, wet cutting with PCD cutter, V=20～70m/min, ƒ=0.025～0.10 Mm / r, ap = 0.2mm; processing efficiency is significantly improved, is 3 to 5 times the grinding of diamond grinding wheel, tool life can reach 10 ~ 30min [6].
The copper commutator for turning the motor commutator with PCD tool has typical cutting parameters: V=300m/min, ƒ=0.08mm/r, ap≤0.15mm; machined surface roughness Ra0.1～0.2μm, tool life> 5,000 pieces. Only a few pieces can be processed with carbide tools.
1.2 Application in Milling Machining gray cast iron with PCBN tools, cutting speeds of 1,000 to 000 m / min; milling aluminum alloy with PCD tools, speeds up to 3,000 ~ 4,000 m / min [5].
The PCD face milling cutter for machining aluminum alloy cylinder heads has a milling speed of 4,021 m/min and a feed rate of 5,670 mm/min. The efficiency is twice that of the introduction of the production line in China in the early 1990s.
The CBN face milling cutter for finishing gray cast iron cylinders has a milling speed of 2,000 m/min, which is 10 times that of cemented face milling cutters [7].
The PCD spiral inner drain milling cutter for milling glass has various diameters of 10mm, 12mm, 16mm and 20mm, and is widely used in glass deep processing.
On the X53K vertical milling machine, the milling of Cr12MoV (HRc59~61) and 45 steel (HRc50～53) materials with PCBN end mill provides useful reference data for the practical application of such tools [8,9].
PCD tools have a high wear resistance when milling graphite. Many experts have used PCD milling cutters on the Mikron Nidau ​​high-speed cutting and milling machine in Switzerland. The processing of 20 toothbrush electrodes with a single clamping tool can still achieve the requirement of a shape tolerance of less than 0.01 mm. PCBN tool hard milling shower nozzle handle steel mold, high precision, only need to be slightly polished after milling.
1.3 Application in boring processing At present, there are many engine manufacturers in China that use PCBN tools to finish the V-cylinders of cylinder cylinders. For example, the engine plants of Shanghai Volkswagen and FAW Group use PCBN inserts and can automatically compensate. (V = 500 m / min, Æ’ = 0.2 mm / r, ap = 0.1 mm). Long tool life, high machining accuracy, dimensional stability and high production efficiency.
FAW uses PCD tools to precision silicon aluminum alloy piston pin holes (V=160m/min, Æ’=0.08~0.10mm/r, ap=0.05mm.), with a durability of 42,500 pieces, which is a carbide tool. 90 times; the surface roughness Ra is reduced from the original 1.12 to 0.15; each class can reduce the auxiliary time of the tool for 30 minutes, and the cost is about 85% lower than that of the cemented carbide tool.
PCBN tools are 50 times more wear resistant than cemented carbide tools, several times higher than coated carbide tools and 25 times higher than ceramic tools, making them the only efficient tool for machining non-metallic materials. The highest cutting speed is 7,000m/min; the efficiency is significantly improved.
CVD tool for boring tungsten carbide (25% Co) cylinder (inner diameter 20mm, length 40mm), adding coolant, cutting speed 0.5m / s, cutting depth 0.12mm, 8 clamping tools can be processed Part [10].
Casting silicon aluminum alloy SAE327 with PCD cutter (Si7～8.6%, Cu1～2%, Mg0.25%～0.6%, Mn0.5%～0.8%; tensile strength>230MPa, hardness 110～130HB, elongation> 1%) The refrigeration compressor connecting rod is used for high-speed dry boring. The cutting speed is 140-180m/min, Ra0.02～0.32μm, and the precision can reach 5~7 [11].
1.4 Application in broaching processing The composite involute toothed inner hole super-hard material broach is used to machine the workpiece hole. The advantages are as follows: (1) Since the coaxiality between the various faces of the workpiece inner hole can be reliably ensured, Therefore, it is possible to uniformly use the small-diameter circular surface as a positioning reference in the subsequent processing steps, which greatly facilitates the production of the post-positioning positioning mandrel and the inspection mandrel, and reliably ensures the positional accuracy of all the machined surfaces; (2) due to the use of reasonable tooth-hopping The arrangement of the teeth and the structure of the serrations of the spline-edge backlash ensure the manufacturing quality of the broach and are easy to manufacture, and the cost is almost the same as that of the conventional composite involute broach.
1.5 Application in Reaming PCBN electroplating reamer has played a role in the reaming of hardened steel or hard casting holes. This type of reamer is made of 45 steel or 9CrSi steel with a hardness of 42 HRc, with front and rear guiding and cutting portions. The manufacturing precision of the substrate is high, the design should be reasonable, the diameter of the front guiding part is smaller than the diameter of the cutting edge part by 0.04mm, the length of the cutting area is larger than the depth of the workpiece; the length of the rear guiding is larger than the length of the cutting area, and the diameter should be larger than the diameter of the cutting edge. Small 0.02mm. In order to rinse the chips with the cutting fluid in the reaming and to cool the lubricated surface, the base has two deep spiral grooves.
For example, a factory processing hardened steel workpiece hole φ12.06±0.05mm, hardness 45HRc, bottom hole size φ12±0.01mm, required hole cylindricity 0.005mm, surface roughness Ra0.2μm. A set of five electroplated CBN reamers were used to achieve better economic results [12].
Some engine manufacturers use PCD or PCBN electroplating reamer to knead the main bearing hole of the cylinder block instead of honing, the processing efficiency is improved several times, and the quality is stable.
Due to the weight reduction and multi-functional requirements, modern automotive gearboxes are increasingly manufactured using die-cast aluminum alloys with a number of stepped shaped holes for surface roughness, roundness, cylindricity, Concentricity, no burr and other quality requirements are very strict. In order to meet the need for efficient and high-precision machining of formed holes, the Japanese company has developed a PCD forming step reamer. High-quality PCD insert materials are used, and high-precision forming grinding technology is used to ensure the shape of the cutting edge, and excellent dimensional accuracy and surface roughness are obtained, so that all cutting edges have excellent cutting performance under different processing loads. The tool achieves satisfactory processing quality, eliminates the disadvantages of sticking knives, extends tool life and reduces machining costs by half.
1.6 Application in drilling processing It is not uncommon to use PCD drill bits to process glass, engineering ceramics and stone. Many glass deep-processing companies and glass shops mostly use PCD drill bits to drill holes in glass and mirrors. Diamond drill bits on the market range in diameter from 3 to 130 mm. Glass drill bits are inlaid with diamond and resin diamond. Using PCD drill bits to process engineering ceramics and stone, the efficiency is high and the processing quality is good.
Diamond electrolytic drilling can be used to form cylindrical holes (through holes and blind holes), tapered holes and special holes in various difficult-to-machine conductive materials (mostly sintered cemented carbide). It can be machined on the same tool on a single machine without the need to re-adjust tools and blanks [13].
The most noteworthy is the use of brazed diamond casing drills to drill the "Kevlar composite-special ceramic-aluminum alloy" composite laminate through-holes on the Z5125 vertical drill press. The material is a new type of lightweight composite material which has appeared in recent years. It has the high strength, high fracture toughness, high energy absorption buffer protection capability of Kevlar composite material, and high hardness, high modulus and high ceramic. It has excellent properties such as compression resistance, wear resistance, corrosion resistance and high temperature resistance. It also has the advantages of anti-rust, anti-penetration and high toughness of aluminum plates. Using a brazed diamond nesting drill, 10 holes were drilled continuously, and there was no significant change in the cutting position.
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