With the extensive application of CNC machining technology, CNC machine tools have a series of advantages such as high precision, good stability, high efficiency and high automation. They are fully reflected in machining, but high-hardness parts, thin-walled parts and fines are processed by CNC lathes. Long-axis, elongated holes and other parts often have technical problems such as easy deformation of parts, difficulty in ensuring part size and surface roughness. In recent years, with the emergence of new tool materials, new surface coatings and new types of tools, new cutting processes and machining methods have been developed to solve the technical problems of such parts in CNC lathe machining. may. 2 Typical parts analysis 2.1 Basic situation Taking a typical part as an example, the part is a high-hardness thin-walled cylindrical part. The inner cavity is composed of threads, step holes and rounded corners. The part material is 30CrMnSiA high-strength steel, hardness HRC50～55 The wall thickness is 1.5 to 2 mm, the inner hole roughness is Ra1.6, the coaxiality between the thread and the outer circle and the inner hole is Φ0.02 mm, and the inner hole is rounded to 0.05 mm. The shape and size are as shown. 2.2 Analysis of main processing difficulties It can be seen that the intermittent processing of Φ64.7mm inner hole, M65×1.5 thread, Φ69mm outer circle and Φ65.7mm inner hole is the most important processing difficulty of the part, and its Φ64.7mm inner hole depth is 122.8mm, the thinnest wall thickness is only 1.5mm. After the parts are quenched, the deformation is very easy due to poor rigidity, and the chip removal is difficult. The surface quality and roundness are difficult to guarantee, and there are tools for intermittent cutting. Easy to chip, wear and other phenomena. In order to ensure the coaxiality of the M65×1.5 thread of the part with the inner hole and the outer circle, and to reduce the amount of thread deformation after the quenching heat treatment, the thread processing of the part can only be performed after quenching. The existence of these processing difficulties makes the selection of the tool during the machining process, the routing of the processing technology, and the determination of the process clamping method become the key to the qualification of the part. 3 Processing process design Through the analysis of the part structure and its processing difficulties, the following processing schemes are formulated: a. blanking b. annealing c. rough roughing outer circle, flat end face, drilling Φ58mm through hole, ensuring both sides The outer end face is perpendicular to the part axis. d. Several cars are rough-processed inside and outside, flat end faces, and perpendicular to the axis of the part. In order to ensure the hardness of the parts after quenching can meet the design requirements, the inner and outer models retain a margin of 1mm. e. Heat treatment quenching HRC50～55. f. Drill the side 6 Φ3.2mm holes. g finishing parts right end, flat end face, fine car inner hole, M65 × 1.5 thread, while the semi-finished car outer circle size to Φ69.4mm (for the final machining of the part to leave a 0.2mm fine car balance), the length is 66mm, And to ensure that the next process can be Φ64.7mm, Φ65.7mm inner hole can be coaxial with the thread. h. Finished parts left end, flat end face, semi-finished car outer circle to Φ69.4mm, length 70mm, respectively, refined car inner hole Φ64.7mm, Φ65.7mm, due to Φ65.7mm inner hole circumference is evenly distributed 6 A small hole of Φ3.2mm, so there is intermittent cutting, should avoid using the same boring knife for machining with Φ64.7mm inner hole. i. Fine car outer circle, use the inner tire to improve the outer circle to Φ69mm. 4 machining process design 4.1 machining tool selection In the tool manual, the sample, most of the cutting hardness is greater than 45HRC cutting is defined as hard cutting. In most cases, hard cutting can only be processed with PCBN (polycrystalline cubic boron nitride) blades or diamond blades. These blades are mostly negative rake angle, the blades are not sharp, the toughness is poor, the crushing is easy, and the cutting speed is high. It is expensive, and if the thin-walled part is machined with such a blade, vibration is easily generated and intermittent cutting cannot be performed. Therefore, for the hardness of the parts after quenching to reach HRC50 ~ 55, the toughness and plasticity of the part material 30CrMnSiA, the author selected the tool according to his research on the tool for many years. The cutter bar has good rigidity and is a positive rake angle cutter. The insert has a positive rake angle, the front angle is 18o, the physical coating (PVD) composite ceramic, and the coating structure is (Ti, Al)N+TiN, which is suitable for intermittent processing. , good toughness, wear resistance, sharp cutting, its processing hardness is 40HRC. Internal thread R166.4KF-20-16 R166.0L-16MM01-250 The 1020 shank is a full-round structure with a large containment area and good rigidity after clamping. The insert is a physical coating (PVD) insert suitable for low-speed cutting. The surface has a TiN coating of 1~2μm, the cutting edge is sharp, the wear resistance is good, the high temperature resistance, the anti-chip hammering ability is strong, the vibration is not easy to be generated during processing, and the processing hardness is 47HRC. Boring A32T-SCLCL12 CCMT120404-WF5015 (semi-precision, fine) arbor is Φ32 circular structure, good rigidity, with internal cooling holes, can effectively cool the tool tip and parts, reduce the cutting temperature of parts, reduce Small deformation. The blade is uncoated cermet, the main component is TiC, TiN, the blade has good toughness, and the blade edge is sharpened throughout the tool life, suitable for low speed machining. At the same time, the blade has a wiper, which can effectively improve the surface roughness and processing efficiency of the part (wiper inserts are twice as fast as the normal blade feed with the same surface roughness requirements). Although the above selected tool can not meet the processing needs in the theoretical processing hardness, the author through the repeated test, after optimizing the cutting parameters and tool geometry parameters, and perfecting the fixture design, the tool finally meets the thin wall, high hardness and break of the part. Continued processing requirements. 4.2 Tool geometry parameters Tool geometry parameters are selected. 4.3 Special fixture design (1) In order to meet the processing needs of this part, the jaw clamping force and cutting force should be calculated before the fixture design, so as to get the pressure that the machine chuck needs to adjust. Claw clamping force formula: W=nDf KM 2 where: n?? number of jaws; K?? safety factor; f?? friction coefficient; M?? cutting torque; D?? part diameter. Cutting force formula: F c=C Fc a xFc pf yFc v nFc c K MF KкrF KγоF KλsF KλεF cutting torque formula: M=2 FcD where: C Fc?? coefficient; x Fc, y Fc, n Fc?? Index; ap?? eating depth; f?? feed rate; V c?? cutting speed; K MF?? material correction factor; KкrF?? lead angle correction coefficient; KγоF?? rake angle correction coefficient; KλsF? ?Edge inclination correction coefficient; KλεF?? Tool nose radius correction coefficient. After checking the cutting manual, the main cutting force of the part is: F c=2795×0.4 1.0×0.15 0.75×88 -0.15×) (650 2109 0.75×0.89×0.9×0.6×0.8N=128N cutting torque: M=2 FcD=0.5×128×70 N?mm=4480 N?mm jaw clamping force: W=nDf KM 2=nf KFc=3. 0 3 128 2×N=284.4N According to the formula calculation result, after setting a certain safety factor, the clamping force of the jaw is determined to be 300N. After the pressure of the hydraulic cylinder of the machine tool is gradually adjusted, the final pressure of the hydraulic cylinder is 0.9. The clamping force of the jaws at bar can meet the requirements. In addition, the fan-shaped soft three-jaw is designed to increase the clamping area and reduce the clamping deformation of the part. The fan-shaped soft three-jaw is as shown. (2) When the inner hole of the part is finished, it is found that there is a local deformation (large diameter) with an average of 0.05 at the circumference of R3 of the Φ64.7 inner hole. The analysis may be caused by the sudden change of the cutting amount when processing R3. Therefore, on the one hand, the author increases the effective wall thickness of the part by increasing the slotted sleeve (as shown), increases the rigidity, destroys the vibration frequency, and reduces the vibration. On the other hand, when the machining program is programmed, the R arc is gradually reduced. Measures to reduce the amount of cutting mutations. (3) In order to ensure that the outer circle finishing can be completed at one time, and the support surface of the part has sufficient rigidity, the inner ring tire (as shown) is used for the outer circle cutting process, so as to avoid the stress deformation of the part caused by the grinding and improve the processing. effectiveness. The inner tire is designed as a rubber expansion type clamping method. When the rod is tightened, the wedge and the supporting tile are pressed by the bolt and the pressing plate, and the rubber sleeve is clamped by the wedge and the supporting tile. Due to the long length of the workpiece and the rigidity of one end near the main shaft, two kinds of wedges are designed for this purpose. The inclination angle of the wedge 1 is 12° and 45°, and the inclination angle of the wedge 2 is 12.5° and 46°, which ensures the process. The rigidity of the system. The central part of the rubber sleeve is transmitted through three supporting tiles, which ensures the effective support and clamping of the central part. 4.4 Selection of cutting parameters Since this part is a high-hardness thin-walled part, the rigidity is poor during processing, and it is easy to generate vibration. The cutting hardness of the tool is not enough to meet the processing requirements. For this reason, when the tool and clamping force are relatively fixed. It can only be adjusted by optimizing the cutting parameters. The surface roughness calculation formula Ra=εr f 50 2×(f is the feed amount, εr is the radius of the tool tip arc) as the reference, and the cutting parameters are selected. 4.5 Cooling method The coolant is a water solvent extreme pressure cutting fluid. When cooling, the cooling system of the machine tool spindle is used to match the cooling system of the tool holder. The cooling is performed simultaneously from the left and right ends of the part. The spindle cooling system aligns the parts and the tool holder. The cooling system is aligned with the tip of the tool to quickly and fully cool the machined part to reduce the influence of the cutting heat on the deformation of the part during cutting. When the coolant is cooled to the part, it is not necessary to avoid the cold and heat of the tool. phenomenon. 4.6 Treatment of chip removal problem Due to the deep processing depth of the hole of the part, the iron filings generated during semi-finishing and finishing are mostly reddish-brown strips, which may cause scratches on the surface of the inner hole and even damage the tip. After the completion of each fine car and semi-finished car, it should be suspended and the iron scraps should be cleaned in time. 5 CNC machining program design 5.1 NC program design flow NC program design flow. 5.2 NC program design This part is processed by Siemens 840D CNC system, the key point processing procedure is as follows. The inner hole and thread machining program at the right end of the part: 7 Conclusion Through the method introduced by the author, the roughness of the inner hole of the machined part reached Ra1.6, the coaxiality of the thread with the outer circle and the inner hole was 0.02mm, and the roundness of the inner hole was 0.03mm, which fully met the design requirements. The passing rate of one inspection has reached 100%. It effectively solves the turning problem of high-hardness and thin-walled parts, and provides some experience for the threading and intermittent processing of high-hardness material parts. The designed fixtures and summarized optimized cutting parameters break some conventional rules of hard cutting. The practice has greatly improved the processing efficiency and reduced the cost of the tool. (Finish) Cans For Alcohol,Alcoholic Cans,Fruity Alcoholic Drinks Cans,Pre Mixed Alcoholic Drinks Guangdong Jasper Import and Export Co., Ltd. , https://www.jaspercans.com