Rational use and wear Countermeasures of the hotte

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Reasonable use and wear Countermeasures of PCBN cutting tools

1 introduction

pcbn is a kind of superhard material made by sintering selected CBN crystals under high temperature and high pressure. The blade made of PCBN material has extremely high hardness, good red hardness (can withstand the high temperature of 1400 ~ 1500 ℃), oxidation resistance (does not react with ferrous metals at the high temperature of 1200 ~ 1300 ℃) and fracture toughness. It is an ideal tool for cutting ferrous materials. At present, PCBN cutting tools have been widely used in processing hardened steel, chilled cast iron, thermal spraying materials, pure nickel and other difficult to machine materials and precision machining, and have achieved remarkable technical and economic benefits. With the continuous expansion of the application scope of PCBN tools, the correct and reasonable selection of PCBN tools and the timely resolution of various problems in processing have become a powerful guarantee to give full play to the maximum processing benefits of PCBN tools

2 applicable processing materials for PCBN tools

PCBN tools are mainly suitable for processing all kinds of high-hard materials (such as cold working tool steel, hot working tool steel, high-speed steel, bearing steel, hardened steel, powder smelting steel, powder smelting metal, martensitic stainless steel, high-strength steel, high manganese steel, white cast iron, austenitic soft iron, etc.), soft materials and wear-resistant materials (such as gray cast iron, sintered iron, etc.) Difficult to machine materials (such as Inconel718, case hardening alloy, sintered WC, ductile iron, CGI, etc.). Some materials or processing conditions (such as typical mild steel, austenitic or ferritic stainless steel, high chromium steel or surface chromium coated materials, high-speed steel with intermittent cutting, iron-based surface hardening alloy, etc.) are not suitable for machining with PCBN tools because they are easy to cause abnormal chemical wear of PCBN blades

3 reasonable selection of PCBN tool geometric parameters and cutting parameters

the selection of tool geometric parameters and cutting parameters has a great impact on the cutting performance, service life and machined surface quality of the tool. In order to give full play to the excellent performance of PCBN tool and achieve ideal cutting effect, it is necessary to reasonably select the geometric parameters and cutting parameters of the tool according to the specific machining object. When choosing the geometric parameters of PCBN tools, we should focus on the strength of the blade and tip. PCBN tools often adopt 0 ° rake angle or negative rake angle, and grind out negative reverse edge to increase the strength of cutting edge; γ o1=-8°~-20°; To increase the strength of the tool tip for closing the oil return valve, it can be ground out γε= 0.2 ~ 0.8mm tool tip arc; The rear angle is generally small (5 ° ~ 7 °), and the inclination of the blade is mostly 0 °. For different processed materials and cutting conditions, according to the "energy saving and new energy vehicle technology roadmap" previously issued by the Chinese society of automotive engineering, the geometric parameters of the tool should be determined through cutting tests. The geometric angles of PCBN tools for rough turning and fine turning hardened steel are shown in Figure 1 and Figure 2 respectively

(a) standard turning (b) profiling turning

Figure 1 geometric angle of PCBN tool when rough turning hardened steel

Figure 2 geometric angle of PCBN tool when fine turning hardened steel

the cutting amount of PCBN tool should be reasonably selected according to the processing machine tool used, blade brand, workpiece to be processed and other processing conditions. Table 1 shows the recommended cutting parameters for seco cbn300 blade (CBN content 90%, grain size 22 m, Al binder) when cutting different materials. Table 1 applicable cutting amount of cbn300 blade

workpiece material cutting speed

(m/min) feed rate

(mm/r) cutting depth

(mm) pearlitic gray cast iron 500 ~ 15000.5 ~ 0.80 25 ~ 1.0 white cast iron 120 ~ 1800.1 ~ 0.40.3 ~ 1.2 chilled cast iron (570 ~ 900HV) 50 ~ 1200.1 ~ 6.0 0 0.1 ~ 1.2 hardened steel (45 ~ 65hrc) 60 understand the type of strain curve of tensile testing machine ~ 1500.2 ~ 0.30.6 ~ 2.5 surface hardening alloy (>35hrc)

80 ~ 2400.12 ~ 0.250.5 ~ 2.5 cemented carbide (co>17%) 20 ~ 400.1 ~ 0.250.1 ~ 0.5 manganese steel (12 ~ 20% Mn) 140 ~ 2000.3 ~ 0.70.2 ~ 2.9

4 choice of PCBN blade brand

the correct choice of PCBN blade brand is the key to whether the tool can obtain the optimal cutting performance. Table 2 shows the characteristics of various brands of PCBN blades of seco company. Figure 3 is the model selection flow chart of PCBN blade brand. Table 2 characteristics of PCBN blades of various brands of seco company

blade brand CBN content

(volume ratio) grain size

(m) binder structure type cbn1050%2tic welded cbn2080%6ti+al welded cbn3090%8al integral cbn10050%2tic integral cbn15045%0.5tin

welded cbn30090%22al integral

Figure 3 PCBN blade brand selection flow chart

5 common wear (breakage) of PCBN tools Damage form and improvement measures

pcbn tools will produce normal wear and abnormal wear during use. The normal wear forms of PCBN tools mainly include oxidation wear, phase change wear, friction wear, bonding wear, micro chipping edge wear, peeling wear, etc., and various wear factors affect and promote each other. The main influencing factors of abnormal wear of PCBN tools are improper selection of cutting parameters and blade geometric parameters, insufficient rigidity of machining system, etc. In order to improve the service life of PCBN tools, the following specific measures can be taken to improve the common wear forms and damage phenomena of PCBN tools in actual use:

1) rear tool surface wear (see Figure 4)

improvement measures: ① increase the cutting line speed; ② Increase the workpiece feed rate; ③ Increase the cutting depth; ④ Check whether the cutting point of the blade is high in the center; ⑤ If the processed material is cast iron, check whether the ferrite content is within the control range

Figure 4 wear pattern of PCBN blade flank

2) crescent depression wear (see Figure 5)

improvement measures: ① reduce cutting speed; ② Reduce the workpiece feed rate

Fig. 5 crescent wear morphology of PCBN blade

3) cutting hammering (see Fig. 6)

improvement measures: ① increase cutting speed; ② Reduce the cutting feed rate; ③ Improve the cutting rake angle of the tool (such as changing to a round blade, etc.)

Figure 6 PCBN blade cutting hammering phenomenon

4) edge collapse (see Figure 7)

improvement measures: ① use the blade with inverted edge or grinded edge; ② Reduce the cutting speed or avoid intermittent cutting as much as possible; ③ Improve the rigidity of the process system; ④ If intermittent cutting is inevitable (such as holes, grooves, etc. on the machined surface), the corresponding cutting entry parts shall be pre chamfered; ⑤ Change the cutting linear speed to optimize the cutting condition and avoid vibration

Figure 7 PCBN blade edge chipping phenomenon

5) blade rake surface peeling off during milling (see Figure 8)

improvement measures: ① reduce the cutting angle of the tool (preferably less than 20 °); ② Adopt the reverse milling method as far as possible; ③ Avoid using coolant; ④ Increase cutting speed

figure 8 peeling off of the front face of PCBN blade

6) serious edge collapse (see Figure 9)

improvement measures: ① reduce the cutting depth or machining allowance to reduce the cutting load; ② Reduce cutting speed; ③ Appropriately increase the fillet radius of the cutter tip (even round blades can be used); ④ Adopt the blade that passes through the inverted edge or grinding edge; ⑤ Check whether the blade is installed correctly and reliably, and whether the mounting surface is intact (especially the overall CBN blade); ⑥ Check whether the center height of the cutting edge of the blade is correct

Fig. 9 PCBN blade edge seriously breaks

6 conclusion

whether the use of PCBN tool is successful or not depends not only on the quality of the tool itself, but also on all links of the whole processing system, such as the performance of the machine tool, the reliability of workpiece clamping, the rigidity of the tool bar system, the rationality of blade selection, the selection of cutting parameters, etc., which will affect the cutting effect of PCBN tool. Only by using PCBN cutting tools correctly and reasonably can we improve the processing efficiency, reduce the production cost and obtain the maximum technical and economic benefits. (end)

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