Study on the process and economy of high speed milling hardened die steel (2)

3. Processability of high speed end mill for machining hardened steel

This paper introduces the cutting performance and process parameters of high-speed end mills by taking several (Ti, Al) N super-hard coated solid carbide finishing end mills from Mitsubishi. Dry cutting (air cooling) and down milling are recommended for these tools.

1 diameter 0.2 ~ 6mm 2 blade right angle flat end mill: commonly used for cutting grooves. When the hardness of the workpiece is less than HRC45, the axial depth of cut is not more than 0.1D (tool diameter D is less than 2mm) ~ 0.2D (D is greater than 2mm); when the workpiece hardness is greater than HRC45, the tool diameter D is less than 0.5mm, less than 2mm and 2mm or more. The axial depth of cut is not more than 0.02D, 0.05D and 0.1D respectively. 2 diameter 1 ~ 6mm 4 blade right angle flat end mill: commonly used for side finishing. When the hardness of the workpiece is less than HRC45, the axial depth of cut is not more than 1.5D, the radial depth of cut is not more than 0.1D (the tool diameter D is less than 3mm) ~ 0.2D (the tool diameter D is greater than 4mm); when the workpiece hardness is greater than HRC45, the axial cut is The depth is not more than the cutter diameter D, and the radial depth of cut is not more than 0.05D. 3R0.1~3mm 2-blade ball end mill: commonly used for surface finishing. The axial depth of cut is not more than 0.1R, and the radial depth of cut is 0.2~0.4R.

At high speed machining, the cutting speed and feed speed of the above tool vary with the hardness of the workpiece and the tool radius: as the hardness of the workpiece increases, the speed of the tool, especially the feed rate, decreases; as the tool diameter increases, the speed of the tool increases. Lowering but the line speed is relatively higher, the feed rate is also increased accordingly.

Recommended cutting conditions

2-blade ball end mill: workpiece hardness <45HRC: R1-R2-R3: speed (r/min); feed rate (mm/min) workpiece hardness 45～55HRC: R1-R2-R3: speed ( r/min); feed rate (mm/min) blade right angle flat end mill: workpiece hardness <45HRC: diameter 0.5mm-2mm-6mm: speed (r/min); feed (mm/min) workpiece Hardness 45～55HRC: diameter 0.5mm-2mm-6mm: speed (r/min); feed amount (mm/min) blade right angle flat end mill: workpiece hardness <45HRC: diameter 1mm-3mm-6mm: speed (r/min); Feeding amount (mm/min) When the workpiece hardness is 45～55HRC: diameter 1mm-3mm-6mm: rotation speed (r/min); feed amount (mm/min): 45-85-150

4. Economical efficiency of high-speed milling of hardened steel

At present, the (Ti, Al)N coated carbide end mills produced by different manufacturers have great differences in cutting performance, and the market price is also very different (compared with other coated tools, the price is relatively expensive). Small-diameter end mills with a diameter of 2mm or less are priced at 100-400 yuan/piece, and the diameter of 4-φφ8mm end mills is about 200-700 yuan/piece. Generally, as the diameter of the tool increases, the price of the milling cutter also increases (the maximum diameter of the milling cutter can reach 20 mm).

When the (Ti, Al)N coated carbide end mill with large tool diameter is used for high-speed machining of hardened materials, its strength can basically meet the requirements, but the milling cutter is easy to break when using a small-diameter tool to machine a narrow groove at high speed. Since the (Ti,Al)N coated carbide end mills are generally not regrind after wear, the cost of the tool is high; when used in some mold processing, the tool cost even accounts for 12% of the total manufacturing cost of the mold. about.

The advantages of machining molds with high-speed milling are: saving machining time, reducing machining processes, increasing productivity, reducing machining costs, and improving processing quality.

According to the analysis, the cost distribution of the cavity mold by the traditional method is roughly as follows: rough processing accounts for 12%, semi-finishing and finishing each accounts for 25%, followed by manual grinding accounts for 16%, and debugging accounts for 22%. The use of high-speed milling method can greatly improve the finishing efficiency, cancel or reduce the subsequent manual grinding process; if the use of rough finishing with the machine "one-off" process, even the roughing and semi-finishing time can be greatly shortened (electrical Spark processing is much faster).

Processing example:

1 Using Mikron's HSM400 machining center to process the pruning and forging die (HRC52) with “rough, finishing one-pass process”, the total time is 194 minutes (the inner and outer cavities are 66 minutes, the ball-end knife cavity) Semi-finishing milling inside and outside for 10 minutes, ball and flat knife 30000r/min high speed finishing milling for 94 minutes, subsequent finishing 24 minutes), the final surface roughness Ra0.5μm. 2HSM400 machining center adopts “rough, finishing one-pass process” processing injection mold (HRC54), with a total processing time of 468 minutes. The roughing machine adopts 4~6-blade rough milling cutter (2~8mm diameter), the rotation speed is 20000~8000r/min, the feed speed is 1500～2600mm/min; the half-finishing ball milling cutter for semi-finishing and finishing milling (diameter 0.8～1.5) Mm), the speed is 36000r/min, and the feed rate is 1000~1600mm/min. 3 Table 3 shows the use of MMC (Mitsubishi) KOBELCO (Kobelco) small diameter super hard coating end mill.

Table 3 MITSUBISHI MSTAR small diameter super hard coating end mill use example tool - workpiece - process characteristics - cutting conditions - processing effect 2 blade ball head knife (R1.5mm) - hot forging die, material SKD61 ( HRC47) - Semi-finishing and finishing with a depth of 0.05 to 0.1 mm - Cutting speed: 94 m/min, Feed: 0.1 mm/tooth, Swing speed: 10000 r/min, Feed rate: 2000 mm/min, dry Cutting - the life of each tool can be increased from 200m to nearly 600m4 right angle end mill (6mm diameter) - plastic mold, S55C - mold cavity side finishing, cutting depth 0.6 × 6mm - cutting speed: 50m/min, feed: 0.04mm/tooth, swivel speed: 2650r/min, feed rate: 212mm/min, dry cutting - after 50m machining, the flank wear height is reduced from the original 0.25mm to 0.15mm

5 Conclusion

The rapid development of high-speed cutting machine tools and tooling technology makes it possible to apply the “roughening and finishing of the same machine” process for hardened molds. The cutting process can be used as the final processing of hardened molds and structural parts to achieve “cutting” Grinding and polishing or "discharging". Therefore, the application of high-speed milling of the mold may bring many benefits such as saving processing time, reducing processing steps, increasing productivity, reducing processing costs, and improving processing quality.

The end mills currently available for high speed machining of hardened die steels are mainly ultrafine grained hard alloy (Ti, Al) N coated end mills. Due to the relatively high price of such tools, and because of their non-reground, brittleness and high requirements for uniform heating, the processing technology and economic adaptability need to be further studied to give full play to the advantages of high-speed milling. At the same time, enterprises should also develop appropriate high-speed processing technology application strategies according to their specific conditions.

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