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. Introduction High-speed cutting (HSC) is an important part of advanced manufacturing technology. Its main advantage is the high efficiency and high quality of processing. In recent years, high-speed machining technology has developed rapidly in the world's major economically developed countries (such as Germany, Britain, the United States, Italy, Japan, etc.). The high-speed cutting machine tools and auxiliary, distribution, software and hardware produced in these countries are almost every year. The speed of the steps has been updated, and the performance indicators that can be achieved so far are already eye-catching. Micron, Jobs, Haas, Fpt, Dmg and other world-renowned machine tool companies have developed the rapid replacement spindle head technology in recent years, so that the same machine can adapt to a variety of load and speed requirements (the so-called rough finishing with the same machine "once"), A large amount of non-processing time can be saved in the positioning, installation and transmission of the workpiece.
The high-speed rotation of the machine tool spindle and the corresponding increase of the feed speed and acceleration can directly shorten the machining time. On the other hand, the high-speed cutting has the advantages of particularly high excitation frequency, stable operation and small vibration, which is beneficial to improve the machining surface. Quality, ie high-speed machining, can be used as the final machining of molds and structural parts, improving machining efficiency and processing quality by “cutting or grinding†or “cutting discharge†(ie no need for time-consuming and inefficient subsequent grinding operations) , mold electrode EDM); the workpiece can also be quenched and then cut, directly cutting the material with hardness up to 65HRC to the final size.
In addition to high-speed machine tools, high-speed machining requires high-speed cutting. According to the special report of Micron, Jobs, Kenner Feishuo and other companies in the 2002 International Mould High Speed ​​Processing Technology Seminar of Guangdong Province, in recent years, German SGS, Mitsubishi (Kobelco) and Sumitomo, Swiss Sandvik, and Kenner Feishuo and other famous foreign tool companies have successively introduced their own high-speed cutting tools, not only high-speed cutting of ordinary structural steel tools, but also super-hard tools such as ceramic tools that can directly cut hard-hardened steel, especially coating tools. It plays a huge role in the semi-finishing and finishing of hardened steel.
In recent years, China's (especially South China) manufacturing industry has developed rapidly, and the manufacturing of molds, automobiles and motorcycles has developed, and the number of enterprises with high-speed cutting machine tools has increased. However, compared with the rapid development of high-speed cutting machine tools and tool technology, these companies are still relatively backward in high-speed cutting technology, testing and application software, and can not be matched with hardware, resulting in the advanced equipment imported by many manufacturers. It should have a role. On the one hand, high-speed machine tools with a spindle speed of tens of thousands of revolutions have been operating at only a few thousand revolutions. The conditions for high-speed finishing are only used for roughing and semi-finishing. Machines and tools that can cut high-hard materials are It is only used to cut ordinary materials; on the other hand, due to improper matching of workpiece materials with tools and processes, processing costs are high and even quality accidents occur from time to time. In order to promote the development of high-speed machining technology and help enterprises to rationally apply high-speed machining equipment and technology, it is necessary to conduct in-depth discussions on the technical and economic issues of high-speed machining.
Commonly hardenable die steel and high speed cutting end mill
2.1 Common plastic mold steel and hot work steel
Common mold hardened steels on the market are mostly used in the manufacture of plastic molds and forging and die-casting cavity molds. The main suppliers are Sweden ASSAB, LUNG KEE, SAARSTAHIL, Japan. Companies such as Datong (DAIDO). Table 1 lists the product names and properties of some plastic mold steels and hot work steels. The traditional mold steel processing method is first milling and then hardening and grinding, while high-speed cutting can be rough milling, hardening and fine milling, and even rough finishing can be completed in one machine.
2.2 High-speed cutting hardened steel common end mill
This article focuses on solid carbide PVD coated end mills for high speed machining (other tools such as CBN and ceramic tools for machinable hardened steel are not the focus of this paper).
(1) Tool coating: The tool coating that can be used for high-speed cutting hardened steel mainly includes (Ti, Al)N or (Ti, C)N, and the tool base is ultrafine grained cemented carbide.
(2) Main form of milling cutter: The main form of integral end mill for high-speed cutting hardened steel includes conventional 2-blade and multi-blade ball-nosed knives, long-neck ball-nosed knives, 2-blade cone-face ball knives, and 2-edge belts. Round head flat bottom knife, long neck with round head flat bottom knife, 2 blade right angle flat bottom knife and multi-blade right angle flat bottom knife.
The main suppliers of end mills for hardened steel in China are: KOBELCO, Mitsubishi, Japan, UNIMAX, HITACHI, SUMITOMO ELECTRIC, SGS, USA KENNAMITAL and coating tool manufacturers in Korea and Israel, domestic companies have also launched products for trial development.
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.
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).
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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