As the key tooling for the production of modern products, the design and production cycle of molds, product accuracy and service life are increasingly becoming the decisive factors for the company's new product development cycle. Therefore, China's mold manufacturing industry ushered in a good opportunity for development, but also faced great challenges.
The level of modern mold manufacturing, the length of the cycle depends on the support of various technologies, including the process design of the mold, the software that directly affects the mold design and manufacturing standards, the equipment for mold manufacturing, the cutting tool for the processing mold, and the final mold There are many aspects such as the standardization and generalization of the repair process, spare parts, and the skill level of the mold design and manufacturing engineering and technical personnel. This article focuses on the processing efficiency of the mold, and will do some research on tool selection and cutting process selection.
High speed milling method
Figure 1 High-speed milling method
Processing features: use a small radial depth of cut (meshing capacity) ae (reduce cutting heat generation); use a small average chip breaking thickness cutting hm (reduce cutting heat generation); use a small axial depth of cut (margin) ap (Reduce cutting heat generation); Adopt harder cemented carbide insert grades (because hard grade carbide insert grades are better at high line speeds and high workpiece hardness but at the same linear velocity Tool life); as far as possible the use of sharp cutting edge and groove type design; using a cooling liquid processing method to take away the large amount of cutting heat generated due to high-speed cutting. (This may affect the tool life, but the overall economy increases.)
The advantages brought by this method are: greatly reducing the time required for subsequent polishing, reducing (or even eliminating) the time required for EDM, shortening the time required for 3D modeling, saving the fearless consumption of processing aids, good quality, and rough surface Ra, to avoid or delay deformation, high production efficiency, low cutting heat generation, thus reducing the impact on the quality of the workpiece.
Use this method to pay attention to: the programming requirements increase, but with the development of the software will be more and more no problem; the requirements for the quality of the operator to improve; due to novel technology, need time to learn, optimize; must ensure that nothing is lost (new software Simulation and simulation techniques provide strong support; apply to high-end products with good planning and sufficient profits; require good coaxiality of the system and small radial runout of the tool.
A large number of test results show that the service life of the tool will increase by 20% to 50% with each increment of about 10 μm radial runout. Tool holders for high-speed milling include a thermal expansion holder, D-type precision chuck holder and hydraulic holder.
The maximum speed of the thermal expansion tool holder is 45000 r/min. The maximum speed of the D-type precision collet chuck is 100 000 r/min. The upper limit of the rotation speed of the HSK-A63 hydraulic tool holder is 40 000 r/min, and the radial runout at 3 times the tool diameter is 3 μm.
Figure 2 Cycloid milling method
"Peeling" milling method
Processing features: The use of smaller radial depth of cut (meshing capacity), greater or greater axial depth of cut, high cutting speed, spiral cutting edge design requirements, not only plays a rough processing effect, but also can save semi-smooth Processing process. The "Cycloid" milling method is a similar machining method to the "skinning" milling method. It reduces cutting heat generation and accumulation by reducing the radial depth (meshing amount) of arc. Use a small radial depth of cut (engagement) and use an actual larger milling swing diameter. Since the cutting heat is effectively dispersed during the cutting process of the cutting tool, the cutting edge is sufficiently cooled to allow a greater axial cutting depth or higher cutting speed than the conventional method.
High feed milling method
Figure 3 High feed milling cutter compared to round insert milling cutter
The machining features are: a smaller axial depth of cut, a very high feed per tooth, and a higher cutting speed. Not only does it have the effect of roughing, but it also eliminates the semi-finishing process. In the processing of pre-hardened or difficult-to-die steel parts, the combination of Seco's F15M insert grades and this high-feed milling process will be particularly effective.
1. Advantages of high feed milling
(1) Despite the smaller axial depth of cut, it seems that the machining efficiency is not as good as that of conventional circular inserts, but in fact it is due to adopting a much larger feed per tooth than conventional (especially when machining large overhang deep molds When the cavity is cut, the axial depth of the conventional circular insert milling cutter is often not large, so the actual metal removal rate is significantly improved.
(2) The main force of the cutting force is the axial force, which improves the cutting rigidity of the tool, especially when machining large overhangs and deep mold cavities, which outperforms the conventional round-blade cutters.
At present, the mold is widely used in the rough open cavity is a round-blade cutter (commonly known as cattle nose knife), the basic diameter of the round-blade cutter blade is 10mm or 12mm, in order to ensure that the roughness after roughing is not bad, go The amount of knife is generally not more than 0.3mm/tooth, while the high feed milling cutter series (R220/217.21) of Seco Tools adopts the standard convex triangular arc blade design can feed 0.5~1.5mm/tooth. Although the axial depth of cut is generally controlled to be less than 0.6mm, the machining of a steel mold as an example, the actual metal removal rate can be as high as 700 cm3/min, and the machining time can be reduced by 2/3 than the conventional round-blade milling cutter. Not only that, because this type of milling cutter has a lower radial cutting force than a round-blade type cutter, even if the cutter bar is relatively long and does not produce significant cutting vibration, the service life of the blade is improved.
2. Processing case
Workpiece name: wrench handle mold cavity, pre-hardened mold steel HRC56, Seco Group 7 materials
Arbor Model:MM10-10045.0-007(Ф 10 mm)
Blade Type: MM10-10.50-HF-MD08, F15M
Cutting parameters: Vc = 200 m/min N = 6350 r/min
Fz = 0.50 mm/tooth
Vf = 6350 mm/min
Ap = 0.5 mm
Ae = 75%
Plunge milling method
Figure 4 Plunge milling method
The processing characteristics are as follows: This method is mainly applicable to the processing of large aspect ratio or the poor rigidity of machine tools; the use of conventional cutting line speed; a processing option applicable to different workpiece materials; commonly used as deep cavity molds and complexes The rough machining of the die has a high metal removal rate and exhibits an unmatched high efficiency.
With the increasingly popularization and improvement of the Z-axis feed function of the machine tool, more and more plunge milling methods and plunge cutters are used. In particular, deep cavities and deep punches are often encountered in tooling. Than the operating conditions. For this kind of machining, if the conventional round-blade cutter is used for contour milling or copy milling, only a small depth of cut, a small feed, and a low number of effective cutting edges can be used to avoid cutting vibrations. In the method of plunge milling, because the cutting force is basically completely along the direction of the main axis, the tool rigidity is excellent, the cutting efficiency is at least 2 to 3 times higher than the conventional method, and the service life of the blade is also significantly improved.
The above describes modern milling methods applied to the milling of molds, but it needs to be combined with the application of the characteristics of the mold itself in practical applications, which will help improve processing efficiency and lay a solid foundation for reducing processing costs. After all considerable progress has been made in all aspects of mold making, China will become a strong country in mold manufacturing.
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