Milling (especially roughing) strategies for the rapid removal of large amounts of metal have changed dramatically from the best developed mid-1990s. A new development that is encouraging at this stage is that toolmakers have designed large-feed milling tools that can be used on machines equipped with lightweight spindles and advanced “forward-looking†controls.
The high feed milling strategy shows the following potential technical advantages:
(1) When rough milling is performed on a light machine with better economy, a high metal removal rate can be obtained.
(2) High-reliability machining can be achieved by using a tool with good consistency and predictable service life.
(3) Parts that have been rough-milled can achieve machining accuracy requirements closer to the final shape.
In the past, in order to improve the metal removal rate, mold manufacturers generally used large-diameter milling cutters on high-power machines to select lower spindle speeds and large depths of cut for machining. Of course, limited to the current state of the art, even if a higher metal removal rate can be obtained, it will leave a high step and a deep knife mark on the side wall of the processed mold cavity, which needs to be removed in the subsequent process.
Although large feed milling has been developed along with indexable tools, the large feed milling of small and medium mold cavities begins with a small depth of cut using a solid carbide ball end mill. By using the principle of chip thinning, machining with a circular cutting edge tool greatly increases the feed rate per tooth of the tool, and accordingly increases the feed rate of the machine tool to 8 m/min or more. Of course, the necessary conditions for increasing the metal removal rate are the spindle with a speed of 8000 rpm and the CNC system with “forward-looking†function and continuous monitoring of tool trajectory.
A few years ago, some toolmakers (such as OSG) developed several new solid carbide high-feed milling cutters for efficient machining of small and medium-sized mold cavities and cores. The main features are: with the ball head Compared with end mills, the cutting width is increased; compared with conventional milling cutters, the chip flutes are shortened to increase the rigidity of the tool, overcoming the conventional end mill to weaken the rigidity of the tool due to the long flutes (1-1.5 times diameter) The disadvantages are that the feed rate can be increased to 12-20 m/min. After roughing with a small depth of cut, the workpiece close to the final shape can be obtained, which enables direct semi-finishing or even finishing, which improves production. Efficiency saves processing time.
The design and development of the composite large feed milling cutter is mainly in two directions: one is the use of a large radius arc cutting edge (can be regarded as part of a large radius ball end mill); the other is a straight cutting with a small inclination angle. blade. The common feature of these two tools is that they have a small plunging angle, which can form a chip thinning effect during machining and achieve large feed cutting. In the tool structure, the indexable insert and the replaceable cutter head structure are adopted to reduce the tool manufacturing cost.
Sandvik's newly developed CoroMill 210 high-feed milling cutter features a straight cutting edge and a 10° plunging angle. The tool's feed per tooth is increased by more than 6 times to 1-1.5mm/tooth. Under such feed conditions, the chip thickness is 0.18-0.25 mm. Since the CoroMill 210 optimizes the cutting performance, the linear cutting edge can continue to achieve the chip thinning effect as long as the maximum depth of cut is not exceeded.
The CoroMill 210 milling cutter's body, insert seat and insert structure are also optimized, combining two different machining methods – high feed milling and plunge milling on the same tool. When a milling cutter with a 10° plunging angle is fed in the tangential direction, a small axial depth of cut can be used to achieve large feed milling; and in axial feeding, a large radial depth of cut is used for insert milling. A high metal removal rate can also be achieved.
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