For moldmakers, efficient and economical machining of parts is an eternal requirement for their production capacity. In roughing, in order to remove a large amount of metal materials, the traditional common sense in the past shop is to select the tool based on the metal removal rate, which will lead to the selection of the tool with the largest possible removal rate to start the roughing, and then the workpiece size will gradually decrease. Small until the desired shape and finish are achieved. Rough milling usually uses ball end mills or button cutters. However, this method of processing may generate a large amount of stress, so it is necessary to use a machining center with excellent rigidity, a firm jig, and a cutting tool with good toughness.
Plunge milling has become another popular processing method for the rapid removal of metallic materials. The cutting force of the plunge is transmitted axially into the main shaft instead of acting radially on the tool. The radial cutting force may cause the tool to flex, which reduces the machining accuracy and shortens the tool life. However, one problem with plunge milling is that the tool is constantly moved into and out of the cavity as it is indexed to each new position.
Basic principle of large feed milling
Today, as more processing plants have high-speed CNC machining capabilities and sophisticated CAM programming techniques, high-feed milling (HFM) is becoming an alternative method of removing as much of the workpiece material as possible in the shortest amount of time. Large feed milling is primarily a roughing method developed to increase metal removal rates to increase productivity and reduce machining time. Large feed milling uses a small depth of cut (typically no more than 2 mm) to produce thinner chips that carry a large amount of cutting heat away from the cutting edge. The feed per tooth for high feed milling is typically up to 5 times that of conventional milling. This type of milling reduces the heat of cutting that can be generated, extending tool life and providing a higher metal removal rate – over 1,000 cm3 per minute, 1-2 times faster than conventional milling.
The reason for the large feed milling has these advantages is the use of a small mounting angle (45° or less) to minimize radial cutting forces and maximize axial cutting forces. Similar to plunge milling, the cutting force is transmitted axially into the machine tool spindle, reducing the risk of vibration and making the machining smoother. This, in turn, allows for greater cutting throughput even during large overhangs. Moreover, unlike plunge milling, the tool is always in a knife-feeding state during large feed milling.
Another reason why high feed milling can reduce machining time is to reduce the number of processes. Since the large feed roughing with a small depth of cut can produce a near-net shape close to the desired shape of the finished product, it is often possible to omit the semi-finishing process, thereby simplifying the numerical control programming. In addition, large feed milling does not require an increase in the speed of the machine.
Introduction to high feed milling
In order to achieve high feed milling, the user needs to evaluate the entire machining system. First, the machine is required to have high-speed CNC machining control functions, high spindle accuracy, and thermal stability to prevent spindle expansion. Second, the CAM software program is required to handle tool path smoothing strategies such as corner rounding and spiral cutting paths. The smooth tool path is machined by a snack knife, allowing the tool to gently cut the workpiece in layers, while the tool's helical feed motion reduces cutting impact, energy consumption and cutting forces.
In addition, the cutting inserts used in high feed milling are also critical. These blades have a thicker cutting point, a larger arc radius, and a higher geometric strength. This means that high cutting speeds can be used while still ensuring process reliability and safety. For most large feed milling, a triangular insert is preferred over a round insert because the main cutting force is at the bottom of the cutting edge. Of course, square blades are also available in some cases, but a smaller mounting angle is required. In general, when a large-power machine tool is used for high-feeding heavy-duty rough milling under stable cutting conditions, or when machining on a horizontal milling machine, a square blade is required, which makes chip removal more effective. However, the triangular insert is a safe choice when it is machined on a vertical milling machine or a machine with low power and high speed, and it has excellent chip evacuation capability.
Application of large feed milling
(1) Face milling
The large feed milling method is ideal for face milling (especially for high volume machining), which provides a good basis for subsequent or final finishing. In most large feed milling operations, very high dimensional accuracy is usually achieved, so that only final finishing is required. Since the machining involves a large workpiece blank, the most used is a large diameter milling cutter. This means that you need to use a tool with a tool holder and a triangular blade on the body. Large feed face milling is also very suitable for processing most soft materials.
The large feed milling method can be used for efficient milling of the cavity, especially for mold processing. The choice of tool and the determination of other cutting parameters depend mainly on the material being machined, the size and stiffness of the part being machined. The use of large feed milling is also very practical when profiling rough surfaces.
(2) helical interpolation milling
In helical interpolation milling, the large feed milling method is also a very suitable solution for machining large diameter holes – it can omit pre-machining or drilling pre-holes. The large feed milling cutter minimizes contact with the workpiece wall section. This has the advantage that the machining process of the large feed milling cutter is more stable than conventional milling cutters with a 90° mounting angle.
The large feed milling cutter can also be used for plunge milling. They are especially suitable for processing difficult-to-cut materials such as titanium alloys and other lightweight alloys. Large feed milling is also suitable for large overhang machining. It reduces vibration risk and extends tool life. However, square inserts should be avoided in machining where the tool overhang is greater than 3 times the diameter. However, plunge milling with a large feed milling cutter relies on a combination of a normal feed rate and a large depth of cut.
Although high-feed milling is not a versatile solution, it is a very good way to achieve high metal removal rates, take full advantage of today's machine tools and extend tool life.
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