Successful high-speed machining requires attention to tooling, spindle and machine dynamics. Advances in tool technology and machine control capabilities have made high-speed machining more widely used in the manufacture of aerospace components. Although high-speed machining technology is particularly suitable for the processing of aluminum alloys, it also has its place in the processing of composite materials and hard metal materials.
Competitive pressures are continually forcing manufacturers to machine parts in a more efficient manner. At the same time, aerospace structural parts manufacturers also need components with higher strength, lighter weight and tighter tolerance requirements. High-speed machining technology allows manufacturers to reduce cycle times while also producing parts that are more compact and thinner than ever.
According to Wayne Reilly, processing manager at Haas, many people are not rigorous in using the term high-speed machining. In Reilly's view, while some people think that any machine with a spindle speed of more than 10,000 rpm is processed at a high speed, others have a more complicated definition. He said, “It actually depends on the context in which the term is used. Tool manufacturers may define it as speed, and machine tool builders may define it as some look-ahead block in CNC systems. High-speed machining The trend in technology is to use faster cutting speeds, feed rates and lighter loads, while conventional machining typically uses low-speed cutting with heavy loads and deep cut depths.†For example, the vertical machining center from Haas (VMC) provides up to 30,000 rpm rated spindle speed and 30 hp (22.4 kW) drive system power for high speed machining.
Randy Von Moll, manager of aluminum processing platforms at MAG Cincinnati, said, “I don't like the term efficient machining in isolation from the spindle speed.†His definition includes the dynamic response of the machine in addition to the spindle speed. He used five parameters to define efficient machining: 1 spindle speed; 2 spindle power; 3 high feed rate and tool path rate; 4 high acceleration and deceleration; 5 high precision. The latter three conditions specifically define the dynamic response of the machine rather than the spindle characteristics. Von Moll said, "In order to cut alloy materials more efficiently (such as aluminum alloys), it is really necessary to combine high-performance spindles with the high dynamic response of the machine."
If the aerospace parts are divided into two categories: "thin plate parts" and "thick plate parts", he believes that high-speed machining can be defined as: for thin plates with a thickness of less than 50 mm, the spindle speed is 30000 rpm and the rated power is 80 hp ( 60kW); for thick plate parts with a thickness of 50mm or more, the spindle speed is 18000rpm and the rated power is 135 horsepower (100kW).
Von Moll explained, “The maximum dynamic response parameters of the machine tool are not much different when cutting thin plates and thick plates. For both workpieces, the acceleration/deceleration should be around 0.5g and should be provided as fast as possible. (non-cutting) reciprocating motion, at least 1500ipm (38m/min)."
When machining complex cavity-like workpieces, the acceleration/deceleration has a large influence on the cutting time because the tool must change direction several times during machining.
The reciprocating time of the machine will affect the cutting time, especially the auxiliary time (the auxiliary time can account for 20% of the total machining cycle time when cutting the aluminum alloy). The assist time includes the positioning time of the tool when cutting a new workpiece or the time the tool moves to the tool changer. According to lean manufacturing, assist time is a waste that needs to be eliminated. A few years ago, Cincinnati introduced the HyperMach vertical copy milling machine line that combines fast reciprocating movement with high acceleration/deceleration. The fast reciprocating speed of these machines is up to 4000ipm (101m/min), which is designed to shorten the auxiliary time. HyperMach's X, Y, and Z axis strokes are 33m, 3500mm, and 1250mm, respectively, and are equipped with additional A, B, or C axes. The spindle speed of the machine is up to 30,000 rpm. Most HyperMach vertical copy milling machines are in a common Two independent spindles are mounted on the X-axis gantry structure. In order to cope with the market demand for improving the processing efficiency of large workpieces (up to 2000mm × 4000mm), Cincinnati will exhibit and demonstrate the HyperMach horizontal series at IMTS 2008 (Chicago International Manufacturing Technology Exhibition 2008).
“Cutting small chips and processing them as quickly as possible†is the definition of high-speed machining by Makino's design engineer Alan Hollatz. He believes that the high speed, small depth of cut processing method can reduce the cutting heat into the workpiece or tool, and the cutting force of the workpiece and the machine tool is also small. Conventional low-speed, large-depth cutting methods tend to deform workpieces with wall thicknesses as thin as 0.030" (0.76 mm) in modern designs. Smaller cutting forces also mean lower workpiece clamping requirements.
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