Info

Cutting Speed (sfm)

Fig. 2.27. Cutting Force vs. Cutting Speed for Aluminum

Then

This is a fairly respectable and easily achievable metal removal rate using conventional machining parameters for aluminum. However, with the advent of high speed machining of aluminum, even higher metal removal rates are obtainable. It should be emphasized that while higher metal removal rates are good, another driver for developing high speed machining of aluminum is the ability to machine extremely thin walls and webs. For example, the minimum machining gage for conventional machining might be 0.060-0.080 in. or higher without excessive warpage, while with high speed machining, wall thicknesses as thin as 0.020-0.030 in. without distortion are readily achievable. This allows the design of weight competitive high speed machined "assemblies" in which sheet metal parts that were formally assembled with mechanical fasteners can now be machined from a single or several blocks of aluminum plate. For example, as shown in Fig. 2.28, an avionics rack that originally consisted of 44 formed sheet metal parts was replaced by a single high speed machined part and five other pieces, resulting in a 73% cost reduction. The final shelf weighs 8.5 lb, needs only five tools, and takes only 38.6 h of manufacturing time, as opposed to the original built-up design that weighed 9.5 lb, required 53 individual tools, and took 1028 h to manufacture.20

Successful high speed machining requires an integrated approach between the cutter, workpiece, machine tool, and cutting strategy. For example, step cutting, as shown in Fig. 2.29, uses the workpiece to help provide rigidity during the machining process. For thin ribs (i.e., side cutting), this means using a large

Sheet Metal Assembly

Sheet Metal Assembly

Number of Pieces 44

Number of Tools 53

Design and Fabrication h (Tools) 965

Fabrication h 13.0

Assembly Manhours 50

Number of Pieces 44

Number of Tools 53

Design and Fabrication h (Tools) 965

Fabrication h 13.0

Assembly Manhours 50

High Speed Machined

High Speed Machined

Number of Pieces 6

Number of Tools 5

Design and Fabrication h (Tools) 30

Fabrication h 8.6

Assembly Manhours 5.3

Number of Pieces 6

Number of Tools 5

Design and Fabrication h (Tools) 30

Fabrication h 8.6

Assembly Manhours 5.3

Fig. 2.28. Comparison between Assembled and High Speed Machined Avionics Rack

Source: The Boeing Company

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