For details, please refer to the PDF file of the "Modern Parts" 2007 issue 5 or the bottom of the download page.
The first special shape crank circle processing
The crankshaft cross-section shapes of various diesel engine crankshafts are different, and have a full circle shape; there are multiple arc combinations (and the trajectory of each arc has a crank circle) shape; there is an elliptical shape; Multi-segment linear combination (and the trajectory of each arc does not accommodate the crank circle) shape and so on. The trajectory of each arc does not accommodate the crank circle. We call it a special shape crank circle. The machining methods of various shapes of crank circles are different, and the crank circle of the entire circular shape and the multi-section circular arc shape is relatively easy to process. It is difficult to process the crank circle with elliptical shape, multi-section arc and multi-segment linear combination shape. They have higher requirements on processing methods, processing equipment and tool selection.
Medical history:
Registered subjects: Difficulties in engine crankshaft treatment: The crank-circular cross-sectional shape on the crankshaft of a diesel engine is a multi-section arc and a multi-segment linear combination (and the trajectory of each arc cannot accommodate the crank circle).
Recommended doctors: Chen Chonghua of China South Locomotive Group Ziyang Locomotive Co., Ltd., German Lyles Machine Tool, Walter Tool Schematic:
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Difficult description:
China South Locomotive Group Ziyang Locomotive Co., Ltd. exports the crankshaft of a foreign company. The material is high-quality alloy steel, which is extruded by full fiber. The length is 4200mm, there are 16 crank circles distributed, the crank circle width is 68mm, and the crank shape is multi-section arc. Combined with multiple straight lines. This type of crankshaft has always been exclusively supplied by a well-known international company. Whether it can enter the international market, the processing of the crank circle is a key and a major difficulty.
Machine selection
According to the particularity of the crank circle, the German Laers N50 UC crankshaft turning and milling center is selected. This machine has functions such as turning, milling, drilling, boring and tapping. Can be completed in one setup: turning the crankshaft main journal and opening; three-axis linkage tracking milling crankshaft connecting rod neck and opening; three-axis linkage tracking milling elliptical, special shape crank circle and other processes. The CNC system of the machine tool is Siemens 840C.
Node coordinate calculation
P1 X2=(88.106+146.844)×2=φ469.9
Y2=-3.18
C1=0°
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Center distance between concentric arc and eccentric arc: 88.1062+3.182=88.163
In order to simplify the calculation of the coordinates of each point, CAD can be used to map, mark each intersection point, make the line of R146.844mm arc center O2 and cut point P2, and then make auxiliary line such as O1 point to O2P2 vertical line O1B, measure each node. Coordinate values, simplify the coordinate calculation, as shown in Figure 2. In the figure, X2, Y2, and C1 are machine tool extension (coordinate) axis names, the same below.
Processing method and steps
1. The first step (1) the tool to point P1.
(2) X2, Y2, C1 three-axis linkage clockwise milling arc to P2, milling R146.844mm arc surface.
(3) The Y2 axis moves forward through the planes of P2 and P3, as shown in Figure 3. (Note: The direction of the arrow in Figure 3 is the positive direction of each axis).
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Tool selection
In order to ensure the correct shape, choose a right-angle wide-blade cutter, according to the factory tool condition, choose Walter's 90° face milling cutter, the tool diameter is φ110mm. The blade has a peripheral blade width of 20 mm and a tip edge width of 12.5 mm. Since the blade end edge is 90° and the blade edge is wide, the cutting of the tool end edge is used to adjust the Y axis height to the proper position to ensure the correct shape of the machined part. Finishing Y-axis coordinate = ± (tool radius - about 0.9 times blade) Width, determined by the arc of the tool tip).
During milling, the three axes of the machine tool X2, Y2, C1 are linked, and the end edge of the blade tracks the path of the circular arc surface of the milling. The machining arc and the cutting edge are always in tangency, and the crank circle is processed into an ideal shape.
Processing program
The processing subroutine is as follows:
%SPF1234
(*****************************************)
N100 Z=R5 S400 M3 (Z-axis position)
N105 Y2=-23.18-R1 (the first step of processing below)
N110 C1=R2 (C to P1 R2 = angle of crank circle distribution)
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The main program is relatively simple. Since the shape of the 16 crank circles of a crankshaft is the same, only the angle and position of each crank circle are different, so in the program, just give the R1 of each crank circle (the distance from the center of the milling spindle to the cutting point, The subroutine can be called after the value of Y2 direction, R2 (angle of the crank circle), and R5 (Z axis position).
When roughing, the amount of backing knife is large, and the machining uses the cutting edge of the tool and the peripheral edge to cut the part to reduce the force of the tool. R1=the tool radius is 55mm. In the finishing process, to ensure the shape and precision of the part, use the edge part of the tool. Cutting, R1=55-12=43mm.
Solution Comments:
The machining of the special shape crank circle utilizes the characteristics of the CNC three-axis linkage machining rotary non-contained surface parts in the turning and milling center, which not only overcomes the difficulty of horizontal machine tool processing, but also makes the non-compensated surface smooth transition, node accurate and shape. And precision and other requirements have achieved the desired processing results. China South Locomotive Group Ziyang Locomotive Co., Ltd. has processed hundreds of crankshafts with this scheme. The shape and precision of the crank circle have reached the design requirements of the drawings.
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