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Crankshaft flange center hole machining tool optimization

1 crankshaft center hole of the process requirements and problems
The center hole of the crankshaft is the process reference of the process design, and also the reference of the post-processing and crankshaft positioning. The quality of the center hole directly affects the product quality of the crankshaft. Therefore, the precision of the center hole is relatively high. EB2DT (S) crankshaft 1.2T turbocharged engine is one of the major components, crankshaft material 38MnSiV5, hardness 255-302HB, crankshaft flange center hole vibration problems seriously affect the production efficiency.
The original processing technology for the combination of twist drill and cone reamer, that is, first with twist drill Φ15.4mm straight hole, and then cone reamer 60 ° and 120 ° tapered hole, the center hole 60 ° cone is the basis of the processing sequence Positioning benchmarks, test benchmarks. Processing equipment is Germany Schenk processing center, processing crankshaft does not turn, tool rotation. Crankshafts machined out in this way show a chatter in the center hole (see Figure 1) and do not meet the roundness requirement of 0.02 mm.

Figure 1 center hole vibration

2 process optimization
Through the analysis of the processing technology, found that the selection of technology and tools unreasonable: ① processing bottom hole twist drills improperly to the rear reaming to bring more margin, especially the 60 ° cone surface margin is too large; ② hinge Center hole, the cutting allowance is large, centering is not good, resulting in vibration and vibration when cutting vibration; ③ hinge 60 ° taper cutting parameters: speed 950t / min, feed per revolution 0.4mm / t; ④ hinge 120 ° Conical cutting parameters: speed 320t / min, feed per revolution 0.3mm / t.
The tool and process optimization and improvement: ① the processing of the bottom hole Φ15.4mm twist drill to Φ15.4mm step drill, the shank from Φ16mm to Φ25mm, when processing the bottom hole, increased rigidity, while the 60 ° Cone processing to only 0.5mm margin. ② Reaming the center hole of the reamer reamer with a self-centering of the center hole reamer, on the one hand because of the taper reaming margin less, on the other hand because of the reaming cone in front of reaming straight hole, Can play an effective anti-vibration effect, straight hole from Φ15.4mm hinge to Φ15.7mm, for the hole after the processing to Φ16mm reduce the machining allowance. ③ optimize the tool at the same time, the processing center hole optimization process (see Figure 2).




 (b) after optimization
Figure 2 Optimization of the center hole processing schematic
3 effect verification
Through the above process improvement, eliminate the vibration, the center hole roundness qualified, are within 0.02mm, to solve the quality problems of the crankshaft. In the tool optimization process, change the tool structure, twist drill thicker. At the same time, through the localization of the tool, the tool price is reduced, the tool life is increased, and the product cost is reduced.

From: Tool Technology