Procedure 3 drilling and expanding Φ 20 holes1. Drill Φ 18mm holeMachine tool: z525 vertical drilling machineCutter: select high speed steel bit W18Cr4V according to table 10-61 of machining process manual(1) According to table 10-66 of cutting manual, when cast iron ≤ hb200, d = Φ 18, take F = 0.3mm/r