Machining Stainless Steel Pump Bodies

A fundamental change to the way stainless steel pump bodies are machined by subcontractor Metaltech Precision Engineers is resulting in far-reaching benefits. They include a drastic reduction in set-up time that lowers economical batch size by a factor of four, shorter lead-times, faster cycles, savings in the cost of tooling and less wear on the machine tool. Additional advantages of the new production route are reductions in power consumption and in space taken up on the shop floor. 

The pump bodies, of which there are eight types ranging in diameter from 160 to 280 mm with numerous different port details, are produced in batches of 50 to 60 to a monthly schedule that might include as many as 15 component variants. Sometimes orders were impossible to fulfil, and discussions had to take place regarding alterations to the schedule.

The traditional machining process takes 10 to 15 hours to set up. After skimming the back face of a 316 stainless steel casting, it involves roughing the same face on an HMC and then roughing the front face, bores and ports on the same machine. The part is transferred to a lathe to turn the port details using single-tip boring bars. It then returns to an HMC to re-skim either the front or back face to provide a location for mounting the part on a window fixture to finish-machine both faces. Production of a batch of 50 to 60 bodies takes four weeks by this method.

In contrast, set-up on the Spinner takes just one hour and the new process route is completed in two clampings, which means that 10- to 15-off can now be produced economically. In the first operation, roughing and finishing of the back face and the interpolated bores are carried out by respective 16 mm diameter, solid carbide end mills from MA Ford. 

A Schunk pneumatic zero-point fixturing system presents the part to the spindle for the second operation in a time that rivals the speed of an automatic pallet changer. A probe double-checks the datum and that the bores machined in the first operation are the correct size. Face mills complete the rough and finish machining on the front of the pump body. The savings offered by this method of production sees all 50 to 60 bodies completed in one week rather than four.
Using a waveform rough milling strategy with the 16 mm diameter cutter at high speeds and feeds, typically 2,700 rpm and 2,400 mm/min, rapid metal removal rates are achieved without unduly heating and stressing the part, helping to maintain accuracy. It is largely this lighter machining that allows the BT40 vertical-spindle machine to attain the same level of precision as a 50-taper HMC when cutting tough stainless steel.
Courtesy of Whitehouse Machine Tools Ltd.
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