This case covers the drilling and chamfering of copper end rings for submersible pump motor rotors. Each ring is 12 mm thick and requires 22 through-holes of Ø6.2 mm, followed by chamfering of the hole openings. SIPENG CNC adjusted the machine configuration and the tooling around the three difficulties of chip wrapping, workholding and flip-over positioning, focusing on making the process easier to control and more convenient to operate.
The Original Process and Its Bottlenecks
The customer originally machined the holes on a basic CNC drilling machine, locating and clamping each ring in a manual three-jaw chuck mounted on the machine's support plate.
To keep the drill from hitting the jaws after breaking through the workpiece, the jaws had to be machined with a step and additional clearance. During machining, copper chips tended to accumulate inside the chuck bore and the clamping area, which made cleaning and continuous operation harder. After every workpiece, the operator had to release the chuck, remove the part, load the next one and tighten the chuck again, with a lot of repetitive handling and physical strain.
Once drilling was finished, the workpiece had to be moved to a second machine for chamfering. The original method was to hold the part by hand at a bench drill press and chamfer all 22 holes one by one, which was laborious and left chamfer consistency to the operator.
The main difficulty in drilling copper is that the chips easily wrap around the drill. Feeding too fast causes poor chip evacuation and drill breakage, while feeding too slow extends the machining time. According to the customer's original production records, this method produced about 96 workpieces in 8 hours, with the Ø6.2 mm through-hole drilling as the most time-consuming step. The customer had tried drilling two holes at once, but scrap rates were high, so the follow-up solution was based on drilling one hole at a time, stably.
The New Setup: CNC Drilling and Tapping
To address these problems, we moved the process to a CNC drilling and tapping machine, bringing the hole positions, drilling cycles and chamfering moves into the CNC program, and arranged two operations with dedicated tooling.
Through-Spindle Coolant and the Drilling Cycle
The machine was configured with through-spindle coolant and matched with internal-coolant drills, so the cutting fluid reaches the drilling zone to assist cooling and chip evacuation. The drilling cycle uses staged feeding with retract-for-chip-clearance: 2 to 3 advances and matching retracts arranged from on-site trial cuts, then adjusted step by step according to the chip shape, drill load and hole condition. The feed rate and retract rhythm are finalized by trial cutting.
Pneumatic Workholding for the First Operation
The first operation uses a pneumatically clamped fixture, removing the repeated manual chuck tightening. The fixture leaves clearance around the workpiece support and the drill breakout points, so the drill never touches the clamping structure and there is room for copper chips to escape and be cleaned away.
Flip-Over Positioning and the Second Operation
After the first operation, the workpiece is flipped over and transferred to another machine. The second-operation fixture locates the part with a large locating pin engaging the center bore, and a small locating pin engaging one of the machined holes to fix the angular position, providing the datum for chamfering the openings on the other face.
With the flip-over location done, the CNC program completes the chamfering of the 22 hole openings on the second side in sequence, replacing manual hole-by-hole handling and making the chamfering process easier to control uniformly.
Fixture Commissioning and Adjustments
During implementation, the focus was on the clamping-area clearance and chip space, and on the fit between the locating pins and the workpiece holes. Pins too large make loading difficult, pins too small leave positioning clearance, so the pin dimensions were corrected against the actual hole sizes and trial assembly, until the workpiece could be loaded and removed smoothly while still meeting the positioning requirement.
Summary
The improvements in this case concentrate on four areas: through-coolant drilling, staged chip evacuation, pneumatic clamping and flip-over positioning. With the machine, program and tooling adjusted together, a drilling and chamfering process that relied on repetitive manual operation was turned into one that is easier to control and continuously optimize. Actual results should be evaluated with records of takt time, hole size, chamfer consistency and tool usage in continuous production.
