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Milling cutters cut cycle time.

Smith International Diamond Products Div, Houston, TX, services down-hole drilling companies. It produces polycrystalline diamond (PDC) bits for oil-well drilling at depths usually below 1000 ft. When customers order a new bit, Smith must be able to deliver in 24 hr or less at a competitive price. An improved milling cutter helps the firm meet machining deadlines.

According to Nick Nichols, manufacturing manager, one of the three types of bits Smith makes is a PDC head bit, in the 7 7/8" to 17 1/2" diameter range. The bits start out as forged 4130 steel turnings machined on NC lathes. Each bit is chucked for rough turning the OD and boring and threading the ID. Then the bit is fixtured on one of two 5-axis Okamoto HMC 3000 horizontal machining centers.

Because cycle time on the machining centers was too long, Rich Borremans, senior manufacturing engineer, programmed a faster way to machine the bits. He followed the Carboloy recommendation of maintaining a constant chip load (chip thickness) per insert.

"I knew that if we met the chip-thickness recommendations for these coated inserts, we could greatly increase feed and even depth of cut, requiring fewer passes and reducing machining time," Mr Borremans says.

On-site training

To help end-user personnel fully understand the new milling-cutter capabilities, Dave Riley, a Carboloy milling specialist, conducted on-site training programs to review the parameters of the tooling and explain the principles of constant chip thickness. From these programs, Mr Borremans and Lead Man Mike johnson learned enough about the cutters to optimize their own operations.

Machining of the bit includes face milling with a 220.69 turbo milling cutter at 3/8" depth of cut (DOC) and 17.25 ipm feed, following rough turning. Then, the machining center proceeds with five-axis work using a 217.69 turbo milling cutter and 1" slotting cutters, with feeds of 12.25 and 13.75 ipm (compared to 6 to 7 ipm previously).

The slotting cutters are followed by Carboloy's 218.19 ball-nose milling cutters that contour the so-called "junk slots" that permit cuttings removal.

Contour routine

To contour the slots in these bits, Smith had programmed a subroutine with its previous tooling that took 21/2 to 3 hr to complete. The previous ball-nose end mill used inserts with only two available corners and was incapable of plunging and milling in the same tool path. Cycle time was high because of the relatively low feedrate possible and because continuous tool paths had to be avoided.

When the firm changed to Carboloy Seco inserts for the turbo mills on the horizontal machining centers to mill the slots, engineers could set feedrate 40% higher. The 218.19 ballnose milling cutters granted more indexes per insert, plus the ability to optimize tool paths without the cutter leaving the workpiece.

Mr Nichols adds, "Our economies in milling operations-hogging off all that steel-primarily came from the new tools' greater DOCs and heavier feeds than allowed by the cutters we had been using.

"We run Carboloy 218.19 ball-nose cutters at 18 and 20 ipm feed, compared to a maximum of 10 to 12 ipm for the old cutter-limited by severe vibration above that feedrate."

In all, Smith uses eight different Carboloy milling cutters on the machining center to complete the PDC bits. The performance advantage and the geometry of the cutters has allowed Smith to cut cycle time per bit an average of 30%, and has permitted engineers and programmers to improve bit design and reduce the cost to manufacture the bits.
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Title Annotation:oil well drilling bits
Publication:Tooling & Production
Date:Jun 1, 1991
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