Machining shaft splines presents special problems because the required form tools substantially increase cutting forces. With their larger contact area at the cutting edge, form tools are definitely not single-point tools and when the job involves splines at both ends of the same shaft, the problems double up.
Although Hudson Machine and Tool (Hammond, WI) regularly delivered in-spec pieces for a repeat double-end splining job, tooling costs were eating them alive. “The form-ground carbide tips cost us about $300 each and lasted just four pieces on average,” said shop foreman Scott Shaver. “In addition, every tip replacement required its own touch-off. It really slowed us down.”
A secondary problem was the difficulty of holding tolerances due to cutter wear. “It required full operator attention,” said Shaver. “Since it was a repeat job, we had to find a better way.” The answer was found in retooling. Now the company is getting 14 pieces per tip, costing about $100 each, which together saves about $65 per part in tooling costs alone.
The retooling also cut cycle time by about two-thirds to 30 minutes per complete part versus 90 minutes before, and eliminated all the downtime for touching-off. “We were satisfied with the tooling cost saving alone. As a result, with the time savings and freed-up machine capacity, we have an opportunity to go after more work,” Shaver said.
Hudson, a 30-man job shop, has established a reputation for quality machined parts that go into food processing, packaging and in-line weighing machinery, and special-purpose vehicles. It runs 24/5.
The tool that made the difference was a Chip-Surfer indexable milling tool from Ingersoll Cutting Tools (Rockford, IL) with custom replaceable tips matched to the spline profile.
Finding the right tooling solution started with a regular visit by Hudson’s distributor, Randy Paape of Blackhawk Industrial, last fall while the job was running. Besides the poor tip life, Shaver mentioned that some tips fractured suddenly due to chatter and the machined surface had a poor finish.
Paape brought in Ingersoll field engineer Bryan Winterlin because of the company’s track record in slotting and grooving. Both men knew that Ingersoll’s Chip-Surfer line of indexable milling tools had improved scores of grooving, slotting, and precision worm-gear jobs in North American shops.
The Hudson job involves cutting 21 four-inch splines into each end of a 2¾ × 40” (70 × 1016-mm) shaft in hardened 4140 steel. The shafts are used in auxiliary equipment in specialized airport vehicles. Total length of cut per part: 320” (8 m). In addition to standard tolerances, the print required 0.005” (0.13-mm) alignment between opposing splines. Lot sizes average 50 pieces and are rising.
Hudson machines the splines to a 0.155” (3.9-mm) depth in a “cut and flip” cycle on a V-Tech bridge mill equipped with an indexer and water-based coolant. Depth of cut is 0.150” (3.8 mm), usually reached in two passes per groove. They check dimension with a ring gage after each end is finished. If oversize, which happened more than occasionally with the old cutter, they run another pass over that entire end.
The recommended Chip-Surfer indexable mill features a husky tool steel shank with replaceable custom form-ground tips to match the profile of the spline groove. The larger shank added the rigidity needed for form milling. All tips can be swapped out in seconds, right in the spindle, and with a 0.0005” (0.013-mm) repeatability that eliminates the need for touching off with every replacement.
The shank is standard; only the tips are custom. “This way, there is none of the supply-chain baggage associated with pure specials,” Winterlin said. “New tips are available within six weeks, and Blackhawk can maintain a stock locally.” He added that Ingersoll regularly makes custom Chip-Surfer tips for dozens of applications.
“We simply took their recommendation,” said Scott Shaver. “In a small job shop like ours, we don’t have the time or resources to test everything that’s out there to optimize every job. It’s good when tooling reps visit us often enough to see what’s actually running and suggest improvements on the spot.” Randy drops in about once a week and Bryan visits as needed.
When the trial tool arrived, Paape and Winterlin oversaw the conversion, startup, optimization, and operator training. Since longer tool life was the priority, they started with the previous parameters: 640 rpm, 0.004” (0.10-mm) feed per tooth, 0.180” (4.5-mm) DOC. Under those conditions, the first tip lasted through 14 complete pieces. The job ran noticeably more quietly as well, and the finished parts all came off in-spec with only two passes.
They pushed the tool to 16 pieces and saw some edge breakdown, so they reverted to 14 to keep the operation secure. The trials also pointed to tool servicing savings since tips could be replaced without removing the tool from the spindle. Then Bryan Winterlin ramped up to the parameters: 1000 rpm, 0.012” (0.30-mm) feed per tooth at the same depth. This reduced cycle time by 3 to 1 with no loss of edge life or as-machined part quality.
Hudson standardized on those parameters and the 14-piece limit between tip changes. There hasn’t been a tool rupture or out-of-spec workpiece since, and the only failure mechanism is gradual flank wear. Winterlin said the key to the debottlenecking was the Chip-Surfer’s combination of heavier tool shank, free-machining geometry and coatings on the tip, as well as the quick, repeatable in-spindle tip change.
For further information about Ingersoll Cutting Tools, go to www.ingersoll-imc.com , or phone 815-387-6600.