Avoiding the daily grind: Cutting hard metals
- February 16, 2016
The Problem: Achieving satisfactory tool life when machining 55-62 HRC steel alloys
The Solution: CBN-tipped turning, profiling, and grooving inserts
Alberta shop overcomes hardened steel machining challenges
In the Coronet Industrial area on the south side of Edmonton, just a few blocks from the junction of the Canadian Pacific and CN Railways, sits Alberta Production Machining Ltd. (APM). The company was founded in 1974 by Hermann Ergezinger, and got its start producing high volume fittings and fasteners on mechanically driven Traub TB-series screw machines.
Ergezinger is still there, but the screw machines have since been replaced by Gildemeister GS 20-6 multi-spindle automatics, cranking out parts by the millions for the furniture and automotive industries. That’s not the only change to the equipment lineup though—the company has also invested in Zeiss measuring machines, Kasto bandsaws, and turn-mill equipment from DMG MORI, including CTV vertical pickup lathes and DMG MORI (Gildemeister) Twin/CTX TC4A, twin-spindle, twin-turret, Y axis turn-mill centres, capable of barfeeding to 160 mm (4 in.) and turning sawed blanks up to 500 mm (20 in.) in diameter.
The company is also in the midst of moving to a new and larger 1,486 sq m (16,000 sq ft) facility to accommodate its growing business.
The leap in machine tool technology has enabled the 18-employee, ISO 9001-certified company to become an area leader in complex, high precision component machining and assembly. Aside from its legacy customer base, APM has expanded into oil and gas, and does a large percentage of hard part turning (HPT). These include rings and disks made from 4140, E52100, 8620, 440C and other steel alloys that have been hardened to 55-62 HRc., work that many shops would either no-quote or subcontract to a grinding house.
Hard turning challenges
“Hard turning is a significant part of our business,” says general manager Bernd Hornauer. The hard part about hard turning, he explains, isn’t so much the material as it is the tolerances. APM routinely meets IT6 and even IT5 requirements according to ISO 286 T1. “We’re doing a 152 mm (6 in.) part right now and holding 18 microns (0.0007 in.) on the diameter,” says Hornauer. “It’s pretty outstanding, especially when you’re talking about steel hardened to 60 Rockwell.”
He says the part is rough machined to within 0.25 to 0.50 mm (0.010 - 0.020 in.) of final part size, heat treated, and then finish machined all over in a single operation on one of APM’s turn-mill centres. After trying several competing brands of carbide and CBN with less than stellar results, Hornauer approached Patrick Ashcroft, technical sales representative at Iscar Tools Inc., Oakville, ON. Ashcroft suggested an uncoated IB55 cubic boron nitride (CBN) insert, which is a brazed tip, “general purpose” grade designed for hardened ferrous alloys and cast irons from 45 to 65 HRc.
Of course, successful hard turning takes far more than a robust cutting tool. Iscar recommends a rigid and thermally stable machine tool, something that Hornauer and his team already had with their Gildemeister and DMG MORI machines. The tooling manufacturer also recommends that parts be machined prior to heat treatment as accurately and consistently as possible. Sharp corners and burrs should be eliminated with a small radius or chamfer, and the cutting tool should enter and exit the workpiece smoothly with no abrupt movements.
According to Iscar, hard part turning (HPT) is an inherently “green” process. No cutting fluids are used, and since secondary grinding operations are eliminated, less energy is consumed overall. Best of all, HPT also reduces machining costs, something that Hornauer can attest to.
“We’ve found that hard turning is approximately 20 to 40 per cent more cost effective than grinding. It also speeds delivery to the customer, since we don’t need additional operations for grinding. We can usually machine all of the part features in a single operation—outer and inner sealing surfaces, grooves, everything—after heat treat. The trick to part quality is getting them off the machine in one shot.”
This approach is a large part of APM’s success in meeting tight tolerances. Part handling is minimized, making it less challenging to achieve geometric accuracy. That’s not to say it’s a cakewalk. “Achieving IT5 is very difficult,” Hornauer says. “The way in which you clamp the part is just as important, if not more so, than the machining itself. For that, we’ve developed a proprietary workholding system, which grips parts in a way that’s nearly distortion free.”
As a result, APM enjoys good parts, high productivity, and consistent tool life, in spite of the material hardness. In fact, most of the CBN inserts can be expected to last an entire eight-hour shift. Says Hornauer, “they’re not inexpensive, and cost between six to ten times a normal insert, but the CBN inserts from Iscar are well worth the price.”
Addressing the skilled trades gap
Tool life aside, one of the biggest challenges faced by APM is finding skilled people. The complexity of the company’s multi-tasking machine tools, together with fierce wage competition from Alberta’s historically robust economy, has led the company to automate wherever possible.
One example of this is the use of DMG MORI CTV vertical pickup turn-mill lathes equipped with workpiece transport belts, something Hornauer refers to as “barfeeders for chuck work.” These eliminate the need for an operator to perform the mundane task of part loading and unloading, and make machine output more predictable.
“Besides our traditional business, production of harden ring and disc style parts is our strongest growing sector. Especially products with 50 mm (2 in.) in diameter, and batch quantities in the 200 to 400 piece range,” Hornauer says. “Even at these low quantities, we see a lot of benefit with automation.”
Hornauer is rightfully proud of APM and its capabilities. The 42-year old company has changed with the times, evolving from simple screw machine work to complex, difficult-to-machine components and materials. By embracing the cutting tools and equipment technology needed for efficient hard turning, Hornauer and the APM team have separated themselves from the pale, in turn carving a niche that is sure to keep the company healthy for the long haul. SMT