From rough to refined

July 1, 2002
Vertical-spindle, rotary-table grinders move into the precision class of machines.

Vertical-spindle, rotary-table grinders move into the precision class of machines.

The PDG Punch and Die Grinder, the IG 180 M, and the IG 280 CNC, all from DCM Tech. Inc., showcase the latest machine innovations for vertical-spindle rotary-table surface grinding.

A PDG vertical-spindle rotary-table surface grinder at Metcam replaced a manual surface grinder for sharpening the shop's punches and dies.

Advent Tool and Manufacturing's IG 280 CNC grinder sports a Mitsubishi C-5 programmable CNC.

A DCM IG 180 M grinder meets Elna Magnetics' demands of finish, accuracy, flatness, and parallelism for ferrite parts.

Most people perceive vertical-spindle, rotary-table surface grinders as dirty machines that quickly rough or hog off large amounts of stock to prepare workpieces for finer secondary operations. That perception has been around since the grinders were introduced, mainly because early models weren't all that accurate and smooth feeding. However, modern features such as servo-driven automatic downfeeding, high-speed spindles, CNC, and integral mist collection along with coolant filtration are earning this grinder a reputation for being a clean precision piece of equipment.

Vertical-spindle, rotary-table grinders from DCM Tech. in Winona, Minn., as an example, hold tolerances to 0.0001 in. in flatness, parallelism, and thickness, while providing surface finishes as good as 6 µin. Integral mist collection and coolant filtration, standard features on most of DCM's grinders, provide shop cleanliness and operator well-being. And because of these integral systems, repositioning the machines on the shop floor does not require replumbing.

All the company's grinders have automatic-feed controls that step wheels down incrementally at a rate of 0 to 0.020 ipm. This consistent, non-manual feed is especially beneficial to shops such as Metcam in Alpharetta, Ga.

The custom-sheet-metal fabricator typically sharpened its small punches and dies on a manual surface grinder and had to farm out its larger tooling. Sharpening manually meant an operator stood at the machine and ran the table back and forth. "Recommended wheel-feed increments were about 0.0005 in., but operators took heavier cuts to get the laborious job over with quickly," says company Vice President Jerry Ward.

Feeding wheels at the proper rate is critical at Metcam because removing too much material in one pass heats the tool, turning it blue and compromising its surface integrity. With its DCM Model PDG Punch and Die Grinder, the shop now predetermines stock-removal rates, and the machine automatically feeds for unattended operation. Its electronic load sensing and dwell cycle keep the wheel from feeding too fast. If it does, the machine backs the wheel off and slows down the feed. "It's impossible to take off too much stock in one pass on the PDG," says Ward.

High-speed spindles
According to Mike Anderson, industrial product manager at DCM, variable-speed spindles on today's vertical-spindle, rotary-table surface grinders provide enough speed to run both conventional and superabrasive wheels. The company uses variable-speed spindle motors on its IG 180 and IG 280 grinders.

The 180 M has a 10-hp spindle for speeds from 1,600 to 3,600 rpm, while the 20-hp 280 delivers speeds from 600 to 2,700 rpm. The PDG, on the other hand, has a fixed-speed 5-hp motor and turns at 3,600 rpm — fast enough for Metcam to run CBN wheels. "By running CBN, we do more parts with fewer wheels," says Ward. "We go through about four wheels in a two-year period." mended

At Elna Magnetics in Woodstock, N.Y., diamond wheels on its four IG 180 M grinders are a must because the shop modifies or creates ferrite parts. Ferrite is a ceramic/magnetic material used in the electronics industry for such products as computers, radios, and TVs. "This material is brittle and prone to chipping and cracking," says Ed Lasagni, custom and facilities supervisor at Elna. "The best way to machine it is with diamond tooling and flood coolant."

"We grind parts measuring from 1 /4 to 15 in. that usually mate to other components," comments Joe Volpe, quality-assurance manager at Elna, "so tolerances, along with finishes, flatness, and parallelism, are important." The 180 Ms hold tolerances to 0.0005 in., create surface finishes of 16 µin., and maintain a 0.0004-in. thickness variation over a 4 3 in. block of material, adds Lasagni.

Elna creates the final part finishes on its DCM grinders. Operators set up the machines, and wheels feed down, removing stock quickly without returning to finish grind.

For loading/unloading, DCM machine wheelheads swing clear of the machine table, as with Elna's and Metcam's grinders. Or, as is the case with the IG 280, they ride on a powered cross slide, which provides servo-controlled spindle positioning.

DCM locates X slide ways, along with other components, above and clear of the workzone. This prevents premature wear from grinding swarf and coolant. In addition, the DCM machines feature through-spindle coolant that keeps wheels clean during grinding and improves superabrasive-wheel performance. The Elna machines also have special shielding, modified by DCM, to protect vital machine components from invasive ferrite particles.

Advent Tool and Manufacturing in Lake Bluff, Ill., grinds carbide inserts on a DCM IG 280 CNC. The 280 CNC, according to DCM's Anderson, provides the most automation a shop can have in a vertical-spindle, rotary-table surface grinder. It sports a Mitsubishi C-5 programmable CNC with flat-panel display and digital readout resolution of 0.0001 in. The CNC controls closed-loop servomotor positioning of the Y and Z axes and lets Advent program spindle and chuck speed along with motor load and feedrates. Controlled feed is from 0.0001 to 125 ipm.

Advent also benefits from CNC because it commands fixturing to grab and release parts. In addition, the shop compensates for wheel wear within the part program and adjusts for different table and spindle-speed parameters. By varying these parameters, Advent can first rough-grind a part at certain speeds and feeds and then finish grind at different ones.

"A lot of parts previously done on surface grinders are now ground on vertical-spindle, rotary-table grinders," says Anderson. "Vertical-spindle rotary-surface grinding is just as accurate as and at least 5 faster than conventional surface grinding. The machines grind much faster because of the rotary action, which removes stock from an entire part face with each pass under the wheel." But more importantly, he adds, this grinding motion, together with the machines' tables, let shops grind multiple parts in one setup.

DCM tables do not position in and out under the wheel. This, according to Anderson, eliminates ways under the table that can collect grinding swarf and eventually wear, creating an unparallel orientation to the wheel. DCM tables, instead, reference the cast base for extremely stable grinding conditions.

Standard table size for the three DCM grinders is 18 in., but the IG 280 offers an optional 24-in. table. Styles are electromagnetic or flat T-slot and can include a through hole for hydraulic, vacuum, or pneumatic lines to power different workholding fixtures for non-magnetic parts.

Elna uses all 18 in. of table space on each of its four DCMs and, according to Lasagni, no longer has to farm work out because of part size. "We did smaller parts on a conventional surface grinder, but for larger ones, we were unable to hold tolerance across the entire part. As a result, we turned down jobs because we lacked capacity."

Metcam, on the other hand, doesn't usually run multiple parts on its PDG. Instead, the machine is fixtured for various types of punches and dies. For example, the shop has a 3-jaw chuck as well as a permanent-magnet chuck, which is interchangeable for square or rectangular tooling. The 3-jaw chuck holds mostly round punches and dies. "It sits on a sine-plate-type fixture that lets us quickly set up and grind special punch-end geometries such as shear angles and roof tops," says Ward.