Grinding out nonproductive time

Grinding out nonproductive time

Quick setups and superior accuracy make for a fast grinder.

Quick setups and superior accuracy make for a fast grinder.

By Charles Bates
senior editor

The Jung J 630-D's profile-dressing system dresses and resharpens wheels without interrupting the grinding operation.

Once grinding-wheel geometry is correct, Intralox measures once and cuts right to dimension on its J 630-D grinder.

According to Shane Jackson, lead moldmaker at Intralox, the Jung J 630-D is fast, but its real speed comes from setting up fast and shortening measuring time.

Having a grinder that removes material fast is great. But according to one mold shop, the key to real grinding speed is setting up the machine quickly and spending less time measuring parts.

Intralox Mold Shop of New Orleans has a Jung J 630-D surface and profile grinder that saves the company as much as 50% on overall production time for mold cavities. "It's not that the Jung grinds any faster," says Shane Jackson, lead moldmaker at Intralox. "Its real competitive benefits are in setup and measuring time."

To speed job setups, the machine's CNC profile-dressing system dresses and resharpens wheels without interrupting the grinding operation. It does so using a horizontally or vertically configured multiple-diamond-head unit or a diamond roller, both of which articulate around the grinding wheel to dress the profile. This system, according to Reinhard Koppen, manager of surface and profile grinding applications at United Grinding Technologies, Miamisburg, Ohio, enables the machine to run unmanned for full shifts.

While J 630- Ds are available with dressing heads holding six or eight diamond stations, Intralox's dresser has four. During grinding, the unit rotates through each one — a rough diamond, a semirough diamond, finish diamond, and an idle diamond. The idle diamond takes a zero pass through the whole form to remove flat spots possibly left by the three previous passes.

With this dressing system, shops like Intralox also have more control over diamond wear. If a section of a diamond wears, the shop changes the angle where the diamond and wheel intersect, thus avoiding the worn section and using more of the diamond.

" Our previous CNC machine," says Jackson, " could do just about everything we wanted, but there were some limitations.The diamond dressers were stationary, which meant the machine had to travel X, Y, and Z to dress the wheel. This created flat spots from where the parts of the diamond surface were worn. When this occurred, machine operators tried to compensate, but the adjustments weren't accurate enough."

Another advantage of the J 630-D's dressing system is that it lets Intralox quickly program complex wheel profiles without using CNC codes. Before the Jung machine, Jackson drew all wheel geometries, posted them through Mastercam, and then downloaded them to the machine.

"Now, we simply plug in a DXF file from the designer into the J 630- D, which runs the wheel profile from that file," remarks Jackson. There's no need for built-in macros or a catalogue of shapes, like on other machines.

To further facilitate quick setup, the Jung has a resident wheel library for "remembering" wheel shapes. "You take the wheel off and store it, but the wheel information stays in the machine's library. Then, when we put the wheel back on, operators type in a library number, and the machine knows the shape and the last time it was used," explains Jackson. This feature also provides Intralox with the flexibility to interrupt a job, run a new one or several others, and return to the original job without complicated reprogramming or setup issues — even if months have passed between jobs.

Typically in moldmaking, shops grind a small amount off a part and then measure. Then they'll grind some more and measure again. According to Jackson, as a shop gets closer to final dimensions, it's spending more time measuring than grinding. "With the Jung," he says, "once the wheel geometry is correct, you measure once and cut straight to dimension."

Intralox uses its J 630-D for its most critical work in tough materials with extremely tight tolerances and requiring superior surfaces finishes. One such job involves special corepin slots 0.2000-in. deep, 0.4000-in. wide, and 12-in. long in a cavity block that's 12 in. 2 and 2-in. thick.

Usually block material is 420 stainless or Elmax, a powdermetal, high-vanadium version of 420 that's comparable to D2 and one of the most difficult materials to grind. Hardness for 420 is generally 50 to 52 Rc, and for Elmax it is 58 to 62 Rc.

Once the cavity block is squared up, Jackson loads the wheel geometry, radii and angles, wheel manufacturer, type, grit size, and other related information into the J 630-D's library and dresses the form. After this, he qualifies the form by grinding it into a piece of graphite, which he then inspects using conventional methods such as comparators, indicators, or a Zeiss CMM. Generally, the shop holds forms to within ±0.0002 in.

"Once the graphite checks out, I know the wheel geometry is fine," comments Jackson. "I'll then touch on either side of the block, find center, calculate my locations — typically programming to location and depth — and then run the part. It comes off right on size without running any test work."

With other grinders and dressing systems, Intralox was unable to quickly set up and run a part on the first pass. To do so meant having to grind to a certain depth, remove the part, and check it before grinding further.

Keeping molds in house

As one of three companies under Laitram LLC, Intralox Inc. is said to be the inventor of modular plastic-conveyor belts. With more than 400 combinations of belt styles, materials, and colors to offer, the company's in-house mold shop runs at full capacity.

The Intralox Mold Shop employs 29 skilled moldmakers and repair technicians using five milling machines, three sinker and two wire EDMs, and nine surface grinders — one of which is the Jung J 630-D.

According to Jules Ceccanti, mold shop manager, the shop started as a mold-repair facility. As the repair activity increased, the company decided to build mold cavities. As that business flourished, the shop invested in new technology and is now the predominant supplier of plastic injection-mold tooling to its parent company.

Having its own mold shop gives Intralox a competitive advantage of time-to-market. The company also gains the confidence that comes from complete process control and consistent product quality as well as being able to retain sensitive, proprietary mold information.

"If Intralox sourced out its mold work," says Ceccanti, "it would be faced with 18 to 20-week leadtimes. The Mold Shop, however, can complete a mold and be producing good parts in six weeks, if need be."

The shop outsources some mold work, but a few jobs have proven too tough for others to tackle. "We used to bid out a couple of parts that we now do efficiently on the Jung," says Ceccanti. "These parts are complicated, highly detailed, time-consuming, and close toleranced. Some shops refused to quote, while others bid high because they were either unsure if they could even make the part or unsure whether they would profit from the job." According to Ceccanti, for two such parts, Intralox got bids of $1,750/part. On the Jung, the shop does them for $400 each.

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