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Quick mold changing; you can keep it simple.

You don't have to spend a lot of money to speed mold changes. In fact, some of the most important aspects of QMC don't cost anything at all.

A decade ago, automatic quick-mold-change (QMC) systems looked like the wave of the future. Driven by JIT schedules and competitive pressures for productivity enhancement, modern molders would need to install fancy systems that could shuttle molds in and out of a machine at the touch of a button. Yet the more elaborate QMC systems did not become runaway bestsellers. Suppliers say the sole market for high-end QMC has been a small group of big molders that supply the automotive or appliance industries. What happened to QMC for everyone else - the smaller custom molders and proprietary shops? Voting with their wallets, the majority of these molders have opted to stick with traditional setup methods rather than invest in sophisticated QMC hardware.

There is, however, a middle ground between high-end QMC and no QMC. A fair number of molders make good use of the simple, inexpensive, manually operated QMC approaches available from a handful of suppliers. And some molders have implemented quicker mold changes without buying any special hardware at all. Their savings came from organizing their shop procedures to make mold changes more efficient. Without such organized procedures, even the fanciest QMC system won't end up saving you any time or money.

PLAIN OR FANCY?

Automatic QMC systems can be expensive, costing between $12,000 and $40,000 for the machine and tooling modifications required on a single 75-ton press (see box, p. 55). Other systems are built around relatively simple QMC products whose costs have fallen well below $5000/press on sizes up to 500 tons. But even the inexpensive manual types run into a common obstacle: While QMC systems work best in conjunction with some degree of tooling standardization, many custom molders work with a confusing jumble of mold sizes and shapes - whatever their customers send them. "Custom molders don't want to spend money modifying molds that they don't even own," notes Roger Martin, president of quick-change tooling supplier Master Unit Die.

Still, QMC systems do have a simple benefit for any molder: Faster tooling changes add up to higher profits in today's short-run environment. Users of manually operated, mechanical-type QMC systems report attachment times - or the time it takes to affix a mold to a platen - of under 30 sec. And the hydromechanical-clamp versions take only a couple of minutes to deploy. Unit-base systems, where you simply swap cavity inserts or plates, take only minutes as well.

HYDROMECHANICAL SYSTEMS

The low end of the price spectrum is occupied in part by hydromechanical clamping systems from American Aerostar and a more recent entrant, Pacesetter Inc. Both systems use hydraulically actuated, mechanically locked clamps to attach molds to special platen-mounted plates (see PT, Feb. '95, p. 22). While the hydraulic pressure temporarily secures the mold, a manual thumbscrew mechanically locks the clamp in the closed position so that the hydraulic power can then be released.

Neither of these systems requires any tooling modifications such as a backing plate. As a result, installation costs stay low. On the downside, these systems do need a separate hydraulic-control unit. And, neither manufacturer sells systems for press sizes over 2000 tons.

American Aerostar recently rolled out a standardized line of its Hydra-Jaws clamps. Now the company offers immediate delivery for most presses sized up to 500 tons. Pacesetter also carries standard clamp sizes for presses up to 2000 tons. Both companies continue to custom-engineer systems when needed, such as for machines with unusual tiebar configurations.

Looking at the two hydromechanical systems side by side, you would notice a few subtle differences. Pacesetter has quick-disconnect fittings on its hydraulic hoses so that the hoses can be removed from the clamps after they are locked closed. This feature reduces clutter around the mold, according to company president Paul Pace. (In addition, the platen-mounted mold plates from both firms contain oil passages so that hoses needn't criss-cross the platen.)

Whereas the Pacesetter clamps can be removed completely from the platens, most Aerostar systems have clamps that ride in fixed U-shaped tracks on the platen plate. Paul Sloane, co-developer of the Aerostar system, says his arrangement ensures that the clamps are always ready to slide into place - there's no inserting them into the T-slots as you might have to with a Pacesetter system. Pace counters that his system is more flexible since clamp positions are not limited by the tracks available.

Aerostar also brings a quick-change knockout system to the table. After special pins have been added to the machine end of the knockout bars, the system's two-position hydraulic latch locks knockout bars onto the machine (see schematic).

MECHANICAL LOW-COST QMC

Other low-cost QMC systems are best characterized as purely mechanical since they forego hydraulics altogether. These manual systems cost around $3000-6000, depending on press size. However, they tend to require mold modification, making them most appropriate for molders who can control tooling designs. Offsetting that constraint is their high speed: These systems literally take seconds to attach a mold to a machine with no need for hydraulic connections.

One such system comes from Master Unit Die (MUD), makers of the Mold Base Adapter for use with standard mold bases. These systems require tooling and machine attachments - an "ear plate" on the mold that slides into an adapter frame bolted to the platen (see PT, June '91, p. 31). Even with those modifications, the system cost doesn't exceed $5000/press.

Switchcraft Inc. of Chicago has become a big user of the Mold Base Adapter. In less than three years, the company has installed the system on over 300 molds and 11 injection machines in the 75-160 ton range. Switchcraft, which makes electrical parts for its corporate parent, Raytheon, also installed MUD's new quick-disconnect water manifolds and spring-loaded knockout bars. "The thing that really attracted me to the MUD system was its simplicity," says tooling engineer Chuck Robertson. He says the ease with which a mold can be simply lowered into the platen-mounted frame outweighed the 18 months it took to modify all his molds. Robertson prefers the necessary mold modification to buying hydraulic units and wheeling them around to be connected to and disconnected from his molds.

With QMC, Switchcraft shaved an average of 60% off its previous changeover time of 50 min. Especially easy changeovers where the material and part geometry remain constant have taken as little as 6 min. Robertson figures that the payback has been about a year.

Though the MUD adapter system has been around for four years, there have been some enhancements over the past couple of years. One is a knock-out-bar-disconnect system that uses spring-loaded knockout bars. Last summer, MUD introduced a quick-disconnect water-manifold system in a recess between the ear plate and frame. Whenever the mold is lifted out of the frame, water lines disconnect automatically; re-connection also takes place automatically when the new mold is lowered into the frame.

Staubli offers another purely mechanical approach to QMC with the bayonet system (Staubli also offers a more costly hydraulic system - see box.) This system generally works for press sizes up to 300 tons or ones having up to 23-ton opening force. It requires addition of a specialized locking ring to both the moving and stationary sides of the mold. The bayonet grabs hold of molds by means of a ratcheting gear system actuated by the flick of a lever. A functionally identical bayonet system has just been introduced by Enerpac, which previously focused on more expensive hydromechanical systems suitable for larger machines.

One user of the Staubli bayonet is Sta-Rite Industries of Waterford, Wis. Sta-Rite formerly required 20 min to clamp a mold to the platens. Now it takes 20 sec on the company's 200- and 300-ton HPM machines, according to Don Grisius, manager of plastics technical services. Part-to-part change-overs have dropped from 2 hr to about 15 min.

According to Grisius, Staubli's bayonet system offers the best clamping method for his money because it accommodates both horizontal and vertical mold changes, as required by Sta-Rite's varied collection of molds, many of which are unscrewing or have unusual water-line configurations. "Our diversity of tools doesn't lend itself to other systems," Grisius says. Also, Staubli's locking ring attaches to the mold's center, where it can't interfere with the water and hydraulic lines.

MORE TO IT THAN CLAMPING

Sta-Rite's experience highlights an often overlooked aspect of QMC: Even molders who have found an advantage in commercial quick-clamping systems discover that there is a lot more involved than just mounting the mold on the machine. Although the Staubli system helped Sta-Rite cut nearly 20 min off the mold-attachment time, there was still plenty of time left to shave from the company's original 2-hr part-to-part changeover time.

Sta-Rite, which molds impellers and other parts for pool filters and pumps, was forced to fine-tune its mold-change procedures when it moved to a cell manufacturing concept whereby it assembles its products at the press without any in-process inventory. One all-too-common problem that had plagued Sta-Rite was a lack of changeover readiness. Setup workers did not always come to the press prepared to make the change. "We used to have guys who would shut down the molding machine, then go get the mold, then take the old mold back to the tool room, and then start up the machine," says Grisius. Now, everything - from hand tools to the molds themselves - is ready by the press when needed.

Grisius encountered further delays in manually resetting the dial-and-knob controls of his older injection machines. Sta-Rite upgraded to Moog microprocessor controls with "recipe storage" capabilities. Now a technician just calls up the processing conditions for the new mold and the controls reset themselves automatically in a matter of seconds.

HOME-GROWN QMC

Taking the lesson Sta-Rite learned a step further, some molders have found ways to speed mold changes without investing in a commercial QMC system. Take American Technical Molding (ATM) of Uplands, Calif., for example. ATM doesn't use any commercial hardware - just self-reliance and good planning. "We like things simple," says company president Rocky Morrison. If ATM were a proprietary molder, then a commercial QMC system would be worth considering, Morrison concedes. "Some systems are faster, but they're more money and not applicable to 100% of our molds." As a custom shop, he says, "We don't know what's coming down the pipe. We can't book specialty things on the mold."

This medical molder makes two to six mold changes a day on its 15 Sandretto presses of 60 to 275 tons. In the case of simple changes - involving tools without actions and no material change - ATM can go from good part to good part in about 30 min. Complex jobs with lots of hydraulic fittings and mold actions might take an hour.

Morrison outlines several strategies that ATM uses to change molds efficiently:

* T-slot platens - When ATM takes delivery of a new Sandretto press, it adds some non-standard T-slots to the platens to accommodate its wide variety of mold sizes. "T-slots are one of the best things you could do for quick mold change," says Morrison. A couple of turns on the wrench to loosen the bolts, and the mold comes right out.

* Color coding - All hoses are color coordinated and keyed so workers can't put them in backward.

* Standardized ejector systems - ATM uses all flush-mounted knockouts (ones that aren't screwed into the ejector plate) so that its standardized ejector plates slip right in place. This time-saving modification is well worth the cost of about $100/mold, Morrison says. Hot sprue bushings have likewise been standardized.

* Quick-disconnect water lines - Normally, quick disconnects would require mold-mounted manifolds. "That's okay if you've got molds in your shop with limited water in/out. We have molds with 25-30 water in/out, plus racks, hot runners, etc. We run out of space." So ATM developed its own manifold that sits on the platen top or side. Water and other services come down next to the press and can be shut off or turned on with the flick of a lever - for example, to switch between tower and chiller water.

* Duplicate screws - Spares are kept on hand in case a material change calls for a new screw.

* Spare parts in stock - "We have spares to cover 80% of what goes wrong," says Morrison.

SWAPPING CAVITIES

For those whose parts lend themselves to unit-base tooling, this approach can offer a fast route to QMC. You can change cavity inserts in minutes - often by hand. That's what Packard Electric of Brookhaven, Miss., does with its electrical-connector molds, every one of which typically makes a cavity change every day (PT, March '95, p. 25).

Quick cavity changes with Master Unit Die's unit-base system simply involve sliding out the old parting-line and ejector plates from their mold-base frames and sliding in the new plates. Most part-to-part changes reportedly take less than 5 min. On small applications, which account for about 50% of MUD's sales, cavity inserts can be swapped by hand. MUD's Martin adds that this is the most inexpensive way to go - at under $1000 per mold.

Martin says the unit-base approach lends itself best to new jobs where the molder has a say in specifying the tooling. "For a lot of existing molds with standard bases, you would go with the adapter system. For tooling on new products, go with a unit die," he says.

ATM likes to use unit-base tools whenever it can. It has about 50 such tools from Pleasant Precision. In this system, the RoundMate cavity inserts simply slide out of their frame. "They have guided ejection, good water cooling, slides, and hot runners," says Morrison. "With these, you can truly do five-minute mold changes." ATM can't use this approach on all jobs since RoundMate's maximum cavity dimension is 7 in. diam.
COPYRIGHT 1995 Gardner Publications, Inc.
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Copyright 1995, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Ogando, Joseph
Publication:Plastics Technology
Article Type:Cover Story
Date:Apr 1, 1995
Words:2315
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