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3-D blow molding: the action is abroad.

Three-D technical parts blow molding is making production car parts in a big way in Japan. And it's coming in Europe, Canada and Brazil for auto and appliance parts. So far, apparently, little is being done in the U.S., outside of two R&D centers trying to develop U.S. applications for Japanese technology.

Three-D blow molding makes long, loopy parts with weird shapes like roller-coaster tracks or corkscrews sometimes alternating hard and soft resins. The key is to do these things without generating large amounts of scrap. There are basically three ways to contort a parison into such a part--using suction to draw a parison through a closed mold before being inflated; having either the extruder or the mold platens capable of x-y-z machine movements so as to drape the parison into the cavity; or using robots to manipulate an uninflated parison into the tool. Suction and x-y-z machines were invented by the Japanese and have been exhibited at shows and plant open houses for at least five years. Robotic tooling was probably shown publicly for the first time at K'92 by a German machine supplier.

The idea behind 3-D blow molding is to create one part to replace a multipart assembly. Three-D parts are also nearly flashless. To produce such shapes by conventional methods could produce as much as 50% flash. This reduced flash means less use of regrind, which could improve part quality. And the same parts can be molded on smaller machines because the parison need not include all the resin lost as flash. And since the pinchoff is a part's weakest point, 3-D parts with little or no pinchoff are stronger than ones with lengthwise seams. Also, a pinchoff in a conventionally molded multilayer part is only as strong as the inner sealing layer, while flashless 3-D molding retains the full strength of all layers.

In addition to strength loss, pinchoffs can affect the function of parts with fluid flow through them, leading to uneven or turbulent flow, note engineers at German automotive molder Freudenberg in a paper on 3-D blow molding recently published in Kunststoffe magazine. Since the pinchoff is also a major site of tool wear, tooling for processes without pinchoff can be made of less expensive materials (e.g. aluminum) and last just as long.

With all these advantages, how come nobody seems interested in the U.S.? Why is this apparently solidly a German and Japanese game? The obstacles seem to be partly economic, partly psychological. The technologies used to make 3-D parts cost a bundle--anywhere from half a million to over a million dollars. And the lead time for developmental parts, like automotive ducts, to pay back such an investment is long. Then too, some of the proprietary equipment is not for sale. And legal battles in Japan over patents between two Japanese x-y-z machine makers has discouraged potential U.S. buyers because of fear of legal action in the U.S.

Another impediment to 3-D blow molding in the U.S. is geography. U.S. distances are much greater than in Europe or Japan, and shipping costs are viewed differently. The potential for higher shipping costs with 3-D parts is that if you create a large, unwieldy part to replace three or four straight sections and connectors, you may need special skids to ship it, and costs run much higher.

Geography also makes psychological differences in how space is used. American homes and kitchens tend to be larger for example. "Europeans, especially in the appliance market, look at things differently. There's no waste space in part design," says blow molding consultant Dave Bank of Papago Plastics Inc. in Rochester, N.Y. "We have too much space around us. We don't feel we have to conserve it when we sit down to design."

'S' IS FOR SUCTION

Vacuum-assisted tooling, while common in thermoforming, is little used in blow molding except occasionally to vent a part or distribute the parison into corners of some double-walled parts. Some 3-D parts are made by pulling a vacuum at the end of the closed tool and drawing the parison on a slipstream of incoming air through the tortuous cavity passages. Once the parison reaches its maximum length, it's inflated. The tool opens wider than normal and on the bias, to allow the odd-shaped part to be removed.

Suction blow molding is commercially available with tooling developed and licensed by Sumitomo Tool Co. in Japan (not related to the Sumitomo industrial conglomerate). It's used on blow molding machines from Tahara Machinery Ltd. (represented by Wilmington Machinery Inc. in Wilmington, N.C.) and Ishikawajima-Harima Heavy Industries Co. (IHI), which has offices in N.Y.C. Besides saving scrap, cycle time with suction molding is "nearly half" that of molding a comparable part with a conventional falling parison, Tahara says.

Technical limitations on suction blow molding, however, are that it doesn't readily allow either compression flanges on parts or metal inserts, the way x-y-z and robotic tooling approaches do.

Suction molding is used in production of S-shaped washing-machine drains at BP Chemicals PlasTec GmbH (formerly Etimex) in Rottenacker, Germany. The drain is molded on a Tahara TBA machine (see PT, Jan. '93, p. 76), one of only two such machines outside of Japan. An earlier TBA-658, shown at NPE '88 in hopes of selling it in the U.S., went instead to AB Volvo in Gothenburg, Sweden. Tahara says 10 of its TBA suction machines are in use at automotive and appliance molders in Japan.

At least two proprietary suction blow molding processes are also commercially used in Germany and Canada. BP in Germany says it uses a second suction process, developed in house, to make similar parts on a modified Battenfeld Fischer machine. And a Canadian automotive blow molder, ABC Group in Rexdale, Ont., says it uses its own patented suction molding processes to make both flashless and "dual-durometer" (sequential soft-hard-soft) automotive air ducts. ABC builds its machines and molds in-house as well.

BATTLE OF THE X-Y-Z MACHINES

X-y-z blow molding is the domain of two Japanese firms with competing patents: Excell Corp., an engineering firm in Tokyo (with a U.S. licensee, MES Corp. in Troy, Mich.) and Placo Co., a Japanese machine builder (with U.S. offices in Torrance, Calif.). Each has technologies in which head tool and/or mold platens move to lay a parison into an unusual shape in the mold cavity. Excell's head tooling moves; Placo's doesn't. Excell's mold is horizontal with three opening sections, two lower and one upper. Placo's mold tilts to a 40 |degrees~ angle with two opening sides. Both have patents for molds that move both up and down and back and forth--Excell's by independent machine movements and Placo's by sliding on an inclined plane.

The other big difference is that Excell is a molder and its machines (built partly by Takahashi Seiki Corp. in Japan) are solely for its own use and that of its licensees. MES (49% owned by Excell) says it has three Excell machines in the U.S. under an exclusive license agreement to make and sell parts in North and South America. Placo, on the other hand, is a machine builder and wants to sell its x-y-z machines around the world.

Excell, Placo and Placo's Japanese systems development partner Mitoyo Co. Ltd. (with a U.S. development office in Royal Oaks, Mich.) have sued and countersued each other since 1987 in Japan--never in the U.S. The battle spilled over to the U.S. because MES continues to claim exclusive rights to x-y-z technology here. MES hasn't yet sued anyone, and depending on whom you talk to (Excell or Placo advocates), the Japanese litigation is more or less resolved.

Both MES/Excell and Placo insist they won the patent infringement battle in Japan, and each says the other one is appealing the decision. "They both are claiming they won...that's good news for molders," says Vincent Pairet, director of marketing for Solvay Automotive in Troy, Mich., "because it means the Placo technology will be available to the market free of restrictions." In fact, Placo says it has "two to five machines on order for the U.S." and plans to offer a less expensive, stripped-down version of its machine later this year. For now, though, Placo machines are still only used in the U.S. by Mitoyo, primarily to develop car parts. Mitoyo in the U.S. has two Placo machines and expects a third.

Placo also sold one x-y-z machine to Hoechst Celanese for a development lab in Cincinnati, which since closed as part of corporate cost cutting. That machine has since been bought by Mitoyo.

In Japan, Mitoyo has two molding plants with about 20 Placo machines making production 3-D parts, Placo says. And Placo has machines in Korea, in Brazil for R&D, and in Germany at Freudenberg.

MES makes multimaterial air ducts with sequential soft-hard-soft-hard-soft sections (for a '93 model Isuzu Rodeo pickup). In Japan, Excell recently developed a new blow molding machine for intake manifolds, which went into production six months ago making a four-cylinder manifold for Subaru, MES says. Excell also has 3-D machines in Korea and Sweden and will have in Germany soon, MES adds.

Critics of both x-y-z processes say they have slower cycles than conventional processes, and that part walls are thicker, raising material cost. The x-y-z machines also have a problem of uneven wall contact because where the parison touches first, it cools slightly. This gives differences in wall thickness and appearance compared with conventional or suction tools, where mold contact is simultaneous. Using a heated tool with the x-y-z process minimizes this problem, Freudenburg's paper says.

PICK-AND-PLACE THE PARISON

Robotic manipulation of the parison in the mold is a much simpler approach than dedicated suction and x-y-z machines. But that's its advantage. It's the cheapest and most flexible approach to making 3-D parts. On a standard blow molding machine, highly robotic tooling can manipulate a falling parison into unusual, flashless shapes. And by using standard vertical platens, they avoid the patent fight over the sideways tools of the x-y-z machines.

Robotic tools have several other advantages too. They can be used on existing machinery, even in some cases, not on the newest of machines. K. Kurz Hessental GmbH in Schwaebisch-Hall, Germany, blow molds a sequential, multimaterial air-intake hose in production on an old Battenfeld Fischer blow molder using a mold that closes in four parts.

Fancy tooling sequences, however, require very fine computer controls and coordination, says Frank Schueller, an engineer at Battenfeld Fischer in Germany, who designed the 3-D tooling Battenfeld demonstrated at K'92 (PT, Dec. '92, p. 21). For this demonstration machine Battenfeld adapted its latest generation "transputer" controls, which so far are commercially available only on its injection molding machines. Another possible limitation is that robotic tooling approaches have only been demonstrated with easily molded resins. They might not work with less forgiving engineered materials. For instance, a parison may need more melt strength because it could hang longer than in conventional molding. Also, robotics can't make as intricate shapes as suction tooling can. And robotics are slower.

Robotic tooling was demonstrated at K making a 4-ft long C-shaped PP automotive air duct on a modified Battenfeld Fischer BFB8 machine (sold in the U.S. by Battenfeld Blowmoulding in Boonton, N.J.). In the demonstration, the parison dropped about 4 ft until it reached a photo cell. Then a gripper cut it off and lowered it into the tool, where a second gripper closed on the bottom of the parison. The center section of the tool then closed, leaving the upper and lower ends of the parison free. The lower gripper traveled upward on a curved track, pulling the lower end of the parison up and to one side. A small needle under the lower gripper entered the parison and preblew it to give stability. At the same time, the upper gripper pulled the top of the parison over, completing the top of the "C" shape. As the top and bottom corepulls closed, two more needles entered the top and bottom sections to blow the parison up.

Each of the three mold sections has four positioning switches. Vacuum is also used to vent the mold at two corners. When the blowing was over, the mold opened and grippers removed the part. Cooling time is 25 sec. (In production, a mask would hold the part while a rotating knife trims the top and bottom.). "Besides less flash, there's an enormous reduction in clamping force," Battenfeld's Schueller notes. "A large part like this could be done on a 20-30 ton machine. The size typically used to make a jerrycan would do. This means much less hydraulics and energy used."
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Title Annotation:three dimensional
Author:Schut, Jan H.
Publication:Plastics Technology
Date:Mar 1, 1993
Words:2130
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