Blow molds grow in sophistication.
Some industrial blow molds are getting so complex they can't always find a machine to run them. The somewhat notorious "T mold" (see photo) was built last year by three different mold builders to make a wheeled, 70-gal refuse bin. The T mold forms a compression-molded lip ring, inserts two axles through the part, and puts reinforcing skid plates on the bottom. Each mold half splits in thirds; the top and bottom thirds move on hydraulic cylinders. But no one could make it work, and the mold went on a one-year odyssey in search of a machine with sufficient computer controls and extra hydraulics to make all that happen.
The story ended happily: The T mold is now making parts at ABC Group in Rexdale, Ont. Even so, the T mold is last year's technology. Kennedy Tool & Die Inc., Birdsboro, Pa., has built an even more complex "J mold" for a large drum, which has a patented injection molded lip ring. Four sets of moving sections are activated by 16 large hydraulic cylinders. Guaranteeing accuracy of the moving sections required large bearing races (imported from Switzerland for $10,000). "I'm willing to bet this is one of the most complicated blow molding tools in America today," says president Richard Kennedy.
A blow molder who has worked with both tools says blow molds are finally approaching the technical complexity and precision of injection molds. Only lately have blow molding machines had the controls and hydraulics to make these new tools work, says blow molding consultant Chuck Chirdon of Advanced Blow Molding Services Inc. in Cleveland. "Blow molding is light years beyond where it was five years ago." And much of the change is due to the leap in sophistication of blow molds.
The change in blow molds from a passive cavity or one with simple moves after the part is blown to a mold with five or six complex, interdependent movements under pressure that actually shape the part, has been gradual. Now it's accelerating as mold makers race to install more powerful CAD software and hardware. More than anything else, these computer-aided design and engineering tools are credited with bringing blow molding up to a new plane of sophistication.
"In the past blow molders and designers had a pretty good idea of how tools worked. Now the tool maker is much more of a contributor to the team," says blow molding consultant David Chaney of Chaney & Associates in Westerville, Ohio. "We have to go to the mold makers and say, |Based on your knowledge, how would you do this?'"
CAD IS THE KEY
Blow mold makers bought CAD programs as long as 15 years ago. Durivage Pattern & Manufacturing in Williston, Ohio, was one of the first. In 1975, Durivage installed an Olivetti program called Datamat. Then Durivage was ready to upgrade again and wanted a program from Schlumberger CAD/CAM in Ann Arbor, Mich. "But their salespeople never took us seriously," says Durivage president Larry Durivage. "They never thought a company this size [15 employees at the time, but now 40] would really buy their product." Two software changes later, Durivage put in an entire new 3-D modeling system from CADkey Inc., Manchester, Conn.
Bottle blow mold maker Heise Industries in East Berlin, Conn., is also a big spender on electronics. Thirteen years ago, Heise bought a $250,000 IDS 80 computer system for CAD and 3-D geometric modeling that was scrapped three years later. "It hurt to spend all that money and have it worth nothing, but the learning experience in 3-D modeling was priceless," president Tad Heise recounts. Now on his fourth-generation engineering system, Heise leases everything: "It's the same basic cost as if you financed the equipment, but the accounting is more favorable, and I know my system will stay up to date." Heise currently uses Hewlett-Packard ME-10 CAD and Bravo 3 CAM/modeling software from Schlumberger on five 700-Series H-P workstations, and one terminal of DUCT from Delta CAM Inc., East Lake, Ohio.
"The first CAD programs got us over the learning curve, but they weren't very powerful," recalls systems engineer Robert Kennedy of Kennedy Tool & Die. Hobson Bros. Aluminum Foundry & Mould Works in Shell Rock, Iowa, started with PC-based AutoCAD from Autodesk in Sausalito, Calif., using CADkey for mold design and SmartCAM to design tool paths for CNC milling of the mold. (SmartCAM comes from Virginia Polytechnic Institute & State University's Manufacturing, Automation and Robotics Center in Blacksburg.) Last year, Hobson upgraded to Solution 3000 PCCAD software (originally from Micro Engineering Solutions Inc., Novi, Mich., but bought by Autodesk and renamed DesignExpert and ManufacturingExpert) with complex surface and solid modeling capability, allowing the software to communicate better with blow molding customers like Rubbermaid. Hobson also upgraded to Micro Engineering Solutions software for CNC milling (also formerly MES, now Autodesk) .
Everywhere mold makers are spending big bucks to upgrade. Wentworth Mould & Die Co. Ltd. in Hamilton, Ont., says it invested over $500,000 last year for a complete new CAD/CAM system, including SmartCAM, and computerized shopfloor controls, among other new equipment. One upgrade frequently requires another. Kennedy Tool started up its first Auto-trol CAD software (from Auto-trol Technology Corp., Denver) in 1985 on a Unix-based workstation. Now Kennedy is installing top-of-the-line solid modeling (ProEngineer software at $75,000 a terminal, from Parametric Technology Corp. in Waltham, Mass.) . ProEngineer's higher math gobbles up so much computing capacity that the CAD operator often waits 4-5 min for the CPU driver to catch up. So Kennedy is now replacing Sun Sparcstation RISC workstations with even more powerful Hewlett-Packards.
CAD SPEED, CAD QUALITY
The big advantage of the new CAD programs is that they can compress the time needed to convert a part design to a mold. Hobson's sales manager Herb Lease says that with CAD/CAM, a mold that would have taken 12 weeks to build can be made in six.
Kennedy Tool recently designed an entirely new-concept oil bottle for Graham Products, York, Pa., in just four weeks. And Ryka Blow Molds Ltd., Mississauga, Ont., has supplied prototype packaging molds in only 10 days for the past 18 months.
CAD software programs easily can place graphics on complex curved surfaces for considerable time savings. Martin Cass, v.p. and general manager of Fremont Plastic Mold in Fremont, Ohio, cites the example of a large doll motif and text in raised relief on a curved piece of children's furniture: "A few years ago, we sent all that work out. Now we do all our own engravings, logos and text on molds."
CAD also saves time and money in making prototype tools, says Michael Ryan, president of Ryka. Prototype tools are usually cast of an inferior grade aluminum or epoxy and thrown away after they have served their purpose. With CAD, a prototype tool can be cut from the same data file as the finished tool but with only a few water lines so cost is kept low. If the pattern is approved, the prototype mold goes back to the shop for finishing as a production tool. The prototype tool might cost only $10,000-12,000, which is later applied to the $35,000-40,000 cost of a production tool.
CAD saves time in mold repairs. If a mold is damaged, replacement parts can be cut from the original CAD file and shipped to the molder, often without returning the mold to the shop.
Accuracy of tools is also far higher with CAD. Custom-Pak in Clinton, Iowa, has a three-yr-old in-house design center and tooling operation that builds molds exclusively for the firm's own use. Custom-Pak uses basic AutoCAD wireframe CAD software on Sun Sparc-stations to draw parts and CADkey wireframe modeling software to design molds. CAD helped Custom-Pak maintain the tight mold tolerances necessary to produce flat rectangular boxes for 3M tape reels (see photo). This difficult needle-blown part is made with a large, thin (0.04 in.) parison. Final wall is only 0.02 in. thick. A solid upper-right corner is compression molded. And a living double hinge is formed with two 90 angles. The part is removed with four ejector pins in each mold half
Some blow molded parts with complex curves couldn't be made at all without CAD, like a bolster-style rear seat armrest for a car, which "probably has 300 surfaces and took the programmer about 180 hours to draw," says Cass of Fremont Mold, which uses AutoCAD and CADkey. Once one side armrest is drawn, it can be mirrored to render the other armrest. By traditional methods, each armrest would have been hand-modeled in wood, and the two would never have quite matched.
LATEST DESIGN TOOLS
CAD/CAM programs for mold design have grown quicker, stronger and generally easier to use in the past five years. "Five years ago you had to be a rocket scientist to use CAD. Now you have to have CAD to get a job," says Fremont Mold's Cass. CAD drafting creates a surface of a part and a mold parting line. The lower priced, more basic programs, like AutoCAD and CADkey, render this surface with wire mesh. AutoCAD can even give the appearance of a 3-D shaded surface, but actually each point on the surface remains a linear plot. The program can't tell mold makers anything about mass or volume of the part they're drawing. If a part surface is drawn with more advanced CAD programs with true solid modeling, like Catia (from IBM's Dassault Systems, Paramus, N.J.) the program automatically calculates mass and volume, for instance of a drum.
Nowadays, mold makers can also convert a part design to a mold without doing a lot of higher math. DesignExpert CAD, for instance, has a built-in ability to "shell" a part design--that is, draw a block of aluminum on the screen, then hollow the shape of the part out of the block.
Most often, the part drawing comes to the tool maker on disk or via modem from a blow molding customer. Hobson says 80% of its work now arrives by some electronic means. Data translation is often imperfect though, and bits of data get lost, so CAD models must be carefully inspected to match surfaces before tool cutting begins. "We just had a big problem with untrimmed surfaces," says Larry Durivage of Durivage Pattern & Manufacturing. "If they're untrimmed, the CNC machine doesn't know how to cut and gouges the tool." Sometimes all data gets lost in translation. Fremont Mold's Cass says he's had designers send him absolutely blank tapes.
A CAD model of a mold cavity can be created with a high degree of accuracy directly from a physical part or model by using laser digitizing. Laser digitizing equipment, which has replaced older and slower methods such as duplicating machines and coordinate measuring machines, is something only a handful of mold shops have. Hobson Bros., for instance, has had a Le Moin Digitizer (Le Moin Multinational Technologies, West Bloomfield, Mich.) for only six months. Heise also just bought a laser scanner from Laser Design Inc. in Minneapolis. To make molds for very high-quality cosmetic bottles, Heise often starts with a wooden model supplied by the customer without any precise dimensional data. The scanner then provides the data to create a CAD surface model, which can then be converted to a CNC tool path.
Once the surface geometry of a part is established, whether it's drawn or digitally scanned, it's transferred from the design file often to a separate workstation where a mold designer draws in every nuance of the mold: blowing needles, air vents, cooling lines, ejector pins, slides and lifters for undercuts. If the mold is drawn in wire mesh, it has no depth, so different levels of the interior and surface of the mold must be indicated by different colors of lines.
Then comes the step that will separate "those who have from those who have not," says blow molding designer Chirdon. Some mold designers and mold makers run powerful and expensive new software that has surface modeling and "full associativity," which means that when a change is made to the part design, it automatically adjusts the mold design and the instructions for CNC milling.
"If you see someone standing at a CNC machine making program adjustments, they don't have it," notes designer Chirdon. Acquiring such associativity is part of what Kennedy Tool hopes to gain with its switch to ProEngineer software, which can cascade information to ProMold for mold design and ProManufacture for CNC cutting instructions.
LOTS OF MOVING PARTS
Some blow molds had small moving sections a decade ago, but relatively few tools were made that way. "Five years ago, maybe only 10% of our tools had hydraulic moving parts," says Fremont Mold's Cass. "Now 40% do." They range from simple ejector pins to large head and tail sections that actually shape the part in the mold as it's blown. Stark Mold & Pattern Inc. in Canton, Ohio, recently built a tool that opens in four parts to avoid backdraft on an air resonator for a General Motors car. The mold also had two blow needles and pneumatic part ejectors.
At least three automotive blow molders are developing techniques for in-mold carpeting, which involves special cooling and clamps that stretch the carpet inserts flat in the mold.
Deflashing in the mold, as opposed to automatic post-mold deflashing, is a recent development from Hobson. The company just made a mold for a medical back support that punches out 21 slots in the mold. Twenty-six pins on the core side hold the long part firmly against the cavity side, while 42 punches (two per slot) knock out the holes. In the same stroke as the hole punching, a big watercooled plate that outlines the part knocks the edge flash off. Because all movement stays on one side of the mold, there's no chance of damage. Hobson has even perfected a technique of retrieving a bit of flash from one part and inserting it as a tab in the next part.
NEW MOLDS FOR DEEP-DRAW PARTS
An intriguing new mold technology from Placo Co. of Japan (offices in Torrance, Calif.) has newly arrived in the U.S. Last month, Hobson became the exclusive North American builder for Placo's new deep-draw, hinged molds (see photo and diagram). This deep-draw mold technique uses a mold that's hinged on four sides, resembling a flower when opened.
The parison drops, is pinched off and preblown. This pillow is positioned in the tool at what becomes the deepest point. Then the male mold half moves in and the hinging sides close around the parison, creating a female mold half. Despite a system that looks as if it should make triple flash, Placo says large parts like cooler chests and planters can be molded with only 3% scrap. Heated molds disguise parting lines, and the pinchoff is at the outer lip.
THE LATEST MOLD MATERIALS
Until now, very large molds have been either cast or made by bolting 6-7 in. slabs of aluminum together. Cast aluminum has the advantage of one-piece construction, but is never as hard or as precise as machined aluminum molds. Now a new alloy, called Alpase K100 from Alpase Inc., Downey, Calif., is avail able in 36-in.-thick slabs, allowing large tools to be cut from one piece. It's also very stable in terms of warpage, mold makers say.
Aluminum hardness ranges from medium 6061grade aluminum to hard 7075 T6 and a slightly harder QC7, which can be welded without losing its hardness. However, mold makers say QC7 has a warpage problem in large molds. And some blow molders have experienced discoloration of QC7 molds. Blow molder and machine builder Johnson Controls Inc., Manchester, Mich., had converted all its mold building to QC7, but returned to 7075 grade because of the discoloration. The discoloration is caused by milling coolants. If molds spend too much time in the green coolant liquid used with CNC cutting, they absorb coolant residues, which eventually discolor.
When a very hard mold is needed to mold something abrasive like glass-filled nylon, mold makers use hard beryllium copper alloys or newer beryllium-free alloys like Ampcolloy 940 from Ampco Metal Inc., Milwaukee.
GREAT EXPECTATIONS FOR CAE
The blow molding (and thermo-forming) simulation software initially developed by GE Corporate Research in Schenectady, N.Y., is now close to commercialization by AC Technology, Ithaca, N.Y. (see PT, Feb. '93, p. 77) . To be called C-PITA, the molding simulation is being released early this month to a consortium of six development partners, which include Ford Motor Co. and Johnson Controls. Full commercial release is planned for October, at a price comparable to the $60,000 fee from the beta-test partners.
The program is a 3-D finite-element simulation of parison inflation and stretching in a mold cavity. AC Technology rewrote the GE software to match standard engineering requirements, which cut in half the computing time required. Computation time depends on part complexity. A simple model like a bottle can be analyzed fairly quickly, while a complex model with thousands of elements could take hours.
C-PITA will run on standard engineering workstations, like Sun or H-P. To build a computer image for analysis, the operator brings over a CAD part drawing from another program and reformats it for C-PITA. Reformatting might take half an hour for a simple part. Or the operator can create part geometry and finite-element mesh using AC Technology's C-VIEW. Then in the actual process simulation, the software analyzes part shape and thickness during blowing. Part-thickness predictions can fine tune processing criteria for optimal wall-thickness distribution and for structural analysis of part performance, AC Technology says. Johnson Controls, which already blow molds with nitrogen cooling, hopes to use C-PITA to gain insight into the effects of mold cooling on cycle time.
Use of cryogenic coolants to speed blow molding cycle time continues to evolve. Airco Gases in Murray Hill, N.J., has decided to phase out CO2 cooling in favor of a more advanced and controllable liquid-nitrogen method called Cool-Kwik. In its latest stage of development, this decade-old technique is a multi-stage process. First, ambient air is blown into the part for a brief time to inflate the parison, which is followed by cold nitrogen gas and then a mist of liquid nitrogen (Airco supplies special blow pins with an atomizing spray tip). Finally, cold nitrogen gas is used to purge any liquid from the transfer lines. Airco leases the equipment to control this process for $475/month.
The patented cooling system has been in commercial use for about three years making products from gas tanks and 55-gal drums to small bottles. The process cuts 20-40% off cycle time Airco says. With nitrogen costing 5-6[cents]/lb and 0.5 0.6 lb of nitrogen required to cool a pound of plastic, this process adds 2.5-3.6[cents]/lb to raw-material costs. Airco has an OEM arrangement with Battenfeld Blowmolding Machines, Inc., Boonton, N.J., for Cool-Kwik systems sold on new machines.
Airco will also lease retrofit systems direct to molders. Demonstration systems will be available for testing on a small Battenfeld-Fischer bottle machine and a large Hartig industrial blow molder at Battenfeld's Boonton plant.
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|Author:||Schut, Jan H.|
|Date:||May 1, 1993|
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