High-tech blow molding at Agri-Industrial Plastics

AIP began developing into the leading manufacturer of fuel tanks for non-automobiles in 2004 when the US EPA first introduced fuel vapor emission standards for the motor sport industry. At the time, AIP was making single-layer HDPE tanks. “We asked ourselves how we could meet the new requirements. We spoke to our customers about their plans to meet evolving standards. We either stayed in tanks looking for a solution or we got out, ”recalls Ward.

AIP tried to use a laminar blend of HDPE with the amorphous nylon additive Selar PA from DuPont Performance Materials but was not happy with the results. AIP also saw fluorination and sulfonation as the most promising solution before opting for coextrusion. It was an expensive way. Each coex machine costs $ 3-5 million. “A publicly traded company could not have made an economic argument for such an investment,” says Ward. “In 2004 we ordered the first Coex machine. The lead time was long – it arrived in 2006 and went into production in 2007. So it took three years for this machine to earn a cent. “

“We were the first custom injection moulder to order a coex machine for making fuel tanks outside of the automotive industry,” says Ward. “We never imagined what would become of it today.”

Fuel tanks made up half of AIP’s business and will grow to 55-60% this year. Ward estimates that 80% of the tanks are multi-layer and 20% are single-layer diesel fuel tanks that do not require barriers. AIP also forms a couple of single layer HDPE tanks that are sent to a third party supplier for fluorination treatment. Ward believes that fluorination as a barrier solution in fuel tanks could have a limited future. He explains, “California is talking about major regulatory changes – stricter certification requirements that require more consistent barrier performance. Our data show that fluorination is much less consistent than a coextruded barrier. California’s changes – including possible later lower emission limits – could displace fluorination. “

AIP’s two largest markets for tanks and other blow molded products are outdoor power equipment (~ 40%) and powersports (~ 30%). The latter includes ATVs, UTVs, snowmobiles, golf carts, and marine applications. The remaining 30% is accounted for by other sporting goods, heavy trucks, agricultural and construction machinery, road safety, defense, furniture, medicine and industry.

HDPE accounts for 90% of AIP’s material consumption, although it also forms some parts from PP, ABS, PC, nylon and Tritan copolyester from Eastman Chemical Co. The company does “quite a bit” of overmolding, Ward notes, including metal fasteners and injection molded components like fuel filler necks, vent barbs, and mounting tabs. “Some OEMs were initially skeptical as to whether overmolding inserts would work in multilayer blow molding, but we proved that from the start.” In some cases, plastic parts are heat-welded onto the tanks instead of overmoulded.

According to Stielow, AIP has fewer than half a dozen direct competitors in coex fuel tanks, as well as a handful of companies that use fluorination or barrier additives such as nanoclays. “We are unique in that we offer both multi-layer co-extrusion and single-layer non-tank production capabilities,” says Stielow. “That works for us because our OEM fuel tank customers also need single-layer coolant tanks, air ducts, ORV doors, tailgates, etc.”

COMPETING WITH TECHNOLOGY
“Due to our blow molding expertise and the willingness of the owners to invest, fuel tanks are a large growth niche for us,” says Stielow. And they invested. All six AIP Coex machines and the one ordered are supplied by Kautex Machines, Inc., North Branch, NJ. “These are state-of-the-art machines,” says Stielow. “There are cheaper multi-shift machines out there, but none of them come close to Kautex machines in terms of process control, consistency and reliability.”

In fact, most of AIP’s machines are from Kautex, with the exception of a few older machines that were bought second-hand when the company was founded in 1978.

AIP makes extensive use of robotics, both in applications inside the injection molding machine – for preform transfer, insert plate loading and demolding – and outside the machine in the finishing / assembly area for trimming and hot plate welding. Multiple presses use simple linear robots to move parts out of the die area, which on some machines can be tall and / or difficult to access. The multi-layer Coex machines grip the preform with six-axis articulated arm robots and transfer it from the extrusion nozzle head to the mold clamp. It’s more efficient than a pendulum press, explains Ward.

Other six-axis robots are used for automated trimming, drilling and welding. These units are mounted on a base with a platform for parts mounting and can be moved to various machines using a forklift truck.

In addition, earlier this year, AIP installed its first “collaborative” robot, a UR10 model from Universal Robots USA, Inc., Ann Arbor, Michigan, which is designed to work safely next to people without having to be guarded . “We use it to load inserts in high volume applications,” notes Ward. One advantage of this type of robot (or “cobot”) is that it uses lead-through teach programming to make setting up for new jobs quicker and easier.

“As with most new technology, there is a learning curve to make sure everyone is comfortable using and programming,” says Ward. “It works well with selected applications. We are still checking whether this option is used where it makes sense. “

Another novelty at AIP is an ERP system from IQMS, Paso Robles, California. AIP went live with the system in December 2016. “There are growing problems with any new ERP system,” admits Ward, “but the amount of data we can generate now is remarkable. We’re learning a different way of doing business. ”Each molding press now has a data entry terminal. “This enables us to monitor what is happening in real time – production efficiency, cycle times and reject rates.”

AIP’s most adventurous research into new technologies – since its first decision to move into multilayer coextrusion – has been its involvement in computer-assisted blow molding simulation. Analogous to the flow analysis software that revolutionized injection molding, the blow molding simulation is still at an early stage of development and is still little known to the vast majority of blow molders.

For the past three years, AIP has been a member of a consortium, the Special Interest Group in Blow Molding (SIGBLOW), founded by the National Research Council Canada (NRC), Ottawa, Ontario. SIGBLOW members have access to proprietary blow molding simulation software called BlowView, which is not available in the commercial market. The consortium currently consists of 14 members who share this small custom injection moulder with companies such as Ford Motor Co., TI Automotive, Plastic Omnium, IAC Group North America, ABC Group-Saflex Polymers Ltd., Kautex North America, Graham. bring together Packaging Co., Amcor PET Packaging and The Coca-Cola Company.

BlowView models the thickness of the preform during extrusion and the finished part after blowing. It takes into account the sagging and swelling of the preform. “It warns us – or confirms our intuition – that there will be a narrow corner,” says Ward. “It helps quantify potential problems – we know it will be thin, but how thin? By repeating iterations, we can determine how thick we have to be here in order to meet the minimum thickness requirements there. ”“ It really helps us to communicate with designers, ”adds Stielow. “It helps validate our recommendations when the customer refuses to make changes. We can now demonstrate how moving a parting line or increasing a localized radius can improve the overall wall thickness distribution and increase the usable liquid capacity of the tank. “

AIP is increasingly using simulations in around half of its new jobs, mostly on the more complex parts. “We can see where the preform first touches the mold,” says Ward. “This helps us to troubleshoot needle positioning for very large parts and to optimize this position if we are flexible.”

Ward notes that AIP engineers can enter parameters into the software and correlate well with real-world results. “The ideal situation would be if the software could tell us which machine parameters we should use in production – that could save us a lot of time during set-up.” How good are the software’s predictions? AIP measured the actual thickness in 22 places of a particularly complex shaped fuel tank with a nominal thickness of 2 to 6 mm. The comparison of the predicted and actual thicknesses ranged from ± 0.0 to ± 0.6 mm. Sixteen of the 22 measurements were within ± 0.2 mm, which was both the mean and median of the differences between predicted and actual thickness. “That’s close enough,” admits Ward. “We can achieve so much in shot-to-shot variations.”

The BlowView consortium continues to research and refine the software in various directions. One of them is the shrinkage / warpage prediction. “I’m very pleased,” enthuses Ward. “Variable wall thicknesses are unavoidable during blow molding and the associated distortion. We have seen parts that met all the important dimensions, but did not fit into the final assembly due to distortion. If you can even predict the correct direction of fault, that’s half the battle. It can save a lot on geometry and tool revision costs. ”The software has not yet been developed for cooling analysis, but Ward says some in the consortium would like to see research and development in that direction.

He adds: “We also use simulation for troubleshooting on the shop floor. One of our very experienced but skeptical technicians initially resisted this, but has now turned to our design team for help using simulations to solve a processing challenge. That is an encouraging sign. We are still a long way from realizing the full potential of simulation. But the results we’ve achieved so far outweigh the costs. “

AIP has nine CAD workstations for parts and mold construction and one seat for the BlowView simulation. It also has a small 3D printer that customers can use to visualize special features of large parts as early as the design or prototype stage. AIP’s quality lab has a laser scanner, which Ward says is much faster than a probe CMM to get a full 3D profile of a part.

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