Water Injection Beats Gas Assist in Lightweighting Car Door Panel

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Recently, Renault in France brought a lightweight-creation prototype vehicle referred to as Ecolab. Among the task, targets turned into the investigation of substances and production techniques applied to outdoor bodywork. The purpose turned into fulfilling modern and future necessities and rules, even as saving automobile weight and delivering new functions and features to the consumer. Of route, expanded use of thermoplastics became one of the answers evaluated, and changing the facet-door modules from metal-body construction to plastics became one of the projects.

Using the technical specs of the doorways on Renault’s famous Megane Coupe, the task became to broaden a replacement for the door’s valuable structural layer the usage of forty% lengthy-glass-filled polypropylene. In the end, the door-frame answer would meet numerous important goals:

• Design freedom, consisting of functional integration of capabilities without assembly or welding.

• Lower weight: The thermoplastic structure weighed nearly 6 kg (13 lb), much less than the metal design.

• The low overall cost of production with an outstanding ninety-sec cycle.

But getting to that result might not be smooth. The engineers wanted to apply the same door additives—seals, home windows, locking systems, handles—as within the unique metallic layout. This intended that the glass-filled PP door could need stiffness and different mechanical residences just like the steel structure. Designers decided to consist of a large-diameter channel across the outside of the door to meet those necessities. This channel would form the higher and side frame for the window and join the top and occasional portions of the door.

To keep weight to a minimum, Renault designers planned to use gas to hole out this vital channel. However, the results of initial molding trials have been disappointing because both fees and cycle instances passed project targets by way of a tremendous margin. So they approached PME Fluidtech in Germany (pme-fluidtech.De) to see if the water-injection era (WIT) ought to achieve higher outcomes. PME Fluidtec specializes in imparting technology for both gas and water injection, in addition to a Combined Injection Technology (CIT) that marries the two.

Water injection is greater usually regular in Europe and Asia than within the U.S. Nowadays. It calls for exceptional mildew-layout features than fuel injection for several motives. First, fuel injection makes use of an overflow chamber to receive the resin displaced by using fuel. PME Fluidtec, alternatively, deliberate in applying a way that uses water to power displaced material through warm-runner valves “again-to-barrel.”

This decision necessitated redesigning the present mold, with a unique interest in the hot-runner system. Hot-runner design generally could be truthful for a regular injection molded part. Still, there had been no installed standards for a component that consists of a large-diameter channel as a structural detail. It changed into difficult to determine the range and region of the recent-runner nozzles and how they go with the flow paths should be configured in an element with wall thicknesses that range from 2.7 mm in most of the part to 30 mm in the channel sections. That’s especially because the pressure had to fill the big-diameter sections is significantly less than is needed to fill the thinner areas. This big strain delta intended that, as soften flows into the channel during the injection phase, filling stops in any respect different gate factors or does now not start at all. Therefore, the gates and series of filling had to be cautiously prepared to gain proper filling and keep away from weld strains.

Also, the huge-diameter structural channel itself had to be reconfigured slightly so that it may want to flow in at one stop and water at the opposite, pushing material back to the barrel on the injection site. The water needed to drain through gravity out of the channel after doing its paintings, so the water injector had to be located at a low point inside the tool. In the end, the mold could be installed inside the device at a perspective (in place of rectangular to the platens) to acquire the perfect orientation for gravity draining.

Renault engineers carried out pc-aided mildew filling research with the unique mildew design, waiting for fuel injection; however, there were not tons of time to re-look at the new device layout. Consequently, the automaker had to depend upon PME Fluidtech technicians’ enjoyment and a certain quantity of trial and error to get the design proper.

WATER OR GAS INJECTION?

One of the reasons that Renault decided to replace gasoline help to water turned into the greater flexibility and balance of water because of its incompressibility. Thus, stress and extent can be managed and managed extra efficaciously throughout the cycle, according to PME Fluidtec.

WIT also makes it viable for the channel to end in the vicinity wherein it’s far required. The water pushes cloth again into the barrel until the hollowed-out vicinity extends as long as it desires to and no farther. PME Fluidtec says the water volume and pressure may be managed precisely that the method is flawlessly repeatable. The WIT device also controls the hot-runner device’s valve gates, in addition to other mold or system moves, so that all features are perfectly synchronized.

Another advantage noted for WIT is the cooling effect of the water within the channel. Water can cool the polymer forty instances better than gas, so the dimensional stability and resistance to deformation required for demolding are executed very quickly. In fact, water injection reportedly can start up to 10 sec earlier than with gas, without the risk of delamination or penetration of the fluid into adjoining thin-wall areas. Thus, cycle time reductions of 15 to 25 sec can be finished without adversely affecting product quality, consistent with PME Fluidtec.