(Published November 2007) The rapid progress made in application of water injection technology (WIT) – and the amount of effort being invested by leading plastics companies – is illustrated in a new development headed by automotive system supplier Magna Decoma to apply the technique to manufacture automotive roof rails.
The six-month project was intended to prove WIT in the production of a roof rail for the Volkswagen Passat car, taking the part from design through to finished component. The project is believed to be the first ever demonstration of the feasibility of WIT for production of a roof rail, with the two-metre long 1.5kg moulded part proposed as an alternative to conventional combinations of metal castings or moulded parts and extruded metal rails.
Magna Decoma worked with mouldmaker Hofmann Werkzeugbau, WIT equipment supplier PME Fluidtec and materials company BASF, which contributed a new material developed specifically for this type of “structural” WIT moulding application.
BASF processing technology specialist Jochen Schmid says WIT can produce parts with channel diameters that, if they would be at all possible in GIT, would be much more variable than with WIT. “Even parts that had never been considered for GIT can be realised in WIT,” he says.
For the roof rail project, BASF contributed its Ultradur B4040 G10 WIT PBT/PET blend grade. Schmid says this uses the company’s High Speed nanoscale additive technology to provide the improved flow needed to fill the two-metre long rail.
BASF’s WIT material line-up also includes a new product developed for automotive media ducts. The glass reinforced easy flow PA66 grade A3HG6 WIT provides enhanced hydrolysis resistance to cooling water. It joins the earlier heat stabilised easy flow PA66 grade A3WGM53, which is intended for hot oil ducts. Other new introductions include a 50% glass fibre reinforced Ultramid B3 G10 SI, which is claimed to deliver an improved surface.
Lanxess has also been active in development of WIT products. Its easy flow 30% glass fibre reinforced PA66 material – Durethan AKV30X HR EF – is used in one of the first commercial WIT cooling water ducting applications at Heyco, which moulds the ducts for BMW four-cylinder diesel engines.
The new Lanxess grade provides high hydrolysis resistance and is claimed to withstand continuous exposure to hot cooling water at 125°C, as well as peaks of up to 143°C. According to Susanne L?derach, Heyco plant manager in Remscheid, the WIT process provides real advantages over gas assisted moulding in this application. “The WIT process enables, with the tailor-made PA66 from Lanxess, much more efficient production of cooling water ducts,” she says.
Channel cross-section appears to be one of the critical factors in determining suitability of WIT. Decoma European engineering centre innovations manager Klaus Münker maintains the technology is ideal for cross-sections above 20mm. And his views are shared by Alexander Jung-K"nig, media system moulding manager at Polytec, which has been using WIT since 1999 in development and since 2004 commercially.
Jung-K"nig says comparative GIT/WIT trials at Polytec have shown that GIT has the edge for media duct interior diameters below 15-20mm, while WIT gains the advantage from 15-20mm up to 60mm. He says that its first commercial application – a window frame module – could not have been produced profitably using gas techniques.
Polytec is now a volume WIT manufacturer, producing 200,000 38mm outside diameter media ducts every year. This component, which is manufactured using PME fluidtec equipment, comprises a 30% glass fibre reinforced PA66 outer layer with a PP internal surface.
Material supplier Schulman worked with Polytec on the project for the part, which weighs 550g and is produced on a cycle time of less than 50s using the short-shot (partial filling) version of WIT. Jung-K"nig sees potential for further reduction in the cycle time in the future.
One of the big advantages that water provides, aside from its cooling capacity, is its incompressibility. Jung-K"nig says it is like having an additional holding pressure within the moulding process. “The WIT process is better to control and I therefore get much high efficiency”, he says. However, he advises that using more water than necessary can risk building up stress in the moulding.
DuPont also offers a WIT optimised product and says that its hydrolysis stabilised 33% glass fibre reinforced Zytel EFE7392 polyamide 66 material is now being used for 650mm long cooling water ducts by Hutchinson in Germany. The ducts are used on a number of VW/Audi group 1.6 litre petrol engine vehicles and withstand internal pressures of close to two bar.
Aside from higher resistance to glycol in the cooling fluid and improved burst strength at temperatures up to 135°C, DuPont says considerable cost savings have been achieved using the new duct designs. A 50% weight saving has been achieved, but also other features including better space management, elasticity of the pipe and the ability to integrate fixing plates and branch connections in the moulded part.
Hutchinson polymer technology manager Olivier Nicolas says: “We compared a number of polyamides, as they have already proven their value in similar fluid transfer systems for the engine compartment over a number of years. In the end, tests conducted at our laboratory showed that Zytel EFE7392 met all of our requirements.”
The performance and application balance between water and gas assisted moulding techniques has also been explored by Volkswagen, which uses WIT to produce the clutch pedal of its Touran medium MPV.
Volkswagen is a large scale plastics processor operating 31 injection moulding machines with clamping forces of 800 to 4,000 tonnes, eight extrusion blow moulding machines and four lines for polyurethane foam processing at its plant at its headquarters facility at Wolfsburg, and a further 120 moulding machines at Brunswick (Braunschweig) where it runs both GIT and WIT equipment.
Andreas Wolff, process technology specialist at the Volkswagen moulding plant in Wolfsburg, says it is at the Brunswick location that it manufactures the WIT clutch pedal. Originally designed and produced as an insert-moulded hybrid metal-plastic part, the pedal weighed 400g. The plastics WIT component, produced in a 30% glass fibre reinforced PA66, weighs half as much.
Speaking about the application at a Battenfeld Injection Moulding assisted moulding seminar this summer, Wolff said the drivers to redesign the pedal were to save vehicle weight, to reduce cost through faster cycle time, to cut the number of process stages, and to ease recycling. The all-plastic WIT-moulded clutch pedal, which is produced in PA66, has cut cycle time by 50%, reduced costs by 10% and saved 50% in weight over the original hybrid design. Product quality is ensured through the use of ultrasonics to monitor and control wall thickness.
Wolff says that VW’s aim is to “achieve leadership in the use of WIT in pedal technology.” He says that, after using this as its entry to WIT processing it now plans to implement it on more pedal projects and in other applications. “In the medium term the aim of the plastics technology business area is intensified use of forward-looking and technically demanding process technologies to increase competence in plastics,” he says.
Also speaking at the Battenfeld Injection Moulding assisted moulding seminar, Müller-Technik managing partner and sales manager Helmut Kohake said the company had achieved great success with the 30% glass fibre reinforced PA6 automotive seat adjustment bars it is moulding in a Schulman PA6 GF grade using WIT.
Replacing metal alternatives, advantages of the polymer solution include through-colouring, which avoids the need to paint, and the potential to integrate functional elements and soft touch features using two-component moulding. And with the plastic WIT-moulded bar weighing 210g against 340g for steel, Kohake calculates that 208 tonnes a year of steel can be saved on the Opel Corsa and Fiat Grande Punto vehicles and 89 tonnes a year for the VW Golf Plus.
Experience with modelling WIT processes has also developed considerably. French engineering consultancy Simplast has carried out simulation studies on 10 WIT projects to date, as well as a further 150 GIT projects.
At the same seminar, engineer Jean-Luc Dreyer says the company uses Moldflow, Master Serie from SDRC for design and finite element modelling, C-Mold for GIT rheology, and Rem3D for GIT/WIT 3D studies. He believes that users get the best from any fluid assist moulding project through simulation. Simplast WIT projects have included the Vorwerk Semco mixer handle and Smoby child’s bicycle applications.
In the gas moulding sector, Simplast was involved in the development of the 2.8kg Slick Slick chair, designed by Philippe Starck and moulded in 142s in 20% talc filled PP at GIDI Production in France using seven gas injection points. Other GIT projects include an 895g Audi TT tailgate component moulded in Bayblend T65N on a 145s cycle.
Dreyer says that success with GIT does not always mean weight saving. The company was involved in development of a sliding automotive roof frame where the GIT version actually weighed slightly more than compact version – up from 4.2kg to 4.3kg – but the number of hot runner nozzles was cut from 12 to 7, the clamping force needed from 1,650 tonnes to 1,250 tonnes and part warping down from 65 to 8mm. This is due to the improved cooling and more homogeneous shrinkage resulting from the better fibre orientation that results from the GIT process.
With a 15% faster cycle time, production costs in the GIT version have been cut by 25%, on top of which there is a saving of €50,000 on the cost of the hot runner system.
The company also helped develop a GIT mixer cover moulded by AI2P in Lourdes, France, which resulted in a 15% weight reduction to 36.2g and a 40% cycle time reduction to 28s compared with compact moulding. Sink marks have also been eliminated.
AI2P, formerly known as Pyrenées Injection, is focused with 56% of its turnover on moulding for domestic appliance applications. Industrial business manager Eric Penfrat says the company is concentrating its efforts today on more technical plastics and on more complex techniques such as gas assisted injection moulding in order to guard against the long term advance of its competitors in northern Africa and China.
PME Fluidtec, which claims to have supplied 42 WIT units for more than 28 series applications by the middle of this year, has now supplemented its product line with its CIT system – Combined Injection Technology. As the name suggests, this combines GIT and WIT assist processes in one tool and was introduced at the Fakuma 2006 fair. The company is also working on new solutions for media duct production, including the projectile injection technique developed by R"chling (former Seeber) Automotive, which was awarded an SPE Central Europe innovation award last year.
Tel: +86 576 84616076
Fax: +86 576 84616079
Mobile: +86 139 0657 3032
Address: No.35-1, Qingfeng Road, North Industrial Estate, HuangYan, Zhejiang,China.