Lightweight air ducts and turbo pipes through extrusion blow molding

The First Extrusion Blow Molding Seminar was held at Novotel Suzhou on November 28-29, 2016. Hosted by EMS-CHEMIE (Suzhou) Ltd. (EMS-GRIVORY), the seminar was attended by more than 150 automotive OEM's, Tier-1, machine and technology suppliers from the Asia-Pacific region. The event served as a technology platform that introduced participants to the latest trends of lightweight engine air intake and air ducts from various technical aspects.

Turbochargers allow smaller displacement engines to deliver the same power output that can be achieved with an original aspirated engine and a larger displacement. However, comparing a turbo charged with an original engine, the fuel consumption can be reduced by 20% up to 40%. With growing demand for turbochargers in the Chinese automotive market, the seminar by EMS-GRIVORY covered almost the entire industry chain of automotive air intake and turbo pipe systems, including OEM's, Tier-1, machine, process and material suppliers. The seminar tackled such topics as challenges and opportunities in intake systems, choosing the right air duct materials, the process of extrusion blow molding (EBM), mold design, requirements for sequential coextrusion technology and selected specialty materials, intercooler pipe quick-connector technology, nylon material drying process, design of air ducts through computer-aided technology (CAT), as well as plastic welding technology for three-dimensional blow molding applications. The following article presents a summary of the event and the covered topics.

OEM application requirements

The Asian automotive market is continuously developing, and recent market changes are forcing OEM's and Tier-1 suppliers to meet stricter CO₂ emission regulations, higher temperatures and offer weight savings, while maintaining the level of performance of the vehicles. On behalf of the OEMs, Dr. Xiong Fei, Chief Engineer at Zhejiang Geely Automobile Research Institute Co., Ltd., highlighted the challenges and opportunities in automotive air intake systems and the advantages of cooperation models. During his presentation, Dr. Xiong Fei explained that the future development needs of air intake systems are mainly driven by China's latest emission regulations, which firstly, put forward stricter requirements for intake system weight savings; secondly, it proposed higher requirements for the economic efficiency of traditional processes; thirdly, the increased use of small-displacement engines will force materials to be more compact and resistant to high temperatures; and finally, the increased demand for NVH. Dr. Xiong Fei explained that in order to be successful and to meet these demands, OEM's, part-, systems and material suppliers must work closely together.

Dr. Xiong Fei believed that nylon material for extrusion blow molding would be the direction of lightweight design for air ducts, which is determined by relevant material and technology characteristics: I. Turbocharged air ducts made of blow molding grade PA6-GF15 or PA66-GF (15-25) materials can be molded in one process and work under long term heat influence up to 150-200℃; II. Compared to metal rubber composite pipes and thermoplastic rubber pipes, nylon based extrusion blow molding turbo intake pipes are 20% cheaper and up to 30+ % lighter; III. Nylon is recyclable and thus environmentally friendly.  

"Extrusion blow molding applications will be increasingly used in automobiles. Nowadays, more than 10kg of blow molded parts are used in a vehicle and the applications using this technology will be further expanding." Evaluating the future, Dr. Xiong Fei believed that extrusion blow molding technology would remain promising, as "in addition to the current application such as fuel tanks, intake pipes and others, the technology of extrusion blow molding can be extended to tool boxes, glove boxes, disposal container, rear seat backrests, rear seat cushions, liftgates, rear bumpers and selected soundproofing pads in the future.”  

In fact, Geely Automobile has partnered together with EMS-GRIVORY in the use of plastics instead of aluminum for a car cross beams (CCBs) application. The mainstream solution to reduce weight in this application is to adopt the magnesium alloy/aluminum alloy material design; however this increases the costs of the application remarkably. Advantageously, the usage of plastics instead of aluminum can reduce the application weight by 25% and can also cut costs. In the process of this CCB application, the Lightweight Team of Geely provided the resources from all parties, including Tier-1 suppliers, while EMS-GRIVORY was fully integrated to jointly develop the CCB through plastics technology and to promote the CCB industrialization feasibility.

Apart from Geely, Volkswagen attended the forum as an OEM representative. Mr. Zhao Bin from the China Materials Technology Laboratory of Volkswagen (China) Investment Co., Ltd. focused on the selection of materials for intake pipes and turbo pipes. According to Zhao Bin, heat resistance, chemical resistance, axial rigidity and other key characteristics for a pipe must be taken into account when selecting the materials. For turbo pipes, extrusion blow molding is used for the hot side of the engine in Volkswagen models and materials are selected based on temperature resistance; while the process of injection molding and welding is used on the cold engine side.

Zhao Bin explained that in addition to the correct selection of material grades, the requirements for functional testing of wall thickness and the corrugated part must be considered. He stressed that in China, Tier-1 suppliers do not pay much attention to the testing of material, while related data is often only provided by material suppliers or third-party laboratories. This results in problems, as some of the test methods may not be consistent enough, as third-party laboratories are not in close communication with Volkswagen. In the case of Volkswagen, mechanical properties tests are conducted with samples taken from products rather than relying solely on standard samples; and nylon may be dry or wet but the state must be figured out in order to assess its thermal aging properties.

High potential for extrusion blow molding process

Nowadays, the world's major automotive markets are facing stringent regulations on carbon dioxide emissions. The turbo technology has become an important choice and according to statistics, there will be 4.9 million vehicles equipped with turbocharged engines every year by 2019. China will lead in the global turbo charged trend, while the annual demand of the Chinese market for turbochargers is expected to reach 13 million units by 2019.

But how are engine intake and turbo plastic pipes molded in order to make use of advanced production technology? Mr. Andreas Lichtenauer, Managing Partner of Kautex Maschinenbau GmbH, presented the company's latest generation of high-yield, double-station 3D suction blow molding machines and their advanced process technology. As a market leader in the area of plastic fuel tanks, Kautex manufactures high-end extrusion blow molding equipment for the automotive industry. According to Mr. Lichtenauer, air ducts produced with Kautex suction blow-molding machines offer advantages over traditional metal-rubber composite pipes, such as no scrap, lower clamping force, simpler molds, wider choice of machinable resins and proven reliable processes.

Furthermore, Mr. Lichtenauer highlighted key features of their KSB10 modular suction blow molding machine. The model is available in single station and double stations and suitable for a wide range of raw material types. Its features include 40% reduction in footprint, extremely low power consumption resulting from servo hydraulic and beltless extrusion drives, intuitive operating system and quick, easy mold change system, making the machine more efficient and easier to operate. Mr. Torsten Schonauer, also from Kautex, focused on the technology related to the molds for 3D suction blow molding machines. When explaining 3D blow molding mold design principles, he mentioned that the design of a mold depends on material blowup ratio, ovality, curvature, corrugated part and the welding area. He also said that it had become a challenge to make an air duct resistant to drastically changing pressure and increasing vibrations  

Mr. Ming-Jiann Cheung from EMS-GRIVORY responded to this challenge with his presentation on computer-assisted technology: "an ordinary bellow has the disadvantage that the axial rigidity is too weak and its axial deformation is too significant under internal pressure. In addition, the fatigue stress brought about by such axial deformation reduces the service life of an intake pipe. EMS-GRIVORY has therefore developed a solution called MOAX® - mono-axial direction, and means that the pipe may be very flexible in one direction but very rigid in another. Through this technology, MOAX® behaves as flexible as an ordinary bellow under the same bending load. With two smooth surfaces in the middle of a pipe, MOAX® makes it axially rigid, thus extends the service life of an air duct. "

Selection of materials is critical

In order to mold a sequential extrusion blow-molded air duct, three key conditions are of importance: the right sequential extrusion blow molding machine, a unique pipe design and the right combination of flexible and rigid materials. According to Mr. Hans Kreil, Application Development Manager of EMS-GRIVORY Asia-Pacific, intake pipes produced with traditional technology are mostly made of metal + rubber and heavier; and assembly costs must not be belittled since there are as many as 15 parts. The use of sequential co-extrusion blow molding technology can reduce costs and the overall application weight by 30%.

EMS-GRIVORY offers a wide range of extrusion blow molding material portfolios, including non-reinforced and reinforced nylon materials. They meet high temperature application requirements of 130 up to 210℃, which almost covers the entire operating temperature range of automotive engine intake and turbo pipes. Presently, EMS-GRIVORY's nylon materials has been used by OEM's in the form of injection or extrusion blow molding, and play an important role in engine intake pipes, turbo pipes, silencers and other areas.

Nylon material drying has been one of the industry's most talked-about topics. Mr. Aaron Lv from Motan Colortronic put forward two pieces of professional advice based on his years of experience: Dehumidifying dryers are the best equipment for drying nylon and keeping a consistently stable dew point is the most important factor for maintaining high drying efficiency, while the drying airflow, drying temperature and drying time may also affect the efficiency of dryers.

Mr. Bruce Pan from EMS-GRIVORY introduced that the company began its step in use of plastics instead of steel more than 26 years ago; nowadays, it has become China's first material manufacturer with professional extrusion blow molding equipment, which is in line with EMS-GRIVORY's orientation "as a professional team in use of plastics instead of steel".

The seminar participants visited the EMS-GRIVORY factory nylon modification production line layout, and got deeper understanding of its customer service: EMS-GRIVORY does not only provides customers with right nylon materials, but also provides them with whole-process technical support, e.g., rapid prototyping, material testing and design optimization specific for different processes. These services were demonstrated with six workstations. The six workstations were Nylon Modification Production Line, with newly purchased machines from Kautex, KraussMaffei, Arburg Injection Molding Machine, and Materials Testing Laboratory and Computer Assisted Technical Service (CATS).

The visitors marveled at EMS-GRIVORY factory production line and equipment configuration. The EMS-GRIVORY factory nylon modification production line shows an orderly distribution of processing facilities for extrusion, granulation, drying, transfer and packaging. The entire process was nearly automated. The second was a combination of extrusion blow molding machine with EMS MOAX patented design, making it possible to mold engine intake pipes. Insert molding technology helped reduce secondary processing and subsequent assembly steps. "First, obtain an intake pipe with the extrusion blow-molding process, and place parts into a mold. After overmolding, these structures will be molded directly on the surface of parts. The two materials will be firmly bonded together. Parts consisting of single component do not only become lighter, but also make the production and assembly processes more efficient and help to reduce costs significantly", introduced by EMS Engineer Mr. Liang.

Finally, it is worth mentioning the application of plastic welding technology in the area of three-dimensional blow molding. Mr. Jacky Liu from Branson focused on the current mainstream plastic welding technology and related applications. He took an air duct made of PA6 + PA66 for example, and mentioned, "a complex intake pipe can be created through the use of clean infrared welding technology (CIT), and there are few limitations on product shape; the features include no material adhesion, no damage to internal components and lower energy consumption."

The podium discussion focused on the future development of air ducts, related extrusion blow molding technology and the trend of new energy vehicles. Most of the guests believed that the trend of new energy vehicles is irreversible; however, the turbo technology would continue to develop in the next 10-20 years, which means that plastic intake pipes and turbo pipes would continue to have a market. Most of the speakers believe that the extrusion blow molding technology will has 10-15 years golden development period. More guests believed that there must be new market opportunities for the extrusion blow molding technology with the advancement on lightweight cars; in the future, many body parts, for example thermal management systems, battery pack assemblies, windshields and tails, may be produced with the extrusion blow molding technology.

Conclusion

After over 100 years of development, the automotive industry is facing a lot of problems and challenges, including power performance, economy, fuel consumption, environmental protection and other issues. Lightweight design covers all outstanding issues of a car. It can be said that now is the best time to start automotive lightweight design, especially lightweight technology for engine peripheries.

The first extrusion blow molding seminar hosted by EMS-GRIVORY attracted OEMs and parts suppliers from many Asian countries. It focused on the lightweight technology of automobile intake pipes and turbo pipes, gave a comprehensive introduction to material selection and testing requirements for OEMs. Industry chain suppliers shared the principles and applications of the latest blow molding technology and equipment, as well as the most cost-effective nylon material solutions and auxiliary equipment.