The automotive industry may not be the largest sales market for tube manufacturers, but it is indeed an important one. Several meters of tubing or tube-like profiles are found in every road vehicle – mostly invisible from the outside. And just like every other component in a motor vehicle, they are continuously being modified with the goal of optimizing costs as well as reducing weight and improving mileage.
The use of “exotic” materials such as carbon fiber and magnesium is limited, especially in mass-produced vehicles, due to cost restrictions. Instead, aluminum and steel remain the most widely used materials. New, high-strength steel grades play an increasingly central role in the reduction of vehicle weight and CO2 emissions, as well as the improvement of mileage.
This progress can be witnessed not only with automobile manufacturers but with suppliers, who play a more important role in the total automotive supply chain today than ever before. One of the companies that invests a great deal in research and development in the area of automobile manufacturing is ThyssenKrupp AG. The primary goal of their InCar plus research project, which involved the entire corporate group, was to be able to offer their customers a broad range of quickly implementable, series production-ready solutions. The project resulted in more than 40 innovative solutions for chassis, steering, drivetrain and body that “…offer component weight reduction of up to 50% and cost savings of up to 20%,” according to Dr Heinrich Hiesinger, CEO of ThyssenKrupp AG.
The CO2 emission reduction targets set by EU legislation pose great challenges for the automotive industry. Lightweight automobile construction with steel is an important contribution to meeting these targets, according to Dr Heribert Fischer, executive board member for ThyssenKrupp Steel Europe AG, “…primarily because it is ecologically sensible and economically workable, making it especially practical for compact and mid-sized vehicles, which are subject to enormous cost pressure.” The same applies to the increasing safety requirements placed on automotive manufacturers’ products, which manifest themselves in more stringent crash tests.
Hot Working is a Major Trend
Hot working is a proven method for manufacturing parts with complex shapes that are crash-relevant and thus require a high level of strength and stability as well as low weight. In this method, plates are heated until red hot, then shaped in a press and subsequently cooled as quickly as possible. In the automotive industry, according to Dr Fischer, “Aluminum and CFK are not the fastest-growing materials in the automobile, but rather hot-worked steel components.”
In experimenting with high-strength steels during the InCar plus project, automobile components made of new steels – such as dual-phase steel with a tensile strength of 1200 or ultrahigh-strength manganese-boron steel – were developed. B-pillars, for example, which are so heavily stressed in a side crash, were manufactured using cold- and hot-working processes. The high strength of the steels allowed the use of thinner metal sheets, thus achieving cost and weight advantages compared to conventional components.
Hot working makes it possible to manufacture extremely complex component geometries. A newly constructed front bumper frame is an excellent example. Made of hot-worked manganese-boron steel, this new component brings a weight reduction of almost 20%, or roughly 2 kilograms. Thus, it weighs about the same as an aluminum component while costing significantly less.
Another example is an A-pillar with hot-worked closed profiles. In addition to a weight reduction of more than 3 kilograms, this cost-saving lightweight construction alternative allows for a more slender A-pillar, which improves the view to the front. A B-pillar of TriBond (a triple-layer steel material composite for hot working) promises to bring significant weight and cost reductions compared to conventional solutions. The combination of high-strength with high-ductility (highly malleable) steels in a steel sandwich material promises characteristics such as high energy absorption and large maximum bending angles.
Optimizing Drivetrain Technology
Another focus of the InCar plus project was the optimization of drivetrain technology toward more efficiency and lower emissions, and that with the conventional internal combustion engine, which – according to Dr. Karsten Kroos, chairman of the management moard, Business Area Components Technology for ThyssenKrupp AG – will remain the dominating drivetrain technology for the foreseeable future and offers the greatest potential for the avoidance of pollutant emissions. Next to increasing thermodynamic efficiency, the primary focus here was avoiding friction losses in the drivetrain.
One of the developments was a camshaft with an integrated oil-separation system that renders the conventional external oil separator unnecessary since the entire gas and oil-separation process takes place in the camshaft itself.
“This integrated solution is not only more efficient than the reference systems, but also saves space, creating new leeway in engine architecture for vehicle manufacturers,” Dr. Kroos said.
A further example for the use of modern light-construction materials for component manufacturing is hybrid adjustable cam elements in which plastic and steel parts are bonded using a special injection molding process. Besides the weight reduction of nearly 30%, this technology promises improved adjustment dynamics, leading to potential fuel savings of roughly 5%.
Next to the classic internal combustion engine, hybrids and 100% electric drivetrains were included in the InCar plus project, with the goal of increasing the efficiency of electric drives. For example, a new rotor architecture was developed that brings a weight reduction of up to 16% thanks to its modular, multi-part construction. Moreover, the concept creates more installation space in the rotor interior, which can be used for functions such as oil feed, active cooling or motor sensors.
New solutions were also discovered in the area of chassis components. Due to new forming processes, the design shock-absorber tubes could be individually adapted to the characteristics of a particular installation space. Furthermore, shock-absorber tubes made of stainless steel were developed for extreme road and weather conditions. Such tubes are corrosion-free and especially well suited for use in off-road or special series vehicles.
In the search for new solutions, ThyssenKrupp engineers are not only focusing on steel materials. The InCar plus portfolio also includes components made of CFK, such as an extremely rigid and light CFK shock-absorber tube that is claimed to be roughly 30% lighter than the lightest aluminum tube. A series production-capable industrialization concept was developed alongside this new CFK component. Utilizing all optimization potential, it should be possible to achieve a weight reduction of approximately 45%.
Heat Pipes Utilize Surplus Energy
Helping customers build better cars by supporting them at an early stage with topics such as lightweight construction, safety or emission reduction is one of Benteler International AG’s primary goals. One project among their product and process developments in the area of automotive technology is aimed at heat recovery from the automobile exhaust system via special heat pipes – so-called loop heat pipes (LHP). A system for heating the passenger cabin has already been tested on an experimental vehicle in practical application and on a standardized dynamometer. Such a system eliminates the need for the conventional electric auxiliary heater in use today, leading to a significant reduction of CO2 emissions from internal combustion engines.
LHPs can also be used in the thermal management of electric vehicles. To this end, a project was initiated under the direction of the German leading-edge cluster, it’s OWL, with the goal of range extension and CO2 emission reduction. What is being examined here is how surplus heat from components such as power electronics and the motor could be utilized to heat the car interior using several coupled and controllable LHP systems.
The so-called varID® concept, which allows the manufacture of tubes with variable wall thickness via a drawing process, belongs to the product area of welded tubes. According to Benteler, this enables them to achieve a weight reduction of up to 50% in tubular anti-sway bars. In addition, initial welding attempts with high-manganese steels that demonstrate extreme malleability show that tubes made of such materials can fundamentally be manufactured. Possible applications include crash structure components in automobiles. In the area of seamless tubes, Benteler was able to increase the maximum possible system pressure in diesel injection tubes for automobile measurement by around 200 bars thanks to a new material and optimization of the process route.
High-Strength and High-Ductility Steels
Similar to ThyssenKrupp, Salzgitter AG is running a corporate group-wide project with their Automotive Initiative. In the middle of 2015 the company presented current developments and solution concepts, including new steel materials, cold-drawn seamless and welded precision steel tubes, as well as prototype and tool construction solutions, all the way to finished IHPF components.
Salzgitter considers HSD® (high strength and ductility) steel to be an innovative material with surprising characteristics. Iron-manganese-aluminum-silicon steel apparently features high strength plus high ductility, making it ideal for the manufacture of hot strip and cold strip, as well as welded precision steel tubes. The high strength of this material allows reduction of the sheet thickness and, with that, lightweight construction applications. The high ductility lends excellent forming characteristics and enables integration of components and functions, making it suitable for complex component geometries. The combination of these two characteristics allows for high energy absorption in crash-relevant components.
A new generation of dual-phase steels is said to feature excellent forming characteristics, which is earning them a reputation as an alternative for micro-alloyed steels, especially for critical forming processes. Among other things, these steels are suitable for components with demanding degrees of deformation (e.g., roof frames) and for parts with high demands on yield strength or special crash requirements.
Salzgitter offers a broad spectrum of individually developed component solutions for lightweight automotive construction. One example of the potential of component-adapted design is an anti-sway bar with a diameter of 22 millimeters and a length of 1,400 millimeters weighing more than 4 kilograms made of solid material. Meanwhile, an anti-sway bar of the same length and a diameter of 23.5 millimeters made of a precision steel tube with a wall thickness of 3.5 millimeters weighs less than 2.5 kilograms – roughly 40% less.
Gear shafts represent another component that can contribute to weight reduction with precision steel tubes. Salzgitter quotes reductions between 20% and 50%. In addition, implementation of an optimized tube manufacturing process can lead to significant cost savings, partly due to a reduction in both production effort and material consumption.
Precision steel tubes for diesel injection lines accommodate the trend in engine production toward higher injection pressure for diesel engines. Thanks to integral material and process development, it is possible to manufacture injection line tubes that can withstand 20% more pressure with the same dimensions and wall thickness as conventional lines.
HFI-welded precision steel tubes of HSD steel also offer great potential. Their high component strength plus high ultimate strain makes them especially suitable in automotive applications for crash-relevant components for energy absorption. Their high residual formability, on the other hand, is welcome during subsequent processing of high-strength components via forming techniques.
The TDT® (tailor drawn tubes) process represents a further lightweight construction concept that allows flexible adaptation of the tube-body wall thickness to the occurring strain. The drawing process developed for this guarantees evenly homogenous mechanical-technological characteristics over the entire length of the component. According to Salzgitter, the weight reduction potential amounts to roughly 20% depending on the initial construction.
Innovative solutions with tubes and tube-like profiles for the automobile industry will play a central role at the next staging of Tube 2016, the International Tube and Pipe Trade Fair. Tube returns to the fairgrounds in Düsseldorf, Germany, April 4-8. Wire 2016, the industry's leading international wire and cable trade fair, will be held concurrently.