Benteler-Sigley has developed a lightweight, space-saving composite leaf spring for Volvo's multi-model SPA global platform, enabling fully automated HP-RTM production.
Volvo's new XC90 crossover SUV is the first model to be produced on Volvo's new global 'extensible vehicle platform architecture ('SPA'), which will eventually include the S60, S90, V60, V90, which have not yet been launched. Several models, such as the XC60. Benteler-Sigley uses a fully automated HP-RTM line to produce fiberglass/PU backplane springs for all of these models on the SPA platform. By 2018, the output will be Up to 500,000 parts per year (picture from Volvo)
As a joint venture between the first-tier automotive supplier Bentler Automotive Industry GmbH (Paderborn, Germany) and the fiber solution provider SGL Group (Wiesbaden, Germany), Bentler was founded in 2008. - Sigri (Rie im Innkreis, Austria) produces a wide range of fiber-reinforced automotive composite components, including flank and columns, doors, spoilers and seats, but by far the most notable achievement is mass production. Expertise in composite sheet springs. Since the acquisition of the automotive business unit of Fischer Composites Technology (Ried im Innkreis, Austria) and the construction of a second composite parts factory near Ort im Innkreis in Austria in 2012, the company has innovated The way to obtain unprecedented automotive composite production capacity.
In 2013, Bentler-SGL replaced the typical epoxy resin matrix material at the time and presented a fiberglass to the Mercedes-Benz Sprinter van of Daimler AG (Stuttgart, Germany). / Polyurethane front axle springs, compared to steel parts, the weight from 15kg to 6kg, weight loss of 65%.
Using Henkel (Düsseldorf, Germany) fast curing LOCTITE MAX 2 polyurethane resin (PU) and high pressure resin transfer molding (HP-RTM) process, Benteler-SGL has achieved 100,000 per year~ Production of 150,000 parts.
With the increase in production of fiberglass/PU rear axle springs for the new XC90 crossover SUV in Volvo (Gothenberg, Sweden), the company is preparing to raise this threshold again. The XC90 is at Volvo's scalable vehicle platform architecture ( Referred to as 'SPA')'s first model produced on this new global platform. As part of this, the leaf springs will also be available in S60, S90, V60, V90 and XC60, as well as any larger cars that may be developed. Get applied on.
'This is the highest-volume composite component project in the automotive industry, and will reach 500,000 parts per year by 2018.' Dr. Robert Ernst-Siebert, Managing Director of Benteler-Sigley, said, 'Besides cooperation from us In addition to the comprehensive expertise of our partners, Benteler and SGL, we have established strong partnerships with our customers and resin suppliers, and we have integrated our existing HP-RTM and preforming processes into a fully automated production line. Important, we have developed a process that is not currently available on the market.'
Benteler-Sigley and Volvo's cooperation in SPA plate spring design comes from extensive experience. 'We have the ability to produce Sprinter van leaf springs, and other suspension system components are available through the Bentler Automotive Group. The production capacity, all of which can be integrated into Volvo's leaf spring project. ' Ernst-Siebert explained.
The design of each leaf spring is determined by its function and requirements. Frank Fetscher, director of business development for FRP chassis applications at Bentler Automotive Group, explains that this design determines the performance and cost of the leaf spring. Designed for Volvo The leaf spring uses up to 60 layers of fiberglass unidirectional fabric to meet performance, durability and cost requirements, as well as very compact mounting space limitations. Although the composite leaf springs and the previous metal leaf springs are generally the same size. The same, but the coil spring and the suspension strut are eliminated, so that the shaft extends less to the trunk area, thus increasing the inventory space.
'Based on material properties, there are some restrictions on design.' He explained that, from the luxury version of the XC90 to the compact X60, a leaf spring design must meet the performance and inventory requirements of all models. That is, the length and width are both 1200 mm and 60 mm. However, the weight of the SUV may vary greatly compared to a small car. Therefore, three curvature shapes are designed to provide a suitable leaf spring for each car weight. For the main indicators of lift and stiffness of different models, on the one hand, the upper and inner bushings can be moved outwards, and on the other hand, by using different pads at the end of the spring, the adjustment can be made for each model. Need to provide additional capacity for adjusting spring performance while ensuring that the production process is as simple as possible. Therefore, Benteler-Sigley is able to manage a large number of complex applications. 'Volvo and we have developed this capability to make springs The stiffness factor adapts to different models. ' Fetscher said.
According to Volvo's request, the design and final production process were verified. 'We support their ideas on how to verify.' Fetscher said, in addition, includes computer-aided engineering (CAE) and physical testing. 'We will also their Requirements are included in our CAE fatigue program and mechanical fatigue testing. 'He pointed out that this includes dynamic fatigue load testing from road load data, as well as static load testing, all of which are done under different environmental conditions. Fetscher added Said that all the chassis components of Benteler Automotive Industry Co., Ltd. and Benteler-Sigrid, such as anti-roll bar or lower control arm, have been similarly tested and used for the service life of the components. A good prediction.
At the plant in Ort im Innkreis, Austria, Volvo's leaf springs are produced using LOCTITE MAX 2 polyurethane resin using the HP-RTM process. However, higher annual production targets need to reach new levels of automation. All processing steps are automated and there is no manual intervention. ' Ernst-Siebert repeatedly emphasized that 'this in-house development line is the key to our successful production of high quality final parts.' Therefore, it is perfectly understandable that Benteler - SGL is not prepared to reveal many details.
The first part of the line includes automatic cutting and preforming of unidirectional reinforcements, which is also an aspect of the production control system. 'We are able to fully control this line, including automatic inspection.' Ernst-Siebert explains , 'There are different quality assurance steps on the entire production line, not only visual inspection, but also automated mechanical testing. Every leaf spring will be tested. ' Fetscher adds that this test checks the stiffness of the spring and 100% of the parts. Functionality, this is the standard practice for this type of application.
Ernst-Siebert insists that the key to achieving stable, powerful machining and obtaining reproducible parts is what he calls online control of all material parameters. Fetscher exemplifies: 'A pre-form that is not suitable for layup, the system will This mismatch is detected between the test parameters and the programmed parameters so that we can immediately know the problem. Then, we remove the unqualified parts and make corrections to ensure that this part of the line is corrected. 'He said that the future Benteler-Sigley will move towards a self-controlled production line. 'This is the first step we have taken in this direction to get an integrated Industrial 4.0 production system.'
Pre-forming is the next step in this automated production line. First, an industrially advanced epoxy or polyurethane-based powder binder is used to stabilize the unidirectional fabric laminate, and the binder is melted by heat and pressure. The molded part is consolidated. Then, the robot transports multiple preforms on one leaf spring to the multi-cavity lower die of the HP-RTM press. 'As part of our proprietary internal development, we have A special fixture was developed for all such transfers. ' Fetscher said.
'Thank you for the help of SGL, we have done a lot of research and development work to define the best material concepts for this special leaf spring application, including fabrics and adhesives.' Ernst-Siebert points out, 'This is not like It seems so simple, only a few fabrics are perfectly suitable. For example, SGL is made up of materials developed for these leaf springs. Its special design not only satisfies the functional requirements of the components, but also provides stable preforms. . '
After the preform is placed, the mold is closed and resin casting begins. However, in order to achieve a high level of automation in the HP-RTM process, deep development is required. 'The key is to optimize the process.' Ernst-Siebert asserts, 'You must be on the resin I have an in-depth understanding. By working with Henkel, we have done this. At the same time, we must have an in-depth understanding of the fabric. By working with SGL, we have done this too. So we know how to adjust the parameters. Meet cycle time requirements and achieve production. '
'Two major challenges are mechanical properties and processes.' Frank Kerstan, global project manager for Henkel's Adhesive Technology business unit, said, 'The leaf springs must be very tough and durable, capable of withstanding hundreds of conditions under different conditions. Thousands of dynamic loads. However, high-volume production requires very fast casting and curing. ' He found that polyurethane is ideal for this application. 'Polyurethane provides high strength similar to epoxy, and also has a high Elongation and toughness, both of which are important for this application. ' Kerstan explained.
'There are a lot of resin suppliers offering epoxy resins, vinyl ester resins and polyurethanes. However, for our special projects, Henkel is able to meet the cycle time and cost structure requirements with high industrial yields,' Fetscher said.
Kerstan explained that because the glass fiber content in the final product is 55%, which is relatively high, the crucible is poured very quickly, but it does not cause fiber misalignment, and it is necessary to ensure that one part to the next is reliable. LOCTITE MAX 2 resin has a viscosity of 200~300mPa or cps at room temperature, but drops to 10cps at 90°C, allowing reliable and rapid impregnation of the fiber without shifting the fiber.
Benteler-Sigley has used a variety of equipment at its Ort im Innkreis plant, including a Hennessy Streamline unit with a custom mixing head and a KraussMaffei mixing metering device. A Dieffenbacher HP-RTM press, and a Cannon Afros custom-designed metering device for the HP-RTM process, with two dedicated FPL14 mixing heads.
In order to produce Volvo leaf springs, the main components of the PU resin are degassed to avoid the formation of air bubbles in the components, which are circulated in the heating jacket and passed through the heating pipe before being metered into the two mixing/injection mixing heads. Keep the temperature. The pressure in the mixing head is 120~ 140 bar. Each mixing head can inject 11kg of resin in 22s.
Typical metering, mixing and pouring equipment, through the mass flow meter to send data to the control system to continuously monitor the flow of each component. If a deviation from the specified value is detected, the system immediately performs the parameters of the relevant metering pump. Management, real-time recovery to the required flow. In a 90m2 area, various resin storage, conditioning and pumping devices are installed.
Just as heating the resin is necessary to optimize the impregnation of the flow and the preform, the heated mold is also very important for the curing of the composite. A multi-cavity mold configuration is used here. Ernst-Siebert said that although The report proposes 8 to 10 or even 12 cavities, but the number of cavities actually used depends on the yield of the project. 'This can be changed according to customer needs and component design.' He added, 'To satisfy For the cycle time required by the customer, we used a multi-cavity mold, which was finished in 10 minutes. 'Although this time does not include the placement of the preform or the removal of the parts, both operations are automated. , its design meets the production requirements of the components.
In order to adapt to the three different spring curvature designs, three different upper molds have been developed. For each upper mold, three lower molds have been developed to change the thickness of the spring. Thus, nine different lower molds can finally be used. It is used in production according to the mixed model order. In addition, there are additional options. Kerstan explained that with LOCTITE MAX polyurethane resin, catalyst can be added according to the size of the part to further shorten the curing time. He also pointed out that the external can be used. Or internal release agent. 'Whether using an external release agent or an internal release agent depends on the part program and the cycle time and dwell time during processing. ' However, he warned that because the leaf spring is dynamically loaded Parts, so internal mold release agents may affect the performance of the part. 'Auxiliary products that match the chemical composition of the resin, such as binders, catalysts and internal mold release agents, are very important. ' Kerstan also pointed out that the mold shape is the most determined. Key factors for a good release method: 'If there is a groove and a difficult angle of release, an external release agent may be required.'
Two new presses were used in the fully automated production line of Volvo leaf springs. 'To achieve maximum production, we have established a second automated production line.' Ernst-Siebert said. Due to the high degree of automation, only a small amount is required. Technicians come to operate these production lines. 'We currently implement two shifts. If necessary, we can also implement three shifts. ' Ernst-Siebert said, 'We are very flexible to meet the needs of our customers. If needed, we can 7 per week. Days, run these production lines 24 hours a day. '
These production presses are comparable to a 1600t shuttle twin-station press in the R&D center of Ried im Innkreis. Ernst-Siebert emphasizes the technology center and the Ort im Innkreis production plant The importance of the relationship: 'We have an automated pilot line in the technology center, which is suitable for small batch production, but can simulate the entire process. Just like we set up this line in the prototype stage, we tried very close to 'How can I make parts in actual production'. ' He added that his team also received a simulation of Benter's concept of the machine, as well as analysis and simulation of materials by SGL experts. 'Because of this, we Through the development of HP-RTM, our process technology has been further improved, and the progress has been rapid.'
'We also apply this to metering devices and casting of resins.' Fetscher said, 'In order to be able to identify problems and improve in the early stages of process development, early involvement of resin suppliers such as Henkel played an important role. '
Ernst-Siebert said: 'This is important because the process is too complicated. It is impossible to adjust one parameter to make every necessary improvement. You have to adjust multiple parameters at once.'
When the parts are fully cured, the robot transfers them from the HP-RTM press to the automated milling unit where it is trimmed and drilled at the end of each leaf spring. Fetscher believes that such automation is the industry standard. However, it is pointed out that the fixture of Benteler-Sigley is special, and its trimming process has no manual intervention.
With the Volvo rear-plate spring project progressing as planned to achieve maximum production in 2018, Benteler-Sigley has turned its attention further. 'We have discovered other opportunities for rear-plate springs and are working hard Develop more applications with OEMs. ' Fetscher said, 'Motivation and market drivers remain the same, and future alternative vehicle structures may bring more potential to this application.'
Kerstan agrees: 'Other car manufacturers have indicated that they intend to adopt this same lightweight composite sheet spring concept, and I am also convinced that this compact plate spring shaft is very suitable for the body/chassis of electric vehicles. Concept. '
In addition, Benteler-Sigley also uses its transverse plate spring design and production experience for longitudinal glass fiber reinforced spring production.
'To maintain the same or slightly improved functionality, the use of composite materials instead of steel to make leaf springs offers tremendous opportunities for weight reduction at a reasonable cost,' explains Ernst-Siebert.
Henkel is targeting a number of other automotive applications, including structural body parts and externally sprayable parts, such as the surface RTM process to make the roof. The company has also developed a suitable high temperature for mass production of carbon fiber reinforced wheels. (Tg>200 ° C) epoxy resin system.