Whether lighter, quieter or cheaper – there are many reasons for replacing metal with plastic. The basis is a comprehensive new parts process. The following examples show the high demands that are placed on plastics, the expert knowledge that is required and which components are well suited for replacement.
faigle is presenting its products at InnoTrans in Berlin, and is happy to answer questions from visitors and give advice.
In the railway sector, metal components are being increasingly replaced by engineering plastics. "Weight, noise and attenuation are driving factors in this industry development," explains Wolfgang Siegl, Head of Sales and rail business development at faigle.
For rail-bound vehicles of all kinds, faigle replaces metal products with components made of high-tech plastics. These special components withstand vibrations, temperature fluctuations, moisture and dirt, are abrasion-resistant and have the best sliding properties. In contrast to metal components, they are also installed faster, are maintenance-free and cause less wear on the counterparts.
Replacing metal with plastic can also be worthwhile if a product is oversized – i.e. the conventional component can do far more than it needs to, such as with roller axles for conveyor systems. These axles are normally made of steel and are thus oversized. Replacing the metal with plastic enables a weight saving of up to 90 per cent, production costs can be halved and the noise reduced.
But before such high-performance products are successfully used, they have to go through a complex new parts process. Experience and expert knowledge have a direct effect on the subsequent quality, functionality and production price. For more than 40 years, faigle Kunststoffe has specialised in the development of engineering plastics and the manufacture of plastic parts for various industries.
"We are good at optimising specific parts or processes," explains Wolfgang Siegl. In the enquiry process, the employees from the sales groups first estimate whether the new workpiece can be produced in compliance with all the high faigle standards. The cost-effective feasibility is assessed on the basis of models, specifications or drawings, and the experience from numerous other projects. If this feasibility analysis is positive, nothing stands in the way of an offer.
"In doing so, enquiries about a standard product such as switch bushings can be answered faster than an enquiry about complex, new components," says Wolfgang Siegl. Good teamwork among the faigle experts is crucial for accurate decision-making. If an enquiry turns into an order, the participants from Sales-Group, design and process technology work together until series production. Experience from various industries makes cross-connections possible and strengthens the innovative development process. The Sales-Group consultant also remains the contact person for the customer – from the beginning to the end of the project.
Construction starts once the order is received. Several factors are mutually dependent here. On the one hand, the knowledge about tribology, i.e. the sliding properties of plastics and thus the selection of the right plastic, the construction of weight-optimised geometries with the appropriate dimensioning of the components and the experience in injection moulding with the flow properties of plastics.
Knowledge about the tribological properties of engineering plastics is one of faigle's specialities. The subject of friction is often the key to success in development. Therefore, faigle already calculates during the design phase which material is best suited for the respective application. faigle uses polymers as base material. These can be precisely adapted to the application by means of mixtures or combinations with other materials. If, for example, glass fibre is added, the rigidity, compressive strength and dimensional stability to heat increase significantly.
Brake rod bushes for freight cars are made of the material PAS-80X. In addition, the polyamide used is significantly improved by incorporating ultra-high molecular weight polyethylene (UHMW-PE). The friction coefficient of this tribologically optimised material is around 0.2, well below the base values and remains the same over the entire service life. This means that the bushes have excellent dry-running properties and – in contrast to steel bushes – do not require lubrication during the entire operating time. In addition, PAS-80X shows little signs of fatigue even with long-term use and has a high attenuation capacity, as well as excellent dimensional stability.
Some plastics can optimally derive electrical charge through special material modifications. This is a decisive advantage in the case of belt pulleys for sorting systems, for example. The support of these belt pulleys is usually an aluminium milled part which is relatively expensive to manufacture. faigle has replaced this fixture with a solution made of high-strength PAS-80 GF30 AST, providing its customers with greater certainty through electrical discharge and cheaper production.
The most diverse requirements need to be taken into account in the design. The demands placed on the bogie pivot insert were optimal friction coefficient friction, low wear, high mechanical weather resistance, toughness, freedom from lubrication and chemical resistance. These requirements were fulfilled with the use of PAS-60X. Production is in the form of injection moulding – the blank is mechanically finished and subjected to a special aftertreatment. The excellent characteristics of this material have been confirmed by approvals from various railway administrations and use for over 25 years.
faigle uses CAD/CAM and tool filling simulation programs to achieve short engineering times in the development of components and assemblies. Strength calculations are carried out using the finite element method (FEM), faigle optimises its injection moulding process using the mouldflow analysis for simulation, and rapid prototyping enables the fast and cost-effective production of demonstration and test samples. faigle also uses 3D printers for this.
A good design example is the shuttle flap –it is a highly stressed part of ashuttle, which is used in modern logistics centres for the automated transportation of goods. Conventional shuttle flaps are milled metal parts, which can hardly be produced economically in large quantities. The extremely high demands on load capacity and fatigue strength require a lot of know-how about the geometry and material design of the component. faigle constructs shuttle flaps with fibre-reinforced high-performance plastic. These are lightweight and can be produced inexpensively even in complex geometries. The shuttle flaps from faigle are an injection-moulded construction. The rib design was optimised based on an FEM calculation, and the use of the carbon fibre reinforced material PAS PAA-LCF was confirmed in the successfully passed endurance test of more than 5 million load changes without failure. The design possibilities in injection moulding can also be integrated with a snap and clutch function, which reduces the number of components.
Once the new parts have been successfully designed, faigle can quickly and cost-effectively produce close-to-production prototypes and first samples within a few days. The company has a variety of tool masters, which makes the new parts process significantly cheaper. With these prototypes, customers can start their first fundamental tests and get many insights. In addition, the prototypes are subjected to a number of test procedures, such as tensile and compression testing and rolling abrasion testing. These test procedures go far beyond the standard, and, in some cases, self-developed test benches are used to ensure a very high standard of quality.
For series production, the tool still has to be designed, taking into account various aspects such as sprue type and number of pieces. The customers decide whether they will take over production of the new part later on or whether faigle will produce the component.
Finally, to complete the new parts process, the injection moulding machine needs to be calibrated in order to comply with low manufacturing tolerances. Smooth closing is tested with surface paste, which helps to detect any bumps and dents. Additional time-consuming tests and test procedures are then carried out. This entire process guarantees reliable production of high-quality components with fast delivery times, and is the basis of faigle's reputation as a reliable partner and innovative developer.