The Finite Element Method (FEM) is an essential tool in modern design and product development. With Siemens NX and the NX Nastran module, a wide range of capabilities are available to precisely analyze mechanical structures and carry out optimizations already in the early development phase.

Methodological Fundamentals

NX Nastran enables a broad variety of simulations:
• Linear and nonlinear structural mechanics
• Thermal analyses
• Dynamic investigations (natural frequencies, vibration behavior)
• Fracture and durability analyses

Thanks to the integration into Siemens NX, modeling takes place directly from the CAD dataset, ensuring consistent and time-efficient calculations.

Fields of Application

FEM analysis with Siemens NX provides practical support in:
• Optimization of plastic and metal components
• Assessment of manufacturability and stability of injection molding tools
• Prediction of deformations and stresses in complex assemblies
• Integration of filling simulations in the design process

Benefits for Development

• Early detection of potential design weaknesses
• Reduction of iterations in the physical prototyping phase
• Increased product reliability and service life
• More cost-efficient design of tools and components

Practical Relevance

Our many years of experience in design and simulation enable us to apply FEM methodology efficiently in development projects. Especially in the area of plastic component design, FEM supports the evaluation of design variants and the safe dimensioning for series production.

Contact

Evosys Laser Services GmbH
Felix-Klein-Straße 75A
91058 Erlangen, Germany

Phone: +49 9131 40180-0
E-Mail: info@evosys-services.com
Web: www.evosys-services.com

Laser direct joining of metals with polymers is based on two main processes: The surface structuring of the metallic joining part and the melting of the thermoplastic joining partner at the interface. Up to now, usually two different beam sources are applied for this purpose. Short pulsed laser radiation is typically applied for surface structuring and continuous wave laser radiation for the transmission joining or heat conduction joining process. In a research project conducted by TH Nuremberg in collaboration with Evosys Laser GmbH, a new approach was developed in which both sub-processes are carried out using a single cw laser beam source. A very efficient structuring process was realized by using the fast power modulation capabilities of the laser.

Metal-plastic composites and hybrid structures are increasingly gaining in significance in many technical applications. In addition to the lightweight construction potential for the mobility sector, the simultaneous use of metallic and polymer materials in many other applications enables local tailoring of the mechanical, electrical, thermal, chemical or haptic product properties. In addition, the combination of different materials enables the use of the established forming processes and thus much greater freedom in the design than with monolithic parts. A number of joining processes are available for the production of such hybrid joints. Compared with alternative processes such as adhesive bonding, laser direct joining is characterized by short joining times and the lack of additional materials. Compared to mechanical joints using rivets or screws, there is no need for through holes for the fastening elements, which lead to reduced cross-sections and unwanted stress concentrations.

The processing principle of laser direct joining is shown in Fig. 1. The process consists of two main steps: First, a surface structuring of the metallic joining partner is carried out. This leads to an increased interaction area between the metal and plastic parts and suitable structures can create additional mechanical interlocking of the parts. In a second step, the thermoplastic joining partner is clamped to the metallic component and heated in the joining zone up to the melting temperature range. The plastic melt flows into the surface structures and can solidify there.

The geometry of the structures has a major influence on the resulting bond strength. In laser direct joining, both sub-processes, the surface structuring and the joining process, can be carried out using laser radiation. Due to the different requirements regarding the laser-material interaction of the two sub-processes, usually two different laser beam sources and processing stations are used.

Surface structuring

Due to the high energy density required for melting and vaporizing the metals, short-pulsed laser systems are usually used for surface structuring. Alternatively, continuous-wave laser systems can also be used in a remote cutting process for surface structuring.

Laser beam joining

Regarding the heating of the joining zone, a distinction is made between transmission joining, where the metallic surface is irradiated through the plastic component, and heat conduction joining, where the back of the metal component is irradiated and the joining zone is heated exclusively by thermal conduction. Transmission joining is limited to materials with sufficient transmission for the laser radiation. These are typically uncolored plastics reinforced only with glass fibers. Due to the direct irradiation of the joining area, a locally limited heat input can be achieved. Heat conduction joining in contrast, is independent of the optical properties of the plastic component. Compared to alternative heat sources for direct joining processes, such as infrared heating elements or induction coils, the heating can nevertheless be limited to a small area and controlled precisely.

A compact and cost-effective system technology was developed in a collaborative research project between the Nuremberg University of Applied Sciences and Evosys Laser GmbH. With this technology, the entire process chain can be realized in a single system and with only one beam source. A highly efficient structuring process was implemented with the help of the fast power modulation of a continuous wave fiber laser. Compared to pulsed systems, this laser provides a high average power at moderate cost and the same beam source can be applied for both the structuring and joining processes. In comparison to remote cutting, the dynamics in the interaction zone required for effective melt expulsion are not primarily achieved by a high scanning speed, but by the power modulation of the laser. This reduces the demands on the scanning systems and the process parameters for structuring and the resulting structure geometries can be controlled much more precisely.

Materials and Methods

With polycarbonate (Makrolon GP 099, Covestro) and polyamide 6 (PA 6 XT, Gehr), one amorphous and one semi-crystalline thermoplastic were used in this study. Due to its excellent optical properties, polycarbonate allows a direct inspection of the joining zone and any process defects can be detected without the need for destructive methods. The metallic materials used were a low-alloyed, cold-rolled forming steel (DC04, 1.0338) and a high-strength aluminum alloy (EN-AW 7075, 3.4365).

For the surface structuring and joining process, a single-mode fiber laser was applied. Additionally, an electromechanical clamping device as shown in Fig. 2 with two separate processing planes and a sliding tool insert with a glass pressure plate was developed.

By selecting suitable process parameters and varying them, it was possible to ensure uniform melting – even in the critical edge areas where uneven heating due to heat conduction in the metal component has to be compensated for.

Summary

By using a fast-modulated fiber laser, the two essential processing steps of laser direct joining, the surface structuring and the joining process, can be carried out with only a single laser beam source. This enables the construction of particularly compact and cost-effective processing stations and can thus contribute to a further spread of the process. Very good joint strengths can be achieved with the developed process. Particularly noteworthy is the highly efficient structuring process, which leads to a significant reduction in processing times.

Temperature control as the key to success in laser welding: temperature-sensitive thermoplastics and focused high-power lasers for welding. What initially sounds like a contradiction in terms opens up a wide range of applications in practice. Online temperature control using a high-speed pyrometer makes it possible. Evosys Laser has developed a processing head that now allows fully automatic, temperature-controlled process control for the quasi-simultaneous welding process.

Non-contact, fast, clean, safe, economical. Laser transmission welding of plastics offers many advantages. With the highly focused laser beam, the energy required for welding can be applied to the joining zone in a very targeted manner, creating resilient, hermetically sealed and visually appealing welded joints. Sensitive components in the surrounding area are not exposed to temperature, vibration or particles, meaning that the process can be used to seal housings for sensitive high-tech electronic products, for example.

However, the high power density in the laser focus also entails risks. A joining gap between the components reduces the heat transfer in the welding zone and can lead to thermal material damage or local burns in the absorbing component. Such an air gap is caused, for example, by dimensional or positional deviations of the components or incorrect adjustment of the clamping device. Contamination of the surfaces of the transparent component or the clamping tools can cause superficial burns. But too low a temperature in the joining zone, for example due to excessive absorption or scattering of the laser radiation in the transparent joining partner, is also problematic, as this leads to reduced joint strength.

Temperature Monitoring using a Pyrometer

Precise temperature control is therefore crucial for the success of the process. For contour and radial welding with fixed optics, a non-contact infrared radiation thermometer (pyrometer) can be inserted coaxially into the beam path of the processing optics. This is used to measure the Planckian heat radiation emitted from the joining zone during the welding process. This allows the current temperature to be measured and used to control the process, for example by adjusting the laser power or feed speed.

However, quasi-simultaneous welding is particularly suitable for compensating for a joining gap. In this process, the laser beam is guided over the desired seam contour several times at very high speed with the aid of a galvanometer mirror scanner. With each scan, the temperature in the irradiated area increases incrementally until the entire seam contour is plasticized simultaneously. This enables the realization of a melting path and thus the compensation of production and position tolerances and hermetic welding even in the case of a joint gap.

Scanner-based real-time Pyrometry

To enable online temperature measurement in scanner-based applications, Evosys has developed a processing head that combines a complex galvanometer scan head and a highly sensitive high-speed pyrometer. The scanner is equipped with particularly large mirrors with an optimized coating in order to capture as much heat radiation as possible from the process zone and direct it to the pyrometer via a beam splitter. By placing the focusing system in front of the scanner mirrors, no F-theta scan lens is required. This ensures the coaxial alignment of the measuring point and the processing laser at every position of the scan field and the transmission properties of the lenses do not influence the temperature measurement. The pyrometer is characterized by high sensitivity and short response times and enables the measurement of temperatures as low as 50 °C. The system can also be used for real-time temperature control in highly dynamic quasi-simultaneous welding processes.

Fully integrated Solution

The new processing module now also allows fully automatic, temperature-controlled process control for the quasi-simultaneous welding process. Seamless integration into the EvoLaP process software simplifies the process setup. As the temperature signals are always recorded at the work point, there is no need to assign positions and the measured values can be evaluated as simple time-temperature curves. A target value of the time-temperature curve can be saved using good parts and provided with practicable tolerances as an envelope curve. This also allows easy consideration of component-specific features, such as partial shading of the beam path and reflections of the heat radiation, for example on the clamping device.

The temperature signal can be used together with other criteria such as the setting distance as a control variable for the quasi-simultaneous welding process. In this way, reliable welded joints can be produced even with major fluctuations in the properties of different components or batches and any process errors that occur, such as local temperature increases, can be reliably detected. In addition to optimizing the joint strength, the real-time control also reduces the average process times, as the welding process for each component can be terminated as soon as the desired combination of setting path and joining temperature is reached.

Application-specific System design

Application-specific adjustment of the laser and pyrometer wavelengths as well as the beam splitters and filters in the beam paths to the optical properties of the transparent joining partner can maximize the signal strength and further increase process reliability. The entire optical system is calibrated at the factory so that the optical attenuation of all components is taken into account in the measurements. For users, this means minimal set-up effort, maximum process reliability and a significantly lower reject rate, even in challenging applications.

You have any questions about this technology? We would be happy to clarify them in a personal consultation. You can reach us by telephone on +49 9131 – 4088 – 1029 (Mr. Holger Aldebert) or by e-mail at sales@evosys-laser.com.