Table of contents:
- Preparation effort for adhesive bonds
- Micro positive locking in the longitudinal press fit
- Braid with tear stop effect
- Less susceptible to settling and thermal expansion effects
- Differences in the power transmission level in the joint
Video: This Is How FKV Components Are Correctly Connected
2023 Author: Hannah Pearcy | [email protected]. Last modified: 2023-06-01 01:49
There are many aspects to consider when choosing the right type of connection for a fiber-plastic composite. The component requirements, for example, such as the level of the load, load profile, quantities or the influence of temperature and media. In addition to the existing technology base in the manufacturing plant, these are in particular the mechanical performance and the manufacturing outlay in relation to the required number of pieces.
For the profile connection, the fiber composite component must have a positive locking geometry ("teeth"). In contrast, cylindrical composite pipes can be used for the adhesive connection and the longitudinal press fit. This simplifies fiber composite production. Even small and medium quantities (<1000 pcs / a) can be produced economically. The preparation of the usually metallic load transfer elements requires a specific preparation effort for all three joining methods discussed.
Preparation effort for adhesive bonds
The adhesive bond must meet high requirements for surface cleaning and activation, as well as for adhesive storage and adhesive application. This harbors quality risks and results in a high total expenditure, which hardly decreases with increasing numbers. This is why this connection at the Lightweight Construction Center Saxony (LZS) is considered for small quantities (<100 pieces / a) or individual prototypes.
Micro positive locking in the longitudinal press fit
The longitudinal press dressing is usually significantly more robust compared to the adhesive connection, since the knurling of the load transfer elements achieves a micro-positive locking, which ultimately shows up on the component level as an increased coefficient of friction. Because of the balanced requirement profile, this type of connection can be used for a wide range of pieces, from prototypes to large quantities (> 10000 pieces / a).
Braid with tear stop effect
With the profile connection, the robustness of the joining technology can be further increased. The engineers at LZS GmbH have developed a profile connection for components subject to torsion. These include both the inner contour ("profile shell") and the outer circular cylindrical layer ("cylinder shell") a continuous fiber reinforcement, which is largely aligned in ± 45 ° for torsional load transmission.
The fluctuations in the cross-sectional thickness are “filled in” with fiber-plastic composite that is primarily oriented along the profile axis (“UD strips”). These are particularly responsible for the bending stiffness of the profile and also absorb loads in the longitudinal direction.
Experimental investigations have shown that a textile bond of the reinforcing fibers, for example fiber mesh, has advantages in the profile shell. This can be explained by the "tear-stop" effect of the textile crossing points, through which a "good-natured" behavior of the FKV is achieved, particularly in the area of load introduction. In the cylinder shell responsible for remote load transmission, on the other hand, ("spiralized") reinforcement layers stored without crossing points are an advantage. The load-bearing capacity of the reinforcement fibers can be exploited very well thanks to the composite, which is not weakened by crossing points.
Less susceptible to settling and thermal expansion effects
The geometrically distinct "teeth" make the connection less susceptible to setting and thermal expansion effects compared to adhesive and press connections. In addition, post-emergence behavior is usually much more good-natured ("fail-safe").
Due to the design, however, geometrically complex load introduction elements are required. The cold forming process predestined here ("axial forming") is more economical for medium to large quantities due to the required tool investments, so that this type of connection has so far been considered at LZS GmbH for later (large) series applications (> 10000 pcs / a).
Differences in the power transmission level in the joint
The often central distinguishing feature is the mechanical performance of the connection. In addition to the robustness already mentioned, which also increases with increasing proportion of positive locking, there are also large differences in the level of force transmission in the joint.
According to experience and experimental investigations at the LZS, an approximately double power density can be expected here for the profile connection compared to a longitudinal press connection designed according to the state of the art. Compared to adhesive connections, it is assumed that the load-bearing capacity is three to four times. The profile connection thus significantly extends the range of applications for hybrid torsion tubes, particularly in the case of limited installation space and extremely high loads.
* Florian Lenz is head of strategic business development at LZS GmbH and Karsten Wippler is chairman and managing director of LZS GmbH