The overmolded busbar is used to safely conduct the electrical current between the high-voltage accumulator, control unit, drive and charging unit.
Key challenges in development & design:
Electrical separation / insulation
The main functions of the busbar are the safe, short-circuit-free conduction of electrical energy between the drive and charging components and the protection of assembly and workshop personnel from touching live components.
Functional performance and manufacturability contradictions
The restricted installation space makes it necessary to arrange the busbars in a space-saving manner while at the same time ensuring adequate insulation (clearance and creepage distances) and protection against accidental contact. In addition, it must be possible to produce corresponding component concepts safely in a fully automated manner. As a rule, multi-stage production processes are required to manufacture busbars. In the development of such a component, the material behavior, the different manufacturing processes (punch-bending, injection molding, handling, and material flow) and the interactions of different materials play a major role.
M.TEC takes all these product and production-relevant influences into account when designing and developing busbars.
Thermal shock test, thermal shock resistance
Automotive components are subjected to severe temperature cycling and thermal shock tests. Busbars are made of several materials (copper, thermoplastics, elastomers) with very different thermal properties (coefficient of thermal expansion). These thermal shock tests, in which the components are stressed by storage in hot and cold environments, can lead to damage to the components and failure to pass the tests. Possible faults or damage include excessive component distortion, cracks in the plastic material or a separation of the connection between plastic and copper. The result is loss of the insulation effect, penetration of moisture and thus corrosion and electrical short circuits.
Early validation of technical concepts
In development, M.TEC carries out thermal simulations from the very beginning to determine the material load. These finite element simulations are complemented by filling simulation calculations so that the fiber orientation is taken into account as a decisive influencing variable.
This makes the decision for a concept easier and reduces the project risks.
Powering tests of the busbars simulate driving cycles and charging cycles under different climatic conditions in a particularly sharp form. In doing so, large temperature differences and changes are deliberately generated in the busbar, which result from the driving operation. Due to the different materials the busbars are made of, large thermal stresses occur in the components. This can lead to faults and damage, such as severe component distortion, cracks in the plastic or detachment of the plastic from the copper conductor. The essential component functions are thereby disturbed or no longer exist, the components fail and the tests are not passed.
Realistic predictions using thermal simulations
M.TEC anticipates these tests through finite element simulations early in the development process. Fiber-reinforced thermoplastics are frequently used. The fiber orientation in the components, which results from the production process, is decisive for the resilience of the material. M.TEC determines the fiber orientation by upstream filling simulations and includes this important influencing variable in the finite element calculations.
Sealing / tightness
If the seal is not completely tight, media can penetrate from the outside (moisture, dust, dirt particles, salts, cleaning agents, oils, greases, brake fluid, etc.) This results in malfunctions or damage to the conductor rail and connected components. In the worst case, a short circuit may occur, which also damages the battery and electronics. Other types of damage that develop over a longer period of time and ultimately lead to functional failure include creeping corrosion and wear on plug contacts. As a rule, the seal must function just as reliably as before even after the component has been removed for maintenance purposes and reassembled.
Seal design - component distortion and tolerances
The basis for the development of a permanently functioning seal at M.TEC is early tolerance analyses and minimization of component distortion using filling simulations. As materials specialists, M.TEC engineers use finite element analyses to design the seal in such a way that it reliably fulfils its function over its service life and the required assembly and disassembly cycles.
M.TEC takes a holistic view of the tolerances, material properties and loads and develops sealing concepts that meet the requirements at all times.
The busbar must function faultlessly throughout its service life. If a failure occurs, high repair costs are incurred in individual cases and in the event of a systemic fault, recall actions must be carried out. The reasons for failure are the stresses and strains during installation in the vehicle, driving operation and environmental influences. During operation, the busbar is mainly subjected to thermal loads and mechanical forces, e.g. vibrations, impacts or torsion. Environmental pollution is mainly caused by the influence of media such as water, dust, sand, salt and chemicals, often in combination with climatic influences.
Understanding loads and material properties correctly
In order to develop a product with a long service life, it is necessary to know all these stresses and to correctly classify their effects. The associated tests for component testing, which are often specified, form the basis for defining the load cases. The load cases, in turn, flow into the simulations and calculations accompanying the development.
As materials experts, M.TEC engineers have the knowledge of how the material characteristics change over time under environmental influences. As product developers, they design components such as a conductor rail in such a way that functionality, load capacity and robust production are equally guaranteed.