Screw connections are among the most commonly used, yet often underestimated, structural elements in mechanical engineering. Their reliability has a direct impact on the safety and availability of a system. If they fail, this can lead to downtime, high maintenance costs, and, in the worst case, production losses.

A medium-sized mechanical engineering company found itself facing exactly this situation: Over a period of several months, recurring screw breakages and loosening occurred on an automated production line, particularly at high-stress connection points between the drive housing and the bearing block. Despite regular maintenance and retightening of the connections, the problem persisted.

Analysis of the Causes

As part of an optimization project, the situation was systematically analyzed. The first step was to review the existing calculation and installation documentation. This revealed that many of the existing connections had been sized based on empirical values —some were significantly oversized, while others had insufficiently defined prestressing forces.

For an objective evaluation, the bolted joints were subsequently analyzed using software-based calculations, in accordance with VDI 2230,among other standards. A key factor in this process was the precise modeling of the load cases, including varying operational loads and temperature effects.

The Path to Optimization

The calculations provided a clear basis for technical adjustments:

• Geometric Optimization: By adjusting the screw length and the contact surfaces, settlement was reduced.

• Material combination: The previous combination of quenched and tempered steel and aluminum has been replaced with a more suitable combination, which has improved the material's flow properties.

• Preload Forces: Optimal tightening torques were determined through simulations to maintain a stable preload force during operation.

• Assembly Processes: By implementing a documented tightening procedure with torque and angle monitoring, assembly quality was significantly improved.

Calculations and simulations showed that many of the screws previously used were oversized. Through targeted adjustments, the load-bearing capacity was increased by up to 40 percent, while at the same time reducing the amount of material used.

The result

The implementation of these measures yielded measurable results within just a few production cycles:

• The failure rate of screw connections decreased by 81.1%.

• The cost of materials decreased by 23.8%.

• At the same time, assembly efficiency improved because the clearly defined torque values minimized variations.

Overall, the optimization resulted in significantly higher plant availability and a long-term reduction in maintenance costs.

Conclusion

This example illustrates just how significant the impact of a thorough bolt calculation can be on the overall reliability of a Design . By using modern calculation software, load distributions, preloads, and material behavior can be accurately determined. This allows weak points to be identified before they become a problem.

Those who systematically analyze bolted joints and design them in accordance with VDI 2230 not only improve technical safety but also enhance the cost-effectiveness of their products.