Helical compression springs are used in numerous end products in a wide range of variants and numbers. To ensure perfect operation and a long service life of the helical compression springs, the mechanical load must be applied in the axial direction. The spring ends are often ground flat for this purpose. However, if the entire manufacturing chain of these helical compression springs is considered, the grinding of the spring ends accounts for 40 to 60 % of the total costs, which is a significant proportion of the manufacturing costs. In addition, basic scientific knowledge regarding the influence of the process variables of spring end grinding on helical compression springs is not sufficiently documented, despite over 100 years of history.

The project is funded by the Federal Ministry for Economic Affairs and Energy pursuant to a resolution of the German Bundestag. The project number for this joint industrial research (IGF) initiative is 01|F22902N. 

The work and results achieved relate to the investigation of process interactions during the grinding of helical compression springs. Due to their function, springs are specifically designed for their intended application, which encompasses the material, design, manufacturing method, and testing. Increasingly, helical compression springs must fulfill multiple functions and be designed for various types of motion, which raises the requirements. The main difference from most other known machine elements is their elastic behavior, which results from the design depending on the spring stiffness. A common trade-off in the manufacturing of helical compression springs exists between the quality requirements of the spring and the grinding performance. Depending on the application, helical compression springs can be used as components subjected to high dynamic loads, which places very high demands on spring quality and, consequently, on the grinding process. The inherent dynamics of the helical compression springs also influence the manufacturing process. Detailed knowledge regarding the influence of grinding parameters on the process and the ground spring ends is necessary for the reliable machining of helical compression springs spring ends through grinding.

As part of the project, it was determined in consultation with the Project steering committee that only cold-formed springs made of oil-quenched and tempered VDSiCr steel would be used. A wire diameter of d ≈ 6 mm was also defined for the springs to be examined. The spring ends of all springs under consideration were finished and unground, in Form B according to DIN ISO 2162-2. Other characteristics of the spring design, such as the outer diameter, the length in the unground state, the winding ratio, and the total number of coils, were varied over the course of the project.

The findings obtained within the scope of the project primarily consist of basic knowledge regarding process influences and interactions during the grinding of the ends of helical compression springs. They can benefit companies by improving their understanding of the challenges involved in grinding spring ends and raising awareness of potential problems, so that these can be taken into account preventively during process design. Furthermore, it was demonstrated that conclusions regarding process behavior in industrial production can be drawn from analog experiments.

The results of the project will be summarized in a final report upon project completion. This report can be purchased through the German Spring Industry Association (Verband der Deutschen Federnindustrie e.V.). Further information is available on the VDFI website:

https://www.federnverband.de/