E-Archive

VOL. 26 January ISSUE YEAR 2025

Interview

in Vol. 26 - January Issue - Year 2025
Enhancing Shaft Durability
Dr.-Ing. Oliver Maiß, Head of R&D and Marketing of ECOROLL AG Werkzeugtechnik

Dr.-Ing. Oliver Maiß, Head of R&D and Marketing of ECOROLL AG Werkzeugtechnik

Mechanical surface treatment by deep rolling

Mechanical surface treatment by deep rolling

Single-roller mechanical tool EG45 for deep rolling of a radius

Single-roller mechanical tool EG45 for deep rolling of a radius

System integration of ECOsense into the machine tool

System integration of ECOsense into the machine tool

MFN managed to get an interview with Dr.-Ing. Oliver Maiß, Head of R&D and Marketing, ECOROLL AG Werkzeugtechnik, Germany.

(?) MFN: Welcome, Mr. Maiß. Thank you for joining us today to discuss your work on improving the lifespan of shafts through the process of deep rolling. Could you start by explaining what deep rolling is and why it’s important?

(!) O. M.: Thank you for having me. Deep rolling is a highly efficient process used to enhance the fatigue strength of mechanically stressed components. It’s relatively simple and can be perform using any lathe or milling machine. The process involves smoothing the surface to reduce the roughness and selectively hardening the surface layer, that is, the area of material directly beneath the surface.

(?) MFN: This sounds interesting. What are the main effects of deep rolling on the material?

(!) O. M.: The main effects include plastic deformation produced by surface roughness peaks, which reduces roughness, increases dislocation density, causes work hardening, and introduces compressive residual stresses. These compressive stresses are particularly beneficial as they can improve the fatigue strength significantly during dynamic loading by preventing or slowing down crack initiation.

(?) MFN: Where does deep rolling have the most significant impact?

(!) O. M.: Mechanically, this process has the most significant impact on notches and radius transitions of shafts or shaft-like components, where the mechanical stress is highest. This is why deep rolling is particularly suitable for these areas.

(?) MFN: Could you elaborate on how notch stresses affect the service life of shafts?

(!) O. M.: Shafts are subjected to various types of loads, such as tensile, compressive, torsional, and bending loads. The highest stress typically occurs at the transition between different shaft diameters or at the flange transition. For example, in a simplified wheel carrier model under bending load, the highest stress is at the transition area, where failure is most likely to occur. By applying deep rolling in these critical areas, the service life can be extended significantly.

(?) MFN: That’s very insightful. Can you share any specific results or studies that highlight the benefits of deep rolling?

(!) O. M.: Certainly. At the 2024 VDI conference “Shafts and Shaft-Hub Connections”, Stefanie Günther presented extensive studies showing load increases of up to 93% through targeted deep rolling. This demonstrates the substantial benefits of the process.

(?) MFN: How exactly does deep rolling work?

(!) O. M.: Deep rolling involves pressing a rolling body onto the surface of a component, and then it rolls off, causing plastic deformation of the surface and the underlying surface layer. The key parameters for the process are geometry of the roller, feed rate, and especially the rolling force, which determines the level of compressive residual stress introduced.

(?) MFN: What should be considered when selecting tools and optimising the process for maximum strength improvement?

(!) O. M.: There are various tools available for deep rolling, usually with different geometries of the individual rolling bodies. The tool, especially the roller, must be matched to the machining task. For example, a roller like the one shown in this figure is not suitable for machining radii and other free-formed surfaces but it is optimal for smoothing cylindrical inner or outer surfaces as it is capable of handling very high feed rates.

(?) MFN: Are there specific tools for deep rolling radii?

(!) O. M.: Yes, single-roller mechanical tools, where the roller is self-supported, are particularly suitable for deep rolling radii. For instance, the EG45 type tool with a 40M roller is directly supported and can handle axial and radial loads. By positioning the roller at 45°, it can machine over an angle of 90°, making it ideal for machining radii on shafts.

(?) MFN: How does the tool’s design affect the rolling force during the process?

(!) O. M.: The rolling force is applied through spring elements that can deflect in one direction, in this case, at 45° to the roller axis. This must be considered when programming the process. For cylindrical surfaces, at an angle of 45°, the actual rolling force becomes the spring force, which is displayed on the gauge. If a constant rolling force is applied over an entire radius, the displayed spring force will change. Therefore, it would be incorrect to program the process to show the same value on the gauge over the entire radius.

(?) MFN: That’s a crucial detail. How important is it to understand and account for this relationship in practice?

(!) O. M.: It’s essential to understand this relationship, especially for applications where precise control of the rolling force is critical. However, in many cases, the programming effort may be too high for the user, and it is sufficient to work with a constant feed over the entire radius. Therefore, the importance of this relationship must be evaluated on a case-by-case basis.

(?) MFN: We know that there are difficulties in measuring the residual stresses after the process. One benefit of deep rolling is that it is much more controllable than shot peening. Are there any possibilities to control residual stresses?

(!) O. M.: Yes, you are right. In deep rolling, the rolling force is the most dominant parameter to generate compressive residual stresses. With our new technology ECOsense, we can measure and store the rolling force for each individual process. And since 2024, we can also connect ECOsense via a gateway with the machine tool´s control. 

(?) MFN: That is a great news. Is it only available for mechanical tools or can it also be used for ECOROLL’s hydrostatic tool line?

(!) O. M.: Of course. We presented a new hydraulic unit last year at EMO 2023. This year at AMB 2024, we have shown the combination of the ECOsense software with our ECOforce hydraulic unit. So, customers can get the same benefits for hydrostatic tools as well.

(?) MFN: Thank you for these detailed insights, Mr. Maiß. It’s clear that deep rolling is a valuable process for enhancing the durability of shafts. Is there anything else you’d like to share?

(!) O. M.: Well, it’s important for users to consider their specific application needs carefully and to optimise the deep rolling process accordingly. The service life of a component can be extended significantly with the right approach.

(?) MFN: Thank you again for your time and expertise, Mr. Maiß. This has been a very informative discussion.


MFN would like to thank Oliver Maiß for this interview!

For Information: 

ECOROLL AG Werkzeugtechnik, 

H.-H.-Warnke-Str. 8, 

29227 Celle, Germany

Tel. +49.5141.9865-0

E-mail: oliver.maiss@ecoroll.de

www.ecoroll.de