Simulation is more than Software

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Realistic mapping of the stiffness behavior of rolling bearings

Quality? We have it in stock!

Mechanical engineering company KAPP NILES, located in Coburg, plays a leading role worldwide as a system supplier for the machining of gears, gear shafts and bolt rotors. To safeguard its quality standards, the company has developed its own software for the modeling of rolling bearings, so that the dynamic behavior of spindles and axes can be analyzed and optimized. The Ansys Extension “Rolling Bearing inside Ansys”, developed by CADFEM, has now been introduced, which brings considerable advantages.

Outstanding manufacturing precision

The grinding machines of the family-owned company KAPP NILES can be found in many industries. These include automotive engineering companies as well as companies from the energy and wind power sectors and drive technology and robotics, who are convinced by the outstanding manufacturing precision of the machines and tools. The workpieces to be machined are just as diverse as KAPP NILES customers. Regardless of whether the diameter is eight meters or just a few millimeters, these grinding machines guarantee maximum precision - down to a thousandth of a millimeter.

Each system solution is individually optimized according to customer requirements and is supported throughout its entire life cycle. In the process, the comprehensive product portfolio is supplemented by high-precision measurement technology to ensure the required quality. In addition, KAPP NILES supports efficient and stable production processes with innovative services and digital solutions.

Software for rolling bearings developed in-house

For the design of the high-quality KAPP NILES machines, a simple mapping of the bearings via joints with definition of the bearing stiffnesses is not sufficient. This is because it does not allow for a sufficiently accurate representation of the stiffness behavior of an assembly for different operating points and installation conditions. Consequently, the company developed its own software for the calculation of rolling bearings, particularly to ensure a realistic representation of the dynamic behavior of spindles and axes by accurately modeling the bearings.

The work steps required for the calculation were outlined by Andreas Wellein in his 2012 diploma thesis, which gives an idea of the extent of the effort and measures required. These included determining the bearing geometry, model preparation, meshing rules, implementing Hertzian theory in spring elements, and linearization for modal analyses.

Although in-depth knowledge of APDL (Ansys Parametric Design Language) was necessary in order to implement the programming of the software, the effort was worthwhile. Automated processes for mapping the real bearing kinematics in simplified computational models led to the benefits anticipated. “In this way, we achieved significant savings in terms of computation time and model setup,” Andreas Wellein emphasizes.

Extensive maintenance and further development

At the same time, however, a wide variety of aspects had to be taken into account in the application, maintenance and further development of the software in recent years, resulting in a permanent workload that should not be underestimated. This included:

  • the adaptations to other bearing types,
  • the acquisition of bearing data (such as number of balls, ball diameter, oscillation),
  • the adaptation of the macro when changing the version of the Ansys software and
  • covering the entire size range from very small to very large bearings.

Likewise, the desire to further automate the processes required a great deal of effort.

Ansys Extention from CADFEM convinces

Since no separate user interface was designed for the internally developed software application, a sound working knowledge of the process and the programming implementation of the macro is absolutely necessary for its handling. This severely limited the range of users. This totality of aspects, which must be taken into account in the use and maintenance of the software, led computation specialists at KAPP NILES to take a closer look at the Ansys Extension “Rolling Bearing inside Ansys,” introduced by CADFEM in 2020. Until that time, no comparable software solution was available on the market.

Software with comprehensive functions

“Decisive criteria for the decision in favor of CADFEM’s solution were, among others, the higher degree of mapping while at the same time reducing the amount of model preparation and benefiting from the associated time savings,” Andreas Wellein reports. “We were also convinced by the more comprehensive functions for evaluation and plausibility checks. And, of course, that we no longer have to worry about constant further development, since this is taken care of by CADFEM and Meshparts GmbH.”

KAPP NILES engineers are also very satisfied with CADFEM’s training and support. The explanations of how the software works and the expected behavior of the models were explained in sufficient depth and thus very easy to understand throughout the process. “Due to our previous knowledge and experience with our own macro, we initially missed a bit of insight into how the software works,” explains Nico Schilling, also a computational engineer at KAPP NILES. “But we found that force flow and deformation properties are mapped very accurately with ‘Rolling Bearing inside Ansys.’ This was also shown by comparative measurements in our test setups.”

Nico Schilling
Berechnungsingenieur, KAPP NILES GmbH & Co. KG

By using "Rolling Bearing inside Ansys" we achieve a time saving of about 50 percent compared to our previous simulation solution. Also, calculations for several operating points, as well as the execution of parameter studies, are now done with ease.

Quality control with frequency response analyses

At KAPP NILES, frequency response function (FRF) analyses are performed on specific individual assemblies for quality control purposes. The aim is to be able to manufacture assemblies with consistent quality in terms of both static and dynamic behavior. In order to ensure a high level of reproducibility and variability of the assemblies manufactured by KAPP NILES, the influences of installation tolerances and preload forces of the bearings are examined by means of FEM simulation during the design phase and correspondingly narrow tolerance specifications are derived.

In order to validate the newly introduced simulation solution “Rolling Bearing inside Ansys,” measurements were carried out on the test rig as well as simulations based on a real application. The FRF measurements and the results of harmonic analyses in Ansys using “Rolling Bearing inside Ansys” and the previous “KAPP NILES Macro” were used for comparison. Here, for simplification, the minimum and maximum radial bearing overlap between inner ring/shaft and outer ring/housing was varied and 20 FRF measurements were compared. In each case, the excitation and response were in the radial direction on the measurement setup. The calculations with “Rolling Bearing inside Ansys” provided a scatter range of min/max bending resonance of 25 Hz and were in accordance with the 20 FRF measurements. In addition, the results of the new software from CADFEM showed an even better agreement with the measured values of the tests than the already good results of the now replaced “KAPP NILES macro.” “Rolling Bearing inside Ansys” has thus become an integral part of both the design of individual assemblies as well as complete machines at KAPP NILES.

About 50 percent time savings

Due to the exact determination of the operating point in the static analysis, the correct bearing stiffnesses can also be determined automatically for the dynamics. Taking the influences of bearing preload and installation tolerances into account significantly increases the accuracy of the simulation. The use of Rolling Bearing inside Ansys now also allows a detailed analysis of the temperature behavior. “The bearing behavior can now be mapped with better accuracy, and creating the geometry and introducing the correct bearing stiffnesses is not nearly as time-consuming,” Andreas Wellein is pleased to say. “The time saving is around 50 percent and calculating multiple operating points, as well as carrying out parameter studies, are now done with ease.”

One future wish of KAPP NILES engineers would be to cover common components – such as ball screws and linear guides – with comparable software packages. This would allow the use of the models developed and tested by Meshparts GmbH for these components in the familiar Ansys environment. A comprehensive bearing database with the rolling bearings of the various bearing manufacturers is also on the engineers’ wish list. But overall, they are already very satisfied with the current solution. This is because the time required in the past for the maintenance and further development of their own software is disproportionate to the cost of the “Rolling Bearing inside Ansys” software offered by CADFEM.

Andreas Wellein

Author: Gerhard Friederici, CADFEM
Images: © KAPP NILES GmbH & Co. KG

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