Swiss thread-rolling specialist Eichenberger Gewinde developed a key design component for an advanced, automated version of a revolutionary coupling systems: the Carry ballscrew features an impressive 90% efficiency of over its entire service life: this results was achieved with an extensive in-house testing.
by Alma Castiglioni
The world of drive technology is constantly changing, it grows and faces new challenges. This is also true for the ballscrews and leadscrews made by Eichenberger Gewinde. Speed, load capacity, precision, maximum service life, encounter small, compact, adaptable, robust, safe, economical.
These quality features on the other hand, relate reciprocally to resource and energy efficiency. Today, an ideal mechanical component has to meet the highest performance standards and must tend to always cost less, whether it be in automation, automotive or machine tool industry, electronics, the medical sector, the textile industry, the printing industry, in building services engineering, etc.
For the Swiss thread-rolling specialist, close customer contact and target-oriented dialogue between partners are essential prerequisites for the development of high-performance customized solutions. A deep understanding of the customer’s product is crucial to success.
The application: an innovative, automated coupling system
For the advanced, automated version of an innovative and revolutionary coupling systems, the thread-rolling specialist was able to develop a key design component and bring it from the manufacture of individual parts to mass production. This coupling system, with a 12 mm diameter cold-rolled ballscrew, caused a sensation among industry specialists.
The outer contours virtually determined the inner workings of the ball screw drive (BSD). One of the greatest challenges was to find the perfect solution for the extremely limited space conditions, while taking all the other specification requirements into account. The complete BSD unit had to be scaled-down. When development, production and quality assurance are grouped closely together, flexibility in terms of the manufacturing process or the creation of prototypes and thread rolling tools, is remarkably high. This one of Eichenberger’s advantages. Thanks to these factors and a modern machine park, it is possible to manufacture flexibly and competitively. A properly-adjusted coupling mechanism demands the utmost in terms of dynamics. For a travel distance of 50 mm, a load from 0 to 2000 N (Newton) is required within 20 ms (milliseconds). The Carry ballscrew drive is easily capable of withstanding these tough requirements, with this combination of dynamic forces and motion variables. Cold forming in a non-cutting manufacturing process produces a very precise profile geometry and thread rolling results in a high surface quality. The extremely low roughness values (≤ Rz 1.0) on the thread flanks have an extremely positive influence on strength, running properties and thus service life.
What is behind these quality features?
The new coupling system described above, required a lot of time, namely 6 years of basic research and development in the fields of dynamics and lubrication. Lifetime lubrication is difficult to achieve and tricky to guarantee.
Here we are talking about 7-digit numbers of highly dynamic load changes at up to 5800 revolutions. The impressive 90% efficiency of the Carry ballscrew over its entire service life required extensive testing. In some cases, the endurance tests ran for over 6 months.
The lubrication lifetime tests alone took more than 2 years, A customized test concept for the special BSD used in the innovative coupling was elaborated by a team in accordance with the customer’s wishes and the specifications.
All elements in the entire unit (spindle, nut, balls, lubrication) have to work together optimally in order to satisfy the most stringent customer requirements.
Due to the tight tolerances for torque, axial play and concentricity, 100 % checks on the fully assembled ballscrew drives are carried out on a special test bench. The BSD unit with the special “nut inner world” is marked by laser. The registered data matrix code allows the content of the final inspection to be traceable 1:1.
Advanced test systems for quality assurance
To a large degree, quality assurance determines a company’s success.
This makes it all the more important not only to maintain quality at a constant level, but ideally it should be continuously improved and adapted to constantly changing conditions and requirements. To successfully overcome this challenge, active, continuous development work in the value-added process is needed. Eichenberger’s high-tech test systems play an essential role in many phases of these process chains.
Wear comparison tests
The research and development department carries out endurance tests to compare different geometries, lubricants and service life. A special test bench for wear comparisons is loaded with weight and tested with a one-sided continuous load. Accelerations and decelerations as well as speed and travel can be programmed via parameters. It displays, for example, how the lubricating film on the BSD behaves in a fast or oscillating application, grease degradation and contamination are observed and evaluated. How do the tribological properties of the various lubricants compare? Does the temperature change when there are signs of wear? Do the noises change? When does profile deformation occur? Investigations of total failures lead to a continuous build-up of knowledge. In this way, exemplary combinations of spindle, nut, balls and lubricants that meet the specified requirements can be identified. This powerful testing system has become indispensable in the field of research and development. It uncomplainingly performs experiments with several million cycles in a single test run. The resulting knowledge is extremely valuable.
Quality is when actual equals target. The tailor-made end-of-line testing systems are used for testing and the 100 % final functional check of the fully assembled ballscrews or leadscrews. Simplified operating states are simulated for as short a time as possible. The torque and axial play of the complete drives are measured.
The running behaviour is tested within the predefined tolerances. A special software program evaluates the measuring signals and compares them with the previously programmed nominal and actual values of perfect screw drives. The test decision is made on the basis of these measured values. The reference data is marked by laser as a data matrix code on the ballscrew or leadscrew drive. With this 2D code, the origin and the stored values of all components can be traced transparently.
Customer-Customer-specific tests, trials, measurements
Based on the know-how it has accumulated over many decades, Eichenberger constantly develops modern and highly dynamic test solutions for the latest products in its own range or for customer-specific applications. Tests and analyses tailored to the respective projects and screw drives are essential for the research and development work of the designers. At the same time, production quality can be internally monitored.
The complex test benches for customer-specific tests and future developments can be loaded on one or both sides. In principle, they simulate real operating conditions under reproduced conditions.
The functions are configured by freely programmable parameters. Important mechanical test parameters such as force, torque, concentricity and axial play are observed and recorded. The efficiency is continuously calculated.
Any noises are recorded, the behaviour of the lubrication and the temperature curve are also measured and recorded. These test systems consist of a unique combination of mechanics, sensors, control and software.