August 2024 Volume 6

ENERGY

Avoiding the washing operations from the process chain offers further potential for saving energy and resources. Generally, and regardless of the applied forming process, two washing operations are usually provided in the process chain design. The first is between the forming and turning operations and the second before hardening. To avoid the washing operations from the process chain, all coolants and lubricants should be replaced by water-based, oil-free lubricants during production. As the probability of lubricant film breakage is relatively low in Felss' incremental forming processes, the replace ment with a water-based lubricant could be carried out successfully.

For the manufacturing of this hollow rotor shaft the entire manu facturing process chain was examined. Additional improvements were made regarding the wear components during the forming process, especially to the forming tool namely the swaging dies. Current trends in the development of rotor shafts are focused on the forming of rotor shafts in the tempered state with an aim to reduce further component distortion due to hardening. Materials in this tempered state possess a tensile strength of 950-1100 MPa and there fore, cause higher tool wear. To realize an economically acceptable tool life within a forming process of such high-strength materials, the swaging dies are generally produced from carbide metal. This means that the entire set of carbide metal tools consisting of 2 to 6 swaging dies (see Figure 3) will be completely disposed of or scrapped after 3-5 possible reworkings of the forming zone. New multi-piece swaging dies as shown in Figure 3 have been developed to avoid material waste which is highly damaging to the environment. This newly developed tool consists of a steel base block and a carbide metal insert that is only placed where the actual forming takes place and therefore, where the wear occurs. Due to this improvement, the following advantages have already been observed through the appli cation of the multi-part swaging dies in series production: 1. No decrease in tool life compared to conventional carbide metal tools. 2. Wear reduction of components in contact with swaging dies, such as wedges (Figure 3). 3. Reduced carbide metal volume and thereby, reduction of the carbide metal waste and CO2 footprint. Despite the successful trials in series production, the development process has not yet been fully completed because investigation regarding the reusability of the steel base block and the number of possible reworkings of the carbide inserts must still be considered.

Figure 2: Potential process chain for manufacturing a rotor shaft by rotary swaging and axial forming. For the application of a water-based lubricant during the manufac turing process, the requirements for the lubricant should first be determined for the respective forming process. In the rotary swaging process, the lubricant must effectively lubricate the machine unit, be resistant to the occurring thermal load, and also to flush metal particles from the forming zone. Whereas with axial forming, the focus is on the minimum possible friction coefficient. Furthermore, targets and advantages were defined in advance for an economical and sustainable application, which should be achieved during the experimental investigation. These include reduced purchasing costs, as the water-based lubricant should not be more expensive than conventional oil; the complete avoidance of the washing operations to significantly reduce the CO2 footprint, and the absence of the fire extinguishing systems during the machining operations for a lower initial investment. In order to meet all the economic and process-related requirements described above, a water-based lubricant, which enables the short ened process chain shown in Figure 2, was developed with the cooperation of various partners from the lubricant industry. The two washing operations shown in yellow can be avoided, including the corresponding energy costs and consumption of fresh water. After the successful completion of the laboratory trial for rotary swaging, this lubricant will be tested in series production in Q2 and Q3 2024 and then, officially marketed. Further trials for the application of water-based lubricants are only planned and required for axial forming.

Figure 3: Design of the rotary swaging unit with a newly developed, multi-part swaging dies (patented). Due to the innovations of the water-based lubricant and the newly developed multi-part swaging dies, the entire process chain can be significantly shortened and designed more environmentally friendly, which also results in a considerable reduction of the CO2 footprint. The next step is an optimization of the axial forming process for the manufacturing of the helical gearing. Considering the constantly rising torque transmission requirements, rotor shafts are increasingly being designed with helical gears which are usually manufactured by hobbing. As part of a further development project, a possible production of helical gears by axial forming was examined and the corresponding advantages compared to hobbing were investigated.

FIA MAGAZINE | AUGUST 2024 13