## 3 Manufacturing Difficulties
### Block Length  
Precise stamping of large shapes is relatively expensive because of the size of the punch and die that would have to be employed for a direct, single-shape stamping. As an extreme example, if the thermal expansion was not a problem, then stamping magnetic core laminations that were 60 m in length would have been impossible to be made on a single flat punch/die (as originally planned for the length of the test track). However, even the much shorter 1.3 m pieces would still require large and thus very expensive tooling, which could not be easily altered if the design of the magnetic core was to be optimised. And since such optimisation was expected (and indeed happened), a different manufacturing strategy was devised. An alternative approach used in prototyping of devices such as rotating machines is typically to employ other techniques such as laser cutting, but this is performed on a much smaller scale, so it is still commercially viable [4]. In this case the LLEA was designed in the \"heavy stator\" configuration, and therefore it would require up to 29 tons of laminated core to be produced for the whole planned length of the actuator. This meant that laser cutting would be uneconomical and could not be justified in this research project. Instead, the cutting was realised with a repurposed progressive stamping machine, which required only moderate redesign and tooling costs to an already existing manufacturing process as used by the company Magneto in Poland. The punch/die system was designed to stamp one \"coil slot\" at a time, but this was tracked by an appropriate feeding system for the \"infinitely\" long electrical steel tape, which was also synchronised with a secondary punch/die tool to introduce the mounting apertures in the laminations (Figure 3). With this system the precision and repeatability of dimensions of cutting of the slots/teeth and the mounting apertures was sufficiently good for the required magnetic circuit. This was defined directly by the dimension of the punch/die tooling, and, therefore, reproducibility at the level of 0.025 mm was possible for the coil slot itself. However, the relative positioning for each stator tooth/slot with respect to the start/end edges of each block lamination was dictated by the accuracy of the feeding system, and it was at the compound worst-case level of 0.5 mm. The main magnetic lateral air gap on each side (between the stators and the movers) was relatively large, between 7.5 and 10 mm (various configurations and gaps were considered during trials, Figure 4), and thus the aforementioned precision of cutting was deemed to be perfectly acceptable  
Figure 3: Cutting of large laminations: (**a**) automated cutting line; (**b**) punch for cutting out a single coil slot; (**c**) outline of a single lamination; (**d**) photograph of one side of the final module, with visible stator “teeth” and “coil slots” (weight of the whole assembled item as shown is 275 kg). from the engineering viewpoint. It should be noted that the dilatation gaps of 2 mm were significantly smaller than the main air gap and thus affected the reluctance to a relatively small degree, acceptable in this case. Further improvements to the reluctance of the dilation gaps could be easily introduced (such as angled overlap, to increase the effective cross-sectional area of this air gap), but they were not implemented in this case due to other reasons such as costs. This modular approach to manufacturing technology proved to be an optimum one in the considered process, because the first prototype was found to exhibit unsatisfactory performance from the viewpoint of achieved forces and the weight/cost of the stator. Therefore the design of the stator core had to be adjusted (various dimensions for the stator and the mover), which obviously meant changes in dimension that had to be manufactured, as well as the assembly technology. The same manufacturing tolerances were achieved in both cases (Figure 4).