# Interaction of Machining Parameters on MRR of Sintered NdFeB Processed by EDM-Milling
## 1 Introduction  
Sintered Neodymium-iron-boron (NdFeB) is widely used for its high magnetic properties [1]. However, it is not suitable to be machined by traditional machining due to its high hardness and brittleness [2, 3]. Electrical discharge machining (EDM) is achieved by the thermal effect between the tool electrode and the workpiece in the dielectric [4, 5], without considering the hardness and brittleness of the materials [6, 7]. Thus, EDM is a viable processing method for sintered NdFeB. Currently, there are fewer studies on EDM of sintered NdFeB. [PERSON] et al. [8] processed the sintered NdFeB material by the EDM wire cutting method and concluded that the surface roughness increased gradually with the increase of pulse on time. It was also observed that the thickness of the recast layer and the damage on the surface were different when the thickness of the processed workpiece was 1.5 mm and 27 mm. [PERSON] et al. [9] investigated the effect of discharge energy on the MRR and SR of sintered NdFeB processed by EDM. It was found that MRR and SR were increased with the increase of discharge energy. [PERSON] et al. [10] proposed ultrasonic-assisted EDM machining of sintered NdFeB and analysed the sintered NdFeB surface morphology of EDM and ultrasonic-assisted EDM machining using scanning electron microscopy. It was found that sintered NdFeB processedby ultrasonic-assisted EDM had fewer microcracks on their surfaces and a more uniform recast layer. EDM milling is a new EDM processing method based on the traditional EDM method [11]. EDM milling is the process of etching material layer by layer by rotating an electrode and controlling the trajectory of the movement [12], with the advantages of high processing efficiency and low processing cost [13]. [PERSON] et al. [14] proposed the application of an improvised tool to enhance rotation and induced debris flushing. The improvised tool enhanced the MRR by 150% compared with conventional cylindrical tools. [PERSON] et al. [15] implemented a combination of unstable arc discharge and stable arc discharge for material removal by adapting the servo control strategy, and improved discharge energy utilization of ED milling in titanium alloy machining. [PERSON] et al. [16] proposed high-speed EDM milling with moving electric arcs and water-based dielectric, which effectively improved the MRR of titanium alloy. [PERSON] et al. [17] proposed a new compound machining method of titanium alloy by super high-speed EDM milling and arc machining. This method could significantly improve the machining efficiency compared with traditional EDM. [PERSON] et al. [18] compared and studied the machining of cemented carbide WC G5 material by a dry EDM milling method and an EDM milling method in oil. It was found that the former had a higher MRR and a lower electrode loss rate, which was more favourable for the machining of WC G5 material considering the machining time and cost. [PERSON] et al. [19] proposed a new high-speed EDM milling method using rotating short arcs under a composite energy field. It was found that this method increased the MRR by 46% compared to traditional EDM. The interactions that exist between processing parameters may affect the discharge physical conditions and processing effects of EDM [20]. To improve efficiency and surface quality, researchers carried out studies on the interactive effects of EDM process parameters on machining. [PERSON] et al. [21] investigated the tool wear rate in tungsten powder hybrid EDM of AA6061/10%SiCp by RSM approach. It was found that the interaction effect of current and pulse on time, and current and pulse off time, are significant to tool wear rate. [PERSON] [22] used response surface methodology (RSM) to assess the significance of the interaction effect of process parameters on MRR and SR of AISI D2 tool steel by EDM. It was shown that the interaction of current, pulse on time, and duty cycle had significant effects on MRR and SR. [PERSON] et al.