The coil-workpiece magnetic coupling coefficient K is one of the factors that influence the efficiency of electromagnetic forming (EMF) process. Along with this, an evaluation of the magnetic coupling coefficient is important in simplifying the electrical representation of the process. The first aim of this study is to analyse the effect of K on the EMF process efficiency, and second is to obtain a simplified relation between K and coil-workpiece gap (h) and thereby study the variation of discharge circuit parameters with h.

The analysis is carried out with the help of experiments, and the finite element based numerical simulation. Aluminum tube of 100 mm length and 1.5 mm thick is electromagnetically expanded using a 7 turn helical coil. Trials are taken for the different gaps between the coil and tube keeping the discharge energy constant. The coupling coefficient (K) variation with the coil-tube gap (h) is related with curve fitting, and this K-h relation is then used to analyze the discharge circuit parameter dependency on h. Simulation results, as well as K-h relation based analytical study, show a good match with the experimental observations. The EMF process efficiency and tube displacement are found to be improved exponentially with the increase in K. Among the discharge circuit parameters, with the increase in h, exponential rise in inductance and exponential decay in peak current is observed with a marginal decrease in the resistance.

线圈工件的磁耦合系数K是影响电磁成型（EMF）工艺效率的因素之一。同时，磁耦合系数的评估对于简化过程的电气表示非常重要。这项研究的第一个目标是分析K对EMF工艺效率的影响，其次是获得K与线圈工件间隙（h）之间的简化关系，从而研究放电电路参数随h的变化。

借助实验和基于有限元的数值模拟进行分析。使用7匝螺旋线圈对100毫米长，1.5毫米厚的铝管进行电磁膨胀。对线圈和管之间的不同间隙进行了试验，以保持放电能量恒定。耦合系数（K）与线圈-管间隙（h）的变化与曲线拟合有关，然后使用该Kh关系式分析放电电路参数对h的依赖性。仿真结果以及Kh基于关系的分析研究，显示出与实验观察结果很好的匹配。发现随着K的增加，EMF的加工效率和管排量得到了指数级的提高。在放电电路参数中，随着h的增加，观察到电感的指数增长和峰值电流的指数衰减，而电阻略有下降。