[ 0020 ] fig1 of the drawing shows a winding mandrel 1 in a side view . the mandrel is composed of the actual mandrel 2 with winding surface and winding area ; the mandrel 2 has shoulders 3 on both sides , wherein the distance between the shoulders 3 determines the axial length of the coils wound on the mandrel . [ 0021 ] fig2 shows in a schematic axial sectional view the mounting of several heating cartridges 4 ; specifically eight cartridges 4 are provided . these heating cartridges 4 are electrically heated and are commercially available . the arrangement of the cables and the control of the heating process is known in the prior art and , therefore , does not have to be explained in detail and is only schematically indicated in the drawing by dash - dot lines . the heating cartridges 4 are preferably uniformly distributed over the circumference and are located closely underneath the outer surface of the mandrel 2 , i . e ., the winding surface . depending on the diameter of the mandrel 2 , it is useful to mount three to eight heating cartridges . [ 0022 ] fig3 of the drawing shows the situation with a mandrel 2 ′ having a smaller diameter . in this case , it is sufficient to centrally mount a single heating cartridge 4 which may be of greater size . another possibility for heating the winding mandrel is to inductively heat the mandrel . for this purpose , a high frequency heating coil is positioned over the winding mandrel , wherein the heating coil heats the mandrel inductively to the desired temperature . this is a very elegant solution , however , with the disadvantage that the cycle times are increased by having to carry out the step of positioning the high frequency heating coil . another possibility is to heat the winding mandrel at a suitable location by means of a gas flame , for example , an oxyhydrogen gas flame . the winding mandrel may be hollow and the position of the nozzle for the flame within the winding mandrel may be selected in such a way that heating of the mandrel can also take place during winding . this method is useful if coils with large diameters and , thus , large copper quantities must be baked . the above - described possibilities for heating the winding mandrel are intended to be examples of many other conceivable possibilities , such as heating of the mandrel by means of infrared radiation , hot air , etc ., or by using the method of winding on hot sleeves which are externally heated and then placed on the mandrel . another advantage which can be achieved by the invention is the fact that winding is carried out quickly so that overheating of the wire is prevented . cold wire is always wound onto a hot mandrel . at the end of the winding process , the innermost winding layer has already been slightly heated , while the mandrel has slightly cooled . consequently , the finished coil can be easily pulled from the mandrel . the coil which has cooled to room temperature , in turn , has an internal diameter which corresponds to the diameter of the hot mandrel . the outer winding layers of the coil “ shrink ” during cooling and , thus , particularly tight and compact coils are obtained . the coils are almost always wound fully automatically . of course , in addition to the actual winding process , this requires various other steps , such as clamping and cutting the wire , closing and opening the machine , ejecting the coils , and the like . normally , depending on the type of coil , the cycle times are 3 sec to 10 sec . these times are usually long enough for an optimum baking of the coils . if this should not be the case at any given time , an additional baking time must be provided in the cycle . depending on the type of coil , the actual baking times are between 0 . 5 sec and 3 sec . it should also be mentioned that very little energy is required for baking the coils according to the present invention because only the winding mandrel itself must be heated . in contrast , when hot air is used , the entire surrounding area is heated in an undesired manner . the invention is not limited to the embodiments described and illustrated herein . rather , various modifications are possible . in particular , it is possible without problems to wind wires into coils whose cross - sections deviate from the circular shape . it is immaterial in this connection whether the outer circumference and / or the cross section of the metal core is polygonal , particularly rectangular , and usually with rounded corners . while specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles , it will be understood that the invention may be embodied otherwise without departing from such principles .