As illustrated in Fig 5, there is shown a schematic view of a bi-metal screw which is made of stainless steel AISI304/316 head 5and threaded bolt 6, as well as a drilling portion including self-tapping section 7and a drilling end section 8 which are formed of carburized steel materials.
The heading process of stainless steel part is shown as Fig1, An austenitic stainless steel round rod is composed of a pre-formed head 51 and a non-threaded bolt 61.
The heading process of low carbon steel part is shown as Fig2, A pre-formed shoulder 9 formed from low carbon steel. A round rod is provided including non-threaded bolt71 and a shaped drilling end portion 81. The carburized area is shown as the coarse black line C.
The welding process is shown as Fig3, The round rod side 61 is welded stainless steel head together and the partially product is finished.
The deburring process is shown as Fig4, The weld flash 62 and the shoulder 9 is cut or removed. It has a L width non-carburized area and near the welded interface W.
The threading process is shown as Fig5, The whole thread of screw is formed.
The induction heating process is for the quenching & tempering of the carburized part and adjust it's hardness to be good for drilling.
The Zinc plating or Ruspert coating process is for increasing the lubrication and anticorrosive function of screws.
The Packing process would be performed for shipment.