Bolt hexagonal head forming can not be generalized, there are cold pier, there are hot pier, there are upsetting directly out of the finished product, there are upsetting and then machined, there are also all machined. The vast majority is pier out, because this can save material. According to the size of the tonnage of the pier forging machine and the diameter of the bolts, cold pier or hot pier process can be used. The head of the upsetting bolt is machined, and at the root there are mold fixture marks.
Small quantities of specialized or special bolts of the hexagonal head is turned and milled. Single pieces of small quantities can be used in a slattern socket, lathe picking, rotary milling milling and other methods.
Mass production is often used in thread rolling machine thread rolling, thread rolling machine rolling method, high efficiency. Because the bolt rod forming method of cold-drawn and shrinkage, so the diameter of the unthreaded part of this bolt is not necessarily slightly smaller (upstairs is wrong). The use of cold-drawn, slightly smaller; the use of shrinkage, can be equal to the diameter of the thread or slightly larger.
There is a machine tool turning, large diameter bolts turned to work. There is also "thread rolling", is to use "thread rolling machine" with "thread rolling plate" extrusion thread, this bolt is not threaded part of the diameter is slightly smaller.