Manufacturing method for hollow rack bar and hollow rack bar manufacturing apparatus

A manufacturing method for a hollow rack bar made of a hollow shaft material and including a toothed section which has a rack on an outer surface and a shaft section which is thinner than the toothed section, the manufacturing method comprising:

• drawing the hollow shaft material between a die and a plug, and preforming regions of the hollow shaft material including a toothed section formation region configured to become the toothed section and a shaft section formation region configured to become the shaft section so as to have thicknesses according to the respective regions;
• cutting off a distal end region of the hollow shaft material;
• and
• forming the rack at the toothed section formation region of the hollow shaft material which is preformed,
• wherein the plug has a first working section and a second working section having a larger diameter than the first working section, the first working section and the second working section defining respective inside diameters of the hollow shaft material,
• wherein, in the preforming,
• a chuck of a drawing unit clamps the distal end region of the hollow shaft material and the chuck is pulled in a drawing direction of the hollow shaft material,
• when the toothed section formation region passes through the die, the first working section of the plug is disposed inside a working section of the die configured to define an outside diameter of the hollow shaft material by:
• (i) identifying a region of the hollow shaft material which passes through the die based on an amount by which the chuck of the drawing unit pulls the hollow shaft material;
• and (ii) driving a driving unit based on the region of the hollow shaft material which has been identified, and
• when the shaft section formation region passes through the die, the second working section of the plug is disposed by the driving unit inside the working section of the die.