Method and apparatus for plastically forming helical internal gears and helical gears

An apparatus for plastically forming a helical internal gear comprising:

• an outer contour restraining container into which metal material blanks each having a central bore are to be inserted;
• a die placed contiguously below said outer contour restraining container and arranged to be circumferentially rotatable relative to said container;
• an upper mandrel disposed inside said outer contour restraining container in alignment with its axis;
• a lower mandrel connected to the lower end of said upper mandrel for being circumferentially rotatable relative to said upper mandrel and disposed in said die in alignment with its axis;
• and a punch for successively pushing the metal material blanks into gaps between said upper mandrel and said outer contour restraining container and between said lower mandrel and said die, wherein the outer peripheral wall of said lower mandrel has formed therein an approach area in which the peripheral surface is gradually varied into a toothed shape of the helical internal gear as it goes ahead from the upper end thereof in the extruding direction of the metal material, and a product configuration area continuously extended from said approach area and having the toothed shape of the helical internal gear, and wherein the inner peripheral surface of said die has formed therein an inwardly contracted portion located facing the start end of said approach area of said lower mandrel for contracting the metal material to define its sectional area necessary for molding the helical internal gear, an outer periphery expanding portion located facing said approach area of said lower mandrel for expansively deforming the outer periphery of the metal material to keep constant the horizontal sectional area thereof despite effective expansion of the inner diameter of the metal material during the flow deformation process in which the inner peripheral portion of the metal material is formed gradually into the toothed shape of the helical internal gear by said approach area, and an outer periphery forming portion located facing the product configuration area of said lower mandrel for defining the outer diameter of the molded product to the normal size.

A method of plastically forming a helical gear that employs a helical gear extruding die unit consisting of an outer contour restraining container into which metal material blanks each having a central bore are to be inserted, a die placed contiguously below said container, said container and said die being circumferentially rotatable relative to each other, and a mandrel disposed inside said outer contour restraining container and said die in alignment with their axes, and arranged to be rotatable circumferentially relative thereto, said method comprising the steps of:

• pushing the metal material blanks successively into gaps between said mandrel and said outer contour restraining container as well as said die by means of a punch;
• defining the sectional area of the metal material necessary to mold the helical gear by a sectional area reduction rate adjusting portion of said mandrel, when the metal material passes between said die and said mandrel;
• and subjecting the outer peripheral portion of the metal material to flow deformation from an incomplete toothed shape to a complete toothed shape as it goes from the upper end of an approach area in a toothed section of said die for molding helical teeth toward the lower end thereof, when the metal material passes between said approach area and a material inner periphery forming portion of said mandrel located in facing relation to the former;
• during said steps said die being allowed to rotate due to relative rotational forces produced between the metal material and said die caused by the helical angle of said toothed section, and also, flow material due to effective contraction of the outer diameter of the metal material during the toothed shape forming process, flow material being absorbed by said material inner periphery forming portion;
• said portion being inclined contractedly in complementary relation to said approach area of said die, thereby keeping constant the horizontal sectional are of the metal material throughout the region of material flow deformation in said die unit.

An apparatus for plastically forming a helical gear comprising:

• an outer contour restraining container into which metal material blanks each having a central bore are to be inserted;
• a die placed contiguously below said outer contour retraining container and arranged to be circumferentially rotatable relative to said container;
• and a mandrel disposed inside said outer contour restraining container and said die in alignment with their axes;
• and a punch for successively pushing the metal material blanks into gaps between said mandrel and said outer contour restraining container as well as said die, wherein the inner peripheral wall of said die has formed therein an approach area in which the peripheral surface is gradually varied into the toothed shape of the helical gear as it goes ahead from the upper end thereof in the extruding direction of the metal material, and a product configuration area continuously extended from said approach area and having the toothed shape of the helical gear, and wherein the outer peripheral surface of said mandrel has formed therein a sectional area reduction rate adjusting portion located in a position near said outer contour restraining container for expanding the metal material to define its sectional area necessary for molding the helical gear, an inner periphery forming portion located facing said approach area of said die for contractedly deforming the inner periphery of the metal material to keep constant the horizontal sectional area thereof despite effective contraction of the outer diameter of the metal material during the flow deformation process in which the outer peripheral portion of the metal material is formed gradually into the toothed shape of the helical gear by said approach area, and a column portion located facing the product configuration area of said die for defining the inner diameter of the molded product to the normal size.