Flow drilling process and tool therefor

Apparatus for forming a rimmed hole in a preselected location of a workpiece, said apparatus comprising:

• an elongated forming tool having a central axis, a first end and a free end, said elongated tool also having a forming portion tapering radially outwardly in an axially rearward direction from a location between the ends towards the first end, said elongated member also including a prepunch portion axially in advance of the forming portion, said prepunch portion including means for locating the tool with respect to the workpiece including an axially leading point located on the central axis, said prepunch portion also including a cylindrical body with an axis coinciding with the central axis and a generally continuous surface tapering axially rearwardly from the point to the outer surface of the cylindrical body;
• drive means connected to the first end for rotating the forming tool about the central axis;
• and
• means for pressing the tool axially forwardly relative to the workpiece while in rotational frictional contact with the workpiece to first heat an area adjacent the prepunch and punch out a slug and thereafter heat and fluidize an area adjacent the forming portion to axially displace the fluidized material.

Apparatus for forming a rimmed hole in a metal workpiece of preselected thickness, said apparatus comprising:

• a forming tool having a central axis with an axially rearward end and an axially forward end, said forward end comprising a punch having a substantially cylindrically-shaped body terminating in a relatively blunt free end, said body including an axis corresponding to the central axis and having an axial length at least approximately equal to the preselected thickness, said forming tool also including generally circularly-shaped forming structure tapering radially inwardly from a first portion adjacent the rearward end toward a second portion adjacent the punch, said first portion having an effective radius greater than the radius of the punch body, wherein the blunt free end of the punch comprises cone-shaped structure having an apex lying on the central axis with an apex angle of between sixty and eighty-five degrees;
• means for causing axial movement of the tool relative to the workpiece to punch a circular slug generally through the thickness of the metal and press the forming structure into contact with the workpiece;
• and
• means for rotating the forming structure in frictional contact with the workpiece to fluidize and form metal adjacent said structure.

A method of forming a rimmed hole in a generally flat portion of a workpiece, including the steps of:

• rotating an elongated tool about its longitudinal axis, said tool having a circular blunt-ended punch portion with a point located on the axis, and a forming portion axially rearward of the punch portion and extending radially outwardly thereof;
• centering the tool with respect to the workpiece, said step of centering including pressing the point against the workpiece;
• and
• pressing the centered tool axially into contact with the flat portion of the workpiece during the step of rotating, said step of pressing the centered tool including punching a circular hole in the workpiece and thereafter fluidizing a portion of the workpiece adjacent the punched hole to extend the axial length and diameter of the hole.

A method of forming a hole in a thickness of a metal workpiece, the hole having an axial length greater than said thickness, the method comprising the steps of:

• (a) providing a tool having a central axis, an axially forwardly-located cylindrical punch portion with a cone-shaped blunt end, and a forming portion axially rearward of and radially outward of the punch portion;
• (b) forcing the punch portion of the tool axially against the workpiece and punching a slug from the workpiece to form a hole therein while preventing substantial deformation of the metal adjacent said hole;
• and
• (c) after the step of forcing, rotating the tool about its axis with the forming portion in frictional contact with the workpiece adjacent the hole to heat and fluidize the metal and increase the axial length and diameter of the hole.

Apparatus for forming a rimmed hole in a metal workpiece of preselected thickness, said apparatus comprising:

• a forming tool having a central axis with an axially rearward end and an axially forward end, said forward end comprising a punch having a cylindrical body terminating in a relatively blunt free end, said body including an axis corresponding to the central axis and having an axial length at least approximately equal to the preselected thickness, said free end terminating in an axially forwardmost apex on said axis for locating the tool on the workpiece, said forming tool also including generally circularly-shaped forming structure tapering radially inwardly from a first portion adjacent the rearward end toward a second portion adjacent the punch, said first portion having an effective radius greater than the radius of the punch body;
• means for causing axial movement of the tool relative to the workpiece to punch a circular slug generally through the thickness of the metal and press the forming structure into contact with the workpiece;
• and
• means for rotating the forming structure in frictional contact with the workpiece to fluidize and form metal adjacent said structure.