Joining assembly including a plastic support member and a plastic threaded element

Abstract

A threaded element of plastic material for a joining assembly has a uniquely formed thread profile of a small profile angle between 30° and 50° and a rounded crest of a relatively large radius of curvature. The gap between the revolutions of the thread is of a volume which exceeds that of the thread. In order to provide for a specific cutting geometry of the thread profile the threaded element comprises a plurality of angular segments which are radially offset with respect to each other such that adjacent angular segments provide cutting edges. Furthermore, a tool and a method for making such a joining assembly are disclosed.

1 . A joining assembly comprising:
 a support member of plastic material,   said support member having a receiving bore defined by a bore wall, said support member of a material which requires substantially a deforming operation for forming said internal threaded portion, wherein the profile of the thread of the external threaded portion is defined as follows:   P=(0.25 to 0.9)·D A      Z=(0.35 to 0.65)·P   R 1 =(0.25 to 0.5)·Z   R 2 =(0.25 to 0.5)·Z   wherein P is the pitch of the thread, Z is the profile height of the thread, R 1  is the radius of curvature of the rounded crest, R 2  is the radius of curvature of the rounded corners between said cylindrical external surface of the core and the flanks of the thread, and D A  is the major diameter of the thread, and   a threaded element of plastic material, said threaded element comprising a core and an external threaded portion which, when the threaded element is threaded into the wall of said receiving bore of the support member forms an internal threaded portion in said receiving bore by a cutting and/or deforming operation,   said external threaded portion of said threaded element comprising a thread extending for a plurality of revolutions and being, in an axial cross-section, of a profile having straight flanks which are joined by a rounded crest,   the core of said threaded element having, between the revolutions of the thread, a cylindrical external surface which, in an axial cross-section, is joined to the flanks of the thread by rounded corners and,   the revolutions of the thread defining therebetween a helical gap of a volume exceeding that of the thread.   
   
   
       2 . The joining assembly of  claim 1  wherein P, Z, R 1  and R 2  have the following preferred values:
 P=0.33·D A      Z=0.55·P   R 1 =0.3·Z   R 2 =0.3·Z.   
   
   
       3 . The joining assembly of  claim 2 , wherein the profile of the thread is of an increased major diameter D A  and a decreased diameter ratio P/D A  for providing a fine thread. 
   
   
       4 . The joining assembly of  claim 1 , wherein said external threaded portion comprises a plurality of threads of an increased diameter ratio P/D A . 
   
   
       5 . The joining assembly of  claim 1 , wherein the threaded element has an axial free end provided with a conical tip area having a cutting chamfer of a predetermined chamfer angle (γ) and a predetermined cutting diameter (D F ). 
   
   
       6 . The joining assembly of  claim 5 , for a support member of a material which requires substantially a deforming operation for forming said internal threaded portion, wherein said chamfer angle (γ) of said cutting chamfer is about 30° and said cutting diameter (D F ) is about 0.5 times the major diameter (D A ) of the thread. 
   
   
       7 . The joining assembly of  claim 7 , wherein said tip area does not include any chip recess. 
   
   
       8 . A joining assembly comprising:
 a support member of plastic material,   said support member having a receiving bore defined by a bore wall, and   a threaded element of plastic material and having a central axis (M), said threaded element comprising a core and an external threaded portion which, when the threaded element is threaded into the wall of said receiving bore of the support member, forms an internal threaded portion in said receiving bore by a deforming operation,   said threaded element comprising a plurality of angular segments which, in radial planes, are of arcuate peripheries having centers of curvature (Ma, Mb) radially offset with respect to said central axis (M) such that adjacent angular segments are offset at their peripheries by steps so as to provide cutting edges to perform a cutting operation when said threaded element is threaded into the receiving bore of the support member.   
   
   
       9 . The joining assembly of  claim 8  for support members of a material which requires substantially a deforming operation for forming said internal threaded portion, wherein the thread of the angular segments does not include any chip grooves. 
   
   
       10 . The joining assembly of  claim 8 , wherein the threaded element has an axial free end provided with a conical tip area having a cutting chamfer of a predetermined chamfer angle (γ) and a predetermined cutting diameter (D F ). 
   
   
       11 . The joining assembly of  claim 10 , for a support member of a material which requires substantially a deforming operation for forming said internal threaded portion, wherein said chamfer angle (γ) of said cutting chamfer is about 30° and said cutting diameter (D F ) is about 0.5 times the major diameter (D A ) of the thread. 
   
   
       12 . The joining assembly of  claim 11 , wherein said tip area does not include any chip recess.