Patent Application
20150266080
The present invention relates generally to clinching apparatuses and more particularly to a clinching punch and joint formed therewith.
It is known to use a punch and die to create a clinch joint between workpiece sheets. Such a device is disclosed in U.S. Pat. No. 5,177,861 entitled “Apparatus for Joining Sheet Material” which issued to Sawdon on Jan. 12, 1993, and is commonly owned with the present application. This patent is incorporated by reference herein. This prior device was a significant step in the industry but there is still room for further improvements.
Another clinching construction is disclosed in U.S. Pat. No. 5,727,302 entitled “Die and Punch for Forming a Joint and Method of Making the Die” which issued to Sawdon on Mar. 17, 1998, and is commonly owned with the present application. This is also incorporated by reference herein. This prior punch includes a 5° frusto-conical taper which was intended to advantageously prevent high stress concentrations and to improve the tool life during high pressure tool flexure misalignments.
In accordance with the present invention, a clinching apparatus includes a clinching punch having a specifically dimensioned tapered surface which improves the strength of a clinch joint created therewith. In another aspect, a tapered surface adjacent a distal end of a clinching punch has an angle of 20-35 degrees relative to a distal end. A further aspect of a clinching apparatus provides a tapered surface adjacent a distal end which is configured in accordance with a specific formula. Additional advantages and features of the present clinching apparatus can be ascertained from the following description and appended claims taken in conjunction with the present drawings.
Referring to
Die 15 includes a body 41, and a fixed and stationary anvil 43 integrally upstanding from body 41. Furthermore, die 15 additionally includes a circular-cylindrical shield 45 attached to body 41 with a set of three movable die blades 47 located between a generally cylindrical side of anvil 43 and shield 45. A coiled spring 49, elastomeric O-ring or other biasing member is located between shield 45 and blades 47 so as to urge distal ends of the die blades toward the side of anvil 43. Punch holder 21 and die body 41 are fastened to a C-frame, fixture or other mechanism such that punch 29 and anvil 43 are always intended to be aligned with each other in all joint forming operating conditions in the preferred embodiment of the present punching apparatus.
Reference should now be made to
Punch 29 further includes a clinch joint-forming tip 81 which ends in a distal or leading end 83. Tip 81 of punch 29 further includes a generally circular-cylindrical peripheral side surface 85 which is located between distal end 83 and an arcuately curved transition section 87. Distal end 83 and a section with surface 85 are the portions of punch 29 that enter into and create a recessed cup for the clinch joint in a punching and deforming action. It is noteworthy that surface 85 has a generally constant diameter B without any discontinuities or steps therein. Alternately, a very small draft angle can be provided on surface 85, but generally equal to 5° relative to the punch centerline. Moreover, arcuately curved section 87 may alternately have a frusto-conical shape thereto although various workpiece deformation or punch strength benefits may not be achieved.
A frusto-conical taper 101, annular in an end view, is located between distal end 83 and cylindrical side surface 85. Taper 101 preferably has an angle F of 20-35 degrees relative to end 83, more preferably 28-32 degrees, and most preferably 30 degrees for two workpieces 17 and 19 of differing thicknesses. Intersecting lines defined between sidewall surface 85, taper 101 and distal end 83 all have angular corners in one version, however, it is alternately envisioned that one or both of the intersecting corners can employ a radius no greater than 0.02 inch. Furthermore, N is a sidewall neck thickness NL or NR of punch-side workpiece 17, A is an axial length of body 61 of punch 29, E is a minor radius measured between centerline CL of punch 29 and an intersection between tapered surface 101 and distal end 83, t1 is a minimum thickness of punch-side workpiece 17 at the bottom or button of the final clinch joint, and t2 is a minimum thickness of die-side workpiece 19 at the bottom or button of the final clinch joint.
Additionally, angle F for taper 101 of punch 29 is preferably determined according to the following formula regarding the desired final clinch joint 111 as illustrated in
where 2E is a minor diameter of side surface 85 where the tapered surface intersects distal end 83, B is a major diameter of side surface 85 where tapered surface 101 intersects side surface 85, Pthk is a nominal (unclinched) punch-side workpiece 17 material thickness, and F is the angle of tapered surface 101.
The angular dimensions for the present taper 101 have been found to be significantly superior in joint performance as compared to conventional punch tips which have no taper or a mere 5° transitional taper, especially for a workpiece arrangement where punch-side workpiece 17 is less than half the nominal thickness of die-side workpiece 19 as measured prior to joint formation. One such arrangement is where workpieces 17 and 19 are mating components or housings in a refrigerator appliance, or alternately an oven appliance, a dish washer appliance, a clothes washer appliance, a clothes dryer appliance or the like. The specific tip dimensional ranges disclosed herein have been found to better control the workpiece material flow throughout the duration of the material joining process, especially creating a more constant and thicker punch-side workpiece thickness NL and NR at the most inwardly constricted diameter 113 of die-side workpiece 19 where the workpieces interlock together after full clinch joint formation. The further interlocking deformation areas are at LL and LR. In contrast, a traditional punch with no taper at the end-to-sidewall transition is prone to causing undesired tearing or piercing of the punch-side workpiece adjacent constricted diameter 113.
By way of further comparison for one example of the present apparatus, workpieces 17 (HRB 55, textured pre-painted) and 19 (HRB 60) are both steel, where the punch-side workpiece has a nominal thickness of 0.19 inch and the die-side workpiece has a nominal thickness of 0.40 inch, clinched together by a punch with taper angle F of 30°. This construction was found to have a finished clinch joint peel strength of at least 25 pounds of force and with a shear strength of at least 75 pounds, while the conventional and untapered punch version had a peel strength of less than 15 pounds of force. In another example, 0.026 inch nominally thick stainless steel (HRB 71) was used for punch-side workpiece 17 with HRB 55 steel of 0.40 inch nominal thickness for die-side workpiece 19; this generated a peel strength of at least 60 pounds and a shear strength of at least 185 pounds for a 30° taper angle F on punch 29. In these examples, a diameter CB of a clinch joint outer button circular periphery is 0.188 inch, a button cap height Z is 0.038 inch, and a total button bottom thickness X is 0.021 inch. Furthermore, the preceding examples employed punch 29 with dimensions of A=3.937 inch, B=0.120 inch, Cp=0.480, E=0.044, F=30° and G=0.015 inch. It should be appreciated that these dimensions are simply exemplary and the dimensions may vary (although the joint performance may also then vary).
While the preferred embodiment of the present clinching apparatus has been disclosed, it should be appreciated that other variations are possible. For example, while three movable die blades have been disclosed, it should be appreciated that two, four or other quantities of die blades surrounding or partially surrounding an anvil of the die assembly may be employed although certain advantages of the present die may not be realized. Furthermore, a punch of a polygonal body periphery can alternately be used although certain manufacturing and cost advantages may not be obtained. The shapes of the punch holder, stripper, spring and stripper retainer can be varied, however, various advantages may not be realized. A moving anvil, fixed die blades, and the absence of the disclosed shield may alternately be used, although such an arrangement would forego many advantageous features of the present device. Additionally, aluminum and other workpiece materials may be employed with the present clinching apparatus although the exact dimensions may need to be slightly varied to account for the material flow differences. It should be appreciated that other modifications and variations may be made to the preferred apparatus without departing from the spirit and scope of the present invention.
