Metal working – Means to assemble or disassemble – Overedge assembling means
Reexamination Certificate
2000-05-16
2003-09-02
Watson, Robert C. (Department: 3723)
Metal working
Means to assemble or disassemble
Overedge assembling means
C029S283500
Reexamination Certificate
active
06612007
ABSTRACT:
BACKGROUND
a. Field of the Invention
The present invention relates to a joiner for clinch joining ductile materials, such as metal sheets, and in particular to a joiner including a die and a punch assembly.
b. Related Art
It is known to join a plurality of sheets of ductile material by causing these to be deformed into an interlocking configuration in a local area. Such joins are made by ductile material joining tools comprising a die with an aperture that is opposite a punch assembly comprising a punch surrounded by a stripper mechanism. Layers of ductile material are sandwiched between the punch assembly and when the punch is pressed towards the aperture, material is drawn into the aperture. The material undergoes plastic deformation in the aperture to flow into a shape in which two or more layers are interlocked, for example by the forming of one layer around another layer.
The aperture has a base with an anvil having an anvil surface and at least two side walls formed from movable blades. The blades are generally transverse to the anvil surface and extend in the direction in which the die and punch are pressed together. The blades help define the local area, for example a circular, square or rectangular area, in which the deformation of the layers of sheet material takes place. Once the material has been drawn and flows into the aperture, the blades move away from each other in a radial direction as sheet material flows laterally.
The outward movement of the blades is constrained by a die shield, which may be separate from but held in a fixed relationship with the die. In order to provide a compact die, the die shield can be joined to or integral with the die.
A circular die and punch can be used to form a clinch joint in which sheet material is symmetrically deformed both axially and radially to form a leak-proof button, for example as disclosed in patent document U.S. Pat. No. 5,150,513. A rectangular die and punch can be used to form a trapezoidal clinch joint (also called a lance joint), in which the sheet material is cut through by the punch along a pair of parallel opposed lines, with the layers of sheet material deformed laterally outwards underneath each of the cuts.
One commercially available example of a joining tool for forming a circular clinch joint is the SR 504 Series die and punch tool set from Bollhoff Fastenings Limited of Willenhall, West Midlands, UK. This tool set has a nominal 5 mm aperture with four movable die blades constrained by a separate die shield having an inner diameter of 16 mm.
A more compact die and punch would be desirable, for example allowing the sheet material joining tool to get further into corners or other awkward locations when fabricating a structure from the sheet material. However, there is a trade off between the strength of the tool and the maximum thickness of sheet material that may be joined, and the overall size, particularly in the direction transverse to the direction in which pressure is applied.
The die shield is arranged so that much of the pressure between the die and punch assembly is born by the die shield and stripper mechanism. However, the die blades experience increasing pressure as material is pressed into the aperture. This pressure can result in restriction of the movement of the die blades, resulting in a bad joint and/or damage to the die blades, particularly if the die blades are made thinner to reduce the lateral extent of the die.
A further constraint results from the necessity to include in the die some means of biasing the die blade back towards the anvil surface after the drawing operation by the punch is completed. For this, a coil spring or o-ring can be provided extending around the outside of the die blades. As the die blades move outwards to dilate the aperture, the spring or o-ring becomes stretched or compressed. When the joined sheet material is withdrawn from the aperture, the die blades return to their start position owing to the tension or compression in the spring or o-ring.
Because the spring or o-ring extends around the outside of the die blades usually between the die blades and the surrounding die shield, lateral space must be provided for the spring or o-ring. This again limits further reduction in the lateral extent of the die. Furthermore, lateral clearance space can result in a die blade being dislodged from between the anvil and die shield, and being lost from the die. This is very inconvenient in a production environment, as any machine using the sheet metal joiner would then have to be stopped to repair or replace the faulty die. If the faulty die were not spotted immediately, a great deal of rework to joined fabrications might then be required.
In some dies, the die blades slide laterally outwards, in which case the aperture depth is unchanged as the die blades move. However, the pressure imparted on the die blades can inhibit such a sliding motion, unless a die shield is used. Such a die shield will increase the lateral extent of the die.
Sometimes the die blades pivot outwards about a pivot mechanism below the level of the anvil surface. The pivot mechanism has a pivot axis or pivot point below and laterally outside an edge of the anvil surface. Because of this and the requirement that die blades should have a wide base or pivot with sufficient surface area to withstand the pressures during drawing, the die blades tend to rise when pivoted outwards. This tends to increase the pressure on the die blades, and again limits the amount by which the lateral dimensions of the die can be reduced.
SUMMARY OF THE INVENTION
The present invention addresses the problems cited above, and provides a die for a ductile material joiner, and also a ductile material joiner for clinch joining two or more layers of ductile material, which addresses these issues.
Accordingly, the invention provides a die for a ductile material clinch joiner, comprising:
a) a die anvil, the anvil having a body portion and an anvil surface;
b) at least two die blades, the blades extending generally transverse above and below the anvil surface and forming with the anvil surface a die aperture for a die punch, the separation between the blades defining a die aperture width or diameter and the extension of the die blades above the anvil surface defining a die aperture depth;
c) at least one pivot recess in the body portion;
d) a protrusion on each of the die blades, each protrusion being seated in a matching pivot recess to form with the recess a pivot joint by which each die blade may pivot with respect to the anvil body portion in order to constrict and dilate the aperture width or diameter;
e) at least one biasing member by which the die blades are biased to constrict the die aperture; and
f) a die shield around the die blades;
wherein the pivot joints extend underneath the anvil surface so that when the die aperture is dilated the aperture depth is decreased.
Also according to the invention, there is provided a ductile material joiner for clinch joining two or more layers of ductile material, comprising a punch tip and a die according to the invention, the die having an aperture matching the punch tip.
In a round clinch joint, the punch tip should match the die aperture with clearance that is sufficient so that ductile material is drawn down between the punch tip and die blades prior to compression of the material against the anvil surface and consequent lateral flow of the ductile material.
In a lance joint, the punch tip should match the die aperture with a close clearance so that ductile material is cut along the die blades prior to compression of the material against the anvil surface and consequent lateral flow of the ductile material under the cut.
The provision of the pivot joint underneath the anvil surface can be used to reduce the lateral extent of the die blade. This is because the joint then extends laterally further inwards, for example towards a central longitudinal axis of symmetry of the die.
At the same time, this arrangement permits the depth of the aperture to be decreased when the aperture is
Krieger Michael F.
Watson Robert C.
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