1. Field of the Invention
The present invention relates to a split die and a die nib defined by the split die which is best used for a continuous drawing process of a fine wire having a generally rectangular or square section.
2. Related Art
For producing a wire having a generally rectangular or square section, a conventional method employs a cutter to cut a sheet made of an electrically conductive material and having a desirable thickness such that the wire has a sectional width generally equal to the thickness.
However, the cutter of the conventional method can not provide a square section wire having a desired strength, which causes a break of the wire, resulting in a disadvantage such as a worse product acceptance percentage thereof. Furthermore, a sheet material used for producing a square wire has a limited length so that the square wire is not sufficient in length.
For producing a round wire, a drawing process employs a die formed with a round wire forming passage, and the forming passage is progressively smaller in section in an axial direction of the die.
On the other hand, a precise forming art such as laser processing and electric charge machining has been developed, and application techniques of a synthetic diamond have also remarkably developed. Thus, such a precise forming art can employ sintered synthetic diamonds used for defining fine forming apertures having various shapes to draw fine wires.
The aforementioned conventional method employing the cutter can not produce a long, square section wire, because the sheet material does not have a strength enough to be well cut by the cutter. Thus, the conventional method is unsuitable for producing a square section wire and achieves a less productivity with a less product acceptance percentage.
Furthermore, there has been recently a need for a fine wire having a square section. Thus, a forming tool for producing such a square section fine wire has been also needed.
To overcome the disadvantage of the conventional method, an object of the present invention is to provide a split die defining a die nib which enables continuous production of a square section fine wire having a sufficient strength to cause less breaks of the wire. The split die attains an improved productivity with a better product acceptance percentage of the wire, allowing a mass production of wire products improved in precision and quality. The split die is easy in handling, parts replacement, and maintenance thereof, resulting in a less manufacturing cost thereof.
For achieving the object, a first aspect of the invention is a split die comprising a plurality of die pieces which can be assembled into a die nib. The die nib defines a central wire forming passage having a cross section of a substantially rectangular shape or a square. The cross section of the wire forming passage is progressively smaller such that the wire forming passage has a predetermined approach angle. Each of the die pieces has a passage segment of a generally triangular shape to partially define the wire forming passage. The die piece has a pair of side lines each passing a point on an axial center line of the wire forming passage.
Thus, the die nib enables continuous production of a square section fine wire having a sufficient strength to cause less breaks of the wire. The split die attains an improved productivity with a better product acceptance percentage of the wire, allowing a mass production of wire products improved in precision and quality. The split die is easy in handling, parts replacement, and maintenance thereof, resulting in a less manufacturing cost thereof.
Preferably, the split die further includes a die holder formed with a receiver recess and a cover plate to cover the receiver recess. Each of the die pieces can be removably received in the receiver recess and the die holder is formed with an inlet opening upstream contiguous with the receiver recess. The cover plate is formed with a material inlet opening communicating with the wire forming passage. The cover plate is removably fitted on a front surface of the die holder.
Thus, the separated die pieces can be easily secured in and removed from the die holder, and the die pieces are easy in partial replacement and maintenance thereof.
Preferably, the cross section of the wire forming passage has two pairs of side edges, and one of each pair of the side edges has a length substantially equal to the other.
Thus, a fine, precise wire forming passage can be obtained. The wire forming passage allows continuous drawing of a square section fine wire without a break or a damage of the wire.
Preferably, the cover plate has a downstream surface formed with a plurality of positioning pins projecting from the downstream surface, and each of the positioning pins is removably inserted into a corresponding cut-out hole or a positioning hole which is formed in the die piece for positioning the die pieces in the receiver recess.
This enables a quick, sure positioning of the separated die pieces received in the recess of the die holder.
Preferably, the die holder is provided with a pushing screw adjustably screwed into the die holder and the pushing screw has a leading end to push one of the die pieces in a lateral direction of the die piece with in the receiver recess.
This enables precise position adjustments of the separate die pieces received in the recess of the die holder to accurately position the die pieces in a predetermined manner.
Preferably, the wire forming passage has at least one of a bell angle portion and a reduction angle portion, the bell angle portion being upstream contiguous with the approach angle portion, the reduction angle portion being downstream contiguous with the approach angle portion.
This enables a continuous drawing process of a square section fine wire in accordance with material properties of the wire such as hardness, tensile strength, compression strength, fatigue strength, a friction coefficient, and a thermal elongation coefficient thereof.
Preferably, the die nib has a profile of a rectangle, a hexagon, or an octagon.
This enables a easy, precise manufacturing of the separate die pieces which are assembled to define a fine, precise wire forming passage. The wire forming passage allows a continuous drawing process of a square section fine wire.
Preferably, the wire forming passage is defined such that a fine wire having a rectangular section of a 0.04 to 0.10 mm width can be drawn through the wire forming passage.
Preferably, the wire forming passage has a cross section having four corners each of which has a curvature radius of about 0.01 mm.
Thus, the wire forming passage allows a continuous drawing process of a generally rectangular or square section fine wire.
Another aspect of the present invention is a die nib comprising a plurality of die pieces which can be assembled into the die nib, wherein the die nib defines a central wire forming passage having a cross section of a substantially rectangle shape or a square. The cross section of the wire forming passage is progressively smaller such that the wire forming passage has a predetermined approach angle, each of the die pieces defining a passage segment of a generally triangular shape to partially define the wire forming passage. The die piece has a pair of side lines each passing a point on an axial center line of the wire forming passage.