Metal deforming – Tool and/or tool holder – Having unitary tool-face
Patent
1981-11-04
1983-11-29
Combs, Ervin M.
Metal deforming
Tool and/or tool holder
Having unitary tool-face
10 24, 10 85, B21J 1302, B21K 146, B21K 164
Patent
active
044174640
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a nib for a forming tool of bolt head or nut, in which a plurality of nib segments of sintered hard alloy with sectional area of symmetric trapezoid are combined into a segment combination nib of regular polygon and a bush is fitted intimately around segments or the segment combination nib, wherein part of the bush is provided with notches thereby durability of the nib is improved.
2. Background Art
When bolt head or nut is to be machined in cold heading or trimming, trimming punch or finishing punch is used usually with a nib of sintered hard alloy fitted thereto. In this case the nib of sintered hard alloy is provided with a hole corresponding to shape of bolt head or nut to be machined.
Sintered hard alloy is superior in abrasion hardness and strength against compression but inferior in strength against tensile stress. A nib of sintered hard alloy therefore is reinforced by pushing it into a nib case called punch case or die case for force fit or shrinkage fit. Even if the nib is reinforced by the nib case, however, sintered hard alloy is fatigued by applying repeated load even below allowable value until crack or flaw occurs in edge portion of the nib.
Flawed portion of the nib is enlarged on account of stress concentration until the nib itself is broken. A flawed nib in turn flaws machined article. Therefore, a flawed nib must be exchanged at once.
However, exchange of the nib is not preferable, since the nib of above mentioned structure is expensive and stopping the machine for every nib exchange causes reduction of productivity. Advent of a nib with high durability therefore has been eagerly desired in the industry.
In order to eliminate above mentioned disadvantages, a nib is proposed where six or four pieces of nib segments, for example, are combined into a segment combination nib with a hole of regular hexagonal or square shape. A bush is fitted intimately around the segment combination nib, and in turn a nib case is fitted intimately around the bush. In such a segment combination nib, stress concentrated in edge portion of nib inner circumference is absorbed by dividing the nib into segments. Therefore, the edge portion of the nib inner circumference is not liable to crack or flaw.
Dividing the nib into segments, however, causes new defect that boundary region between segment is liable to crack. Reason of the crack generation in boundary region may be explained by various factors such as (a) stress from strain, (b) maximum stress, (c) strain energy and (d) deformation energy, but there is no established theory.
An object of the present invention is to provide a nib for a forming tool of bolt head or nut wherein crack generation in boundary region between nib segments as seen in conventional segment combination nib is prevented, thereby improving durability.
SUMMARY OF INVENTION
In a nib for a forming tool of bolt head or nut according to the present invention, a plurality of nib segments with sectional surface of symmetric trapezoid are combined into a segment combination nib with inner and outer circumference of regular polygon. A bush with inner circumference of regular polygon is fitted intimately around the segment combination nib, the regular polygon in inner circumference of the bush being similar to that in outer circumference of the segment combination nib. Moreover, a stress absorbing hole is formed on edge portion of outer circumference of the segment combination nib or inner circumference of the bush. In such constitution, boundary region between segments is not liable to crack. Accordingly a nib for a forming tool of bolt head or nut is provided with long life in comparison to conventional one.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an exploded perspective view of a finishing punch in schematic representation using a segment combination nib in prior art;
FIG. 2 is a front view illustrating breaking state of nib segments in FIG. 1;
FIG. 3 is a front view of essential part of a first embodiment of the present invention;
F
REFERENCES:
patent: 567606 (1896-09-01), McCool et al.
patent: 1971548 (1934-08-01), Wilcox
patent: 1977163 (1934-10-01), Wilcox
patent: 2578229 (1951-12-01), Clement et al.
Combs Ervin M.
Mitsutoyo Kiko Co., Ltd.
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