Metal deforming – Tool and/or tool holder – Tool comprising closed periphery deforming passageway
Patent
1995-09-20
1996-11-26
Jones, David
Metal deforming
Tool and/or tool holder
Tool comprising closed periphery deforming passageway
724819, B21C 312
Patent
active
055774067
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a forming tool having a die and a prestressing ring surrounding the die.
Such a forming tool can be used for cold-extrusion. The die optionally consists of steel, especially of sintered hard metal.
In a known forming tool of that kind (DE 38 34 996 C2), which is used for cold extrusion the die is cylindrical, and the prestress exerted by the prestressing ring ensures that plasticizing, fatigue or rupture of the die as a result of internal excess pressure is avoided.
Dies used for extrusion of workpieces are, however, often polygonal in cross-section and axial section, that is to say, they have a transition from one to the other of two converging inner faces of the die that form an angle of less than 180.degree.. In the region of these transitions, as a consequence of stress concentrations and the repeated cyclic loading very high tensile stresses which exceed the yield stress of the die material can occur, or cracks and fatigue fractures can appear.
The service life of such a forming tool is accordingly short. It is therefore also known (U.S. Pat. No. 3,810,382) for the die, which is prestressed by an encircling band, to be constituted by several individual parts. Such a solution is expensive, however.
Such cracks and fatigue fractures can also appear in a region of the die in which its stress by radial pressure during deformation of the workpiece changes abruptly from a low value, usually zero, to a high value, for example approximately level with the end face of a workpiece located in the die on which a press stamp is acting, when the edge of this end face is contacted by the inside of the die, even when the inside is cylindrical.
The invention is based on the problem of providing a forming tool of the kind mentioned in the introduction, which, when using a one-part die, can be subjected to relatively high stress at transitions of the said kind without the risk of the die being destroyed.
According to the invention, this problem is solved in that the prestressing ring is constructed so that the radial prestress exerted by it on the die in the region of a transition from one to the other of two converging inner faces of the die, which together form an internal angle of less than 180.degree., and/or in the region of a sudden transition from a low to a high value of the pressure exerted by the workpiece during its deformation radially on the die, is less than in the regions adjacent to the transition.
In this solution a flexural prestress is produced around the transitions. This counteracts the formation of cracks.
With a cylindrical die or a cylindrical prestressing ring, the connection of the two can be effected by thermal shrinking, in that the prestressing ring is heated or the die is cooled and the prestressing ring is then pushed onto the die.
Preferably, the engagement surfaces of prestressing ring and die are conical. This facilitates joining of the same by axial pressing, so that a force fit is obtained.
Preferably, at least one of the two engagement surfaces of prestressing ring and die is machined in accordance with a desired prestress distribution. Instead of that, or in addition thereto, the material properties of the die and/or prestressing ring can be selected in accordance with a desired prestress distribution. This enables the radial forces in the region of the transitions to be matched in an optimum manner.
Using conventional shrink rings of solid steel, it is not in practice possible to achieve a radial prestress distribution with a modification of more than 10 to 15%.
By dividing the prestressing ring into at least two concentric rings, however, these values can be increased. At least one of the prestressing rings can therefore be surrounded by a reinforcing band. This lengthens the service life of the prestressing ring. In addition, the entire reinforcing is strengthened from 50 to 70%, and consequently an increase in the modification of the prestress distribution is possible, so that its maximum value can be around 75 to 125% of the minimum value.
Thus, at leas
REFERENCES:
patent: 2568440 (1951-09-01), Friedman
patent: 3628370 (1969-10-01), Phillips, Jr.
Danfoss A/S
Jones David
LandOfFree
Forming tool does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Forming tool, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Forming tool will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1965234