Metal working – Method of mechanical manufacture – Shaping by direct application of fluent pressure
Reexamination Certificate
2000-05-30
2002-06-04
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Shaping by direct application of fluent pressure
C072S058000, C072S061000
Reexamination Certificate
active
06397449
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and apparatus for expansion forming of tubing.
Various methods for expansion forming of tubing are known. For example, it is known to form frame members by pressurizing and expanding a tubular blank within a die cavity having a rectangular cross-section with rounded corners corresponding to the cross-section of the final frame member. This allows frame members to be produced with very accurate dimensions at high speed and at relatively low cost. Preferably, the expansion of the circumference of the blank is less than about 5%, so that frame members of excellent strength properties can be obtained using, for example, starting material tubular blanks of ordinary grades of steel. Commonly assigned U.S. Pat. No. 4,567,743 dated Feb. 4, 1986 and U.S. Pat. No. Re. 33,990 dated Jul. 14, 1992, each in the name I. G. Cudini, disclose techniques for allowing a blank to be confined without pinching in a die having its die cavity circumference exceeding the circumference of the blank by no more than about 5%.
Various methods may be employed for sealing an end of a tubular blank to allow the interior to be pressurized. U.S. Pat. No. 2,837,810 in the name Ekholm, for example, discloses a circular plug having a resilient annular sealing element which is inserted inside one end of a tube to be expanded within a die, and the annular sealing element is compressed to seal on the inner circumference of the tube.
Copending and commonly assigned U.S. patent application Ser. No. 07/860,553 filed Mar. 30, 1992 (now U.S. Pat. No. 5,525,836) discloses tube sealing means having an elastomeric sealing element compressible between ring members to radially expand the sealing element into sealing engagement with the tube from a normal or relaxed position in which it is normally nested inwardly between the ring members. When such sealing arrangements are used for the expansion of tubes to form them into, for example, frame members having a rectangular or other elongated cross-section, it is necessary to provide a transition portion between the tube end receiving the sealing element and the inner elongated cross section portion. Applicant has found that if the angle of inclination of the wall of the transition portion relative to the tube axis is made too great, the transition portion tends to wrinkle longitudinally. The wrinkling tends to extend to the expansion formed portion and is not removed by the pressures ordinarily used for expansion and can render the frame member or other product unusable. As a result, with the known method, for a given starting material tube and a desired final product of, for example, rectangular section having given dimensions it is necessary to provide a transition portion of a certain minimum length. Since in many cases a frame member wholly of certain cross sections is desired, it is usually necessary to cut off the transition portion. With the known methods, the excessive length of the transition portions results in considerable waste of materials and resources.
SUMMARY OF THE INVENTION
In the present invention, before confining a blank within a die having a cavity corresponding to the desired final expanded member, an end of the tubular blank is deformed to provide it with a cross-section of continuously smoothly curved elongated profile. The blank is sealed by applying a sealing member of corresponding profile and the blank is pressurized after sealing to expand it within the confines of the die cavity. The pressure is then released, the sealing member removed and the expanded blank is withdrawn from the die.
By providing the sealed end of the blank and the sealing element with an elongated cross-section the profile of the sealed end can be made to match more closely the profile of the final expanded blank and as a result a much shorter transition portion may be employed so that there is considerably less wastage of materials and resources.
In a preferred form, a transition portion of the cavity has a cross section that varies continuously smoothly between an elongated cross-section of an inner cavity portion and the cross section of the said deformed end, and the deformed end is elongated in a direction substantially parallel to the direction of elongation of the cross-section of the inner cavity portion. Preferably, in order to achieve excellent strength properties for the frame member, a blank is used of circumference such that forming it to the shape of the final frame member results in expansion of the circumference of the blank by no more than about 5%.
The method of the invention may be used to advantage when the sealing portion is applied to the outside of the wall of the end of the tubular blank or is applied to the inside of the wall.
One preferred form of apparatus for expansion forming of tubular members, in accordance with a further aspect of the invention, comprises:
(a) die sections movable from an open position, in which a tubular blank to be formed may be placed between said open die sections, through an intermediate position wherein said die sections partially close together, to a closed position wherein said die sections define between them a die cavity wherein said tubular member may be expansion formed, said cavity opening to at least one end of said die sections;
(b) an auxiliary clamp member mounted on said at least one end of one die section through a lost motion linkage, and biased to a normal position extended relative to said one die section in the direction of die closure and engaging an end portion of the tubular blank to locate the blank relative to the or each other die section before said one die section contacts the blank on closure from said open to said intermediate position and retracting from the normal position relative to said one die section, in a direction opposite to the direction of die closure against the action of the biasing means, as said die sections move from the intermediate to the closed position;
(c) a sealing member having a resilient sealing portion of continuously smoothly curved cross-sectional profile corresponding to said throat cavity profile reciprocable into and out of sealing engagement within said deformed end; and
(d) means for applying hydraulic pressure internally with respect to said sealing portion whereby the blank may be pressurized and expanded to conform with said die cavity.
In the preferred form of apparatus for carrying out the method of the invention, said cross-sectional profile of the throat cavity is elongated and the auxiliary clamp member cooperates with the or each other die section in the intermediate position to deform the end of the blank to the said elongated profile.
REFERENCES:
patent: 5233854 (1993-08-01), Bowman et al.
patent: 5233856 (1993-08-01), Shimunouski et al.
patent: 5235836 (1993-08-01), Klages et al.
patent: 5445002 (1995-08-01), Cudini et al.
patent: 6154944 (2000-12-01), Mason et al.
patent: 63220929 (1988-09-01), None
The assignee of applicant has, since before Aug. 16, 1992 manufactured product in a facility located outside the United States in accordance with the methods claimed in claims 31 to 34, 41, 42 and 51 to 56 and employing the apparatus as claimed in claims 43, 49 and 50 of the present application, and has, since before Aug. 16, 1992 sold such product into the United States.
Klages Gerrald A.
Mason Murray R.
Blount Steven
Hughes S. Thomas
Ridout & Maybee LLP
Vari-Form Inc.
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