Claims:We Claim:
1. A method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation comprising steps of:-
- Placement of bar (102) on panel (100) along the axis where area moment of inertia is maximum over the centerlines of the stiffeners, wherein the panel (100) is provided between two stiffeners (101);
- Marking of the zone to be corrected;
- Positioning of fixture (103) by stopper plate depending on the direction of distortion;
- Reduction of the distortion mechanically at cold condition to a set value;
- Heating and prevention of further buckling of the plate by the fixture that induces thermal stresses;
- Raising of temperature limited to the point where no metallurgical changes occur followed by cooling the system upto ambient temperature.

2. The method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation as claimed in claim 1, wherein the system is allowed to cool upto ambient temperature, where the desired plastic deformation for correcting would have been achieved.

3. The method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation as claimed in claim 2, wherein the same procedure is followed for further correction to bring the distortion levels under the acceptable limits.
4. The method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation as claimed in claim 1-3, wherein the extent to which the heat needs to be applied is determined by the zone selected for correction.

5. The method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation as claimed in claim 1-4, wherein to correct the distortion in the other side of the stiffener, an arrangement similar to the one used in the stiffener side is provided.

6. The method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation as claimed in claim 1-5, wherein the direction of mounting of the fixture (103) is such that the force exerted by the fixture (103) increases the distortion first and produces plastic deformation which in turn results in correction or reduction of distortion of the deformed sheet metal panel (100).
, Description:A method for correction of buckling distortion in stiffened thin sheets using low temperature plastic deformation
FIELD OF INVENTION
[001] The present invention relates to a method to carry out thermo-mechanical correction to reduce the hard to correct buckling distortion arising during fabrication and assembly of thin walled sheet metal panels.
BACKGROUND/PRIOR ART OF THE INVENTION
[002] Thin plates or sheet metals are used in a variety of applications ranging from ducts, wind boxes of boilers to panel modules in ship building. In order to reduce the operational deflection and to strengthen the sheet metal, stiffeners are attached with the sheet metal at pre-determined locations. When thin sheets are welded with high section modulus stiffeners, distortion occurs at an amplified rate due to the eccentricity between the line of application of heat and the neutral axis of the stiffener.

[003] With the application of heat energy, as a part of fabrication process, high aspect ratio panels or in other words, sheet metal and thin plates distort; when the heat energy is sufficient enough to induce thermal stresses exceeding the yield stress of that particular material at elevated temperature. Reduction of distortions results in the escalation of residual stresses as they are complimentary in nature and hence, either of these occur when the other outcome is being controlled.

[004] Distortion, in general can be classified into longitudinal distortion, angular or twisting distortion and buckling or waviness. When the number of stiffeners increase, the magnitude of distortion also increases accompanied with the difficulty in correcting the distortion.
[005] Buckling or waviness method of distortion is harder to correct and in this present invention, an entirely new technique is proposed and verified for reducing the amplitude of the dished mode of distortions occurring in thin plates constrained between stiffeners.

PRIOR ART SEARCH:

[006] Chinese patent CN 201410129396 describes the method for calculating the flame parameter in feeding the input for the correction of welding deformation of stiffened panel a planking and beam structure used in ship building applications. This method involves a pure thermal correction methodology and uses oxy acetylene flame for heating the distorted sheet metal. Whereas our invention describes a technique to use thermo-mechanical means to correct distortion at much lower temperatures.

[007] US patent US2969299A describes a method of retaining the preferred shape or flatness of the sheet metal by applying pressure on the sheet metal using rigid plates thereby enabling the thin sheet to slide in between to account for the thermal expansion. This is a control methodology as the distortion is prevented from happening and happens during the process of welding. Whereas, our invention describes a post weld distortion correction, with the application of one rigid plate applying pressure from one side of the distorted plate and uses thermal assistance to induce plastic distortion to reduce the distortion, even in assembled condition.

[008] Thus, none of the above can fulfill the requirements of the present invention, for which it is designed.

OBJECTS OF THE INVENTION
[009] The object of the invention is to provide a method for correction of dished mode of distortion occurring in stiffened thin sheets made of high strength low alloy steel (DMR249A), that are used for ship building applications.

[010] Another object of the invention is to propose a method for correction of dished mode of distortion in stiffened thin sheets which involves the highest resistance against correction.

[011] Still another object of the present invention is to provide a method for correction of dished mode of distortion in stiffened thin sheets which is simple and noiseless.

[012] Further object of the present invention is to provide a method for correction of dished mode of distortion in stiffened thin sheets which is capable of reducing the distortion drastically and also has the provision to make parallel fine variations when the correction procedure is in progress.

[013] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION
[014] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[015] According to this invention, there is a method provided for correction of dished mode of distortion in stiffened thin sheets comprising the following steps:-
- Placement of bar (102) on panel (100) along the axis where area moment of inertia is maximum over the centerlines of the stiffeners, wherein the panel (100) is provided between two stiffeners (101);
- Marking of the zone to be corrected;
- Positioning of fixture (103) by stopper plate depending on the direction of distortion;
- Reduction of the distortion mechanically at cold condition to a near zero value;
- Heating and prevention of further buckling of the plate by the fixture that induces thermal stresses;
- Raising of temperature limited to the point where no metallurgical changes occur followed by cooling the system upto ambient temperature.

[016] The system is allowed to cool upto ambient temperature, where the desired plastic deformation for correcting would have been achieved.
[017] The same procedure is followed for further correction to bring the distortion levels under the acceptable limits.

[018] The extent to which the heat needs to be applied is determined by the zone selected for correction.

[019] To correct the distortion in the other side of the stiffener, an arrangement similar to the one used in the stiffener side is provided.

[020] The direction of mounting of the fixture is such that the force exerted by the fixture increases the distortion first and produces plastic deformation which in turn results in correction or reduction of distortion of the deformed sheet metal panel.

[021] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[022] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[023] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[024] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein: -
FIG. 1 shows: Schematic diagram of a distorted plate.
FIG. 2 shows: Cross sectional view of the fixture.
FIG. 3 shows: Schematic diagram of mounted fixture on a distorted assembled panel according to present invention.
FIG. 4 shows: The convention for mounting the fixture on the panel.
FIG. 5 shows: The method for carrying out the correction process.
[025] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS

[026] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[027] The present invention is pertinent to a technology regarding a method for correction of dished mode of distortion in stiffened thin sheets.

[028] According to the invention, the technique is for carrying out correction of buckling distortion in stiffened thin sheet panels made of high strength low alloy steel (DMR249A), that are used for ship building applications and also for other thin sheet panels that are stiffened by stiffeners. The invented technique is capable of reducing the distortion drastically and also has the provision to make parallel fine variations when the correction procedure is in progress. The notable advantage of the invented technique is that it requires lesser crew demanding lesser effort and results in close to acceptable flatness levels with lesser noise.

[029] A stiffened thin plate with buckling mode of distortion is depicted in figure 1. The kind of distortion shown in figure 1 is harder to correct than the others and is even difficult to correct when assembled as the overall stiffness escalates. The cross sectional view of the fixture is shown in figure 2. Based on the direction of distortion, the fixture (2) for correction needs to be mounted on the panel (1). Prior to correction, the zones intended for correction are marked and stopper bar as indicated in figure 3 is attached to the panel. The representation of the fixture mounted on a deformed panel with the stopper plate in position is shown in figure 3. The direction of mounting of the fixture (103) should be in such a way that the force exerted by the fixture (103) should increase the distortion first and then produce plastic deformation which in turn will result in correction or reduction of distortion of the deformed sheet metal panel (100). The method for the same is depicted in figure 4. The process involved in correction of a buckled stiffened plate (101) is picturized and detailed in figure 5.

[030] In order to reduce the amplitude of distortions in thin sheet panels (100) between two stiffeners (101), a rectangular bar (102) is attached with the panel (100) along the axis where area moment of inertia is maximum over the centerlines of the stiffeners. Depending on the direction of distortion, the fixture (103) is positioned and the following steps are performed to rectify the distortion.

[031] The zone to be corrected is marked. The fixture is placed in position with the help of stopper plate and the distortion is reduced mechanically at cold condition to a set value. Now, using high velocity non oxidizing gas burners, heat energy is pumped in and further buckling of the plate is prevented by the fixture that induces thermal stresses by restricting the thermal expansion. The temperature is raised limited to the point where no metallurgical changes occur. It is from this stage; the system is allowed to cool up to ambient temperature, where the desired plastic deformation for correcting would have been achieved. Further correction to bring the distortion levels under the acceptable limits, the same procedure shall be followed. The extent to which the heat has to be applied is decided by the zone selected for correction. To correct the distortion in the other side of the stiffener, suitable arrangement similar to the one used in the stiffener side is made.

Features of present invention
- The said technique being carried out locally over the panels.
- The said technique simplifies the effort involved in the correction of hard to correct mode of welding distortion (buckling) especially under assemble conditions.
- The correction of panels made of High strength low alloy steel is carried out using the advantage of the self-locking property of irreversible machines.
- A noiseless technique to correct or reduce distortion using self-locking machines to press and reduce or redistribute the amplitude of distortion into multiple modes.
- Thermally assisted technique to induce yielding in the distorted panel during correction.

[032] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[034] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[035] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[037] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[038] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.