Claims:1. A method for producing distortion free sheet metal components, said method comprises steps of:
(a) placing a first sheet metal component between a bottom fixture plate and a middle fixture plate;
(b) placing a second sheet metal component between the middle fixture plate and a top fixture plate;
wherein the first and second sheet metal components are sandwiched between the bottom, middle and top fixture plates to form a stack;
(c) clamping the stack with nut and bolt arrangement; and
(d) tempering the clamped stack arrangement;
wherein the fixtures are arranged in a row with the sheet metal components in horizontal direction.

2. The method as claimed in claim 1, wherein the sheet metal components are quenched.

3. The method as claimed in claim 1, wherein the clamped stack arrangement is preferably heated so as to increase mechanical properties of the sheet metal components.

4. The method as claimed in claim 1, wherein quenching distorts the sheet metal components.

5. The method as claimed in claim 1, wherein the fixture plates are high temperature resistance material.

6. The method as claimed in claim 1, wherein fixture plates having tensile strength greater than the tensile strength of the sheet metal components.

7. The method as claimed in claim 1, wherein the fixture plates having thickness greater than that of the sheet metal components.

8. The method as claimed in claim 7, wherein the thickness of the fixture plates is 10 times the thickness of the sheet metal components.

9. The method as claimed in claim 6, wherein the tensile strength of the fixture plates is between about 400 MPa to about 470MPa.

10. The method as claimed in claim 9, wherein the tensile strength of the fixture plates at temperature ranges of about 300°C to about 500°C is between 400 MPa to 470MPa.

11. The method as claimed in claim 1, wherein the stack is clamped preferably by a torque gauge.

12. The method as claimed in claim 1, wherein step grooves of about 20% to about 50% of sheet metal component thickness on fixture plates for proper holding of the sheet metal components.

13. The method as claimed in claim 1, wherein a load is applied to the clamped stack arrangement.

14. The method as claimed in claim 1, wherein the sheet metal components are quenched in salt bath just above or just below the martensite starting temperature (Ms) between about 160°C to about 230°C.

15. The method as claimed in claim 7, wherein thickness of the sheet metal components is about 0.5mm to about 3mm.

16. The method as claimed in claim 1, wherein the clamped stack arrangement with a load to flatness of about 0.1mm is tempered.

17. The method as claimed in claim 1, wherein the tempered sheet metal components exhibit flatness of below 0.15 mm.
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to heat treatment fixture and more particularly, pertains to a process for distortion free heat treatment using fixtures.

BACKGROUND OF INVENTION

[002] Heat treatment is a group of industrial and metalworking processes employed to alter the physical and/or chemical properties of a material. They involve the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, normalizing and quenching. The term heat treatment applies only to processes wherein heating and cooling are performed for the specific purpose of altering the properties of a material intentionally.

[003] The purpose of heat treatment is to cause desired changes in the metallurgical structure and thus increase the properties of metal parts. Heat treatment can affect the properties of most metals and alloys, however, ferrous alloys, principally steels and the like undergo the most dramatic increases in properties, and therefore structural changes in iron–carbon alloys. Heat treatment is also used to improve the mechanical properties of steel components, and commonly involves quenching that may cause undesired geometrical distortions in the processed parts. The dimensional accuracy of these parts is affected and leads to production and economical losses. Quenching commonly causes a geometric distortion in the parts, associated with the thermal contraction and with the change in the mechanical and geometrical properties.

[004] A method of fabricating sheet metal components by steps of stamping and heat treatment fixturization by clamping the sheet metal parts to correct distortion by fixture plate. Notably, the main industrial concern for distortion is owing to design and manufacturing. From the manufacturing process it can create distortion in component. Distorted of components can create erosion, noise and non-function of the mechanism, that require a heat treatment process to decrease the distortion on the mechanism assembly. The effects of various factors on distortion are residual stress, pre-heating, cracking of steel components, volume change due to phase change on heating and cooling, part geometry, rate of cooling and heating etc.

[005] Significantly, distortion as an irreversible and usually unpredictable dimensional change in the component during processing from heat treatment and from temperature variations and loading in service. The term dimensional change is used to denote changes in both size and shape. Size distortion, which involves expansion or contraction in volume or linear dimensions without changes in geometrical form; and shape distortion, which entails changes in curvature or angular relations, as in twisting, bending, and/or non-symmetrical changes in dimensions. Size distortion is the result of a change in volume produced by a change in metallurgical structure during heat treatment. Shape distortion results from either residual or applied stresses. Residual stresses developed during heat treatment are caused by thermal gradients within the metal (producing differing amounts of expansion or contraction), by non-uniform changes in metallurgical structure, and by non-uniformity in the composition of the metal itself, such as that caused by segregation.

[006] Various processes studied on the complicated sheet metal component to minimize distortion have indicated that the said can be achieved by controlling the rate of quenching. Martempering and Austempering are processes to reduce the thermal gradient between surface and centre as the part is quenched in isothermal temperature and then air cooled to room temperature. Marquenching or Martempering treatment uses an elevated temperature quench. The components are heated to the austenitizing temperature range and quenched, normally in molten salt at a temperature above the martensitic transformation start point (Ms). Molten salt is used for martempering in the range of 160 to 400 °C. Components are held in the quenching medium for sufficient time until the temperature of the component is uniform and then air cooled through the martensite formation range. The quenched components are cooled, cleaned and fixturized for tempering. The tempering fixture takes care of distortion control of shape and size of components of complex structure components.

[007] Reference is made to US 5672216 A, wherein a method of fabricating sheet metal parts is disclosed. The distortion corrected by heat treatment process wherein two parts are welded together in a clamped position. In particular, the two sheets are clamped together, then heat treated in pairs and welded together in clamped position. By stamping the two sheets simultaneously, it achieves greater accuracy and distortion control when compared to a process wherein two different parts would be welded together to eliminate distortion.

[008] Reference is also made to US 4375997 A, wherein a method of inductively heat treating a thin-walled work piece to control distortion is disclosed. The surface layer of a thin-walled, hollow, cylindrical steel body is hardened while controlling thermal distortion by first heating with an inductor and fluid quenching in one direction over the surface and then repeating the process in the reverse direction. Most of the heat treatment process fixture are used during hardening and tempering process but here using in tempering process only.

[009] Significantly, machining or any other secondary process after the heat treatment process are not only time consuming, but also involve escalated costs. Notably, sheet metals are very thin and complex shape components that are prone to distortion and cannot be subjected to secondary processes. In the event, there is a need for controlling distortions in the sheet metal complex components when they are being subjected to heat treatment tempering processes.

[0010] Therefore, there is a need for a process that controls heat treatment distortion of steel components, during tempering to decrease geometrical distortions in the sheet metal processed parts.

SUMMARY OF THE INVENTION

[0011] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0012] An object of the present invention is to provide a process for distortion free heat treatment using fixtures.

[0013] Another object of the present invention is to provide a process to control heat treatment distortion of sheet metal components during tempering.

[0014] Another object of the present invention is to decrease geometrical distortions in processed sheet metal components, post tempering.

[0015] Another object of the present invention is to provide stacking of distorted sheet metal while tempering to decrease geometrical distortions in processed sheet metals components.

[0016] Another object of the present invention is to provide dimensional accuracy of processed sheet metal components to reduce rejection.

[0017] Another object of the present invention is to provide a process that increases the production of sheet metal components at economic rates.

[0018] Yet another object of the present invention is to provide a process wherein after hardening, multiple distorted sheet metal components are bundled for tempering.

[0019] Yet another object of the present invention is to provide a method for tempering multiple distorted sheet metal components and fixtures stacked over one another.

[0020] Yet another object of the present invention is to apply a load to the stacked sheet metal and fixtures bundle.

[0021] Yet another object of the present invention is to sandwich quenched sheet metal components between fixtures.

[0022] Yet another object of the present invention is to sandwich the sheet metal components between top, middle and bottom lower fixture plates.

[0023] Yet another object of the present invention is to provide a method to control distortion of a stack of distorted sheet metal and fixtures during heat treatment

[0024] Yet another object of the present invention is to heat treat a stack of distorted sheet metal and fixtures clamped together to increase their mechanical properties.

[0025] Yet another object of the present invention is to clamp the stack of distorted sheet metal and fixtures with applied load.

[0026] Yet another object of the present invention is to bend the distorted sheet metal back to shape and correct the distortion by clamping.

[0027] Yet another object of the present invention is to clamp the quenched distorted sheet metal components placed between a pair of fixtures of desired component shape.

[0028] Yet another object of the present invention is to clamp the sheet metal components and fixtures sandwich with nut and bolt.

[0029] In the present invention, after hardening the sheet metal components by quenching, the distorted sheet metal components are sandwiched between fixtures and clamped shut by nut-bolt arrangement. The sheet metal components are sandwich between top, middle and bottom lower fixture plates. The clamped structure is subjected to tempering to control distortion of the sheet metal components. Quenching hardens the sheet metal components and also distorts them owing to thermal gradient of sheet metals. So fixtures are used during the tempering process to do away with the distortion brought about by quenching. The achieve the desired objective, the distorted sheet metal components are placed between top, middle and bottom fixture plates that are fashioned as per the sheet metal component shape and size, and subjected to tempering. This process decreases the geometrical distortions in the sheet metal, improve their dimensional accuracy leading to lower chances of less rejection and an increase in the production of sheet metal components at economical rates.

[0030] A method for producing distortion free sheet metal components is disclosed. The method comprises the steps of placing a first sheet metal component between a bottom fixture plate and a middle fixture plate; placing a second sheet metal component between the middle fixture plate and a top fixture plate; wherein the first and second sheet metal components are sandwiched between the bottom, middle and top fixture plates to form a stack; clamping the stack with nut and bolt arrangement; and tempering the clamped stack arrangement; wherein the fixtures are arranged in a row with the sheet metal components in horizontal direction.

[0031] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0032] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0033] Figure 1 illustrates the side view of side plate left (11) according to one implementation of the present invention.

[0034] Figure 2 illustrates the front and top views of side plate left (11) according to one implementation of the present invention.

[0035] Figure 3 illustrates the side view of side plate right (14) according to another implementation of the present invention.

[0036] Figure 4 illustrates the front and top views of side plate right (14) according to another implementation of the present invention.

[0037] Figure 5 illustrates the side view of loading a fixture with side plate right (14) according to another implementation of the present invention.

[0038] Figure 6 illustrates the side view of the loading fixture top, middle and bottom plate with multiple side plate right (14) according to another implementation of the present invention.

[0039] Figure 7 illustrates the front view of loading fixture top and bottom plate according to another implementation of the present invention.

[0040] Figure 8 illustrates the enlarged view of the fixture according to another implementation of the present invention.

[0041] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0042] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0043] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0044] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0045] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0046] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0047] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0048] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0049] The subject invention lies in providing a method of tempering sheet metal components to control component distortion.

[0050] The present invention pertains to a method of tempering sheet metal components to control component distortion during heat treatment process. The distorted sheet metal components, i.e., the quenched sheet metal components, are placed between top, middle and bottom fixture plates that are based on the size and shape of the sheet metal components and subjected to tempering. This procedure decreases the geometrical distortions in the sheet metal components, improves their dimensional accuracy leading to lower chances of less rejection and increases production at economical rates.

[0051] In one implementation, a process for distortion free heat treatment using fixtures, is provided for.

[0052] In one implementation, a process to control heat treatment distortion of sheet metal components during tempering, is provided for.

[0053] In one implementation, decreasing geometrical distortions in processed sheet metal components, post tempering, is provided for.

[0054] In one implementation, stacking of distorted sheet metal while tempering to decrease geometrical distortions in processed sheet metals components, is provided for.

[0055] In one implementation, dimensional accuracy of processed sheet metal components to reduce rejection, is provided for.

[0056] In one implementation, a process for increasing production of sheet metal components at economic rates, is provided for.

[0057] In one implementation, a process where after hardening, multiple distorted sheet metal components are bundled for tempering, is provided for.

[0058] In one implementation, a method for tempering multiple distorted sheet metal components and fixtures stacked over one another, is provided for.

[0059] In one implementation, application of load onto the stacked sheet metal and fixtures bundle, is provided for.

[0060] In one implementation, sandwiching of quenched sheet metal components between fixture plates, is provided for.

[0061] In one implementation, sandwiching the sheet metal components between top, middle and bottom lower fixture plates, is provided for.

[0062] In one implementation, a method to control distortion of a stack of distorted sheet metal and fixtures during heat treatment, is provided for.

[0063] In one implementation, heat treating of a stack of distorted sheet metal and fixtures clamped together to increase their mechanical properties, is provided for.

[0064] In one implementation, bending the distorted sheet metal back to shape and correction of distortion by clamping, is provided for.

[0065] In one implementation, clamping the quenched sheet metal components placed between a pair of fixtures of desired component shape, is provided for.

[0066] In one implementation, clamping of the sheet metal components and fixtures sandwich with a nut and bolt arrangement, is provided for.

[0067] Significantly, quenching hardens the sheet metal components and also distorts them owing to thermal gradient of sheet metals. So, the present invention discloses the use of fixtures during the tempering process to do away with the distortion brought about by quenching. In the present invention, after hardening the sheet metal components by quenching that produces the undesirable side effect of distortion, the distorted sheet metal components are sandwiched between fixtures and clamped shut by a nut-bolt arrangement. In particular, the sheet metal components (11, 14) are sandwich between top (17), middle (16) and bottom lower (15) fixture plates. The clamped structure is then subjected to tempering, in order to control distortion of the sheet metal components. Notably, the distorted sheet metal components (11, 14) are placed between fixture plates that are fashioned as per the sheet metal component shape and size, and subjected to tempering. This process decreases the geometrical distortions in the sheet metal, improve their dimensional accuracy leading to lower chances of less rejection and an increase in the production of sheet metal components at economical rates.

[0068] Figures 1 to 4 illustrate the top and side view of sheet metal components. These sheet metal components have bending, embossing and hole on components. The square holes have low thickness wall when compare to mechanical design parameter that is prone to high level distortion during mechanical operation and heat treatment quenching.

[0069] Figure 5 illustrates the fixture stacking loading step of side plate top plate and bottom plate of fixture, first fixture bottom plate (15) and then place right side plate as per the desired shape of the sheet metal component. It also illustrates the bend (13) and protrusion (12) part, placed on with fixture by grooves (18) on top and bottom fixture plate. The bend (13) part of the sheet metal components is placed on fixture grooves (18) without affecting the radius of bend (13) part.

[0070] Figure 6 illustrates the stack of a plurality of sheet metal components over a plurality of fixture plates. The metal sheet components are sandwiched between the fixture plates as per the sample desired structure, in the sequence of fixture bottom plate (15), followed by a sheet metal component, followed by fixture middle plate (16), followed by sheet metal component and finally the fixture top plate (17). The fixture plates are arranged in a row with multiple sheet metal components in horizontal direction. This stack is clamped (19) with nut and bolt.

[0071] Figure 7 illustrates the front view of the loading fixture top and bottom plate while Figure 8 illustrates the enlarged view of the clamped (19) fixture stack.

[0072] In the present invention, carbon steel of 0.3% carbon to 1.0% carbon is heat treated. The sheet components have variable lengths and material thickness of about 0.5 to 3mm. Notably, sheet components having different thickness, size, shape and mechanical properties can be heat treated in one heat treatment cycle and also get lower distortion. In martempering process the carbon steel is heated to austenite temperature, followed by quick cooling by quenching in a salt bath just above or just below the martensite starting temperature (Ms) between 160°C to 230°C. These quenched distorted sheet metal components (11, 14) are then sandwiched between the fixture plates (15, 16, 17) that are clamped (19) shut by a nut-bolt arrangement. Load is then applied to the clamped (19) fixture. The distorted components are placed in the sequence of first bottom fixture plate (15), first sheet metal component (11), middle fixture place (16), second sheet metal component (14) and finally the top fixture plate (17). Clamped (19) with nut and bolt to the fixture plates with a load to flatness of about 0.1mm of distorted components, the clamped (19) stack is tempering. Notably, load is applied to all components within the fixture stack.

[0073] The flatness issue of side plate during heat treatment of sheet metal is achieved to be about 0.15mm after proper use of fixture during tempering process. The trials have resulted in flatness of sheet metal components to be below 0.15 mm. A step grooves of 20-50% components thickness on fixture plates provide for proper holding of the sheet metal components. Significantly, the thickness of the fixture plates is more than 10 times that of the sheet metal components thereby providing the requisite load required to flatten the sheet metal components. After tempering of the clamped stack (19), the sheet metal components that were bent due to quenching get back to their desired shapes and proper distortion component.

[0074] The fixture-sheet metal component combination is clamped (19) by a torque gauge. The strength of the fixture plates is such that the load delivered to the sheet metal components is more than the spring back force of the distorted sheet metal components. The strength of the clamped fixture and that of the fixture material are higher than the sheet metal component strength at temperature ranges of about 300 to 500°C. The tensile strength of high temperature resistance material at temperature ranges of about 300 to 500°C is between 400-470MPa. The tensile strength of the sheet metal component is quite less when compared to those of the fixture plates. The materials used for the fixture are SS304 and high temperature resistance material. The clamped (19) fixture with sheet metal components are heat treated to increase the mechanical properties of distorted component.

[0075] Although a simple, economic and cost effective method of controlling heat treatment distortion of sheet metal components during tempering has been described in language specific to structural features and/or methods as indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations of a process for distortion free heat treatment of sheet metals using fixtures.