FORM2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: Functionally Graded Longitudinal pre-forms and
Process for making them
2. Applicants - a) Mahindra & Mahindra Ltd
b) Gateway Building, Apollo Bunder, Mumbai 400001,
Maharashtra, India
(c) an Indian Company.
a) Tube Investments of India
b) DARE House, 234 NSC Bose Road, Chennai
600001, Tamil Nadu
c) An Indian company.
The following specification particularly describes the nature of this invention and the manner in which it is to be performed

Field of Invention
The invention relates to novel Functionally Graded Longitudinal pre-forms [FGLP] comprising plurality of materials for applications in dynamically loaded components. Further the invention relates to a cold draw process for manufacture of FGLP
Background of the invention
Conventionally, hollow gudgeon pins for IC engines & particularly for automotive engines are manufactured from steel bar by drilling & boring operations to make a hollow cylinder of the required size which is case hardened by carburizing / induction hardening, followed by grinding & lapping to the desired final dimension & surface finish. The gudgeon pins (in the form of hollow cylinder) may also be made by forging or by use of seamless tubes to conserve material loss arising from drilling & boring operations.
The best diameter to thickness (d/t) ratio that can be manufactured through welded steel tubing route without having to resort to multiple levels of cold drawing is about 6:1.
The production of hollow gudgeon pins with low d/t ratio of 4:1 or lower from welded tube would require multiple stages of cold drawing, with intermediate annealing between cold drawing stages making the process commercially unviable.
Alloy steel is generally used for gudgeon pin application. Service stresses are high at the outer surface of the gudgeon pin as compared to the inner region.
There have been several attempts in the past to provide processes to overcome the issues related to production of FGLPs
US patent no. 6659137 discloses a two layer clad pipe construction using two drawn tubes as starting stock, fitting one over the other and drawing them together, with a moving core or without a core to produce two layer clad pipe. A core, which is used for drawing, is subsequently removed after the cold drawing operation in this case. This method is primarily intended for different materials, usually to enhance anti- corrosion properties. Such clad construction are not suitable for dynamically loaded applications due to the risk in loss of integrity under dynamic loading due to lack of reliable interference.
US patent no. 5958602 describes multi walled steel pipe using intermediate brazed copper layer that is also designed for corrosion resistance.
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US patent no. 6691397 describes a clad pipe using composite billet and extruding it at high temperature to form metallurgically bonded clad pipe for corrosion resistance.
Such clad pipes are generally applicable only for constructional tubing to withstand differential corrosive environment and fall short of the requirements for dynamic loading cases that require high interference levels required for structural integrity.
There is a longstanding need to provide functionally graded longitudinal preforms, which can withstand dynamic stress conditions.
The present invention not only overcomes problems of the conventional methods but also provides a process wherein the wasteful usage of alloy steel as mono material for gudgeon pin and material loss by drilling and boring is avoided. Further the present invention enables the production of FGLPs of varying d/t ratio including constructions such as tube in tube, solid bar in tube, pre-forms made by other material consolidation processes like casting, forging, extrusion, powder metallurgy etc. as an input member.
Summary of the invention
The main object of the present invention is to provide a process for the manufacture of functionally graded longitudinal pre-forms of a plurality of materials with interface interference levels ranging from 0.08~0.3mm appropriate for dynamic service stress applications.
Another object of the invention is to provide a process wherein the wasteful use of alloy steel as mono material for gudgeon pins and material loss by drilling and boring is avoided by the use of functionally graded performs as starting stock.
It is yet another object of the invention is to develop a process for interference fitting of long members like tube in tube, solid bar in tube etc with 0.08~0.3mm interference without resorting to thermal means.
It is yet another object of the invention is to provide a process for the production of multi- layer tubes with d/t ratio of 6:1 or lower using welded tubes without multiple stages of cold drawing and intermediate annealing between cold drawing stages.
It is yet another object of this invention is to produce longitudinal pre-forms of multi layer construction by substituting input long member with previously manufactured pre-forms.
Thus, in accordance with this invention, functionally graded longitudinal preforms of plurality of materials with interface interference levels by tailoring

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interference using a cold draw process producing multi-layer tubes with varying d/t ratio using welded tubes and interference fitted long members like tube in tube or solid bar in tube, without resorting to thermal means wherein the plurality of material construction is achieved in single step or multiple steps processing of pre-forms.
Detailed description of the invention
The FGLP of a plurality of materials produced by the process of this invention exhibiting interference levels ranging from 0.08~ 0.3mm appropriate for dynamic service stress applications like automotive gudgeon pins is achieved by a judicious selection of deformation characteristics, elastic properties of materials and tailoring the amount of cold working in co-axial drawing.
Brief description of drawing:
Figure 1 shows schematic of longitudinal pre-forms prepared by cold draw process. Two hollow tubes, the larger tube #3 of thickness t2 and the smaller tube #4 of thickness t1 are fitted one inside the other with radial clearance of g, and coaxially drawn over fixed mandrel #2 through die #1 to give a functionally graded two layered tube consisting of integral thickness t, formed of tube #5 and #6 held together by high interference.
Process description
The process is described for a preferred embodiment of the invention for production of bimetallic pre-forms hollow cylindrical gudgeon pins by selection induction hardenable alloy steel as functional outer layer & plain carbon steel as inner layer to achieve the functionality and geometrical features as outlined in figure 1. This is only a non-limiting example illustrating the process.
The starting stock consisting of two tubes - one larger that is welded (#3) & the other smaller (#4) are held co-axially one-over-the-other, with clearance (g) & coaxially drawn, to produce pre-form (#5) of the two parent tubes, having a combined thickness (t) which is higher than the thicknesses of the individual parent tubes (t1,t2), but marginally lower up to 1 mm, than the sum (t1+t2)of the individual input tube thicknesses. The input tubes have elastic modulii that are within 10% of each other, of which the outer functional tube is induction hardenable steel & inner tube of plain carbon steel.
The preferred ratio of thickness of inner and outer tube is selected to have a largely elastic stress level acting on the inner tube, with plastic deformation being largely confined to the outer tube. The stress levels in the inner tube remain largely elastic when the thickness of the thinner of the two tubes is at least not less than half the thickness of the thicker tube, both referred thickness in coaxially drawn condition.
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When drawing the outer induction hardenable welded steel tube (#3) over the inner steel tube (#4) through the die (#1) and over fixed mandrel (#2) clearance (g) maintained between the two tubes is less than 10% of the thickness of the thinner of the two input tubes. Performance is maximized for dynamic purposes when the interference levels between the inner and the outer layers of the tubing in coaxially drawn condition are between 0.08mm to 0.3mm.
Interference levels is measured by taking a small cut length of the pre-form and longitudinally extracting the inner element of the pre-form by applying a high mechanical push out force, while restraining the outer element and then physically measuring the inner dimension of the outer element and outer dimension of the inner element over mating surfaces.
The pre-form produced by the above method is subsequently processed to manufacture gudgeon pins for automotive applications by induction hardening on outer surface followed by finishing operations like grinding lapping etc.
The process of the present invention in contrast to conventional methods avoids wasteful usage of alloy steel as mono material for gudgeon pins and material loss by drilling and boring as it uses functionally graded performs as starting stock.
The process of the present invention for manufacture of bimetallic gudgeon pin manufacture in addition to tailoring the construction for applications in dynamically loaded components provides a process in which material usage is minimised, production cycle time increased thereby substantially reducing the production costs as compared to any conventional method.
As stated earlier the process described above is only a preferred embodiment of the process.
In another embodiment of this invention tubes with d/t ratio of 6:1 or lower in a multi-layer construction using welded tubes as starting material may be produced without multiple stages of cold drawing and intermediate annealing between cold drawing stages. Two or more tubes are held co-axially one-over-the-other, with clearance & co-axially drawn with fixed mandrel/core/plug, to produce pre-form of multiple layers. The thickness of the tubes, elastic properties & deformation characteristic of materials and amount of cold working are so chosen that after co axial drawing as disclosed above, a tube with d/t ratio of 6:1 or smaller is produced with a multi-layer construction with interference level at the interfaces of 0.08~0.3mm.
In yet another embodiment of this invention, two or more closed longitudinal sections such as solid bar in tube are co-axially held one-over-the-other, with clearance & coaxially drawn to produce longitudinal pre-forms. In processing of solid bar in tube construction, a plug is not used, as the bar itself acts as
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plug and is contained as part of the pre-form after drawing. The cross sectional dimensions of the members, elastic properties & deformation characteristic of materials and amount of cold working are so chosen that co axial drawing as disclosed above produces a long pre-form with 0.08~0.3mm
interference. Thus interference tailored fitting of long members is achieved without resorting to thermal means.
In yet another embodiment of the invention, longitudinal pre-forms of multi layer constructions are produced by substituting one or more inputs in the embodiments stated above by previously produced pre-forms.
The starting stock in the process of this invention may be selected from preforms or tubing made by casting, forging, extrusion, powder metallurgy etc.
These functionally graded pre-forms may subsequently be formed, machined, surface treated or otherwise worked on for graded enhanced performance benefits, material conservation and cost reduction. Parts like shafts, pins, rollers, gears, bearing races, sleeves, tools and dies, transmission parts automotive parts for crash energy management are some of the examples that can be made using these such pre-forms.
We Claim:
1. A functionally graded longitudinal pre-form as dynamically loaded
component comprising:
combinations of at least two tubular members of plurality of materials with interference level in the range of 0.08 to 0.3 mm adapted for dynamic stress applications.
2. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in anyone of claim 1 wherein said selective interference fitting comprise preferably interference fitted long member combinations selected from tube in tube and solid bar in tube.
3. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in anyone of claims 1 to 2 comprising multi layer welded tubes with diameter / thickness ratio of 6:1 or lower.
4. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in anyone of claims 1 to 3 comprising functionally graded two layered tube consisting of integral thickness upto 15mm held together by high interference.
5. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in claim 4 comprising selectively induction hardenable alloy steel as functional outer layer and plain carbon steel as the inner layer.
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6. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in anyone of claims 1 to 5 wherein said pre-form component comprise shafts, pins, rollers, gears, bearing races, sleeves, tools and dies, transmission parts, automotive parts for crash energy management and the like.
7. A functionally graded longitudinal pre-form as dynamically loaded component as claimed in anyone of claims 1 to 6 wherein the combined thickness of the pre-form is higher than the thickness of individual tubular members of which the pre-form is obtained but marginally lower than the sum total of the said individual tubular member thickness.
8. A process for the manufacture of a functionally graded longitudinal pre-form
as dynamically loaded component comprising:
at least two tubular input members one of larger dimensions than the other and coaxially placed one over the other with a clearance there between;
coaxially cold drawing the thus coaxially disposed tubular members to thereby produce the pre-form of said tubular members with the selective Interference level in the range of 0.08 to 0.3 mm adapted for dynamic stress applications.
9. A process as claimed in claim 8 comprising interference fitting input tubular
member combinations are selected from tube in tube and solid bar in tube.
10. A process as claimed in anyone of claims 8 or 9 comprising using more than two said tubular members which are disposed coaxially one over the other with desired clearance and co-axially drawn with fixed mandrel /core/plug to thereby obtain the pre-form of multiple layers.
11. A process as claimed in claims 8 or 10 comprising using two or more solid bar in tube, coaxially disposed one over the other with clearance and coaxially drawn to thereby produce longitudinal pre-forms.
12. A process as claimed in anyone of claims 8 to 12 wherein the pre-forms are obtained such that the combined thickness of the pre-form is higher than the thickness of individual input tubular members but marginally lower than the sum total of the individual input tubular member thickness.
13. A process as claimed in anyone of claims 8 to 12 wherein the input tubes used have selective elastic modulii that are within 10% of each other.
14. A process as claimed in anyone of claims 8 or 13 wherein two said input tubular members are used of which the outer functional tube is induction hardenable steel and inner tube plain carbon steel.
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15. A process as claimed in anyone of claims 8 to 14 wherein the preferred ratio of thickness of inner and outer tube is selected to have a largely elastic stress level acting on the inner tube with plastic deformation selectively largely confined to the outer tube.
16. A process as claimed in anyone of claims 8 to 15 wherein the stress level in the inner tube is largely elastic when the thicknesses of the thinner of the two tubes is atleast not less than half the thickness of the thicker tube to thereby achieve the selective interference between the coaxially drawn tubes.
17. A process as claimed in anyone of claims 8 to 16 wherein while drawing the outer induction hardenable welded steel tube over the inner steel tube through die and over fixed mandrel, the clearance maintained between the two tubes is less than 10% of the thickness of the thinner of the two input tubes.
18. A process as claimed in anyone of claims 8 to 17 wherein a fixed plug mandrel of appropriate size is used during the cold drawing.
19. A process as claimed in anyone of claims 8 to 18 comprising selectively determining the inter relationship of thickness, clearance and interference levels between the tubular members used for optimizing the fit between the said tubular members and suitability for dynamic service conditions.
20. A process as claimed in anyone of claims 8 to 19 comprising processing the pre-form thus obtained for desired end applications.
21. A process as claimed in claim 20 wherein said processing of the pre-forms comprise induction hardening or any other selective hardening processes on the outer surface followed by finishing operations.
22 A process as claimed in claim 21 wherein said finishing operation comprises anyone or more of grinding, lapping.
23. A process as claimed in anyone of claims 8 to 22 wherein the thickness of the tubes, elastic properties and deformation characteristics of materials and amounts of cold working are selected such that after said coaxial drawing a tubular pre-form with diameter / thickenss ratio of 6:1 or smaller is produced with multi-layer construction and interference of 0.08-0.3mm.
24. A process as claimed in anyone of claims 8 to 23 wherein the input tubular members comprise previously produced pre-forms.
25. A process as claimed in anyone of claims 8 to 24 wherein the input tubular members are selected from pre-forms, tubings made of casting, forging, extrusion, powder metallurgy and the like.
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26. A process as claimed in anyone of claims 8 to 25 wherein the input tubular members or solids are selected from tubings or pre-forms made of casting, forging, extrusion, powder metallurgy and the like.

Date: JULY 6TH 2005 Dr. Prabuddha Ganguli
Agent on Behalf of Applicant
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Abstract
The invention relates to a process of manufacture of Functionally Graded Longitudinal pre-forms [FGLP] comprising plurality of materials for
applications in dynamically loaded components like gudgeon pin by tailoring interference using a cold draw process producing multi-layer tubes with varying diameter / thickness ratio using welded tubes and interference fitted long members like tube in tube or solid bar in tube, without resorting to thermal means where the plurality of material construction is achieved in single step or multiple steps processing of pre-forms.

Dr. Prabuddha Ganguli Agent on Behalf of Applicant