EP3294491A1

EP3294491A1 - Method for manufacturing a shaft with shaped profile

Info

Publication number: EP3294491A1
Application number: EP16726184.1A
Authority: EP
Inventors: Claudio Mondini; Davide FERRARIO
Original assignee: STREPARAVA SpA CON SOCIO UNICO
Current assignee: STREPARAVA SpA CON SOCIO UNICO
Priority date: 2015-05-13
Filing date: 2016-05-13
Publication date: 2018-03-21
Also published as: WO2016181363A1; ITMI20150668A1

Abstract

A method for manufacturing a shaft (1) with shaped profile, the method comprising the steps of: - making a bar (2) which extends along a first axis (A1); - making an annular element (3) having an opening (10) about a second axis (A2); - depositing material (24) on the bar (2) so as to form a coupling stretch (5); - inserting the annular element (3) on the bar (2); and - fixing by interference the annular element (3) on the bar (2) in the coupling stretch (5).

Description

"METHOD FOR MANUFACTURING A SHAFT WITH SHAPED PROFILE"

TECHNICAL FIELD

The present invention relates to a method for manufacturing a shaft with shaped profile and to the shaft with shaped profile made by means of said method.

BACKGROUND ART

The use of shafts with shaped profiles, for example camshafts, is very widespread in the automotive field both for private vehicles and for commercial vehicles.

Usually, a shaft with shaped profile comprises a bar and annular elements fixed to the bar. The method for manufacturing a shaft with shaped profile comprises, for each annular element, the steps of: defining the housing of an annular element; knurling a tube at the housing defined; and fixing the annular element by interference in the housing. The process of knurling of the tube presents the disadvantage of being very sensitive to the variations of diameter of the tube. In other words, the knurling process requires the tube to have a diameter defined in a highly precise way, i.e., so that it falls within a very narrow range of values. In fact, in the case where the diameter of the tube does not fall within the range of values defined, a knurl will be obtained that could give rise to a poor fixing between the annular element and the tube, not guaranteeing transmission of the torque in an effective way.

DISCLOSURE OF INVENTION

The aim of the present invention is to provide a method for manufacturing a shaft with shaped profile that will reduce the drawback of the known art.

According to the above purpose, a method for manufacturing a shaft with shaped profile is provided, the method comprising the steps of:

- making a bar which extends along a first axis;

- making an annular element having an opening about a second axis ;

- depositing material on the bar so as to form a coupling stretch;

- inserting the annular element on the bar; and

- fixing by interference the annular element on the bar in the coupling stretch.

Thanks to the present invention, a manufacturing method is provided, which enables manufacture of a shaft with shaped profile that is more tolerant to the dimensional variations of the bar as compared to the prior art. Moreover, the manufacturing method is versatile and can be easily adapted to shafts of different sizes. In addition, since the manufacturing method is very versatile, it is advantageous even for low volumes of production.

According to a further embodiment of the present invention, the method comprises the step of providing at least one tooth within the annular element along an inner face that delimits the opening.

According to a further embodiment of the present invention, the method comprises the step of providing a plurality of teeth within the annular element, distributed about the second axis so as to form an annular toothing preferably by broaching . According to a further embodiment of the present invention, the method comprises the step of making the bar from a tube preferably obtained by wire drawing.

According to a further embodiment of the present invention, the step of depositing material on the bar is carried out with an additive manufacturing process.

According to a further embodiment of the present invention, the additive manufacturing process includes depositing metal powder on the bar, and fixing the metal powder on the bar by a heat source.

According to a further embodiment of the present invention, the additive manufacturing process includes using a metal- powder injector.

According to a further embodiment of the present invention, the method comprises the step of forming in the coupling stretch at least one projection, which extends in height so as to be radial to the first axis.

According to a further embodiment of the present invention, the method comprises the step of measuring at least one dimension of the projection during deposition of material so as to adjust the deposition of material according to the at least one measured dimension of the projection.

According to a further embodiment of the present invention, the method comprises the step of forming a projection that extends about the first axis so as to define an annular projection.

According to a further embodiment of the present invention, the method comprises the step of forming the projection having a helix shape about the first axis.

Thanks to the present invention, the step of forming the projection is simplified. In fact, the projection is obtained through a single continuous passage in the coupling stretch so as to reduce production time. Moreover, thanks to the present invention, the fixing, obtained by interference, between the annular element and the bar presents a very high performance in so far as it develops an excellent grip between the annular element and the bar.

According to a further embodiment of the present invention, the manufacturing method comprises the step of measuring a radial dimension of the tube and of adjusting the additive manufacturing process according to the radial dimension of the tube . Thanks to the present invention, an amount of material is deposited with a high precision so as to minimize any lack of matching and thus enable an optimal interference.

According to a further embodiment of the present invention, the manufacturing method comprises the steps of:

- forming a further annular element having a further opening about a further second axis;

depositing material on the bar so as to form a further coupling stretch;

- inserting the further annular element to the bar; and

- fixing by interference the further annular element on the bar at the further coupling stretch.

According to a further embodiment of the present invention, the step of providing the further coupling stretch is carried out once the annular element has been fixed to the bar.

According to a further embodiment of the present invention, at least one of the annular element and the further annular element is a cam. According to a further embodiment of the present invention, at least one of the annular element and the further annular element is a ring. Another aim of the present invention is to provide a shaft with annular elements that is inexpensive and easy to produce.

According to the above purposes a shaft with annular elements is provided, obtained through the manufacturing method according to any one of claims 1 to 16.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will emerge clearly from the ensuing description of a non-limiting example of embodiment thereof, with reference to the annexed drawings, wherein:

Figure 1 is a perspective view of a shaft with annular elements obtained according to the present invention;

- Figure 2 is a lateral view with parts in cross section of the shaft of Figure 1;

Figure 3 is a lateral view with parts in cross section according to the line III-III of Figure 2;

- Figure 4 is a lateral view of one of the annular elements of Figure 1;

- Figure 5 is a cross-sectional view according to the line of section V-V of Figure 4;

- Figure 6 is a lateral view with parts in cross section of a portion of the shaft during a step of the manufacturing method;

- Figure 7 is a lateral view with parts in cross section of a portion of the shaft during a step of the manufacturing method and a device used during a step of the manufacturing method;

- Figure 8 is a lateral view with parts in cross section of portions of the shaft during a step of the manufacturing method; - Figures 9 to 11 are perspective views that show steps of the method for manufacturing the shaft of Figure 1; and

- Figure 12 is a lateral view of a detail of an alternative embodiment of the shaft of Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

In Figure 1 a shaft with shaped profile for a commercial vehicle is designated by the reference number 1. In particular and with reference to Figures 1 to 3, the shaft

1 with shaped profile comprises a bar 2 that extends along an axis Al, and a plurality of annular elements 3 fixed on the bar 2. In particular, the bar 2 has coupling stretches 5 having an external dimension Dl in a radial direction with respect to the axis Al and free stretches 6 having an external dimension D2 in a radial direction with respect to the axis Al that is smaller than the dimension Dl . In other words, the bar 2 has a greater radial thickness in the coupling stretches 5 than in the free stretches 6. The coupling stretches 5 house the annular elements 3 that are fixed to the bar 2 by interference . In a preferred non-limiting embodiment of the present invention, the difference between the dimension Dl and the dimension D2 is comprised between 0.05 mm and 1 mm.

For each coupling stretch 5, the bar 2 comprises at least one projection 7 set in a radial direction with respect to the axis Al obtained in the respective coupling stretch 5.

In an embodiment illustrated in the attached figures, the bar

2 is a tube 4 with circular cross section. Consequently, the dimension Dl and the dimension D2 are respective external diameters of the tube 4.

The bar 2 is obtained by wire drawing of a material, in particular metal material.

In an alternative embodiment, not illustrated in the attached figures, the bar comprises a plurality of tubes aligned along the axis and welded together. Each tube is obtained by wire drawing of a preferably metal material. In another embodiment, the tubes are obtained from a sheared metal plate bent about the axis A of extension of the plate itself.

In an alternative embodiment, the bar 2 is obtained by extrusion of a material, in particular metal.

In another alternative embodiment (not illustrated in the attached figures), the bar has a cylindrical shape and is internally full. With reference to Figure 2, each projection 7 extends in height so as to be radial to the axis Al .

With reference to Figure 8, the projection 7 entirely occupies the coupling stretch 5, extending in length along the axis Al throughout the coupling stretch 5 and in an annular way about the axis Al throughout the coupling stretch 5 so as to form an annular projection 9.

In an alternative embodiment (not illustrated in the attached figures), the coupling stretch comprises a plurality of projections. The plurality of projections entirely occupies the coupling stretch.

In another embodiment (not illustrated in the attached figures), each projection of the plurality of projections is distributed about the axis Al in an annular way, and the projections of the plurality of projections are set at a distance apart from one another within the coupling stretch. In other words, the projections lie in planes parallel to one another and consequently, the coupling stretch is not occupied entirely by the plurality of projections.

In an alternative embodiment of the present invention, each projection does not extend annularly about the axis of the bar, and the projections of the plurality of projections are distributed about the axis of the bar so as to define a set of annular projections about the axis of the bar.

In an alternative embodiment of the present invention illustrated in Figure 12, the projection 7 is replaced by the projection 107, which extends along the axis Al and about the axis Al . In particular, the projection 107 occupies the coupling stretch 5 only partially. Moreover, the projection 7 has a helix shape that develops about the axis Al . With reference to Figures 3, 4, and 5, the annular elements 3 have an axis A2 and have an opening 10 having a dimension D3. In a preferred embodiment, the opening 10 is circular and the dimension D3 is the diameter D3 of the opening 10. The dimension D3 of the annular elements 3 is greater than the dimension D2 of the bar 2. With reference to Figure 2, when the annular elements 3 are fixed to the bar 2, the axis A2 and the axis Al coincide.

With reference to Figure 1, a certain number of the annular elements 3 is constituted by cams 11 and another number of the annular elements 3 is constituted by rings 12.

Each opening 10 of each annular element 3 has an annular inner face 13 that develops about the axis A2 and has a plurality of teeth 14. Each tooth 14 develops in length parallel to the axis A2 and in height so as to be radial to the axis A2. The plurality of teeth 14 is distributed about the axis A2 so as to provide an annular toothing 15 on the inner face 13 of the opening 10. With reference to Figures 1, 2, and 3, the annular elements 3 are fixed to the bar 2 at the projections 7 by interference. In greater detail, and with reference to Figure 2, the annular elements 3 are fixed to the bar 2 in the coupling stretches 5 at the projection 7, in such a way that the annular toothing 15 of the annular elements 3 and the projection 7 of the bar 2 provide a fixing by interference.

In an alternative embodiment of the present invention (not illustrated in the attached figures) , the inner annular face of each annular element is smooth. The annular elements are fixed to the bar by interference in the coupling stretches thanks to the projections of the coupling stretches.

With reference to Figures 8 and 9, and as regards the method for production of the shaft 1, the projections 7 of the bar 2 are obtained by an additive manufacturing process carried out on a bar 2 having a smooth surface and thus define the coupling stretches 5 of the bar 2. In particular, designated by the reference number 20 is a processing device that carries out an additive manufacturing process. By the term "additive manufacturing process" is understood an operation through which one or more layers of material are added to a semifinished object to obtain a finished object or to provide a step of production of a finished object.

The processing device 20 comprises a metal-powder injector 21 and a heat source 22. In a preferred embodiment, the heat source 22 is a laser beam. The processing device 20 provides a process of deposition of material thanks to the powder injector 21, which directs a flow of metal powder 24 onto the bar 2 with smooth surface of Figure 6. The powder is fixed to the bar 2 thanks to the heat source 22. Moreover, the processing device 20 comprises a gas injector 23, which injects a flow of gas that develops in an annular way about the flow of metal powder 24 and the heat source 22 in order to isolate the flow of powder 24 and the heat source 22 from the surrounding atmosphere.

In one embodiment of the present invention, the processing device 20 comprises a rotation unit (not illustrated in the attached figures) coupled to the bar 2 for controlling the angular position of the bar 2 during processing.

The projection 7 is obtained through the processing device 20. In greater detail, the processing device 20 forms each projection 7 by moving parallel to the axis Al and causing the bar to turn about the axis Al .

Moreover, the processing device 20 comprises a measuring device 25 for measuring the dimensions of the projection 7 during deposition of the metal powder. The processing device 20 adjusts the flow of powder 24 according to the measurement of the dimensions of the projection 7 carried out by the measuring device 25 in real time.

With reference to the embodiment of Figure 12, where the projection 107 has a helix shape, the processing device 20 forms the projection 107 by moving in a direction parallel to the axis Al and simultaneously causing the bar 2 to turn about the axis Al .

Moreover, the measuring device 25 is configured for measuring the dimensions of the bar, and the processing device 20 is configured for adjusting the flow of powder 24 according to the measurement of the dimensions of the bar 2. With reference to Figures 3, 4, and 5, the annular elements 3 are obtained by a forging process. Next, within the annular elements 3 the plurality of teeth 14 is obtained, in particular along the inner face 13 of the opening 10 to form the annular toothing 15. The plurality of teeth 14 is obtained through a broaching process. In particular, the annular elements 3 are obtained in such a way that the annular element 3 can be inserted on the bar 2. In particular, the annular elements 3 are sized in such a way that the internal dimension D3 is greater than the external dimension D2 of the bar 2.

In an alternative embodiment of the present invention (not illustrated in the attached figures), the annular elements are obtained by a process of sintering of metal powder. In another alternative embodiment of the present invention (not illustrated in the attached figures), the annular elements are obtained by an additive manufacturing process.

In other words and with reference to Figures 6 to 11, the shaft 1 is obtained at least through the following steps:

a) making the bar 2, preferably through the wire drawing process, having the outer surface smooth with an external dimension D2 in the radial direction with respect to the axis Al (Figure 6);

b) identifying a coupling stretch 5 on the bar 2 for the annular element 3;

c) forming at least one projection 7 on the coupling stretch 5 (Figure 7) through the processing device 20;

d) forming the annular element 3 having the opening 10 with dimension D3;

e) forming the plurality of teeth 14 on the inner face 13 of the opening 10 of the annular element 3 to obtain the annular toothing 15, preferably by broaching;

f) fixing the annular element 3 on the bar 2 in the coupling stretch 5 by interference, causing the annular element 3 to slide axially with respect to the axis Al along the bar 2; and

g) repeating steps b) to f) for all the annular elements 3. Steps d) and f) may be obtained not in sequence with steps b) and c) . In other words, in an alternative embodiment, the manufacturing method includes forming all the annular elements 3 through steps d) and f) and then implementing in sequence steps b) , c) , and d) for each of the annular elements 3.

It is moreover evident that the present invention also covers embodiments not described in the detailed description and equivalent embodiments that fall within the scope of the annexed claims.

Claims

1. A method for manufacturing a shaft (1) with shaped profile, the method comprising the steps of:

- making a bar (2) which extends along a first axis (Al) ;

- making an annular element (3) having an opening (10) about a second axis (A2);

- depositing material (24) on the bar (2) so as to form a coupling stretch (5);

- inserting the annular element (3) on the bar (2); and

- fixing by interference the annular element (3) on the bar

(2) at the coupling stretch (5) .

2. A manufacturing method according to claim 1, comprising the step of making at least one tooth (14) in the annular element

(3) along an inner face (13) delimiting the opening (10) .

3. A manufacturing method according to claim 2, comprising the step of making a plurality of teeth (14) distributed about the second axis (A2) so as to form an annular toothing (15) preferably by broaching.

4. A manufacturing method according any one of the preceding claims, comprising the step of making the bar (2) from a tube (4) preferably obtained by wire drawing.

5. A manufacturing method according to any one of the preceding claims, wherein the step of depositing the material (24) on the bar (2) is carried out with an additive manufacturing process.

6. A manufacturing method according to claim 5, wherein the additive manufacturing process includes depositing metal powder (24) on the bar (2), and fixing the metal powder (24) on the bar (2) by means of a heat source (22) .

7. A manufacturing method according to claim 5 or 6, wherein the additive manufacturing process includes using a metal powder injector (21) .

8. A manufacturing method according to any one of the preceding claims, comprising the step of making at least one projection (7; 107) in the coupling stretch (5) which extends in height so as to be a radial to the first axis (A) .

9. A manufacturing method according to claim 7 or 8, comprising the step of measuring at least one dimension of the projection (7; 107) when depositing the material (24) so as to adjust the deposition of material according to the at least one measured dimension of the projection (7; 107) .

10. A manufacturing method according to claim 8 or 9, comprising the step of making the projection (7; 107) so as to be distributed about the first axis (Al) in order to define an annular projection (9) .

11. A manufacturing method according to any one of claims 8 to

10, comprising the step of making the projection (7; 107) having a helix shape about the first axis (Al) .

12. A manufacturing method according to any one of claims 5 to

11, comprising the step of measuring a radial dimension of the bar (2) and adjusting the additive manufacturing process according to the radial dimension of the bar (2) .

13. A manufacturing method according to any one of the preceding claims, comprising the steps of:

making a further annular element (3) having a further opening (10) about a further second axis (A2);

- depositing material (24) on the bar (2) so as to form a further coupling stretch (5);

- inserting the further annular element (3) onto the bar (2); and

- fixing by interference the further annular element (3) on the bar (2) at the further coupling stretch (7) .

14. A manufacturing method according to claim 13, wherein the step of making the further coupling stretch (5) is carried out once the annular element (3) has been fixed to the bar (2) .

15. A manufacturing method according to any one of the preceding claims, wherein at least one of the annular element

(3) and the further annular element (3) is a cam (11) .

16. A manufacturing method according to any one of the preceding claims, wherein at least one of the annular element (3) and the further annular element (3) is a ring (12) .

17. A shaft with shaped profile made by means of a manufacturing method according to any one of the preceding claims .