CHAMFERING METHOD

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102019000005886 filed on April 16, 2019, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a tool to chamfer a raw gear wheel and a relative chamfering method.

PRIOR ART

Tools to chamfer edges between a front surface and the sides of each tooth of the raw gear wheel are known. In particular, the chamfering is performed downstream of the roughing operation, in which the raw gear wheel is made with the help of a hob. Therefore, the chamfer removes the sharp edges of each tooth so as to prevent the raw gear wheel from being damaged or damaging another gear wheel with which it meshes during use. Furthermore, by removing the sharp edges, it is possible to avoid injuring the operator during the handling, for example the assembly, of the gear wheel.

The chamfering tool generally comprises a plurality of tooth shaped cutting elements, in which the cutting profiles are made on the external lateral sides thereof. In particular, the cutting elements have a shape which is substantially complementary to the shape of the space comprised between the two teeth of the raw gear wheel.

During the chamfering process, both the tool and the raw gear wheel are set in rotation. In particular, the tool is configured to rotate around an axis skewed relative to the axis of the raw gear wheel. During use of chamfering tools of a known type, each cutting element passes through a respective compartment of the raw gear wheel and chamfers, by means of the cutting profiles on the external lateral sides, two sides, facing one another, of two adjacent teeth, which laterally delimit a respective compartment of the raw gear wheel.

Therefore, substantially, a chamfering tool of a known type simultaneously chamfers the left side of the previous tooth and the right side of the following tooth which are held, during mutual rotation, by the chamfering tool.

It is evident that a shift of the chamfering tool with respect to the raw gear wheel results in a non-symmetrical chamfering, namely one of the two sides is chamfered more than the other. This is absolutely not wanted and therefore should be avoided, because it compromises the function of the chamfer and a subsequent correct meshing of the gear wheel with another gear wheel .

The known chamfering tools substantially work by plastic deformation of the sides of two adjacent teeth, creating a track in the material, which compromises the finishing operations following the finishing step.

DESCRIPTION OF THE INVENTION

The object of the present invention is, therefore, to provide a tool to chamfer a raw gear wheel and relative chamfering method which are free from the drawbacks of the state of the art and which are easy and inexpensive to manufacture.

According to the present invention, a tool is provided to chamfer a raw gear wheel according to what is claimed in the attached claims .

According to the present invention, a chamfering method is provided according to what is claimed in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, an embodiment is described purely by way of non-limiting example wherein:

- Figure 1 is a schematic and perspective view of a chamfering tool according to the present invention in an operating configuration;

- Figure 2 illustrates a detail of Figure 1 in a first processing stage ;

- Figure 3 is similar to Figure 2 and illustrates the same detail in a second processing stage;

- Figure 4 is a schematic view, with some parts removed for clarity, of a tool according to the present invention during use; and

- Figures from 5 to 8 illustrate respective different types of chamfers which can be made with the method according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In Figure 1, the number 1 generally denotes a tool to chamfer a raw gear wheel 6.

As illustrated in Figure 1, the raw gear wheel 6 is a cylindrical element having a rotation axis Y and a thickness s. The raw gear wheel 6 is axially delimited by two surfaces substantially perpendicular to said axis Y and hereinafter referred to as the front surface 3A and the front surface 3B, respectively. The front surfaces 3A and 3B are opposite to one another.

Furthermore, the raw gear wheel 6 comprises a plurality of teeth 5 which project radially outside the raw gear wheel 6. The teeth 5 are equidistant.

Each tooth 5 has a right side 4* and a left side 4**. In the following the terms right and left are used with reference to the rotation direction of the raw gear wheel 6 during use. The sides 4* and ** extend along the thickness s of the tooth 5. The term side 4* or 4** refers to the entire side surface of the tooth 5, that is the side surface which extends between the head circumference dt and the foot circumference dp of the raw gear wheel 6. The head circumference dt is, in a known way, the circumference that externally delimits the tooth 5 and the foot circumference dp is, in a known way, the internal circumference that internally delimits the tooth 5. The terms internal and external are used with reference to the rotation axis Y of the raw gear wheel 6.

In particular, the raw gear wheel 6 has an edge 2A between the front surface 3A and the sides 4* and 4**. Similarly, the raw gear wheel 6 has an edge 2B between the front surface 3B and the sides 4* and 4**.

As will be better illustrated in the following, the chamfering tool 1 is configured to chamfer each edge 2A, 2B. In other words, the tool 1 is configured to remove material along each edge 2A, 2B so as to create a chamfer 20A and 20B, respectively (Figure 3) . As illustrated in Figures from 5 to 8, the chamfer 20A can be continuous, i.e. the entire edge 2A is chamfered, or intermittent, i.e. some portions of edge 2A are not removed.

The tool 1 comprises a cylindrical body 7 having a rotation X axis and a substantially cylindrical side surface 8.

The tool 1 comprises a plurality of cutting elements 9 each radially projecting from the side surface 8.

Each cutting element 9 has a right cutting profile 10 and a left cutting profile 11, which laterally delimit a groove 12. Similarly, as stated above, the terms right and left are used with reference to the rotation direction of the tool 1. As illustrated in greater detail in Figure 4, the groove 12 is configured to house, in use, a respective tooth 5 of the raw gear wheel 6. The right profile 10 is configured to chamfer, in use, the left side 4** of a respective tooth 5. The left profile 11 is configured to chamfer, in use, the side right 4* of a respective tooth 5.

In other words, each cutting element 9 simultaneously chamfers both the sides 4* and 4** of the respective tooth 5.

Advantageously, the right profile 10 and the left profile 11 are different from one another. In other words, the profiles 10 and 11 do not have the same shape. Therefore, the cutting element 9 is not made symmetrical along a plane transverse or perpendicular to the rotation axis X.

According to an alternative, the profiles 10 and 11 can be arranged in a mirror like manner to one another.

The groove 12 has a profile designed, in particular calculated, to cut a profile with the shape of an involute of a circle. In other words, the profiles 10 and 11 that laterally delimit the groove 12 are profiles made to cut the profile into an involute of a circle of the tooth 5.

Advantageously, each cutting element 9 helically projects around the side surface 8. In other words, each cutting element 9 is arranged along an imaginary helix which extends around the side surface 8 of the cylindrical body 7, so as to allow, in a known manner, the meshing between the tool 1 and the raw gear wheel 6 during use. In particular, the chamfering tool 1 has a plurality of cutting elements 9 which radially project from the same axial portion pa of the tool 1 itself. In this case, it is stated that the tool 1 has a plurality of threads/starts .

Advantageously, each cutting element 9 of an axial portion pa lies on a respective start.

In use, as illustrated in Figure 1, the rotation axis X and the rotation axis Y are arranged substantially skewed relative to one another and set the tool 1 in rotation around the rotation axis X and the raw gear wheel 6 in rotation around the rotation axis Y, respectively.

Then the tool 1 is moved close to the raw gear wheel 6. Advantageously, the tool 1 is synchronized with the raw gear wheel 6 so as to mesh with one another without impact.

Advantageously, the tool 1 and the raw gear wheel 6 are synchronized with one another, so that a tooth 5 of the raw gear wheel 6 is made to slide through a groove 12 of a respective cutting element 9.

In this way, chamfering of at least a part of the edge 2A between the front surface 3A and sides 4* and 4** of the respective tooth 5 of the raw gear wheel 6 is obtained by means of the cutting element 9.

The chamfering of the edge 2A can take place by means of one or more runs, i.e. several runs of a tooth 5 by means of the respective groove 12. In the case of performing several runs, between one run and the following run, there is the further step of radially feeding the tool 1 towards the raw gear wheel 6.

The geometry 20A, 20B of the final chamfer depends both on the shape of the profiles 10 and 11 of each cutting element 9 and on the reciprocal displacements between tool 1 and raw gear wheel 6 during machining. Figures 5 to 8 illustrate examples of different types of chamfers 20 that can be made with the tool 1 and the method according to the present invention.

Once the chamfering of the edge 2A is finished, the chamfering of the other edge 2B can be carried out, i.e. of the edge 2B between the front surface 3B and the sides 4* and 4**. In order to chamfer the edge 2B first the assembly direction of the tool 1 itself must be inverted, by disassembling it and reassembling it with the opposite direction to the previous one, so as to ensure that the right profile 10 and the left profile 11 face the edge 2B to be cut. Subsequently, the tool 1 is moved axially along the axis X, so as to set each cutting element 9 gripping the respective edge 2B. Furthermore, the rotation direction of the tool 1 is inverted, so as to also chamfer the edge 2B between the front surface 3B, opposite to the front surface 3A, and the side 4* and the side 4** of the respective tooth 5 of the raw gear wheel 6.

Alternatively, in order to chamfer the edge 2B, it is possible to mount two tools 1 side-by-side one another having an assembly direction inverted with respect to one another, so as to carry out the chamfering of the edge 2B without requiring any disassembly and reassembly of the tool 1.

Ihe tool 1 and the method described hitherto have a plurality of advantages .

During chamfering, a cutting process is performed with the tool 1. The chamfering thus created has a better precision, a higher quality and avoids the tracking of the material, with consequent plastic deformation.

The groove 12 of the cutting elements 6 is substantially complementary to the shape of the tooth 5 of the raw gear wheel 6. Therefore, it is ensured that the entire edge 2A or 2B of the tooth 5 is chamfered.

Thanks to the tool 1 it is possible to obtain a plurality of different types of chamfers 20. For example, it is possible to manufacture: constant chamfers 20 affecting the entire edge 2A or 2B (Figures 1 and 5); constant chamfers affecting only part of the edge 2A or 2B (Figures 6 and 8) ; and comma-shaped chamfers, i.e. chamfers which have a chamfered surface decreasing from the head towards the foot of the tooth 5 (Figure 7) .