GB2116463A

GB2116463A - Process and apparatus for grinding the surface of a cam

Info

Publication number: GB2116463A
Application number: GB08305717A
Authority: GB
Inventors: Pio Panelli
Original assignee: Fiat Auto SpA
Current assignee: Fiat Auto SpA
Priority date: 1982-03-17
Filing date: 1983-03-02
Publication date: 1983-09-28
Also published as: DE3309424C2; IT8267341A0; FR2523495B1; DE3309424A1; IT1155645B; GB8305717D0; FR2523495A1; GB2116463B; JPS58171253A; JPH0635102B2

Abstract

A process for producing by grinding a surface extending around a straight longitudinal axis and serving as the operative surface of a cam, comprises providing a grindstone (4) having a plane working surface (5) and rotating around an axis (YY) perpendicular thereto; and placing such surface in contact with the cam surface to be treated. The cam is rotated around its longitudinal axis (XX) and at the same time has imparted to it an angular oscillatory motion (K) around an oscillation axis (ZZ). The grindstone (4) has imparted to it a displacement parallel to its rotational axis (YY), and control means are provided which associate in a predetermined relationship cam rotation, oscillation of the cam longitudinal axis and grindstone displacement, the action of the control means being such as always to maintain the plane working surface (5) of the grindstone (4) in contact with the cam surface to be treated. <IMAGE>

Description

SPECIFICATION Process for producing by grinding the operative surface of a cam, and an apparatus for the performance of the process The invention relates to a process for producing by grinding a fluted surface extending around a straight longitudinal axis and serving as the operative surface of a cam and to an apparatus for the performance of the process.

The grinding operation produces the circumferential profile which is the cam external surface. The circumferential profile is the operative profile with which the cam-actuated element co-operates.

The problem arises in this connection of producing a profile which is rounded everywhere and is therefore devoid of discontinuity.

Another problem, which arises in connection with the production of large numbers of cams, is the need to be able to produce such a profile by means of a rapid, continuous and automatic operation.

These difficulties are overcome according to one aspect of the present invention by a process for producing by grinding a fluted surface extending around a straight longitudinal axis and serving as the operative surface of the cam, the process comprising the steps of: providing a grindstone having a plane working surface and rotating around an axis perpendicular thereto; placing such surface in contact with the cam surface to be treated; rotating the cam around its longitudinal axis; imparting to the cam longitudinal axis an angular oscillatory motion around an oscillation axis; imparting to the grindstone a displacement parallel to its rotational axis; and providing control means which associate in a predetermined relationship cam rotation, oscillation of the cam longitudinal axis and grindstone displacement, the action of the control means being such as always to maintain the plane working surface of the grindstone in contact with the cam surface to be treated.

According to another aspect of the present invention there is provided an apparatus for producing by grinding, in accordance with the process just specified, a fluted surface which is the operative surface of a cam, the apparatus comprising a workpiece slide on which the cam blank is mounted for rotation around its longitudinal axis, and a tool spindle on which a rotatable plane grindstone is disposed, wherein the workpiece slide is rotatable around an oscillation axis and the tool spindle is disposed on sliding carriage, control means being provided to associate in a predetermined relationship the rotation of the cam around its longitudinal axis, the angular movement of the workpiece slide around the oscillation axis and the displacement of the sliding tool spindle carriage, such relationship being adapted always to maintain the plane working surface of the grindstone in contact with the cam surface to be treated.

The invention will be more fully understood from the following description given by way of example only with reference to the several figures of the accompanying drawings, in which~ Figure 1 is a diagrammatic exploded view in oblique perspective of a cam on which it is required to produce the operative surface by means of the process of the invention, the Figure also shows a plane grindstone adapted to treat the cam surface; Figures 2 and 3 show the cam and grindstone of Figure 1 during consecutive working steps of the process of the invention Figures 4, 5 and 6 are plan views corresponding to Figures 1 and 2 and 3 respectively;; Figures 7, 8 and 9 are views looking in the directions indicated by arrows VII, VIII and IX respectively of Figures 4, 5 and 6 respectively, and Figure 10 is a view in oblique perspective of an apparatus for the performance of the process of the invention.

A cam shown generally at 1 has an operative surface 2. The operative surface 2 is produced as the envelope of consecutive positions taken up by a plane which rotates around an axis X-X and which, as it rotates, takes up different angular positions relatively to the axis X-X. In Figure 1 the generating plane is shown in two consecutive positions position A and position B. The Plane A is placed tangential to the operative surface 2 of the cam along a generator 7 whereas the plane B is tangential to the surface 2 along a generator 8.

In the case shown the generators 7, 8 are inclined relative to the axis X-X. However, the generators could be parallel to the axis X-X or intersect the same, in which evext they would belong to those planes containing the axis X-X. The cam 1 is carried by a simple shaft 3 having at its axis the said axis X-X. A right cylindrical grindstone shown generally at 4 has a plane front working surface 5 in the form of a circular annulus.

Grindstone 4 is rotatable about an axis Y-Y that in Figure 1 intersects the axis X-X at X, and is normal thereto. The plane A of Figure 1 is also normal to the plane YYX1X defined by the two axes X-X and Y-Y, the plane A intersecting the said plane bounded by the two axes X-X and Y-Y along broken line 6 which in Figure 1 is parallel to the axis X-X. Consequently, when the grindstone 4 is fed towards the cam 1, the grindstone working surface 5 engages the operative surface 2 of the cam 1 along the generator or line 7.In the position shown in Figure 2 the grindstone 5 and the cam axis X-X remain in the same relative position to one another, but the cam 1 has rotated to bring the plane B perpendicular to the plane YYX1X of the axes X-X and Y-Y. The plane B intersects the plane YYX,X bounded by the two axes X-X and Y-Y along a line 9 which in this case is not parallel to the cam axis X-X but intersects axis XX to form with it an angle K.Consequently, the generator 9 is not even parallel to the grindstone surface 5 and forms therewith the angle K. Referring to Figure 3, the broken lines indicate the grindstone 1 in the same position as in Figure 2, whereas the solid lines indicates the grindstone 1 in the position obtained by rotating the cam axis X-X through the angle K around an oscillation axis Z-Z perpendicular to the plane YYX1X bounded by the axes X-X and Y-Y, so that the generator 9, the intersection of the plane B with the plane of the axes XX and Y-Y, is disposed parallel to the grindstone surface 5.In this position, when the grindstone 4 is advanced parallel to its axis Y-Y, the grindstone surface 5 engages with the cam surface 2 along the line or generator 8. Consequently, to change from the working position shown in Figure 1 to that shown in Figure 2, the following steps must be performed: (i) rotate the shaft 3 through an angle F in Figure 2, (ii) revolve the axis X-X of the shaft 3 through the angle K, as shown in Figure 3, and (iii) move the grindstone 4 parallel to its axis Y-Y.

The three steps are performed simultaneously.

If the shape of the cam operative surface 2 required to be produced by the grinding step is known, it is possible to calculate for every value of the angle F the corresponding value of the angle K of rotation of the cam axis X-X and the corresponding value for movement of the grindstone 4 along its axis Y-Y.

The value of grindstone movement and of the angle K can therefore be determined in dependence upon the value of the angle F by varying the same from zero to three hundred and sixty degrees arc. Consequently, if the shaft 3 is revolved slowly around its axis XX, so that the same oscillates by an amount equal to a continuously varying angle K while the shaft 3 rotates about its axis and if the grindstone 4 is moved correspondingly parallel to itself, the grindstone, rotating at high speed about its own axis W produces by means of its surface 5 the required operative surface 2 of the cam 1.

Figure 10 shows an apparatus 20 for the performance of the process illustrated in Figures 1 to 6. The apparatus 20 has a base shown generally at 21 with two longitudinal guides 22 at the top. A headstock 23 serving as tool carrier is disposed for sliding on the guides 22. The tool carrier 23 receives drive means for rotating a spindle 24 on which a grindstone shown generally at 4 is mounted. The head 23 also receives drive means for moving the head 23 lengthwise along the guides 22. Disposed on the base 21 in front of the head 23 is a support plate 25 on which a platform 26 is disposed for rotation around an axis Z-Z. An elongated base 27 having transverse guides 27a is secured to platform 26. A cross-slide 28 is slidable on the guides 27a and has at the top a first upright 29 serving as workpiece head and a second upright 30 serving as a back centre. Upright 29 carries a motor 31 which transmits its movement to a spindle on which a shaft 3 is disposed. The shaft 3 is a cam shaft and has four cams 1. The apparatus 20 has numerical control means not shown arranged to provide the movements required for the operation. Consequently, when the cam shaft 3 is rotated around its axis X-X by the motor 31, the base 27 is simultaneously rotated together with the platform 26 and performs an oscillatory motion of angle K.

Simultaneously too, and again through the agency of a known numerical control, the tool head 23 is reciprocated cyclically along the guides 22 in the direction of the axis Y-Y to ensure that the grindstone operative surface 5 remains in constant engagement with the operative surface 2 of the cam 1 being treated.

Claims

1. A process for producing by grinding a fluted surface extending around a straight longitudinal axis and serving as the operative surface of a cam, characterised in that it comprises the steps of; providing a grindstone having a plane working surface and rotating around an axis perpendicular thereto; placing such surface in contact with the cam surface to be treated; rotating the cam around its longitudinal axis; imparting to the cam longitudinal axis an angular oscillatory motion around an oscillation axis; imparting to the grindstone a displacement parallel to its rotational axis;; providing control means which associated in a predetermined relationship cam rotation, oscillation of the cam longitudinal axis and grindstone displacement, the action of the control means being such as always to maintain the plane working surface of the grindstone in contact with the cam surface to be treated.

2. The process as claimed in claim 1, wherein the oscillation axis is perpendicular to a plane parallel to the cam longitudinal axis and to the grindstone rotational axis.

3. The process as claimed in claim 1 or claim 2, wherein the fluted operative surface of the cam consists of side-by-side straight segments each disposed in a corresponding plane passing through the cam longitudinal axis.

4. An apparatus for producing by grinding a fluted surface which is the operative surface of a cam, the apparatus comprising a workpiece slide on which the cam blank is mounted for rotation around its longitudinal axis, and a tool spindle on which a rotatable plane grindstone is disposed, characterised in that the workpiece slide is rotatable around an oscillation axis and the tool spindle is disposed on a sliding carriage, control means being provided to associate in a predetermined relationship the rotation of the cam around its longitudinal axis, the angular movement of the workpiece slide around the oscillation axis and the displacement of the sliding tool spindle carriage, such relationship being adapted always to maintain the plane working surface of the grindstone in contact with the cam surface to be treated.

5. The apparatus as claimed in claim 4, characterised in that the oscillation axis is perpendicular to a plane extending parallel to the cam longitudinal axis and to the tool spindle axis.

6. The apparatus as claimed in claim 4 or claim 5, wherein the cam has a fluted operative surface embodied by side-by-side straight segments each disposed in a corresponding plane passing through the cam longitudinal axis.

7. A process as hereinbefore described with reference to the several figures of the accompanying drawings.

8. Apparatus constructed and arranged substantially as hereinbefore described with reference to the several figures of the accompanying drawings.