The invention concerns a method of and an apparatus for grinding cams of a camshaft.
From JP 12005052912, a machine for finish machining of camshafts is known. To simultaneously machine all the cams, a corresponding number of finishers are positioned around the camshaft. As a result, the operating personnel can only access the machine with difficulty. In addition, the camshaft cannot be supported with steady rests, as the space needed for them is occupied by the finishers. Hence the machine is not suitable for grinding at high removal rates. Moreover, for loading and unloading, multi-axial sequences of motion are required because the camshafts have to be moved into the working area or out of the working area lengthwise. EP 0,085225 [U.S. Pat. No. 4,443,976] shows a method of grinding camshafts in which a uniform feed speed is achieved by adapting the speed of rotation of the camshaft to the cam shape. According to this method, the cams are individually machined one after the other.
The object of the invention is to improve the above-described method and machine in such a way that grinding with increased removal rates is possible. Simultaneously, access to the machine is to be improved.
This object is attained by a method according to claim 1 and a grinding machine according to claim 5. Advantageous further developments of the invention are the subject matter of the dependent claims.
When grinding cams with high removal rate, uniform feed speed is achieved by adapting the speed of rotation of the camshaft to the cam shape, i.e. while grinding the sections between the cam lobe and the basic circular shape, the rotating speed is slowed down. An advantageous aspect of the invention is that according to this method, camshafts with diametrally opposite cams are machined simultaneously with two grinders. The method is particularly well suited for machining camshafts for four-cylinder combustion engines. These camshafts are provided with four cams or cam pairs located in pairs diametrally opposite each other relative to the longitudinal axis of the camshaft. According to the invention, in a first step the first two cams or cam pairs are machined, the grinders are moved along the longitudinal axis of the camshaft to the still unmachined cams and in a second step the second cams or cam pairs are subjected to the grinding process. As a result of diametrally opposite orientation of the grinders, the loading and unloading can take place from the front operator side and the support of the camshaft by, for example, by steady rests, can be from the back side. Because contrary to what is the case in prior art, only two grinders are used, there is sufficient space available for the holder and the automatic loader. In an advantageous embodiment, two workpiece grabs are provided for the loading and unloading. While the first workpiece grab grips the completely machined camshaft and deposits it on an output conveyor, the second workpiece grab grips an unmachined camshaft from an input conveyor and fits it into the workpiece holder.
In the following, the invention is explained in greater detail with the reference to several embodiments.
FIG. 1 is a front view of a machining apparatus
FIG. 2 is a top view partly in cross section of a machining apparatus
FIGS. 3 and 4 show, together with FIG. 2, the three steps of loading
FIG. 5 shows a detail from FIG. 4 in enlarged scale
FIG. 6 shows a camshaft in an end view
FIG. 1 shows an apparatus 1 for machining camshafts 7, details of the drive, its controller, and the housing not essential to the invention not being shown. The camshafts 7 are chucked in a workpiece holder 6 consisting of a headstock 8 and a tailstock 9 and rotated. Two grinders 10 and 11 diametrally flank the workpiece rotation axis 16. They can each move in two mutually perpendicular directions relative to each other (X and Z axis) on a machine frame 2. To this end, vertical guides 3 are provided on the frame 2 for vertically movable slides 4, and these in turn have respective horizontal guides 12 for horizontally movable carriages 5. The transporting in an out of the camshafts 7 is done by respective conveyors 13 and 13′. Loading and unloading is performed by respective workpiece grabs 14 and 14′.
FIG. 2 shows that the workpiece rotation axis 16 and rotation axes 19 and 19′ of the grinders 10 and 11 are coplanar. A steady rest 15 is mounted between the vertical guides 3 to support the camshaft 7. In an advantageous embodiment, the guides 3, the workpiece holder 6 and the steady rest 15 are secured to one vertical wall 20 of the frame 2. The unmachined camshafts 7 are fed in by the input conveyor 13, and completely machined camshafts are taken out by the output conveyor 13′. While the workpiece is being changed, the first workpiece grab 14′ grips the completely finished camshaft and deposits it on the output conveyor 13′. Simultaneously, the second workpiece grab 14 grips an unmachined camshaft from the input conveyor 13 and places it into the workpiece holder 6. The provision of the grinders 10 and 11 on opposite sides of the workpiece rotation axis 16 and the provision the steady rest 15 between the vertical guides 3 significantly improves accessibility. Moreover, the camshafts 7 can be inserted into the workpiece holder 6 by pivoting them in circular arcs on the operator side.
In FIGS. 3 and 4 views of the loading process are shown. FIG. 3 shows the workpiece grabs 14 and 14′ during a pivoting movement. The workpiece grabs 19 and 19′ are pivotal arms. With them, the camshafts 7 are moved for loading and unloading between the conveyors 13 and 13′ and the workpiece holder 6 on respective circularly arcuate paths 21 and 21′. According to FIG. 4, an unmachined camshaft is inserted into the workpiece holder 6 while at the same time a completely machined camshaft 7 is deposited onto the output conveyor 13′. To show the details in the area of the workpiece rotation axis 16, in FIG. 5, grinding wheels 22 and 22′ are shown partially broken away. For holding the camshafts 7, the workpiece grab 14 is provided with a two-arm gripper 23. When the gripper is open, the workpiece grab 14 can swing along the respective arcuate path 21 into or out of alignment with the workpiece rotation axis 16 for gripping or releasing a camshaft 7.
FIG. 6 shows details of the camshaft 7 with the workpiece rotation axis 16 in an end view. Each cam has a basic circular shape 17, beyond which the cam lobe 18 projects. In the camshafts for four cylinder combustion engines, the cam lobes 18 are located relative to the workpiece rotation axis 16 in mirror image, offset by angles of 90° degrees.
REFERENCE NUMERALS
1 machining apparatus
2 frame
3 guide
4 vertically movable slide
5 horizontally movable carriage
6 workpiece holder
7 camshaft
8 headstock
9 tailstock
10 grinder
11 grinder
12 guide
13
13′ conveyor
14
14′ workpiece grab
15 steady rest
16 workpiece rotation axis
17 basic circular shape
18 cam lobe
19
19′ axis of rotation
20 wall
21
21′ track
22
22′ grinding wheel
23 tongs
Patent Application
20100233939
