Device for Production of a Pre-Formed Shape on a Workpiece by Grinding and Corresponding Method

Abstract

The invention relates to a device and method for production of a pre-formed shape on a workpiece having a blank piece shape, by means of grinding in several working steps, preferably on cams of a camshaft, comprising a grinding machine and a controller, for controlling the grinding machine. A measuring device is provided, for measuring the actual blank piece shape of the workpiece before grinding, directly or indirectly connected to the controller by means of a data transmission device such that the measured values, as determined by the measuring device, may be provided to the controller and set points for the control determine from said measured values by the controller. Either a grinding program matching the actual blank piece shape is calculated from said measured values, whereby the control of the grinding machine is carried out with relation to the actual blank piece shape, or a given stored grinding program is selected, which best matches the control of the grinding machine to the actual blank piece shape, by comparison to the usually selectable grinding programs.

Description

The invention is explained in greater detail by means of the examples shown in FIGS. 1 and 2.

FIG. 1 diagrammatically shows the construction of the inventive device for grinding camshafts.

The cam lobe and the position of the contour of the finished part, as well as the lower and upper tolerance limits of the contour of the unfinished part are shown in FIG. 2.

FIG. 1 diagrammatically shows how the camshaft 1 with the functional component 2, which is to be ground, such as the cam lobe, is located in the measuring station for measuring the contour of the unfinished part at the end of the assembly line (not shown here). The profile data of the cam lobe 2 are determined with sensor technology 13 used for measuring, in the present example a measuring stylus or a laser triangulation device. The values measured are provided over the signal lead 9 to a plant control computer 5. The plant computer 5 has a data memory 7 for storing several grinding programs, which contain, input programs, particularly delivery programs. Moreover, the plant control computer 5 has an arithmetic unit 6, a second data memory 8 and appropriate internal data leads 10, which are realized usually by a data bus. In the arithmetic unit 6 of the plant control computer 5, an appropriate grinding program is selected from the data memory 7 and filed in the data memory 8 on the basis of the input of the value measured at the signal lead 9. The appropriate grinding program, which contains, in particular, the corresponding delivery program, is transferred to the control unit 4 of the grinding machine 3 over the data lead 11.

Parallel to this, the camshaft 1 is brought into the grinding machine 3 for processing by means of an appropriate transfer manipulation 14, such as a robot. The data, required for controlling the grinding machine, I transferred over control signal leads 12a and 12b and the camshaft 1 is ground in accordance with the control program selected.

In a modification of the method described above, the camshaft, after the contour of the unfinished part is measured, is marked clearly (for example, with a bar code) and an identification signal for identifying the camshaft in the grinding machine is also transferred over the control lead 12a to the control unit 4. The marking contains information about the contour of the unfinished part measured or the grinding program that is to be selected. Subsequently, the control unit 4 selects the appropriate grinding program from an allocation of identification signals to the grinding programs.

In an alternative embodiment, the control unit 4, starting out from the identification signal, requests the grinding program from the plant control computer 5.

Pursuant to the invention, the plant control computer 5 and the control unit 4 may be integrated in one computer unit 15. The precise configuration of the computer unit may, however, be very different. The data leads 9, 10, 11, 12a, 12b may also be integrated in a bus system, as is customary in mechanical engineering.

The prior art and the inventive method are compared by means of Table 1 and FIG. 2. A camshaft 1 with cam lobes 2, the oversize of the unfinished parts of which lies within the enveloping curves 17 to 18, has been selected as an example. After the installation, this oversize of the unfinished parts relative to the contour 16 of the finished part, which is also referred to as allowance, fluctuates in the example from the contour of the finished part plus 0.1 mm (enveloping curve 17) to a finished dimension plus 0.5 mm (enveloping curve 18). Moreover, the oversizes at all points of the outer peripheral contour of the cam lobe must lie between the enveloping curve 17 and the enveloping curve 18. In the example selected, the actual oversize at any point of the contour is 0.35 mm.

The grinding wheel must be delivered at such a rate, that it does not dip into the surface of the workpiece at the highest speed used for moving the wheel up to the workpiece.

In accordance with the state of the art, as shown in the left half of Table 1, the grinding wheel is therefore moved up to the enveloping curve 18 for the largest possible oversize. Subsequently, a certain delivery path is covered for each revolution of the workpiece until, in the last step, which is the seventh revolution here, there is “free sparking” with a delivery of 0 mm and the workpiece has been ground to the finished contour 16. According to the prior art, this means 7 deliveries with a total delivery path of 0.5 mm. The whole process time then is approximately 7 seconds, for example.

As can be seen from the Table, the delivery, however, was carried out for a distance of 0.15 mm with a speed, adapted for the grinding, although no material was ground off. This process is also referred to as air grinding in the industry.

This air grinding is eliminated completely with the inventive method, as shown in the right half of Table 1. Delivery takes place directly to the enveloping curve of the measured oversize, which is +0.35 mm here. The grinding operation is completed in 5 further revolutions of the workpiece. In the example given, the process time saved is about 2 seconds per cam lobe.

As furthermore shown in Table 1, the deliveries for the first two revolutions are greater in the case of the inventive method than in the case of the prior art. An advantageous further development of the method is shown here, for which the delivery rate is adapted to the thickness of the oversize. For relatively large oversizes, grinding is usually carried out at a high delivery rate (rough machining). Only when the oversize is small is the delivery rate lowered (finishing, fine finishing or spark machining). The high delivery rate during the rough machining must be such that excessive power is not introduced into the workspace and that, correspondingly, there is no overheating of the workpiece. For example, for an oversize of 0.500 mm, a delivery of 0.400 mm per 4 revolutions up to an allowance of 0.100 mm and a corresponding introduction of power may be provided. However, if the oversize is only 0.350 mm, this delivery can even be increased up to and allowance of 0.100 mm. However, the total delivery must not exceed the value of the original power introduction. The time-shaving volume may be used as a measure of this.

	TABLE 1
	Delivery according to prior art	Delivery according to inventive method
				Air				Air
	Allowance	Workpiece	Delivery	grinding	Allowance	Workpiece	Delivery	grinding
	in mm	revolution	in mm	in mm	in mm	revolution	in mm	in mm
	0.350	1	0.100	0.100				0.000
	0.350	2	0.100	0.050				0.000
	0.300	3	0.100	0.000	0.350	1	0.130	0.000
	0.200	4	0.100	0.000	0.220	2	0.120	0.000
	0.100	5	0.070	0.000	0.100	3	0.070	0.000
	0.030	6	0.030	0.000	0.030	4	0.030	0.000
	0.000	7	0.000	0.000	0.000	5	0.000	0.000
Total	0.350	7	0.500	0.150	0.350	5	0.350	0.000

Over and above the advantages described, the inventive method offers further important advantages. For example, the measurement enables the shafts, for which the contour of the unfinished part of the functional components is already too small, that is, no longer lies within the tolerance range, to be sorted out before the grinding. In this case, the shaft can no longer meet specifications, so that grinding no longer is necessary. As a result, rejects are not processed further and the processing times and costs, required for this, are saved.

An even larger advantage can be seen therein that workpieces having an oversize, which goes beyond the maximum permissible enveloping curve 18, can be processed without sequential damage, so that it becomes possible to lower the tolerance requirements partly or for the time of particular production problems.

Furthermore, the quality of unfinished parts can be specified with a statistical range, so that early recognition of problems in the offing in the case of future manufacturing processes becomes possible.

It is obvious that the method and device described here can also be used for components other than constructed camshafts. For example they may also be used for cast and forged camshafts, crankshafts, control shafts and for the grinding of points of support for transmission shafts.

LIST OF REFERENCE SYMBOLS

• 1 camshaft
• 2 functional component, cam lobe
• 3 grinding machine
• 4 control unit
• 5 plant control computer
• 6 arithmetic unit
• 7 data memory
• 8 data memory
• 9 signal lead
• 10 internal data lead
• 11 data lead
• 12 a control signal lead
• 12 b control signal lead
• 13 sensor technology, measuring stylus
• 14 supplying camshaft to grinding machine, transfer treatment
• 15 arithmetic unit
• 16 contour of finished part
• 17 enveloping curve, lower tolerance limit of the contour of the unfinished part
• 18 enveloping curve, upper tolerance limit of the contour of the unfinished part

Claims

1. Device for producing a finished contour of a workpiece having the contour of an unfinished part by grinding in several steps, preferably at cam lobes of a camshaft, comprising a grinding machine, which has grinding means for grinding away an oversize corresponding to the difference between the contour of an unfinished and that of a finished part, and a control device for controlling the grinding machine, wherein a measuring device for measuring the actual contour of the unfinished part of the workpiece is provided, which is coupled directly or indirectly by means of at least one data transfer device with the control device, so that the values determined by the measuring device can be supplied to the control device and at least specified values for controlling the delivery of the grinding agent can be determined from these measured values by the control device.

2. The device of claim 1, wherein a measuring unit is disposed separately from the grinding machine and that a device for transporting the workpiece is provided between the measuring device and the grinding machine.

3. The device of claims 1 or 2, wherein a plant control computer, to which the values from the measuring device are to be supplied over the first data transfer device is connected between the measuring device and the control device, so that a grinding program, which is suitable for the present grinding task and can be transferred over a second data transfer device to the control device, can be selected via the plant control computer on the basis of the values measured.

4. The device of claims 1 or 2, wherein means are provided, with which the values, determined by the measuring device, and/or the grinding program selected can be assigned directly or indirectly to the individual workpiece.

5. The device of claim 4, wherein the means assign to the workpiece a coding containing the values measured and that further means are provided, which can read the coding when the workpiece is placed in the grinding machine.

6. The device of claims 1 or 2, wherein means are provided with which workpieces, after the contour of unfinished parts are measured in the measuring device, are not supplied for further processing if the measured contour of the unfinished parts falls below the contour of the finished parts by more than a permissible tolerance range.

7. Device for grinding a finished contour of cam lobes of a camshaft with a grinding machine and a control device controlling the latter, grinding programs being specifiable by the control device and containing specified values for the grinding parameters of the RPM of the grinding means and/or of the workpiece, when RPM of the grinding means and/or of the workpiece, rate of advance, delivery and axial position of the workpiece, wherein at least the following components are provided: a measuring device for measuring the unfinished contour of the workpiece, which is to be ground,a plant control computer for determining and/or selecting one or more grinding programs,a first data-transfer device between the measuring device and the plant control computer as well as a second data transfer device between a plant control computer and the control device, it being possible to supply the values of the contour of the unfinished part, measured by the measuring device, over the first data transfer device to the plant control computer and, depending on these values, to determine and/or select at least one grinding program in the plant control computer and supply it over the second data transfer device to the control device and to control the grinding machine from the control device one in accordance with the grinding program determined and/or selected.

8. Method for producing a finished contour of a workpiece having an unfinished contour by grinding in several steps, preferably at cam lobes of a camshaft, for which the contour of the unfinished part of the workpiece is ground away in each step by a specifiable amount, so that the finished contour of the workpiece is present after the last step, comprising the following steps: a) the contour of the unfinished part of the workpiece is measured before the grinding process is commenced;b) the values determined are transmitted directly or indirectly to a control device;c) depending on these values measured, either a grinding program is calculated, which is adapted to the actual contour of the unfinished part and for which the supplying of grinding agent to the grinding machine is controlled taking into consideration the actual contour of the unfinished part, or a specified and stored grinding program is selected, for which, in comparison to the remaining grinding programs that may be selected, the control of the delivery of the grinding agent of the grinding machine is adapted best to the actual contour of the unfinished part.

9. The method of claim 8, wherein, for a grinding program with several grinding steps, which cannot be changed, a first grinding step is skipped depending on the measured values of the contour of the unfinished part that has been determined.

10. The method of claim 9, wherein, in addition to the first grinding step, further grinding steps that follow the first one are skipped.