WO2003082502A2

WO2003082502A2 - Method for machining workpieces using a machining process, in particular an electrochemical machining process

Info

Publication number: WO2003082502A2
Application number: PCT/DE2003/000975
Authority: WO
Inventors: Gerhard Moeckl
Original assignee: Robert Bosch Gmbh
Priority date: 2002-04-03
Filing date: 2003-03-25
Publication date: 2003-10-09
Also published as: DE10214619C5; DE10214619A1; DE10214619B4; WO2003082502A3

Abstract

The invention relates to a method for machining workpieces using a machining process, in particular an electrochemical machining process. According to said method, a voltage is applied between an electrode and a workpiece, in such a way that a current runs between the electrode and the workpiece via a working medium, in particular an electrolyte solution, in order to remove or deposit material. During the test operation, the current is compared with a predetermined range, which is formed by a lower limit value and an upper limit value. If the current lies within the range, the total resistance is satisfactory and a correct machining process can be expected.

Description

Method for machining workpieces using a machining method, in particular the electrochemical machining method

State of the art

The invention is based on a method for machining by means of a machining method, in particular the electrochemical machining method, according to the preamble of the main claim.

In such a method for editing

Workpieces by means of a machining method, which can be the electrochemical machining method, a voltage is applied between an electrode and a workpiece. The voltage applied creates a current flow between the electrode and the workpiece through a working medium - the electrochemical material processing being an electrolyte solution - whereby material is removed or applied.

To ensure that between the workpiece and the

If there is no short circuit in the electrode, a small test voltage is first applied and the current flowing is measured. If a specified value is not exceeded, processing can begin. The default value is an upper limit. DE 40 40 590 Cl also discloses a method for machining workpieces using the electrochemical machining method. The current is regulated here. That is, the tension corresponding to that

Specification for the set current value is set. Particularly when there are several workpieces to be machined in parallel, the case may arise here that the resistance to the electrode, for example due to dirt between the electrode and the workpiece, is significantly higher than that of the others. As a result, a correspondingly lower current flows through this workpiece and there is a risk that too little material will be removed. The other workpieces, however, are then processed excessively. Electrochemical machining with a current control should therefore be limited to machining one workpiece.

There are also electrochemical processes in which the electrode is moved so that the distance between the electrode and the workpiece remains constant. As a result, the resistance between the electrode and the workpiece remains approximately constant, and with it the current.

Advantages of the invention

The method according to the invention for machining by means of a machining method, in particular the electrochemical machining method, with the characterizing features of the main claim has the advantage that it can be estimated at the beginning of machining whether the parts are being machined correctly. Before machining, the resistance between the electrode and the workpiece must also be in a certain range Range lie so that the required current flows at a predetermined time for processing with a predetermined voltage curve. If the resistance is too high, the result at the end, especially when machining with a predetermined time, is too little machining. If the resistance is too low, too much material is removed or applied. So if you measure the current during the test process and compare it with a specified range, you know whether the machining is likely to deliver good parts or whether it - when exceeded or

Falling below this range - must be canceled.

An advantageous development of the invention consists in that when monitoring the current, much narrower limits can be set in which the current moves. This also results in a higher dimensional accuracy of the workpieces. In addition, the load on the electrode is lower, which means that it heats up less, which leads to an increase in service life. This is achieved by increasing the voltage after the test cycle to a predetermined value using a ramp. The current follows this rise and changes within much narrower limits.

It is advantageous to change the voltage curve during the

Specify processing, measure the current and compare with a predetermined range, which is formed by a lower limit and an upper limit. Processing should be interrupted if the measured current is outside the at least one predetermined range, this can prevent damage from excessively high currents or faulty parts due to insufficient processing. In a further development, the voltage can be increased to a larger value or reduced to a lower value via a ramp after the first value has been reached. By choosing the right ramps, a relatively constant current profile can be achieved.

Workpieces that are in order after processing are characterized by a certain resistance range in the gap between the electrode and the workpiece. This also results in a certain area in which the current must lie. This fact can be used for quality control by comparing the current measured at the end of the machining with a second predetermined range that is smaller than a predetermined range during the machining. If the current is in this range, the workpiece is OK.

It is particularly advantageous to machine several workpieces in parallel and to measure the current through each workpiece.

The method can also be used particularly for machining with an electrode that is not moved relative to the workpiece during machining.

Further advantages and advantageous developments of the method according to the invention for machining using a machining method, in particular the electrochemical machining method, result from the subclaims and the description.

drawing

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. FIG. 1 shows the graphical course of the Voltage and current in an electrochemical material processing over time and Figure 2 shows the graph of the voltage and current in a second electrochemical material processing over time.

Description of the embodiment

The principle of electrochemical material processing is based on the fact that a direct voltage is applied to two electrodes, which are in an aqueous electrolyte solution used as working fluid. For this purpose, the workpiece to be treated is connected to the positive pole (anode) of a current source with the aid of a transmission element, while an electrode serving as a tool is connected to the negative pole (cathode) of the current source due to its electrically conductive properties.

The composition of the electrolyte solution depends on the material of the component to be machined. For metals such. B. a sodium chloride or a sodium nitrate solution is selected. The electrochemical process itself is known from physics and is therefore not explained in more detail here. In addition to the composition of the electrolyte solution, the method of operation also depends on the current strength used, which in turn is to be matched to the material of the workpiece to be machined.

1 shows the course of the voltage and the current during electrochemical machining of a workpiece over time. The top line represents the voltage and the bottom line the current.

The present invention is a machining in which the electrode or a plurality of electrodes are machined relative to the workpiece or Workpieces are not moved, this case is also conceivable.

The following applies to the abbreviations used in FIG. 1:

Uprüf'- This is a test voltage that is applied at the beginning of the process. A short circuit between the workpiece and the electrode is detected early on using the test voltage Up _r ^ f. The test voltage Up _ru f is applied before each machining process; the range is, for example, between 2V and 5V. The validity of the test voltage on the workpieces must be checked for the valid test.

ϊprüfmax- ^{D it} is a maximum current that may flow when the test voltage Up _rü f is applied. If the actual current Iprüfmax exceeds this setpoint, the test is considered unsuccessful. The range of the current iprüfmax is, for example, 2A to 5A.

tp _r üf: This is the time during which the test voltage Up _r ü is applied.

UI: This is a voltage value which, after a successful test taking into account the time tyi, is next approached via a ramp; i.e. there is a gradual increase in tension. In the present case, a ramp can run continuously or in small voltage levels.

U2: This is the final voltage value of the process. If there is a difference between Ul and U2, there is a successive change in voltage depending on the time ty2, also along a ramp. tj2 ^: This is the time for the process from reaching UI to reaching the final voltage value U2.

-'- min ¹ ^{This is} a lower current limit during the actual processing or during the time tj2 ■

If the current falls below the current value I i _n during machining when the voltage increases from UI to U2, the machining of the workpiece is interrupted. After a predetermined number of such errors, processing is stopped.

I _max : This is the upper current limit for time tg2 • If the current exceeds this value during the process or during the transition from Up _r üf to UI to U2, the voltage source is switched off immediately.

Processing status limit max / min: This is a window or area towards the end, for example a few seconds before the end or at the end of the processing. Here it is checked whether the current lies in the window defined with the processing status limit value max / min. This allows conclusions to be drawn about the workpiece geometry. The limit values are decisive for the dimensional accuracy and quality of the workpieces.

In the method for machining workpieces by means of the electrochemical machining method, a voltage is applied between at least one electrode and at least one workpiece. With the present method, several workpieces can easily be processed in parallel. To remove material, current flows through the electrolyte solution between the electrode and the workpiece. It is important that the voltage for machining the workpiece is the control or command variable. The current follows this predefined variable and is monitored in the process. So it's a live process. If the current is at several Monitoring workpieces in parallel on each workpiece means that all workpieces can be machined well.

The voltage, which may also be set while omitting the test procedure, must not be suddenly increased. Rather, it must be increased via a ramp to the predetermined value UI, at which significant processing then takes place. This means that there is no current spike, which protects the electrode. In addition, the current is during the actual processing time ty2 i ⁿ narrower limits.

After the value UI has been reached, the voltage is increased via a ramp to the larger value U2. The ramp or voltage rise is specified so that the current remains as constant as possible. However, it is also possible that the voltage remains constant or is reduced to a lower value via a ramp after reaching the value UI. This is useful, for example, in processes in which material is applied and the distance between a workpiece and an electrode decreases. Importantly also, the limit values I _m i _n and I _max, with which the current is compared are. In order to avoid damage to the workpieces, the processing is stopped when the measured current lies outside the range specified by the limit values I _m j_ _n and I _max . If the current exceeds or falls below the specified range at the end of the test process, processing should also be interrupted.

It is also possible to connect further processing stages of this type after the voltage U2 has been reached.

-'- min ^and d Imax can be fixed values during the entire process starting with tUl until the end of the process and as a variable be defined for each processing stage; that is, they can change over time.

A processing with an additional check is shown in FIG. Another window is visible towards the end of the test process. This window is formed by an upper current value and a lower current value. The upper current is advantageously lower than the maximum permissible current value I _p rüfmax. ^The lower current value is greater than zero. If the measured current at voltage ^u test is in the window towards the end of the test process, this means that the total resistance between the workpiece and the electrode formed by the lines, the workpiece, the electrode, etc., and in particular the working gap formed with the electrolyte solution has the correct value or is in a specified range. This value or range, which can be determined, for example, by reference measurements or can be calculated with the aid of a computer, makes it possible to conclude that, given a given voltage profile, a specific current profile and thus a specific degree of processing must be set up at the end. This makes it unnecessary to compare the current with the "Processing status limit max / min" area at the end of processing.

The described method is not only limited to electrochemical material processing with an electrolyte solution as the working medium. The method can also be applied to the galvanic, electroerosive or spark erosive machining of a workpiece, the coating of a workpiece or the like, in which another working medium may be used. Not only does material have to be removed. Methods are also conceivable in which material is applied.

Claims

claims

1. Method for machining workpieces by means of a machining method, in particular the electrochemical machining method, in which a voltage is applied between at least one electrode and at least one workpiece, so that a current between the at least one electrode and the at least one for removing or applying material Workpiece flows through a working medium, in particular an electrolyte solution, a test process being carried out with a test voltage, characterized in that during the test process the current is compared with a predetermined range, which is formed by a lower limit value and an upper limit value.

2. The method according to claim 1, characterized in that the processing is terminated when the range is exceeded or undershot.

3. The method according to claim 1 or 2, characterized in that the voltage is increased via a ramp to a predetermined value (UI) for machining the workpiece.

4. The method according to any one of claims 1 to 3, characterized in that the voltage after reaching the first Value (Ul) is increased via a ramp to a larger value (U2).

5. The method according to any one of claims 1 to 3, characterized in that the voltage is reduced to a lower value after reaching the first value (Ul) via a ramp.

6. The method according to any one of claims 1 to 5, characterized in that after reaching the first value (U1) the voltage is increased via a ramp to a larger value (U2) or is reduced via a ramp to a lower value, that an essentially constant current profile is achieved.

7. A method according to any one of claims 1 to 6, characterized in that the voltage curve is determined during the machining and that measured the power and having at least a predetermined range defined by a lower limit value (I _m i _n) and an upper limit value ( I _ma χ) is formed, compared.

8. The method according to claim 7, characterized in that the processing is stopped when the measured current is outside the at least one predetermined range.

9. The method according to any one of claims 1 to 8, characterized in that a current measured against or at the end of the processing is compared with a second predetermined range, which is preferably smaller than a predetermined range during processing.

10. The method according to any one of claims 1 to 9, characterized in that at the end of the test process, the current is compared with a predetermined range and the Processing is interrupted when this area is exceeded or undershot.

11. The method according to any one of claims 1 to 10, characterized in that several workpieces are processed in parallel and the current through each workpiece is measured.

12. The method according to any one of claims 1 to 11, characterized in that the at least one electrode is not moved during processing relative to the at least one workpiece.