WO2005118220A1

WO2005118220A1 - Method for adjusting the size of boreholes

Info

Publication number: WO2005118220A1
Application number: PCT/EP2005/052327
Authority: WO
Inventors: Rüdiger GARN; Sebastian Tetzlaff
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-06-03
Filing date: 2005-05-20
Publication date: 2005-12-15
Also published as: DE102004027145B3

Abstract

The invention relates to a method for adjusting the rate of flow through at least one borehole of a workpiece by means of a working fluid, during which the working fluid is fed through the borehole of the workpiece. An actual value (Q_AV) of the rate of flow of the working fluid through the borehole of the workpiece is recorded and a set value of a quantity characteristic of a drop in pressure of the working fluid inside the borehole is determined and set according to the actual value (Q_AV) of the rate of flow. The adjustment is terminated when the actual value (Q_AV) of the rate of flow is greater than or equal to a set value (Q_SP) of the rate of flow. Alternatively, an actual value of the quantity is recorded. The set value (Q_SP) of the rate of flow is determined and set according to the actual value of the quantity, and the adjustment is terminated when the actual value of the quantity is less than or equal to the set value of the quantity.

Description

description

Procedure for adjusting holes

Bores to which high precision requirements are placed, and in particular microbores, such as those produced, for example, as throttle bores or injection nozzles for injection valves for internal combustion engines, must be adjusted so that they meet the requirements placed on them. Such a requirement is, for example, that under predetermined test conditions the flow of a fluid through the bore deviates as little as possible from a desired flow. When making the bores, e.g. Spark erosion can cause bumps and edges in the hole, so that the flow through the corresponding hole in the workpiece deviates from the desired flow. This deviation in the flow can be improved by subsequent adjustment. For this purpose, the bores are ground and rounded, for example, hydroerosively or electrochemically. In hydroerosive grinding, a suspension of suitable viscosity containing abrasive grain is pressed through the hole. The electrochemical processing is carried out with an electrolyte solution, which is pressed through the workpiece, and an electrode. An electrical voltage is built up between the electrode and the workpiece, which leads to a current flow through the electrolyte solution and to material removal.

DE 199 41 472 AI discloses a method and a device for calibrating throttle bores, in particular in injection valves for internal combustion engines, by hydroerosive machining. A suspension is pressed from a tank through a throttle bore of a workpiece by means of a pump. The flow through the throttle bore, the pressure and the temperature of the suspension are recorded on the upstream side of the throttle bore and processed in a computer. A back pressure is recorded on the downstream side of the throttle bore. which is built up by an orifice that limits the outflow of the suspension downstream of the throttle bore. This back pressure can inhibit cavitation of the suspension, which can occur with very large pressure differences upstream and downstream of the throttle bore. In the process, a suitable processing pressure, for example about 100 bar, is set and the resulting flow through the throttle bore is measured. The flow through the throttle bore increases with the machining time, with the machining pressure remaining the same, and machining ends when the measured flow corresponds to a predetermined flow.

DE 102 14 616 AI discloses a method and a device for processing at least one flow channel of a workpiece with a working fluid. The working fluid, e.g. can be an acid or an electrolyte solution or a suspension for hydroerosive grinding is conveyed through the flow channel. The mass flow of working fluid flowing through the flow channel is measured and the processing is carried out until a predetermined mass flow is reached. In order to obtain more accurate measurement results, the mass flow is measured statically, i.e. the processing of the flow channel is interrupted for the duration of the measurement, for example by using a fluid without abrasive grain.

The disadvantage of the described methods is that the machining of the bores of the workpiece takes place during the entire machining time with a largely constant pressure drop in the bore, that is to say with a constant upstream and downstream pressure. This leads to very different processing times due to the different size deviations of the flow from the desired flow. This is particularly disadvantageous for mass production, where it is important that the processing tents are as uniform and short as possible. The object of the invention is to provide a method which improves the adjustment of bores.

The object is achieved by the features of the independent claims. Advantageous developments of the invention are characterized in the subclaims.

According to a first aspect of the invention, the invention is characterized by a method for adjusting the flow through at least one bore of a workpiece by means of a working fluid, in which the working fluid is conveyed through the bore of the workpiece. An actual value of the flow of the working fluid through the bore of the workpiece is recorded and a setpoint value of a size that is characteristic of a pressure drop in the pressure of the working fluid in the bore is determined and set depending on the actual value of the flow. The adjustment is ended when the actual value of the flow is greater than or equal to a setpoint of the flow. This has the advantage that the adjustment process can be adapted to the state of the hole in the workpiece. Holes that only need to be machined a little because the actual value of the flow is already very close to the setpoint of the flow can, for example, be machined with less intensity than holes whose actual value of the flow are at a greater distance from the setpoint of the flow. This makes it possible to actively influence the duration of the adjustment process, and thus to adjust the processing tents of the workpieces and, if necessary, shorten the cycle times in mass production.

In an advantageous embodiment of the first aspect of the invention, the working fluid is conveyed at the beginning of the adjustment process until a first reliable actual value of the flow can be detected, so that the first reliable actual value of the flow is certainly less than the setpoint of the flow. This makes the adjustment process so slowed down until a reliable actual value of the flow can be recorded. In this way, it can easily be prevented that holes are ground too large by the time the first reliable actual value of the flow can be recorded. In this way, waste can be avoided.

According to a second aspect of the invention, the invention is characterized by a method for adjusting the flow through at least one bore of a workpiece by means of a working fluid, in which the working fluid is conveyed through the bore of the workpiece. An actual value of a variable, which is characteristic of a pressure drop in the pressure of the working fluid in the bore, is recorded and a setpoint value of the flow is determined and set depending on the actual value of the variable. Adjustment ends when the actual value of the size is less than or equal to a setpoint of the size. This has the advantage that the adjustment process can be adapted to the state of the hole in the workpiece. Holes that only need to be machined a little because the actual value of the size is already very close to the target value of the size can, for example, be machined with less intensity than holes whose actual value of the size are at a greater distance from the target value of the size. This makes it possible to actively influence the duration of the adjustment process, and thus to adjust the machining tents of the workpieces and, if necessary, shorten the cycle times in mass production.

In an advantageous embodiment of the second aspect of the invention, the working fluid is conveyed at the beginning of the adjustment process until a first reliable actual value of the variable can be detected, so that the first reliable actual value of the variable is certainly greater than the nominal value of the variable. The adjustment process is slowed down until a reliable actual value of the size can be recorded. So it can be easily prevented that bores already lead to the The point in time at which the first reliable actual value of the variable can be recorded has been ground too large. In this way, waste can be avoided.

In a further advantageous embodiment of the invention, the size is a form which acts on the upstream side of the bore. This has the advantage that the form can be measured in a very simple manner.

In a further advantageous embodiment of the invention, the size is a difference between the upstream pressure and a back pressure which acts on the downstream side of the bore. The back pressure counteracts cavitation of the working fluid, i.e. gas bubble formation. The bores can be adjusted without cavitation through the appropriate selection of the upstream pressure and the back pressure. This is particularly advantageous if no cavitation is to occur on the bore even in later operation. The holes can be adjusted more precisely.

Exemplary embodiments of the invention are explained below using the schematic drawings. Show it:

FIG. 1 shows a block diagram of a device for adjusting bores, FIG. 2 shows an ablating diagram of a first exemplary embodiment of the method, and FIG. 3 shows an ablating diagram of a second exemplary embodiment of the method.

1 shows a device for adjusting bores in a workpiece 1. A pump 2 conveys a working fluid from a container 3 through a flow meter 4 and through the bore of the workpiece 1. The flow meter 4 detects an actual value O AV of the flow. A pre-pressure meter 5 detects the pre-pressure built up by the pump 2 on the upstream side of the bore. A throttle 6 can do this on the Limit the working fluid emerging on the flow side of the bore in its outflow into a collecting container 7. A back pressure meter 8 detects a back pressure building up by limiting the outflow between the bore of the workpiece 1 and the throttle 6. A control device 9 processes the detected actual value Q_AV of the flow, the upstream pressure and the back pressure and controls the delivery of the working fluid by the pump 2 and the limitation of the outflow of the working fluid through the throttle 6.

Figure 2 shows a first embodiment of the method. The method begins with a step S101, in which preparatory measures can be carried out, e.g. the establishment of defined starting conditions. In one step

5102 a target value DE1TA_P_SP of a pressure drop in the bore of the workpiece 1 is determined and set on the basis of the desired flow through the bore of the workpiece 1. A current time t is stored as a switching time t_S and a switching interval T_S is determined.

The working fluid is pumped by means of the pump 2 through the device shown in FIG. 1. In one step

5103, a first waiting period T_W_1 is waited, which is selected such that the pressure drop in the bore can build up in accordance with the setpoint DELTA_P_SP of the pressure drop and suitable measurement requirements are met. The setpoint DEIιTA_P_SP of the pressure drop is set so low in step S102 that the adjustment process takes place only slowly during the first waiting time period τ_w_l in order to prevent the bore from being ground too large before the suitable measuring conditions are met. The first waiting period T_W_1 is approximately six to eight seconds.

After the first waiting period T_W_1 has elapsed, the actual value Q_AV of the flow is determined in a step S104. If the actual value Q_AV of the flow is larger in a step S105 ß or equal to a target value O SP of the flow rate, then the method is ended in a step S106. The flow through the bore is then checked, for example, under specified test conditions using a test fluid instead of the working fluid for compliance with the requirements, and faulty workpieces are rejected. The goal is to end the adjustment process when the actual value Q_AV of the flow is equal to the setpoint O SP of the flow.

If the condition in step S105 is not met, then the difference between the current time t and the switching time t_S is checked in a step S107. If this difference is smaller than the switching interval T__S, the processing is continued in a step S108 in a step S104 after a second waiting period τ_w_2. If the condition in step S107 is not met, the processing is continued in step S109.

In step S109, the target value DELTA_P_SP of the pressure drop is determined and set as a function of the actual value O AV of the flow. The current time t is stored as the switching time t_S and the switching interval T_S is determined.

In a step S110, a third waiting period T_W_3 is waited until suitable measurement conditions are present. Processing continues in step S104.

The third waiting period T_W_3 in step S110 can depend, for example, on how large the change in the setpoint DELTA_P_SP of the pressure drop at the switching time t_S is. If the change in the setpoint DEIιTA_P_SP of the pressure drop is very small or equal to 0, then the third waiting period T_W_3 can also be very short or equal to 0, since suitable measurement conditions already exist, but if the change in the setpoint DELTA_P_SP of the pressure drop is large, it can be up to take several seconds to flow of the working fluid through the bore, which allows a reliable detection of the actual value Q_AV of the flow.

In practice, the third waiting period T_W_3 can usually be chosen to be shorter than the first waiting period T_W_1. The first and third waiting times T_W_1, T_W_3 can be selected, inter alia, depending on the viscosity of the working fluid and on the geometry of the device used for adjusting the bores and on the geometry of the bore of the workpiece 1.

The second waiting period T_W_2 in step S108 can preferably be selected to be shorter than the first and third waiting periods τ_w__l, τ_w_3. The interval in which the switch-off condition of the method is checked in step S105 is dependent on the second waiting period T_W_2. If this is very short, for example a few milliseconds, or equal to zero, the actual value Q_AV of the flow is detected and evaluated quasi-continuously and thus enables the process to be terminated at the right time, i.e. when the actual value O AV of the flow is equal the setpoint GL_SP of the flow is a very precise adjustment of the bore.

The setpoint DELTA_P_SP of the pressure drop can be adapted to the currently recorded actual value 0__AV of the flow after the switching interval T_S. The switching interval T_S can be, for example, a time period of about 10 seconds that must elapse before the machining conditions are readjusted to the current state of the bore. The switching interval T_S can also be adjusted in the course of the adjustment process, for example depending on an expected machining time, and can also be omitted entirely if a quasi-continuous adjustment is desired. The setpoint DELTA__P_SP of the pressure drop, the first, second and third waiting time periods τ_w__l, T_W_2, T_w_3 and the switching interval T_S are preferably selected, taking into account the aforementioned aspects, so that, on the one hand, high precision is achieved when machining the bore of the workpiece 1 and on the other hand, the duration of the adjustment process is limited to a duration suitable for mass production, for example about 30 seconds. This reduces the deviations of the flow from the desired flow and standardizes the processing time.

FIG. 3 shows a second exemplary embodiment of the method. Steps S201, S203, S206 to S208 and S210 correspond to steps S101, S103, S106 to S108 and S110 of the method shown in FIG. 2. Only the steps that deviate from the method shown in FIG. 2 are explained below.

In a step S202, a setpoint Q_SP of the flow is determined and set. The current time t is stored as the switching time t_S and the switching interval T_S is determined. In a step S204, an actual value DELTA_P_AV of the pressure drop is determined after suitable measurement conditions have developed after the first waiting period T_W_1 in step S203. In a step S205 it is checked whether the actual value DELTA_P_AV of the pressure drop is less than or equal to the target value DELTA__P_SP of the pressure drop. If the condition is met, the method is ended in a step S206. If the condition in step S205 is not met, the method is continued in step S207. In a step S209, the setpoint Q_SP of the flow is determined and set as a function of the actual value DELTA_P_AV of the pressure drop. The current time t is stored as the switching time t_S and the switching interval TS is determined. The statements already made for the first exemplary embodiment in FIG. 2 regarding the first, second and third waiting time periods T_W_1, T_W_2, T_w_3 and the switching interval T_S apply correspondingly to the second exemplary embodiment of the method in FIG. 3.

A variable that is characteristic of a pressure drop in the pressure of the working fluid in the bore can be, for example, the admission pressure. This is particularly advantageous when the back pressure does not reach a size relevant for the adjustment process. This is achieved if the throttle 6 does not limit the outflow of the working fluid or the throttle 6 is not provided in the device for adjusting the bores. In this case, the counter pressure meter 8 can also be dispensed with. Such a device is particularly suitable for the adjustment of bores in which a large pressure drop occurs in the bore during later operation, which may lead to cavitation.

The magnitude that is characteristic of a pressure drop in the pressure of the working fluid in the bore can also be a difference between the upstream pressure and the back pressure. This is particularly advantageous when the back pressure reaches a size relevant for the adjustment process, so that the back pressure can no longer be neglected. The back pressure can be set in a targeted manner by limiting the outflow of the working fluid by means of the throttle 6. The back pressure can counteract the development of cavitation and prevent it. This is particularly advantageous for the adjustment of bores that are not to be operated in cavitation. The difference between the upstream pressure and the back pressure can also be determined, for example, using a differential pressure meter.

If the admission pressure is essentially constant during the adjustment process, then the back pressure can also be characteristic of the pressure drop in the pressure of the working fluid in the drilling tion. Furthermore, for example an electrical voltage or an electrical current can be characteristic of the pressure drop. The pressure drop can be adjusted by changing only the back pressure, only the back pressure or both the back pressure and the back pressure. It can be advantageous to keep the admission pressure substantially constant during the adjustment process and to adjust the pressure drop in the bore by changing the counter pressure.

The process sequence shown in FIG. 2 has proven to be particularly advantageous for the adjustment of inlet throttles which are adjusted with back pressure in the non-cavitating area. The process sequence shown in FIG. 3 has proven to be particularly advantageous for the adjustment of flow restrictors which are adjusted in the cavitating area without counter pressure.

The advantageous value range of the admission pressure is approximately 70 bar to 110 bar and the preferred value range of the counter pressure is approximately 45 bar to 80 bar. The value ranges mentioned are particularly advantageous because they allow the bores to be precisely adjusted. Other ranges of values for the pre-pressure and the counter-pressure can also be used in the method.

The working fluid is advantageously a suspension with a suitable viscosity that contains abrasive grains. The type and the concentration of the abrasive grains in the suspension as well as the speed with which the suspension is pressed through the bore are influencing factors for the duration of the adjustment process. Other working fluids can also be used, for example acids or electrolyte solutions which, if necessary with the aid of an electrical current, cause the material to be removed in the bore.

Another factor influencing the duration of the adjustment process is the geometry of the hole, e.g. taper or constrictions.

The duration of the adjustment process can be shortened by increasing the flow through the bore. This can be achieved by increasing the pressure drop in the bore. Shortly before the end of the adjustment process, i.e. shortly before the condition in step S105 or S205 is fulfilled, it can be advantageous to determine the pressure drop in the bore, i.e. the setpoint DELTA_P_SP of the pressure drop, or the flow through the bore, i.e. the setpoint O SP of the flow. This slows down the adjustment process so that the actual value O AV of the flow rate approaches the setpoint 0_SP of the flow rate more slowly or the actual value DELTA_P_AV of the pressure drop approaches the setpoint DELTA_P_SP of the pressure drop more slowly. The process can thus be ended very precisely in a simple manner as soon as the actual value Q_AV of the flow is equal to the setpoint (D_SP of the flow or the actual value DELTA_P_AV of the pressure drop is equal to the setpoint DELTA_P_SP of the pressure drop. On the one hand, the duration of the adjustment process can be actively shortened and on the other hand, the precision of the adjustment process can be increased.

Claims

claims

1. Method for adjusting the flow through at least one hole in a workpiece (1) using a working fluid, which comprises:

conveying the working fluid through the bore of the workpiece (1),

- Detecting an actual value (CL_AV) of the flow of the working fluid through the bore of the workpiece (1),

determining and setting a setpoint value of a quantity which is characteristic of a pressure drop in the pressure of the working fluid in the bore, depending on the actual value (G__AV) of the flow, and

- an end of the adjustment if the actual value (Q_AV) of the flow is greater than or equal to a setpoint (Q_SP) of the flow.

2. The method according to claim 1, characterized in that at the beginning of the adjustment process until a first reliable actual value (O AV) of the flow can be detected, the working fluid is conveyed such that the first reliable actual value (Q_AV) of the flow is less than the setpoint of the (Q_SP) flow.

3. A method for adjusting the flow through at least one bore of a workpiece (1) by means of a working fluid, which comprises:

conveying the working fluid through the bore of the workpiece (1),

detection of an actual value of a quantity which is characteristic of a pressure drop in the pressure of the working fluid in the bore,

- Determining and setting a target value (Q_SP) of the flow of the working fluid through the bore of the workpiece (1) depending on the actual value of the size, and

- an end of the adjustment if the actual value of the size is less than or equal to a nominal value of the size.

4. The method according to claim 3, characterized in that at the beginning of the adjustment process until a first reliable actual value of the size can be detected, the working fluid is conveyed in such a way that the first reliable actual value of the size is greater than the target value of the size.

5. The method according to any one of the preceding claims, characterized in that the size is a form which acts on the upstream side of the bore.

6. The method according to any one of claims 1 to 4, characterized in that the size is a difference between the upstream pressure and a back pressure which acts on the downstream side of the bore.