EP0401819A2 - Method of bending tubes - Google Patents

Abstract

The invention relates to a method for bending tubes made of a certain material and having a certain cross-sectional shape through a desired angle alpha i and with a certain bending radius (referred to below as bending objective), in which first of all a check is made as to whether an appropriate bending angle gamma i and a characteristic quantity, which is a measure of the springback of the tube in the case of the bending objective concerned, are already known for the bending objective. If the appropriate bending angle and the characteristic quantity are unknown, the tube is bent through an angle alpha i; the characteristic quantity which is a measure of the springback of the tube in the case of the bending objective concerned, and any bending angle gamma i, which is chosen so that, after the bending of the tube through gamma i = alpha i + epsilon i taking into account the springback, a bend through the desired angle alpha i remains, are determined and stored. The tube is bent further to the bending angle gamma i. If the same bending objective has already been accomplished, then, in the case of further identical bending objectives, the tube is bent through the bending angle gamma i. When these further identical bending objectives have been accomplished, the characteristic quantity is determined and compared to the already known characteristic quantity and, where required, a new appropriate bending angle is determined.

Description

The invention relates to a method for bending pipes of a certain material and with a certain cross-sectional shape by a desired angle a; and with a certain bending radius.

When pipes are bent, the pipe is deflected after the bending tool has retracted a counter rail of the pipe bending machine from the pipe. The suspension results; that the specified bending angle no longer corresponds to the actual angle of the bent pipe: To correct the spring deflection, a measurement of the pipe angle is carried out with a subsequent re-bending. Such a method is known from DE-OS 27 04 399, in which a measurement of the post-bending angle is carried out for each bending angle.

The measurement of the actual angle and the subsequent bending is associated with a time expenditure which is greater than that for the actual bending process. For the production of bent pipes, in which a large number of bending processes have to be carried out, a re-measurement of the bent angle leads to considerable expenditure of time, which makes the production more expensive. Statistical samples are used to help reduce these costs.

However, this procedure has the disadvantage that pipes which do not meet the required tolerances are also passed on to the customer. Another disadvantage is that if a discrepancy is found, rejects have already been produced before this point. This can be very costly, especially in the case of bent pipes for the chemical industry, which are made of high quality materials.

The present invention has for its object to achieve a more economical production of bent tubes while ensuring one or more required bending angles.

This object is achieved by a method for bending pipes made of a certain material and with a certain cross-sectional shape by a desired angle αi and with a certain bending radius with the features specified in claim 1. Advantageous further developments are the subject of the dependent claims.

• - Querschnittsgestalt,
• - Werkstoff,
• - Sollwinkel α_i,
• - Biegeradius,
• - Dornstellung im Rohr,
• - Lage der Rohrschweißnaht,
• - Härte des Rohres,

mehrere oder alle ändern. Für eine zu lösende Biegeaufgabe ist es von Vorteil festzustellen, ob für die zu lösende Biegeaufgabe bereits ein passender Überbiegewinkel und eine Kenngröße bekannt sind. Unter einem passenden Überbiegewinkel wird solch ein Winkel verstanden, der um eine Rückfederung des Rohres korriegiert ist, sodaß nach Biegen des Rohres um y_; + α_i + _Ei unter Berücksichtigung der Rückfederung"eine Biegung um den Sollwinkel α_i verbleibt. Ist der Biegewinkel y_; bzw. der Überbiegewinkel _Ei und die Kenngröße bekannt, so wird das Rohr um den Biegewinkel y_; gebogen. Durch diese Vorgehensweise entfällt ein Nachmessen des tatsächlichen Winkels, wodurch eine kostengünstigere Herstellung gebogener Rohre erzielt wird.When bending pipes, there is always a new bending task if one of the parameters, in particular

• - cross-sectional shape,
• - material,
• - target angle α _i ,
• - bending radius,
• - mandrel position in the tube,
• - position of the pipe weld,
• - hardness of the pipe,

change several or all. For a bending task to be solved, it is advantageous to determine whether a suitable bending angle and a parameter are already known for the bending task to be solved. A suitable overbend angle is understood to mean such an angle which is corrected for a springback of the tube, so that after the tube has been bent by y _; + α _i + _Ei , taking into account the springback ", a bend remains by the set angle α _i . If the bend angle y _; or the overbend angle _Ei and the characteristic variable are known, the pipe is bent by the bend angle y _; . This procedure eliminates the need for Measure the actual angle, resulting in a cheaper manufacture of bent tubes.

If a bending task has not yet been solved, a parameter is determined during the bending of the tube, which is a measure of the springback of the tube for the bending task in question. To solve this task, the appropriate bending angle _{Ei is} determined, whereby a pair of values consisting of characteristic variable and bending angle _{Ei is} available for further identical bending tasks, which pair is used for bending in the same bending tasks.

According to the development of the method according to claim 2, the parameter should be determined when solving other identical bending tasks and compared with the already known parameter. If the current parameter differs from the previously known parameter by a preselected limit value, steps 1d to 1g are repeated. Checking the parameter has the advantage that tubes, which have a certain cross-sectional shape and are made of a certain material, but have different bending behavior, can be discovered and bent to the desired angle.

It is an advantage to determine the bending force or a quantity proportional to it, since this parameter can be determined during the bending process and so there is no or only a very slight increase in the processing time required. the determination of the bending force or a size proportional to it is associated with little effort, since here e.g. a pressure sensor can be used with hydraulically operated bending machines or another sensor which depends on the type of bending machine.

The determination of the force or a quantity proportional to it according to step 2a is advantageously carried out in the same places as in step 1 c. In this way, comparable parameters are made available which immediately reveal a different behavior of the tube during the bending process. For the bending task, a characteristic curve can be created from the pairs of values, parameter and setpoint angle, from which a prognosis of the bending behavior of the pipe at other setpoint angles can be given.

The use of dimensionless indicators is preferred in order to arrive at a general statement about the behavior of pipes in different bending tasks.

It is an advantage to determine the parameter at least in the elastic region of the tube, since this determines reliable and reproducible bending angles. This has the further advantage that the process works reliably and no rejects are produced, and thus the costs are reduced.

The change in the characteristic variable per bending angle is preferably also determined and stored. This has the advantage that, on the one hand, the specific values can be checked and, on the other hand, a prediction of the bending angle can be made for a new bending task.

The slope of the parameter is preferably determined over a larger angular range than the elastic range.

From this, e.g. the behavior of the pipe depending on the material in the flow area with elastic expansion can be predicted. This has the advantage that the effort for determining the bending angle is reduced and the execution of the bending process is accelerated.

To compare the current parameter with the stored parameter, only the parameter lying in the angular range of the elastic pipe material behavior is preferably used. This angular range is advantageously determined from the slope of the parameter. The slope in this area is constant and follows Hook's law.

A mean slope is advantageously determined in the elastic range from several parameters. This has the advantage that fluctuations can be filtered out and the mean slope can be used to determine the tolerance range.

Preferably, using the average slope in the elastic angular range, one of the parameters is approximated as closely as possible. This has the advantage that the slope is the same for all bending angles lying in the angular range of the elastic pipe behavior. This slope is advantageously used to compare the current variable with the stored parameter.

The bending angle _Ei is always determined in the case of multi-bent pipes during the first bending process of each pipe. The determination can be made from a measurement of the spring-back angle, as described in DE-GM 89 02 140 ben. If the determination of the bending angle _Ei and a comparison with already solved bending tasks leads to the result that the currently determined bending angle corresponds to the known bending angle, it can be concluded that the tube behaves in accordance with the known spring behavior. This check has the advantage that a re-measurement of each individual angle is not necessary, which leads to a reduction in the amount of work and thus in the production costs.

Advantageously, the bending angle _{Ei is} determined by comparing the target angle α _i with the actual angle β _i . This has the advantage that an overbend angle _{Ei is} determined, which can be traced back to an exact measurement.

The bending angle _Ei is advantageously determined from known data of similar bending tasks that have already been solved. This has the advantage that there is no need to measure the bending angle. This reduces the processing time for the pipe. The measurement errors and uncertainties that may occur during the measurement cannot occur when compared with similar bending tasks that have already been solved.

In step 1b, the tube is advantageously bent exactly by the desired angle α _i . This ensures that the pipe is not bent over and no rejects are produced. This is particularly important for bent tubes for the chemical industry, as these are regularly manufactured in small series from high-quality materials. The bending of the tube by the set angle α _i also has the advantage that it is on the safe side and can be disregarded to what extent a spring occurs, which depends, among other things, on the tube material.

It is particularly advantageous if the angle «; is already determined in such a way that it is equal to the appropriate bending angle y; is. If the two angles match, the bending angle only needs to be measured if there is a deviation in the parameters.

Advantageously, to determine the bending angle α ' _i , for a new bending task, the parameters already known from similar, similar bending tasks or the slopes of the parameters are used. This has the advantage that an independent choice of the bending angle α _i he follows. The determined angle α ' _i is advantageously approximately or equal to the bending angle γ _i , so that after the springing of the tube, the required target angle α _i for the bent tube curvature remains within the permissible tolerance range. As a result, an adaptation and learning program is installed in connection with the bending machine. With a sufficiently large number of bending tasks solved, a large number of parameters and bending angles are available, from which dependencies in the behavior of the pipes can be determined and laws can be established.

With increasing certainty in the prediction of the appropriate bending angle γi and the spring-back behavior of a pipe, a determination of the parameter can be omitted or this only needs to be done on a random basis.

Another advantage can be seen in the fact that a successive approach to the bending angle is omitted, which leads to time and cost savings.

The characteristic variable is advantageously determined during the bending process and the suitable bending angle is determined by comparing the current characteristic variable with known parameters for similar bending tasks. The angle α _i 'is not known at the beginning of the bending process and is continuously redetermined by comparing the current parameter with parameters from similar bending tasks that have already been solved until the required target angle α _{i is reached} or until a predetermined limit is reached. The limit value is intended to prevent the pipe from overbending.

Advantageously, steps 1d to 1g of the method are repeated if the characteristic quantity exceeds a predetermined limit value in the case of several successive bending processes. This ensures, as in claim 20, that the number of bent angles that have to be measured can be kept very low.

Further advantages and features of the method result from the following description of the method.

• - einem Rohr um einen Sollwinkel,
• - mehreren Rohren um einen Sollwinkel,
• - mehreren Rohren um mehrere Sollwinkel.

The method is applicable for bending

• - a pipe around a set angle,
• - several pipes around a set angle,
• - several pipes at several set angles.

The implementation of the method is described below for the bending of several pipes by several different set angles α _i .

The tubes have a certain cross-sectional shape and consist of a certain material. They are to be bent by a certain bending radius by several specific target angles α _i . If the process is carried out for the first time, no data are yet available for solving the bending tasks. In step 1a, a check as to whether a suitable bending angle γ _i or overbending angle _Ei and a parameter which is a measure of the springback of the tube for the bending task in question are known for the bending tasks, and the method becomes the same the step 1 b continued.

The first tube in the series is bent through an angle ai. During the bending process, a parameter is determined which is a measure of the springback of the tube in this bending task. The parameter is e.g. around the bending force or a quantity proportional to it. In bending machines which are operated hydraulically, the parameter corresponds to the fluid pressure with which the hydraulically operated bending machine works. This parameter is saved. The storage is advantageously carried out in such a way that it is assigned to the bending task.

In addition to the determination of the parameter, the determination of an overbend angle zugehörigen1 associated with the current bending task, which is selected so that after bending the tube by γ ₁ = α ₁ + ∈ ₁ , taking into account the springback, a bend about the set angle ai remains. In the event that α ' _i ≠ α _i , the bending angle _E applies; = Α _i '-α _i + x with x a Korrekturwinkei, the α, the deviation between the selected angle _i and the target angle α _i considered.
The transfer angle _E1 or γ ₁ is saved and the tube is bent to the angle y. It goes without saying that the bending of the tube to the angle γ _{1 is} only necessary if there is a deviation between the required and the actual angle. The first angle ai has been reached and a check then follows whether there is a new task when bending the tube to the angle α ₂ , since, as assumed at the beginning of the example, all angles are different from one another and there is a new bending task.

If the overbend angle α ₂ or the bend angle y ₂ and the associated parameter are not known for the further bend angle α ₂ , these are determined in accordance with method steps 1 b to 1 g.

If the known bending angles γ ₁ and y _{2 are} approximately 20 ° apart, a suitable overbending angle _Ei or bending angle γ _i can be predetermined for all required set angles a _i with i> 2 of up to 180 °.

This extrapolation provides sufficiently precise values for the bending angles inkel _i to be expected and for the bending angles γ _i . With increasing number of known suitable bending angles y; or the overbend angle ∈i increases the security when predicting the appropriate bend angle γ _i for the setpoint angle α _i .

The bent pipe can be removed from the bending machine and the next pipe can be inserted into the bending machine. At every angle to be bent, the method begins with the query according to step 1a. In the normal case, the pipe behavior at the first bending angle of a pipe is not sufficiently known, so that the test according to step a in claim 1 must be denied. _'The process is then continued with step b in Claim. 1

If a comparison between the ascertained parameter and the already known parameter leads to a deviation which is below a preselected limit value, if the bending angle is known, the method is ended; the possibly following angles of the pipe are bent according to the procedure.

The following pipes of the series are bent according to the procedure described. If the comparison between the ascertained parameter and the current parameter results in a deviation which exceeds a preselected limit value, the method steps 1 d to 1 g are repeated.

During the bending of the angles, a parameter is determined and this is compared with the already known parameter. If there is no deviation which exceeds a limit value, the further or the further angles of the tube are bent after the bending process has been completed.

When bending several pipes by several set angles a _i , it is advantageous to measure the first angle of each pipe. If the result of the re-measurement leads to the fact that there is no deviation from the required target angle α _i , it can be assumed that the known parameter is valid for this tube and that the bent angle is not re-measured.

The method shows its great advantages in particular in the series production of bent tubes, that is to say in the case of a large number of tubes which are to be bent by several angles, since a re-measurement of the bending angle can be limited entirely or to one re-measurement per tube which affects the validity of the determined characteristic variable, bending angle ∈i or bending angle y; verified depending on the target angle a _i .

With the increasing number of bending tasks, the knowledge about the bending angle y matching a target angle α _{i also increases} ; as well as the associated parameter. From this, the bending angle y; be determined or forecast for bending tasks that have not yet been solved. This forecast can also be carried out during the bending process, in which the behavior of the tube during bending is included in the forecast value determination.

Claims (20)

1. Process for bending pipes made of a specific material and with a specific cross-sectional shape by a set angle α _i and with a specific bending radius (hereinafter referred to as the bending task) a) Check whether a suitable bending angle y is already available for the bending task; and a parameter is known which is a measure of the springback of the tube in the bending task in question; if yes, continue the procedure with step i; if no, continue the procedure with step b; b) bending the tube by an angle α ' _i , which is approximately as large as the target angle a _i ; c) determining a parameter which is a measure of the springback of the tube in the bending task concerned; d) storing the parameter; e) determination of an overbend angle ∈ _i , which is selected such that after bending the tube by γ _i = α _i + unter _i , taking into account the springback, a bend by the set angle α _i remains; f) storing the overbend angle ∈ _i determined as appropriate or the associated bending angle y _i = α _i + ∈ _i ; g) bending the tube further to the bending angle y ;; h) Check whether there is a new bending task; if yes, continue the procedure with step a; if no, continue the procedure with step i; i) Bending the tube for other identical bending tasks by the bending angle γ _i , if the parameter and the suitable bending angle y; are already known. 2. The method according to claim 1, characterized by a) determining the parameter when solving these other identical bending tasks and comparing it with the already known parameter; b) repeating process steps 1 d to 1 g if the deviation between the current and the known parameter exceeds a preselected limit value. 3. The method according to claim 1 or 2, characterized in
that the parameter is the bending force or a quantity proportional to it, which is measured during the bending process at at least one point within the bending angle. 4. The method according to claim 3, characterized ge indicates that the determination of the bending force or a variable proportional to it takes place in step 2 a at the same point or the same points of the bending angle as in step 1 c. 5. The method according to claim 3, characterized in
that the parameter is determined or stored for several places of a given angular range. 6. The method according to any one of the preceding claims, characterized in that
that the parameter is determined at least in the elastic region of the tube. 7. The method according to any one of claims 1 to 6, characterized in that
that in addition the change in the parameter per bending angle unit (gradient of the parameter) is determined and stored. 8. The method according to claim 7, characterized in that
that the slope of the parameter is determined over a larger angular range than the elastic range. 9. The method according to claim 8, characterized in
that the slope of the parameter is determined over the entire bending angle. 10. The method according to claim 8 or 9, characterized in
that the elastic angle range is determined from the slope of the parameter (it is the area to which the slope is approximately constant) and accordingly only the parameters lying in the elastic angle range will be used for the comparison in step 2a. 11. The method according to claim 10, characterized in
that an average slope is determined from several parameters in the elastic range. 12. The method according to claim 11, characterized in
that using the mean slope in the elastic angular range, a characteristic curve which approximates the characteristic as closely as possible is formed and is used for comparison in step 2a. 13. The method according to claims 1 or 2, characterized in
that in the case of pipes bent several times, the characteristic variable is the overbend angle _Ei , which is determined when each first desired angle a _{i of} a pipe is bent. 14. The method according to claim 1, characterized in that
that the bending angle _{Ei is} determined by comparing the target angle α _i with the actual angle β _i . 15. The method according to claim 1, characterized in
that the bending angle e; is determined from sizes of similar bending tasks already solved. 16. The method according to claim 1, characterized in
that the tube is bent exactly by the desired angle α _i in process step 1b. 17. The method according to any one of claims 1 to 16, characterized in that
that the parameters known from similar bending tasks that have already been solved or the slopes of the parameters for determining the bending angle y; can be used for a new bending task. 18. The method according to any one of claims 1 to 12, characterized in
that the parameter is determined during the bending process and the angle a; is determined by comparing the current parameter with known parameters for similar bending tasks. 19. The method according to any one of claims 2 to 18, characterized by
Repeat steps 1d to 1g for another pipe in a series if, when comparing according to step 2b, the deviations for several successive pipes exceed the preselected limit. 20. The method according to any one of claims 2 to 19, characterized by
Repeat steps 1d to 1g for further bending processes if, when comparing according to step 2b, the deviations for several successive bending processes exceed the preselected limit.