To deter m i ne spr i ngback ,elonga tion and bend i ng rad ius i n tube bend i ng process

B y the bending theo ry ,exp eri m en tal research and lo ts of exam p les ,determ ine the m ethod to choo se sp ringback ,elongati on and shap e radiu s w h ich are effective to the bending accu racy ,and u se in telluctu ral tester of ben t tube to get the above data to in struct the real p roducti on .

Thesaurus steel pipe bending research

It is well known that pipe bending is elastoplastic bending and bending back.

After the bombing, the bending angle becomes small, the axis of the pipe becomes longer, and the bending radius becomes larger. The processing of modern ship piping parts is increasingly moving towards the production line, and the production of the production line must adopt the production process of no-bending elbow and first-weld flange bending. When using the above process technology, especially after using the CNC tube bender, how to deal with the problems of rebound, elongation and forming radius is more important and outstanding. However, this problem has not been solved for a long time. For this reason, through a lot of work, we have summarized the methods for determining the rebound, elongation and forming radius which have an important influence on the forming precision of pipe bending.

1 Treatment method for tube bending rebound problem

Prior to this, the solution to the rebound was:

1 List the rebound data sheet based on experience. For example, the CNC bending machine purchased by several shipyards in the United States from W ALLA CE COA ST in the United States has set up empirical data in the control system for rebound compensation. However, due to the large error of this method, the bending precision of the CNC tube bending machine is not ideal.

2 using theoretical calculation methods. Because the force is very complicated when bending, the calculation needs to make assumptions and simplifications, and the material properties and actual working conditions are difficult to predict. Therefore, there is no precedent for the success of the rebound theory calculation formula in actual use. Explore.

3 In the aircraft and automobile manufacturing industry, the method used by the American EA TON L EONA RD company has been used for many years [1]. The method considers that although there are many factors affecting the springback of the elbow, the process parameters (bending radius, bending speed, clamping force, etc.) have been determined after the machine tool is adjusted, and at this time, the pipe of a certain batch of material is bent.

In the case where the bending angle is determined in relation to the forming angle after the rebound, the angle of the bender arm and the forming angle of the tube can be regarded as a linear relationship. The method is to bend the pipe by 125° and 22° on the pipe bending machine. After the pipe is bent, the actual forming angle is 120° and 20° on the numerical control tubular measuring machine, and the straight line equation of two points can be obtained. The relationship between the corner of the bender arm and the desired forming angle of the tube. This method works well.

In order to solve the rebound problem of pipe bending, we have done the following work [2]:

111 A large number of rebound experiments were carried out. In order to improve the accuracy of the pipe angle measurement, the "bend pipe measuring instrument" was used in the experiment. Through various coreless and cored bend experiments on multiple benders in five shipyards, and regression analysis of the measured data, it can be seen that the bending angle Η and the forming angle Η′ are not The linear relationship of the origin. which is:

Η=K 1Η'+C 1(1) where K 1——linear slope

C 1 - line intercept

The regression analysis of the measured data shows that the correlation coefficient Χ is above 019999, which shows that the linearity is very high. Therefore, it can be concluded that the tube bent out of the same batch of materials has a linear relationship between the bending angle 成形 and the forming angle Η′ within the engineering bending angle range.

112 A data regression check was performed on the experience rebound data sheet of the shipyard. For example, the regression analysis of the empirical rebound data of the “tube bending rebound angle table” of Dalian Shipyard indicates that the bending angle Η and the forming angle Η′ are also in a straight line relationship with the origin, and the correlation coefficient

Both of them are above 01999, which shows that their linearity is also very high, which once again proves the correctness of the conclusion of the rebound experiment. 113 Theoretical analysis of the springback experiment of elbows. In order to analyze the rebound experiment

5Method for determining springback, elongation and forming radius in 3 pipe bending process

The correctness of the conclusion, we have exerted force on the working condition of the pipe bending machine.

Analysis, a lot of calculations were made after some assumptions and simplifications were made. The calculation results show that there is a curve relationship between the bending angle 成形 and the forming angle Η′ in the range of small bending angles; after the bending angle is greater than 1°, there is a linear relationship between the bending angle Η and the forming angle Η′. And the trend of the linear relationship with the experiment is the same, which explains the correctness of the conclusion of the rebound experiment. It should be noted that the values between the two differ greatly, which is due to the assumptions and simplifications of theoretical calculations and the fact that the actual bending conditions are much more complicated than the calculation.

It can be seen that the above work is more in-depth than the research on the "rotation angle of the bender arm and the bending angle of the tube as a linear relationship" represented by EA TON L EONA RD.

In summary, the best way to deal with the bending back of the pipe is to bend the machine to a given bend.

Experiment with two different elbows (eg 30° and 90°) on board. Record the actual two corners of the bender arm Η1, Η2 and measure the tube during the experiment.

The two forming angles Η'1, Η'2. Then calculate the coefficients of equation (1) according to the following formula:

K 1=(Η2-Η1) (Η'2-Η'1)

(2) C 1=Η1-Η'1(Η2-Η1) (Η'2-Η'1)

(3) The linear equation obtained by substituting equations (2) and (3) into equation (1) is the rebound law of the batch of tubes. Easy to use smart tube measuring instrument

The ground gets a rebound law.

2 Treatment method for elongation of pipe bending axis

After a certain length of pipe is bent on the bender, the length of the axis of the pipe increases, and the amount of increase is called the elongation of the pipe. For this

The problems solved in the past are:

1 According to experience, the elongation data table is listed for production use, but the error is large when using this method.

2 Calculation method for the theory of bending tube elongation. As with the rebound, there is no precedent for the successful use of theoretical calculation formulas in practice, which remains to be further explored.

3 In the aircraft and automobile manufacturing industry, the method adopted by EA TON L EONA RD has been used for many years, that is, while measuring the springback with a CNC tubular measuring machine, the so-called circle is calculated by using the calculation formula. The arc constant ARC, which is the length of the material used when the bending angle is 100°, is also considered to be proportional to the forming angle of the tube.

In order to solve the problem of elongation of the pipe bending, we did the following work [2]: 211 A large number of elongation experiments were carried out. Through multiple units at five shipyards

The coreless and cored bend experiments of various specifications were carried out on the pipe bending machine, and the regression analysis and calculation of the data obtained from each batch of materials showed that the elongation ∃L and the forming angle Η′ were not the origin. straight line

relationship. which is:

∃L = K 2Η'+C 2

(4) where K 2 - the slope of the line

C 2 - line intercept

After the regression analysis of the measured data, the correlation coefficient is calculated at 0197.

Between ~0199, it can be seen that the linear relationship is obvious. Therefore, it can be concluded that the tube of the same batch of material has a linear relationship between the elongation ∃L and the forming angle Η′ within the range of the engineering bending angle.

212 Data regression calculations were also carried out on the experience rebound data sheet for the shipyard. According to the empirical calculation, the elongation ∃L and the forming angle Η′ are also linear, and the correlation coefficient Χ is above 0199. It can be seen that the linearity is also high, but the intercept is generally small. 213 Theoretical analysis of the bending tube elongation test. In order to analyze the correctness of the conclusion of the elongation experiment, we carried out the force analysis on the bending condition of the bending machine, and made a lot of calculations after making some assumptions and simplifications. The calculation results show that the elongation is within a small bending angle range.

∃L and forming angle Η

There is a curve relationship between the two; after the bending angle is greater than 3°, the elongation ∃L and the forming angle Η′ are linear. The linear relationship between the theoretical analysis and the straight line relationship in the experiment is the same, indicating the correctness of the experimental results of the bending elongation. It should be noted that the values between the two differ greatly, which is due to the assumptions and simplifications of theoretical calculations and the fact that the actual bending conditions are much more complicated than the calculation.

In the above-mentioned study, the tube of the same batch of materials has a linear relationship between the elongation ∃L and the forming angle Η′ in the range of the engineering bending angle, which is proportional to the conventionally recognized elongation and the forming angle. Different views, the former is more in line with the actual situation of the pipe bender.

In summary, the current best treatment method for the bending elongation of pipes should be: when bending a batch of pipes, the lengths of the two test pieces can be the same on the given pipe bender, and the bends are different (for example, 30). °

And 90°

The bending test, after the experiment, remove the tube and measure the two actual forming angles Η'1, Η'2 of the tube and the length L ′1, L ′2 of the two actual tube axes, then the elongation Let ∃L 1=(L ′1-L ) and ∃L 2=(L ′2-L ). From this, the coefficient of the linear equation (4) can be obtained by the following equation:

K 2=(∃L 2-∃L 1) (Η'2-Η'1)

(5) C 2=∃L 1-Η'1(∃L 2-∃L 1) (Η'2-Η'1)

(6) Substituting equations (5) and (6) into linear equation (4) yields the elongation law of the batch of tubing. This elongation law can be conveniently obtained using a smart bend gauge.

3 Treatment method of forming radius problem after tube bending rebound

After the pipe is bent back, its forming radius R ′ is smaller than the die radius R

63 forging machinery 1 1997