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The press precision press produces elastic deformation after being subjected to load, and is expressed in three forms of vertical displacement, bending and lateral misalignment. These three forms of elastic deformation will directly affect the shape, size and precision of the forged product being processed. The workpiece is defective in size, misalignment, and the like. In addition, the manufacturing and installation accuracy of the equipment and the gap between the guide rail and the column will affect the forming precision of the press. Therefore, the forming precision of the press mainly depends on three aspects: the vertical stiffness above the pressure; the angular stiffness between the table and the slider; and the amount of lateral misalignment perpendicular to the downward direction of the pressure.
Vertical stiffness of the press The vertical stiffness of the press refers to the force exerted by the press when the unit is vertically deformed downward. It can be expressed by Cz, ie: Cz=Fnh(kN/mm) (1) where: Fn The nominal force of the press (kN); the vertical deformation (mm) of the height of the mold when the press is subjected to Fn, h=he-ha; the distance between the slider and the table when the press is subjected to Fn; The distance between the slider and the table when the machine is not subjected to the working load.
The angular stiffness of the angular stiffness press refers to the force exerted by the slider of the press against the work surface when the unit is angularly deformed under the eccentric load (2), which can be expressed by C. The total angular deformation of the press: K = Ka + Ke in the formula: Ka initial angular deformation (such as deformation due to the guiding gap); elastic deformation of the Ke press when subjected to eccentric load.
The basic relationship between the column and the tightening bolts When the closed combination fuselage press is working, no gap or misalignment should occur between the upper beam, the base and the column. Therefore, it is necessary to tighten the bolts to pre-tighten the pressure of the fuselage and have a certain amount of compression. The tension bolts are pulled correspondingly and have a certain amount of elongation. It is the relationship between the force and deformation of the column and the tension bolt.
The influence of the pre-tightening force in the tension bolt on the accuracy of the closed combination fuselage press The effect of the pre-tightening force on the vertical stiffness of the tension bolt is as shown in the figure. As the pre-tightening force in the tension bolt increases, the vertical stiffness of the press The change is not big. When the preload force Fv in a single bolt increases from 760kN to 1900kN, the vertical deformation is only reduced by 4.3%, while the vertical stiffness is only increased by 4.3%.
The bending deformation in the Y direction and the increase in the pre-tightening force in the angular stiffness tightening bolt have little effect on the bending deformation and the angular stiffness in the Y direction. When the pre-tightening force Fv is increased from 760 kN to 1425 kN and 1900 kN, the angular deformation of the slider is increased by 0.5% and 1.5%, respectively. That is to say, the pre-tightening force has little influence on the bending deformation KA and the angular stiffness CKA in the Y direction.
The effect of the preload on the lateral misalignment is as shown. As the preload force increases, the lateral misalignment amount VX of the slider is greatly reduced. When the pre-tightening force Fv is increased from 760kN to 1425kN and 1900kN, the lateral displacement of the slider is reduced by 65% ​​and 72% respectively. However, when the Fv is increased from 1425kN to 1900kN, the lateral displacement of the slider is only reduced by 7%. This means that a larger preload can no longer significantly improve the accuracy of the press.
Conclusion The analysis results of a new closed-type combined fuselage press KDH160/1250 in Germany show that: (1) The pre-tightening force in the tightening bolt has a great influence on the forming precision of the press, especially on the X along the X. The bending deformation and angular stiffness in the direction, the lateral misalignment, the maximum gap generated between the slider and the column, and the compressive stress on the fuselage have a great influence. As the preload force increases, the bending deformation and angular stiffness in the X direction increase, the amount of lateral misalignment is greatly reduced, and the maximum gap generated between the slider and the column is greatly reduced. It can be seen that the accuracy of the press can be improved by increasing the preload in the tightening bolt. (2) The pre-tightening factor of the device is 3.5 (Fv is 1425kN). When the pre-tightening coefficient is greater than 3.5, it has little effect on the improvement of the precision of the press. The pre-tightening coefficient of 4.75 (Fv=1900kN) is indeed larger.
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