CN113118379A - Method for controlling size of casting based on reverse deformation - Google Patents

Abstract

The invention discloses a method for controlling the size of a casting based on reverse deformation, which establishes a finite element thermal stress model by comprehensively considering the influences of casting solidification, cooling, boxing, casting system removal and heat treatment, and accurately predicts the deformation of the casting in the whole hot working procedure. And then, according to the difference of the structural characteristics of the casting and the restraint degrees of different areas, setting different inverse deformation relaxation coefficients, and performing inverse deformation treatment on the original model. The relaxation coefficient of the inverse deformation is determined by the stress level at the calculation node, and the larger the stress value is, the smaller the relaxation coefficient is. And (3) performing numerical simulation calculation and iteration of the whole hot working process aiming at the model added with the reverse deformation, finally determining the reasonable size of the casting model, and producing the casting with proper and uniform machining allowance.

Description

Method for controlling size of casting based on reverse deformation

Technical Field

The invention belongs to the technical field of casting, and particularly relates to a method for controlling the size of a casting based on reverse deformation.

Background

The casting has thermal stress and phase change stress in the hot working process, and the size precision of the casting is influenced because the casting has uneven wall thickness, complex shape and uneven stress and must deform. In recent years, thermal stress and deformation of castings during casting have received more and more attention, especially for complex structural members. Many studies on the theory and numerical simulation of thermal stress and deformation were conducted, but because of the various processes in the casting production process: solidification, cooling, boxing, removal of a gating system and heat treatment all affect the final shape of the casting, so that accurate prediction of residual stress and machining allowance of the casting before machining becomes a difficult problem. In order to ensure that the castings have enough machining allowance during machining, most manufacturers usually increase the machining allowance during design to ensure that the castings do not have meat deficiency finally when producing complex castings. However, the increase of the machining allowance brings about the problems of energy consumption increase, low yield, long time consumption of subsequent machining and the like, so that the production cost of an enterprise is greatly increased, and the national energy-saving and consumption-reducing requirements are not met.

Disclosure of Invention

The invention aims to provide a method for controlling the size of a casting based on reverse deformation, which can successfully predict the residual stress and deformation of the complex casting after casting, and give the reverse deformation of each part of the casting according to the structural characteristics of the casting, thereby well designing the casting structure, ensuring that the final machining allowance of the casting is smaller and is uniformly distributed, and reducing the production cost.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for controlling the size of a casting based on reverse deformation comprises the following steps: (1) establishing an integrated thermal stress model of solidification, cooling, boxing, casting system removal and heat treatment, and visually reproducing the thermal stress and deformation conditions of the casting in each process by using the model to obtain the final geometric shape of the casting before machining; meanwhile, actual measurement is carried out on key points of the casting, and the accuracy of a simulation result is proved; (2) on the basis of a casting deformation simulation result, setting an anti-deformation relaxation coefficient according to the structural characteristics of the casting and the restraint degrees of different areas, and increasing the anti-deformation amount of the casting model coordinate; (3) carrying out full-flow numerical simulation on the casting model added with the reverse deformation amount in the processes of casting, boxing, dead head cutting and heat treatment to obtain the distribution of the deformation amount of the casting before machining; comparing the deformed model with a final product design model, and if the machining allowance of the casting is uniform and is within a reasonable range, designing the casting model according to the reverse deformation model; otherwise, continuing to perform the next cycle of anti-deformation design and calculation simulation according to the anti-deformation model, the deformation and the anti-deformation relaxation coefficient until the final geometric shape of the casting meets the requirement of the machining allowance, and producing the casting with proper and uniform machining allowance.

Preferably, the casting model reverse deformation amount is determined by the product of the reverse deformation relaxation coefficient and the negative deformation vector.

Compared with the prior art, the invention has the advantages and positive effects that: the method can accurately predict the flow field, the temperature field and the stress field of the casting in the whole hot working process, and has important significance for improving the qualified rate, the yield and the like of the casting; the deformation prediction and the anti-deformation measures designed by the invention can effectively solve the problems of insufficient and uneven machining allowance of the casting, greatly improve the production efficiency, reduce the subsequent machining difficulty and improve the product performance.

Detailed Description

In the embodiment, a set of large-scale water turbine blade casting model is designed by the technology of the invention. The profile dimension of the blade is as follows: 3400 × 3400 × 1100mm, and is used for 700MW large-scale turbine runner. The blades are acted by water flow to push the rotating wheel to rotate in the rotating process of the rotating wheel, so that the molded line design is very complex and the twisting is serious. The complex curved surface modeling ensures that the blade is extremely easy to deform in the hot processing procedures such as casting, heat treatment and the like, the deformation trend and the deformation of the blade are difficult to predict by experience, the phenomenon of 'meat shortage' is ensured not to finally appear only by increasing the processing allowance of a casting in the prior art, and the manufacturing cost and the subsequent mechanical processing difficulty are greatly increased. In the embodiment, the die design of the blade is carried out according to the design target that the machining allowance of each final part of the blade is 20 mm. The specific implementation is as follows:

1. modeling the net blade model by using three-dimensional modeling software, and adding uniform 20mm machining allowance on the basis of the net blade; designing a blade casting process and a casting head system according to a casting feeding theory and actual production experience, and dividing a finite element mesh by using finite element mesh dividing software;

2. since the deformation of the blade is affected by the processes of solidification, cooling, boxing, cutting off a gating system, heat treatment and the like before machining, an integrated model of the blade deformation simulation must be established first. The deformation simulation at the solidification and cooling stages takes into account the effect of the phase change. And (3) simulating the processes of boxing and cutting off the gating system, and removing the limiting effect of the casting mold on the casting and the gating system on the casting body in a boundary condition mode. The simulation of the heat treatment process mainly takes into account the effect of the radiation. And during simulation calculation, the temperature and displacement of all nodes of the casting are stored before the end of each stage and are used as initial conditions for the calculation of the next stage. And simulating the deformation of each stage of the blade manufacturing process by adopting numerical simulation software of the casting and heat treatment processes. When the blades are cooled to 150 ℃ in the sand box, the deformation in the X direction is mainly distortion deformation, the blades are deformed from bending to straight direction, wherein the deformation of one side connected with the lower ring is larger than that of the upper crown side 4, and the deformation of the water outlet side 3 is larger than that of the water inlet side 1. The deformation of the vane in the direction Y, Z is primarily a shrinkage deformation, but this deformation can be compensated for by increasing the casting reduction. After the blades are boxed and cooled to room temperature, the deformation tendency of the blades is the same as that of the blades cooled to 150 ℃ in a sand box, the blades are still deformed towards a flat plate from bending, but the deformation amount and the deformation area are increased. After the casting head system is cut off, the internal stress of the blade is redistributed and balanced, the integral deformation trend of the blade is the same as that before the casting head system is not cut off, but the deformation of the lower ring side 2 is reduced to a certain extent, the deformation of the upper crown side 4 is increased to a certain extent, and the integral change is small. After the heat treatment is finished, casting stress in the blade is gradually reduced in the heating and heat preservation processes in the heat treatment process, but heat treatment stress caused by different heating and cooling speeds of all parts of the blade is reintroduced in the heat treatment process, so that deformation is caused. Compared with the deformation of the blade after the casting head system is cut off, the deformation tendency of the lower ring side 2 along the X direction is reduced after the heat treatment, but the deformation tendency of the upper crown side 4 along the X direction is increased; meanwhile, since the blade is constrained differently between the heat treatment process and the casting process, the deformation in the direction Y, Z is greatly changed.

3. And setting the reverse deformation amount for different areas according to the calculation result and the specific structure of the blade.

4. And simulating the whole hot working procedure of the geometric model added with the inverse deformation again, wherein the simulation initial condition and the boundary condition are completely the same as the previous simulation. The final shape of the deformed blade model is compared with that of a clean blade, so that the machining allowance of each part of the blade is basically uniform (the machining allowance range is 15-25 mm), the production requirement is met, and the blade can be molded according to the model.

The above examples are only a few of the several preferred embodiments of the present invention, and it should be noted that the present invention is not limited to the above examples; for a person skilled in the art, modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.

Claims (2)

1. A method for controlling the size of a casting based on reverse deformation is characterized by comprising the following steps: establishing an integrated thermal stress model of solidification, cooling, boxing, casting system cutting and heat treatment, and visually reproducing the thermal stress and deformation conditions of the casting in each process by using the model to obtain the final geometric shape of the casting before machining; meanwhile, actual measurement is carried out on key points of the casting, and the accuracy of a simulation result is proved; (2) on the basis of a casting deformation simulation result, setting an anti-deformation relaxation coefficient according to the structural characteristics of the casting and the restraint degrees of different areas, and increasing the anti-deformation amount of the casting model coordinate; (3) carrying out full-flow numerical simulation on the casting model added with the reverse deformation amount in the processes of casting, boxing, dead head cutting and heat treatment to obtain the distribution of the deformation amount of the casting before machining; comparing the deformed model with a final product design model, and if the machining allowance of the casting is uniform and is within a reasonable range, designing the casting model according to the reverse deformation model; otherwise, continuing to perform the next cycle of anti-deformation design and calculation simulation according to the anti-deformation model, the deformation and the anti-deformation relaxation coefficient until the final geometric shape of the casting meets the requirement of the machining allowance, and producing the casting with proper and uniform machining allowance.

2. The method for designing a casting model based on quantitatively setting the reverse deformation amount according to claim 1, wherein: the casting model reverse deformation amount is determined by the product of the reverse deformation relaxation coefficient and the negative deformation vector.