DJM Technical Introduction

    Deformation and vibration stress relief of casting

    Deformation and vibration stress relief of casting
    Deformation of casting in cooling process
    Casting in the cooling process, due to the different cooling rates, the volume contraction caused inconsistent, but each part is connected to this, restrict each other, is bound to produce deformation. The flexure is the most common casting deformation. The following with T shaped austenitic steel castings on cooling flexural deformation of hair development process were discussed.
    The cooling rate of t0~t1: casting thick bulk (I) is slower than that of thin section (rod II). At the same time, the free linear shrinkage of the rod II is smaller than that of the rod I, and the result of the interaction of the rod I makes the rod produce the deflection of the outer convex.
    T1~t2: with the continuation of time, the flexural deformation increases. When the two rod temperature reaches the maximum value, the rod I convex bending deformation reaches its maximum value. After I bar cooling rate than rod II fast, free linear contraction velocity greater than rod II, therefore, deflection value decreases, until at a certain time casting restoration (zero deflection).
    T2~t3: casting section still exists temperature difference. After that, the rod II cooling rate is still faster than the rod I, rod I occurs inside the concave deformation, cooling to room temperature, the deformation of the casting direction is rod I (thick most) inward concave, rod II outward convex.
    Through the above analysis, it can be known that the uneven cooling of the casting and the distribution of the temperature on the cross section are the main reasons for the deformation of the casting.
    With solid phase transition of the alloy castings, due to the different cooling conditions of castings in different parts, arrived at the phase transition temperature and phase transformation in different degrees. Therefore, the deformation process of the alloy castings also with the transformation of the alloys. Right above for gray cast iron T shaped beam casting in the cooling process of the deflection of the development process.
    Casting the flexural deformation and alloy composition. Right below said WC + Si value of T-shaped beam casting residual deformation effect. Can be seen, carbon and silicon content is small, thick most of the produce of the inward deflection, deflection decreased gradually with the increase of carbon and silicon content, and even reverse bending deformation.
    Two, the deformation of the casting in storage and mechanical processing
    In casting stress state is unstable, can spontaneously deformation and stress relaxation to reduce internal stress, stable state. Obviously, there are residual pressure should be part of the spontaneous elongation, and residual tensile stress force shorten automatically, can make the casting residual stress decreases. As a result, the casting deflection.
    Lathe bed guide rail is thick, side a book, in the cooling process temperature, resulting in the rail surface residual tensile stress, the side of compressive stress. When stored in bending deformation, guide surface is concave, thin side convex upward, pictured right. Right below the plate casting deformation.
    After machining, the residual stress is re distributed, and the two bending deformation occurs. The bending deformation of the casting can only reduce the stress, but can not completely eliminate the residual stress.
    Deflection of the castings produced. If the alloy ductility can be corrected; for brittle materials, such as gray cast iron is not easy correction, possibly due to machining allowance is not enough and is damaged, resulting in unnecessary waste.
    In order to prevent deformation, should as far as possible to make the casting wall thickness or the shape of the section of the symmetry, as shown in Figure C; in the casting process should take corresponding measures, and strive to enable the simultaneous solidification; sometimes, of slender easy deformation of the casting, in the manufacturing model, model is made with the deformation direction is the opposite of the shape to offset its deformation and the method for anti deformation method. In addition, the principle of simultaneous solidification, is an effective way.

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