Application of modeless NC machining technology in the production of large steel castings

1. Pouring process selection

According to the structural and functional characteristics of components, two feasible pouring schemes are determined before pouring large castings, namely, pouring upward at the main flange end and pouring downward at the main flange end.

The sand core stability of the main flange end downward pouring process is strong and the box closing operation is less difficult, which is conducive to adjusting and controlling the size and accuracy of large castings. However, when pouring from top to bottom, the installation of the lower feeding smoke outlet is more difficult and it is easy to leave pore defects on the upper surface; The sand core stability of the main flange end upward pouring process is poor, it is difficult to achieve the operation regulations, and it is not conducive to the observation of size and accuracy during the pouring process. Therefore, there is a deviation in the accuracy control of bottom-up pouring, but it is conducive to the realization of sequential solidification, and smoke vents can be configured under direct vision. It is a pouring process that reverses the advantages and disadvantages of downward pouring.

In the actual pouring process, it is inevitable to encounter a variety of problems. There is no perfect Pouring Scheme. We can only avoid the disadvantages and reduce the risk of defects as much as possible through adjustment and control. In this project, the pouring scheme of pouring down the main flange is finally selected. Compared with surface defects and smoke outlet assembly, ensuring the stability of sand core is a necessary condition to ensure the stability of component structure and the success of large-scale casting. Therefore, the scheme of pouring down the main flange end is finally selected.

2. Sand core scheme

In the processing and manufacturing of large steel castings, generally, the sand core has been completed before pouring, so as to ensure that the corresponding sand core can be used during pouring and avoid delaying the construction period. In this case, considering the characteristics of the two pouring schemes and the structural characteristics of large castings, whether the main flange is poured upward or the main flange is poured downward, the sand core model used is basically the same, and the live block can be used to replace the differences, so that the sand core can be applicable regardless of which pouring scheme is selected, so as to avoid material waste.

When using the NC forming machine for large casting mold, the finer the particle size of the cast raw sand is, the higher the surface finish of the cast large casting mold will be. Considering that preparing the molding sand alone will bring more difficulties to the production, and the air permeability of the mold will be affected after selecting the finer raw sand, the resin sand cast for the current molding is directly selected as the molding sand, Compared with the mold surface made by the model, the number of coating layers needs to be increased to meet the quality requirements of the surface of large-scale casting mold.

3. Packing and unpacking scheme

After the completion of sand mold processing, the riser shall be placed, coated, closed, melted and poured according to the formulated large-scale casting process requirements. After unpacking, large castings shall be subject to relevant mechanical property inspection, dimensional inspection, visual inspection, 100% radiographic inspection, 100% liquid penetrant inspection and other inspections after sand cleaning, heat treatment, cutting and grinding. From the inspection results, the surface quality of large castings is equivalent to that of castings poured by mold molding, and the dimensional accuracy of large castings is higher than that of castings obtained by mold molding. In addition, there are many slag inclusion defects on the upper surface of large castings, which will increase the workload of subsequent grinding, which is consistent with the expectation. Because the riser at the main flange is large and arranged in the core, it is found that the cutting difficulty is greatly increased when cutting the riser.

4. Overall process summary

On the whole, there are three links in the modeling free NC manufacturing of the large steel casting: ① input the actual values into the computer to obtain the process three-dimensional diagram and three-dimensional model; ② Carry out sand mold making, pouring and box closing simulation step by step, determine the corresponding parameters, and input the collected data into the processing programming software to determine the production and manufacturing process; ③ Manufacture and process according to the established scheme, and finally open the box for inspection and commissioning.