1 Introduction

When developing a new product fan “three impellers”, our company encountered internal shrinkage hole defects and dynamic balance that could not meet the quality standards Quality issues. Internal defect problem: The customer required the internal defect of the product to meet the quality standard of level 2, and the product is a ductile iron product weighing 152kg, with a wall thickness of 18-35mm, and isolated hot joints in many places. There are 3 places in the size of the protruding hot joints in φ36 and 2 in φ80, and the existing casting technology cannot effectively solve the internal defects of these parts. See Figure 1. Dynamic balance problem: The dynamic balance of the product is mainly related to the dimensional accuracy of the product (dimensional tolerance: DCTG7) and the density of the material. The casting process of this product is divided into Figure 2.

Figure 1 Basic structure of the product

Figure 2 Casting process parting

2 Technical background

The length of the product is 635mm, and the inner cavity is formed by a small core. The core is formed by the combination of left and right sections in the length direction (see Figure 3), and it is difficult to ensure the coaxiality of the core after the core is assembled in the middle part, and it is easy to break The size of the product fluctuates greatly, resulting in uneven wall thickness of the product, which is difficult The product dynamic balance of 113.396 grams was met.

Figure 3 The basic structure of the core

The original casting process technical scheme (Fig. 4): 6 risers were set up at the parting surface for the hot-junction part, which could not solve the problem in the product There are different degrees of shrinkage porosity defects at the φ36 and φ80 hot junction circles (Fig. 5 and 6). Coated sand hot core process core making, the size of the core fluctuates greatly, and the density of the core is uneven
The combination of the upper core does not use tooling, and the conventional method is adopted, and the dimensional accuracy of the combination of the two cores cannot meet the requirements, resulting in uneven wall thickness of the product, and the dynamic balance requirements cannot be guaranteed.

Figure 4 Original casting process

Fig. 5 φ80 defect at the hot junction

Fig.6 φ36 Defect at the hot junction

3 Introduction and characteristics of process design

(2) Product internal defects: Corresponding countermeasures have been formulated for the riser shrinkage position, cooling conditions and insufficient riser shrinkage effect, and the internal defects of the product have reached the level 2 quality standard. There are 3 shrinkage porosity defects at the φ36 hot junction, and there are 2 risers at the original design of the 2 defects, but the position of the riser neck is far away from the hot junction position, and the shrinkage channel is long, so the filler shrinkage effect of the riser cannot be fully exerted Use. The other 1 is not designed to be filled with risers because it is underneath type, can not be arranged riser, by using a cold iron, using its quenching The action realizes rapid solidification, so as to solve the internal quality deficiency of the product Sink. (Fig. 7 and 8) φ80 hot junction is mainly reflected in the riser shrinkage effect foot, by changing the normal riser into a model 80/110 heating riser sleeve, The riser shrinkage volume was increased from about 10% to about 50%, which solved the crater quality defect and improved the product at the same time 2~5% process yield. (Fig. 8)

Figure 7 Comparison of process adjustments

Figure 8 Adjusted process

(3) Dimensional accuracy assurance for product size problems: one is to abandon our tradition
The hot core box coated sand core making process adopts the self-hardening sand cold core process to make the core accurate. The second is to design a special fixture for the core (Fig. 9) to ensure the accuracy of the core, and the working principle of the core tooling is to achieve theoretical dimensional accuracy through mechanical pushing after the core is positioned. The special tooling for the core is composed of a set of core fixtures (the following figure is the assembly drawing of the core fixture) and a plurality of base plates. The structural installation, connection relationship and working principle of the core clamp are described as follows, in Figure 9: 1-limit block 1;2-motherboard; 3-limiting block 2;4-limiting block 3;5-bolt; 6-bolt; 7-rubber pad; 8-plug; 9-rocker head; 10 nuts; 11-bolt; 12-a screw connecting block; 13-a nut; 14-rocker tail.

Figure 9 Adjusted process

The bottom plate is to facilitate the transfer of the tooling board of the core when the core binder is not cured, and a suitable bottom is prepared according to the actual production quantity the number of plates, and there are requirements for parallelism and flatness. When using the core tooling core, a base plate is placed first On the core clamp, utilize this base plate to control the height direction dimension of the composite core, and control the horizontal direction size of the composite core by utilizing the limiting block 1, the limiting block 2, the limiting block 3, and the limiting block 4, so as to meet the dimensional accuracy requirement of the composite core. The method of assembling the core is to put the left core on the bottom plate of the core fixture, and then put the right core on the bottom plate of the core after putting the core binder in the glue tank, and shake the handle to push the right core forward. When the core reaches the dimensional accuracy control line, stop shaking the handle, release the handle, remove the combined core together with the bottom plate, and store it in a fixed position. (Fig. 10)

Figure 10 Schematic diagram of the core fixture

4 Verification results and conclusions

The current process technology fully illustrates the importance of the position arrangement of the riser neck, without changing the shape of the riser and the size of the riser neck
, only the position of the riser neck was adjusted to solve 2 shrinkage defects; In the case that the riser cannot be used, making full use of the chilling effect of the chilled iron is also another way to solve the problem of shrinkage porosity in the product; For oversized hot junction products, the ordinary riser cannot completely eliminate the internal defects, and it is necessary to make reasonable use of the hot riser. Passed on The application of technical means has solved the internal defects of the product. (Fig. 11, Fig. 12) The self-hardening sand cold core process is used to make the core, which overcomes the deformation problem caused by the change of cold and hot temperature, and greatly improves the dimensional accuracy of the core itself. The use of core clamps ensures that the core is assembled
The size can be effectively controlled in all three directions, and the core error is controlled to a minimum, which solves the problem of the dimensional accuracy of the combined core, meets the DCTG7 dimensional accuracy standard of castings, and reaches the product Balancing requirements.