Inspection and analysis of brake caliper mold pouring test

(1) The 3D scanning equipment is used to scan the casting surface one by one, and then the three-dimensional surface obtained is spliced together through the reference surface, and then compared with the original three-dimensional model, the datum fitting method is selected, and the positioning surface deviation of X, y, z directions is set to 0 After that, the overall tolerance scale is defined and the deviation of all other surfaces is compared. Different display colors represent the deviation degree between the actual 3D and the original 3D. The deeper the color is, the greater the deviation is. It can be seen from Figure 1 below that the scale is selected as ± 0.5mm. Except that the burr position of individual parting line is red or orange, other parts are within the range of yellow green, so it is determined that the casting size meets the requirements of the drawing.

(2) The metallographic structure, mechanical properties and spheroidization rate difference of four cavities in the first mold and four mold castings in the tail mold were detected. The relevant properties of the castings were determined by the temperature limit test to meet the design requirements of the drawing. The specific data and detection positions are as follows. Through comparison, it can be seen that the mechanical properties of the castings with different cavities have little difference, that is The effect of temperature variation at 40 ℃ on mechanical properties can be ignored.

(3) The internal defects of the head and tail die castings were detected by X-ray machine. The minimum defect resolution was 1 mm and the maximum penetration wall thickness was 50 mm. It was found that there were suspected micro shrinkage porosity and shrinkage porosity ratio at the bridge deck of two brake calipers (one for each of 3 and 4) 25%. After cutting along the shrinkage porosity position, the coloring test was carried out on the section. It can be seen that the imaging agent intrudes into the shrinkage porosity hole, and the outline of the shrinkage porosity area is shown. The defect size is beyond the standard. The shrinkage porosity is located in the center of the brake caliper bridge deck, far away from the riser neck. Compared with the layout of the mold, it is found that the two defects are close to the common riser side in the middle (Fig. 2).

It is found that there is no shrinkage pipe on the upper part of the common riser of 3 × 4, as shown in Figure 3 below. As a result, negative pressure is formed inside the riser feeding process, and the liquid metal cannot flow to the casting rapidly by gravity, which reduces the feeding utilization rate of liquid metal, and shrinkage porosity appears at the center of hot spot on the bridge deck.

Generally, if a good tubular shrinkage cavity is formed at the top of the riser, the shrinkage porosity is rarely found in the casting, otherwise, the feeding of the casting is not sufficient, and the shrinkage porosity defect appears in the casting. In 1982, r.w.heine put forward the feeding technology of conical riser. He thought that the shape of the riser should be conducive to the top-down cooling. The diameter of the top surface of the conical riser is very small, which will make the shrinkage pipe form quickly. Based on this, the design method of the conical riser is put forward, which not only has good feeding effect, but also can improve the process yield. At the same time, it is emphasized that in order to make the riser form a shrinkage pipe, the first thing is to ensure that the riser is solidified immediately after pouring, so that the riser and the casting can be integrated and isolated from the molten iron of the sprue. This can not only improve the liquid feeding efficiency of the riser, but also prevent the metal liquid in the casting from losing through the riser neck and pressure relaxation due to expansion, so as to make full use of the graphite expansion for self feeding The runner should be as thin as possible.