In casting production, mold is very important. All kinds of process knowledge we talked about before should be included in the mold finally. And the mold itself has some specific requirements.
1.Mold design principles
The original traditional production mode is: after getting the part drawing, first make the casting process drawing, then design the detailed two-dimensional structure drawing, according to the two-dimensional drawing to make the mold blank wood mold, and then cast the mold blank. For complex castings, we need to make a variety of samples to test the accuracy of common machining parts.
With the widespread application of CNC machining center, the design of mold is more and more fast, and the manufacturing cycle is greatly shortened. After getting the part drawing of the product, first make the casting process drawing, and then design in two-dimensional and three-dimensional simultaneously. The two-dimensional drawings are only the detailed design of the assembly drawings and the detailed drawings of the assembly parts. For the die body, it is only a simple design of the size of the assembly and connecting parts, and the size and shape of the inner cavity can all be transferred out in three dimensions. Even, sometimes the wood mold is also made in the CNC machining center, so that the production cycle is greatly shortened, the processing amount is even, and the casting defects are less.
As mentioned before, all castings with sand cores shall be designed with horizontal or vertical positioning of core heads and reasonable core head clearance to avoid sand extrusion defects.
At the core of upper formwork, the air pin or air sheet must be designed to reduce the occurrence of air hole defects.
According to the structure of core head, the reasonable technological structure of pressing ring, anti pressing ring and sand squeezing groove should be designed.
3.Hot box design
(1) According to the size of the sand core and the size of the mold, the required heat is calculated, and the number and power of the heating rod are determined.
(2) According to the shape of the sand core and the structure of the mold, different structures of the coated sand nozzles are designed to meet various requirements.
(3) For heavy components, lifting holes shall be designed to facilitate disassembly and transfer.
(4) According to the size of the die, the reasonable locating pin and locating sleeve are designed, and the fit clearance is reasonable. The simple mold uses two circular dowel sleeves, the complex mold uses three long circular dowel sleeves, and the direction should be reasonable.
(5) In order to facilitate the sand core out of the mold smoothly, the core box should be designed with a top core rod. The top core rod shall be evenly arranged. According to the sand core structure, the reasonable number and diameter size shall be determined, and the matching clearance shall be controlled within 0.15-0.2mm.
(6) For the complex sand core, the exhaust device should be designed at the corner. There are four ways to exhaust the core box: first, install a special exhaust plug to exhaust; second, exhaust through the clearance of the top core rod; third, design the exhaust slot to exhaust, the depth of the exhaust slot is 0.3mm; fourth, exhaust through the clearance of the core box parting surface.
4.Cold box design
The design principle of the cold core box is basically the same as that of the hot core box, because the cold core box is solidified by blowing gas, and it has some specific requirements.
(1) When installing the vent plug, try to avoid the sand shooting direction to avoid “short circuit”.
(2) For the vertical core box, the vent plug shall be arranged as little as possible on the top and more on the bottom.