Pressure casting is a method of filling cavity with liquid or semi-liquid metal at a higher speed under high pressure, forming and solidifying under pressure to obtain castings. Die-casting process is a process in which three elements of die-casting machine, die-casting mold and die-casting alloy are organically combined and used comprehensively. In molding process, conditions such as pressure, speed, temperature and time are mutually restricted and interrelated. Balance must be ensured to obtain qualified castings. ADC12 is a die-cast aluminum alloy, which is commonly used in production of cylinder head covers, sensor brackets, end covers, and cylinder blocks. Connector of vibrating machine is a plate-type part, which is a non-load bearing part, structural strength is not high, so it can be mass produced by die-casting. Aiming at die-casting molding of this part, a two-plate die-casting mold with a double-inclined guide pillar side core pulling mechanism is designed to provide a reference for mold design of similar castings.

 

Figure 1 Vibration machine connector
Shape of vibrating machine connector is shown in Figure 1. It is similar to a thin-walled plate and has a "bow" shape. From perspective of mold design, casting is divided into 3 areas by F1 and F2 virtual surfaces: K1 lateral area, K2 flat plate area, and K3 cladding area. Three areas all have characteristics of relatively porous, buckle, screw column, etc. It can be seen from views from A and B that ejection direction of K1 area is inconsistent with K2 and K3 areas, they are perpendicular to each other. Ejection direction of the K3 area and K2 area same.
Table 1 Composition of ADC12 alloy and YL113 alloy

 

Molding material adopts ADC12 alloy, which is equivalent to domestic alloy YL113. ADC12 alloy and YL113 alloy composition are shown in Table 1.
When die-casting, thicker die-casting parts will reduce mechanical properties, thin-walled die-casting parts have good compactness, which improves their strength and pressure resistance. If wall thickness of die-casting parts is too thin, it will cause insufficient filling of aluminum alloy melt, which will make aluminum alloy melt poorly welded and bring difficulties to die-casting process. Try to keep thickness of wall thickness section uniform.

 

Figure 2 Casting structure
Structure size of casting is shown in Figure 2. Its external dimension is 189mm*178mm*46mm. According to its mass production requirements, a 1-cavity mold structure is used for die-casting. Difficulty in forming is: ①Casting has a large volume, structural characteristics of K1, K2, and K3 areas are different, and material flow resistance is large; ②Wall thickness of casting is thin, and melt flow is difficult; ③K1 area demoulding should use integral side core pulling, and a large core pulling slider mechanism is required; ④Hole and screw column have many characteristics, which affect casting out of cavity as a whole.

 

(A) Parting surface design

 

(B) Cavity plate insert
Figure 3 Type setting

(1) Parting setting is shown in Figure 3(a), using 2 parting surfaces for parting, P0 is main parting surface, and P1 is secondary parting surface. Opening direction of main parting surface P0 is set according to ejection direction of K2 and K3 areas, and side of K1 area is ejected from core in C direction, so P1 auxiliary parting surface is set. Cavity plate insert is shown in Figure 3 (b ).

 

Figure 4 Gating system design
1. Pressure chamber 2. Diversion block 3. K1 slider 4. K1 slider seat
(2) Design of gating system is shown in Figure 4. Gating system is equipped with R1, R2, and R3 runners to inject K3, K2, and K1 areas respectively. For exhaust tank to overflow and exhaust, K1 area is equipped with 2 overflow grooves and 2 exhaust grooves. Considering complexity of filling K1 area with R3 runner, a thicker runner is used at the end of R3 runner to ensure reliability of filling in this area.
(3) In runner design behind guide block 2, length of main runner R2 is 35mm, and demoulding angle is 6º on one side. Ends of cross runners of R1 and R2 runners are curved runners, and more than two steps are designed to prevent cold material from entering cavity through cross runners, resulting in cold barrier lines on the surface of casting. Cavity plate inserts protruding on the opposite side of R1, R2, and R3 runners are designed to avoid. Overflow grooves on the opposite side of 3 runners process waste holes, then set up exhaust grooves and overflow grooves according to test conditions. Overflow groove is opened on a relatively flat parting surface, cross-sectional shape is semicircular, inlet and exhaust grooves of overflow grooves arranged in parallel must be separated with a distance of more than 5mm. Turning point of exhaust groove is set as a circular arc transition to facilitate machining. At the end of runner before gate, pouring size is set in three levels to ensure that runner waste and casting can be separated easily after demolding.
(4) Guide block 2 should be cooled with cooling water to prevent cracks. Diameter of cooling pipe of core insert 3 is ϕ10mm, height from the lowest surface of casting is 25mm, and cooling water pipe of core insert 3 is connected from mold base. Therefore, a high temperature and high pressure resistant waterproof ring is used between molding insert and mold plate.

 

Figure 5 Mould structure
1. Compression chamber 2. Diversion block 3. Fixed template 4. Movable template 5. Cushion block 6. Support column 7. Push rod 8. Push rod fixed plate 9. Push plate 10. Support column 11. Core insert 12 .Cavity plate inserts
Mold structure is shown in Fig. 5, cavity plate insert 12 and core insert 11 are respectively fixed on fixed mold plate 3 and movable mold plate 4 by screws, pressure chamber 1 is cooled by a cooling ring. Mold base is composed of a fixed mold plate 3, a movable mold plate 4, and a spacer block 5. Outer surface is required to be bright and flat. Movable and fixed mold frames are processed with 2 holes, which are set at a position where there are no other inserts to prevent core insert 11 and cavity plate insert 12 from falling out. Installation gap of insert in mold plate groove is 0.1~0.15mm, and a baffle is set on the outlet side of exhaust groove to prevent aluminum liquid from leaking out. Five support columns are provided to prevent mold plate from deforming, and a support column 6 with larger bearing capacity needs to be set directly under deflector block 2.
Remaining support columns 10 are arranged under core insert and cannot interfere with other parts. Push plate 9 is guided by two guide posts, and guide posts have a limit function. Bottom plate of spacer should be processed through to facilitate heat dissipation. Four corners of mold must be set with prying angles to prevent collisions with guide post during installation. Depth of prying groove is 8-10mm. Surface of inner hole of pressure chamber 1 is required to be carbonitrided after circular grinding, and polished along mold ejection direction. Cooling ring is installed by hot pressing, mold base plate must be quenched and tempered. In order to facilitate replacement of inserts in the cavity, several large holes are set on the surface of mold parts and then fastened with headless screws. Hoisting holes on mold plate are M30mm, hole depth is 45mm, and at least two at the top. External spring on push rod fixing plate 8 should be equipped with a spring protective sleeve to prevent spring from deforming.

Core insert 11, cavity plate insert 12, and insert 20 (see Figure 6) are all made of alloy steel 8407. After processing, stress relief treatment should be carried out before heat treatment, and quenching hardness is 46~48HRC. Matching tolerance of core insert 11, cavity plate insert 12 and corresponding template should be less than 0.05~0.08mm of mold frame to facilitate lifting of ring. Installation of molded parts is shown in Figure 6. Fit tolerance of push rod 7, 15, 16 and core insert 11 is 0.025~0.05mm. Excess holes on the surface of core insert 11 and cavity plate insert 12 are all blocked, and corners of molded parts must be chamfered at least C1mm.

 

Figure 6 Molded parts installation
13. Guide post 14. Reset lever 15. Push rod 16. Push rod 17. Slider rear seat 18. Slider 19. Inclined guide post 20. Insert
In view of demoulding requirement of K1 surface, designed double inclined guide post slider mechanism is shown in Figure 6, which is composed of parts 17~20. In slider mechanism, two oblique guide posts 19 of same model are used to drive slider 18 to move. Slider 18 is provided with lifting screw holes for easy movement and assembly. Bottom of slider is machined with a lubrication groove for sliding, and wear-resistant block at the bottom of slider is made into two pieces, which are higher than bottom mold base surface and convenient for processing waste slag in production process. Sliding mechanism is flexible to guide sliding, stable movement, and matching clearance is 0.08~0.12mm. After mold is closed, sliding block 18 and fixed mold plate 3 are compressed by locking block, contact area is not less than 2/3 and has a certain prestress.
A pair of two-plate die-casting mold is designed for die-casting molding of vibrating machine connector. Mold is equipped with 3 runners for partition pouring of cavity. For molding and demolding of casting side, sliding block of double inclined guide column mechanism is designed. Slide block adopts a split structure, which is convenient for processing and assembly. Gate system is designed reasonably and casting quality is good, which can provide a reference for die casting production of similar castings.