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How to design the impeller mold of cnc machining center?

Release time: 2020-01-09 09:58:05

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The product is a plastic impeller, we should look very familiar, because this product is a typical part of a CNC cnc five-axis machining center . However, if we want to use a mold to produce this product in batches, the planning of the mold will require a big brain. How to release the product and how to eject it are difficult. There are not a few brushes that can make this mold! We will provide us with rare dry goods.

Schematic diagram of demolding and ejection of CNC machine tool mold:

Impeller Die Casting Process and Mold Planning
1 Introduction
The quality and cost of castings depends on the production process and mold structure. The impeller castings shown in Fig. 1 are difficult to demold due to the disorder of the blade structure, so the mold structure is messy and the cost is high. The sand core structure for the mold core uses low-pressure die-casting technology, which can solve the problem of difficult demolding of the casting, and makes the mold structure simple and low cost. When planning the impeller die casting mold, full consideration must be given to the removal of gases, gas inclusions, residual coatings and cold-contaminated metals in the process of filling the cavity, otherwise the internal quality of the casting will be affected. Therefore, the casting system and drainage The rational planning of the system is an important factor to ensure the quality of castings.

2 Process analysis of casting structure
2.1 Analysis of casting data
Figure 1 shows a 3D model of the impeller casting. Data YL108, hardness 90HB, compressive strength Ơb = 240MPa, density ρ = 2. 65 g / cm3, pouring temperature 610 ~ 650.


1. small flange 2. large flange 3. blade
2.2 Analysis of Casting Structure Process
As can be seen from Figure 2, the overall dimensions of the casting are relatively small, the structure is basically symmetrical, the wall thickness is relatively uniform, and the minimum thickness is 3mm; there are fewer dimensions with tolerance requirements, except for the surfaces that require machining, and the roughness requirements of other surfaces Ra = 12. 5 m.

The impeller casting consists of a large inner flange with a diameter of 65mm, a small inner diameter of the barrel with a diameter of φ23.5mm, and a small flange with a large flange standing on the large flange. The inner hole is composed of 4 blades and 6 blades evenly distributed around the periphery The 6 blades of the part form a lateral groove, and a circular arc transition of R6 mm is selected at the junction with the bottom surface of the flange with an outer diameter of φ130mm. An internal buckle groove is formed between the rib and the inner rib plate to form a lateral core extraction. difficult.



Figure 2 Casting dimensions

There are two plans for making this type of impeller: ① the core of the blade part is made of sand core, and the low-pressure casting process is used; ② through improving the structure of the casting, trying to remove the inner buckle groove formed by the R 6mm circular arc transition, The inner shape of the blade is formed by the method of side core pulling or insert, and the high pressure die casting process is used. A comparison of the two plans is shown in Table 1.

Table 1 Comparison of plans



From Table 1, it can be seen that: from the perspective of die-casting, the use of low-pressure casting with liquid metal filling is relatively stable; the casting has good formability, which is conducive to clear casting contours and smooth surface castings; good labor conditions; equipment is simple, so the plan ① is better than Plan ②. Considering the complexity of the mold structure, the difficulty of production, the cost of production, and the production cycle, plan ① is also better than plan ② From the perspective of the accuracy of forming castings, plan ② is better than plan ① because only a few dimensions of the casting have higher requirements, and other standards The accuracy requirements are not high, and the plan① is also satisfied with the production requirements.

Based on the above analysis, the final selection plan① Although the post-processing of the impeller die-casting blanks requires an additional sand core cleaning process, the mold structure is simple, which is conducive to reducing the cost of castings when the batch size is not large.

3 Mold planning plan
3. 1 parting surface confirmation
When selecting the parting surface, comprehensive consideration should be given to the planning of the casting to remain in the movable mold, the pouring system and the overflow system after the mold is opened, the smooth ejection of the casting, the coaxiality of the two flange inner holes and the aesthetic requirements of the casting. And exhaust, which facilitates the production of molds and the simple removal of flashing of castings. The selection of casting parting surface is shown as A-A parting surface shown in Figure 3.



Figure 3 Parting surface selection

3.2 Planning of the pouring system
The pouring system plays an important role in controlling the direction and condition of metal liquid flowing in the mold, exhaust overflow conditions, and pressure transmission. Planning a reasonable pouring system is an important part of the mold planning operation. The impeller casting is a regular rotating body with a through hole in the center. The selection of the central gate can minimize the projection surface of the mold parting surface during casting. The flow of each metal liquid is the shortest, the mold structure is compact, and the exhaust effect is compared. it is good. The gating system is planned as the center gate method shown in Figure 4.



Figure 4 Orientation of the center gate and overflow channel

3. 3 Spillover System Planning
The overflow system and the pouring system are an integral part of the entire cavity filling process. The overflow system consists of an overflow tank and an exhaust tank. There are 8 mold overflow grooves, and the cross-section is selected from the more commonly used semi-circular cross-sectional shape. The total volume of the planned overflow grooves is not less than 20% of the casting volume. Figure 5 shows the dimensions.

The mold exhaust groove is provided at a portion where the molten metal is finally filled. The exhaust groove of the fixed cavity is arranged at the rear end of the overflow cavity and cooperates with the overflow groove to enhance the overflow and exhaust effect.Although there is a short vertical distance between the exhaust groove of the moving cavity and the parting surface, It is the contact surface between the sand core and the fixed mold insert, and it is also close to the parting surface, which does not have much influence on the exhaust effect. In order to reduce the exhaust resistance, the projection shape of the exhaust groove on the parting surface is made into an extended horn shape, as shown in Figure 5.



Figure 5 Main dimensions of overflow tank and exhaust tank

4 Mold structure and operation progress
4.1 Mold structure
After checking and checking the casting quality, clamping force, mold opening stroke, mold thickness, and mold installation dimensions, and taking into account the existing equipment of the manufacturer, the J452B cantilever vertical low-pressure die casting machine was selected for production. The remaining material is taken out from the two parting surfaces of the mold, so the structure shown in Figure 6 is used for the die-casting mold. The molding parts are composed of a movable mold insert 18, a fixed mold insert 19, a sand core 26, and a core insert 28. The movable mold insert 18 is fixed on the movable mold fixing plate with a shaft shoulder, and the fixed mold fixing plate 20 and the guide post fixing plate 21 are I-I parting surfaces. The fixed mold insert is not suitable for the shoulder and shoulder type. Here, socket holes and screws 25 are used for fixing on the fixed mold fixing plate. Because the mold has 2 parting surfaces, in order to guide the positioning of the guide post on the I-I and II-II planes, the sliding of the fixed and movable mold fixing plate guides and positions the guide pillar 31 through the guide pillar fixing plate 21 It is fixed to the fixed mold seat plate 22. The core of the forming wind blade part uses the sand core plan. Under the action of the push rod, the casting has a sand core together with the ejection die, so the mold structure is simple and the cost is low.
4.2 Process of mold operation
The mold is closed, the molten metal is poured into the pressure chamber and injected into the cavity. After cooling, crystallization, and solidification, the movable mold is moved backward, first in the I-I disposal type, the remaining material is pulled off, and then the II-II disposal type. The runner condensate is separated from the fixed mold insert 19 and attached to the movable mold. The ejection structure of the die-casting machine advances the mold push plate, drives the push rods 6, 7 to push the die-casting part and the sand core away from the movable mold insert 18, and completes. Demolding action.

1. screw 2. screw 3. limit nail 4. reset lever 5. push plate guide 6. push rod 7. push rod 8. screw
9. Push rod fixing plate 10. Push plate 11. Screw 12. Movable plate 13. Spacer 14. Cylindrical pin 15. Round
Pin 16. Support plate 17. Movable plate 18. Movable plate 19. Movable plate 20. Movable plate
21. Guide post fixing plate 22. Fixed mold seat plate 23. Screw 24. Screw 25. Screw 26. Sand core 27. Gate sleeve
28. Core insert 29. Cylindrical pin 30. Guide bushing 31. Guide post 32. Guide bushing
5 Conclusion
The impeller blade structure is more complex. The sand core low pressure casting process is selected to meet the customer's technical requirements for the casting, avoiding the side core drawing structure, and greatly simplifying the mold structure. After the test, the demoulding equipment is reliable, the casting quality is good, and the requirements of the user are completely satisfied.