Cooling system design for narrow space of automobile injection mold
The automotive interior is mainly composed of plastic parts, and more than 70% of the plastic parts are formed by injection molding. It can be said that the quality of the injection mold determines the quality of the automotive interior parts.
The production principle of the injection mold is that the molten plastic particles are injected into the steel cavity formed according to the shape of the product by high temperature and high pressure, and after cooling, the cavity is opened to obtain a product of a desired shape. When the plastic particles are cooled, a large amount of heat is released. If the heat is not discharged into the mold cavity in time, many product defects may occur, such as color difference, surface burnt, warpage, etc., and extreme cases may cause the mold to bite or even die. scrapped.
In order to solve this problem, the general mold is to process horizontal or vertical water paths in the mold core and cavity. Under normal circumstances, the distance between the waterway and the molded product is controlled at about 20mm, and the cooling water is passed through the waterway to achieve the purpose of heat dissipation through the flow of water. However, this type of heat dissipation has certain limitations. It is only suitable for molds in which the product modeling space is sufficient to arrange waterways. As consumers' requirements for automotive functional parts gradually increase, more and more product shapes cannot meet the layout space requirements of mold waterways. The ordinary waterways cannot cool the mold products evenly, and the appearance quality and size cannot be guaranteed.
According to the particularity of the shape of the sub-dash storage box, this paper optimizes the cooling system of the mold by introducing a cooling rod, and finally achieves the purpose of improving product quality and molding cycle.
Product design details
The 3D solid model of the side and front of the sub-dashboard storage box is shown in the figure. The material of the product is PP-T20, the maximum length is 209mm, the maximum width is 246mm, and the maximum height is 215mm. In order to meet the corrosion requirements of the product skin texture. The three sides of the product are designed with a draft angle of 6 degrees. The product is assembled in front of the shifting mechanism. The upper part of the product is connected with the stupid part of the main instrument panel by snaps, the lower part is matched with the carpet, and the middle part is connected with the body bracket by the positioning pin. The dimensional accuracy of the whole product is relatively high. The storage box in the middle of the product is designed to facilitate the driver to store the mobile phone, keys and other items. Since the appearance of the product is just on the side of the driver, the surface of the product is highly demanded and cannot be obviously flawed.
In the product design process, in order to make the storage box space larger and more practical, the distance between the inner wall of the storage box and the outer wall of the product is continuously compressed, and the cross section of the final product shape is as shown in the figure, and the distance between the inner wall and the outer wall of the storage box is the smallest. The position is 3.28mm, the maximum is 21.76mm, and the height difference between the two places is about 111.75mm.
Since the product circle is closed on three sides, the gap of the side wall of the storage box cannot be arranged by ordinary waterway cooling, and the appearance quality of the product cannot be guaranteed; if the water well is partially cooled, the distance between the inner and outer walls of the storage box is conical, and the distance between the largest end is Only 21.76 mm, so the mold core can not be arranged with larger diameter wells, and the distance between the bottom of the well and the product is far greater than 20mm, and the cooling effect cannot be reached. The local strength of the mold will also be reduced due to the drilling of the well. . In view of the above reasons, we will use a cooling rod solution in the design of the storage box mold to solve the cooling problem of the product.
Mold cooling system design
1 cooling rod introduction
The mold cooling rod is made by adding a special copper tube to the mesh tube and then adding a certain amount of cooling liquid. The working principle is as follows: the cooling liquid absorbs external heat in the closed tube and volatilizes, and the volatile coolant is pressed by the air pressure. Poorly moving to the low temperature end, liquefying after releasing heat at the low temperature end, and the liquefied coolant returns to the high temperature end due to the suction force of the mesh die, as long as the cooling water is turned on at a suitable position of the cooling rod to make it a low temperature end, The cooling rod can absorb heat by cooling water and discharge it, thereby achieving an efficient heat transfer mode. This heat transfer mode is about 200 times that of copper and has excellent thermal responsiveness.
The cooling rod does not rust and does not produce scale. The temperature range is -50~200 °C. The diameter of the cooling rod is 2mm and the length is up to 225mm. It is especially effective for the narrowing of the product and the abyss. Another advantage of the cooling rod is that the diameter of the mounting hole is small, and the cooling rod is filled in the hole, so the cooling rod can be closer to the molded product (generally controlled to about 5 mm) without affecting the strength of the mold, so that the mold is cooled. Both effectiveness and longevity are guaranteed. The working principle of the cooling rod on the mold, in the part where the mold can not effectively arrange the cooling water path, the processing hole (diameter D1) which is parallel to the product surface is processed, and the grease is applied on the surface of the cooling rod (the grease can improve the heat conduction of the cooling rod) And can be used as a lubricant for the cooling rod), and then loaded into the process hole, a cooling hole (diameter D2) is processed in the lower part of the cooling rod loaded into the process hole, and the cooling hole is connected with the mold cooling water path, so that the cooling rod is The lower part becomes the low temperature end of the heat dissipation system. The heat ht released by the injection molding product can be cooled and squeezed by the medium, and is continuously absorbed by the cooling water source to be discharged. In order to achieve the best cooling effect, the relevant dimensions of the cooling rod are as follows:
D1=D+0.1 mm (convenient to disassemble the cooling rod and not easy to fall off)
D2=D x 2 (to ensure the rapidity and reliability of heat conduction)
2 mold cooling system design
Detailed design of the sub-dashboard storage box mold core cooling system.
Four cooling rods (number 1) with a diameter of 6 mm are fixed in the process hole by a thimble (No. 3), and the lower part of the cooling rod is connected to the cooling water path (No. 2), and the cooling water path is connected to the external circulating water path. Through the action of the cooling rod, the heat accumulated between the narrow side walls of the auxiliary instrument panel storage box is absorbed by the circulating cooling water and discharged to the outside of the mold, and the product sidewall does not suffer from defects such as surface chromatic aberration and product deformation due to local overheating, and the product is also The entire molding cycle is also significantly shortened by the action of the cooling rod. After many trials and verifications, the molding cycle of the product is about 38s (the mold uses the cylinder to eject and reset).
In conclusion (injection mold)
The cooling system of the sub-dashboard storage box mold introduces the design method of the cooling rod, so that the problem that the local area of the mold cannot be effectively dissipated is fundamentally improved, the appearance quality and dimensional accuracy of the product are reliably guaranteed, and the molding cycle of the product is successfully controlled within 40s. The entire production cost and mold life have reached the expected requirements.