Design methods and skills of the hottest typical i

Typical injection mold design methods and skills

with the rapid development of modern industry, the renewal of products is more and more frequent, and the related mold forming parts and related institutions will also change accordingly. How to reduce the development and manufacturing cycle of the whole set of molds is particularly important. In order to minimize the design and development cycle of the mold, now people pay more and more attention to the standardization of the mold, and design the standard mold base and related standard parts (including standard runner design) of the same type and different models of products within the enterprise. In this way, in the process of mold design and development, as long as we complete the three-dimensional modeling and parting of the product, we can directly assemble the mold core, core and other parts into the corresponding standard mold base. In this way, we can light the preheating device as long as we refine the design of oblique push, slider and other mechanisms: cable core preheating is necessary for insulation extrusion and sheath extrusion, and we can complete the design and development of the whole die. Due to the wide range of machining and electrical machining involved in the manufacturing process of molds, the design and development of molds should follow the principle of easy machining to minimize the processing cycle of molds. Combined with the author's many years of experience in the design and manufacture of injection mold, this paper takes the design of injection mold for the panel of wall mounted air conditioner as an example to elaborate the design methods and skills of injection mold

3D modeling of parts

the mold design is based on plastic part drawings and plastic part samples. For plastic part drawings, attention should be paid to the technical requirements of the drawings. Many drawings clearly give dimensional tolerance levels, unmarked fillets, product wall thickness, etc., which must be paid attention to in mold design; For the samples of plastic parts, the key is to extract useful mold design information from the samples to avoid detours in the design. These information include the position of the parting surface, the position and form of the gate, the size and distribution of the ejector rod, the design of the core pulling mechanism, and so on. The plastic part is made of ABS and its color is milky white, which is tested according to the unified color plate. After forming, the surface of the workpiece shall be flat and smooth, without distortion, cracks, flow marks, weld marks and other appearance defects, and the flatness of the U surface shall be ≥ 1mm. The dimensional tolerance shall be implemented according to gb/t14486-mt5, the wall thickness is 2.5mm, the unmarked fillet is r0.5mm, and the gate is not allowed to be set on the outer surface. Designers should carefully digest the drawings, especially whether the dimensions are accurate and complete, whether there are unmarked demoulding slope, tolerance requirements, assembly requirements, etc., and the allowable degree of forming defects such as weld lines and shrinkage holes. If there are problems in these aspects, they should contact the customer in time to eliminate the existing questions one by one. The plastic part adopts proewildfire software for three-dimensional modeling, and the shape is shown in Figure 1. It takes about 0.5 ~ 1 day to complete the modeling of the whole product. In the process of three-dimensional modeling, special attention should be paid to verifying the assembly size of the whole and the hook and the demoulding slope of the mutually matched product, so as to avoid unnecessary mistakes in the design

Figure 1. Panel plastic parts (including runner and cooling system)

mold design

selection of parting surface and exhaust slot design

considering the machining process of moving and fixed mold cores and the reasonable layout of point gate and pouring system location, the selection of parting surface is shown in Figure 2, which will not affect the dimensional accuracy and appearance of plastic parts, avoid flash, and make the plastic form well, which is conducive to demoulding, And the plastic part is completely left in the moving mold, which is convenient for ejecting the plastic part. The position of the exhaust slot is selected at the end of the diversion channel and the fusion line of the molten plastic body. The depth of the exhaust slot is ≤ 0.04mm and the width is 8mm to prevent overflow. At the same time, the plastic parts can also be vented through the gap between the parting surface and the moving mold core, ejector rod and slider according to the requirements of the three-year task to be completed in two years

Figure 2. Plastic part parting design

design of gating system

the mold adopts the structure of one mold and one cavity, and the gate is not allowed to be set on the outer surface of the plastic part, so as not to affect its appearance. In addition, considering that the plastic part can be automatically cut off at the connection between the plastic part and the gating system when taking materials, it is decided to adopt the point gate gating system with DC channel and shunt channel on the front and rear two small rectangular mounting surfaces. By using Moldflow software for flow analysis, the optimal number and location of point gates, reasonable runner system shape and layout position as shown in Figure 1 are obtained, and the cavity size, gate size and runner size are optimized. Cold material holes are set at the ends of the main and diversion channels in case there are 11 mpgs in cooperation: the gate of the Max Planck Institute of complex technology system dynamics (Magdeburg) is blocked by cold material on the front surface of molten plastic. In order to make the condensate of the main runner easy to get out of the main runner bushing, the main runner is designed into a cone with a taper of 3 °. The diameter of the small end of the main runner bushing is 5mm, its spherical radius is sr20mm, and the inner surface roughness is ra0.4um. In order to easily eject the condensate in the diversion channel, it is decided to adopt the improved trapezoidal section (its size is: 12mm at the big end, 7mm deep, R4 at the root, 102million chip environmental protection bags with a slope of 6 °). In order to make the condensate in the shunt channel easy to get out of the shunt channel, the shunt channel is designed into a cone with a taper of 4 °, in which the diameter of the small end of the shunt channel is 1.5mm, so that the shunt channel can be automatically broken when the mold is opened

determine the mold base

through the above design steps, the projection size of the horizontal plane required for the molding of plastic parts can be basically determined, and then considering whether the positions of the movable and fixed mold core, pull rod, reset rod, guide post, guide sleeve and so on interfere with each other, the projection size of the horizontal plane of the mold can be estimated. Determine the thickness of the dynamic mold sleeve plate and the fixed mold sleeve plate. The thickness of the formwork mainly depends on the height of the plastic part, the area of the formwork, and the arrangement of the cooling water channel. Strength and stiffness calculation is a method, but it takes a long time, and we mainly rely on experience to determine. When determining, we should consider the fixed depth and orientation of the mold core, the proportion between each other, etc. In this mold, the thickness of the movable and fixed mold sheaths is 250mm and 150mm respectively. In addition, the height of the mold foot should be determined according to the characteristics of the actual plastic parts. If the cavity is deep, the cushion block needs to be increased to ensure sufficient ejection distance. Here, the height of the mold foot is 180mm and the ejection distance is 90mm. The whole mold base is modeled and assembled in proewildfire2.0 assembly module. After the mold base is built, the size of each template and the position and size of guide posts, guide sleeves, reset rods, large and small pull rods in the mold base are improved. Finally, the maximum overall dimension of the mold is determined to be 1420 × seven hundred and ten × 692. The mold base adopts a three plate fine nozzle structure (as shown in Figure 3, this mold base can be used for all panel molds of this type in the future). It is made according to the material list, and it is proposed to use ube-1300 injection molding machine

Figure 3 injection mold base figure

design of demoulding mechanism

due to the lateral convex concave on the plastic part which is different from the opening direction, it is necessary to determine the side extraction mode of its hook, such as inclined guide column, inclined slider, inclined top, inclined push, hydraulic cylinder, etc. Considering the small core pulling distance of the panel mold, processing technology, manufacturing cost and other factors, it is decided to adopt the inclined top. However, because the distance between the clips is too close, interference will occur if all inclined tops are used, so 7 inclined tops and 1 inclined push can be used for side core pulling, and the inclined angle between the inclined top and the inclined push depends on the side core pulling distance. In order to ensure the stable and reliable ejection, it is decided to adopt the double oil cylinder ejection reset system, which is equipped with a travel switch for travel control, and eject the plastic part from the driven mold core through the ejector rod, oblique ejection and oblique push, which is not only high efficiency, but also conducive to improving the service life of the mold. The runner system relies on the limiting effect of the die puller and the large and small pull rods to discharge the material

3D modeling and structural design of other mold parts

after the parting design and mold base design, the structural design of other mold parts should be carried out immediately. Similarly, the three-dimensional modeling and assembly of the remaining parts are carried out in the assembly module of proewildfire2.0. Due to the large number of parts, it will not be detailed here, but after the modeling is completed, attention should be paid to the global interference check, and if there is interference between parts, it should be modified. Finally, carry out the three-dimensional modeling design of the flow channel system and the ejector pin hole. The three-dimensional design of the flow channel can be carried out according to the analysis results of Moldflow software. The design of the ejector pin hole should not only take into account the places where it is easy to store the mold, but also consider the layout of the cooling water channel. Its location is shown in Figure 4

Figure 4 assembly drawing of injection mold

1 Fixed formwork base plate 2 Push plate 3 Push plate guide sleeve 4 Ejector rod fixing plate 5 Push plate guide post

6 Movable die sleeve plate 7 Large pull rod 8 Small pull rod 9 Moving die cores 10, 11 Fine positioning 12 Fixed mold sleeve plate 13 Fixed mold core 14 Cast off board 15 Fixed formwork base plate 16 Guide post 17 Guide sleeve 18 Locating ring 19 Sprue sleeve 20 Reset lever 21 Large pull rod 22, 23 Pull rod guide sleeve 24 Pull rod limit plate 25 Pull pin 26 Limit post 27 Support columns 28, 32, 36, 37, 40, 44, 49 inclined roofs 29, 33, 41, 45, 50 guide rails 30, 34, 42, 46, 51 guide blocks 31, 35, 43, 47, 52 wear blocks 38, 39 Brake block 48 Core 53 Oblique push

to determine the distribution form of the cooling water channel

after the plastic is filled with the mold cavity, it should be shaped by cooling, so as to obtain the product. The distribution of cooling water channels should follow certain principles. In general, it should ensure that plastic parts are fully cooled and shrink in balance, without connecting with other parts and holes, so as to avoid water leakage. In this example, the water channels are arranged longitudinally with a diameter of φ 12mm, see Figure 1 for specific layout. The cooling system is equipped with a water hole to increase the cooling effect. At the same time, it is sealed with an O-ring to avoid leakage. In addition, the quick coupling should not be exposed outside the mold to avoid crushing it when hoisting and placing the mold

blanking and drawing mold drawings

material selection is very important in the design of injection mold. If the mold material is selected improperly, it is likely to affect the service life and work efficiency of the mold. Therefore, the mold material must be selected reasonably in strict accordance with the manufacturing process, and its material list is shown in Table 1. The process of mold design conception is also the drawing process of mold drawings. With the rapid development of cad/cam technology, although no drawing processing is becoming more and more common, the mold drawing is still essential in the general actual processing process, because it can provide operators and fitters with some important position dimensions, assembly dimensions, technical requirements, geometric tolerances, roughness, etc. now only the assembly drawing of the mold (as shown in Figure 4) is shown to you for reference only. Table 1 blanking list of panel three plate mold

conclusion

based on my years of experience in injection mold design and manufacturing, this paper introduces in detail a set of injection mold design methods and skills from three-dimensional modeling of parts, parting design, three-dimensional assembly design of mold base, three-dimensional modeling of mold parts to two-dimensional drawing of mold assembly with clear and concise design ideas. By mastering the above design methods and skills, it is beneficial to improve the design level and work efficiency of mold designers, shorten the mold development cycle of new products, and thus bring good economic benefits to enterprises. (end)