(1) Accuracy of dimensions
Refer to 2-17 of the mold design and manufacturing manual for recommended dimensional tolerance of plastic parts, and refer to table 2-18 for accuracy grade of plastic parts.
Table II: recommended accuracy
材料 高精度 一般精度 低精度
Material high precision general precision low precision
ABS 3 4 5
ABS 3 4 5
As a Wahaha bottle cap, its accuracy does not need to be too high, so the general accuracy it4 is selected. Refer to table 3-8 (sj1372-78) of plastic part tolerance textbook plastic forming process and mold design.
(2) Surface roughness
As a Wahaha bottle cap, its appearance must have a good glossiness, which depends on the surface roughness of the mold cavity. The surface roughness of the mold is 1-2 levels lower than that of the plastic part. The surface roughness of the plastic part is generally between Ra0.8. If Ra0.8 is selected for this product, the surface roughness of the mold cavity is Ra0.4.
The demoulding inclination of the product is the recommended value, cavity: 1030, core: 40
(4) Wall thickness
According to the products provided, the wall thickness is uniform, with a value of 2mm.
Injection process parameters of ABS
Injection type screw type
Screw speed (R / min) 30 ~ 60
Nozzle type straight through
Temperature (℃) 190 ~ 200
料筒温度 前段 （℃） 200~210
Drum temperature front section (℃) 200 ~ 210
中段 （℃） 210~230
Middle section (℃) 210 ~ 230
后段 （℃） 180~200
Back section (℃) 180 ~ 200
Mold temperature (℃) 50 ~ 80
Injection pressure (MPA) 70-120
Holding pressure (MPA) 50 ~ 70
Injection time (s) 3-5
Pressure holding time (s) 15-30
Cooling time (s) 15-30
Forming cycle (s) 40-70
(5) . calculation of strength and rigidity of formed parts
During the working process of the injection mold, it needs to bear many kinds of external forces, such as injection pressure, holding pressure, closing force and demoulding force. If the external force is too large, the injection mold and its formed parts will produce plastic deformation or fracture damage, or produce large elastic bending deformation, which will cause the formed parts to have a large gap at their mating surface or mating surface, resulting in overflow and flash phenomenon, which will lead to the failure of the whole mold or fail to meet the technical quality requirements. Therefore, in the mold design, the strength and stiffness calculation and verification of the formed parts are essential.
Generally speaking, the thickness of the side wall and the bottom of the cavity of the concave model can be determined by the strength calculation, but the punch and the core are usually determined by the internal shape of the product or the pass on the product, so the strength can only be checked during the design.
Because in the design of the use of inlaid circular cavity. Therefore, the calculation reference formula is as follows:
Basic characteristics: ABS is made of acrylonitrile, butadiene and styrene. The properties of these three components make ABS have good comprehensive mechanical properties. Acrylonitrile makes ABS have good chemical resistance and surface hardness, butadiene makes ABS tough, styrene makes ABS have good processability and dyeing performance. ABS is nontoxic, tasteless and yellowish. The plastic parts formed have good luster. The density is 1.02-1.05g/cm?.
ABS has excellent stamping strength and does not decrease rapidly at low temperature. It has good mechanical strength, wear resistance, oil resistance, water resistance, chemical stability and electrical performance. ABS has certain hardness and dimensional stability, and is easy to form and process. It can be matched into any color through color matching. Its disadvantages are low heat resistance, continuous working temperature of about 70 ° C, thermal deformation temperature of about 93 ° C. Poor weather resistance, hardening and embrittlement under the action of ultraviolet.
Main uses: ABS is widely used in water case, textile equipment, electrical parts, cultural and educational sports goods, toys, etc.
Molding features: ABS viscosity increases when heating up, so the molding pressure is relatively high, the demoulding slope on the plastic should be slightly larger, ABS is easy to absorb water, and should be dried before molding; weld marks are easy to occur, so attention should be paid to reducing the resistance of the gate to the flow channel during mold design; under normal molding conditions, wall thickness, melt temperature and shrinkage rate have little impact. When the precision of plastic parts is required to be high, the mold temperature can be controlled at 50-60 ° C. when the luster and durability of plastic parts are required, the temperature shall be controlled at 60-80 ° C.
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