As shown in Figure 1, the charger shell is made of black ABS with a general precision level (Level 4). The surface is smooth, visually appealing, and features fine patterns. ABS is a thermoplastic polymer with a density ranging from 1.05 to 1.07 g/cm³, tensile strength between 30 to 50 MPa, flexural strength from 41 to 79 MPa, tensile modulus of elasticity spanning 1587 to 2277 MPa, and flexural modulus from 1380 to 2690 MPa. The shrinkage rate lies between 0.3% and 0.8%. ABS has excellent overall properties, including high impact strength, dimensional stability, ease of molding, and good heat and corrosion resistance. Additionally, it performs well in low temperatures. Currently, ABS is one of the most widely used and produced plastics.
Figure 1 Three-Dimensional View of the Charger Housing
Due to its high moisture absorption, ABS must be thoroughly pre-dried before molding. Drying at 80–90°C for at least two hours ensures a moisture content below 0.3%. Parts with high surface gloss require longer preheating—drying for at least three hours at 80–90°C.
Heating temperature significantly impacts material quality, as temperatures above the decomposition point (270°C) can degrade the plastic. The recommended temperature for the material barrel ranges from 180 to 260°C, with 245°C being optimal.
The wall thickness of the part is generally uniform, all exceeding the minimum thickness of 0.8mm, which ensures proper filling during injection molding without voids, as analyzed using Moldflow software. The plastic shell features complex structural elements such as two holes on the top, three grooves on the side, internal supports, and decorative patterns. It measures 66mm in length, 44mm in width, and 10mm in height, making it small yet intricate, thus requiring a three-plate, double-parting line mold with moderate precision.
Using UG software, the volume VV of a single plastic part is calculated to be 9.1 cm³, yielding a mass MM of 9.6g. Considering the sprue system, which accounts for 60% of a single part's volume, the sprue volume VsprueV_{\text{sprue}} is estimated at 5.46 cm³. The total volume for four parts plus the sprue is 41.86 cm³, and the total mass is approximately 43.95g.
Based on data from the "Practical Mold Technology Handbook" (Table 12-10), the injection molding parameters for ABS plastic are as follows:
These parameters can be adjusted appropriately during mold trials to optimize performance.
The primary parameters of an injection molding machine include nominal injection volume, injection pressure, injection speed, plasticizing capacity, clamping force, basic dimensions of the clamping unit, mold opening and closing speed, and dry cycle time. These factors are crucial for designing, manufacturing, and choosing the right injection molding machine.
Considering the actual injection volume should be between 20% and 80% of the rated injection capacity, the SZ-250/1250 horizontal injection molding machine is preliminarily selected, offering a nominal injection volume of over 270 cm³.
