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The Solution For The Thickness of Plastic and Magnet Overmolding

In the design of functional plastic parts, the application of magnet embedding encapsulation technology is becoming increasingly widespread. From magnetic closure devices in smart homes to magnetic induction components in industrial sensors, precise control of encapsulation thickness is required to ensure product performance and reliability. The design of this parameter is not simply based on empirical values, but requires a systematic engineering approach that takes into account multiple factors such as material properties, magnet performance, and usage environment.

The determination of the thickness of the magnet coating should first consider the magnetic attenuation characteristics. Experimental data shows that under plastic wrapping conditions, the surface magnetic induction intensity of neodymium iron boron magnets decreases by about 8% -12% for every 1mm increase in thickness. Taking the common 10mm diameter cylindrical magnet as an example, when the coating thickness increases from 0.5mm to 1.5mm, the effective adsorption force may decrease by 40%. Therefore, the magnetic interface in consumer electronics products usually controls the thickness of the encapsulation within the range of 0.8-1.2mm, while maintaining sufficient magnetic force to meet the structural strength requirements.

The material selection has a direct impact on the design of the coating thickness. When using engineering plastics such as fiberglass reinforced nylon, due to the high strength of the material itself, the coating thickness can be reduced to 0.6-1.0mm; When using ordinary ABS or PP materials, it needs to be increased to 1.2-1.5mm to compensate for the difference in mechanical properties. The comparative test of a certain car door lock component shows that the impact resistance of PA66-GF30 material at a rubber coating thickness of 1.0mm is equivalent to the performance of ordinary ABS at a thickness of 1.5mm.

Structural mechanics requirements are another key consideration point. The coating layer needs to withstand assembly stress and repeated impacts during use, and its thickness is positively correlated with the size of the magnet. Engineering experience shows that for square magnets with a side length not exceeding 20mm, the coating thickness should not be less than 1/15 of the short side size of the magnet; For circular magnets with a diameter of 25mm or more, a coating layer of 2mm or more must be maintained to prevent cracking. A medical equipment manufacturer found through FEA analysis that optimizing the adhesive thickness of a 10mm magnet from 1.0mm to 1.3mm increased the pass rate of drop testing by 65%.

The production process parameters also affect the thickness design. During injection molding, a thin coating layer (<0.5mm) is prone to insufficient filling, while a thickness exceeding 3mm may cause shrinkage marks. By using a mold temperature machine to control the mold temperature within the range of 80-100 ℃, the flowability of the melt can be improved, making it possible to encapsulate thin walls below 0.8mm. The practice of a certain electric tool manufacturer has confirmed that after increasing the mold temperature from 60 ℃ to 90 ℃, the yield of 1.0mm encapsulated parts has increased from 85% to 97%.

The requirement for environmental adaptability cannot be ignored. In humid or chemically corrosive environments, the coating layer also needs to serve as a protective barrier. Industrial applications typically require a safety margin of 0.3-0.5mm increase in adhesive thickness and the use of flame-retardant modified materials. The case of magnet components in outdoor security equipment shows that a 1.8mm TPU coating layer can extend the service life by three times compared to a 1.2mm thick sample in salt spray testing.

Innovative solutions for specific application scenarios are emerging. When using magnetic permeability optimization design, by thinning the coating layer (locally to 0.5mm) at the corresponding position of the magnetic pole and maintaining the standard thickness in other areas, a balance between magnetic force and mechanical strength can be achieved. After applying this solution, a certain smart door lock manufacturer not only met the requirement of 200 opening and closing tests per day, but also increased the magnetic induction distance by 20%.

In the specific implementation process, it is recommended to use the DOE experimental design method to systematically optimize variables such as material selection, magnet size, and coating thickness. With the help of flow analysis software, the feasibility of forming at different thicknesses can be evaluated in advance, while magnetic testing instruments can accurately quantify the impact of thickness changes on performance. Professional mold manufacturers typically have a database of material thickness magnetic relationships, which can provide customers with accurate thickness design recommendations.