Compared with metal parts, plastic electroplated products can not only achieve a good metal texture, but also reduce the weight of the product. While effectively improving the appearance and decoration of the plastic, it also improves its electrical, thermal and corrosion resistance. However, the selection of plastic materials for electroplating requires comprehensive consideration of factors such as material processing performance, mechanical properties, material cost, electroplating cost, ease of electroplating, and dimensional accuracy. Because of its structural advantages, it not only has excellent comprehensive properties, is easy to process and shape, but the surface of the material is easy to corrode to obtain a higher bonding force of the coating, so it is currently widely used in electroplating. So what are the factors that affect plastic plating?
One, injection machine selection
Improper selection of the injection machine, sometimes due to too high pressure, improper nozzle structure or mixing, which will cause greater internal stress on the part, which will affect the bonding force of the coating.
Two, plastic parts selection
There are many types of plastics, but not all plastics can be plated. Some plastics and metal coatings have poor bonding strength and have no practical value; some of the physical properties of some plastics and metal coatings, such as expansion coefficients, are too different, and it is difficult to ensure their performance in a high temperature difference environment. At present, ABS is the most used for electroplating, followed by PP. In addition, PSF, PC, PTFE, etc. also have successful electroplating methods, but they are more difficult.
Three, plastic parts modeling
Under the premise of not affecting the appearance and use, the plastic part shape design should meet the following requirements as much as possible.
(1) The metallic luster will make the original shrinkage more obvious, so the uneven wall thickness of the product should be avoided to avoid shrinkage, and the wall thickness should be moderate to avoid the wall being too thin (less than 1.5mm), otherwise It will cause poor rigidity, easy deformation during electroplating, poor adhesion of the coating, and deformation during use to cause the coating to fall off.
(2) Avoid blind holes, otherwise the treatment liquid remaining in the blind holes will not be easy to clean, which will cause pollution in the next process and affect the quality of electroplating.
(3) The electroplating process has the phenomenon of thickening of sharp edges. The sharp edges in electroplating will cause the tip discharge, causing the corner plating to bulge. Therefore, rounded corners should be used as much as possible, and the radius of rounded corners should be at least 0.3mm. Flat-shaped plastic parts are difficult to electroplating. The center part of the plated parts has a thin coating. The more the edge is, the thicker the coating will be. The entire coating is uneven. The flat surface should be changed to a slightly rounded surface or an orange peel pattern should be used to make a matte surface. . The greater the surface area of the plating, the greater the difference in gloss between the center and the edge. A slightly parabolic surface can improve the gloss uniformity of the plating surface.
(4) Minimize grooves and protrusions on plastic parts. Because the deep concave part is easy to expose plastic during electroplating, and the protruding part is easy to be scorched. The depth of the groove should not exceed 1/3 of the groove width, and the bottom should be a circular arc. When there is a grid, the hole width should be equal to the beam width and less than 1/2 of the thickness.
(5) The plated parts should be designed with enough mounting positions, and the contact surface with the hanging tools should be 2 to 3 times larger than the metal parts.
(6) The design of the plastic part should make the part easy to demold when it is sinking, otherwise the surface of the plated part will be strained or sprained during forced demolding, or the internal stress of the plastic part will be affected and the coating bonding force will be affected.
(7) When knurling is required, the knurling direction should be consistent with the demolding direction and be in line. The distance between knurled stripes and stripes should be as large as possible.
(8) Try not to use metal inserts for plastic parts, otherwise the inserts will be easily corroded during pre-plating treatment.
(9) The surface of the plastic part should be guaranteed to have a certain surface roughness.
Four, mold design
In order to ensure that the surface of the plastic plated parts is free of defects, no obvious directional structure and internal stress, the following requirements should be met when designing and manufacturing the mold.
(1) Do not use beryllium bronze alloy as the mold material. It should be made of high-quality vacuum cast steel. The surface of the cavity should be polished along the mold ejection direction to a mirror-brightness with an unevenness less than 0.2mm. The surface is best plated with hard chrome.
(2) The surface of the plastic part faithfully reflects the surface of the mold cavity, so the mold cavity of the electroplated plastic part should be very smooth, and the surface roughness of the mold cavity should be 1 to 2 levels higher than the surface roughness of the part.
(3) Parting surface, weld line and core inlay line cannot be designed on the plating surface.
(4) The gate should be designed at the thickest part of the part. In order to prevent the melt from cooling too fast when filling the mold cavity, the gate should be as large as possible (about 10% larger than the ordinary injection mold). It is best to use the gate and runner with circular cross section, and the runner length should be shorter.
(5) Exhaust holes should be left to avoid defects such as air filaments and bubbles on the surface of the part.
(6) When selecting the ejector mechanism, ensure the smooth demolding of the part.
