Plastic electroplating is a kind of electroplating process developed with the wide application of plastics. It can not only save a lot of metal materials, reduce the complexity of the processing process, reduce the weight of the equipment, but also effectively improve the appearance and electrical and thermal properties of the plastic parts, and improve its surface mechanical strength. Therefore, it has been widely used in electronic industry, national defense research, household appliances and even daily necessities. The quality of plastic electroplating is not only closely related to electroplating process and operation, but also has a great relationship with plastic parts design, material selection, mold design, plastic molding process, plastic parts post-processing and other factors. There are many factors affecting the quality of plastic electroplating, such as improper selection of plastic parts, unreasonable design, unreasonable mold design, improper selection of injection molding machine, incorrect molding process conditions, etc.. Various factors may also be intertwined with the impact of plastic plating.
Influencing factors of plastic electroplating
1. Material selection of plastic parts
There are many kinds of plastics, but not all plastics can be electroplated. Some plastic and metal layer binding force is very poor, no practical value; some plastic and metal plating of some physical properties such as expansion coefficient difference is too large, in high temperature difference environment is difficult to ensure its performance. At present, ABS is the most widely used electroplating, followed by PP.
2, plastic parts modeling design
Under the premise of not affecting the appearance and use, the plastic parts should be designed to meet the following requirements.
(1) metallic luster will cause the original deflated becomes more obvious, so to avoid products uneven wall thickness, so as to avoid the deflated, and wall thickness should be moderate, lest the wall is too thin (less than 1.5mm), otherwise it will cause poor rigidity, easy deformation in electroplating, poor adhesion, use the process is also prone to deformation and peeling.
(2) avoid blind hole, otherwise the residual liquid in the blind hole is not easy to clean, which will lead to the pollution of the next process, thus affecting the quality of electroplating.
(3) the plating process has sharp edge thickening phenomenon. Sharp edges in electroplating lead to point discharge, which results in bulge of edge and corner coating. Therefore, fillet transition should be used as far as possible, and fillet radius is at least 0.3mm.
(4) reduce the groove and the protruding part as possible as possible.
3. mould design and manufacture
In order to ensure that the plastic plating surface has no defects, no obvious directional structure and internal stress, the design and manufacture of the mold should meet the following requirements.
(1) the mould material should not be made of beryllium bronze alloy, and should be made of high quality vacuum cast steel. The surface of the cavity should be polished to the surface of the mirror along the direction of the die, the roughness is less than 0.2m, and the surface is hard to be plated with hard chromium.
(2) the surface of the plastic parts truthfully reflects the surface of the mold cavity, so the mold cavity of the electroplating plastic parts should be very smooth, and the surface roughness of the mold cavity should be 1~2 higher than the surface roughness of the workpiece.
(3) parting surface, weld line and core inlay line can not be designed on the plating surface.
4. Selection of injection machine
Injection machine is not suitable, sometimes because of the pressure is too high, nozzle structure is not suitable or mixed material to produce larger internal stress, thereby affecting the adhesion of the coating.
5. Forming process of plastic parts
Due to the forming process characteristics, the injection molding parts inevitably exist internal stress, but the proper control of the process conditions will reduce the internal stress of the plastic parts to the minimum extent, and ensure the normal use of the parts.