[Abstract] Through this article, the article introduces the cases of rectifying defects of molded parts, and the main content is how to apply molding trace technology to rectify various defects of molded parts. That is to say, through the identification, analysis and interpretation of various molding traces of problem parts; So as to find out the causes of the defects in molding; Then find a way to cure the defects of molded parts, so as to achieve the purpose of radically curing the defects of molded parts; It is also fully proved that the molding trace technology can be applied to cure all kinds of defects of molded parts. The forming marks on the formed parts are objective facts. The question is how to apply the forming marks technology to analyze the defects of the formed parts. The case provides some skills and methods to deal with the defects of molded parts by applying the molding trace technology.
Key words: molding mark molding mark technology to rectify the shortcomings of product quality
[Abstract]: Through the introduction of five cases about molding defects rectification, this article indicates how to fix molding defects by using molding trace technique. In other word, the reasons of molding defects can be found by identificating, analysing and interpretating the molding traces on issued moulds; by doing that, the most efficient method can be found to fix the molding defects; it is also proved that various molding defects can be fixed completely by molding trace technique. It is objective fact that molding traces exist on m oulds, the question is how do we utilize trace technique to analyze the molding defects? The molding defect cases offered techniques and methods to treat molding defects base on molding trace technique.
Keywords: molding trace, molding trace technique, defects rectification, product quality
1 introduction
The newly manufactured injection molds need to be tested to check whether the molds are qualified. However, there are many factors to judge whether a mold is qualified. There are factors of product structure design and modeling; There are factors of mold design and manufacture; There are factors of plastic parts materials; There are factors of machine tool equipment selection; There are factors to choose molding process parameters; There are also factors of pre-treatment and post-treatment of plastic parts materials. If we want to find out the defects that affect the problem parts in the test, we can find out the real causes of the defects by distinguishing and analyzing the molding marks on the outer surface and the inner part of the problem parts. Finally, we can find the measures to rectify the defects and solve them easily. Because, the factors causing defects in the forming process of plastic parts always leave corresponding traces on the plastic parts. These molding marks are the best basis for us to analyze and solve the defects of problem parts.
2 Case 1: Determine the plastic material and filler composition according to the service condition and traces of the molded parts
2.1 information of molded parts
Name and composition of molded part: Transfer switch assembly, which consists of a large part 1 and a small part 2, and three inserts 3 are installed on the large part 1, as shown in Figure (1). This product is a change-over switch on a mechanical hand in a production line, which is connected with air source, and its working pressure is 3 atmospheres, so it needs to complete two turning movements at 26 degrees. It is a localized export type product, and it must be interchangeable with imported parts after localization.
2.2 technical requirements of molded parts
There are seven holes with 1-φ14H8 mm, 3-φ6G7 mm and 3-φ4H8 mm for large pieces, and four holes with 1-φ14H8 mm and 3-φ6G7 mm for small pieces. The precision of the hole is high, and the taper and ovality cannot be greater than 0.01 mm Otherwise, the change-over switch is prone to air leakage and cannot maintain 3 atmospheres, and the manipulator cannot work normally. After the big and small pieces are bonded, the seven holes should keep the same coaxiality, the joints should not leak air, and the three Φ φ1．8 mm vent holes between the bonding surfaces should not have the phenomenon of cross-talk and gas blocking, and have certain strength. The surface of the product is matt, smooth and delicate.
2.3 material condition of molded parts
Because the material of the imported parts is not clear, the manufacturer first used PTFE to test the mold, and many problems appeared.
2.4 status of problem parts
Polytetrafluoroethylene with shrinkage of 3.1 ~ 7.7%. Shrinkage marks are large and numerous, warpage and deformation are serious, the roughness of the bonding surface exceeds 0.4 mm, the gap between the two pieces is 0.7 ~ 0.8 mm, and the ovality and taper of the seven holes are also very large, which can not meet the use requirements completely.
2.5 treatment plan
It is necessary to identify the material of imported parts and the composition of filler, and then apply the methods of selecting appropriate injection equipment and adjusting injection process parameters to reduce shrinkage and deformation of molded parts.
2.6 analysis of defects of problem parts
Shrinkage marks are a phenomenon, and deformation is the main cause, which is caused by improper selection of materials. In other words, the shrinkage of materials is the main contradiction between deformation and shrinkage marks.
2.7 rectification process of problem parts
First determine the material of plastic parts to control the deformation and shrinkage marks of plastic parts; Then arrange the technological process to radically cure the silver marks and overheating marks of plastic parts; Finally, the problem of non-cylindricity of cylindrical hole of plastic parts is solved by using the secondary restrictive shrinkage of plastic in the molding process.
2.7.1 determine the material of plastic parts to cure the deformation and shrinkage marks of plastic parts
First, the physical method (fire) is used for analysis, then the chemical method (dichloroethane or chloroform) is used for analysis, and then the spectral analysis method is used. Make sure that the material of imported parts is PC. The shrinkage of pure PC is 0.5 ~ 0.7%, which is still too large. Then 30% glass fiber reinforced polycarbonate was used for mold testing, and the injection process parameters were constantly adjusted. The shrinkage mark of the product disappeared completely, and the ovality and taper of the hole were controlled within 0.06 mm However, the over-tolerance of ovality and taper is still serious, which still needs to be rectified. The plane roughness is within 0.03 mm, which can meet the bonding requirements of molded parts. Because glass fiber is suspended on the surface of the molded part, the surface of the change-over switch appears rough, so only the glass fiber is removed and the filler is added. After that, 25% glass beads were used as filler, and its shrinkage rate was 0.3% ~ 0.4%, which not only solved the problem of rough surface, but also improved the wear resistance of products, and the performance of products exceeded that of imported parts.
