33 reasons for the production of black spots in all products
2016-8-31 16:07:27
One, what is the thin wall injection molding Thin wall injection molding technology is also known as thin wall plastic parts injection molding technology. About its definition of the following three: A: the flow length and thickness ratio L/T, flow length L cavity from the melt into the mold to melt filling the furthest point and the corresponding average wall thickness ratio of T in 100 or more than 150 of the injection molding for thin-wall injection; Second: the plastic molding thickness less than 1 mm, and the projection area on a plastic injection molding method of more than 50 square meters c; Third: the wall thickness of the molded plastic parts is less than 1 mm (or 1.5mm), or t/d (plastic thickness T, plastic parts diameter D, for the disc type plastic parts) in 0.05 of the following injection molding is defined as thin wall injection molding. It can be seen that the definition of the critical value of thin-walled injection molding will also change, it should be a relative concept. Two, the choice of raw materials The requirements on raw materials: high flow length, high impact strength, high heat deformation temperature, high thermal stability, low directivity and good dimensional stability; consider plastic raw materials, low temperature impact rigidity, flame retardancy, mechanical assembly and appearance quality etc.. The materials used are: thin injection molding of polycarbonate (PC), acrylonitrile - butadiene - styrene (ABS), PC /ABS and PA6 blends. As the wall thickness decreases, the plastic is needed to maintain the strength of the product with better physical properties. Three, common defect analysis While the plastic part has many advantages, it can reduce the formability of the plastic parts, so that the thin wall plastic parts can not be formed by the conventional injection molding method. During the forming of thin wall plastic parts, there are some common problems: 1, short shot Short shot refers to the incomplete quality defect caused by the filling of the mold cavity, that is, the melt has been condensed before the completion of the filling. The filling process and cooling process of conventional injection molding are intertwined. When the melt flow of polymer melt, the melt front meets the core surface or the cavity wall with lower relative temperature, and a layer of condensation layer is formed on the surface of the polymer melt. The melt flows forward in the condensing layer. With the increase of the thickness of the condensation layer, the flow channel of the actual channel becomes narrow and the thickness of the condensation layer has a significant effect on the flow of the polymer. Because of the thickness of the plastic part in the conventional injection molding, the influence of the condensation layer on the injection molding is not very great. But in the thin wall injection molding, when the ratio of the thickness of the condensation layer and the thickness of the plastic part increases gradually with the thickness of the plastic part, the effect is very great. In particular, the size of the two can be more prominent when compared with each other. When the thickness of the plastic part is reduced, the influence of the condensation layer on the flow will be increased in exponential form, which also shows the influence of the condensation layer in the thin wall injection molding. If only from the injection molding, injection molding machine needs to have high injection rates, the rate of the plastic melt filled cavity over layer growth rate of condensation (or the condensate layer growth rate is slow, so it) can be filled in action before the closure of the flow section, injection molding thin wall plastic parts. When the flow length is 300mm, the wall thickness of plastic parts is 3 mm, the L/T was 100, with the conventional injection molding technique is easy to achieve; but when the wall thickness of plastic parts decreased to below 1.0mm, the once easily reach the flow length / thickness ratio (100) becomes very difficult to achieve. 2, warping deformation Warping deformation is an inhomogeneous internal stress resulting from defects of the plastic parts. The reason of warping deformation is that the shrinkage is not uniform, the orientation is not uniform and the cooling is not uniform. Methods: by improving balance cooling system, adjust the cooling time, packing pressure and packing time and other measures to improve the warpage of the product defects. 3, welding wiring Weld line is the boundary line formed by the fusion of two or more melt flow front in the mold cavity. It is easy to produce stress concentration and weaken the mechanical strength of the plastic parts in the weld line, especially the mechanical properties of the plastic parts, especially the thin wall plastic parts. Methods: improvement in the design can reduce or change the weld line by reducing the number of gates or changing the position of the gate position, to meet the design requirements of plastic parts. 4, lack of material Small parts and finished products at the corner of not fully formed, because the mold is not in place or poor exhaust, forming due to injection dose or insufficient pressure, resulting in the design defects (lack of flesh). Methods: the lack of material can be modified to improve the mould, adopted or modified exhaust measures, and improve the flesh, the gate (gate, gate, increase increase) increase the dose, increasing the injection pressure and other measures to improve. 5, shrink Often occurs in the molding thickness or thickness uneven, due to different cooling or hot melt plastic shrinkage and curing. As the rib on the back, the side wall of the edge, the back of the BOSS column to steal meat, but at least 2/3 flesh. Improvement: can prolong the dwell time through bold measures to improve channel, enlarge gate, exhaust, elevated temperature, injection pressure, increase. 6, surface image Often occurs in the back after the stolen meat BOSS column, or ribs, or as the core, the thimble design caused by excessive stress reducing marks. Improve methods: through modified core, thimble, mold surface blasting treatment, the lower mold surface brightness, lower injection speed, reduce injection pressure etc.. 7, gas lines The injection speed and the pressure is too high, the injection speed is too high, the injection gate is arranged improperly, and the plastic is in the disturbed flow structure. The improvement method: by changing the gate channel, channel lighting, cold material, into the gate, to increase the increase on the surface of bite flower (by machine or mold repair line can solve, catch with) the mold temperature increased, reduce the injection speed, decrease injection pressure etc.. 8, combined with the line Occurred in the two streams confluence, such as the two gate of the flow of material flow, bypassing the core of the material flow, is due to the decline in material temperature, exhaust caused by. Improvement: through changes in the gate, and the cold well, open the exhaust groove or male mold surface texture etc., also can increase the melt temperature, mold temperature increased. 9, flash The combination of male and female die often occurs, due to poor close mode, or the mold surface edge angle is not processed properly, the molding is often due to the locking force is not enough, the material temperature, pressure is too high. Improvement: can die modification, re mold, increase the clamping force, reduce the material temperature, reduce injection pressure, reduce the pressure holding time, reduce the pressure. 10, deformation Long and thin piece, large area thin wall part, or structural asymmetry of the larger finished product due to the cooling stress is uneven or the top of the force is not a result of. Improve methods: modified thimble, setting up the tension effect of pull pin, when necessary with the male die bite flower regulation deformation, adjustment of male and female mold temperature decreased pressure, small deformation regulation mainly depends on the pressure and pressure time, large deformation of the general regulation of temperature profile. 11, the surface is not clean Is due to the rough surface of the mold. Methods: to improve the PC material, sometimes because the mold temperature is too high, the die surface residue, grease, need to clear the mold surface, polishing treatment, reduce the mold temperature. 12, pull the white Easy to occur in molding thin-walled corner or thin-walled RIB root, is due to release stress caused by bad or improper thimble draft is not enough. The improvement method: increase the corner angle of R, increase the release angle, increase or increase the sectional area of the thimble, thimble or die surface polishing, oblique pin lighting, reduce speed, reduce injection pressure, reduce the pressure and time etc.. 13, die To release or die bad injury, lahua. Mainly because the draft is not enough or die surface roughness, also affect the molding conditions. Improve methods: increase the draft angle of die surface polishing, stick mold surface can increase or change the pull pin, the feed horn note horn diameter, male mold and texture, reduce injection pressure, reduce the pressure and time etc.. 14, stomatal Transparent finished PC material forming is easy to appear. Because the gas is not discharged in the process of injection molding, the mold design is improper or the forming condition is improper all has the influence. To improve the methods to increase the exhaust gate (gate change increases), PC material flow must be smooth, strictly drying conditions, increasing the injection pressure, injection speed decreased. 15, broken Occurs in the joint of the male and female module, the sliding block and the slanting pin, and the level of the binding surface is not neat, etc., because of the improper mold closing or the mold itself. Improvement: Die revision, or re closing. 16, size tolerance The mold itself, or improper molding conditions caused by improper molding shrinkage rate is not suitable. Methods: the effect of holding pressure time and injection pressure (second segments) on the size of the largest. For example: improve the injection pressure, improve the compression effect can significantly increase the size, reduce the mold temperature can also increase the gate or increase the gate can improve the effect of regulation.
