BÁO CÁO CÔNG NGHỆ NHỰA ĐỦ 25 BÀI_SPKT
DEFECTS IN INJECTION MOLDING PRODUCTS 1) Products deviations size Reason The variables that influence shrinkage - Shrinkage in molding If the thickness of the product increases, the shrinkage increases - shrinkage after the product removed from the mold - Pressure: + Long retention time and maximum pressure higher, lower shrinkage -Temperature: + If the temperature increases, the shrinkage increases in the process of injection - Molecular orientation in injection molding: + The molecular orientation due to shear modulus and is retained by the combination with the process of cooling 2) Products warping Reason The variables that influence Solution - Shrinkage change across products - Thickness difference in product - Increased time and pressure - Products take off too soon, therefore the product - - Controlled the temperature on the surface of the is not shaped + The material compression uneven mold - Mold design inconsistent and thickness difference - - Test the structure of product and the accuracy of in product + High mold temperature would make that the Influence of pressure Influence of temperature product product cool slowly => warping increases - Influence of Molecular orientation: + The orientation is not the same => very high risk of warping - Avoid internal stress by choosing materials and shapes products 3) Focus Bubble Description - The gas bubbles form the hole inside product or Reason - make products that are not filled completely When products have the gas line focus, Air Solution - is pushed into one place cause air bubbles - The air is left in the product in the area product filled final cause air bubbles Design thickness of production in the appropriate positionĐổi vị trí cổng phun - Reduce speed injection Optimized exhaust system Reduce the pressure lossy of the screw or reduced pressure by reducing the speed - If there are air bubbles, you need to put them in areas that can exhaust or more the entrance to the exhaust sound 4) Products with the dimples Reason - Material shrinkage Where the crust of hard enough to not be shrinkage, the product will form a hollow inner part Solution - Change the parameters pressed (pressure, temperature, time) Changes plastic shrinkage coefficient smaller 5) The phenomenon of injection lack : Reason Solution - Melting temperature, mold temperature and injection speed too low - Increased melting temperature or temperature mold and injection speed - - Plastics are not flexible Valve exhaust system mismatch: The air in the mold is not drained Product thickness too small or too long Lack of raw materials (installation screw itinerary insufficient) Low injection pressure - The glossy surface of the mold should not hinder the flow Increased volume injection (injection volume is too small, no buffer) Install matching between injection pressure and injection volume, increased injection pressure - Improved exhaust valve system, reducing mold clamping force Increased the size channel system (runner) - If the temperature is low, increase the temperature mold 6) Products with burrs Reason - Solution Moldmaking inaccuracies, errors between the two halves of the mold too - big or mold damage - Mold clamping force is too low - Reduce the injection pressure, speed injection or pressure smaller mold too high - - Mold does not close by: mold mounting unmatched, with channels (due to - - Melting temperature, cylinder temperature, injection speed or pressure in the dirt, corrosion) Repair mold and Correct damaged places Mold clamping forces higher or change larger machine Reduced melting temperature and mold temperature Check the correct surface fabrication closed mold Select the appropriate port position 7) Products have welded Reason - Similar to the product not filling the mold Solution - Check the exhaust system of mold or adding gas drainage - Design unreasonable gateway - Can be designed to take the road to the location weldline unseen - The air is trapped - Use materials with lower viscosity - Influence of color, the position weldline usually affects the mechanical - Identification of specific areas by analyzing MOLDFLOW properties 8) Products with many wrinkles Reason - Surface product uneven - Injection pressure is low Mold temperature is too high - Gateway is size too small or high Cách khắc phục - Reduced thickness Make multiple tendon 9) Surface peeling, scratch, uneven Description - Reason The surface is separated into sheets, flake - Very difficult to identify because the surface is - The dirt incompatible with thermoplastic not cracked - The surface is damaged when using hard objects scratch lightly High shear modulus layers formed Solution - Increased temperature and decreased speed injection 10) Cracks Reason - The impact from the outside, appears as the power grab Due to residual stresses form Internal stress in the parameters by pressing inappropriate Solution - Reduce the force on mold or using thermoplastic less susceptible to stress - Review the design of products to improve the flow Increase the mold surface temperature and melting temperature of the - Because of structural weaknesses products difficult to obtain products from plastic, reducing pressure maintenance, reset the time and injection speed the mold or adhesive partial product in the mold accordingly - - Reduce the injection pressure, reduced pressure compression Reduce mold temperature, check the temperature uniformity mold 11) Products with black burn marks Reason - High pressure injection The temperature of the plastic is too high Air is trapped in the mold Solution - Reduce injection pressure, injection speed Check the exhaust system