Shanghai Daoqin Plastics Co., Ltd.

        1, precision injection molding concept

         precision injection molding is processing molding injection molding products dimensions heavy degree very high, use general purpose injection molding machine, injection molding process difficult to requirements types injection molding methods.

        “ precision injection molding ” this concept, main/primary is difference 于“常规 injection molding ”, it is polymer/macromolecule material speed development, in table/sheet, electronics field/area using/adopting precision plastics parts high degree metal parts technology. currently for precision injection products indicators has 两: is products dimensions heavy degree, is products quality heavy degree. main/primary from products dimensions heavy degree 方面阐述 precision injection molding. due to various material property and processing process different, can plastics made parts degree and metal parts degree and other 同起.

         molding products mold is 决定该 products can to design requirements dimensions important conditions, precision injection molding machine is ensure products in requirements dimensions scope/range inner molding, and ensure high formed product rate key/critical equipment.

         plastics products most high degree and other grade is grade.

        1.1    precision injection features

        (1) made parts dimensions degree high, small, has high degree dimensions 界限;

        (2) products weight heavy degree high, requirements has day, month, year dimensional stability;

        (3) mold material good, rigid property 足, type dimensions degree, light degree and sheet/plate 间 定位精 degree high;

        (4) using/adopting precision injection machine more 换常规 injection machine;

        (5) using/adopting precision injection molding process;

        (6) selection precision injection molding material.

        评定 products most important technology indicators, is injection molding products degree (dimensions 公差, 形位公差 and products surface light degree). injection molding precision plastics products, from material selection, mold design, injection molding process, as technology water and other 4 large factors 进行严格 control.

         precision injection molding machine requirements products dimensions degree generally in 0.01～0.001mm以 inner, many precision injection molding also requirements injection molding machine tool has high injection pressure, high injection speed degree; requirements clamping system tool has large rigid property and high 锁模精 degree, 谓锁模精 degree is clamping force uniform property, can 调, stability and heavy property high, clamping 位置精 degree high; requirements for pressure, amount, temperature degree, amount and other can control to versus 应 精 degree, using/adopting more grade or grade injection, ensure molding process again conditions and products dimensions heavy degree and other.

        1.2  effect/influence products dimensions degree factors

        (1) mold degree;

        (2) molding shrinkage;

        (3) products use ring temperature degree, wet degree and 波动 幅 degree.

        2, most is what?

         machine strong/high degree high, dimensional stability good, resistant creep property can good, ring 境适应 scope/range 广.

         commonly used has types material:

        (1) polyoxymethylene (POM) （POM） and carbon fiber (CF)  reinforcement or glass fiber (GF) reinforcement POM. this type of material features is creep resistance can good, resistant fatigue, weather resistance, electrical property can good, flame resistant, add lubricant easy demolding.

        (2) nylon （PA） and GF reinforcement PA66. features: impact resistant can force and wear resistance can strong/high, flow property can good, can molding 0.4mm壁 thick products. GF reinforcement PA66 tool has relatively high heat resistant property (melting point 250℃), its disadvantages is tool has wet property, generally molding rear need through wet 处理.

        (3) reinforcement polyester, polybutylene terephthalate (PBT) （PBT）. molding time short. molding time comparison lower: PBT≤POM≈PA66≤PA6.

        (4) polycarbonate (PC) （PC） and GF reinforcement PC. features: good wear resistance, reinforcement rear rigid property improve/increase, dimensional stability good, weather resistance, flame resistant and molding processing property good.

        3, precision injection molding in shrinkage issues

         effect/influence shrinkage factors has types: hot shrinkage, versus shrinkage, orientation shrinkage and pressure shrink shrinkage.

        3.1   hot shrinkage. hot shrinkage is molding material and mold material solid has hot material features. mold temperature degree high, products temperature degree high, shrinkage rate increase, therefore precision injection mold temperature degree high.

        3.2   versus shrinkage. due to crystallization type resin in toward process in, polymer/macromolecule crystallization 化, ratio decrease/reduce 而引起 shrinkage, versus shrinkage. mold temperature degree high, crystallization degree high, shrinkage rate large;但另一方面, crystallization degree improve/increase make products density increase, 线膨胀系数 decrease small, shrinkage rate reduce. therefore shrinkage rate 由两者 comprehensive function 而定.

        3.3   orientation shrinkage. due to separation in flow direction upper strong/high tensile, make in cooling large separation has heavy new 卷曲恢复 trend, in orientation direction will generate shrinkage. separation orientation degree and injection pressure, injection speed degree, resin temperature degree and mold temperature degree and other has 关. main/primary is injection speed degree.

        3.4   pressure shrink shrinkage and elastic property 复位. generally plastics tool has pressure shrink property. in high pressure lower ratio 容发生 significantly 变化. in generally temperature degree lower, improve/increase pressure molding products ratio decrease small, density increase, 膨胀系数 decrease small, shrinkage rate significantly decline. for pressure shrink property, molding material tool has elastic property function, make products shrinkage decrease small. effect/influence products molding shrinkage factors and molding conditions and as conditions has 关.