Shanghai Daoqin Plastics Co., Ltd.

         design plastics 模时, mold structure 之後即 can for mold separation detailed design, 即确定各模 sheet/plate and parts dimensions, type and type dimensions and other. this will and has material shrinkage rate and other main/primary design parameters. has specific formed plastics shrinkage rate can type 腔各部 separation dimensions. make mold structure positive 确, use parameters 不当, can can production quality combined 格 塑 parts.

        一, plastics shrinkage rate and its effect/influence factors

         thermoplastic property plastics features is in add hot 後膨胀, cooling shrinkage, add pressure 以後体积也 will shrink small. in injection molding formed process in, will melt plastics injection mold type inner, 充填结束後熔 material cooling solid 化, from mold in 取出塑 parts 时即出现 shrinkage, shrinkage is formed shrinkage. parts from mold to stability this time inner, dimensions still 会出现 micro small 变化, types is shrinkage, shrinkage is shrinkage. types is certain wet property plastics wet 而出现膨胀.

        例如 nylon 6 10含 water amount is 3%时, dimensions increase amount is 2%; glass fiber reinforcement nylon 66 含 water amount is 40%时 dimensions increase amount is 0.3%. its in main/primary function is formed shrinkage. currently various plastics shrinkage rate (formed shrinkage +後 shrinkage) methods, generally recommendation Germany standards in DIN16901 规定. 即以23℃±0.1℃时 mold type dimensions and formed 形後放置24 small 时, in temperature degree is 23℃, versus for wet degree is 50±5% conditions lower amount versus parts dimensions 之差算出.

         shrinkage rate S由 lower table/sheet 示: S={(D-M)/D}×100%(1)

         its in: S- shrinkage rate; D- mold dimensions; M-塑 parts dimensions.

         if already parts dimensions and material shrinkage rate mold type is D=M/(1-S) in mold design in is 简化计算, generally use lower mold dimensions:

        D=M+MS(2).

         if 需实施 relatively is 精确 计算, application lower 式: D=M+MS+MS2(3)

        但 in shrinkage rate 时, 由於实际 shrinkage rate need more factors effect/influence can use value, use 式(2)计算 type dimensions basic upper meet/satisfy requirements. in manufacturing mold 时, type according to lower processing, type 芯则按 upper processing, necessary can as 适当 修整.

         difficult 於精确确定 shrinkage rate main/primary causes, is various plastics shrinkage rate is 一 定 value, is scope/range. is different factory production types material shrinkage rate same, make is factory production different 批号同 types material shrinkage rate 也不一样. 因而各厂 can is use provide production plastics shrinkage rate scope/range. its 次, in formed process in shrinkage rate also to parts 形状, mold structure and formed conditions and other factors effect/influence.

        二, parts 形状

         for formed parts thick 说, generally thick cooling time relatively long, shrinkage rate relatively large, 如图1 示. for generally parts 说, material flow direction L dimensions and 垂直於熔 material direction W dimensions relatively large 时, shrinkage rate 差异也 relatively large. from material flow 距离 看, gate separation pressure loss large, 因而该处 shrinkage rate ratio gate large. add strong/high 筋, 孔, and and other tool has shrinkage resistant force, this shrinkage rate relatively small.

        三, mold structure

         gate for shrinkage rate has effect/influence. use small gate 时, holding pressure 结束之 front gate solid make parts shrinkage rate increase large. injection molding in cooling structure is mold design in key/critical. cooling design 不适当, 则因塑 parts temperature degree 不均衡而 generate shrinkage 差, its is make parts dimensions ultra- 差 or deformation. in thin separation, mold temperature degree distribution for shrinkage rate effect/influence more is obvious.

         separation type and gate

         mold separation type 面, gate and dimensions and other factors effect/influence material direction, density distribution, holding pressure shrink function and molding time.

         using/adopting gate or large gate can decrease/reduce shrinkage, toward property large, material direction shrinkage small, 沿垂直 material direction shrinkage large;反之, gate thick degree relatively small 时, gate separation 会 早凝结 hard 化, type inner plastics shrinkage rear to and 时补充, shrinkage relatively large.

        点 gate fast, in made parts conditions 允许 情况 lower, can more gate, can has 效 延 long holding pressure time and increase large type pressure, make shrinkage rate decrease small.

        四, formed conditions

         material temperature degree: material temperature degree (plastics temperature degree) relatively high 时, pressure relatively good make shrinkage force decrease small. use small gate 时, gate solid 化早而 make shrinkage rate still relatively large. for thick parts 说, make material temperature degree relatively high, its shrinkage still relatively large.

        补 material: in formed conditions in, amount decrease/reduce material make parts dimensions maintain stability. material 不足则无 method maintain pressure, make shrinkage rate increase large.

         injection pressure: injection pressure is for shrinkage rate effect/influence relatively large factors, especially is 充填结束後 holding pressure 页号335 pressure. in generally lower, pressure relatively large 时因材 material density large, shrinkage rate relatively small.

         injection molding in pressure injection pressure, holding pressure pressure and mold cavity pressure and other. this factors for parts shrinkage is has obvious effect/influence.

         improve/increase injection pressure can reduce products shrinkage rate. this is is pressure increase large, make injection speed degree improve/increase, process add fast rear, 一方面因 plastics melt 剪切发 hot improve/increase melt temperature degree, decrease small flow retardant force;另一方面 also can in melt temperature degree high, flow retardant force relatively small lower relatively 早进入 holding pressure material stage/phase. especially for/regarding thin parts and small gate parts, due to cooling speed degree fast, more 应该尽 amount shrink short process.

         relatively high holding pressure pressure and mold cavity pressure make type inner products 密实, shrinkage decrease small, especially is holding pressure stage/phase pressure for products shrinkage rate generate effect/influence more large. this can understanding is melt resin in molding pressure function lower to pressure shrink, pressure high, pressure shrink amount large, pressure understanding remove rear elastic property 恢复也越 large, make parts parts dimensions more add type dimensions, therefore shrinkage amount small.

         can is, make is for/regarding products 说, mold cavity inner resin pressure in separation 并不一致; in injection pressure difficult function and easy function 部位, injection pressure 也不一样. in addition, more type mold mold cavity pressure design uniform, 否则就会 generate mold cavity products shrinkage rate 不一致.

         injection speed degree: injection speed degree for shrinkage rate effect/influence relatively small. for thin parts or gate non small, and use strong/high material 时, injection speed degree add fast shrinkage rate small.

         mold temperature degree: thermoplastic property plastics melt type rear, a large amount of hot amount solid, different plastics product types, need mold cavity in 一适当 temperature degree. in temperature degree lower, will most has 利于塑 parts molding, parts molding efficiency most high, internal stress and warpage deformation most small.

         mold temperature degree is control products cooling type main/primary factors, it for molding shrinkage effect/influence main/primary performance in gate rear products demolding front this process. in gate 冻结之 front, mold temperature rise high has increase large hot shrinkage trend, positive is relatively high mold temperature make gate time long, injection pressure and holding pressure force effect/influence reinforcement, shrink function and negative shrinkage amount increase large.

         therefore, shrinkage is types toward shrinkage comprehensive function 结果, its value 不一定随 mold temperature rise high increase large. if gate 发生冻结, injection pressure and holding pressure pressure effect/influence will 会消失, mold temperature rise high, cooling type time will long, demolding rear products shrinkage rate generally increase large.

         formed cycle: formed cycle and shrinkage rate 无直接关系. attention/notes, add fast formed cycle 时, mold temperature degree, material temperature degree and other 必然也发生变化, from effect/influence shrinkage rate 变化. in as material experiment/testing 时, according to 由 需 output/production volume formed cycle formed 形, for parts dimensions 进行检验. use mold plastics shrinkage rate experiment/testing 实例如 lower.

         injection machine: clamping force 70t, screw 直径Φ35mm, screw speed 80rpm.

         formed conditions: most high injection pressure 178MPa, material temperature degree 230(225-230-220-210)℃, 240(235-240-230-220)℃, 250(245-250-240-230)℃, 260(225-260-250-240)℃, injection speed degree 57cm3/s, injection time 0.44～0.52s, holding pressure time 6.0s, cooling time 15.0s.

        五, mold dimensions and manufacturing 公差

         mold type and type processing dimensions remove through D=M(1+S)公式计算 basic dimensions outer, also has processing issues. according to 惯例, mold processing is parts 公差 1/3. 但由於 plastics shrinkage rate scope/range and stability property has 差异, 首先必 must combined 理化确定 different plastics formed parts dimensions 公差. shrinkage rate scope/range relatively large or shrinkage rate stability relatively plastics formed parts dimensions 公差应取 large 一. 否则就 can can a large amount of dimensions ultra- 差 waste product. is 此, for plastics parts dimensions 公差专门 made 订 国家 standards or industry standards. China made 订 部 grade standards. large versus mold type dimensions 公差. Germany standards in made 订 塑 parts dimensions DIN16901 standards and versus mold type dimensions DIN16749 standards. standards in world upper tool has relatively large effect/influence, can plastics mold industry 参考.

        六, about/regarding parts dimensions and 允许偏差

         is combined 理 确定 different shrinkage features material formed parts dimensions 公差, let standards formed shrinkage 差△VS this concept. △VS=VSR_VST(4)

        式 in: VS- formed shrinkage VSR-熔 material flow direction formed shrinkage rate VST- and material flow direction formed shrinkage rate.

         according to plastics △VS value, will various plastics shrinkage features separation is 4 组. △VS value most small is high degree 组, type 推, △VS value most large is low degree 组. according to basic dimensions made precision technology, 110, 120, 130, 140, 150 and 160公差组. 并规定, use shrinkage features most stability plastics formed parts dimensions can selection 110, 120 and 130组. use shrinkage features in and other stability plastics formed parts dimensions selection 120, 130 and 140. if use this category of plastics formed parts dimensions selection 110组时, can can a large amount of dimensions ultra- 差塑 parts. use shrinkage features relatively plastics formed parts dimensions selection 130, 140 and 150组. use shrinkage features most plastics formed parts dimensions selection 140, 150 and 160组. in use 此公差 table/sheet 时, also attention/notes below/following 各点. table/sheet in generally use 於不注明公差 dimensions 公差. 直接标注偏差 公差 is use for parts dimensions 标注公差 公差 belt/tape. its upper, lower can design 人员自行确定. 例如公差 belt/tape is 0.8mm, can selection below/following various upper, lower 偏差构 formed, 0.0;-0.8;±0.4;-0.2;-0.5 and other. 每一公差组 in has A, B两组公差 value. its in A is mold parts combined formed dimensions, increase mold parts for combined 处不密 combined formed 错差. increase value is 0.2mm. its in B is 直接由 mold parts dimensions. precision technology is 专门设立 一组公差 value, tool has high degree requirements parts use. in use parts 公差之 front, 首先必 must use plastics suitable several 公差组.

        七, mold manufacturing 公差

         Germany standards for parts made versus mold manufacturing standards DIN16749. table/sheet in 共设4 types 公差. 不论何 types material parts, its in 不注明 dimensions dimensions mold manufacturing 公差均 use 序号1 公差. specific value basic dimensions scope/range 确定. 不论何 types material parts in and other degree dimensions mold manufacturing is 序号2 公差. 不论何 types material parts relatively high degree dimensions mold manufacturing is 序号3 公差. precision technology versus mold manufacturing is 序号4 公差.

         can combined 理 确定 various material parts combined 理公差 and versus mold manufacturing 公差, this not only to mold manufacturing belt/tape 方便, also can decrease/reduce waste product, improve/increase 经济效期益.