模内微装配成型预成型微型部件颈缩熔断的失效机理
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摘要
基于聚合物微型机械模内微装配成型加工面临的共性关键科学问题——在二次成型高温熔体充填流动环境下,如何避免预成型微型部件产生颈缩熔断失效问题,研究建立了高温熔体充填流动诱发颈缩熔断失效过程的机理模型。研究表明,预成型微型轴颈缩熔断损伤的直接驱动力是应变软化,一旦预成型微型轴出现应变软化,就必然会诱导颈缩熔断损伤。而应变软化现象的形成受控于其材料的初始屈服应力,初始屈服应力与二次成型注射温度呈负关联关系。当熔体注射温度由200℃增至240℃时,聚甲基丙烯酸甲酯(PMMA)微型轴的初始屈服应力由16.5 MPa降至9.89 MPa,降幅高达40.1%,而其颈缩断面的颈缩率由44.5%增至70%。二次熔体注射温度越高,微型轴越易诱发应变软化和颈缩熔断损伤。
How to avoid the necking and fusing failures of preformed micro component under the environment of high temperature melt filling flow is a critical scientific problem for the in-mold micro assembly process of polymer micro machine. In this paper, we established a mechanism model of necking and fusing failure for the preformed micro-component induced by high-temperature melt filling flow. The investigation results indicated that the direct driving force of necking and fusing failure for preformed micro-size shaft was derived from its strain softening. Once the strain softening was induced, the necking and fusing damages for preformed micro-size shaft might happen. The strain softening phenomena were controlled by the initial yield stress of preformed micro-size shaft and were negatively correlated with the secondary molding injection temperature. The initial yield stress of preformed PMMA micro-size shaft decreased by 40.1 % from 16.5 MPa to 9.89 MPa when the injection temperature increased from 200 ℃ to 240 ℃. The necking shrinkage of neck section increased from 44.5 % to 70 %. The higher the secondary molding melt injection temperature, the easier was the strain softening and necking fusing failure of preformed micro-size shaft.
How to avoid the necking and fusing failures of preformed micro component under the environment of high temperature melt filling flow is a critical scientific problem for the in-mold micro assembly process of polymer micro machine. In this paper, we established a mechanism model of necking and fusing failure for the preformed micro-component induced by high-temperature melt filling flow. The investigation results indicated that the direct driving force of necking and fusing failure for preformed micro-size shaft was derived from its strain softening. Once the strain softening was induced, the necking and fusing damages for preformed micro-size shaft might happen. The strain softening phenomena were controlled by the initial yield stress of preformed micro-size shaft and were negatively correlated with the secondary molding injection temperature. The initial yield stress of preformed PMMA micro-size shaft decreased by 40.1 % from 16.5 MPa to 9.89 MPa when the injection temperature increased from 200 ℃ to 240 ℃. The necking shrinkage of neck section increased from 44.5 % to 70 %. The higher the secondary molding melt injection temperature, the easier was the strain softening and necking fusing failure of preformed micro-size shaft.
引文
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[2] WOJCIECH B. In-Mold Assembly of Multi-Functional Structures[D]. 2010, University of Maryland, USA.
[3] ISLAM A, HANSEN H, MARH?FER M, et al. Two-Component Micro Injection Moulding for Hearing Aid Applications[J]. the International Journal of Advanced Manufacturing Technology, 2012, 62(5/8):605-615.
[4] MICHAELI W, KAMPS T. Micro Assembly Injection Moulding with Plasma Treated Inserts[J]. Microsyst Technol, 2008,14(12):1 903-1 907.
[5] ATTIA U M, HAUATA M, WALTON I, et al. Creating Movable Interfaces by Micro-Powder Injection Moul-ding[J]. Journal of Materials Processing Technology, 2014, 214(2):295-303
[6] MEISTER S, DRUMMER D. Micro Assembly Injection Moulding with Variothermal Mould Tempering[J]. Microsystem Technologies, 2017, 23(4):1 017-1 025.
[7] 周国发, 胡舵, 刘岑. 剪切变稀效应对微型机械模内组装成型流固耦合变形的影响[J]. 高分子材料科学与工程,2012,28(12):183-186. ZHOU G F, HU D, LIU C.Influence of Shear-Thinning on Polymer Micromachine Fluid-Solid Coupling Deformation in In-Mold Assmbly Molding Process[J]. Polymer Materials Science and Engineering, 2012, 28(12):183-186.
[8] 周国发,王文光,刘岑. 过程参数对微型机械模内组装成型流固耦合变形影响[J]. 塑性工程学报,2012, 19(1):107-112. ZHOU G F, WANG W G, LIU C. Influence of Process Parameters on Polyme Micromachine Fluid-Solid Coupling Deformation in In-Mold Assembly Molding Process[J]. Journal of Plasticity Engineering, 2012, 19(1):107-112.
[9] 杨先鲁. 聚合物微型机械模内组装成型过程数值模拟研究[D]. 南昌: 南昌大学, 2013.
[10] 周国发, 阳培民, 罗智, 等. 基于黏弹性热流固耦合作用的模内微装配成型过程数值模拟[J]. 化工学报, 2017, 68(3):1 129-1 137. ZHOU G F, YANG P M,LUO Z, et al. Numerical Simulation on In Mold Micro Assembly Molding Process Based on Viscoelastic Thermal Fluid Structure Coupling[J]. CIESC Journal,2017,68(3):1 129-1 137.
[11] 江先念. 多场耦合作用下模内微组装成型机理研究[D]. 南昌: 南昌大学, 2016.