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The process capability of multi-cavity pressure control for the injection molding process. 多腔的注射成型加工中对压力控制的能力 翻译：多腔的注射成型加工中对压力控制的能力论文摘要：模腔压力被认为是对高质量注塑的热塑性部分的一个关键工艺参数。这种研究就是闭环模腔压力控制，但也只有在模具型腔研究中才用到。系统介绍了最新研究的通过在模具多个地点增加动态阀来同时实现对模腔压力的控制熔体输送系统，这种动态阀每一个都可以独立控制仪表流量和压力。多型腔的压力控制系统能提高生产能力从而改善塑造产品的质量。试验结果表明,先进的工艺技术,能够灵活通过改变任意平衡流来控制多个部分注塑的尺寸，控制在典型的生产过程中存在的干扰,。但这些能力存在一定的局限性,在聚合物工程和科学领域，还有很多有待我们去提高。全文：说明：热塑性塑料注射成型法是迄今最为重要的提供高质量和高附加值工业产品的加工方法。但日趋激烈的全球竞争在不断提升产品性能和质量标准的同时要求降低产品开发时间和单位产品的生产成本。尽管不断采用先进的设计方法和新的加工工艺技术，这种加工方法的一些问题仍然在变得越来越明显：注塑成型法既不灵活，也没有强大到足以可靠地满足这些行业的要求。利用这种技术可能会使产品开发周期长，模具成本高，生产效益低,而有些时候用这种方法生产的产品的质量又无法满足人们的要求。 高分子的状态（压力，温度和形态），直接决定了成型零件的质量。因此，最新技术的发展，正确地集中在缩小机器参数和聚合物状态之间的循环上。如果这个目标实现，这些先进的控制系统将很大程度上提高成型零件的强度。然而，即使是完美的控制，也就是能够控制进口熔体温度和压力的情况下，仍然无法满足行业的日益严格的要求。因为这种加工方法本身的缺陷：一般注塑成型工艺是只有一个自由度的加工方法。腔中的温度和压力分布有着密不可分的联系，到入口融化塑料的动态又被模具的形状限制。因此，没有办法同时控制聚合物熔体在模具内的多个位置 没有用于调整的额外自由度。而这些调整在良好的制造业生产中却会被用到（1）。由于热塑性材料在先进技术应用方面的不断引入，只有一个自由度的加工工艺的道路变得更加局限，禁止热塑性材料在许多先进技术上的应用证明把一个具有多重严格要求的技术应用在注塑加工工艺中的风险太高了。事实上，一个知名的开发经理说：“我们看到客户正在开始转移到其他更有效率的制造工艺”（2）。 Kazmer（3）最近描述一个方法，多自由度的联合闭环腔的压力控制。本文探讨了这一新的工艺能否真正为新产品创造价值和提高热塑性塑料模压件的生产能力。 相关的工作：成型过程中产生变异的原因：在一批次产品的注塑零件中总是有不一致，这是由于许多常见的材料特性变化造成的。例如，当一种材料被另一个有“类似的”流动体所取代时、回用料与新用料混合后使用时、已经过了一个较长的保质期或是由不同批次相同材料等级之间产生转换时都（4）可能会在粘度，密度，或成分上出现微小变化。而在材料性能的微小变化可以肯定地导致部分重量，零件尺寸，外观，强度等不一致，但材料不一致只有一个变异的来源 其实有许多原因存在，其它的常常不考虑。表1列出了在注射成型过程中变化的几个来源。未知因素主要有：类型的变化（变异源），材料的性能（粘度、密度、组成、等），机器因素 (机器动力学、调整,控制调整、桶和液压磨损,抛丸颗粒的大小、速度、转换、压力,等等)，工艺工程师因素（调整点的选择,设置,等），经营者因素（周期时间、零件事务等），环境因素（温度、湿度,噪声）。第二个变异的主要来源来自于加工机械。例如，不同注射缸及夹具设计成型机将具有非常不同的计算机动态，运用同样的加工设置也会生产出不同质量水平的成型零件。甚至来自同一制造商的同一机型当使用不同的控制调整不同的熔体数量和液压输送系统时也可引起严重的质量变化。最后，同样压力下生产的成型零件可能会有所不同是因为内部控制的变化与很多的因数有关，如注射量，注射速度，转换点，折压等 。第三个来源的变化如表1所示源于与人类互动的过程。例如，不同的工艺工程师对“最佳”（5）有不同的定义。因此，他们可以使用他们自己的标准进行设置，如注射速度、正压、背压，冷却时间，脱模设置。同样的，压力控制者能直接决定时间周期及零件处理，还可能会影响某些程序设置。因此，所有人类的互动都会被无意中引入到注塑成型的变化过程。 其他来源的变化是使成型加工运作的物理环境。例如，室外温度和相对湿度可能会影响蒸发冷却器的效果，这可能决定内部水分是我温度。室内温度同样可以显著影响模具壁面温度以及成型件成型的过程。湿度会影响进入炉里干燥的材料，这些因素都可能会导致各种各样的质量不一致。 对过程的稳定性追求 由于这些变异的来源的多样性，为了保证成型零件的品质，典型的行业惯例是：首先把加工条件定位在认为是最佳的操作条件上。然后随意得干扰加工过程，以确定一个范围的能产生可以接受的产品的“过程窗口”。相关的工艺条件与成型零件的最终质量的关系得到了广泛的实验和理论研究（7）。这些研究提高了对注塑成型过程的物理上的理解。然而,由于他们的工艺条件只对某个特定的机器有效，对于其他机械，还要继续的进行摸索。但是随着越来越多的研究力量进入到这个领域中,这种方法正在被改进。但是这种方法仍需要大量的实验数据和计算，不是所有的机器都能提供这样的条件。抛开一致性问题，新的工艺技术已经被纳入注塑工艺，以解决特定的质量问题。通过调整和振动材料，“流变仪”工艺使流动在分子水平上混合在一起，使纤维慢慢混合，增加零件的强度。这个过程也声称控制收缩和内应力，减少零件翘曲和双折射。最近，一些人努力使用不同的方法完成了类似的结果。加德纳和马洛伊（9）利用一个凸轮顶针，促使灌浆期后的融化振荡。贝克尔等人（10）利用两个注入单位“推拉”融化振荡。格罗斯曼等通过把活塞插入一个多分支浇道系统（11）完成融化振荡。 Kazmer和Roe则通过在一个普通的热流通系统中添加一个简单的可控制阀门的开关和允许熔体凝固及收缩来引导通过腔体的流动获得了相似的结果，增加了在普通热流道系统编织线强度。编织线是一个可能由上述技术造成的常见的结构缺陷。在塑料进一步扩大技术的应用与大规模的功能整合时，尺寸稳定性已成为日益重要的问题。为了实现尺寸稳定性，在模腔压力必须均匀，以保证整个腔水平低模内残余应力，同时避免后成型翘曲的情况。在高粘度的流阻和熔融时，大多数设计的薄壁断面和流程长长度将很难实现统一的压力分布。低压发泡成型，气体辅助注塑成型和高压成型的工艺都是可供选择的加工工艺，可以用来发展成为满足特定工业需要的稳定的加工工艺。不论这些工艺中的哪一个，目标都是让一腔压力与分布较为均匀，减少收缩和翘曲。但是，每个技术都需要特殊设计的考虑，可能会导致在产品开发周期中出现问题。此外，这些工艺的可靠性被公认是低于常规注射成型工艺的（13，14）。很明显，所有这些工艺的发展都在试图解决传统注塑成型工艺的目前的不足之处。过程控制系统使注塑成型工艺使生产的能力更加可靠和强大。一个一致的产品，但这并不意味着产品的好的品质或可取的好属性它一样可以是质量低劣的一致产品。最先进的控制系统最终将能够消除变化，同时多个生产目标之间作出权衡。然而，控制系统将不能够解决多个相互冲突的目标，因为工艺的动态特性和品质特性是相互联系的勉强对工艺中一个过程进行改变用来提高产品质量很可能会无意中在别的过程中降低的零件质量。多腔压力控制 多腔压力控制是用来减弱模具内多个区域的工艺动态的。从理论上讲，闭环控制应提供增强的成型零件的一致性，而在多个地点的压力控制提供了巨大的灵活性。这些自由度可以被用来弥补复合材料的性能，拒绝输入的变化，并适应不断变化的生产要求。有了这个生产阶段的灵活性，产品的上市时间将不可避免地减少，同时确保产品质量和产生过程在可接受的水平。此外，生产阶段的灵活性和允许在概念设计阶段拥有更大的冒险空间的能力，最终可能实现以前没有实现产品功能。总之，本研究为产品设计者提供了更多的自由，同时产品设计简化了模具工程师和机器操作人员的任务。标题： 注塑成型（分析） 高压（科技）（研究） 塑料（成型） 作者： Kazmer，大卫 巴靳，菲利普 出版日期： 1997年11月1日 出版： 名称：聚合物工程与科学出版社；出版者：塑料工程师协会，公司观众：学术格式：杂志/杂志；科目：工程及制造业；科技版权：Copyright 1997塑料工程师协会。国际标准期刊编号：0032-3888 发行： 日期：十一月，1997 ；源卷：37；来源问题：11 ；登录号： 54171833 原文取自论文网站freepatentsonlion：/article/Polymer-Engineering-Science/54171833.html：The process capability of multi-cavity pressure control for the injection molding process. Abstract:Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality thermoplastic parts. This interest has led to the achievement of closed loop cavity pressure control, but only at one point in the mold cavity. A system has been recently described that extends this capability to provide simultaneous control of cavity pressure at multiple locations in the mold through the addition of dynamic valves in the melt delivery system, each of which can be independently controlled to meter flow and pressure to its portion of the mold. This paper describes the ability of the multi-cavity pressure control system to improve process capability and molded part quality. Experimental investigation has shown that the technology enables significant process flexibility to arbitrarily balance flow, move knit-lines, and control multiple part dimensions. In the presence of typical production process disturbances, moreover, closed loop multi-cavity pressure control was shown to increase the process capability index, Cp, from 0.52 for the conventional injection molding process to 1.5. After these capabilities have been discussed, several limitations of the process are described that lead to promising areas of future research. Subject:Injection molding (Analysis)High pressure (Technology) (Research)Plastics (Molding)Authors:Kazmer, DavidBarkan, PhilipPub Date:11/01/1997Publication:Name:PolymerEngineeringandScience Publisher:SocietyofPlasticsEngineers,Inc. Audience:Academic Format:Magazine/Journal Subject:Engineeringandmanufacturingindustries;Scienceandtechnology Copyright:COPYRIGHT1997SocietyofPlasticsEngineers,Inc. ISSN:0032-3888Issue:Date:Nov, 1997 Source Volume:37 Source Issue:11Accession Number:54171833 Full Text:INTRODUCTION：Injection molding of thermoplastics has emerged as the premier vehicle for delivering high quality, value added commercial products. Continued global competitiveness has increased standards for product capability and quality while requiring reduced product development time and unit cost. Despite advanced design methods and new process technologies, it is becoming apparent that the injection molding process is neither flexible nor robust enough to reliably meet these industry requirements. The lack of robustness is sometimes evidenced by long product development cycles, excessive tooling costs, low process yields, and unacceptable product quality.It is the polymer state (pressure, temperature, and morphology) that directly determines the molded part quality. As such, recent technology development has rightly focused on closing the loop between the machine parameters and the polymer conditions. If achieved, these advanced control systems would provide increased molded part consistency. However, even perfect control, i.e. the ability to profile the inlet melt temperature and pressure, will be unable to satisfy industrys increasingly stringent requirements. Because of its physical implementation, conventional injection molding is inherently a one degree of freedom process. The temperature and pressure distribution in the cavity is inextricably linked to the inlet melt conditions and the process dynamics forced by the mold geometry. As such, there is no way to simultaneously control the polymer melt at multiple locations inside the mold - there are no degrees of freedom available for adjustment as good manufacturing practice would dictate (1).As thermoplastic materials continue their thrust into advanced technical applications, access to only one degree of freedom will become even more constricting, prohibiting thermoplastic materials from entering many advanced applications. The risks of proving out the injection molding process for a technical application with multiple stringent requirements are too excessive. In fact, a well-known development manager has said that we are starting to see the migration of customers to other manufacturing processes for time-critical applications (2).Kazmer (3) has recently described one method that combines closed loop cavity pressure control with multiple degrees of freedom. This paper examines the capability of this new process to actually deliver value to the development and production of molded thermoplastic parts.RELATED WORKSources of Variation in the Molding ProcessProduct inconsistencies among a batch of molded parts is most frequently attributed to lot-to-lot variation in material properties. For instance, small changes in viscosity, density, or composition may occur when one material is replaced by another having similar flow properties, regrind is mixed with virgin material, a material is used after it has been stored over an extended period of time, or a switch is made between different batches of the same material grade (4). Small changes in material properties can clearly lead to inconsistencies in part weight, part dimensions, aesthetic, strength, etc. However, material inconsistency is only one source of variation - many others exist that are often not considered. Table 1 lists several sources of variation in the injection molding process.A second major source of variation arises from the process machinery. For instance, molding machines of different injection cylinder and clamp design will have very different machine dynamics, providing different levels of molded part quality for the same process set-points. Even identical machine models from the same manufacturer can induce significant quality variation given differences in controls tuning and varying amounts of wear in the melt and hydraulic delivery systems. Finally, parts molded from the same press may vary because of internal controller variation relating to the shot size, injection velocity, switchover point, pack pressure, etc.The third source of variation shown in Table 1 stems from the human interaction with the process. For instance, process engineers have different definitions of optimal (5). As such, they can induce product inconsistency through their modification of standard process set-points such as injection velocity, pack pressure, back pressure, cooling time, and ejection setup. Similarly, press operators directly determine cycle time and part handling, and may influence some process settings. As such, all human interaction will inadvertently tend to introduce variation to the injection molding process.An additional source of variation is the physical environment in which the molding process is operating. For instance, outdoor temperature and relative humidity may affect the effectiveness of evaporative coolers, which may determine the temperature of the plant water. Indoor temperature can likewise have significant effect on the mold wall temperature as well as the post-molding behavior of the molded parts. Humidity can affect the dryness of the materials entering the barrel, which may introduce various quality inconsistencies.The Search for Process RobustnessBecause of these sources of variation, typical industry practice for ensuring molded part quality is to 1) place the process at what are perceived as optimal operating conditions, then 2) casually perturb the process to identify a local process window that produces acceptable moldings (6). The correlation of process conditions to a molded parts final quality has been widely studied both experimentally and theoretically (7). These studies enhance the physical understanding of the injection molding process. However, they only relate the process conditions to a few particular molded part properties for a particular machine and material. With more and more research in this area, the power of this method is growing. Nevertheless, this method requires intelligent experimental design or large number of experiments to create results that are application specific. With such a diverse variety of plastics and applications, it is not possible to experimentally exhaust all the studies.Going beyond consistency issues, new process technologies have been incorporated into the injection molding process to address specific quality issues. Ibar et al. recently developed a device that utilizes reciprocating action of one or more melt-accumulator pistons adjacent to the flow path to induce melt-flow oscillation in the post-filling stages of the molding process (8). These flow-fields can be used to alter and improve the extent of orientation in amorphous plastics and the morphology of semicrystalline plastics. By orienting and vibrating the material, the rheometric process forces flow fronts to intermingle at the molecular level, diffusing knit-lines and increasing part strength. The process is also claimed to control shrinkage and internal stresses to reduce part warpage and birefringence.Several recent efforts have described different methods of accomplishing similar results. Gardner and Malloy (9) utilized ejector pins on a cam to induce melt oscillation after the filling stage. Becker et al. (10) utilized two injection units to push-pull the melt. Grossman et al. accomplished melt oscillation by inserting pistons into a multi-branched runner system (11). Kazmer and Roe produced similar results of increased knit-line strength in a conventional hot runner system simply by closing one valve gate in the post-filling stage and allowing the melt solidification and shrinkage to induce flow across the cavity (12). Knit-lines are one common structural defect that may be addressed by any of the above techniques.Dimensional stability has become an increasingly significant issue as plastics penetrate further into technical applications with significant levels of functional integration. To achieve dimensional stability, cavity pressures during molding must be uniform throughout the cavity to assure low levels of molded-in residual stress and avoid post-molding warpage. Uniform pressure distributions are difficult to achieve given the high viscosity of the plastic melt and the flow resistance of most designs thin wall sections and long flow lengths.Low pressure foam molding, gas-assisted injection molding, and high pressure molding are alternative process technologies developed to provide robust solutions to specific industry needs. In each of these processes, the goal is to enable an acceptable filing profile with more uniform cavity pressure distributions and less shrinkage and warpage. However, each technology requires special design considerations that may lead to complications during the product development cycle. Moreover, the measured consistency of these processes is acknowledged to be below that of the conventional injection molding process (13, 14).It is clear that all these process developments are attempting to resolve current inadequacies of the conventional injection molding process. Process control systems for injection molding have become substantially more repeatable
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