Layer thickness and draft angle selection for stereolithography injection mould tooling

The introduction of rapid prototyping has allowed engineers and designers to generate physical models of required parts very early on in the design and development phase. Further to this, the use of stereolithography (SL) cavities as a rapid tooling method has allowed plastic prototype parts to be produced in their most common production manner -- by injection moulding. The process is best suited to small production runs where the high costs of conventionally machined tooling is prohibitive. One of the major drawbacks of the SL injectionmoulding process is the susceptibility of the tools to premature failure. SL tools may break under the force exerted by part ejection when the friction between a moulding and a core is greater than the tensile strength of the core, resulting in tensile failure. Very few justified recommendations exist about the choice of mould design variables that can lower the part ejection force experienced and reduce the risk of SL tool failure. This research investigates the ejection forces resulting from SL injection moulding tools which are identical in all respects except for their build layer thickness and incorporated draft angles in an attempt to identify appropriate evidence for recommendations with respect to these design variables and SL injection moulding. The results show that adjustment of draft angle results in a change of part ejection force as a reasonably linear relationship. An adjustment of the build layer thickness results in a change in part ejection force as a more non-linear relationship. The adjustment of build layer thickness had a greater effect on ejection force than the adjustment of draft angle. The results also show that the surface roughness of all tools remains unchanged after moulding a number of parts in polypropylene. A mathematical model was used in an attempt to predict ejection forces according to the moulding material used. This model reflected the experimental results in terms of relative values but not in absolute values, which may be due to inappropriate specific values used in their calculation. Finite element analysis (FEA) was used in an attempt to identify the factors involved in the ejection process. Results indicate that the effect of draft angle on ejection force is due to elastic deformation of the surface roughness. A fact borne out by the lack of damage to the surface after ejection.     

Behaviour of core materials during resin transfer moulding of sandwich structures

Abstract

The use of sandwich structures is a well documented and accepted engineering approach. Composite sandwich structures, consisting of a fibre reinforcement impregnated with resin surrounding a foam core, can be used to improve bending stiffness, thermal insulation, and specific mechanical properties at relatively low cost. Such materials can be produced by the resin transfer moulding (RTM)process by incorporating the core within the fibre preform before resin injection. However, this process may result in a number of defects including core shifting, deformation, and delamination, which will have a detrimental effect on mechanical performance. The occurrences of these defects have been studied as a function of the fibre volume fraction, resin pressure, and skin thickness. Delamination between the skin and the core is also a major concern, although this can be controlled by abrading the core surface before moulding. The effect of process parameters on moulding quality and, in particular, the response of the core during moulding and the subsequent delamination resistance of the resulting sandwich structure are presented. This is applied to a range of commercially available core materials.     

Effects of gate design and cavity thickness on filling,morphology and mechanical properties of microinjection mouldings

Miniaturized parts weighing up to tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding cause material to experience high shear rates and high cooling rates, and to have different morphology and final properties from conventional injection moulding. It also makes mould design quite challenging. This study investigates micro gate design (opening and thickness) and cavity thickness (100–500 μm) on filling, morphology and mechanical properties of Poly(ether-block-amide) miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects: increased shear heating increases flow length; increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, skin ratio reduces from ∼70% to ∼10%, when part thickness increases from 100 μm to 500 μm. Such oriented skin layer determines molecular orientation and broadly influences Young’s modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. Mechanical properties of microinjection mouldings are significantly different from conventional injection mouldings and measurement at the microscale is required for successful miniaturized product design.     

Compression moulding of Carbon/PEEK Randomly-Oriented Strands composites: A 2D Finite Element model to predict the squeeze flow behaviour

Compression moulding of Randomly-Oriented Strands (ROS) of pre-impregnated thermoplastic composites is a process that enables the forming of complex parts with features such as ribs, thickness variations and holes in one single moulding step. This paper focuses on the macroscopic squeeze flow behaviour that occurs during forming. This mechanism rules the filling of intricate features of the mould initially empty. A 2D Finite Element model was developed to predict the squeeze flow of ROS composites. The material was modelled as a Bingham fluid and the equivalent viscosity and yield stress of three different strand sizes were determined using an inverse method. The viscosity and yield stress were found to increase with strand length. Experimental validation of the model was performed using Carbon/PEEK ROS flat samples and the average difference between experimentally measured and predicted final strain was below 5% for all cases.     

Structure and anisotropy of stiffness in glass fibre-reinforced thermoplastics

Techniques which are readily available, and which may be considered suitable for the qualitative or quantitative assessment of fibre orientation distribution in short glass fibre-reinforced thermoplastics are reviewed. The results of using several of these techniques in structural studies on injection mouldings of glass fibre-reinforced grades of polypropylene and polyamide 66 are presented. Uniaxial tensile creep tests were carried out on specimens cut from the mouldings and the anisotropy of stiffness of each moulding is compared with that predicted from the structural studies. Certain of the structural techniques are considered to be unreliable or of restricted applicability and it is concluded that the technique of contact micro-radiography is the most versatile; being capable of yielding reliable qualitative or quantitative information on fibre orientation distribution. Detailed structural studies on edge-gated injection moulded discs, using the technique of contact micro-radiography, show that the fibre orientation distribution varies dramatically through the thickness of the mouldings, even in cases where uniaxial tensile creep tests suggest isotropy of stiffness in the plane of the moulding. Care must therefore be taken when seeking to relate flexural data to tensile data and strength data to stiffness data.     

非牛顿液体注射成型过程中的层流剪切混合

本文分析了从碰撞式混合室流出的非牛顿液体混合物在直圆管形流道中的层剪切混合机理，得出了条纹厚度作为半径ｒ和流道长径比Ｌ／Ｄ的函数的分布规律。分析表明，在圆管流道中的层流剪切混合能进一步减小条纹厚度，从而保证两组分在模腔中的迅速而充分的化学反应。     

An intelligent hybrid system for initial process parameter setting of injection moulding

Currently, determination of the initial process parameter settings for injection moulding is mainly performed by moulding personnel, and the effectiveness of the parameter setting is largely dependent on the experience of these personnel. In this paper, an intelligent hybrid system, called HSIM, is described, which is used to determine a set of initial process parameters for injection moulding based on the artificial intelligence (AI) techniques, case-based reasoning (CBR), and hybrid neural network (NN) and genetic algorithm (GA). HSIM can determine a set of initial process parameters for injection moulding quickly, without relying on expert moulding personnel, from which moulded parts free from major moulding defects can be produced.     

Flexible grippers for handling systems Design possibilities and experiences

The paper gives a survey of problems that occur for the gripper system when handling systems are applied in small batches production. In order to solve these problems, a systematic approach is described in the paper. Solutions can be found, for example, in a universal gripper for a whole work-piece spectrum or using gripper changing systems. In order to develop a universal gripper, it is necessary to analyse significant areas on every work-piece type of the whole work-piece spectrum. If it is impossible to design a universal gripper, an automatic moulding gripper could be a possibility. Thus, moulding grippers were developed that use sensors and positioning drives. This paper presents new types of automatic moulding jaws that can be fixed on various grippers. The moulding jaws have been developed as a simple system for moulding purposes in comparison to moulding grippers with sensors and positioning drives. Those automatic moulding jaws will be described in detail. Experiments with moulding jaws were made by means of a special gripper test station. Results of the experiments will be presented as well as a future outlook on gripper technology     

“离位”增韧预成型体压缩特性

针对"离位"增韧预成型体的液态成型工艺性,研究了两种不同结构形式增韧层"离位"增韧预成型体的厚度压缩特性。分别采用多孔薄膜结构增韧层、高孔隙率无纺布结构增韧层与碳纤维织物交替铺层制备"离位"增韧预成型体,采用力学试验机测试其厚度压缩特性。实验结果表明,预成型体压缩过程中,在相同压力水平下,增韧层的引入会降低预成型体的纤维体积分数;不同压力水平下,预成型体的压缩行为与增韧层结构形式有关。此外,采用织物预成型体厚度压缩本构模型,对"离位"增韧预成型体的压缩厚度进行了预测,通过模型预测值与实验值的比较,确定了模型中的经验指数k=2时,两者吻合较好。     

纵向超声波辅助微注塑方法

微注塑过程中,聚合物熔体在微小腔体中流动时充模阻力比常规注塑大,这影响了熔体填充效果,同时热量损失的不均衡性和不确定性容易导致注塑精度不高．提出了纵向超声波辅助微注塑方法,并对超声波振动对聚合物熔体的作用机理进行了探讨,分析了超声换能器结构对应力、振幅和响应频率的影响．基于对微注塑过程的模拟结果,开发了纵向超声波辅助微注塑装置．通过在微注塑过程中纵向超声波对熔体的能量作用降低熔体黏度,改善了熔体流动和充填性能．为了验证超声波辅助微注塑的效果,进行了菲涅尔透镜实际注塑实验．实验结果表明,相同的注塑工艺条件下,超声辅助微注塑过程中聚合物熔体的充填性能提高了6．91％．     

Recycling of epoxy resin compounds for moulding electronic components

This study reports the recycling of the cured epoxy resin compounds containing silica filler and additives for moulding electronic components, which is generated as a mould residue in moulding process. The pulverized residue (moulding resin powder) showed good surface reactivity due to the functional groups contained (silanol, hydroxy and epoxy) and reacted with polar resins such as epoxy resin and phenol resin in a similar manner to silica powder. Recycling a low-stress-type moulding resin powder containing silicone elastomer into a standard moulding resin yielded a new moulding resin that has far better thermal impact resistance than that made with the original standard moulding resin. Moreover, the moulding resin powder was found to be suitable as a filler for epoxy resin products such as insulating materials, paints and adhesives to supply them with sufficient insulating, strength and adhesive properties. Use of the powder as a decorating agent for an acrylic-resin-type construction material also produced a marble-like appearance and improved the surface hardness of the material.     

Effects of defects in hybrid sheet moulding compound – Evaluation of defects and the impact on mechanical properties

Sheet moulding compound is a widely used fibre‐reinforced material. Generally, it consists of discontinuous glass fibres in a thermoset matrix system. Due to the finite fibre length, mechanical properties of structural components are limited. To overcome this drawback, sheet moulding compound is locally reinforced with a unidirectional carbon fibre sheet moulding compound material in the approach presented in this contribution. The manufacturing of this hybrid material consisting of discontinuous glass fibre sheet moulding compound and continuous carbon fibre sheet moulding compound can result in different defects, such as folds or fibre misalignments. These defects may affect mechanical properties of the hybrid material. Consequently, this article deals with the investigation and analysis of defective hybrid sheet moulding compound components, which were examined by means of tensile tests. Results point out that investigated defects have different effects on mechanical properties. However, independent from the type of defect, mechanical properties were reduced. With a reduction of 68.86 %, folds have one of the greatest influences on tensile strength. In addition, depending on the angle deviation, even greater reductions can occur. Furthermore, the reduction of the mechanical properties can be identified clearly with increasing angle deviation.     

Development of micro-form-fitted amorphous thermoplast/light metal hybrid components

In order to meet the high demands on tolerances and surface qualities, for example in automotive lighting applications, a hybrid part composed of a light metal (aluminium) and an amorphous thermoplastic (polycarbonate) could be an alternative to the established mono-materials used today. Due to the lack of adhesion promoter systems for joining this specific material combination, a micro-form-fitted connection by creating undercut microstructures by laser ablation is used to achieve a full-surface bond. First investigations are carried out to ensure the filling of these microstructures with different polycarbonate moulding compounds by over moulding in the injection moulding process. Subsequently, the influence of the moulding compound, the structure arrangement and the influence of a pickling treatment on the bond strength are analysed by tensile shear testing.     

羊毛角蛋白塑料的制备和力学性能

利用羊毛制备了角蛋白塑料,考察了模压压强、模压温度以及增塑剂等对角蛋白塑料力学性能的影响。结果表明,随着模压压强的增大,塑料的最大拉伸强度升高,断裂伸长率降低。模压温度对塑料的力学性能影响不大。水和甘油都是角蛋白塑料良好的增塑剂,水含量为27%和甘油含量为20%时的增塑作用最好。     

Application of roll forming to SMC forming

Sheet Moulding Compound (SMC) is suitable for mass production of FRP. It is usually formed by compression moulding. Though compression moulding can make production time short, this moulding method needs a huge forming energy because of the hydrostatic stress in the mould. Roll forming needs a smaller forming energy than compression moulding, because most of the forming load works as deviatoric stress. We proposed to apply roll forming to SMC, expecting a decrease of the forming energy, a short production time and a controllability of the fibre orientation. In this paper, we investigate the effect of the reduction, the roll velocity and the roll diameter on the forming pressure and the deformation behaviour of the materials. Considering these results, we try to construct a design system for roll forming of SMC.     

Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 1. Static tests and stiffness degradation at failure studies

The analysis of stiffness and the identification of rupture mechanisms during and after static tests of sandwich panels and their components have been investigated. The sandwich panels, having cross-ply laminates skins made of glass fibre and epoxy resin were manufactured by vacuum moulding and subjected to three-point bending tests. Two polyvinyl chloride cores of similar type but with differing densities were investigated. The effect of core density and its thickness on the behavior and the damage was highlighted. In terms of stiffness and load at failure, the sandwich structure has better mechanical characteristics compared to its components. __________ Translated from Problemy Prochnosti, No. 2, pp. 88–98, March–April, 2007.     

Optimization of injection moulding conditions with user-definable objective functions based on a genetic algorithm

This paper applies a Genetic Algorithm (GA) method to optimize injection moulding conditions, such as melt temperature, mould temperature and injection time. A GA is very suitable for moulding conditions optimization where complex patterns of local minima are possible. Existing work in the literature has limited versatility because the optimization algorithm is hard-wired with specific objective function. However, for most of the practical applications, the appropriateness of optimization objective functions depends on each specific moulding problem. The paper develops a multi-objective GA optimization strategy, where the objective functions may be defined by the designers, including using different criteria and/or weights. For parts with general quality requirements, an objective function is also recommended with some quality measuring criteria, which are either more accurately represented or cover more moulding defects than those from existing simulation-based optimization approaches. The paper also elaborates on the effective GA attributes suited to moulding conditions optimization, such as population size, crossover rate and mutation rate. A case study demonstrates the effectiveness of the proposed approach and algorithm. The optimization results are compared with those from an exhaustive search method to determine the algorithm's accuracy in finding global optimum. It is found to be favourable.     

纳米陶瓷的成型方法研究进展

简述了纳米陶瓷的各种成型方法,如冷等静压成型、超高压成型、原位成型、离心注浆成型、凝胶直接成型、渗透固化法等等,并列举了若干研究实例,由于各种方法都有其局限性,所以新的成型方法将成为研究的重点.     

浸塑成型中冷却时间的优化

采用数学建模的方法对浸塑成型中制件的冷却过程进行了模拟。通过对浸塑件冷却过程中的传热作合理简化,建立传热过程的扩散方程,并由边界条件的齐次化等数学方法,推导出确定浸塑件冷却时间的计算方程。将方程应用于聚氯乙烯(PVC)浸塑件冷却时间的计算与确定,并对比经验公式做了讨论与分析。结果表明,通过公式计算确定的冷却时间可以减少生产中脱模困难的问题,降低制件的后收缩率,达到优化浸塑工艺和改善制件性能的目的。     

Spritzgießen keramischer Bauteile

Powder injection moulding of ceramic parts Powder injection moulding is a parts production technology that combines the advantages of plastics injection moulding with the materials properties of ceramics. It makes possible the production of complex shaped parts for high production numbers. Almost all possibilities of parts design used in plastics injection moulding can transfered to ceramics. Paying attention to the special properties of highly filled thermoplastics and the well known rules for parts and tools construction, new parts can be realized in short development times. This article will have a closer look at the parameters for injection moulding, at rules for design of ceramic parts and the corresponding tools as well at a never debinding technology.