3D Forming of Paperboard: The Influence of Paperboard Properties on Formability

Paper and paperboard are widely used in various types of packaging. Paper‐based packaging is a recyclable, biodegradable, renewable and sustainable product, which gives it certain advantages over most plastic‐based packaging materials. Although paper‐based packaging, in some areas, lacks attractiveness in terms of visual appearance, 3D forming is an important method for producing advanced shapes from paper and paperboard, suitable, for instance, for modified atmosphere packaging. That said, very little is known about the deformations experienced by paper‐based materials in 3D forming. Understanding the role played by the mechanical properties of paper and paperboard in the 3D forming process is key to improving performance. This paper presents experimental results obtained using three different forming devices designed to be used with paper‐based materials and links the formability data with specific mechanical properties of the paperboard samples. Paperboard properties that were found to correlate with formability were as follows: compressive strength and strain, tensile strain, paper‐to‐metal friction and out‐of‐plane stiffness. The requirements for formability are different for the fixed blank forming process and sliding blank forming process. Copyright © 2013 John Wiley & Sons, Ltd.     

简单形状零件拉深成形智能化控制技术研究

板材成形智能化是冲压工艺的一项新技术.以圆锥形件和锥壁盒形件为研究对象,分别讨论了实现实时监测、实时识别、实时预测和实时控制所需的关键技术,逐步形成了拉深成形智能化控制的理论基础.在实时识别和实时预测阶段采用人工神经网络,在压边力控制阶段采用基于破裂临界曲线的控制方法,能够得到较满意的结果.研究过程中开发了智能化拉深实验系统,实验证明识别、预测精度较好.     

Investigation into the wrinkling behaviour of thin sheets in the cylindrical cup deep drawing process using bifurcation theory

The initiation and growth of wrinkles are influenced by many factors such as stress ratios, the mechanical properties of the sheet material, the geometry of the workpiece, and contact condition. It is difficult to analyse wrinkling initiation and growth while considering all the factors because the effects of the factors are very complex and studies of wrinkling behaviour may show a wide scattering of data even for small deviations in factors. In the present study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. Wrinkling initiation is found by checking the determinant of the stiffness matrix and wrinkling behaviour is analysed by successive iteration with the perturbed guess along the eigenvector. Wrinkling initiation and growth in the cylindrical cup deep drawing process are analysed by using the proposed bifurcation algorithm. The mechanism of wrinkling initiation and growth in the cylindrical cup deep drawing process is investigated in detail. The results of the finite element analysis are compared with the experimental results. Through the finite element analyses of wrinkling growth for various material constants, the effects of plastic anisotropy and the strain hardening coefficient on the wrinkling behaviour of sheet metal are investigated. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermal and mechanical durability of starch‐based dual polymer coatings in the press forming of paperboard

The runnability and convertibility of biopolymer dispersion–coated paperboard were determined using a novel adjustable packaging line equipped with a tray‐pressing mould. Commercial paperboard was dispersion barrier coated on the back‐side using a dual polymer system containing both a synthetic and a renewable biopolymer, of which the latter was the main component in the dispersion. The effect of the addition of a high‐aspect‐ratio platy pigment and synthetic polymer on both the grease resistance and the convertibility of the product was evaluated in addition to the evaluation of runnability and crack resistance in tray pressing and die cutting. The addition of synthetic polymer into bio‐based dispersion improved the elastic properties, plasticity and, subsequently, mechanical convertibility of the product. Moderate additions of the synthetic polymer provided improved grease resistance for the biopolymer coatings. It revealed that the addition of synthetic polymer was sufficient in providing improved barrier properties, although the chemical compatibility and process window for the convertibility need to be considered. In addition to mechanical stability, the heat stability of the substrate needs to be investigated. Copyright © 2013 John Wiley & Sons, Ltd.     

New Methods for Quality Analysis of Deep‐Drawn Packaging Components from Paperboard

Optimization of the quality of deep‐drawn cups requires methods for precise measuring of quality criteria. This paper presents new objective methods to describe the quality of deep‐drawn packaging components made of paperboard. The state of the art for quality analysis in three‐dimensional paperboard forming is presented. Methods for the analysis of visual quality using image analysis and for the analysis of shape accuracy using surface scans are developed. Experimental results are used for the verification of the methods and for the investigation of influences of main process parameters. The new methods are found to be both precise and objective. A large blankholder force has been shown to cause an increasing number of wrinkles and has a negative influence on the shape accuracy. A high die temperature also increases the number of wrinkles but enhances the shape accuracy. The punch temperature has no effect on the number of wrinkles, but high punch temperature has a significant and positive effect on the shape accuracy. Copyright © 2014 John Wiley & Sons, Ltd.     

New Quality Level of Packaging Components from Paperboard through Technology Improvement in 3D Forming

Three‐dimensional forming is a key technology for the application of sustainable materials, like paperboard, in packaging technology. Until now, deep drawing is not considered as a suitable process for manufacturing of packaging components with advanced geometrical design because of the sensitive process and a large number of failure mechanisms. To better understand and apply the physics of deep drawing, the process was studied by experimental investigations. Therefore, an evaluation strategy for formed parts was developed to describe their quality by measurable values. The influence of the technological parameters temperature configuration, moisture content of material and blank holder force on the quality of formed parts was described by a statistic regression model. This model gives an indication of the quantity and the direction of effects that parameter changes have on the quality of 3D‐formed parts. An optimization of the process according to quality criteria showed that, in a first step, the quality of cylindrically drawn paperboard parts was increased drastically compared with that of the state of the art. Furthermore, the existing limits in the height of formed parts were exceeded, and the geometrical shape of the base offered far more opportunities for packaging design than expected. The process turned out to be suitable for a flexible manufacturing of packaging components for multipart packages from paperboard, which are highly sustainable in terms of recycling and reuse of fibres and thereby able to compete in the marketing‐oriented packaging sector. Copyright © 2011 John Wiley & Sons, Ltd.     

Explicit FEM analysis of the deep drawing of paperboard

An explicit finite element model of the deep-drawing of paperboard has been developed utilizing a custom yet simple material model which describes the anisotropy and plasticity of paperboard. The model was verified with a variety of tests and was then utilized to compare the punch force that was measured during the deep-drawing experiments to the punch force that was calculated during the deep-drawing simulations. All material parameters were calibrated based on individual experiments; thus, no parameter fitting was utilized to match the experimental deep-drawing results. The model was found to predict the experimental results with reasonable accuracy up to the point when wrinkling began to dominate the material response. Since most failures during paperboard deep-drawing occur before wrinkling begins to play a major role, this model can probably be utilized to study and predict the failure of deep-drawn paperboard cups. The overall trends and the effects of major process parameters are predicted by the model. The process parameters that were varied and compared for both experiments and simulations were: blankholder force, die temperature, and thickness. The model was utilized to discover that friction of the blankholder and die have significant effects on the punch force and thus the stress, implying that low-friction dies and blankholders can considerably reduce the failure probability and thus also improve the quality of deep-drawn paperboard cups.     

Analysis of sheet steel fracture during deep drawing

Low-carbon steel sheet used for the fabrication of automotive brake components was tearing during deep drawing. The associated mill certificates revealed that the coil met the specified chemical composition and mechanical properties. Metallographic evaluation revealed a severe variation with respect to grain size through the thickness of the steel sheet, as well as a slight segregation of pearlite. Insufficient temperature during hot rolling in combination with a high coiling temperature resulted in the observed microstructural gradient. The anisotropic mechanical properties were amplified by the slight carbon segregation.     

Odorous compounds in paperboard as influenced by recycled material and storage

Many volatile compounds can be identified in unprinted paperboard by means of steam distillation in combination with capillary gas chromatography, mass spectrometry and olfactometry. Paperboards produced with recycled material exhibit additional volatiles which partly contribute to off‐odours. Using sniffing techniques, benzaldehyde, acetophenone, 1‐octen‐3‐ol, 1‐octen‐3‐one, 2‐nonenal, methylguajacol, butanoic and 3‐methyl butanoic acid were identified as the most odorous volatiles. The aromatic substances mainly exude from inks and printing solvents in waste materials used for paperboard manufacturing. During storage under controlled conditions, the microbial load of paperboard decreased slightly, and no odorous metabolic products were generated. Copyright © 2001 John Wiley & Sons, Ltd.     

Method for Fast Quality Evaluation of Deep‐drawn Paperboard Packaging Components

The visual and mechanical quality of paperboard packaging components formed by deep drawing closely corresponds to the wrinkle distribution within the material wall section. Assessing this quality of paperboard packaging components currently relies on very slow or even subjective methods. Therefore, counting the number of wrinkles and measuring the mean distance between wrinkles proved to be a sensitive strategy for the evaluation of quality levels in deep drawing formed paperboard containers like cups or trays. A method introduced by Hauptmann proposes the measurement of the distances between 10 wrinkles in machine direction and 10 wrinkles in cross direction for each sample. However, this method is unsatisfactory because it can only observe a small part of each sample and is subject to deviation through the individual judgement of the person carrying out the survey. Further methods, as well as their respective application range, are listed in Table  1 . Hence, it is desirable to automate the wrinkle survey to be carried out without operator influences to the measurement. This paper introduces such an automated measuring method. The given method relies on recording the sample surface topography through laser‐distance measurement. An evaluation algorithm, which enables the detection of wrinkles in the topographic data, is proposed. Furthermore, it is shown that the method yields feasible results and is capable of generating reliable quality information in considerably reduced time frames.     

玻璃纤维/聚丙烯复合材料层合板拉深成型性

为研究纤维增强树脂复合材料零部件快速成型,加速复合材料零部件大规模产业化量产,以玻璃纤维/聚丙烯复合材料层合板为实验对象,首先利用设计加工的拉深成型模具,进行了玻璃纤维增强热塑性树脂复合材料（Glass fiber reinforced thermoplastic resin composite,GFRTP）板材外表面纤维方向和模具长轴方向为0°和90°的试件在不同温度和不同拉深深度条件下的深拉深成型实验,将成型件制备金相试件在光学显微镜下进行微观组织观察,并对试件的成型情况和不同拉深力-行程曲线进行分析。其后进行了GFRTP板材外表面纤维方向和模具长轴方向为0°、45°和90°的试件的不同温度下的浅拉深成型实验,并对成型后的试验件进行了室温条件下的拉伸性能测试,对其拉伸失效情况及具体力学性能进行了对比分析。试验结果表明,在室温25℃到基体树脂的熔融温度165℃之间,随着温度的升高,板材的极限拉深深度增大,最大拉深力呈下降趋势。在选取的试验温度范围内,85℃时试件成型性能较好且0°试件优于90°试件,温度对拉深成型试件的皱曲改善不明显。浅拉深成型试件拉伸力学特性受试件铺层纤维方向的影响较大,防止皱曲等缺陷的发生对GFRTP板材拉深成型十分重要。     

锥形件拉深智能化控制中压边力的控制规律

法兰起皱、侧壁起皱和侧壁破裂是拉深成形的主要障碍,而合理控制压边力是防止起皱破裂的关键所在.在总结前期研究成果的基础上,结合拉深成形过程的特点,在成形三极限图中给出了圆锥形零件拉深成形的成功区域,并提出了获得最佳压边力控制规律的方法.这为圆锥形零件拉深成形中的模具设计、工艺参数的制定提供了依据,也为拉深智能化控制提供了保证.     

非轴对称件拉深的破裂临界压边力控制原理

变压边力控制技术在拉深工艺中是一种简单有效的工艺手段,可以有效地改善成形质量.本文以锥壁方盒形件为例,以板材成形极限图(FLD)为理论依据,通过数值模拟的方法获得了破裂的压边力-行程临界曲线,得出了压边力沿着该曲线加载有利于改善成形质量的结论,进而提出了破裂临界压边力控制原理,给出了实际应用中获得变压边力加载曲线的方法,为实现非轴对称件拉深智能化控制的压边力变化规律预测奠定了基础.     

Bending stiffness loss of paperboard at conversion — predicting the bending ability of paperboard

The ability of paperboard to resist bending has been investigated. Paperboard is often bent in converting and packaging machines. The paperboard is bent over rolls and thus formed to certain curvatures. If the roll diameter is small the paperboard will be highly curved. This means that high tensile stresses occur on the convex side and high compression stresses on the concave side. If these stresses are too high the paperboard will be damaged by fractures and wrinkles on the surfaces. The bending stiffness of the board will also be reduced. The importance of certain parameters, such as roll diameter, angle of wrap, board thickness, board compression strength and others, have been investigated. In this study seven qualities of paperboard were investigated. It has been shown that the bending force–bending angle curve can be used to obtain information about the ability of different board qualities to be bent to certain curvatures without being damaged. © 1998 John Wiley & Sons, Ltd.     

蜂窝纸板受压时的有限元分析

利用有限元程序对蜂窝纸板的压缩进行了模拟,得到了蜂窝纸板以及芯纸在不同压缩量下的应力分布规律和变形特点.结果表明,蜂窝纸板的承载能力主要由芯纸决定,芯纸的破坏从靠近面纸的附近区域开始,理论分析结果与试验吻合.为蜂窝纸板的研究提供了一种新的思路.     

深度学习在材料显微图像分析中的应用与挑战

材料的组织结构主要受成分和制备加工工艺的影响,是决定材料性能的关键因素,在材料研发的全周期内具有重要作用。材料组织结构以非结构化图像数据的形式呈现,利用人工经验性的手段进行分析和信息抽取,遗漏了大量的材料学信息和隐含知识。深度学习技术的发展和应用,为材料显微图像中信息的精准、快速、自动获取提供了重要的研究手段。本文从图像处理、图像分析和图像理解3个方面概述了材料显微图像处理与信息挖掘的主要研究内容和关键技术,详细介绍了深度学习在图像分析中的图像识别、图像分割和图像生成3个任务中的研究进展,讨论了深度学习在材料显微图像分析和信息挖掘中的发展方向和挑战。     

预胀对筒形件充液拉深变形和硬化的影响

为定量分析预胀对塑性成形的影响,以变形量差异较大的平底筒形件为研究对象,采用实验和数值模拟方法研究了预胀高度对双相钢DP340/590板材充液拉深的影响,分析了预胀对试件等效应变、壁厚减薄率和硬度分布的影响.研究表明,预胀显著增加平底筒形件底部的变形,即试件底部壁厚减薄率增加、硬度升高、等效应变增大.与普通充液拉深相比,相对预胀高度为20%时,试件等效应变差减小16.7%,底部维氏硬度值提高23.8%.     

Characterization of in‐plane load bearing of a honeycomb paperboard

The in‐plane bearing capacity of the face layer and core layer of a honeycomb paperboard is limited and unstable. However, a combination of the face layer and core layer of the honeycomb paperboard protects cardboard from small‐load buckling instability and provides sufficient stiffness and bearing strength. In the study, the platform theory models of the machine direction and cross direction are established based on plastic deformation, plastic energy dissipation, and the energy conservation theory. Additionally, the marginal pressure strength in the machine direction and cross direction are deduced by combining the practical application of the honeycomb paperboard. A comparison of theoretical and experimental data indicates that the two are in good agreement. Therefore, the theoretical results of the study provide a theoretical basis for the scientific and reasonable selection of important parameters of honeycomb paperboards with different strength requirements.