Injection-molded Parts Research Articles

EVALUATION OF POST-CONSUMER MIXED POLYOLEFINES AND THEIR INJECTION MOULDED BLENDS WITH VIRGIN POLYETHYLENE

Recycling of solid plastic waste composed of post-consumer mixed polyolefines (polypropylene and polyethylene) was carried out by injection moulding of secondary material streams. The materials have been characterized by melt flow index (MFI), tensile, bending and impact measurements, density and differential scanning calorimetry (DSC). The sink-float technique was used to separate the polyethylene fraction, which was then blended into virgin polyethylene at different ratios and processed anew. The mechanical and physicochemical properties were likewise determined and these results were compared to theoretical values, predicted by the law-of-mixtures. It was found that the different postconsumer mixed polyolefines were of similar quality and had comparable properties. Furthermore, it was demonstrated that the tensile and bending properties of blends consisting of recycled separated polyethylene and virgin polyethylene follow the law-of-mixtures, while the impact strength does not and is in fact strongly reduced by the presence of different phases within the injection moulded part.

Thermal Comparison of Conventional and Conformal Cooling Channel Designs for a Non-Constant Thickness Screw Cap

Complex parts are manufactured with high production rates using plastic injection. Defects in injection moulded parts are typically caused by non-uniform cooling. The design of cooling channels is a key step in the mould tool design process. Laser sintering allows for the direct fabrication at reasonable price, complex 3D tools with integrated cooling channels without the need of fixtures. This technique allows the designer to optimise the position of cooling channels relative to the heat source. This paper presents a simulation study for a non-constant thickness threaded screw cap. Results comparing conventional to conformal cooling channel show that the range between the highest and the lowest part surface temperatures is reduced by 18.8%. On the other hand, there is only a decrease of 3.9% for the maximum temperature in the interior of the threaded screw cap. Conformal cooling using laser sintering in tool manufacturing achieves an improved heat transfer leading to a better part quality.

Increasing the Injection Moulding Productivity through EDM Surface Modulation

The productivity of the injection moulding process is considerably deteriorated due to the demoulding issues as a result of increasing part and polymer complexity. An effective method to overcome some of the issues is the application of coatings on mould surface to reduce adhesion and friction during the moulded part ejection. In such solutions, the mould is coated after the machining by methods such as milling and EDM. In fact, die-sinking EDM is widely used to machine moulds with high accuracy, surface quality and aspect ratios. In this research, a novel method is analysed where the texture of the EDM surface is modulated to achieve desirable surface functionality, leading to reduction of part sticking during ejection in injection moulding. The effect of primary parameters of EDM process on the resulting surface is analysed. It is seen that while the surface amplitude parameters such as Ra and Rz remain similar to the standard eroded surface, the spacing parameter RSm and slope measure RΔq can be modulated. The effect of the surface texture during injection moulding is evaluated by measuring the forces during the ejection stage to characterise part sticking. Similar or considerably reduced ejection forces are observed for the modulated EDM texture compared to the polished surfaces, depending on the polymer type and part geometry. The ejection force observations are correlated to the static and dynamic friction coefficient of surface textures against different polymers. The reduction of ejection forces comparable to the coated surfaces places surface texturing as an effective alternative or a supplement to reduce the demoulding issues and thus increasing the injection moulding productivity and part quality.

Geometrical shape improvement of steel moulds by robot polishing process for polymer optic replication

ABSTRACTThe quality of injection-moulded polymer optic parts depends on the surface finish of the respective mould. In order to improve the surface finish of the mould, it is important to use a tactical material removal, which allows a controlled correction of the mould’s surface geometry. The aim of this work is to use a polishing correction technique to improve and correct the flatness of hardened steel samples in order to reduce the need for manual polishing. A polishing tool function is simulated from the contact between the tool and the hardened steel sample and used to determine the material removal rate per time. A feed profile is calculated, which allows the industrial robot to tactically control the material removal. It is observed that a correction improves the surface’s flatness by up to 70%.

Analysis of Shrinkages in ABS Injection Molding Parts for Automobile Applications

Shrinkage in a molded plastic part is important in defining finishing measurements of the part. In this paper it has been tried to find effect of the injection pressure, Gate sizes and cooling system that plays on the shrinkage rate of a ABS component in automotive components during injection molding process. Finite numerical solution was used to find the solution for the physical model. Molding is widely used for producing parts in large volumes it can be used for producing complex parts and can be produced with minimum effect. Still, the setting of the process parameters has to be optimized otherwise there will be defects caused due to the process parameters, such as shrinkage. In this paper, it is tried to optimize the molding process in order to reduce the molding defects like shrinkage by using Taguchi’s experimental design and the analysis of variance (ANOVA) methods

Influence of different polishing materials in the material removal of steel samples

The quality of injection moulded polymer optic parts depends on the surface finish of the respective mould. In order to improve and control the surface finish of the mould it is important to be able to keep the material removal constant during the polishing process of these moulds. This will provide a tactical material removal therefore allowing a controlled correction of the mould’s surface geometry. The aim of this work is to study the influence of different polishing materials in the material removal rate and its reproducibility during the polishing process of hardened steel. Different polyurethane polishing materials with different fillers were tested. It was observed that the filler material of the polyurethane is crucial in order to obtain constant and reproducible results. Experiments were carried out with an industrial robot and the material removal’s depth value was compared.

Comparison of long-term properties of laser sintered and injection molded polyamide 12 parts

Abstract Selective laser sintering (SLS) of polymers is on the edge from a pure prototyping technique to a small-scale production. For this transition, characteristic values such as long-term properties, and thus the degradation mechanism, are crucial factors for enabling a series application. Due to the specific characteristics of SLS parts like porosity and rough surfaces, a direct transfer of known mechanisms and models for injection molded (IM) parts is not or just to a limited extent possible. This leads to the aim of this paper, which is to investigate and compare the degradation behavior of polyamide 12 parts produced by SLS and IM.

Investigations on Flexural Fatigue Strength of Conductor Paths Fabricated by LPKF-LDS® Technology

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially, molded interconnect devices (MID), which enable numerous applications with three-dimensional (3D) circuitry on 3D shaped injection-molded thermoplastic parts are often under particular stress, e.g., as component of a housing. In this study, a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser-based LPKF-LDS® technology is presented. For characterization of test samples, a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So, the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore, test specimens are tested under different types of mechanical load, i.e., tensile stress and compressive stress. For a holistic view on reliability of MID, experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system, which is often used in MID technology.

Effective thermal properties of an isotactic polypropylene (α‐iPP) injection moulded part by a multiscale approach

AbstractIn injection moulding processes, the melt undergoes a complex deformation and cooling history, which results in an inhomogeneous distribution of crystalline superstructures in semi‐crystalline thermoplastics, which significantly influences their final mechanical and thermal properties. In this paper we describe the determination of local effective thermal properties of a moulded part via a multiscale simulation approach. First a macroscopic filling and heat transfer simulation is performed followed by a microstructure evolution calculation on the micro‐scale. Then, the effective thermal properties are derived via a two‐level homogenization scheme. The results show that the effective thermal conductivity is anisotropic and that it varies asymmetrically over the analysed plate sections.

Unexpected Strength and Toughness Reinforcement of the Injection-Molded Isotactic Polypropylene Parts with Oriented β-Crystals

In this work, three profiles of injection temperatures were adopted to tune the morphology of a β-nucleating agent and further affect the resulting β-crystal morphology of isotactic polypropylene (iPP) during an injection molding process. When the middle injection temperature profile was adopted (the maximum temperature was 220 °C), abundant oriented β-crystals with the c-axis perpendicular to the injection direction were presented throughout the whole injection-molded part, and their existence and distribution were confirmed by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). These oriented β-crystals give rise to simultaneously enhanced tensile and impact strength of the β-nucleated iPP part. In a novel outcome, this work transformed the usually mechanically weak and soft component (i.e., the β-crystals) of iPP into one that added to its self-reinforcement and overall strength. This finding provides a new idea that a soft structure can be utilized to reinforce itself.

Enhancement of the mechanical and thermal properties of injection-molded polylactide parts by the addition of acrylated epoxidized soybean oil

This work reports the effect of acrylated epoxidized soybean oil (AESO) addition on the mechanical, thermal, and thermomechanical properties of polylactide (PLA) parts obtained by injection molding. To this end, AESO, a chemically multi-functionalized vegetable oil, was incorporated into PLA during melt processing. The PLA parts with AESO contents in the 2.5–7.5wt% range showed a remarkable enhancement in both elongation at break and impact-absorbed energy while their tensile and flexural strength as well as thermomechanical properties were maintained or slightly improved. Additionally, the AESO-containing PLA parts presented higher thermal stability and lower crystallinity. The improvement achieved was ascribed to a dual effect of plasticization in combination with a chain-extension and/or cross-linking process of the PLA chains by the highly reactive acrylate and epoxy groups present in AESO. The use of AESO thus represents an environmentally friendly solution to obtain toughened PLA materials of high interest in, for instance, rigid packaging, automotive or building and construction applications.

Influence of clamping force on tie-bar elongation, mold separation, and part dimensions in injection molding

In injection molding, the magnitude of clamping force may affect the quality of plastic parts. A small clamping force may produce defects such as flashes and poor geometrical accuracy, whereas a large force could result in insufficient air venting during mold filling/packing, leading to the generation of short shot. Traditionally, clamping force is set at the highest machine specification, which may lead to additional energy consumption. Moreover, heavy loading at the tie bars is detrimental to the durability of processed molds and the machine itself. In this study, we developed a measuring system for recording tie-bar elongation and mold separation during injection molding at each corner of the mold. To determine the consequences of proper and improper clamping force settings on the quality of injection-molded parts, we systematically evaluated the effects of relevant parameters such as cavity layout and gate location on cavity pressure distribution during packing and the reactive force from cavity pressure acting on mold walls. Correlation analysis on experimental results depicted that the maximum increase in tie bar elongation and the maximum mold separation during injection molding are highly correlated with the thickness of plastic parts, and we suggested that the two features are good indicators of part quality. Moreover, cavity layout of generating diverse filling patterns and the distribution of cavity pressure is influential to mold separation as well as tie-bar elongation during mold filling. This phenomenon is further change the degree of mold separation at each corner of the injection mold and should be concerned in practice.

Application of Metallography in Solving of Manufacturing Defects of Galvanically Plated Polymers

Galvanic plating of polymeric structural parts is widely used in many industrial branches, e.g. in automotive. Minor errors in their manufacturing process are responsible for presence of surface defects. These defects, especially in the case of visual and decorative parts, are unacceptable. This paper demonstrates the usage of metallography to reveal and solve common problems in industrial production. Different types of galvanic plating defects on injection molded parts made of ABS, PC/ABS and PA manifest themselves by different ways.

Three-dimensional numerical simulation of total warpage deformation for short-glass-fiber-reinforced polypropylene composite injection-molded parts using coupled FEM

Abstract Based on the effects of natural cooling on the warpage of the injection-molded parts, a concept of total warpage deformation was proposed. A three-dimensional numerical model of total warpage for the injection-molded parts of short-glass-fiber-reinforced polypropylene (PP) composites was established using coupled finite element method (FEM). The total warpage deformation is composed of two parts: stress-induced deformation during injection molding and thermally induced shrinkage deformation after ejection. The residual stress, temperature, and anisotropic thermal and mechanical properties formed in injection molding were subsequently transferred into the thermal stress analysis package as initial conditions. On account of the difference between the fluid and structural mesh, the tetrahedral and hexahedral mesh types were used in injection molding simulation and thermal stress analysis, respectively. The comparison between the simulation and experimental results showed that the simulated warpage deformation agreed well with the experimental measurements quantitatively and qualitatively, suggesting the validation of the proposed numerical model.

Effects of Different Thermoplastic Wax-based Binders on Properties of 316L Stainless Steel Injection Molding Parts

A thorough understanding of thermoplastic polymer in the wax-based binder is essential for ensuring the dimensions and mechanical properties of 316L stainless steel metal injection molding parts. The effects of three thermoplastic polymers, high density polyethylene, high density polyethylene/polypropylene and polypropylene, on the dimensions and mechanical properties of 316L stainless steel metal injection molding parts have been compared. The tensile bars were tested to examine the dimensions and mechanical properties of sintered parts against different thermoplastic polymers in the binder. Among the three thermoplastic polymers in the binder considered herein, high density polyethylene/polypropylene performs better than others in solvent debinding stage and in terms of the metal injection molding compact quality. High density polyethylene/polypropylene has significantly increases the stabilities of length, width and thickness by up to 46%, 40%, 20%, respectively. The density, hardness and tensile strength of the sintered parts are 7.28 g/cm 3 , 72.3 HRB and 579Mpa, respectively.

Cost analysis in injection moulded plastic parts designing

One of the major problem in plastic part design consists in the cost optimization. The designer should take into consideration some relevant aspects that are related to the functional role of the part, the mechanical and thermal loads, and the part cost. The part cost depends on three main components: the mould cost, the equipment operation cost and the material cost. The injection cycle time, the part volume and the material nature can estimate the last two components of the part cost. The mould cost is more difficult to estimate, and current CAD software did not integrate such a feature. The paper present a methodology to estimate the mould cost, taking into consideration the part geometry and its dimensional prescriptions. In addition, a spreadsheet is provided in order to estimate the mould cost.

Analysis of the shrinkage of injection-molded fiber-reinforced thin-wall parts

Injection molding of thin-wall parts is characterized by a highly shear-stressed melt flow, which could affect the morphology of the moldings and consequently their shrinkage and warpage. This study focuses on the impact of injection molding processing conditions on dimensional accuracy of thin-wall fiber-reinforced parts. The reduction of shrinkage was taken in consideration by analyzing how the processing parameters affected the final dimensions of a 350μm thick part. Moreover, the relation between the distribution of short glass fibers within the part and its dimensional accuracy was investigated by means of X-ray computed tomography. The experimental results showed that melt temperature and packing pressure were the processing parameters that most affected the shrinkage of thin-wall parts. In particular, a selection of high values for these parameters allowed for the minimization of the dimensional difference between the mold and the final parts. The analysis of the cross sections of the moldings allowed the observation of an almost flat trend of the orientation tensor for parts molded at lower injection speed, indicating the absence of the core layer. This caused a higher shrinkage along the cross-flow direction that eventually led to a differential shrinkage and to the warpage of the final part.

Thermal joining of foamed thermoplastic injection-moulded parts using laser radiation

The foam injection moulding is an established process to produce plastic components with reduced density. Due to the fragile foam structure, contactless welding methods such as laser transmission welding are suitable for foamed components. In a research project, the correlation between the injection moulding parameters and the resulting foam structure is determined in preliminary tests. Specimens with four different foam structures are produced, which differ in terms of their surface layer thickness and cell density. Measurements of the transmittance, as well as the intensity profile after irradiation of the transparent specimen, show that the transmission of the foamed test specimens is lower than compared to compact specimens. In particular, foam structures with low cell density and low surface layer thickness show a low transmittance. The weld strength is influenced only by the foam structure of the transparent joining partner. Additionally, a possible post-expansion of the enclosed gas during the welding process has to be taken into account. The temperature within the laser-absorbing joining partner is locally increased above the melting point of the plastic. Once the surrounding material is melted, the gas can expand due to the temperature increase and defects during the solidification of the melt are formed.

The Development of Lead-Free Sliding Contacts Based on Bronze-Graphite Composites through Powder Injection Moulding

Sliding electrical contacts are traditionally produced by conventional compacting technologies. Employing the powder injection moulding process (PIM) as a new manufacturing method can offer several advantages such as the fabrication of complex net-shaped parts, cost-effectiveness and high volume productions. The PIM process route consists of the following steps: powder processing, compounding, injection molding, debinding and sintering. A two-stage process consisting of solvent debinding and thermal debinding is often used to remove the moulding binder. In the present paper, the suitability of the powder metallurgical processes: mechanical alloying and powder mixing for the preparation of bronze-graphite powder mixtures for the compounding and injection moulding of sliding contacts is discussed. The use of a suitable binder is of central importance for the preparation of injection-moldable feedstocks. For this purpose, two commercial ready-to-use binder systems were utilized and evaluated. The essential challenge of the process route is to optimize all parameters of the subprocesses to achieve a damage-free debinding and sintering of the injection-moulded parts. First results on the influence of the graphite content, the binder fraction, the debinding and sintering parameters are presented and discussed.

Tailored Inserts Based on Continuous Fibre for Local Bearing Reinforcement of Short Fibre Thermoplastic Components

The injection molding process is an economical process for manufacturing of thermoplastic components. Complex geometries can be realized with high automation and short cycle times. However the mechanical properties of injection-molded parts are not suitable for mechanical demanding components even by adding short or long fibre. As bold connections are used frequently for load transfer, the load introduction area particularly is limited by low bearing strength. The present paper shows the influence of tailored inserts based on continuous fibre on the bolt-loaded hole of injected test specimen.