Shrinkage Of Parts Research Articles

Ultrasound Tomography for Spatially Resolved Melt Temperature Measurements in Injection Moulding Processes

In injection moulding processes, the measurement of the temperature distribution is very important for the validation of models used for simulative part design due to the high influence on shrinkage and warpage of the moulded part, but is also very challenging to measure. During the injection moulding process high mould pressures occur and the cavity is not easily accessible. Therefore, contact sensors cannot be used since they induce shear stress into the melt, which changes the flow behaviour of the melt and thus the temperature field. In this work, we present a method for the contactless determination of the temperature distribution of a moulded part during injection moulding using ultrasound tomography. With time-of-flight ultrasound measurements from different directions it is possible to reconstruct the distribution of ultrasound velocity in the cross-section of a moulded part. With this distribution, the temperature field can be calculated using additional material characteristic properties. Based on this concept, an injection mould was designed, that allows performing ultrasound tomography with 20 ultrasound transducers radially arranged around a cylindrical shaped cavity. This allows the temperature determination under real process conditions with a spatial resolution of 3.5 mm2. A highly parallelised measurement device allows recording of several complete datasets before no more signals can be detected due to shrinkage of the moulded part. During several injections moulding-cycles all sensor positions were able to detect noticeable signals. Due to internal signal processing of the measurement device, it is not yet possible to calculate arrival times of the ultrasound signal but amplitude-scans show the general feasibility of ultrasound tomography during injection moulding..

Effects of Hot Isostatic Pressing on Copper Parts Fabricated via Binder Jetting

Binder Jetting, an Additive Manufacturing process that fabricates parts via selective inkjet deposition of binder into a powder bed, is capable of cost-effectively producing complex metal and ceramic components without the need for support structures or anchors. Printed green parts are then sintered for added densification and strength. However, printed parts typically contain porosity due to the use of coarse powders and a loosely packed powder bed. While researchers have investigated many techniques (e.g., process parameter and powder morphology optimization) for achieving full theoretical density in binder jetted parts, 100% density is difficult to achieve without infiltration of a secondary lower melting point material. In this work, the authors investigate the use of Hot Isostatic Pressing (HIP) as a post-process heat treatment of sintered parts to evaluate its effect on density, porosity, and shrinkage of parts printed in Binder Jetting. The authors conduct this investigation in the context of copper. It is demonstrated that the use of HIP can improve the final part density from 92% (following sintering) to 99.7% of theoretical density.

Smoother and stronger high speed sintered elastomers through surface modification process

High speed sintering is a novel additive manufacturing process which creates parts by employing a combination of inkjet printing and infrared heating to sinter successive layers of polymer powder. This paper investigates the effect of a new surface modification method called the PUSh™ process on the mechanical properties of high speed sintered elastomer. ALM TPE210-S elastomeric powder was used to manufacture specimens, and the PUSh™ process was subsequently performed on selected specimens. Surface roughness and mechanical properties of TPE210-S specimens were measured. The results show that the PUSh™ process reduced surface roughness by 50% from 20 to 10 µm. Finished specimens had 50% higher values of ultimate tensile strength, Young's modulus and elongation at break compared to unfinished specimens, and tear strength was significantly improved by 233%. The process resulted in 3% average part shrinkage while part hardness remains unchanged. Overall, the mechanical properties of high speed sintered TPE210-S elastomer were improved by the PUSh™ process.

Smoother and stronger high speed sintered elastomers through surface modification process

High speed sintering is a novel additive manufacturing process which creates parts by employing a combination of inkjet printing and infrared heating to sinter successive layers of polymer powder. This paper investigates the effect of a new surface modification method called the PUSh™ process on the mechanical properties of high speed sintered elastomer. ALM TPE210-S elastomeric powder was used to manufacture specimens, and the PUSh™ process was subsequently performed on selected specimens. Surface roughness and mechanical properties of TPE210-S specimens were measured. The results show that the PUSh™ process reduced surface roughness by 50% from 20 to 10 µm. Finished specimens had 50% higher values of ultimate tensile strength, Young's modulus and elongation at break compared to unfinished specimens, and tear strength was significantly improved by 233%. The process resulted in 3% average part shrinkage while part hardness remains unchanged. Overall, the mechanical properties of high speed sintered TPE210-S elastomer were improved by the PUSh™ process.

Effects of solid loading on the fabrication of ceramic microparts by soft molding

The effects of solid loading on the fabrication of ceramic microparts by soft molding were studied. Alumina microchannel parts of different dimensions (60–160µm) were fabricated from well-dispersed suspensions with different solid loadings (70, 75 and 80wt%). The structural integrity of the green microchannel parts was examined to study the moldability of the suspensions. It was found that the minimum feature size and linear shrinkage of the microchannel parts decreased with increasing solid loading, while the green density and sintered density showed the opposite trend. The reasons for incomplete filling and demolding failures were also discussed.

Towards thresholds of disaster management performance under demographic change: exploring functional relationships using agent-based modeling

Abstract. Effective disaster management is a core feature for the protection of communities against natural disasters such as floods. Disaster management organizations (DMOs) are expected to contribute to ensuring this protection. However, what happens when their resources to cope with a flood are at stake or the intensity and frequency of the event exceeds their capacities? Many cities in the Free State of Saxony, Germany, were strongly hit by several floods in the last years and are additionally challenged by demographic change, with an ageing society and out-migration leading to population shrinkage in many parts of Saxony. Disaster management, which is mostly volunteer-based in Germany, is particularly affected by this change, leading to a loss of members. We propose an agent-based simulation model that acts as a "virtual lab" to explore the impact of various changes on disaster management performance. Using different scenarios we examine the impact of changes in personal resources of DMOs, their access to operation relevant information, flood characteristics as well as differences between geographic regions. A loss of DMOs and associated manpower caused by demographic change has the most profound impact on the performance. Especially in rural, upstream regions population decline in combination with very short lead times can put disaster management performance at risk.

Interface development and numerical simulation of powder co-injection moulding. Part II. Numerical simulation and experimental verification

A numerical model was proposed to predict the co-injection step of the powder co-injection moulding (PCM) process. Several assumptions were established for the purpose of simplifying the physical models. The melt front was traced by a modified control volume method, in which the maximum thickness of core feedstock was taken into consideration. Such modification can overcome the shortage of Hele-Shaw equitation in predicting 3D flow behaviour. By using this model, the movement of the skin melt front and core/skin interface, and the profile of temperature and pressure fields were obtained. The simulations were in good accordance with the experimental results. The thickness and the penetration distance of the core feedstock were accurately predicted. The deviation between the simulated and experimental results was due to the uneven shrinkage of the green part during cooling.

Effect of gas counter pressure on shrinkage and residual stress for injection molding process

Abstract Plastic products are common in contemporary daily lives. In the plastics industry, the injection molding process is advantageous for features such as mass production and stable quality. The problem, however, is that the melt will be affected by the residual stress and shrinkage generated in the process of filling and cooling; hence, defects such as warping, deformation, and sink marks will occur. In order to reduce product deformation and shrinkage during the process of molding, the screw of the injection molding machine will start the packing stage when filling is completed, which continuously pushes the melt into the cavity, thus making up for product shrinkage and improving their appearance, quality, and strength. If the packing pressure is too high, however, the internal residual stress will increase accordingly. This study set out to apply gas counter pressure (GCP) in the injection molding process. By importing gas through the ends of the cavity, the melt was exposed to a melt front pressure, which, together with the packing pressure from the screw, is supposed to reduce product shrinkage. The aim was to investigate the impacts of GCP on the process parameters via the changes in machine feedback data, such as pressure and the remaining injection resin. This study also used a relatively thin plate-shaped product and measurements, such as the photoelastic effect and luminance meter, to probe into the impacts of GCP on product residual stress, while a relatively thick paper-clip-shaped product was used to see the impacts of GCP on shrinkage in thick parts. According to the experimental results, the addition of GCP resulted in increased filling volume, improvement of product weight and stability, and effective reduction of section shrinkage, which was most obvious at the point closest to the gas entrance. The shrinkage of the sections parallel and vertical to the flow direction was proved to be reduced by 32% and 16%, respectively. Moreover, observations made via the polarizing stress viewer and luminance meter showed that the internal residual stress of a product could be effectively reduced by a proper amount of GCP.

A novel method of increasing ceramic shell permeability and optimizing casting shrinkage and tensile strength of the investment cast parts

This study explores about enhancing the permeability of the ceramic shells used in the investment casting process using cheaply available sawdust particles. An increase in shell’s permeability augments the cooling rate of the casting which enhances its mechanical properties. It was found that the inclusion of sawdust particles into the ceramic slurries exhibited positive impact on the shell’s permeability. It is a well-known fact that electromagnetic stirring process increases the mechanical properties of the castings, but its effect on casting shrinkage has never been realized. Thus, this study further throws light on the impact of electromagnetic stirring in reducing the shrinkage and improving the tensile strength of the casting. In a nutshell, it was found that the final product quality of the investment cast part improved by the combinational treatments adopted in this research work.

Experimental Investigation of Comparative Process Capabilities of Metal and Ceramic Injection Molding for Precision Applications

The purpose of this paper is to make a comparative study on the process capabilities of the two branches of the powder injection molding (PIM) process—metal injection molding (MIM) and ceramic injection molding (CIM), for high-end precision applications. The state-of-the-art literature does not make a clear comparative picture of the process capabilities of MIM and CIM. The current paper systematically characterizes the MIM and CIM processes and presents the process capabilities in terms of part shrinkage, surface replication, tolerance capability, and morphological fidelity. The results and discussion presented in the paper will be useful for thorough understanding of the MIM and CIM processes and to select the right material and process for the right application or even to combine metal and ceramic materials by molding to produce metal–ceramic hybrid components.

Statistical Approach to Analyze the Warpage, Shrinkage and Mechanical Strength of Injection Molded Parts

Abstract The aim of this study is to assess the effects of different parameters of the injection molding process in warpage, shrinkage, and mechanical properties of the plastic parts using the Taguchi method and the Analysis of Variance (ANOVA). The polyacetal copolymer (POM) and acrylonitrile-butadiene-styrene copolymer (ABS) were injected; and then the following processing parameters were analyzed: the mold temperature, holding pressure, holding time, melt temperature, cooling time, mold water flow, and injection speed. According to the results, statistically the most significant parameters in shrinkage were the mold temperature and cooling time for the POM molded parts; and the holding time and holding pressure for the ABS molded parts. The most significant parameters in warpage and flexural strength were the holding time and holding pressure for the POM and ABS parts, respectively. A multiple linear regression analysis was carried out to predict a theoretical ideal experiment to maximize the results.

Analysis of Shrinkage on Thick Plate Part using Genetic Algorithm

Injection moulding is the most widely used processes in manufacturing plastic products. Since the quality of injection improves plastic parts are mostly influenced by process conditions, the method to determine the optimum process conditions becomes the key to improving the part quality. This paper presents a systematic methodology to analyse the shrinkage of the thick plate part during the injection moulding process. Genetic Algorithm (GA) method was proposed to optimise the process parameters that would result in optimal solutions of optimisation goals. Using the GA, the shrinkage of the thick plate part was improved by 39.1% in parallel direction and 17.21% in the normal direction of melt flow.

Semiempirical approach to predict shrinkage and warpage of fiber-reinforced polymers using measured material properties in finite element model

The automotive industry has great interest in designing and producing lightweight high-performance components using fiber-reinforced polymers (FRPs), primarily due to their high specific strengths. Injection molding of FRP is one of the preferred processes to meet low-cost, high-volume objectives. It is imperative to account for shrinkage and warpage while designing the tools for injection molding. However, predicting shrinkage and warpage of injection-molded FRP parts remains a challenge. This is because both the structural and thermal properties depend on the condition of the fibers in the resin, that is, variation in the orientation, length, and concentration throughout the part. Additional challenges come from the fact that the material properties of polymers are a function of temperature, which varies as the parts cool. In this study, we are presenting a finite element-based semiempirical approach to address both these challenges and predict warpage due to cooling for a fiber-reinforced resin component in solid phase. The approach is demonstrated to predict warpage of an injection-molded flat plaque made of glass fiber-reinforced polypropylene, cooled from 160°C to room temperature of 23°C. First, the fiber orientation in the plaque is estimated. Next the material properties for the combined material, that is, glass and resin, are measured as a function of temperature. Then the combined material properties and calculated fiber orientations are used to estimate the ‘in-mold’ condition resin properties using reverse engineering. Finally, the warpage of the plaque is predicted using the estimated resin properties and fiber orientations. Warpage predictions using this method compare well with the measured experimental results. Our study demonstrates that valid predictions for shrinkage and warpage of injection-molded fiber-reinforced thermoplastic parts in solid phase can be made if accurate material properties are used.

Development of Porous Ti-6Al-4V Mix with Palm Stearin Binder by Metal Injection Molding Technique

Good potential of biocompatibility and excellent mechanical properties, porous Ti-6Al-4V has become a great interest for biomedical applications. In this study, porous Ti-6Al-4V was fabricated by Metal Injection Molding (MIM) using Palm Stearin (PS) and Polyethylene (PE) binder together with sodium chloride (NaCl) as a space holder. Rheological characterization was performed to evaluate the flowability of the feedstocks for injection molding and the feedstocks exhibited a pseudoplastic behavior which is suitable for injection. The as-sintered parts were fabricated as the mixing, injection molding, debinding and sintering were conducted successfully. The mechanical properties of the as-sintered parts were investigated via tensile test and the results obtained were closed with the established range. Shrinkage, density and X-Ray Diffractometry (XRD) of the as-sintered parts were compared with the theoretical values which were found closed to the acceptable ranges. The microstructure of the surface and cross-section were observed under Scanning Electron Micrograph (SEM) and optical microscope to analyze the specimens before and after sintering. Generally, palm stearin binder system added with space holder to fabricate porous Ti-6Al-4V by MIM is feasible and has shown a good potential for biomedical applications.

Processability and Mechanical Characteristics of Glass Fiber and Carbon Fiber Reinforced PA6 for Reinforcement Content

There is a need for light weight and high stiffness characteristics in the building structure as well as aircraft and cars. So fiber reinforced plastic with the addition of reinforcing agent such as glass fiber, carbon fiber, aramid fiber is uti- lized in this regard. In this study, mechanical strength, flow property and part shrinkage of glass fiber and carbon fiber rein- forced PA6 were examined according to reinforcement content such as 10%, 20%, and 30%, and reinforcement type. The mechanical property was measured by a tensile test with specimen fabricated by injection molding and the flow property was measured by spiral test. In addition, we measured the part shrinkage of fiber reinforced PA6 that affects part quality. As glass fiber content increases, mechanical property increased by 75.4 to 182%, and flow property decreased by 18.9 to 39.5%. And part shrinkage decreased by 52.9 to 60.8% in the flow direction, and decreased by 48.2 to 58.1% in the per- pendicular to the flow direction. As carbon fiber content increases, mechanical property increased by 180 to 276%, flow property decreased by 26.8 to 42.8%, and part shrinkage decreased by 65.0 to 71.8% and 69.5 to 72.7% in the flow direction and the direction perpendicular to the flow respectively.

Equivalent self-adaptive belt grinding for the real-R edge of an aero-engine precision-forged blade

Because of the special characteristics of aero-engine precision-forged blade edges such as heat-resistant and high-strength materials, the unequal distribution and small removal allowance, and easy deformation in processing, edge profile shape errors are easily caused by using conventional processing methods. These errors include chamfered, sharp, flat, and obtuse edges and cervical part shrinkage, so the real-R shape of the edge is difficult to guarantee, and the aero-engine air dynamic performance is seriously affected. The purpose of this research is to improve the dimensional precision, profile shape errors, and surface quality of the real-R edge of the precision-forged blade. With these aims, the method of equivalent self-adaptive belt grinding (ESBG) using a cubic boron nitride (CBN) belt is developed in this study. First, the grinding characteristics and process planning to the blade real-R edge are analyzed. The methodologies of equivalent belt grinding (EBG) and ESBG using a CBN belt are then illustrated, the control equation for EBG is established, and the method of force adaptive control is introduced. Finally, the ESBG method using the CBN belt is verified by experimental investigation of the aero-engine precision-forged blade and comparison with manual and EBG methods. The experimental results showed that the ESBG method using the CBN belt achieved the requirements of the aero-engine precision-forged blade real-R edge. It was verified that the method of ESBG using the CBN belt has the advantages of real-R shape dimensional precision and surface quality for the blade edge compared with the conventional method.

Warpage control of headlight lampshades fabricated using external gas-assisted injection molding

Headlight lampshades with an uneven part thickness and large-area complicated geometry often exhibit uneven shrinkage and considerable deformation when fabricated using injection molding. Conventional strategies for controlling shrinkage and warpage involve optimizing the gate number and location, cooling system, and mold conditions and performing annealing in a secondary process; however, conventional strategies are limited in improving the quality of injection molding. This study involved employing conventional approaches and external gas-assisted injection molding (eGAIM) to control part shrinkage and warpage effectively. The research consisted of three stages: (1) using computer simulations to optimize the mold design and molding conditions and, thus, reduce the shrinkage and warpage of headlight lampshades; (2) verifying the performance experimentally using a miniaturized geometry of the one use in (1); (3) applying eGAIM to show the potential of further improving part warpage. Simulation and experimental results indicated that optimizing the gate location facilitates improving the flow balance and reducing the filling pressure, leading to a reduction in part deformation. An optimal layout of cooling channels combined with two-stage holding conditions contributed to a superior cooling effect and low volumetric shrinkage. Parts fabricated using eGAIM exhibited less volumetric shrinkage than did parts fabricated using conventional injection molding. Moreover, annealing treatment can further reduce the deformation of molded parts. This case study investigated headlight lampshade deformation and was systematically conducted; the experimental results showed the feasibility of using eGAIM to minimize part warpage.

Multi-objective Optimization of the EMS Processed IC by Grey-fuzzy Method

In the present investigation, investment casting (IC) has been combined with the electromagnetic stirring (EMS) process. The process parameters are chosen on the basis of literature review on IC and EMS processes and these parameters are shell preheat temperature, stirring current, stirring time and pouring temperature. The responses are linear shrinkage, volumetric shrinkage and tensile strength of the investment cast parts. The experiments were conducted as per Taguchi's L9 orthogonal array (OA). As the optimal condition determined for each response was different, grey-fuzzy method was used to combine individual objective functions into a single objective function so as to form a common optimal setting for all the chosen responses. Further, confirmative experiments were done at the obtained common optimal condition to validate the adopted approach in enhancing the quality of the investment cast parts.

Stress and Deflection Development During Die Embedding into Printed Circuit Boards

Thermally induced stresses created during package manufacturing and their roles in mechanical failure are important issues for the microelectronic industry. In the present paper, a numerical analysis of the die embedding process into a printed circuit board by means of the package assembling and lamination is presented. The complex package consisting of a silicon die, an adhesive, a copper foil, an epoxy resin and prepregs (an E-glass woven structure pre-impregnated with an epoxy resin) is investigated in terms of warpage and stress development. Both are mainly introduced due to a mismatch of coefficients of thermal expansion and particularly to shrinkage of the polymer parts (adhesive, epoxy resin). Their impact on possible package failures is discussed. A two-dimensional axisymmetric numerical model is employed for investigation of the embedding process flow. Temperature dependent material properties for all materials are used in the analysis. A special focus is set on the orthotropic properties of the prepreg materials. Those are analytically homogenized based on the lamination theory of plain woven fabric composites and implemented into the numerical model. The numerical results of embedding process steps are validated experimentally by an X-ray diffraction method (Rocking-Curve-Technique) showing a good agreement of the calculated and measured curvature radius values.

Warpage control of thin-walled injection molding using local mold temperatures

Currently, 3C products are required to be lightweight, portable, and convenient. Injection molding is among the most used techniques for mass production in plastic processing industries; however, producing thinner parts that do not warp is challenging. Although plastic components warp for numerous complicated reasons, warpage primarily is caused by variations in shrinkage during the injection process of plastic part manufacturing. Material properties, part design, mold design, and processing conditions are factors influencing variations in the part shrinkage. For example, inconsistent thickness in component geometry, poor sprue–runner–gate or cooling design in the injection mold, and improper molding condition settings may cause plastic parts to warp excessively. Warpage causes unpredictable component shapes, which may cause poor assembly quality. Although mold cooling achieved by adjusting mold temperatures improves warpage, the conventional single mold temperature setting for each male or female mold plate limits the cooling capability. Therefore, this paper describes local mold temperature settings for a cooling system that can prevent severe warpage in an asymmetric plastic cover for handheld communication devices. The neutral axis theory is introduced to analyze the temperature distribution in the cross section of a part, and then predict the warping trend. Through simulation and experiments conducted in this study, the feasibility of using an effective local mold temperature setting in a cooling system to reduce part warpage was verified.