Weld Line Location Research Articles

Simulation‐based analysis of weld line strength of glass fiber‐reinforced polymer in injection molding

AbstractThe injection molding market is expected to grow with the increasing demand from various industries, such as automotive and furniture. However, weld lines in the injection molded part reduce the structural strength and affects its appearance. This study evaluates the effect of the weld line on the structure by shifting the position of the weld line outside the area where the load is applied by manipulating the opening time of the injection gates. We examined the effect of weld lines on the strength of a chair through coupled resin flow and structural analyses. The analysis revealed that the position of the weld lines is crucial for structural strength if the knockdown factor (KDF) is low. Additionally, controlling the opening time of the gate and shifting the position of the weld line improved the structure's appearance, number of weld line and avoid the lower meeting angle. However, depending on the material, the effect may be weak. For example, when the weld line location did not change much despite changing the gate timing, little change was observed in the number of weld lines. Hence, the improvement strategy of weld line should be considered for material types and strength.Highlights Injection molding growth driven by automotive, packaging, furniture demand. Weld lines impact structural strength and appearance. Shifting weld line position outside load area improves the structural appearance and strength. Effects of shifting weld line position depended on the material types. Weld line position is crucial for low knockdown factor and affects strength.

Analysis of Weld Lines in Micro-Injection Molding.

Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are present on the parts: the so-called weld lines. As weld lines are crucial in determining mechanical part performances, it is mandatory to clarify weld line position and characteristics, especially at the industrial scale during mold design, to limit failure causes. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. This work examines the influence of mold temperature on the weld line position and strength by both experimental and simulation approaches in µIM. At mold temperatures below 100 °C, only short shots were obtained in the chosen cavity. At increased mold temperatures, weld lines show up to a 40% decrease in the whole length, and the overall tensile modulus doubles. This finding can be attributed to the reduction of the orientation at the weld line location favored by high mold temperatures. Moldflow simulations consistently reproduce the main features of the process, weld line position and length. The discrepancy between experimental and simulated results was attributed to the fact that crystallization in flow conditions was not accounted for in the model.

Molding gate optimization for weld line location away from structures loaded area

Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. A flat product case was considered as an example of a typical aircraft structural element – a pin-joint lug molding from short-fiber reinforced thermoplastic composite material. The Golden-Section search method allowed to solve the optimization problem. Autodesk Moldflow in batch mode controlled by Matlab code through Synergy API was used to solve the direct molding task of determination of the weld line location from gate location dependence. An experiment of the lugs injection molding from several gate positions was carry out to verify the numerical weld line prediction. The solved problem allows choosing the gate position for ensuring the weld lines location away from structures loaded area.

Optimised Design of Mold for Vehicle Throttle Body Bracket Based on CAE

The throttle body bracket is a structure to support and fix the throttle body. Its quality not only affects the performance of the throttle body, but also affects the running performance of car. Excellent mould is important guarantee for quality of the throttle body bracket. In this paper, mould of vehicle throttle body bracket is taken as research object. Methods combining structural design, simulation analysis with optimization design are adopted. First, process and structure of the bracket are analysed. Three plate mould structure and single-impression layout are determined. Based on mould flow optimization analysis, gate type and location are selected, structural dimensions of forming parts are calculated to design the side core pulling mechanism, remoulding mechanism and cooling system. Simulation analysis for filling time, weld line location, cavitation, cooling effect and warpage deformation are carried out by CAE to realise the optimal design of mould for the throttle body bracket.

Numerical simulation of mold filling water blown polyurethane foams: Effects of sequential pour

Batch molding of polyurethane foams is a widely used processing technique to produce crosslinked cellular structures which form to the shape of the mold. For water-blown polyurethane foams, water is reacted to form gaseous carbon dioxide resulting in a foam which expands to fill the mold completely. Batch molding typically requires an operator to coat the surface of a mold, introducing a significant lag time during the filling stage where significant asymmetric volume change can occur. The purpose of this work is to show, through simulations, that this lag time is significant when predicting flow profiles and part quality. When the mold geometry is complex enough to force bifurcation of the flow, simulations incorporating various filling lag times predicted significantly different locations of knit or weld lines where the flow fronts meet. Current simulation techniques, which assume the filling stage occurs instantaneously, are unable to predict variations in weld line locations. The introduction of a lag time, referred to herein as sequential pour, was achieved through user-defined modules incorporated into Ansys Fluent software.

Mechanical characteristics of short fiber composite samples located behind circle, rectangle, triangle obstacles

The article investigates the influence of the weld line on the mechanical characteristics of flat samples on tensile strength according to ISO-527-2, cut from a plate with an obstacle, molded from polyamide-6, reinforced from 30% short glass fibers. There are considered circular, rectangular, triangular obstacles. Melt front, weld line location and reinforcing fiber orientation are calculated in Moldex3D. The stiffness and strength of the samples were predicted in ANSYS using an anisotropic nonlinear composite material model obtained in the Digimat by reverse engineering method. The transversely isotropic criterion of Tsai Hill in the first pseudo-grain failure statement was used for predict strength. The paper presents the influence of the weld line on the stress, deformation and first pseudo-grain failure strength criterion. The greatest contribution to the samples mechanical characteristics was made by the rectangular obstacle.

The influence of the weld line location on the mechanical characteristics of lugs from short fibers reinforced composite material

The work is devoted to assessing the influence of the weld line on the mechanical characteristics of lug from short-reinforced composite material PA6 Aramid SV 30-1ETM. Lug molding process was calculated in Moldex3D, including prediction of weld line position and fiber orientation. Static structural analysis was done in ANSYS Workbench with nonlinear anisotropic material model, constructed in Digimat MX by reverse engineering. For failure prediction Tsai Hill 3D transversely isotropic model with FPGF (PGA) formulation was used. The ultimate load is taken as the minimum load at which the maximum value of the FPGF criterion reaches unity. Three cases of melt entrance point position was compared. The smallest stiffness and strength were shown by lug in which the weld line located closest to the maximum values of the strength criterion.

Modeling and simulation of weld line location and properties during injection molding based on viscoelastic constitutive equation

Weld lines are one of the typical quality issues of injection molded parts. They are unavoidable even for moderate complex products. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location and properties, in which Rolie-Poly constitutive equation is used to describe the viscoelastic properties of polymer melts and level set method is used to capture melt front. Furthermore, the formation and evolution processes of weld lines are investigated by co-injection molding technique in simulation, since the processes are determined by the flow front and rheological history of the melt streams. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. In addition, properties of polymer melt such as velocity, pressure, principal stress difference, and molecular orientation in the weld line regions are investigated and presented.

Optimum parameters to minimize weld line movement in the warm forming of tailor-welded blanks

This paper deals with optimizing geometric parameters such as thickness ratio and weld line location, to minimize the movement of weld line during the stamping of tailor-welded blank (TWB) components. Weld line movement (WLM) is an important aspect to consider; otherwise, it leads to wrinkling and other forming-related problems. The major contributors to WLM are thickness ratio, weld line location, and strengths of the respective blanks. Selective heating is a recent technique adopted to reduce the material properties of the higher strength TWB blank by heating it locally, thus allowing a shift in the weld line. In this work, laboratory and simulation experiments were conducted under warm forming conditions on the TWB blanks. Experiments were also conducted by placing the weld line at an offset distance of ± 1 mm from the centre of blank. The situation is to choose the best possible value among thickness ratio and weld line location under the influence of selective heating to minimize the WLM. The objective function of WLM is obtained from the MINITAB statistical software by conducting ANOVA method. The optimum values of the parameters were obtained by minimizing the objective function.

Sensitivity analysis and reliability based design optimization for high-strength steel tailor welded thin-walled structures under crashworthiness

Tailor welded blanks (TWB) have been widely applied in automobile industry. This paper firstly conducts experimental tests to investigate the crashworthiness of three different types of TWB hat-shaped structures. Their combinations provide three representative TWB configurations: namely the same material grade with different wall thicknesses; different grades with the same thickness, different material grades with different thicknesses, respectively. Secondly, the finite element (FE) models corresponding to each of the samples are established to perform crashworthiness analysis. It is exhibited that the FE simulations are in good agreement with the experimental tests. Thirdly, the surrogate models are constructed to approximate the crashworthiness responses of these TWB structures. Fourthly, a sensitivity analysis is conducted to explore the effects of the weld line location, wall thickness and material properties for each segment of TWB structures subject to crashing load. The results showed that the wall thickness is most sensitive to the crashworthiness of TWB structures. Finally, reliability based design optimization is carried out by taking into account the uncertainties in the TWB configuration. The results demonstrate that the optimized TWB tubes are capable to improve energy absorption as well as enhance the reliability, potentially being an ideal structure for crashworthiness.

Dynamic axial crashing of tailor-welded blanks (TWBs) thin-walled structures with top-hat shaped section

In this paper, dynamic axial crashing analysis of tailor-welded blanks (TWBs) thin-walled structures with top-hat shaped section under front impact is presented. The crash tests are performed through a sled test in order to model a car-to-car front impact. The strain rate dependence of both high strength steels (DP590 and DP780) is considered to study its influence on acceleration and energy absorption involved into high speed impacting process. The FE model about the front dynamic crashing is conducted, and different weld line modeling types on the dynamic simulation results such as acceleration history are compared. It demonstrates that coincide node (CN) model is considered appropriate for simulating the dynamic impacting. Additionally, the effects of weld line locations and spotweld spacing are also performed. It may be concluded that the material and thickness properties of front end have certain influence on the crashworthiness performance of TWBs. The simulation results show that the acceleration curves of three TWB combinations are insensitive to spotweld spacing. A comprehensive analysis including the crash mode, the acceleration curves and the energy absorption is carried out for crashworthiness assessment. The obtained results can provide some insightful guide information and fundamental supports for light-weight and crashworthiness design of TWBs to a certain extent.

Two-Time-Dimensional Model Predictive Control of Weld Line Positioning in Bi-Injection Molding

The application of bi-injection molding, a simple variation of the conventional injection molding process, is limited because of the lack of a good control of the weld line location. The weld line is an inevitable consequence of the meeting of two polymer melt fronts from different gates in the mold cavity. Positioning the weld line to avoid critical areas for the sake of aesthetics or mechanical strength is the key to the success of bi-injection molding. This remains a challenge for control engineers. This paper proposes a two-time-dimensional model predictive control for the process by combining a conventional model predictive control with an iterative learning control to explore the repetitiveness of the process. To predict the final position of the weld line, the approach takes the geometric dimension of the mold cavity into consideration. Simulation shows that the proposed method has good ability to control the weld line position ultimately within a narrow range of the desired position.

Experimental investigation on high strength steel (HSS) tailor-welded blanks (TWBs)

This paper aims to investigate mechanical characteristics of the new tailor-welded blank (TWB) components made of high strength steel (HSS). A series of HSS-TWB thin plates with different orientations of weld line are studied through three-point bending tests to evaluate the effects of different design parameters, such as weld line locations and material combinations, on the deformation behaviors. The experimental results exhibit good repeatability of tests. And the relative shift phenomenon between indenter and specimen is observed and analyzed for the TWB steel sheets with different weld line orientations at parallel and 45° to the bending moment, respectively. The results from the experiment include the force versus displacement curves and some detailed photographical images throughout the loading process. It is found that the discrepancy of different combinations is quite noteworthy. In this paper, the peak force, absorbed energy and bending strength are presented to evaluate the mechanical characteristics of HSS-TWB thin plates with different weld line orientations and material combinations. The comparison demonstrates that the TWB structures with the weld orientation at 45° angle to the bending moment have the greatest advantages of different TWB steel sheets.

Experimental study on crashworthiness of tailor-welded blank (TWB) thin-walled high-strength steel (HSS) tubular structures

This paper aims to investigate the crushing behaviors of tailor-welded blank (TWB) thin-walled structures. A series of TWB high-strength steel (HSS) square tubes with different weld line locations is used to perform the crushing tests for evaluating the effects of different TWB parameters, such as weld line locations and material combinations, on crushing characteristics. These TWB specimens are fabricated through the laser welding process to ensure sufficiently narrow weld line. In the study, the center edge of TWB square specimens is not welded so that such special TWB structures have open cross section. The crushing test results exhibit excellent repeatability. The collapse modes and force–displacement relationships are compared with each other. It is found that the crushing behaviors of different material combinations are fairly significant for a given weld line location. Such key crushing characteristics as specific energy absorption (SEA), average crush force (Favg), peak force (Fmax) are also evaluated for understanding crashworthiness of these TWB structures. The experimental results provide us with some insightful guidance to crashworthiness design of TWB thin-walled HSS structures.

Strength of the Weld Line and Warpage Defects on the Molded Parts in Injection Molding Process

Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. Many researchers had emerged with several improvement techniques to reduce these problems that been applied to a verity of customer products that injected with various types of polymers. This paper reviewed the improvement techniques previously studied to maximize strength at weld line location and minimize warpage or deflections of the molded parts. From the review, it can be seen that by using mechanical and thermal assistance during injection molding process, and the optimization of machine parameters for stated problems can be improved. However, there was lack on the multi objectives optimization which should be apply to ensure the weld line and warpage were improved together to get the best quality products.

Tensile Testing on Formability of Different Gauge Tailor-Welded Blanks

The formability of tailor welded blanks (TWBs) which combined with different blanks is difference to single material blanks. It has the benefits to improve the forming process by the study on the formability of TWBs. As an effective and practical material property test method, tensile test were applied to study it. Base material and tailor welded blanks test specimens had been designed for tensile testing and the test was carried out. The strength and plastic properties of different TWBs were acquired and the results were discussed. The results of tensile test indicated that the tensile strength of TWBs was between higher strength base material and lower one but formability was lower than any base material. At the same time the weld line location in the TWBs had a significant impact on the formability also. Tailor welded blanks (TWBs) are composed of more than two materials with similar or different strengths or thicknesses joined together to form a single part before the forming operation (1). In recent years, different gauge TWBs are commonly used in automotive panels manufacturing to satisfy the demand of the automotive industry's developing new cost effective methods to enhance the performance of the vehicle weight reduction and fuel economy (2). While the character and behavior during the forming process of different gauge TWBs is not alike single thickness (material) sheet behavior. The forming behavior of TWBs is critically influenced by thickness and material combinations of the blanks welded and weld line location etc. Considerable investigations on the behavior of different gauge TWBs have been done in the aspect of stress-strain curve, forming limit strain, dome heigh, deep-draw ability, and weld line movement based on experimental and computer simulation method (3-7). However, little has been reported on formability investigation of different gauge TWBs by tensile testing (8, 9).

Study on the Formability of Different Gauge Tailor Welded Blanks Based on Tensile Test

The formability of different gauge tailor welded blanks is difference to single material blanks. As an effective and practical material property test method, tensile test were applied to study it. Base material and tailor welded blanks test specimens had been designed for tensile testing. The results of tensile test indicated that the strength difference and weld line location in the TWBs plays an important role on the formability aspect.

Experimental validation of simulated weld line formation in injection moulded parts

The interest in weld line analysis of injection-moulded parts has increased in the past few years, mainly because of the ever-increasing requirements for the performance of injection-moulded items. Weld lines are formed when two melt fronts come in contact with each other. Whereas the total elimination of weld lines is not always possible without modifying the part geometry, their negative influence on part performance and appearance can be minimized. This can be done by trial and error experiments or by model prediction. The cost and time efficiency of the latter makes it a preferred route for weld lines analysis. Computer simulation packages of injection moulding are capable of accurately predicting the weld line location, but none of the current ones can predict the weld line contact angle or mechanical properties quantitatively. This paper focuses on the analysis of weld line formation and suggests ways to modify the finite element mesh to get better results.

Powstawanie obszarow laczenia strumieni tworzywa w wypraskach z wielogniazdowej formy wtryskowej

The results of investigations of weld lines locations in polyacetal moldings, prepared in 16-cavity injection mold with parallel cavities lay-out, were presented (Fig. 1, 3, 4). A method of melt flow visualization was used to record the weld line location on the surface of molding prepared at the proper injection conditions (method of "record grooves effect" formation control) (Fig. 2, 5). Despite using the geometrically balanced runners the cavities were not filled simultaneously (Fig. 6) and asymmetrical flow front of the polymer in the cavities led to weld lines shifts in relation to expected locations (Fig. 8-11). These results were obtained for both small and high injection velocities (Table 1). The reason of the weld line shift is the polymer melt movement in the runners, determined by runners' configuration. The results presented can be used in design of runners' sets in multicavity injection molds allowing preparation of moldings with no deterioration of mechanical strength in weld line area.

유동방향과 밀도이방성 분석을 위한 세라믹 분말사출성형 해석

This study has focused on manufacturing technique of powder injection molding of watch case made from zirconia powder. A series of computer simulation process was applied to prediction of the flow pattern in the inside of the mould to clarifying the change of sintering shrinkage depended on flow direction. The material properties of melted feedstock inclusive of the PVT graph and thermal viscosity flowage properties were measured for obtaining the input data in computer simulation. Also, molding experiment was conducted and the results of experiment showed that good agreement with simulation results for flow pattern and weld line location. On the other hand, gravity and inertia effect have an influence on velocity of melt front because of high density of ceramic powder particles in powder injection molding against the polymer injection molding process. In the experiment, the position of melt front was compared with upper gate and lower gate position. The gravity and inertia effect could be confirmed in the experimental results.