The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Plastic manufacturing can be unpredictable. Deviations in material batches, moisture content, machine calibration, among other variables, lead to issues in manufacturing quality and final part properties. This webinar will introduce how dielectric analysis (DEA) sensors be used to directly measure material behavior in-mold. New technology has been developed to combine dielectric analysis with machine learning and material models, allowing for dynamic adjustments to machine settings, removing uncertainty from your process, and optimizing cycle times. The material covered will include:
Due to rising demands on the quality of the final plastic product, it becomes increasingly important to influence the thermal behavior of the injection molding tools. Due to this fact the geometry of heat control channels becomes very complex, leading to a change in the manufacturing strategy of large-scale tools: manufacturing of a layered structure followed by joining the complete component. Besides the influence of the surface roughness and precision of the mold making the possibility of joining non-planar surfaces is elucidated. To demonstrate and to evaluate the diffusion bonding process, a demonstrator injection-molding tool was constructed and realized by joining the nozzle side and the ejector site of the mold by diffusion bonding after the contour conformal cooling channels were integrated. The cycle time for the production of fan wheels with the finalized mold could be reduced by 10%. Moreover, the concentricity of the fan wheels could be improved.
Background: In Spring of 2020, Instaversal was contracted to test our newly developed conformal cooling technology, CoolTool™, against existing production benchmarks for a plastic injection molded Pipe Bracket Adapter. The Product Innovator was going through a period of elevated demand where the current cycle time of the existing injection mold tool prohibited them from meeting their demand. When cooling cycles were sped up this led to higher scrap rates due to sink marks. This left the Product Innovator with two options: delay delivery of the product to their top customer with the risk of losing the sale and potentially losing the customer or to invest in additional injection mold tools to double production capacity. To meet the customer’s demand, 100,000 parts needed to be produced in a 60-day time period. This request created conflict with the contract manufacturer. They were being asked to absorb the cost of additional molds to meet the timing or run full 24-hour (Monday-Friday) shifts over the 60-day period which would create losses in revenue by eliminating other clients’ scheduled jobs.
In injection molding, the heat transfer coefficient (HTC) is a parameter defined as the polymer-mold interface's heat transferring ability. HTC depends on many factors, including polymer properties and processing conditions. Computer-Aided Engineering approaches use a constant preset value of HTC, which might lead to incorrect prediction of simulation results. In this work, a new approach is developed to validate and calibrate HTC using a numerical model. The model is based on Fourier's heat conduction law applied at the interface between the plastic part and the steel mold. Different HTC values on part temperature distribution, fill pressure, and fill time are studied. Moreover, the model is used to validate an injection mold design that could be used for experimental HTC measures using in-mold sensors. The results highlight the effect of HTC on the prediction of crucial injection molding parameters, suggesting the importance of experimental calibration.
The cooling phase in injection molding has a very high influence on the resulting part warpage and is crucial for the resulting quality of the parts. Therefore, an automatic and reproducible design of cooling channels can contribute to produce highly precise parts. In this paper, cooling channels are generated based on the results of an inverse thermal optimization of an injection mold. This optimization calculates the optimal heat flux inside the surrounding injection mold such that the part is cooled as homogeneously as possible. Iso-surfaces, which indicate locations, where the calculated heat flux would be equal to a cooling channel with a certain temperature, can be derived and are used as a basis for the presented path-planning problem Based on the iso-surfaces, cooling channel segments are generated close to those surfaces based on a geometric minimization problem. In a next step, these segments need to be connected in an optimal way concerning fluid flow and path length. Path planning algorithms usually determine a path between a single start and end point, whereas in this case multiple combinations have to be evaluated. Thus, an algorithm is presented which determines a reasonable sequence of the channel segments to be connected and ensures that the found finished cooling channel is collision-free - both to obstacles such as the cavity or parting plane of the injection mold and to itself. Validation simulations show that the results are comparable in time and performance to a manual design, but need less effort by the user.
The replication accuracy of submicron surface structures by micro injection molding control the replicated part functionalities, such as tissue engineering. In this work, we propose a multi-scale model for the replication quality of laser-induced periodic surface structures by micro injection molding of different bio-based polymers. The model decouples the macro cavity flow, investigated through a numerical simulation, from the micron-scale flow, that is modeled with a novel analytical approach. The macro model determines the boundary conditions for the filling of the sub-micron surface structures. An in-depth characterization of the mold topography of the polymer thermal, rheological, and wetting properties was carried out to feed the model. Injection molding tests were performed, varying the mold temperature to manufacture sub-micro textured parts for the model validation. The sensitivity of the replication accuracy to mold temperature and polymer selection was captured. The multi-scale model showed a maximum deviation of 8% from the experimental results.
In injection molding, the cooling stage has significant impact on the overall part quality. Cooling time is a major contributor towards the molding cycle time. In conventional molding, the mold is maintained at a constant temperature for the entire duration of molding cycle. To achieve this, coolant at a constant temperature is pumped through the mold cooling channels. A relatively new molding technology called ‘Rapid Heating and Cooling Molding’ (RHCM) involves varying the inlet temperature of the coolant fluid, so as to maintain the mold temperature relatively hotter during filling stage and reduce the surface temperature to ejection temperature during the packing and cooling stages of the injection molding cycle. RHCM is best achieved with mold designs that allow for conformal cooling ofthe mold. Some of the key benefits of using RHCM are mitigation of weld line effects, improvement in the weld line strength, achievement of high-gloss surface finish, reduction of molding pressures, residual stresses and clamping force. In this paper, a comparative study is carried out between Conventional and RHCM molding to quantify the benefits of RHCM. The component chosen for this study is arepresentative center bezel part typically seen in automotive industry; a center bezel is used in the interiors of the car, and is required to be of high-quality surface finish and devoid of surface defects such as weld lines. Different materials, i.e., filled and unfilled grades from SABIC were used for this study. The molded parts were evaluated for gloss, L*, a*, b* values, visual defects, weld line appearance and its depth, scratch and mar resistance performance.
A feed zone geometry was developed which adapts the specific throughput when processing regrind to that of virgin material without adjustable means. This leads to an enlarged process window of the extruder. For this, the filling zone of a single-screw extruder was increased and a conical section was implemented in the feed zone which was designed with helical grooves. The experimental investigations with a 35mm extruder show that a complete alignment of the specific throughput is possible depending on the enlargement of the filling zone, the grooving as well as the angle of the conical section. Here, the self-adjusting compression is used which varies depending on the material’s particle shape. Additionally, approaches for the three-dimensional description of the throughput behavior using the discrete element method are shown. The uneven shape of regrind particles is transformed into so called superquadrics.
Surface activation by plasma is a widely used process technology for connecting several components to each other. Usually, the activation takes place outside the injection molding machine as an additional step. With the development of the InMould-Plasma technology, the surface activation is fully integrated in the injection molding process, which eliminates an additional process step. Therefore, a plasma nozzle is directly connected to the mold. The plasma runs along a defined channel and activates the substrate surface in the closed mold. Through the technology, a strong bond of originally incompatible materials has been achieved. Without a surface activation, there is no adhesion of polypropylene (PP) and thermoplastic polyurethane (TPU). Studies on the peel strength of PP with TPU show that a treatment time of 5 s can drastically increase the material compatibility and achieve a peel strength of > 12.5 N/mm over the entire treatment area.
Plastic parts are becoming more and more complex. Thus, the demolding of such parts is becoming more and more challenging. Meanwhile it is difficult to reproduce the conditions, appearing during the demolding of a part from a molding tool. To overcome this gap a simple and robust test setup has been developed to measure the necessary torque to demold a plastic test specimen from a defined surface of a test blank. During the test, two variables are measured and evaluated, the adhesion torque, which describes the loss of adhesion between the plastic test specimen and the metal surface of the test blank, and the sliding integral, which describes the torque needed to overcome the sliding friction between friction partner. As a result of the tests the influence of the used plastic, the influence of the process and the influence of the functionalizing of the metal surface via structuring and coating on the demolding behavior is shown.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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