Injection Overmolding Research Articles

Ultra-high-rate Manufacturing of Thermoplastic Window Plug using Hybrid Overmolding

Highly loaded complex parts are machined from a solid block of metal by removing material through cutting, boring, drilling, and grinding to obtain the three-dimensional shape. Most cases, this involves removing as much as 80 percent of the material from a billet, which is time-consuming and inefficient considering the cost of the materials. Alternatively, these complex parts can be manufactured using hybrid overmolding process which involves injecting plastics over a reinforced substrate with continuous fiber-reinforcement eliminating subtractive machining or joining of multiple parts. The substrate is typically heated using an infrared (IR) oven and preformed over a solid mold to a three-dimensional shape using thermoforming. Injection overmolding material can also be reinforced with discontinuous fibers based on the design requirements. Both thermoforming and injection molding are matured automotive ultra-high-rate manufacturing processes. Adopting these technologies to aerospace requires advanced aerospace-grade thermoplastic material systems and developing the hybrid overmolding process that combines both thermoforming and injection molding processes. Material compatibility is one of the key enablers for the fusion across the overmolded interfaces. To demonstrate the overmolding technology for an aerospace application, Victrex AE250 low-melt polyaryletherketone (LM-PAEK) system reinforced with AS4 fibers and a 30% carbon fiber-reinforced polyetheretherketone (PEEK) were used to overmold aircraft window plugs to be used for cargo conversion of passenger aircraft. The fully automated overmolding process was demonstrated using KraussMaffei multi-robotic thermoforming and injection molding system. Thermal and mechanical test evaluations were employed to assess the material compatibility and overall part quality. Photomicrographs and flexure tests conducted on test samples extracted from the window plugs indicated satisfactory fusion across the overmolded interface and optimized holding of PEEK materials.

Injection over-molding process of PEEK composites

Abstract This study utilizes experimental and microscopic characterization methods to investigate the prospects and feasibility of using the Injection Over-Molding (IOM) process to replace traditional adhesives in the manufacturing of complex ribbed panel structures with Polyether Ether Ketone (PEEK) composites. The results indicate that the IOM process can achieve the optimal bonding strength of adhesives while significantly reducing the processing cycle, demonstrating substantial potential. Additionally, enhancing the melt temperature and mold temperature can further improve interface bonding quality and increase bonding strength. Based on the experimental results, it is inferred that increasing the melt temperature can elevate the interface temperature while raising the mold temperature can slow down the interface cooling rate, suggesting mechanisms by which these parameters influence interface bonding quality.

Application of machine learning methods in the analysis of interface bonding strength for overmolded hybrid thermoset‐thermoplastic composites

AbstractThe focus of this study is to apply finite element method (FEM) and machine learning methods to investigate the interfacial bonding strength of continuous fiber reinforced thermoset composite (TSC)‐thermoplastic structures manufactured through co‐curing and overmolding processes, with polyamide 6 (PA 6) as the thermoplastic material. A model for interfacial healing degree in TSC‐PA 6 structures was developed. Then, FEM was employed to study the influence of various injection overmolding process parameters on the interfacial bonding strength of TSC‐PA 6 structures. The results show that there is a strong correlation between the degree of interface healing and the bonding strength. Subsequently, six machine learning methods were employed to correlate interfacial healing degree with diverse injection molding process parameters. Simulation data were utilized for training, calibration, and validation of the six machine learning models. Based on the results of simulation and machine learning predictions, a quantitative analysis of the significance of injection molding process parameters on healing degree was conducted. These parameters are ranked in descending order of importance as follows: insert temperature, melt temperature, and injection rate.Highlights The interfacial healing degree model of PA 6 was established and validated through the integration FEM and experiment. Six machine learning models were built to predict the interfacial healing degree. Grad boosting performed best in predicting the interfacial healing degree. Insert temperature had the greatest impact on the interface healing degree.

A method for manufacturing a mechanically strong and durable hybrid structure of polyethylene–hydroxyapatite composite and titanium alloy

AbstractThe integration of polymer, metal, and ceramic materials in hybrid structures represents a potential but underexplored alternative for biomedical applications. Here, we present a methodology for manufacturing a mechanically strong and durable hybrid overlap structure from a composite of green high‐density polyethylene (HDPE) and hydroxyapatite (HA) compatibilized with HDPE‐g‐MAH joined to a substrate of Ti6Al4V alloy. This process involves laser structuring of micro‐scale grooves on the metal surface, followed by injection overmolding of the polymer composite. A hybrid overlap joint with strong interfacial anchoring was achieved, resulting in outstanding joining strength and fatigue life. This achievement holds significant promise for future biomedical applications.Highlights Joining of composite of HDPE–HA with Ti6Al4V alloy via injection overmolding Laser texturing was effective in improving mechanical interlocking A hybrid joint with high shear strength and fatigue life was developed The hybrid joint is promising for biomedical applications

Processing understanding, mechanical durability and hygrothermal stability of PC/AA6061 hybrid joints produced via injection overmolding

In the present study, single-lap joints of polycarbonate (PC) and laser-textured aluminum alloy AA6061 were manufactured by injection overmolding (IOM) and characterized in terms of the microstructure, quasi-static and long-term mechanical performance and hygrothermal stability. The injection overmolding parameters were optimized through design of experiments and analysis of variance, which showed that the parameters of barrel temperature, injection speed and holding pressure positively affected the ultimate lap-shear force (ULSF). PC/AA6061 injection overmolded hybrid joints exhibited outstanding joining strength of 7.2 ± 0.5 MPa. Under fatigue cyclic loading, hybrid joints produced with optimized IOM processing conditions showed a fatigue life of 35 % ULSF at 106 cycles, demonstrating excellent mechanical durability. Moreover, PC/AA6061 injection overmolded hybrid joints showed good hygrothermal stability, with no significant variations in joining strength after aging in water at 80 °C for 30 days.

Development of polyamide 6‐graphene oxide nanocomposite and direct‐joining with aluminum alloy for lightweight engineering applications

AbstractLightweight polyamide composites and structures have been widely studied and employed in several industrial sectors. In this study, the development of a nanocomposite of polyamide 6 and graphene oxide (PA6‐GO) by melt‐compounding and the joining with aluminum alloy AA6061 through direct‐adhesion injection overmolding are addressed. PA6‐GO nanocomposite exhibited well‐dispersed thin (300 nm) GO platelets distributed within the PA6 matrix, which resulted in an increase of 21% in the tensile modulus and 16% in the yield stress for a filler loading of 0.5 wt%. PA6‐GO/AA6061 hybrid joints showed good mechanical anchorage through the complete filling of the polymer into micro‐scale grooves designed onto the metal surface, which ensured outstanding shear strength of 7.1 ± 1.0 MPa, comparable to other polyamide‐metal hybrid joints reported in the literature. This indicates that the processing routes and materials developed are promising for lightweight engineering applications.Highlights A PA6‐GO nanocomposite with enhanced tensile properties was developed. A joint of PA6‐GO and AA6061 with outstanding shear strength was obtained. Fast and efficient melt‐processing routes were employed. These materials are promising for lightweight engineering applications.

Sustainable Production Insight Through LCA and LCC Analysis of Injection Overmolded Structural Electronics Manufactured through Roll-to-Roll Processes.

Printed electronics (PE) have provided new material and application opportunities for devices and systems as well as new manufacturing routes that all need to be considered for commercialization. This paper introduces a case study with universally relevant manufacturing processes and applications in the PE area, focusing on the Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) of the Personal Activity Monitor (PAM) device. In the study, the PAM device's most important costs and environmental impacts during the prototype pilot production and device use phases are identified and assessed. Additionally, the potential environmental impacts of post-consumption scenarios are considered. The LCA results indicate that the roll-to-roll (R2R) assembly of electronics and the R2R injection over-molding are generally the most prominent production process steps affecting the results. From the LCC perspective, the capitial expenditure (CAPEX) contributor is the R2R assembly pilot line, due to its high investment cost and long operating time compare to other production assets. The traditional electronic components are the major operating expenditures (OPEX), especially the microcontroller units (MCUs) and accelerometers, in contrast to the low impact from the printed electronics. There are several advantages to applying LCA and LCC since they provide explanations of the relationships between cost, environmental, design, and manufacturing characteristics.

Effect of Injection Overmolding Parameters on the Interface Bonding Strength of Hybrid Thermoset-Thermoplastic Composites.

In this study, the thermoset-thermoplastic structure was produced through a co-curing technique together with an injection overmolding technique. Continuous fiber reinforced thermoset composite (TSC) was selected as thermoset material, while polyamide 6 (PA 6) was chosen as thermoplastic material. The influence of injection temperature, preheating temperature and injection speed on the interfacial bonding strength of hybrid thermoset-thermoplastic composites was investigated. The results show that increasing injection temperature and preheating temperature have significant effects on the increase in bonding strength, while injection speed has little effect on it. In addition, the bonding strength of the co-cured interface is enhanced after the injection overmolding process, which is further studied through molecular dynamic (MD) simulation. The molecular dynamic simulation result shows that the high temperature and pressure during the injection process only have a weak effect on enhancing the bonding strength of the co-cured interface, while the chemical reaction at the co-cured interface is the main reason for the enhancement. Furthermore, the more chemical reactions occur at the interface, the stronger the interface will be.

Parameter Study on Force Curves of Assembled Electronic Components on Foils during Injection Overmolding Using Simulation.

The integration of assembled foils in injection-molded parts is a challenging step. Such assembled foils typically comprise a plastic foil on which a circuit board is printed and electronic components are mounted. Those components can detach during overmolding when high pressures and shear stresses prevail due to the injected viscous thermoplastic melt. Hence, the molding settings significantly impact such parts' successful, damage-free manufacturing. In this paper, a virtual parameter study was performed using injection molding software in which 1206-sized components were overmolded in a plate mold using polycarbonate (PC). In addition, experimental injection molding tests of that design and shear and peel tests were made. The simulated forces increased with decreasing mold thickness and melt temperature and increasing injection speed. The calculated tangential forces in the initial stage of overmolding ranged from 1.3 N to 7.3 N, depending on the setting used. However, the experimental at room temperature-obtained shear forces at break were at least 22 N. Yet, detached components were present in most of the experimentally overmolded foils. Hence, the shear tests performed at room temperature can only provide limited information. In addition, there might be a peel-like load case during overmolding where the flexible foil might bend during overmolding.

Mesoscale failure analysis of the hybrid structure by injection overmolding after compression process

The injection overmolding after compression (IOAC) is a promising hybrid process that manufactures the load-bearing parts by assembling the fiber-reinforced thermoplastic (FRTP) laminate with FRTP ribs. However, the size effects of interfacial mechanical interlocking on failure evolution are unclear. A mesoscale model of representative volume element, including the fibers, matrix, matrix-fiber interface as well as the IOAC interface, is established to predict its failure process and failure modes. The influence of IOAC interface waviness (height, width, and thickness) on shear and tensile strength is investigated. The results show that the increased height and thickness positively affect the shear and tensile strength, while the increased width has a negative effect. The crack originates from the wave trough of waveform interface at tensile loading, while it originates between the wave trough and the wave crest under shear loading. The primary failure modes of IOAC structure include interface fracture, matrix damage, and matrix-fiber interface debonding. The results in this work can guide the interface design by changing its waviness through the surface pretreatment and IOAC process control. Visualizing the failure process of IOAC structure can provide some information difficult to capture in tests, which is useful in predicting the failure degree and location of IOAC structure in engineering application.

Tow placement effects on fiber waviness and tensile performance of 3D-tow reinforced hybrid-molded composites

Three-dimensional (3D) tow reinforced hybrid molding combines continuous fiber composite tow with injection overmolding to improve mechanical performance of molded components, but tensile performance is not accurately captured by conventional modeling processes. When wrapped around load introduction points, the fibers of a thick tow traverse a shorter distance at the inner radius than the outer radius leading to waviness on the inner region of each wrap. The Hsaio and Daniel model was used to predict local elastic properties of the wavy fiber composite and spatially varying material properties were applied to 3D finite element models of a suspension link. Neglecting fiber waviness overpredicted experimental tensile stiffness and strength by 36% and 33% respectively while modeling waviness overpredicted stiffness and strength by only 9% and 14% respectively. Tow wrap configuration, waviness propagation, and material parameters have significant effect on tensile performance while the tow has little effect on compressive performance.

Injection overmolding of polymer‐metal hybrid structures: A review

AbstractPolymer‐metal hybrid (PMH) structures, also known as metal‐polymer hybrid (MPH) structures, have received considerable attention from industry and academia due to the societal need for developing strong, lightweight, and durable structures for several applications in strategic areas, such as transportation, household appliances, energy, and biomedical devices. Injection overmolding is an advantageous technique for manufacturing PMH structures as it combines automation, a fast process, cost efficiency, and dimensional accuracy. This review presents a comprehensive discussion of recent advances reported in the literature concerning PMH structures fabricated by direct‐adhesion injection overmolding. Following a general introduction, the fundamentals of the injection overmolding technique are presented. Next, the potential of some metal surface preparation methods to ensure good adhesion, and thus outstanding mechanical performance in injection overmolded PMH structures is discussed. Correlations are then made between metal surface features, processing parameters, and the mechanical strength of injection overmolded polymer‐metal joints. Some applications of injection overmolded PMH structures are explored, and, lastly, the main conclusions and prospects on the use of injection overmolding are presented.

Overmolded hybrid thermoset‐thermoplastic structures: Experimental study on the bonding strength of co‐curing thermoplastic film onto thermoset composite

AbstractIn the present study, an innovative approach to produce hybrid thermoset‐thermoplastic structure by means of co‐curing technique together with injection overmolding technique is proposed. To make thermoset composite bondable, a thermoplastic film was firstly co‐cured on the surface of thermoset composite. Five different types of thermoplastic film were chosen to co‐cure with thermoset composite. The bonding strength between thermoplastic film and thermoset composite was evaluated with lap shear strength. The results show that plasma treatment on thermoplastic film can promote polar groups at interface, which has positive effect on increasing wettability and can increase bonding strength by up to 69.7% of co‐cured structure. Meanwhile, increasing the surface roughness of thermoplastic film can also increase bonding strength by 162.9% because of mechanical interlock. Especially, because of low melting temperature of metallocene polypropylene, some fiber bundles in the interface zone were impregnated with molten metallocene polypropylene, resulting in strong bonding strength increased by 266.2% of the resultant co‐cured structure. Based on these results, polyamide 6 film was selected as the best thermoplastic boundary for co‐cured structure. Finally, hybrid thermoset‐thermoplastic was fabricated by injection overmolding of molten polyamide 6 on co‐cured structure, which has high average lap shear strength of around 14.9 MPa.

Process Optimization of Injection Overmolding Structural Electronics with Regard to Film Distortion

The integration of structural electronics in injection-molded parts is a challenging step. The films-comprising of laminated stacks with electronics-are exposed to shear stresses and elevated temperatures by the molten thermoplastic. Hence, molding settings have a significant impact on the successful, damage-free manufacturing of such parts. In this paper, test films with polycarbonate (PC) sheets as outer and two different thermoplastic polyurethanes (TPUs) as middle layers incorporating conductive tracks on a flexible printed circuit board (flexPCB) are manufactured and overmolded with PC. Parameter studies investigating the influence of the melt temperature, mold temperature, injection speed and used TPU layer were performed. The molded parts were inspected visually and compared with a numerical simulation using injection molding software. A shear distortion factor for the TPU layer was derived based on the simulations that linked the shear stresses with the injection time and the softening (melting) of the TPU. The distortion of the films was found to reduce with higher melt temperature, lower mold temperature and faster injection speed. Films using the TPU with the higher melting temperature yielded significantly better results. Moreover, distortion on the films reduced with the increasing distance to the gate and a larger cavity thickness was found to be beneficial. All those relations could be correlated with the shear distortion factor.

Injection over-molding warpage prediction of continuous fiber-reinforced thermoplastic composites considering yarn reorientation

The injection over-molding process combines thermo-stamping of continuous fiber reinforced thermoplastic (CFRTP) laminates and injection of plastic onto the surface of the CFRTP insert. A challenge for this process is to predict the warpage due to the influence of CFRTP insert. This work proposed a simulation method for predicting the warpage considering yarn reorientation induced in the thermo-stamping. In detail, the geometry and yarns reorientation of the deformed CFRTP inserts in thermo-stamping were calculated by a hybrid lamination model. Then the local thermo-mechanical properties were calculated according to the directions of reorientated yarns. Finally, the geometric and material information of CFRTP insert were imported into injection analysis, especially warpage prediction. The simulation method was validated by experiments on centrally injected bilayer plate and stiffened square box. This work highlights the importance of anisotropy induced from thermo-stamping on the final warpage of injection over-molded composite parts.

Joining of Macroscopic 3D Steel Transition Wire Structures to Steel Sheets: Study on the Mechanical, Microstructural, and Phase Characteristics of Brazed and Glued Joints

With an increased demand for the combination of different material classes in lightweight applications like automobiles, aircraft construction, etc., the need for simple and energy-efficient joining technologies to join these different material classes has been extensively researched over the last decades. One such hybrid material combination is the metal–plastic hybrid structure, which offers the combinational characteristics of high strength and stiffness of the metal part along with characteristic elasticity and low density of the plastic part. In this research work, the focus is laid on generating a graded property transition at the interface of metal–plastic joints by brazing a three-dimensional (3D) macroscopic transition wire structure (TWS) strucwire®, over the metal part before being molded with plastic at a later stage using an injection over-molding process. This helps in providing a mechanical interlocking facility and thereby achieving a higher load transfer at the interface of metal–plastic hybrid joints. The graded steel wire structures with different carbon content were brazed onto the galvanized steel sheets using the hotplate brazing technique. In addition to the Zinc layer on the galvanized steel sheets, electroplated Zinc coatings were fabricated on the wire structures to provide better brazing quality. The microstructural, mechanical, and intermetallic phase characteristics of the resulting brazed joints were evaluated using light microscopy, adhesion tests, and scanning electron microscopy, respectively.

Effect of plasma treatment parameters on the interfacial joining strength of overmolded hybrid fiber reinforced thermoplastic composites

AbstractIn this study, hybrid fiber reinforced thermoplastic composites (hybrid thermoplastic composites) with high interfacial joining strength were fabricated using a plasma treatment strategy and injection overmolding technique. A series of experimental investigations were carried out to ascertain the effects of various plasma treatments on the interfacial joining strength of the overmolded hybrid composites. Test results reveal that compared with the untreated continuous fiber reinforced thermoplastic (CFRT) substrates, the surface roughness of the CFRT substrates treated by plasma with air for the 10 min–160 W set‐up increases by 28.7%, the contact angle decreases by 50.5%, the silicon and fluorine are effectively removed, and the content of polar functional group increases remarkably, which bring about the increase of 24.76% of the interfacial shear strength of the overmolded hybrid composites. Further increase of plasma treatment time does not contribute to increase the interfacial shear strength of the overmolded hybrid composites. The interfacial shear strength at 60 W is 6.38% higher than that at 160 W, which is ascribed to the increase of the oxygen‐containing functional group content. Compared with the air and nitrogen plasma treatment, the interfacial shear strength of the overmolded hybrid composites after oxygen plasma treatment reaches the maximum value.

Overmolding of Hybrid Long and Short Carbon Fiber Polypropylene Composite: Optimizing Processing Parameters

Injection overmolding was used to produce hybrid unidirectional continuous-short carbon fiber reinforced polypropylene. Polypropylene pellets containing short carbon fibers were melted and overmolded on unidirectional carbon fibers, which act as the core of the composite structure. Four factors were varied in this study: fiber pretension applied to unidirectional fibers, injection pressure, melting temperature, and backpressure used for melting and injecting the composite pellet. This study aimed to evaluate the effect of these factors on fiber volume fraction, flexural strength, and impact strength of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken Response Surface Methodology (RSM) and analysis of variance (ANOVA). Each aspect was divided into three levels. There were 27 experimental runs carried out, with three replicated center points. The results showed that the injection molding process parameters had no significant effect on the fiber’s volume fraction. On the other hand, melting temperature and fiber pretension significantly affected impact strength and flexural strength.

Plasma treatment to improve the adhesion between ABS and PA6 in hybrid structures produced by injection overmolding

In this article, we investigate the possibility of combining ABS and PA6 in one structure by means of injection overmolding. The combination of these polymers in one structure is very promising, as PA6 offers good mechanical performance and high melting temperature and abrasion resistance. In contrast, ABS offers excellent impact properties, high water resistance, and cost competitiveness. However, these polymers are incompatible and do not adhere to each other. This study proposes atmospheric plasma treatment to create bonding between ABS and PA6 processed by injection molding. We demonstrated that bonding was created between ABS and PA6 due to the hydroxylation and the chemical conversion of nitrile groups to amide and carboxyl acid after the plasma treatment of ABS. Therefore, the plasma-treated ABS surface enabled the formation of various H-bonds, and the strong coupling of ABS and PA6 via secondary chemical binding forces appears. These results were also proved by mechanical tests, which showed that the bonding strength of the ABS/PA6 material pair reaches 12 MPa after plasma treatment, while an untreated case demonstrated no bonding at all.

Enhancement of interfacial strength of overmolded hybrid structures of short fiber reinforced polyamide 6 on continuous fiber reinforced epoxy composites under various surface pretreatments

AbstractHybrid thermoset‐thermoplastic composites were fabricated by injection overmolding technique in this paper. To improve the interfacial bonding between short fiber reinforced polyamide 6 and continuous fiber reinforced epoxy composites, three different surface pretreatment methods (i.e., surface silanization, plasma treatment and CO2 laser ablation) were employed. The results show that surface silanization leads to a weak increase in polar functional groups of thermoset composites surface, resulting in a weak increase in interfacial bonding strength of overmolded composites. Compared with plasma pretreatment, CO2 laser ablation can achieve a highest shear bonding strength due to the formation of interface between injected melt polymer and carbon fibers. This kind of structure is favorable for the bonding strength due to mechanical interlocking. CO2 laser ablation is a promising technology to improve the bonding strength between short fiber reinforced polyamide 6 and continuous fiber reinforced epoxy composites.