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We investigated products manufactured by in situ polymerization, which were reinforced with overmolded ribs. We developed our own mold and prototype product for the project. We used three different materials as preform: a material with a magnesium catalyst, manufactured by in situ polymerization, a Brüggemann AP-NYLON-based in situ polymerization material and an injection-molded PA6 (Durethan B30S, Lanxess GmbH) material. The ribs were formed from the same PA6 material (Durethan B30S, Lanxess GmbH). We examined the effect of the different technological parameters through the pull-off of the overmolded ribs. We measured the effect of melt temperature, holding pressure and holding time, and mold temperature. Considering the individual preforms, we pointed out that monomer migration and binding strength are related, which we concluded from the temperature-dependent mass loss of the materials, measured by thermogravimetric analysis (TGA). Finally, we designed a mold suitable for manufacturing overmolded parts. We designed and built pressure and temperature sensors into the mold to examine and analyze pressures and temperatures around the welding zone of the materials.
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Thermoplastic Overmolding onto Injection-Molded
and In Situ Polymerization-Based Polyamides
Róbert Boros, Praveen Kannan Rajamani and József Gábor Kovács *
Department of Polymer Engineering, Budapest University of Technology and Economics,
1111 Budapest, Hungary; (R.B.); (P.K.R.)
Received: 7 October 2018; Accepted: 29 October 2018; Published: 30 October 2018
We investigated products manufactured by in situ polymerization, which were reinforced
with overmolded ribs. We developed our own mold and prototype product for the project. We used
three different materials as preform: a material with a magnesium catalyst, manufactured by in
situ polymerization, a Brüggemann AP-NYLON-based in situ polymerization material and an
injection-molded PA6 (Durethan B30S, Lanxess GmbH) material. The ribs were formed from the same
PA6 material (Durethan B30S, Lanxess GmbH). We examined the effect of the different technological
parameters through the pull-off of the overmolded ribs. We measured the effect of melt temperature,
holding pressure and holding time, and mold temperature. Considering the individual preforms,
we pointed out that monomer migration and binding strength are related, which we concluded from
the temperature-dependent mass loss of the materials, measured by thermogravimetric analysis
(TGA). Finally, we designed a mold suitable for manufacturing overmolded parts. We designed
and built pressure and temperature sensors into the mold to examine and analyze pressures and
temperatures around the welding zone of the materials.
Keywords: overmolding; in situ polymerization; polyamide
1. Introduction
The importance of polyamides cannot be questioned as many automotive parts are made from
them, among others. Their mechanical properties, such as long-term properties, are increasingly
important [
]. Also, special technologies are developed which help shape the final parts.
Among others, overmolding, special joining techniques [
] and also the development of some special
electrical or thermal properties [4] could play a key role in their future development.
Injection molding—today’s most widely used plastic forming technology—is gaining popularity
fast in the automotive industry, too. In addition to conventional technologies, increasingly
special technologies are gaining ground in the manufacturing of automotive parts, including
gas- and water-assisted injection molding, bright surface molding and also reactive technologies.
Reactive injection molding (RIM) and resin transfer molding (RTM), however, cannot be integrated
into car factory assembly lines due to their considerably longer cycle times. Despite this, more and
more and larger and larger parts are manufactured with these technologies, for example, the whole
body of the BMW i3, which is produced with a cycle time of a few minutes [
]. The technology can
produce a functional part as a whole composite structure, but recycling is a problem because these
technologies produce cross-linked structures. For this reason, much research has been done in the past
few years into the practical application of in situ polymerization. The technology produces polyamide
structures of a thermoplastic matrix [
]. The advantage of the technology is that the mold is filled with
a low-viscosity oligomer, which can also impregnate complex textile systems, and then polymerization
also takes place in the mold [7].
Materials 2018,11, 2140; doi:10.3390/ma11112140
Materials 2018,11, 2140 2 of 9
This technology is known as thermoplastic-resin transfer molding (T-RTM), which combines low
viscosity to form the complex reinforcement-based structures and the recyclability of thermoplastics.
The low-viscosity reactive caprolactam system used in the T-RTM technology completely wets the
reinforcement, then polymerizes in the temperature-controlled mold in a few minutes, creating the
polyamide 6 polymer. This technology makes it possible to manufacture composite parts at low
injection pressure, and with cycle times as short as 1–2 min. The first step of manufacturing is cutting
the required geometry from the reinforcement. The layers are placed on top of each other with a binder
and preformed in a press. The type of binder has to be chosen so that it does not impair the adhesion
between the fibers and the matrix. The preformed parts are cut around their contour and placed in the
T-RTM mold. The preheated material reaches the heated mold through a mixing head (Figure 1).
Figure 1.
Scheme of the T-RTM process (A—nitrogen source; B—dosing unit; C—cold trap; D—vacuum
pump; E—dynamic mixing head; F—mold carrier; G—metal mold; H—textile preform; I—tank with
ε-caprolactam + initiator; K—tank with ε-caprolactam + activator [8].
Some of the first industrial parts for the T-RTM technology were produced by injection molding
machine developers, such as KraussMaffei [
] and Engel [
]. KraussMaffei produced some
demonstration parts for the automotive industry, such as a hybrid fiber-reinforced car roof cover
frame and a B-pillar [
]. They reached 58 to 70 percent fiber content with a cycle time of 2 to 5 min.
This demonstration project also involved a compression phase in the process, when the filling phase
was finished. With this uniform holding phase, their goal was to reduce shrinkage and void content,
and also to improve surface quality. Wakeman et al. [
] also used the advantage of this compression
method, where a small gap was maintained in the mold to provide space for injecting extra melt
for compensation.
The edge of products produced by T-RTM have to be either cut off or molded around, due to the
characteristics of the technology. The products are typically flat, with a simple geometry, and their
required rigidity can be achieved by overmolding ribs on them. As a result, overmolding will be
especially important as a supplementary technology of T-RTM. The thermoplastic-based continuous
fiber-reinforced preforms and overmolding on them are spreading because of the low mass of the
hybrid structure, short cycle times, and because the process can be automated very well and recycled
materials can be used. Interfacial adhesion is determined by the temperature of the welding zone,
the pressure in the mold cavity, and the intensity of the cooling of the welding zone [1113].
Multi-component hybrid thermoplastic parts can have overmolded parts all over the product or
overmolded parts, for example ribs, in just some parts. To examine the mechanical properties of the
two different parts, Joppich et al. [
] developed two different injection molds. The specimens that
they produced were suitable for pure tensile, pure shear and peeling tests. They performed the tensile
and peeling tests using a clamping system developed by Weidenmann et al. [
]. The results of the
tensile tests had high standard deviation; they explained this by claiming that local defects greatly
influence the measurement results, and also when the samples were prepared, some elements may
Materials 2018,11, 2140 3 of 9
have been weakened during cutting, and perhaps in the relatively small welding areas there may
have been differences in the morphology of the preform. They claimed that grouping the samples
according to the flow path would have decreased the standard deviation of the measurement results,
but later—as opposed to this—they pointed out that they could not differentiate the samples right after
the gate or at the end of the flow. The variance of the pure shear test was far lower, which indicates
good reproducibility, and suggests that due to the larger connecting surface, local defects affect the
shear strength of the structure to a lesser extent. They performed the peeling test of the overmolded
rib according to the DIN EN 6033 standard. The results had little standard deviation, which shows
good reproducibility, and proves that the method can be used in the testing of overmolding.
Kisslinger et al. [
] designed an injection mold which had an insert that could be moved when
the mold was closed, and had it manufactured. With this mold, they produced specimens with which
they examined the bonding strength between various materials. After the first component was injected
and solidified, the inserts were pulled back while the mold was still closed, and in the space thus
freed up, the second component was injected, whose melt front reached the cooled surface of the first
component. The authors claimed that the interphase of overmolded parts can be characterized by
Computed Tomography (CT) and Raman spectroscopy effectively, which they performed, but they
came to their conclusions after testing only one pair of materials with each method without trying
other methods.
Giusti and Lucchetta [
] worked out a method to determine the bonding strength between the
components of in-mold forming (IMF) hybrid composites. The matrix of the specimen they made
for the tensile tests was PA6 and its preform was a composite plate with fabric as reinforcement.
The overmolded component was 50% long fiber PA66. However, their preform was not large enough.
They examined seven specimens with each setting at a crosshead speed of 50 mm/min, but before the
test, they discarded visibly delaminated specimens, which was a mistake because they did not explain
the cause of the defect and did not specify how many defective specimens they had at each setting.
They showed with a one-way analysis of variance that both melt temperature and injection rate have
a considerable effect on welding strength.
2. Materials and Methods
Our goal was to analyze the overmolding of ribs on the PA6 preforms made by in situ
polymerization. For this, we designed our own product geometry (Figure 2), in which a rib of
a basic area of 30 mm
5 mm and a height of 15 mm with a side draft of 2
was overmolded on
a 50 mm
30 mm, 2 mm thick base plate. We designed a manually operated prototype aluminum
mold for the task (Figure 2) in which the rib was formed with a direct sprue.
Figure 2.
The mold and the part: left—molding (base plate overmolded with a rib through the gate),
right—the 3-plate-like aluminum prototype mold (half transparent).
We examined preforms of three different materials to obtain information about the effect of the
material and the manufacturing technology of the preform on the bond strength of the rib. The first
preform was a large sheet of 2 mm thickness, made by magnesium catalyst-based in situ polymerization
Materials 2018,11, 2140 4 of 9
(IS-A). The second material was the Brüggemann AP-NYLON-based (Versmold, Germany) in situ
polymerization plate where 3% of Brüggemann Brüggolen C10 was used as catalyst and 3% of
Brüggemann Brüggolen C20P was used as activator (IS-B). The third preform was an injection-molded
PA6 (Durethan B30S, Lanxess GmbH, Cologne, Germany) plate of 80 mm
80 mm and its thickness
was also 2 mm (IM).
The material of the overmolded ribs was also PA6 (Durethan B30S, Lanxess GmbH).
The granules—and later on the pre-plates as well—were first dried in a Heraeus UT20 hot-air dryer
(Heraeus Holding GmbH, Hanau, Germany) at 80
C for 6 h. The pellets were injection-molded with
an Arburg Allrounder 370S 700-250 injection molding machine (Lossburg, Germany) equipped with
a 30 mm diameter, L/D = 25 screw.
The tensile tests were performed on a Zwick Z005 universal testing machine (Zwick Roell AG,
Ulm, Germany) equipped with a special grip that we designed (Figure 3) to test the debonding force of
the ribs. All tests were executed at room temperature and at a relative humidity of 50%. Five specimens
were tested for each measurement and a 5 mm/min travel speed was used for the experiments.
Figure 3. The special grip for the rib pull-off tests.
3. Results and Discussion
For overmolding, the most important parameters are pressure (filling pressure too, but mainly
holding pressure) which holds the plate and the rib together, the duration of the pressure (holding time)
and also melt temperature and the preheating temperature of the plate. Based on Differential Scanning
Calorimetry measurements (ISO 11357-3:2018), the melting temperatures of the different types of PA6
are 218–223
C, thus the surface temperature of the pre-plate must reach its melting temperature to have
a welding effect. The suggested melt temperature range for injection molding varies from 260
C to
C, therefore the two limits were tested. The suggested mold temperature range varies from 80
to 100
C, but the mold temperature for the prototype mold cannot be controlled precisely, thus it was
controlled externally between the cycles, then the temperature was measured with a thermal imaging
camera right after the cycle. Three different mold temperatures were used; the low mold temperature
was about 30
C, the medium temperature was 50
C, while the high temperature was
70 ±10 C.
With the first tests the effect of the melt temperature of the injected material was evaluated.
The base plates were the commercially available plates produced by in situ polymerization. The mold
was cold; all the plates were kept cold for the measurements and prior to injection molding, their surface
was cleaned with acetone. As expected, the pull-off force increased with melt temperature (Figure 4).
Materials 2018,11, 2140 5 of 9
Figure 4. The pull-off force with the low and the high melt temperature.
The holding pressure was set to 200 bar and 400 bar for two series of tests, while holding time
was set to 15 s. Contrary to expectations, increasing holding pressure and holding time decreased
the bonding strength between the plate and the rib (Figure 5). Welding only occurred in the corners,
while the center of the plates only had adhesion.
Figure 5. The pull-off force as a function of holding time.
We performed scanning electron microscopy tests and found two different surfaces where the
base plate and the rib connected. One type was where the overmolded material did not melt the
base plate (Figure 6a), while in the other case the overmolded rib melted the base plate (Figure 6b).
Figure 6a shows an area at the edge of the middle of the rib. The whitish part is the contour of the edge
of the rib, the part above it is the part connected to the rib, while the part below it was covered by the
mold and did not come into contact with the melt. These two parts are identical, which proves that in
these areas connected to the rib the base plate did not melt and so no cohesion occurred between them.
In the case of the other type (Figure 6b) there is a tough break area, which proves that the base plate
melted, and cohesion occurred between the two components. In the individual tests, the proportion of
these two areas, that is, the melted and non-melted areas, changed.
Figure 6.
Scanning electron microscopy tests (100
magnification): (
) non-welded; (
) welded areas.
Based on these results, for the comparison of the materials, the high melt temperature and
the low holding pressure with a short holding time were used. Three different base plates were
Materials 2018,11, 2140 6 of 9
tested; the reference plate was the commercially available plate produced by in situ polymerization,
while the two others were the injection-molded plate and the in situ polymerization-based plate that
we produced. As can be seen, the best results were achieved with the in situ polymerization-based
plates, while the two others showed greatly inferior results (Figure 7).
Figure 7.
The pull-off force for the three different plates (IM—injection-molded plates;
IS-A—magnesium catalyst-based in situ polymerization plates; IS-B—Brüggemann AP-NYLON-based
in situ polymerization plates).
The results are in parallel with the residual monomer content of the given materials. It, however,
cannot be proved that this is the root course of the welding problems. We used thermogravimetric
analysis (TGA, Q500, TA Instruments, New Castle, DE, USA) to measure the monomer content of the
plates at 200
C and the lowest monomer content was found in the commercially available in situ
polymerization plate, which was 1.34%. The next was the injection-molded material, which had 1.49%
of monomer content, while the worst results came from the test version of the in situ polymerization
material, where the residual monomer content reached 1.82%.
As can be seen in Figure 7, the mechanical properties of the IS-B material
(Brüggemann AP-NYLON-based in situ polymerization plate with 3% catalyst and 3% activator) are
extremely weak. This phenomenon is a consequence of the degradation (depolymerization) of the
material over its melting temperature, as can be seen in Figure 8in the TGA results. Contrary to
the two consumer materials (IS-A, IM), the material we produced does not contain a stabilizer,
thus significant degradation occurred over its melting temperature.
Figure 8.
Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) curves for
the three different plates.
Although we used an aluminum prototype mold without a cooling system, the approximate
mold temperature was controlled externally between the cycles, then the temperature was measured
with a thermal imaging camera right after the cycle. The low mold temperature was about 20–40
the medium temperature was 40–60
C, while the high temperature was 60–80
C. With increasing
mold temperature, the possible monomer content of the surface of the plates increase, thus the pull-off
Materials 2018,11, 2140 7 of 9
forces decrease accordingly. Also, standard deviation decreases as mold temperature increases because
the possible monomer content on the surface more uniformly decreases the binding force (Figure 9).
Figure 9.
The pull-off force as a function of mold temperature (commercially available in situ PA6 plate
(IS-A); holding pressure was 200 bar and holding time was 1 s).
To verify the results obtained in this paper, we designed a mold suitable for overmolding,
which can overmold a 70 mm
50 mm rib on an 80 mm
80 mm preform (Figure 10). The mold
was designed to incorporate two pressure sensors and three infrared (IR) temperature sensors for the
analysis of the welding environment. The temperature of the welding environment can be analyzed
with the help of the temperature sensors, both from the side of the preform and the side of the rib,
close to the actual surface of welding. Also, temperature control of the mold and the inserts were
designed so that the temperature of the preform could be controlled well and the temperature could
be set over 100 C as well.
Figure 10.
Injection mold for the overmolding investigation equipped with pressure and infrared
temperature sensors.
4. Summary
Our goal was to investigate the reinforcement of products manufactured by in situ polymerization
with injection-molded ribs. To this end, we developed a prototype product and mold which made it
possible to overmold on different preforms with different technological parameter settings. We used
three different materials for the plate preforms. The first preform was from a material made by
in situ polymerization and with a magnesium catalyst. The second material was a Brüggemann
AP-NYLON-based in situ polymerization plate. The third preform was an injection-molded PA6
(Durethan B30S, Lanxess GmbH) plate.
Through the pull-off test of the overmolded ribs, we pointed out that in most cases,
most technological settings produce an effect opposite to what is expected. The only exception was
Materials 2018,11, 2140 8 of 9
melting temperature; increasing melt temperature improved binding strength between the rib and the
plate. On the other hand, increasing holding pressure and holding time impaired the quality of welding.
We assume that there is a connection between monomer migration and binding strength in the case of
the individual materials. Thermogravimetric analysis (TGA) showed that the most stable material is
the Polyamide (PA) made by in situ polymerization and with a magnesium catalyst—it showed the best
welding properties in the investigated range of technological parameters. Increasing mold temperature
also impaired the efficiency of binding, which is presumably also connected to the depolymerization
processes of the base material.
We designed an injection mold suitable for producing overmolded parts. We are going to
investigate the effect of injection molding parameters on the binding strength between the preform and
the overmolded part with the help of pressure and temperature sensors designed to be in the mold.
Author Contributions:
The research was conceived by J.G.K., R.B. and P.K.R. The methodology was planned by
J.G.K. and R.B. Injection molding was performed by R.B. and J.G.K. Experimental tests were performed by P.K.R.
and R.B. The manuscript was written by R.B. and P.K.R. with support from J.G.K.
The project is funded by the National Research, Development and Innovation (NKFIH) Fund, Project
title: “Production of polymer products by a short cycle time, automatized production technology for automotive
applications, with exceptional focus on the complexity and recyclability of the composite parts”; The application
ID number: NVKP_16-1-2016-0046. The developers are grateful for the support.
Conflicts of Interest: The authors declare no conflict of interest.
Szakács, J.; Mészáros, L. Effect of Fiber Contents on Fatigue Behavior of Injection Molded Polyamide 6 Matrix
Composites. Period. Polytech. Mech. Eng. 2017,61, 74–78. [CrossRef]
Chebbi, E.; Mars, J.; Wali, M.; Dammak, F. Fatigue Behavior of Short Glass Fiber Reinforced Polyamide
66: Experimental Study and Fatigue Damage Modelling. Period. Polytech. Mech. Eng.
,60, 247–255.
Leisen, C.; Drummer, D. Infrared welding of cross-linkable polyamide 66. Express Polym. Lett.
849–859. [CrossRef]
Fredi, G.; Dorigato, A.; Pegoretti, A. Multifunctional glass fiber/polyamide composites with thermal energy
storage/release capability. Express Polym. Lett. 2018,12, 349–364. [CrossRef]
Schmidhuber, S.; Fries, E.; Zimmermann, P. It couldn’t be more hybrid. Thermoplastic-matrix RTM on the
roof frame of the roading roadter. Kunstst. Int. 2017,1–2, 36–38.
Renkl, J.; Schmidhuber, S.; Fries, E. Variety of Lightweight Construction Processes. Kunstst. Int.
Bitterlich, M.; Ehleben, M.; Wollny, A.; Desbois, P.; Renkl, J.; Schmidhuber, S. Tailored to reactive polyamide
6. Kunstst. Int. 2014,3, 47–51.
Ageyeva, T.; Sibikin, I.; Karger-Kocsis, J. Polymers and related composites via anionic ring-opening
polymerization of lactams: Recent developments and future trends. Polymers 2018,10, 357. [CrossRef]
Sealy, C. Molding the future: Engel takes composite approach to composites. Reinf. Plast.
,60, 138–141.
Wakeman, M.D.; Zingraff, L.; Bourban, P.-E.; Månson, J.-A.E.; Blanchard, P. Stamp forming of carbon
fibre/PA12 composites—A comparison of a reactive impregnation process and a commingled yarn system.
Compos. Sci. Technol. 2006,66, 19–35. [CrossRef]
Joppich, T.; Menrath, A.; Henning, F. Advanced Molds and Methods for the Fundamental Analysis of Process
Induced Interface Bonding Properties of Hybrid, Thermoplastic Composites. Procedia CIRP
,66, 137–142.
Bouwman, M.B.; Donderwinkel, T.; Wijskamp, S.; Costa, F. Overmolding: An Integrated Design Approach
for Dimensional Accuracy and Strength of Structural Parts. In Proceedings of the 3rd Annual Composites
and Advanced Materials Expo, Anaheim, CA, USA, 26–29 September 2016.
Materials 2018,11, 2140 9 of 9
Ferfecki, F.J.; Chung, S.; Hayduke, D. Performance and Simulation of a Thermoplastic Paek Hybrid Composite
System. Available online:
a-thermoplastic-paek-hybrid-composite-system-whitepaper.pdf (accessed on 30 October 2018).
Weidenmann, K.A.; Baumgärtner, L.; Haspel, B. The Edge Shear Test—An Alternative Testing Method for
the Determination of the Interlaminar Shear Strength in Composite Materials. Mat. Sci. Forum
806–813. [CrossRef]
Kisslinger, T.; Bruckmoser, K.; Lucyshyn, T.; Langecker, G.R.; Resch, K.; Holzer, C. Interface conditions of
two-shot molded parts. AIP Conf. Proc. 2014,1593, 170–174.
Giusti, R.; Lucchetta, G. Modeling the Adhesion Bonding Mechanism in Overmolding Hybrid Structural
Parts for Lightweight Applications. Key Eng. Mater. 2014,611–612, 915–921. [CrossRef]
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... Up to now, the molding processes has mainly focused on the solvent method, extrusion and injection, compression molding, VARI and other processes. However, the in situ injection molding process [19] with high productivity and easy automation is rarely studied. Unlike the melting method, in in situ injection molding, low viscosity monomer or oligomer is impregnated with reinforcing fiber to form thermoplastic composite material after ringopening polymerization in the mold. ...
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In situ injection molding of continuous fiber reinforced thermoplastic composites is challenged by unbalanced dual-scale infiltration flow due to the pronounced capillary effect. In this paper, a general and efficient approach was proposed for dual-scale infiltration flow balancing based on numerical simulation. Specifically, Stokes and Brinkman equations were used to describe the infiltration flow in inter- and intra-fiber bundles. In particular, capillary pressure drop was integrated in the Brinkmann equation to consider the capillary effect. The infiltration flow front is tracked by the level set method. Numerical simulation and experimental results indicate that the numerical model can accurately demonstrate the unbalanced infiltration flow in inter- and intra-fiber bundles caused by the changes of the injection rate, the resin viscosity, the injection rate, the fiber volume fraction and the capillary number. In addition, the infiltration flow velocity in inter- and intra-fiber bundles can be efficiently tuned by the capillary number, which is mainly determined by the injection rate for a specified resin system. The optimal capillary numbers obtained by simulation and experiment are 0.022 and 0.026, which are very close to each other. Finally, one-dimensional in situ injection molding experiments with constant injection pressure were conducted to prepare fiber reinforced polymerized cyclic butylene terephthalate composite laminate with various flow rates along the infiltration direction. The experimental results confirmed that the lowest porosity and the highest interlaminar shear strength of the composite can only be obtained with the optimized capillary number, which is basically consistent with the simulation results.
... A control over microstructure can provide parts with tailored mechanical and thermal properties and enables more flexibility in their design. Currently, overmolding is often used to locally strengthen and support localized week spots in molded structures [12,13]. Typically, overmolding reinforcements onto base parts is expensive and involves a secondary manufacturing process [14]. ...
In this work, large-scale multimaterial preforms produced by additive manufacturing (AM) underwent compression molding (CM) to produce high-performance thermoplastic composites reinforced with short carbon fibers. AM and CM techniques were integrated to control the fiber orientation (microstructure) and to reduce void content for the improved mechanical performance of the composite. The new integrated manufacturing technique is termed “additive manufacturing-compression molding” (AM-CM). For the present study, the most common materials were used for large-scale printing, i.e., acrylonitrile butadiene styrene (ABS), carbon fiber (CF)–filled ABS (CF/ABS) and glass fiber (GF)–filled ABS (GF/ABS). Three different manufacturing processes; (a) AM (b) extrusion compression molding (ECM), and (c) AM-CM were used to prepare four different panel configrations: (1) neat ABS, (2) CF/ABS, (3) overmold (CF/ABS over neat ABS), and (4) sandwich (neat ABS between two CF/ABS layers). The mechanical properties (tensile and flexural strength and modulus, and Izod impact energy) of samples prepared via all three manufacturing processes were compared. X-ray microcomputer tomography was employed to evaluate the fiber orientation distribution and the volumetric porosity content. The preform maintained high fiber alignment (≈ 82% of fibers within the range of 0° to 20° in the deposition direction), and the volumetric porosity was reduced by 50% from 3.79% to 1.91% after compression. The alignment of long pores along the deposition direction was also observed. The mechanical properties are discussed with correlation to the fiber alignment and void content in the samples. CF/ABS samples prepared by AM-CM showed significant improvement of 11.15%, 35.27%, 28.6%, and 74.3% in the tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively, when compared with samples prepared by ECM. Unique aspects of this study are the demonstration of large-scale multimaterial AM and the use of multimaterials as preforms to make high-performance composites.
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The presented research was focused on the development of a new method of sandwich structure manufacturing involving FDM-printing (fused deposition modeling) techniques and compression molding. The presented concept allows for the preparation of thermoplastic-based composites with enhanced mechanical properties. The sample preparation process consists of 3D printing the sandwich’s core structure using the FDM method. For comparison purposes, we used two types of GPET (copolymer of polyethylene terephthalate)-based filaments, pure resin, and carbon fiber (CF)-reinforced filaments. The outer reinforcing layer “skins” of the sandwich structure were prepared from the compression molded prepregs made from the LCP (liquid-crystal polymer)-fiber fabric with the GPET-based matrix. The final product consisting of an FDM-printed core and LCP-based prepreg was prepared using the compression molding method. The prepared samples were subjected to detailed materials analyses, including thermal analyses (thermogravimetry-TGA, differencial scanning calorimetry-DSC, and dynamic thermal-mechanical analysis-DMTA) and mechanical tests (tensile, flexural, and impact). As indicated by the static test results, the modulus and strength of the prepared composites were slightly improved; however, the stiffness of the prepared materials was more related to the presence of the CF-reinforced filament than the presence of the composite prepreg. The main advantage of using the developed method is revealed during impact tests. Due to the presence of long LCP fibers, the prepared sandwich samples are characterized by very high impact resistance. The impact strength increased from 1.7 kJ/m2 for pure GPET samples to 50.4 kJ/m2 for sandwich composites. For GPET/CF samples, the increase is even greater. The advantages of the developed solution were illustrated during puncture tests in which none of the sandwich samples were pierced.
The overmolding of short fiber reinforced polymer compounds onto continuous fiber reinforced composite substrates provides design flexibility and the ability to tailor stiffness, strength, and damage tolerance for structural applications. In this work, a novel molding approach that enhances the bonding strength by mechanical interlocking is presented. The effectiveness of the proposed approach was validated by characterization of the bonding strength between a short glass fiber PP (SGFPP) composite overmolded onto a continuous glass fiber reinforced PP (CGFRPP) prepreg. Enhancement of the bonding strength was achieved by judiciously drilling tapered holes on the CGFRPP substrate before molding, which facilitated better interlocking with the injection molded SGFPP composite. The overmolding of preheated composites with tapered holes yielded up to 60% improvement in bonding strength. In general, having multiple holes helped improve bonding up to certain hole diameter. Similarly, preheating of the substrate over a short time improved the interfacial adhesion, while extended preheating resulted in a reduction of bonding quality. SEM analysis of the fracture surfaces after the tensile debonding test revealed that the SGFPP filled the holes on the substrate during overmolding. Preparation of overmolded composit.
A great deal of attention has been paid in recent years to the integration of two and three-dimensional integrated electronic parts into plastics, both for their potential applications in modern human lives and for their outstanding properties, which include the ability to reduce product weight and space while increasing product reliability. The development of integrated electronic devices into plastics is advancing rapidly, owing to advancements in methodology and manufacturing techniques, which have significantly raised researcher interest in this topic. In-mold electronics (IME) is a term that describes an injection molding technology that integrates a printed foil with electrical components into a plastic part during the molding process. It is a revolutionary way to form two and three-dimensional products using electronic printed circuits. IME technology is comprised of three fundamental disciplines of study: electronics, materials science, and plastic manufacturing processes. Therefore, this review article aims to summarize the knowledge of these three primary fields to present an overview of in-mold technology. This article covers background history, a description of the In-mold process flow, and summarizes the recent real-life applications. Additionally, this article discusses some of the present technology challenges that must be overcome.
Overmolding process is one of the growing advanced technologies for fabricating lightweight composite structures used in the aerospace and automotive industries. This technology enables integrating multiple types of reinforcements from macro- to nano-scale in thermoplastic and thermoset matrices and assembling of dissimilar polymeric materials. Besides, this process is well suited to a digitalization of advanced composite manufacturing for complex geometries with outstanding performance and high adaptation to multifunctionality. The present review aims to cover the recent developments in the design and fabrication of thermoset- and thermoplastic-based composite systems via overmolding process under i) multi-material injection molding and ii) insert molding technologies with the employment of nano/micron-scale reinforcements. Multi-material injection molding (or over injection) is investigated by considering two or more thermoplastic polymeric systems in a single mold to obtain high structural performance and bonding quality. On the other hand, the insert molding process is evaluated through matrix and reinforcement types to understand the strength and structural integrity during composite manufacturing. The main bottleneck of adhesion strength in the overmolding process is elaborated with the discussion of distributive approaches and offers a new perspective in producing multi-functional composites in a single-step process with design tools.
This work reports the preparation and characterization of fully bio-based polymer composites with coconut fibers (CFs) as an alternative to wood-plastic composites (WPCs), typically based on petroleum derived materials. Polyamide 1010 (PA1010) was melt-extruded with 20 wt% of CFs and, after that, shaped into pieces by injection molding. Four different multi-functionalized compatibilizers were tested to increase the polymer-fiber interactions with the subsequent improvement on toughness. These consisted of two chemically modified vegetable oils, namely maleinized and epoxidized linseed oil (MLO and ELO) respectively, and two commercial additives derived from petroleum and based on glycidyl functionality, that is, low-functionality epoxy-based styrene-acrylic oligomer (ESAO) and polystyrene-glycidyl methacrylate random copolymer (PS-GMA). The addition of all four compatibilizers improved both the mechanical and thermomechanical properties of the composites, thus resulting in high-performance composite materials with relatively low water uptake. Furthermore, the morphology of the obtained composites revealed an extraordinary embedment of the fibers into the biopolymer matrix, which plays a crucial role in improving toughness. Among all the tested compatibilizers, those derived from vegetable oils can be considered the most interesting ones due to they offer a more sustainable solution.
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This paper presents a comprehensive overview of polymers and related (nano)composites produced via anionic ring opening polymerization (AROP) of lactams. It was aimed at surveying and showing the important research and development results achieved in this field mostly over the last two decades. This review covers the chemical background of the AROP of lactams, their homopolymers, copolymers, and in situ produced blends. The composites produced by AROP were grouped into nanocomposites, discontinuous fiber, continuous fiber, textile fabric, and self-reinforced composites. The manufacturing techniques were introduced and the most recent developments highlighted. Based on this state-of-art survey some future trends were deduced and as their "driving forces" novel and improved manufacturing techniques identified.
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Thermoplastic composite laminates with thermal energy storage (TES) capability were prepared by combining a glass fabric, a polyamide 12 (PA12) matrix and two different phase change materials (PCMs), i.e. a paraffinic wax microencapsulated in melamine-formaldehyde shells and a paraffin shape stabilized with carbon nanotubes. The melt flow index of the PA12/PCM blends decreased with the PCM concentration, especially in the systems with shape stabilized wax. Differential scanning calorimetry showed that, for the matrices with microcapsules, the values of enthalpy were approximately the 70% of the theoretical values, which was attributed to the fracture of some microcapsules. Nevertheless, most of the energy storage capability was preserved. On the other hand, much lower relative enthalpy values were measured on the composites with shape stabilized wax, due to a considerable paraffin leakage or degradation. The subsequent characterization of the glass fabric laminates highlighted that the fiber and void volume fractions were comparable for all the laminates except for that with the higher amount of shape stabilized wax, where the high viscosity of the matrix led to a low fiber volume fraction and higher void content. The mechanical properties of the laminates were only slightly impaired by PCM addition, while a more sensible drop of the elastic modulus, of the stress at break and of the interlaminar shear strength could be observed in the shape stabilized wax systems.
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Hybrid thermoplastic composites play an increasingly important role in lightweight applications. One key challenge in the intrinsic hybridization is to achieve an adequate interface bonding strength. In order to optimize the interface strength specific methods for characterization and process monitoring need to be developed. Thus, within this paper two advanced mold concepts are presented allowing online monitoring of the welding conditions at the spot and time of interest. The resulting part geometries are optimized for characterization of interface properties in a defined and reliable manner. Regarding this, adopted characterization setups are presented and validated allowing the characterization of three stress states.
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In this study the effect of basalt and carbon fiber content on quasi-static and fatigue mechanical properties of polyamide 6 are investigated. Composites with different fiber contents were melt compounded, then specimens were injection molded. The presence of basalt and carbon fiber caused significant change in tensile properties; the effect of carbon fibers was major as expected. Fatigue life of composites decreased compared to the neat matrix, but it should be mentioned that higher load was applied in case of composites. Carbon fibers had remarkable effect on the decrement of cyclic creep. This means that the deformation of carbon fiber reinforced composites was lower than that of basalt fiber composites, even if load level was higher. Scanning electron microscopy of the fracture surfaces revealed larger tough fracture surface for carbon fiber reinforced composites compared to the basalt fiber reinforced ones.
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The aim of the present paper is to study and model the fatigue behavior of short glass fibers reinforced polyamide-66. The effect of fiber content on the fatigue and static behavior of this composite is investigated. In such composites fatigue damage growth exhibits three stages. A continuum damage based model is presented to predict damage evolution during these three stages. Experimental results show that increasing the fiber content increases the elastic modulus and the tensile strength of the studied materials under tensile tests. However, the rupture behavior changes from ductile to brittle. Moreover increasing the fiber percentage changes the S-N curves slope and decreases the fatigue life. Analytical results predicted by the proposed model, compared to experimental ones shows good agreement and the developed model predicted fatigue damage growth in its three stages of evolution with good performance.
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Radiation cross-linking of polyamide 66 with electron beams alters the material’s characteristics. This leads to a varied relationship amongst the process, structure, and properties for infrared welding cross-linked polyamide 66. A threedimensional network of covalent bonds results in an impeded melt flow and altered welding characteristics. Compared to non-cross linked polyamide, a changed energy input in the weld during infrared heating and a reduced meltdown can be observed. Such thermal developments and a reduced meltdown affect the resulting weld strengths. Welding factors of almost 60% of base material strengths can be achieved. A clear influence of the heating time on the weld strength can be observed. The scope of this article is to investigate the influence of radiation cross-linking on the material characteristics and, by extension, the resulting processing and welding characteristics. Mechanical and optical investigations serve to highlight the influence of radiation cross-linking on the infrared welding process of polyamide 66.
High-pressure resin transfer molding (HD-RTM) is an established process for the series production of fiber-reinforced parts, with many variants. It therefore covers a variety of possibilities for part design and material selection.
Austrian company ENGEL has grown from a machine manufacturer to a worldwide leader in injection-molding system solutions over the last 70 years. Peter Egger, Director of ENGEL's Center for Lightweight Composite Technologies, tells Reinforced Plastics how ENGEL has done it and what the future holds.
The interlaminar shear strength is a characteristic value describing the mechanical behavior of composite materials such as laminates. Several methods for the determination of the interlaminar shear strength are described in open literature by several authors. Among these methods, the ILSS test (DIN EN ISO 14130) measuring the apparent interlaminar shear strength by using a modified bending test is the state of the art technique, as both the necessary testing equipment and the sample geometry are quite common. However, the ILSS tests implements shear loads indirectly by bending often leading to sample failure which is then not solely initiated by shear loads. Particularly for ductile matrices or those showing pronounced elastic behavior under bending, no interlaminar shear failure can be implemented and the interlaminar shear strength can not been determined or – if the user is not sensitized to the identification of non-shear failure behavior – the determined value is not correct.Up to now, alternative methods for determining the interlaminar shear strength implementing a shear load directly to the sample are quite elaborate regarding the test equipment to be used or the specimen preparation and geometry. In this contribution the authors present a novel test setup for an edge shear test which allows both a direct shear load and at the same time a reduced complexity of the specimen geometry which is comparable to those used in the ILSS test. The authors present results based on this novel testing method in comparison to conventional ILSS tests.