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Artículo Científico / Scientific Paper |
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https://doi.org/10.17163/ings.n24.2020.03 |
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pISSN: 1390-650X / eISSN: 1390-860X |
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RAPID PROTOTYPING IN THE MANUFACTURE OF 3D PRINTED
MOLDS FOR PLASTIC BLOWING |
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PROTOTIPADO RÁPIDO EN LA FABRICACIÓN DE MOLDES IMPRESOS EN 3D PARA SOPLADO DE PLÁSTICO |
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Gilberto Carrillo1,*, Carolina Nuila2, Jorge Laínez3 |
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Abstract |
Resumen |
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In the Salvadoran industry, we can find entrepreneurs and microentrepreneurs who do not have the resources to make
plastic bottles with stylized designs that differentiate them from other
brands and products, which prevents them from escalating to other market
segments or international markets, slows the growth of their business. One
possible cause is that the manufacture of blow molds requires a very
expensive initial investment. However, there are alternatives such as the
manufacture of low-run molds, which have lower resolution and shorter life time, but, at the same time, offer as a benefit a
lower manufacturing cost and, therefore, lower acquisition cost for the
entrepreneur, opening in this way the opportunity to be able to produce
stylized bottles at convenience. Among the various ways to manufacture
low-run molds, there is the reverse engineering technique, which requires
rapid prototyping equipment. This article describes the reverse engineering
procedure to generate the mold for blowing. With the available design the necessary mold was printed and with this, the
bottles were manufactured, which were scanned to verify with computer program
their dimensions comparing them against the original mold file.
Simultaneously, the containers were verified in the industrial metrology laboratory to validate the
computer results, these results are presented in the document. |
En la industria salvadoreña pueden encontrarse empresarios y microempresarios que no tienen los recursos para fabricar botellas de plástico con diseños estilizados que los diferencien de otras marcas y productos, lo que les impide escalar a otros segmentos de mercado o mercados internacionales, frenando el crecimiento de sus negocios. Una posible causa es que la fabricación de moldes de soplado requiere una inversión inicial muy costosa. Sin embargo, existen alternativas como la fabricación de moldes de bajo rendimiento, que tienen una resolución más baja y un tiempo de vida más corto, pero, al mismo tiempo, ofrecen como beneficio un menor costo de fabricación y, por lo tanto, un menor costo de adquisición para el empresario, posibilitando la producción de botellas estilizadas a conveniencia. Entre las diversas formas de fabricar moldes de bajo rendimiento está la técnica de ingeniería inversa, que requiere un equipo de creación rápida de prototipos. Este artículo describe el procedimiento de ingeniería inversa para generar el molde para soplado. Con el diseño disponible se imprimió el molde necesario y con esto se fabricaron las botellas, que se escanearon para verificar con el programa de computadora sus dimensiones comparándolas con el archivo original del molde. Simultáneamente, los contenedores se verificaron en el laboratorio de metrología industrial para validar los resultados de la computadora, estos resultados se presentan en el documento. |
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Keywords: Mold for blowing,
3D printing, rapid prototyping, plastic bottles. |
Palabras clave: molde para
soplado, impresión 3D, creación rápida de prototipos, botellas de plástico.
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1,*Centro de Innovación en Diseño Industrial y Manufactura, Universidad Don Bosco, El Salvador. Corresponding autor ✉:
gilberto.carrillo@udb.edu.sv. 2Laboratorio de
Metrología, Universidad Don Bosco, El Salvador. 3Herramientas
Centroamericanas S. A. de C. V., El Salvador.
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Received: 04-02-2020, accepted after review: 06-05-2020
Suggested citation: Carrillo, G.; Nuila, C.
and Laínez, J. (2020). «Rapid prototyping in the manufacture
of 3D printed molds for plastic blowing». Ingenius.
N.◦ 24, (july-december). pp. 28-35. doi: https://doi.org/10.17163/ings.n24.2020.03 |
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1. Introduction The manufacturers
of plastic containers and the Salvadoran entrepreneurs cannot acquire new
steel and aluminum alloy molds for new products, since it requires a high
initial investment that can only be amortized with
the high production of products [1]. As an example, the metal versions of the
bottle blow mold can cost from US$ 2,000 up to US$ 5,000, which regionally
manufactured can be received between 30 and 60 days and manufactured in
Europe or North America can be received from 90 to
150 days [2]. This implies that the micro, small and medium-sized Salvadoran
companies with low profit margins cannot incorporate new products with
differentiated plastic containers in their offer. As alternative solution for molds, 3D printing becomes a “disruptive
technological innovation driven by the flexibility it provides and the
potentially favorable economics” [3]. Another applications
of printed molds are used for hand-manufacturing composite parts [4]],
manufacturing plastic parts [5], develop low-cost wax injection mold [6].
Whereas it alters traditional manufacturing
approaches and promotes the expansion of rapid prototyping and digital
manufacturing technologies. Figure 1. Digital manufacturing techniques. Digital manufacturing technologies can be classified into additives
such as 3D printing and subtractive as |
cutting equipment with CNC
controls (computerized numerical control), as shown in Figure 1. There are practices in the United States and Europe, where they use
additive technologies such as SLA ( Stereolithography)
and SLS (Selective Laser Sintering) in the manufacture of molds by injection
[7]. These technologies are high investment and useful in small-scale
production. To the knowledge of the authors the technique
FDM (Fused Deposition Modeling) has been used little in the manufacture of
molds. This work presents the manufacture of a mold by means of rapid
prototyping and low investment FDM technology, with which containers with
stylized designs are produced for each need. 2. Materials and
Methods Considering the
modeling techniques, the mold generation methods could be classified
in reverse engineering and CAD process (Computer Aided Design), represented
in Figure 2 and described as 5 stages. Applying reverse engineering, we scanned a container provided by the
industry from which the mold was obtained for study. Figure 2. Stages of rapid prototyping applied. In stage 1, the SmartScan R2-C2 scanning and
scanning equipment with an accuracy of 0.01 mm and its |
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Optocat 2015®software was used. The developer liquid is CANTESCO D101-A to
attenuate the brightness and reflection of the surfaces to be scanned. The
scanning procedure is in accordance with the user manual OPTOCAT version
2015R2 [8]. The temperature of the rapid prototyping room was kept
in stable conditions (24 oC) and the entrance of
light from outside was reduced less than 25% of the live image illuminated to
avoid noise in the scanned images due to the light variations. The final
cloud of points is saved in a file with STL format (Standard
Triangle Language), to work then in other software. During stage 2, the edition of the scanned surface was
done with the treatment of the point cloud, using the CAD software GeoMagic Design X. The generated file was
saved in STEP format (Standard for the Exchange of Product Data) which
prevents the loss of design information. For stage 3, the mold construction was carried out
with Inventor software. Was incorporated block dimensions, alignment holes,
thread, air exhaust holes, nozzle design. Within stage 4, the material used in the 3D printing of the blow molds
was ABS-plus (acrylonitrile styrene butadiene P430XL), the support material
is SR-30XL (soluble support), the bottles material
is PET (polyethylene terephthalate). Likewise, 3D printing process was done according with the user manual of the uPrint SE Plus printer, the software used is called CatalystEX and the system of elimination of support is
the WaveWash equipment that works by means of
ultrasonic washing [9]. The mold was used in the POLIFLEX
company to manufacture 25 test bottles. With this first run
the recommendations that make up stage 5 arise. In stage 5 the surface finishes of the mold
were made with automotive putty in the cavity where the container is formed. The
manual sanding was carried out with sandpaper 1000
to improve the surface smoothness that facilitates the sliding of the PET
during the blow. Outside the reverse engineering process, the containers were scanned for comparison by software, and tests were
performed in the industrial metrology laboratory to validate the software
results. 3. Results and
Discussion In this section the results are presented in the order of blocks
shown in Figure 2. |
Stage 1. A cloud of points was obtained from
the scan and digitization process, as shown in Figure 3. It was not necessary
to scan the container’s nozzle, since in the later stage of digital
construction the nozzle design was incorporated. according to the blower machine. The possibility of change
of nozzle in the mold occurs when planning to produce containers with
machines that require preforms.
Figure 3. Nube de puntos del recipiente con formato STL, resultante del proceso de escaneado 3D y de escaneado y listo para ser procesado con software CAD.
Stage 2. The scanned surface edition consists of the set of operations
to obtain a smoothed body, like cutting, merge, repair, smooth surfaces and
borders. The STL file can be improved with any CAD
software. The final bottle is shown in Figure 4, and
can incorporate characteristic final details such as additional forms, areas
for labeling, texts and logos in high and low relief, etc. Figure 4. Bottle smoothed by computer and finished. |
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Stage 3. The digital construction of the mold consists in transforming
the bottle from the previous stage (stage 2) to solid in the CAD. The solid
body in the shape of a half bottle is joined by means of a process of cutting
solid objects in the CAD software and later the details of the mold are
added, for example, the fixing holes, threads, exhaust holes and nozzle
spaces. Some important considerations foreseen in the digitization of the
mold, and that influence the quality of the products are: • There were no defects in
the overlapping of the container and mold block volumes. • The thickness of the
surfaces at the edges allowed to resist the loads received. • The curvatures of the geometries
and the surfaces are correct to reduce the stress concentration. • The alignment of holes,
pins, surfaces and edges were indicated to avoid
unevenness in the surfaces of manufactured products [10]. • The tolerances of holes
were correct so that both parts could be coupled
during the production of containers with a sliding fit [11]. • The dimensions of the air
exhaust were adequate so that no marks are seen in
the manufactured containers. Figure 5. Sequence of processes for mold manufacturing: The
solid body in the shape of a half bottle is joined by means of a process of
cutting solid objects in the CAD software and later the details of the mold
are added, for example, the fixing holes, vents and nozzle spaces. The nozzle depends on the type of machine where the mold will be installed and the type of raw material. For
example, the nozzle of the blow molding machine forms the external thread and
uses granulated material, while |
the nozzle of the preform
machine is smooth because it receives the preforms with its already
manufactured thread. With this information a nozzle
was drawn to the mold as shown in Figure 5. The molds were designed with a removable
bottom, which should be removed during the demolding of the container and
installed during the closure of the mold. Its function is to evacuate the air
during the blowing and form the bottom of the container to provide stability
of it while remaining on flat horizontal surfaces. The designed
mold was analyzed by means of a computer with CAE Inventor software (Computer
Aided Engineering), applying a pressure of 350 psi in the curved surfaces
which is the blowing pressure for the manufacture of bottles. The results are
shown in Figure 6, it is observed that could be an
average deformation of 0.66 mm represented by the green area, and a maximum
deformation of 1.026 mm at the bottom of the mold represented by the red
area. Figure 6. Critical points of the deformation of the mold,
considering the points of concentration of efforts calculated by the software
and shown in the color palette. The simulated charge pressure was 350 psi,
analysis temperature 100 °C, and the units for deformation shown in the color
scale in millimeters. Stage 4. ABS was used as printing material,
Figure 7. The height of the printing layers is 0.25 mm, shell thickness of
outer surface 10 mm, infill density 100% in the wall, infill density in the
middle 60%, top/bottom thickness solid layers 10 mm, with the uPrint SE plus equipment, which generates low resolution
curved surfaces. This is difficult when you need smooth bottles, while for
stylized designs with rough surfaces is an advantage. In our case the bottom
of the mold was printed |
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as part of one
of the halves and although it showed some interference in the demolding, it
affected 2 bottles of 25 so we considered that it had no negative effect during
the manufacturing Figure 7. Blow molds for bottles printed in ABS. The mold for blowing bottles is shown in
Figure 7. The 3D printing mold includes ABS material and support material of suppliers
in El Salvador, Table 1 shows 3D printing costs. The main cost is about
materials and designer time, the cost of materials can be reduced when uses a open source 3D printer, and
allows research about new 3D printing materials with better mechanical
properties. The working time in CAD can be optimized
practicing to improve skills. Table 1. Cost of 3D printed molds, using prices of existing
materials in the Salvadoran market |
Figure 8. Plastic bottles made with the use of printed molds.
With printed mold, 25 containers were obtained
in a production company, the mold was installed in one of its blowing
machines and bottles were produced as shown in Figure 8. The mold and the
bottles were verified with the help of the scanner,
determining that they are in good dimensional conditions. It is considered that the surfaces of interest to evaluate
are those that supported the pressure of the preforms during the blowing
operation and the surfaces that supported the closing pressure of the
machine. The bottles were scanned and compared to the design
of the mold in CAD format. Figure 9 shows the points of the digitally
verified containers, based on the critical points resulting from the CAE Inventor
analysis of the mold in Figure 6. In general terms,
the dimensions of the containers are in the range of a tenth and a half
millimeter above the average dimensions, and three tenths of a millimeter
below the average. Figure 9. Digital verification of the dimensions of the
containers produced with the printed mold together with its color palette. |
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The colors blue, light blue, green and yellow in Figure 9 denote
minimum deviations of the scanned model with respect to the digital model, so
it is verified that the manufactured bottles are kept in the ranges of +0.15
and -0.2 mm. The measurement results obtained with digital technique are shown in Table 2. Brown color denotes high positive/negative
deviation and yellow color indicates low positive/negative deviation from the
average dimensions, the dimensions are A=168.168 mm (high), B=61.130 mm
(upper width), C=72.610 mm (lower width), D=41.518 mm (higher depth),
E=43.049 (lower depth). |
The containers were analyzed in the metrology
laboratory to verify hermeticity, dimensions and
weight [12]. The verification points and part of the equipment used are shown in Figure 10, and Table 3 shows an extract of
the determined average and extreme values. Similarly, Table 4 presents an
extract of the determined weights, indicating the extreme and average values.
It is important to note that none bottle presents leaks after being tested with water. |
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Table 2. Results of the difference of measurements between
the produced containers and the printed mold |
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Table 3. Reference diagram for the dimensional analysis and execution of
dimensional tests with the dimensions A high, B upper width, C lower width, D
higher depth, E lower depth. Table 4. Weight measurement results of the 25 containers |
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Figure 10. Reference diagram for the dimensional analysis and
execution of dimensional tests with the dimensions A high, B upper width, C
lower width, D higher depth, E lower depth. Stage 5. To improve the surface finish, automotive putty was applied to the mold and smoothed with 1000 grade sandpaper,
which achieved a smooth surface with roughness not noticeable to touch.
This operation is variant to the normal prototyping procedure, where the
models printed in 3D FDM are used without further
processing. This artisanal process is recommended
because it is inexpensive and does not take a long time or makes the mold
more expensive, which transforms into a benefit for an SME with a low budget.
The technical note of Hernández [13] refers to the level of roughness or
smoothness effects on the flow of the parison
during blowing because of friction against the surface of the mold. This fact
may seem counterproductive, however, after observing
the first containers, the surface texture can be a distinctive element for
SMEs that can incorporate different designs in their packaging. A useful result for SME users of the mold is the time elapsed from scanning
until delivery of the finished and clean mold, which was 6 days. Delivery
time is a positive factor when compared to mold delivery times at the
regional level and outside the Central American region. 4. Conclusions The work done
shows that it is possible to apply reverse engineering to manufacture a 3D
printed mold with FDM technique [14]. Reverse engineering resources are
usually 3D scanning equipment, computers and scanning |
software, 3D printing
equipment, measurement and verification equipment, among others. The digitization process is replicable by institutions that have a
high definition 3D scanner, where their product will be the digital file of
the mold. The resulting file will be used to manufacture the mold in any
institution that has a 3D printer, when resources are scarce,
however, when the necessary resources are available, the file can be used to
generate codes that are entered into computerized numerical control
manufacturing equipment. This work gives perspective to carry out research on superficial
treatments of polymer molds for the increase of durability, study of the use
of molds of low cadence in thermoforming processes, molding of biodegradable
plastics with the use of printed molds, molds for reinforced composite materials.
These results are precedents for those who have software and 3D printers can be incorporated in the productive field, providing
design services and manufacturing of printed molds. 5.
Acknowledgments This research was carried out thanks to the financial support of the
United States Agency for International Development (USAID) on its Higher
Education for Economic Growth program, the economic support and
infrastructure of Don Bosco University, and the collaboration of the company Polietileno y Flexografía S. A
de C. V. References
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