New prepreg for compression molding in RAPM | World of Composites

Solvay and Boeing combined aerospace performance with process knowledge to achieve high-speed, low-cost composite material production. #Autoclave#Automation#Boeing
The rib part (top) was tested in the RAPM program funded by DARPA and Boeing through spring frame forming (shown here as the bottom with a curved C-channel part) and double diaphragm forming (DDF) process, which served as The cooperative is managed through an agreement reached by the Army Research Office. Source | Boeing, DARPA, Solvay.
For decades, carbon fiber/epoxy resin prepreg has been the basic material of aerospace composites because of its high mechanical properties, precise resin/fiber content, and easy layup and autoclave curing. However, as aircraft and urban air mobility (UAM) manufacturers explore higher productivity and lower costs, compression molding is attractive compared to autoclaves, shortening production cycles and increasing efficiency. The simplest compression molding involves preheating the molding material, placing it in an open tool cavity, and consolidating it by hydraulic pressure at a certain temperature. In this process, the liquid thermoset material will turn into a solid. The cured part is then ejected for any required trimming and finishing steps.
Source | Boeing, DARPA, Solvay. Slide 8 “”Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding” by Timothy J. Luchini et al. et al., SAMPE 2019.
The combination of compression molding and prepreg not only can provide high-efficiency and high-efficiency process, but also the performance and ease of handling of prepreg, and it also avoids the use in processes such as resin infusion and resin transfer molding. The dynamics of the complex process of filling dry reinforced materials with liquid resin. (RTM). Especially for smaller aircraft structures, prepreg compression molding can provide less than 30 minutes of cycle time, while still obtaining high-quality, complex geometrical parts.
Solvay Composites (Alpharetta, Georgia, U.S.) is an important partner in the Rapid High Performance Manufacturing (RAPM) program led by Boeing (Chicago, Illinois, U.S.). RAPM is the “forming” part of the Customizable Materials and Forming (TFF) program initiated by the Defense Advanced Research Projects Agency (DARPA, Arlington, Virginia, USA) in 2015. Its goal is to achieve rapid, low-cost and agile manufacturing of small, complex-shaped composite parts, and to enhance the ability of composite materials to compete with machined aluminum in defense applications.
Source | Boeing, DARPA, Solvay. Slide 7 “Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”, etc., SAMPE 2019.
As Boeing’s long-term supplier in the defense field, Solvay has also been a leader in new commercial aerospace solutions, such as ultra-high pressure autoclave (OOA) epoxy prepreg CYCOM 5320-1, and new models in the automotive field. Solutions, such as a beat time of 1 minute, vinyl mixed with SolvaLite 730 prepreg.
RAPM is an excellent opportunity for Solvay to test and improve its experimental system XEP-2750, which is now commercialized as CYCOM EP2750, which was developed for the production of composite materials for aerospace and automotive applications. This blog is an online sidebar in May 2020. The topic is “Innovative composite material cost paradigm, Part 2: Molding”, reviewing the development and the compression molding process used, and CYCOM EP2750 for aerospace and automotive composite materials manufacturing The product provided by the supplier.
1 The Boeing Company, St. Louis, Missouri 63134; 2 Solvay Composites, Anaheim, California, USA; 3 Solvay Composites, Sinoor, UK
WTS, WCS-Wet Tensile Strength and Wet Compressive Strength RT-Room Temperature CTD, HW-Cold Dry, Moist Heat IPSS, IPSM-Interlayer (Interlayer) Shear Strength and Shear Modulus Webinar held by SolvayCW ( April 2020)
Source | Slide 5, Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”. Wait, SAMPE 2019.
CYCOM EP2750 was developed to meet the performance goals set by Boeing for aviation toughened epoxy resins, with a glass transition temperature (Tg) of up to 350°F and good notch performance-for example, open-cell compression ( OHC) and open cell tension (OHT)-and solvent resistance. These new prepregs can be used in primary and secondary aerospace structures, and are also compatible with a variety of reinforcing materials (such as carbon fiber and glass fiber).
CYCOM EP2750 also has the ability to expand production scale through automatic processing and compression molding. This includes curing time of 15-30 minutes on tools at 330-370°F, and post-curing time at 350°F for 1 hour. The cycle time is 30 minutes or less, and the annual output of each tool is 10,000 parts.
Solvay used two compression molding methods in the RAPM program: spring frame molding and double diaphragm molding (DDF). Both use the principle of keeping a flat blank, then transport it to the infrared (IR) preheating stage, and then thread it into a matching metal tool cavity. Then, the press closes the steel mold according to an automated procedure and applies full pressure to the prepreg for the remaining time on the tool.
The blank is transferred from the preheater to the tool before closing (top) and releasing the part (bottom). Source | Figure 10, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
Both the spring frame forming and DDF use matching metal tools, and provide a method of heat in and heat out, thereby eliminating the heating and cooling process of the tool, thereby achieving high productivity. Both are used to successfully mold many types of complex geometrical parts, including spacers, vertical flanges and parts with thicknesses ranging from 3.8 to 8.9 mm. These parts are manufactured at the Solvay Application Center in Heanor, UK. Although not available during RAPM, Heanor now has a fully automated compression molding line from prepregs to molded parts. For aviation made with EP2750 and takt For parts, the cycle time is 15 to 60 minutes. For small and medium-sized parts using automobile prepreg, the time does not exceed 3 minutes. Solvay has seen many benefits in the DDF process, including:
The features of EP2750 that contribute to compression molding include: low viscosity for automatic pick and place processing and full impregnation characteristics compared to CYCOM 5320-1, while CYCOM 5320-1 is partially impregnated to promote edge breathing, which is useful for processing using OOA The void-free laminate is required. However, due to the higher pressure applied, for example, up to 350 psi (typical maximum value of EP2750), compared to 35 psi commonly used in autoclave processing and 14.7 psi in pure vacuum OOA processing, compression molding uses very fast Force the resin to flow.
Comparison between CYCOM 5320-1 OOA prepreg and CYCOM EP2750 prepreg. Source | Form 1,
Even if the resin content is only slightly higher (40% in CYCOM EP2750 and 36% in CYCOM 5320-1), it has a more fully impregnated prepreg, which can be used in matching metal tools during compaction and curing. The hydrostatic pressure is maintained in the cavity, thereby reducing the risk of pre-soaking. In the dry area, the cured part thickness (CPT) is inconsistent, wrinkles and other defects, while ensuring good surface quality.
It is worth noting that Solvay has developed a patented deformable membrane that can increase the hydrostatic pressure when using a lower resin content CYCOM 5320-1 prepreg. Transformer Film can be applied to laminate parts before compression molding, thereby increasing the resin content and helping CPT meet the requirements of the RAPM part molding test.
As CW explained in a feature article in May 2020, CYCOM EP2750 is one of the main materials tried in the production of RAPM thermoset prepregs. Includes Pathfinder parts that are tried out during the initial manufacturing and development stages
TS-RAPM-001 and -009 beaded access panels, TS-RAPM-002 ribs and TS-RAPM-003 curved C-shaped channels. The parts were designed at Boeing (multiple locations worldwide), the tools were manufactured at C-Con GmbH (Munich, Germany), and the parts were manufactured at the Solvay Application Center in Heanor, UK, and then performed at Solvay Anaheim, California, USA test. Boeing St. Louis, Missouri, U.S.
TS-RAPM-001 (bottom) and -009 (top) beaded access panels, TS-RAPM-002 ribs (middle) and TS-RAPM-003 curved C-shaped channel (right) components. Source | Boeing, DARPA, Solvay.
Cross section of TS-RAPM-009 part made of EP 2750 prepreg. Source | Figure 3.2, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Wait, SAMPE 2019.
Example test matrix variables for testing of spring frame formed parts. Table 2, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Etc., SAMPE 2019, edited by CW.
Use non-destructive inspection (NDI) to evaluate the surface quality and cross-cut the selected panel’s porosity, short beam shear, fiber volume fraction, resin content, curing degree and glass transition temperature.
Due to the high consolidation pressure of compression molding, a porosity of less than 0.5% can be easily achieved. Although the process parameters must be optimized for each different part, once locked, the process can be repeated.
The geometry of the TS-RAPM-009 beaded panel. Source | Figure 2, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
This 600 mm long flat part has parallel beads of various geometric shapes. The thickness of one corner increases from 3 mm to 6 mm (upwardly), while the opposite corner has a constant thickness variation. The opposite edge includes a vertical flange whose draft angle varies linearly from 0° to 20°.
The initial test was carried out with the cushion layer stacked on the surface of the cushion layer. However, because the cushion layer is located near the edge of the part, it is possible to squeeze it out of the part, creating low pressure areas and voids during curing. The solution is to stagger the bedding layers within the laminated stack. In late parts where the filler is far from the edge and is effectively locked by the surrounding material, there is no risk of slipping and porosity.
Comparison of photomicrographs of TS-RAPM-009 beaded panel parts extracted from thin, tapered, thick and beaded areas. Source | Figure 6, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
If the residence time is too long, the porosity will also increase. The porosity of the beaded board made with a residence time of 8 minutes is lower than that of the beaded board made with a residence time of 10 minutes. This is especially true in the filled area, where the porosity at 10-minute residence is 5.5% and the porosity at 8-minute residence is 0.4%. A short dwell time can maintain high resin fluidity, effectively wet the fibers and maintain the pressure in the tool cavity through curing.
The longer holding time reduces the resin flow and pressure, especially in the filling area, because it is close to the edge of the tool cavity and there is no shearing edge or cross-sectional reduction. As a result, the pressure in the tool cavity is reduced at the edge of the part, especially in thicker areas with larger cross-sections. The absence of pressure here increases the risk of slippage of the cushion. “When designing tools, reducing the area around the tool cavity will help build and maintain pressure, especially for parts with different thicknesses,” explained Gail Hahn, a researcher at Boeing and the lead researcher on the RAPM project. “You need some form of squeezing or sealing to promote the hydrostatic pressure state in the cavity.”
TS-RAPM-002 The geometry of rib parts. Source | Figure 9, Aurele Bras et al. “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding”. Wait, SAMPE 2020.
Once the processing parameters have been determined for the TS-RAPM-009 beaded panel, the process is repeated for the TS-RAPM-002 rib. The length of the longest edge of the rib is 540 mm. The center thickness of the ribs is between 3.3 and 5.2 mm, and the final drawing depth of the trimmed part is 42 mm. All four edges have vertical flanges. Note that the spring-in compensation angle was determined during the beaded panel test and then applied to the tool geometry of the rib. The beaded panel test also resulted in higher tensile strength and modular spring position on the spring frame.
Before and after molding, close the TS-RAPM-002 ribs in the spring frame. Source | Figure 10, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
The ribs are made of spring frame molding and DDF. Due to the deepening of the ribs, additional material is required to secure the spring frame clip, but this can be reduced when using DDF. Another problem is that the tool design limits the space in which the spring clip fits in the tool cavity.
The cured layer thickness (CPT) of the flat part of the rib is higher than the cured layer thickness (CPT) of its vertical edge. It is reasonable to assume that the geometry of the part keeps the resin in the central flat area, and points out that the vertical flange can act as a resin seal. This facilitates compaction and finishing of parts in the central flat area. However, the vertical flange will be subjected to a large shear force during the closing process of the tool, which causes surface roughness, but does not cause porosity (see porosity data below). CYCOM EP2750 is a lower bulk material that helps to mitigate this effect-its lower thickness reduces shear forces.
Quality studies have shown that the repeatable rib porosity is less than 0.1%, and the fiber wrinkles/undulations are minimal. However, although it is assumed that the variation of the part thickness can be minimized by matching mold processing, inspections of the material processing parameters and the finished part CPT show that although the tool gap in the vertical flange of the rib is fixed and consistent, the web thickness May change with changes in functions. The resin content of the prepreg (less than +/- 2%) and the process-because the resin is allowed to migrate in the cavity, the CPT may change between the flange and the web.
TS-RAPM-002 rib cross section, used for optical porosity research. Source | Figure 3.8, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Wait, SAMPE 2019.
The part has a length of 640 mm and a 40 mm deep U-shaped section on the final trimmed part. The inner radius of the section is larger than the outer diameter, and the thickness increases from 6.6 mm at the narrow section to 8.8 mm at the wide end. Due to its thickness, the C-channel section is much heavier than the section discussed earlier. Therefore, the spring frame requires more fixing points than previous parts.
TS-RAPM-003 Curved C channel part geometry and spring frame configuration. Source | Figures 14 and 15, Aurele Bras et al. “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding”. Wait, SAMPE 2020.
Figure 16-C-scan analysis of an initial C-channel part made using CYCOM EP2750 (top) and pre-merged CYCOM 5320-1 (bottom).
Figure 18-The thickness and position of the C channel measured by the microscope (from the thickness of 36 samples (point 1) to the thin (point 36)) versus the position of 36 samples. Source | “The Challenge of Aerospace Structural Components…” by Aurele Bras et al. Wait, SAMPE 2020.
The C-scan of the molded part shows the wrinkles from the inner radius to the outer radius of the part using the pre-reinforced blank. The gray scale indicates that the wrinkles are also porous.
CYCOM EP2750 prepreg parts eliminate these wrinkles and voids by using a “dual stay” process. This includes immediately applying a certain amount of pressure during the dwell period after the viscosity of the material rises. Hahn explained: “This is determined by the data provided by the press and tools during the process development.” “Basically, before applying full pressure, there are two steps to build up the pressure gradually. As a result, the pressure-time curve has the same value as The shape of the resin viscosity curve is similar. The initial residence time at the bulk thickness is used to increase the resin viscosity to prevent the material feed (blank or preform) from becoming thinner. If the thickness of the charge is large, use two pauses. Prevent pressure loss due to resin shrinkage. The first dwell interval is X, the second dwell interval is Y, and Y
Figure 18 above shows the effect of double dwell on the thickness of the C-channel part. Matching the pressure with the resin viscosity allows more resin to be retained in the part, so that the fibers become wet, thereby reducing the porosity and thickness, so as to achieve the required nominal value and maintain low fiber deformation. However, the RAPM team emphasized that this double dwell process is only suitable for thicker parts, and pointed out that it will cause CPT unevenness in parts with different thicknesses.
The RAPM part test discussed here provides knowledge for the high-speed manufacturing of aerospace structural parts using prepreg compression molding. Lessons learned include:
RAPM shows that prepreg compression molding can produce high-quality aerospace-grade structures while reducing cycle time and labor. This allows composite materials to better compete in industry research in the aviation industry, while reducing weight and improving component performance (for example, corrosion resistance, cracking resistance, and fatigue resistance, etc.).
Solvay and Boeing worked together to perfect the new EP2750 prepreg system. Due to the combination of material chemistry, prepreg and process knowledge, and automation technology, its cycle time can be reduced to 20 minutes.
In addition to the “manufacturing development” section discussed above, RAPM has also produced multiple “challenges and transitions” sections designed to challenge initial development and transition candidates, and may rival machined aluminum in defense applications. These include:
The results and lessons learned from these part tests and other RAPM manufacturing function studies will be released in 2020/2021.
Source | Slide 10, Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”. Wait, SAMPE 2019.
Solvay also demonstrated the performance of EP2750 in automotive parts, such as a B-pillar measuring 36 by 16 by 2 inches and a thickness of .0725 inches, which includes 5 layers of Solvay THORNEL T650-35 standard modulus 3K towed carbon fiber. The size is 376 g/m² 8 silk satin fabric. This part is manufactured at Solvay Heanor in the UK using DDF. Compared with standard prepregs that are autoclaved, the combination of CYCOM EP2750 and DDF can reduce cycle time by 60% and cycle time by 85% (the time between the start of production of one part and the next part of the production line, that is, the pulse of the production line time). .
As composite materials occupy a larger share (and form a larger part) in the field of aerospace structures, this is not just a proposition that “success or failure is destined”.
The process of turning the precursor into carbon fiber through careful (and proprietary) manipulation of temperature and tension.

Solvay and Boeing combined aerospace performance with process knowledge to achieve high-speed, low-cost composite material production. #Autoclave#Automation#Boeing
The rib part (top) was tested in the RAPM program funded by DARPA and Boeing through spring frame forming (shown here as the bottom with a curved C-channel part) and double diaphragm forming (DDF) process, which served as The cooperative is managed through an agreement reached by the Army Research Office. Source | Boeing, DARPA, Solvay.
For decades, carbon fiber/epoxy resin prepreg has been the basic material of aerospace composites because of its high mechanical properties, precise resin/fiber content, and easy layup and autoclave curing. However, as aircraft and urban air mobility (UAM) manufacturers explore higher productivity and lower costs, compression molding is attractive compared to autoclaves, shortening production cycles and increasing efficiency. The simplest compression molding involves preheating the molding material, placing it in an open tool cavity, and consolidating it by hydraulic pressure at a certain temperature. In this process, the liquid thermoset material will turn into a solid. The cured part is then ejected for any required trimming and finishing steps.
Source | Boeing, DARPA, Solvay. Slide 8 “”Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding” by Timothy J. Luchini et al. et al., SAMPE 2019.
The combination of compression molding and prepreg not only can provide high-efficiency and high-efficiency process, but also the performance and ease of handling of prepreg, and it also avoids the use in processes such as resin infusion and resin transfer molding. The dynamics of the complex process of filling dry reinforced materials with liquid resin. (RTM). Especially for smaller aircraft structures, prepreg compression molding can provide less than 30 minutes of cycle time, while still obtaining high-quality, complex geometrical parts.
Solvay Composites (Alpharetta, Georgia, U.S.) is an important partner in the Rapid High Performance Manufacturing (RAPM) program led by Boeing (Chicago, Illinois, U.S.). RAPM is the “forming” part of the Customizable Materials and Forming (TFF) program initiated by the Defense Advanced Research Projects Agency (DARPA, Arlington, Virginia, USA) in 2015. Its goal is to achieve rapid, low-cost and agile manufacturing of small, complex-shaped composite parts, and to enhance the ability of composite materials to compete with machined aluminum in defense applications.
Source | Boeing, DARPA, Solvay. Slide 7 “Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”, etc., SAMPE 2019.
As Boeing’s long-term supplier in the defense field, Solvay has also been a leader in new commercial aerospace solutions, such as ultra-high pressure autoclave (OOA) epoxy prepreg CYCOM 5320-1, and new models in the automotive field. Solutions, such as a beat time of 1 minute, vinyl mixed with SolvaLite 730 prepreg.
RAPM is an excellent opportunity for Solvay to test and improve its experimental system XEP-2750, which is now commercialized as CYCOM EP2750, which was developed for the production of composite materials for aerospace and automotive applications. This blog is an online sidebar in May 2020. The topic is “Innovative composite material cost paradigm, Part 2: Molding”, reviewing the development and the compression molding process used, and CYCOM EP2750 for aerospace and automotive composite materials manufacturing The product provided by the supplier.
1 The Boeing Company, St. Louis, Missouri 63134; 2 Solvay Composites, Anaheim, California, USA; 3 Solvay Composites, Sinoor, UK
WTS, WCS-Wet Tensile Strength and Wet Compressive Strength RT-Room Temperature CTD, HW-Cold Dry, Moist Heat IPSS, IPSM-Interlayer (Interlayer) Shear Strength and Shear Modulus Webinar held by SolvayCW ( April 2020)
Source | Slide 5, Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”. Wait, SAMPE 2019.
CYCOM EP2750 was developed to meet the performance goals set by Boeing for aviation toughened epoxy resins, with a glass transition temperature (Tg) of up to 350°F and good notch performance-for example, open-cell compression ( OHC) and open cell tension (OHT)-and solvent resistance. These new prepregs can be used in primary and secondary aerospace structures, and are also compatible with a variety of reinforcing materials (such as carbon fiber and glass fiber).
CYCOM EP2750 also has the ability to expand production scale through automatic processing and compression molding. This includes curing time of 15-30 minutes on tools at 330-370°F, and post-curing time at 350°F for 1 hour. The cycle time is 30 minutes or less, and the annual output of each tool is 10,000 parts.
Solvay used two compression molding methods in the RAPM program: spring frame molding and double diaphragm molding (DDF). Both use the principle of keeping a flat blank, then transport it to the infrared (IR) preheating stage, and then thread it into a matching metal tool cavity. Then, the press closes the steel mold according to an automated procedure and applies full pressure to the prepreg for the remaining time on the tool.
The blank is transferred from the preheater to the tool before closing (top) and releasing the part (bottom). Source | Figure 10, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
Both the spring frame forming and DDF use matching metal tools, and provide a method of heat in and heat out, thereby eliminating the heating and cooling process of the tool, thereby achieving high productivity. Both are used to successfully mold many types of complex geometrical parts, including spacers, vertical flanges and parts with thicknesses ranging from 3.8 to 8.9 mm. These parts are manufactured at the Solvay Application Center in Heanor, UK. Although not available during RAPM, Heanor now has a fully automated compression molding line from prepregs to molded parts. For aviation made with EP2750 and takt For parts, the cycle time is 15 to 60 minutes. For small and medium-sized parts using automobile prepreg, the time does not exceed 3 minutes. Solvay has seen many benefits in the DDF process, including:
The features of EP2750 that contribute to compression molding include: low viscosity for automatic pick and place processing and full impregnation characteristics compared to CYCOM 5320-1, while CYCOM 5320-1 is partially impregnated to promote edge breathing, which is useful for processing using OOA The void-free laminate is required. However, due to the higher pressure applied, for example, up to 350 psi (typical maximum value of EP2750), compared to 35 psi commonly used in autoclave processing and 14.7 psi in pure vacuum OOA processing, compression molding uses very fast Force the resin to flow.
Comparison between CYCOM 5320-1 OOA prepreg and CYCOM EP2750 prepreg. Source | Form 1,
Even if the resin content is only slightly higher (40% in CYCOM EP2750 and 36% in CYCOM 5320-1), it has a more fully impregnated prepreg, which can be used in matching metal tools during compaction and curing. The hydrostatic pressure is maintained in the cavity, thereby reducing the risk of pre-soaking. In the dry area, the cured part thickness (CPT) is inconsistent, wrinkles and other defects, while ensuring good surface quality.
It is worth noting that Solvay has developed a patented deformable membrane that can increase the hydrostatic pressure when using a lower resin content CYCOM 5320-1 prepreg. Transformer Film can be applied to laminate parts before compression molding, thereby increasing the resin content and helping CPT meet the requirements of the RAPM part molding test.
As CW explained in a feature article in May 2020, CYCOM EP2750 is one of the main materials tried in the production of RAPM thermoset prepregs. Includes Pathfinder parts that are tried out during the initial manufacturing and development stages
TS-RAPM-001 and -009 beaded access panels, TS-RAPM-002 ribs and TS-RAPM-003 curved C-shaped channels. The parts were designed at Boeing (multiple locations worldwide), the tools were manufactured at C-Con GmbH (Munich, Germany), and the parts were manufactured at the Solvay Application Center in Heanor, UK, and then performed at Solvay Anaheim, California, USA test. Boeing St. Louis, Missouri, U.S.
TS-RAPM-001 (bottom) and -009 (top) beaded access panels, TS-RAPM-002 ribs (middle) and TS-RAPM-003 curved C-shaped channel (right) components. Source | Boeing, DARPA, Solvay.
Cross section of TS-RAPM-009 part made of EP 2750 prepreg. Source | Figure 3.2, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Wait, SAMPE 2019.
Example test matrix variables for testing of spring frame formed parts. Table 2, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Etc., SAMPE 2019, edited by CW.
Use non-destructive inspection (NDI) to evaluate the surface quality and cross-cut the selected panel’s porosity, short beam shear, fiber volume fraction, resin content, curing degree and glass transition temperature.
Due to the high consolidation pressure of compression molding, a porosity of less than 0.5% can be easily achieved. Although the process parameters must be optimized for each different part, once locked, the process can be repeated.
The geometry of the TS-RAPM-009 beaded panel. Source | Figure 2, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
This 600 mm long flat part has parallel beads of various geometric shapes. The thickness of one corner increases from 3 mm to 6 mm (upwardly), while the opposite corner has a constant thickness variation. The opposite edge includes a vertical flange whose draft angle varies linearly from 0° to 20°.
The initial test was carried out with the cushion layer stacked on the surface of the cushion layer. However, because the cushion layer is located near the edge of the part, it is possible to squeeze it out of the part, creating low pressure areas and voids during curing. The solution is to stagger the bedding layers within the laminated stack. In late parts where the filler is far from the edge and is effectively locked by the surrounding material, there is no risk of slipping and porosity.
Comparison of photomicrographs of TS-RAPM-009 beaded panel parts extracted from thin, tapered, thick and beaded areas. Source | Figure 6, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
If the residence time is too long, the porosity will also increase. The porosity of the beaded board made with a residence time of 8 minutes is lower than that of the beaded board made with a residence time of 10 minutes. This is especially true in the filled area, where the porosity at 10-minute residence is 5.5% and the porosity at 8-minute residence is 0.4%. A short dwell time can maintain high resin fluidity, effectively wet the fibers and maintain the pressure in the tool cavity through curing.
The longer holding time reduces the resin flow and pressure, especially in the filling area, because it is close to the edge of the tool cavity and there is no shearing edge or cross-sectional reduction. As a result, the pressure in the tool cavity is reduced at the edge of the part, especially in thicker areas with larger cross-sections. The absence of pressure here increases the risk of slippage of the cushion. “When designing tools, reducing the area around the tool cavity will help build and maintain pressure, especially for parts with different thicknesses,” explained Gail Hahn, a researcher at Boeing and the lead researcher on the RAPM project. “You need some form of squeezing or sealing to promote the hydrostatic pressure state in the cavity.”
TS-RAPM-002 The geometry of rib parts. Source | Figure 9, Aurele Bras et al. “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding”. Wait, SAMPE 2020.
Once the processing parameters have been determined for the TS-RAPM-009 beaded panel, the process is repeated for the TS-RAPM-002 rib. The length of the longest edge of the rib is 540 mm. The center thickness of the ribs is between 3.3 and 5.2 mm, and the final drawing depth of the trimmed part is 42 mm. All four edges have vertical flanges. Note that the spring-in compensation angle was determined during the beaded panel test and then applied to the tool geometry of the rib. The beaded panel test also resulted in higher tensile strength and modular spring position on the spring frame.
Before and after molding, close the TS-RAPM-002 ribs in the spring frame. Source | Figure 10, “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding” by Aurele Bras et al. Wait, SAMPE 2020.
The ribs are made of spring frame molding and DDF. Due to the deepening of the ribs, additional material is required to secure the spring frame clip, but this can be reduced when using DDF. Another problem is that the tool design limits the space in which the spring clip fits in the tool cavity.
The cured layer thickness (CPT) of the flat part of the rib is higher than the cured layer thickness (CPT) of its vertical edge. It is reasonable to assume that the geometry of the part keeps the resin in the central flat area, and points out that the vertical flange can act as a resin seal. This facilitates compaction and finishing of parts in the central flat area. However, the vertical flange will be subjected to a large shear force during the closing process of the tool, which causes surface roughness, but does not cause porosity (see porosity data below). CYCOM EP2750 is a lower bulk material that helps to mitigate this effect-its lower thickness reduces shear forces.
Quality studies have shown that the repeatable rib porosity is less than 0.1%, and the fiber wrinkles/undulations are minimal. However, although it is assumed that the variation of the part thickness can be minimized by matching mold processing, inspections of the material processing parameters and the finished part CPT show that although the tool gap in the vertical flange of the rib is fixed and consistent, the web thickness May change with changes in functions. The resin content of the prepreg (less than +/- 2%) and the process-because the resin is allowed to migrate in the cavity, the CPT may change between the flange and the web.
TS-RAPM-002 rib cross section, used for optical porosity research. Source | Figure 3.8, “Manufacturing of Spring Frame Press for Aerospace Production Parts” by Timothy J. Luchini et al. Wait, SAMPE 2019.
The part has a length of 640 mm and a 40 mm deep U-shaped section on the final trimmed part. The inner radius of the section is larger than the outer diameter, and the thickness increases from 6.6 mm at the narrow section to 8.8 mm at the wide end. Due to its thickness, the C-channel section is much heavier than the section discussed earlier. Therefore, the spring frame requires more fixing points than previous parts.
TS-RAPM-003 Curved C channel part geometry and spring frame configuration. Source | Figures 14 and 15, Aurele Bras et al. “The Challenge of Geometry of Aerospace Structural Parts for High Rate Compression Molding”. Wait, SAMPE 2020.
Figure 16-C-scan analysis of an initial C-channel part made using CYCOM EP2750 (top) and pre-merged CYCOM 5320-1 (bottom).
Figure 18-The thickness and position of the C channel measured by the microscope (from the thickness of 36 samples (point 1) to the thin (point 36)) versus the position of 36 samples. Source | “The Challenge of Aerospace Structural Components…” by Aurele Bras et al. Wait, SAMPE 2020.
The C-scan of the molded part shows the wrinkles from the inner radius to the outer radius of the part using the pre-reinforced blank. The gray scale indicates that the wrinkles are also porous.
CYCOM EP2750 prepreg parts eliminate these wrinkles and voids by using a “dual stay” process. This includes immediately applying a certain amount of pressure during the dwell period after the viscosity of the material rises. Hahn explained: “This is determined by the data provided by the press and tools during the process development.” “Basically, before applying full pressure, there are two steps to build up the pressure gradually. As a result, the pressure-time curve has the same value as The shape of the resin viscosity curve is similar. The initial residence time at the bulk thickness is used to increase the resin viscosity to prevent the material feed (blank or preform) from becoming thinner. If the thickness of the charge is large, use two pauses. Prevent pressure loss due to resin shrinkage. The first dwell interval is X, the second dwell interval is Y, and Y
Figure 18 above shows the effect of double dwell on the thickness of the C-channel part. Matching the pressure with the resin viscosity allows more resin to be retained in the part, so that the fibers become wet, thereby reducing the porosity and thickness, so as to achieve the required nominal value and maintain low fiber deformation. However, the RAPM team emphasized that this double dwell process is only suitable for thicker parts, and pointed out that it will cause CPT unevenness in parts with different thicknesses.
The RAPM part test discussed here provides knowledge for the high-speed manufacturing of aerospace structural parts using prepreg compression molding. Lessons learned include:
RAPM shows that prepreg compression molding can produce high-quality aerospace-grade structures while reducing cycle time and labor. This allows composite materials to better compete in industry research in the aviation industry, while reducing weight and improving component performance (for example, corrosion resistance, cracking resistance, and fatigue resistance, etc.).
Solvay and Boeing worked together to perfect the new EP2750 prepreg system. Due to the combination of material chemistry, prepreg and process knowledge, and automation technology, its cycle time can be reduced to 20 minutes.
In addition to the “manufacturing development” section discussed above, RAPM has also produced multiple “challenges and transitions” sections designed to challenge initial development and transition candidates, and may rival machined aluminum in defense applications. These include:
The results and lessons learned from these part tests and other RAPM manufacturing function studies will be released in 2020/2021.
Source | Slide 10, Timothy J. Luchini et al. “Rapid High Performance Molding of Structure xEP-2750 Prepreg for Compression Molding”. Wait, SAMPE 2019.
Solvay also demonstrated the performance of EP2750 in automotive parts, such as a B-pillar measuring 36 by 16 by 2 inches and a thickness of .0725 inches, which includes 5 layers of Solvay THORNEL T650-35 standard modulus 3K towed carbon fiber. The size is 376 g/m² 8 silk satin fabric. This part is manufactured at Solvay Heanor in the UK using DDF. Compared with standard prepregs that are autoclaved, the combination of CYCOM EP2750 and DDF can reduce cycle time by 60% and cycle time by 85% (the time between the start of production of one part and the next part of the production line, that is, the pulse of the production line time). .
As composite materials occupy a larger share (and form a larger part) in the field of aerospace structures, this is not just a proposition that “success or failure is destined”.
The process of turning the precursor into carbon fiber through careful (and proprietary) manipulation of temperature and tension.


Post time: Mar-19-2021
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