Thermoforming Explanation From Ronbus
Ronbus owner Dong and his son Austin recently went to the China factories to work on a few paddle projects. One of them being the newly released Ronbus Nova.R1.
After their trip, they created a paper documenting many hot topics in Pickleball right now and they have allowed me to share it with you. It covers how gen 1, gen 1.5, and gen 2 paddles are created as well as some of the new technology they are using in the Nova to eliminate core crushing.
Below is their paper.
A review of RCF (Raw Carbon Fiber) Paddle Technologies
By: Austin @Ronbus | austin003@ronbus.com
Introduction
The introduction of raw carbon fiber (RCF) paddles has been one of the major innovations in the game of pickleball. These paddles provide greatly improved spin and power generation and have become increasingly popular among pickleball players. Since their introduction, RCF paddles have gone through a series of improvements and technical evolution. In this paper, we will go through the main technological developments of RCF paddles.
Note that the following terminology of generations, up to Generation 2, was originally coined by Chris Olson of Pickleball Studio. All release dates are based upon the approval date by the USAP approved paddle list.
Gen 1 RCF
The first model to popularize the use of RCF was the Electrum Model E (approved on June 5, 2021). Since then, countless brands have released their own RCF paddles. In this section, we review the main technology behind Generation 1 RCF.
RCF Face sheet
Anyone who has played with a RCF paddle before will have noticed the textured surface on the paddle. This RCF textured surface is one of the keys behind the paddle’s success. It enables the paddle to generate lots of spin on the ball and has changed the way the game is played.
A typical manufacturing process for a RCF facesheet is described here. Three plies of unidirectional carbon fiber prepregs in the rectangular shape are laid on top of one another in alternating perpendicular directions. A common dimension used in the industry is 500 mm by 600 mm. Carbon fiber prepregs are carbon fiber ply that have been pre-impregnated with epoxy resin. As shown in Figure 1, if we define the direction along the axis of the paddle to be 90 degrees, and the direction perpendicular to that axis to be 0 degrees, then the three unidirectional
carbon fiber prepreg plies are placed in a 90-0-90 orientation. Further, a peel ply is placed on the outer most layer. JohnKew Pickleball has a video describing how peel ply works.
Figure 1. Paddle with axes defined.
Three plies of unidirectional carbon fiber prepregs, along with the peel ply, are placed into a hot press molding machine (Figure 2). The upper mold is aligned with the lower mold symmetrically and the mold halves are closed. Pressure is applied using hydraulic presses while the mold is cured at high temperature for a certain amount of time. While curing, the epoxy resin is configured to flow and fully disperse and impregnate the matrix of carbon fibers. After the cooling cycle, the carbon fiber reinforced composite facesheet is removed from the mold.
Figure 2. A hot press molding machine. Molds are placed in between metal trays while heat and pressure are applied.
During the curing cycle of the manufacturing process of the composite, the peel ply fabric absorbs some of the matrix epoxy resin and becomes an integral part of the laminate. When this fabric (peel ply) is peeled off, the resin between it and the first layer of carbon fiber reinforcement is fractured. This leaves a fresh, clean, roughened surface of matrix resin, thus the raw texture. Figure 3 shows how the peel ply can be removed from the facesheet.
Figure 3. Peel ply (semi-opaque top layer) is removed from the underlying carbon fiber facesheet (black).
Paddle Construction
Generation 1 paddles are often called “cold mold” paddles. This is because apart from the facesheet, which is pre-made with hot press molding, the rest of the manufacturing process does not involve heat. Polypropylene (PP) honeycomb cores are precut into a typical 500 mm x 600 mm panel of the specified thickness (e.g., 16mm). Facesheets are attached on either side of the PP core with epoxy glue under pressure. Figure 4 shows the three-layer structure before it is laminated together. A computer numerical control (CNC) machine is then used to cut out paddle blanks from this three-layer laminated structure. Note that these paddle blanks have their PP honeycomb cores exposed along the side, thus requiring an edge guard to be placed around the paddle.
Figure 4. Three layers of the facesheet, PP honeycomb core, and then another facesheet. The top facesheet still has its peel ply on. The bottom facesheet peel ply is face down on the table.
Generation 1.5
The success of the Generation 1 RCF paddles led to new innovations. What has retroactively been called Generation 1.5 was first seen in the JOOLA Ben Johns Hyperion CFS paddle (approved on April 1, 2022). The reason these paddles have been termed Generation 1.5 rather than Generation 2 lies in the fact that they only use thermoforming in a limited context.
Foamed Edge
The main change in the Generation 1.5 paddles is the addition of a foamed edge (Figure 5). Taking a cut out Generation 1 paddle blank (the three-layer structure of a facesheet on either side of the PP honeycomb core), uncured foam is injected along the edge of the paddle. This structure is then placed into a hot press molding machine. During the heating and curing cycle, the foam expands and fills the open PP honeycomb cells around the edge. After this thermoforming process, an edge guard is placed around the paddle. However, because the paddle blank is constructed as a Generation 1 paddle, the epoxy glue is already dispersed and fully attaches the facesheets to the PP honeycomb core. As a result, the foamed edge is not connected to the facesheets and only fills out the open cells of the PP honeycomb core. This thermoforming process thus does not create a fully unibody paddle.
Figure 5. Dissection of a JOOLA Ben Johns Hyperion CFS paddle reveals a foamed edge (yellow).
Benefits of a Foamed Edge
The primary benefit that the foamed edge provides is enlarging the sweet spot of the paddle. Hits that are farther from the center still feel more stable. In terms of physics, by adding weight on the edge of the paddle, the moment of inertia of the paddle increases. The further weight is from the axis of rotation, the more resistance to rotation it provides. This makes the paddle less willing to rotate on off-center hits, thus creating a larger sweet spot. This effect can also be achieved through other methods of increasing the weight on the edge of the paddle, such as adding lead tape around the edge of the paddle.
Generation 2
The full use of thermoforming defines the Generation 2 paddle. The Legacy Pro paddle was the first to be approved on September 20, 2022. In this section, we will cover how Generation 2 paddles are made, as well as one of the biggest pickleball controversies that happened as a result.
Thermoforming
The term thermoforming has been popularized by the pickleball paddle industry to generally refer to the manufacturing process of Generation 2 paddles. But in fact, thermoforming technically only includes processes where a plastic is heated up and formed into a desired shape. The foamed edge from Generation 1.5, which Generation 2 paddles also use, is thus thermoformed. More accurately, the manufacturing process that creates a Generation 2 paddle is hot press molding. All RCF paddles use hot press molding in their facesheet fabrication, Generation 1.5 paddles use hot press molding a second time for the foamed edge, but only Generation 2 paddles use hot press molding for the entire process. However, hot press molding is not unique to pickleball paddle fabrication; it has been a standard composite material manufacturing process for many decades.
Generation 2 paddles largely use the same materials and structure as previous generation paddles. However, because each paddle is thermoformed, the facesheets and PP honeycomb core are first separately cut into paddle shapes. This contrasts with the previous generations’ method of using epoxy glue to fully attach entire 500 mm x 600 mm sheets together before cutting into paddle blanks. Then, as shown in Figure 6, the facesheets and PP honeycomb core are attached together in a three-layer structure. A carbon seam foam edge is then placed around the edge.
Figure 6. Lay-up of facesheets and PP honeycomb core into three-layer structure.
Finally, this entire structure is placed into a mold (Figure 7), which is then placed into the hot press molding machine. The thermoforming process bonds the paddle layers together and forms the Generation 2 paddle. The application of heat and pressure during the thermoforming process enables the epoxy resin to flow and fully disperse between all layers of the paddle (facesheets, PP honeycomb core, carbon seam foam edge). This creates a unibody paddle that is significantly stronger than before. Figure 8 shows how the resulting edge is fully attached to the body of the paddle.
Figure 7. Thermoforming mold. Paddles are placed into the lower half of the mold before the top half of the mold is closed.
Figure 8. Generation 2 paddle after the thermoforming process. The carbon seam edge is fully attached to the rest of the paddle, creating a unibody structure.
Delamination, Disbonding, and Crushed Core
Generation 2 paddles were incredibly popular soon after their release. However, a few months in, many players started noticing an abnormal popping sound and high levels of power in these paddles. After cutting the paddles open, it was revealed that these paddles had lost their structural integrity. This problem has come to be known as a combination of the phrases delamination, disbonding, and crushed core. Chris Olson from Pickleball Studio has examined the issue, as has JohnKew Pickleball.,
First, we define what each of the three terms mean. Delamination refers to the issue of the carbon fiber plies coming apart in the facesheet. Disbonding refers to the issue of the separation of the facesheet from the PP honeycomb core. Crushed core refers to the issue of the PP honeycomb core being crushed and losing its structural integrity. Although the three are often used interchangeably, delamination itself is quite rare. Disbonding and crushed core are far more common.
The root cause behind the problem lies in the structure of the Generation 2 paddle and its thermoforming fabrication process. Although the PP honeycomb core looks perfectly flat and smooth to the naked eye, there are unavoidable variations in the thickness of the core at the microscopic level. This results in space for air in between the facesheet and the PP honeycomb core. Furthermore, the carbon seam foamed edge around the paddle creates a fully enclosed unibody structure. With the use of high temperatures and pressures, the air from the imperfection in the PP honeycomb core expands and creates intense internal pressure. Thus, parts of the PP honeycomb core could be crushed. After a certain amount of play, the constant force of the ball hitting the paddle leads to more areas of the core being crushed (Figure 9). The increased power players experience when using such a paddle can be explained by these unintentionally created pockets. Rather than the ball coming into contact with a solid paddle surface, the crushed core paddle’s pockets create a trampoline effect.
Generation 3 Thermoforming: Ronbus NOVA
The NOVA series from Ronbus (approved June 9, 2023), brings a new technology into the RCF paddle space. In this section, this patent pending innovation and its benefits will be discussed.
Carbon Fiber Grid Foamed Edge
The key innovation of the Ronbus NOVA paddles is its use of a carbon fiber grid along with foam on the edge of the paddle. Recall that the Generation 2 paddle, foam is injected along the edge and encased in a fully enclosed carbon seam layer. The Ronbus NOVA replaces the fully enclosed carbon seam layer with a carbon fiber grid layer. This grid is permeable whereas previously, the carbon seam layer was not. The rest of the paddle layup and thermoforming process is as before. While curing, the epoxy resin is configured to flow and fully disperse such that the carbon fiber grid foamed edge, the facesheets, and the core will be securely fastened together. Figure 10 shows the resulting paddle edge after the thermoforming process.
Figure 10. Ronbus NOVA.R1 after thermoforming fabrication. The carbon fiber grid (black) can be seen in the foamed edge (yellow).
There are two main benefits that this carbon fiber grid foamed edge creates. First, it solves the delamination/disbanding/crushed core issue structurally, and second, it creates a more balanced paddle with both power and control.
Solving the Delamination/Disbonding/Crushed Core Issue
As detailed before, the delamination/disbonding/crushed core issue of the Generation 2 paddles was caused by the inability to release the internal pressure during the thermoforming process. The carbon seam layer along the edge is not permeable. With the carbon fiber grid, which is permeable, the internal pressure of the paddle can be released during the thermoforming process. This significantly reduces delamination/disbonding/crushed core risk. Figure 11 shows a Ronbus NOVA.R1 paddle dissection after the manufacturing process.
Figure 11. Ronbus NOVA.R1 dissection after manufacturing process. The expanded foam edge (orange) is visible. The PP honeycomb core maintains its structural integrity (the black specks are carbon fiber dust from the surface that fell onto the core during dissection).
We further tested the integrity of the Ronbus NOVA.R1 paddle by using a machine to strike it 10,000 times at a speed of over 150 mph. For reference, the top speed of a pickleball serve is only 40 mph. The machine is shown in Figure 12. Afterwards, we dissected the paddle to inspect the inside. As shown in Figure 13, the paddle’s core integrity is preserved.
Figure 12. The machine used to strike the paddle 10,000 times. The paddle is rotated downwards to strike the knob (yellow) at over 150 mph.
Figure 13. Ronbus NOVA.R1 dissection after 10,000 machine strikes. The expanded foam edge (orange) is visible. The PP honeycomb core structure preserves its integrity.
A Balance of Power and Control
Generation 1 RCF paddles are able to generate large amounts of spin and thus provide controlled play. Generation 1.5 RCF paddles do not significantly change the spin or power generation of the paddle relative to Generation 1, but they do provide a better feel for players with the enlarged sweet spot. Generation 2 RCF paddles are able to generate tremendous amounts of power, though at the risk of having a crushed core. In contrast, the Generation 3 Ronbus NOVA series is noticeably stronger than the Generation 1 or 1.5 paddle while also significantly reducing the risk of a crushed core. This makes the Ronbus NOVA series the ultimate balance between power and control.