Use of Insert Fasteners in Molding Technology for Glass Fiber Reinforced Composite Materials

Summary

Rapid global population growth and the consequent expansion of industry create an intensely competitive environment. This competition manifests itself in the need for continuous improvement, innovative approaches, and reduction of production costs. Due to these competitive pressures, producing more goods with minimum cost while using fewer resources and energy, and developing innovative and sustainable projects, are of major importance for our company competing in the global arena. Operating in accordance with the Industry 4.0 concept, our company ranks among the top 3 firms globally active in the water parks and entertainment sector, with over 3,000 projects completed in 103 countries. Our company places particular emphasis on innovative and sustainable work, especially during production stages, and these efforts continue rapidly. In this context, one of our innovative R&D and production initiatives is the project to extract L-RTM slide components with connection fasteners directly from the mold as a single unit, rather than opening connection holes after demolding, and to prepare them directly for on-site installation. This aims to obtain the product in a single operation without any additional operations after demolding from the mold. Our primary objective with this method is to achieve significant improvements in parameters that greatly affect cost, such as labor, time, and error ratios.

1. Introduction

Our L-RTM slide components produced from molds made of CTP material are extracted from the molds in plain form, without any connection fasteners or operational processes such as drilling, cutting, or grooving on the part. All operational processes on the slide component, including finishing required by the part's production process, are performed using mechanical systems after extraction from the mold. Mechanical systems applied include robotic drilling, robotic grooving, robotic cutting, and manual cutting and drilling. Particularly, bolt connection holes opened mechanically are time-consuming and error-prone operations when considering production stage time, labor, and post-production drilling errors and associated costs. Additionally, these cost losses incurred during and after production compound as additional costs during on-site assembly in the form of time and labor. Figure 1 shows the slide component extracted from the mold without any operational processing. The part does not have locations for bolted connections and is extracted from the mold in the form shown. Holes for connecting the parts are drilled and cut, either through robotic-mechanical systems or manually, after extraction from the mold. Figure 2 shows the manual mechanical drilling operation applied to parts extracted from the mold. Figure 3 shows the slide component with robotic system cutting, drilling, and grooving operations performed on parts extracted from the mold. Figure 4 shows the bolted and nutted connection of slide components extracted from two mold halves, upper and lower.

Figure 1. Slide material extracted from mold without operational processing

Figure 2. Manual drilling operation on parts extracted from mold

Figure 3. Part with connection hole and slot opened by robotic systems on parts extracted from mold

Figure 4. Slide component with bolted-nutted connection

Part connections are made from four surfaces: face-to-face and side-to-side. For parts with an average inner diameter of 825 mm, face-to-face connections have a total of 24 bolt-nut connections, while side-to-side connections vary depending on part length. For an average 1,500 mm long upper-lower slide component, the number of holes we open on the part is approximately 100. This number reaches very high quantities of fasteners in our long-length projects as the number of parts increases, presenting very time-consuming operations.

2. Material and Method

As the first stage, the region where parts to be inserted into the mold are positioned must achieve optimal gripping behavior, apparatus must not be exposed to slipping, bending and similar errors within the mold, and the material supplied to the mold must ensure homogeneous distribution around the fastener parts, as shown in Figure 5.

Figure 5. Bolt and nut welded apparatus positioned in mold

As the second stage, using standard mold materials, mold production was performed suitable for the L-RTM process to enable the product to be extracted from the mold with bolts. In the experiments, glass fiber reinforced gelcoat composite material with 8 mm wall thickness from this mold was used. During product pressing in the lower mold, cavities were created for positioning the bolt and nut, as shown in Figure 6.

Figure 6. Bolt-nut holes opened in lower mold

The designed connection apparatus was positioned in the upper mold. The CTP plate mold, created with fibers placed between the bolt and gelcoat for support, is shown in Figure 7. In the third stage, parts with bolted connections subsequently made from standard molds and parts from the insert mold were prepared for testing equipment. Figures 8 and 9 show parts from two different molds with completed connections, prepared for tensile testing.

Figure 7. Connection apparatus positioned in upper mold

Figure 8. Bolted connection of CTP parts after drilling operation following extraction from mold

Figure 9. Bolted connection of CTP parts following extraction from insert mold

Figure 10. Tensile test apparatus

For the tensile test, an Instron brand Series No: 3367L5704 POL192, Model 3367 tensometer apparatus with 20 kN tensile capacity, clipon extensometer, capable of compression, tensile-rupture test was used. M6x24 bolts were used in connecting the CTP parts.

Figure 11. Tensile test setup-1

Tensile testing was applied to our CTP parts produced in the standard mold in the setup shown in Figure 11.

Figure 12. Tensile test setup-2

Tensile testing was applied to parts from the insert mold with bolted apparatus positioned in the upper mold in the setup shown in Figure 12.

Figure 13. Tensile test setup-1 test result image

Figure 13 shows the image of tensile testing applied to the CTP part produced from standard mold. Visible fractures and cracks formed around the connection holes on the CTP composite parts. The graphic results of the test are shown in Figure 15.

Figure 14. Tensile test setup-2 test result image

Figure 14 shows the image of tensile testing applied to the CTP part produced in the insert mold. No visible fractures or cracks formed around the connection holes on the CTP composite parts. The graphic results of the test are shown in Figure 15.

3. Results and Discussion

In this study, it is proposed to extract slide components with bolts as a single unit from the mold, to bring them to connection-ready condition, and to install mechanical connections performed during assembly directly according to modular system logic. These components are normally extracted from the mold without any operational processing, mechanically processed later, and bolted together during the assembly stage.

Table 1. Tensile test values of CTP composite parts obtained from bolted and insert molds

Figure 15. Tensile test graph of CTP composite parts from standard mold with bolted connection compared to insert mold

The results of tensile testing applied to slide components obtained from two different molds (insert and bolted connection) are shown in Table 1. According to the table values, the elongation at break and maximum tensile load of the part obtained from the insert mold appear to be close values. However, there is nearly a twofold difference in maximum tensile value. In the graph shown in Figure 15, values from the insert mold appear to fall below the tensile strength values from the bolted mold. As a result, CTP composite parts obtained from the insert mold demonstrate better strength compared to CTP parts obtained from standard molds and subsequently drilled and connected. Additionally, torque measurement was also performed on parts obtained from the insert mold. In the torque measurement performed, 8 mm wall thickness CTP composite sheets produced from two different standard molds are provided in Figure 16.

Figure 16. Torque measurement on 8 mm wall thickness CTP composite sheet produced from insert mold

The torque measurement value of the CTP sheet obtained from the insert mold according to M8 bolt was performed according to 8.8 torque criteria and was found to be 100 Nm. In our CTP sheets produced from standard mold, the measured torque value according to M8 bolt was found to be 25. Cracking on the sheet and embedment of the bolt head into the CTP composite sheet were observed at these values. Overall, the tests conducted on glass fiber reinforced composite material produced in the insert mold system showed superior performance compared to parts produced as standard and with drilling and other operations performed after extraction from the mold. This superiority is expected to provide advantages in many parameters including production costs, post-production operational errors, and assembly time losses.

Acknowledgments

We extend our thanks to our R&D Mechanical Manager Serçin Basut, R&D Director Ali Cansun, and Polin Waterparks who supported this study from its inception. Mehtap Türkmen R&D Specialist Polin Waterparks         Sibel Yıldız R&D Engineer Polin Waterparks         Selen Gül Güzeliş R&D Engineer Polin Waterparks