RTM Closed Mold Forming Process and Mold Design and Production Process

 

The so-called Closed Mold Molding Process is a process method for molding composite material components when the female and male molds are closed. SMC, BMC molding, injection molding, RTM, VEC and other technologies are all closed mold molding processes. Due to the formulation of environmental laws and the improvement of product requirements, the open mold molding of composite materials has been increasingly restricted, which has prompted the application of closed mold molding technology, especially the innovation and development of RTM technology in recent years.

 

RTM refers to a process technology in which low-viscosity resin flows in a closed mold, infiltrates reinforcing materials and solidifies into shape. It belongs to the category of liquid forming or structural liquid forming technology of composite materials. The specific method is to pre-place reinforcing materials that have been reasonably designed, cut or mechanized pre-formed in the designed mold. The mold must have peripheral sealing and tightening, and ensure smooth flow of resin; after the mold is closed, a certain amount of resin is injected, and the desired product can be demolded after the resin is solidified.

 

This process has many advantages, and can use a variety of fiber-reinforced materials and resin systems, and has an excellent product surface. It is suitable for manufacturing high-quality products with complex shapes, and has high fiber content, less volatile components during molding, less environmental pollution, strong adaptability to production automation, low investment, and high production efficiency. Therefore, RTM technology has been widely used in the automotive industry, aerospace, defense industry, mechanical equipment, and electronic products. The primary factor that determines RTM products is the mold. Since RTM molds generally use the male and female mold matching method, finding ways to improve the surface quality and dimensional accuracy of the male and female molds has become a key factor in determining product quality.

 

1) RTM, resin transfer molding. This technology is derived from polyurethane technology. During molding, the mold is closed and resin is injected into the preform. The glass fiber content is low, about 20-45%.

2) VARIT, vacuum-assisted resin transfer injection molding. This technology uses vacuum to suck the resin into the preform, and can also press the resin in. The vacuum degree is about 10-28 inches of mercury.

3) VARTM, vacuum-assisted resin transfer injection molding. The product generally has fewer pores and the glass fiber content can be increased.

4) VRTM, vacuum resin transfer molding.

5) VIP, vacuum infusion method.

6) VIMP, variable infusion molding method. The resin moves with the help of vacuum or deadweight, and the impregnation is compacted.

7) TERTM, thermal expansion RTM. Insert the core material into the preform, let the resin impregnate and heat the mold and the molded product. The core material expands due to heat, compacting the layers. This compaction effect is combined with surface pressure molding.

8) RARTM, rubber-assisted RTM. In the TERTM method, rubber is used instead of core material. The rubber mold presses the molded product, greatly reducing the porosity, and the glass fiber content can be as high as 60-70%.

9) RIRM, resin injection cycle molding. Vacuum and pressure are combined to alternately inject resin into multiple molds to circulate the resin until the preform is fully impregnated.

10) CIRTM, Co-Injection RTM. Co-injection RTM can inject several different resins, and can also use several preforms. Vacuum bags and molds with flexible surfaces can be used.

11) RLI, resin liquid impregnation. Resin is injected into the lower mold, and after the preform is inserted, the upper mold is covered, heated and molded with the molding pressure of the autoclave. Heating reduces the viscosity of the resin, improves fluidity, and is easy to impregnate.

12) UVRTM, ultraviolet (curing) RTM. Similar to the SCRIMP method, it cures quickly and must use a UV light source, a vacuum bag that can transmit ultraviolet light, and a soft mold.

13) VECTM Virtual Design of Composite Materials The core technology of VEC is the patented “floating mold” concept. The composite mold is installed between two liquid-filled steel pressure vessels, and the mold forms a seal along the entire length of the container. The container is filled with a compressible heat-conducting liquid, which is usually water.

 

⊙ According to the requirements of the production scale, molds of different materials and grades can be used to minimize costs and obtain better economic benefits.

⊙ It is a closed mold resin injection method, which can minimize the harm of harmful components such as resin to the human body and the environment, and meet environmental protection requirements.

⊙ Low-viscosity fast-curing resin is used, and the RTM mold can be heated during the production process, thereby further improving production efficiency and product quality.

⊙ It is conducive to the preparation of large and medium-sized, complex shapes, and smooth overall structural parts on both sides, with good dimensional accuracy, high surface quality, and good mechanical properties.

⊙ The reinforced material preform can be selectively reinforced, locally reinforced, mixed reinforced, and embedded and sandwich structures can be used according to performance requirements, which can give full play to the performance designability of FRP.

01RTM Molding Process Mold Technology

 

1) RTM overall process route: RTM has three important components: 1 raw material system; 2 injection equipment; 3 mold system.

 

2) RTM Molding Mold Technology: All RTM products require molds suitable for the process, and RTM is no exception. RTM molds can be made of aluminum steel and FRP. Since aluminum steel molds are not easy to deform but are expensive, they are not introduced here. The following mainly introduces FRP molds.

 

1. RTM mold type and material

FRP molds are used for RTM. According to general regulations, a 7-10mm thick mold layer is made, and then a heating core is installed under the surface of the base mold to form a sandwich structure. The total thickness of the mold layer is 20mm. Since this thickness is not enough for the strength required by the RTM molding process, it needs to be further enhanced. Box-shaped steel profiles are much cheaper than composite materials and are generally reinforced with box-shaped steel profiles.

 

FRP mold practice has proved that the service life of molds made with inferior resins is extremely short, and it also has a direct impact on product quality, so the mold surface is required to be made of heat-resistant and chemical-resistant materials. The cost of mold making is mostly labor, and the cost of material selection has almost nothing to do with the total mold cost. Currently, vinyl ester mold resin system and gel coat are generally selected, and it has been proven to have better service life and temperature resistance than traditional epoxy materials. According to foreign data, molds made with vinyl ester mold resin have been molded more than 18,000 times and are still in use.

 

2. Mold Heating

Most resins used in the FRP industry have a curing curve that is directly related to temperature, so it is of great practical significance to find a way to control the temperature of the production mold, which helps to optimize production efficiency. In fact, for every 10°C increase in mold temperature, the gel time will be halved. Therefore, at ambient temperature (20°C), a molded part may take 60 minutes to cure and demold, while at 50°C, the same resin system, molding the same part, can be demolded within 7.5 minutes.

 

Electric heating cloth heating: The electric heating method of applying heating cloth to the memory of the mold in RTM molds has been used for many years. The heating is relatively uniform, and the mold can easily be heated to more than 100°C, but the standard application maximum mold temperature is 75°C.

 

Liquid heating: Liquid heating is to install a hot and cold circulation system into a suitable mold structure, which can replace electric heating. This also provides a cooling system for the mold. The temperature can be controlled by the circulating medium in the pre-buried pipe.

 

3. Mold Sealing

All closed molds for RTM and vacuum molding (VM) require a seal to control resin overflow at the edge of the mold cavity. In the case of VM molding, an additional external mold flange vacuum seal is required.

 

There are many different forms of seals, but the seal material is required to have high temperature resistance and consistent recovery rate. At present, organic silicone materials are the most successful for basic mold resin sealing. If used correctly, it is enough to provide a service life of more than 1,000 times.

 

Passive seal: Almost dedicated solid silicone rubber seal section, designed to compress 1.0-1.5mm at its “Z” end closed position when the mold is closed. To achieve effective sealing without increasing the mold closing force, the hardness and compression size of the seal are critical. However, because the required pressure is too large, it is easy to cause mold deformation. The mold contact surface is generally 3-5mm enough to prevent resin seepage, thereby achieving effective sealing.

Dynamic seal: The dynamic form is better than the passive seal form. It can permanently control the cross-sectional changes. The cross-sectional size change of the illustrated form can be up to 4mm. This allows the vertical sealing track to be embedded in the mold flange. On the contrary, passive seals will only “plastically deform” and wear extremely. Once the inner section of the dynamic seal is pressurized, it can provide a good adjustment of the sealing effect. When the mold is closed or opened, the seal elastically deforms with the vacuum gap, which prevents wear caused by “plastic deformation” in the vertical direction.

 

5. Mold accuracy

RTM molds are often under stress, so for a successful closed mold, mold accuracy is one of the key factors. The mold cavity accuracy is controlled at ±0.2mm, which is the target accuracy of the closed mold. Failure to achieve this accuracy will inevitably lead to glue shortage and unpredictable resin filling, and the size of the molded part is out of tolerance. The most common is overthickness, and the material shrinkage parameter must be taken into account.

 

02 RTM process operation

 

RTM process injection operation is generally required to be completed within 1/4-1/2 gel time, the transfer time is 2-15 minutes, and the transfer pressure is 0.3-07Mpa.

 

Resin transfer pressure is the main parameter that should be controlled in the RTM process. This pressure is used to overcome the resistance encountered when injecting into the mold cavity and soaking the reinforcement material. The time for the resin to complete the transfer is related to the system pressure and temperature. A short time can improve production efficiency. However, if the resin flow is too large, the glue will not have time to penetrate the reinforcement material, and it may cause accidents due to the increase in system pressure. Therefore, it is generally required that the rising speed of the resin liquid level entering the mold during the transfer process is not more than 25mm/min. Monitor the resin transfer process by observing the discharge port. It is generally believed that when all the observation ports on the mold have glue overflowing and no more bubbles are discharged, and the actual amount of resin added is basically the same as the expected amount of resin added, the transfer process is completed. Therefore, the setting of the discharge port should be carefully considered.

 

03 Resin Selection

 

The selection of the resin system is the key to the RTM process. To get the resin into the mold cavity and quickly soak the fiber, the viscosity of the resin should be 0.025-0.03Pa•s. Polyester resin has a low viscosity and can be completed by cold injection at room temperature. However, due to different performance requirements of the product, different types of resins will be selected, and their viscosities are not the same, so the size of the pipeline and injection head must be designed to meet the fluidity requirements of the special components.

 

Resins suitable for RTM process include polyester resin, epoxy resin, phenolic resin, polyimide resin, etc.

 

04 Selection of Reinforcement Materials

 

In the RTM process, reinforcement materials can be selected from glass fiber, graphite fiber, carbon fiber, silicon carbide and aramid fiber, etc. Varieties can be selected according to design needs. Chopped fiber, unidirectional fabric, multi-axial fabric, Woven Roving, knitting, core material or preforms.

 

05 Design and Production of Molds

 

1. Requirements for mold production environment and selection of raw materials
2. Environment

Ambient temperature: The ideal range is 25±3℃.

Relative humidity: Not more than 60%.

Production workshop: Should maintain higher cleanliness and daily maintenance than the product production area.

 

1. Materials

We recommend the following materials for this process:

① Main materials

Gel coat: ccp-071 (excellent heat resistance, HDT is 160-173℃)

Mold resin: RM2000 (fast curing, fast mold manufacturing, low shrinkage, and reduced mold cost)

F-010 (epoxy modified vinyl resin, good strength and heat resistance, and low shrinkage)

Surface mat: 300g/m²

Alkali-free chopped mat: 450g/m²

Basketwood: used to improve the rigidity of the mold and reduce weight

Wax sheet: used to control the thickness of the mold cavity, good thickness uniformity

② Auxiliary materials

Polyester sealer, easy-to-grind primer, high-gloss gel coat, glass beads, butanone, acetone, curing agent, accelerator, sandpaper of various meshes, injection port.

 

2. Skirt Production

The production of lightweight RTM mold skirts is particularly important, as it is the basis for ensuring the effective and reliable implementation of the process. Based on the existing original mold, we make a 250mm wide skirt around the product. The purpose of making such a wide skirt is to ensure that the mold can provide sufficient clamping force when the mold is vacuumed to ensure the success of our injection.

 

Therefore, we can easily transform ordinary hand-made molds into injection molds.

 

3. Processing of the Original Mold

After the mold skirt is made, it needs to be processed. First, correct its size to the required degree; second, make appropriate chamfers between the skirt and the product part.

 

If our original mold is a local problem, first use atomic putty to level it locally, and then spray the easy-to-grind primer locally (see below for specific operations).

 

If the overall surface condition of our original mold is not very good, it needs to be fully processed as follows:

 

• Easy-to-grind primer treatment

In order to ensure a high-quality RTM mold surface, it is necessary to treat the original mold with an easy-to-grind primer. It has excellent leveling properties, can obtain a low-porosity surface, and can be continuously sprayed in a wet state to obtain the required thickness.

 

4. Production of the Lower Mold

After the original mold is processed to our satisfaction, we start to make the lower mold. The layer design is as follows: gel coat (CCP071) + 1 layer of surface mat (F010 resin) + 1 layer of 450 g/m² chopped mat (F010 resin) + 5 layers of 450g/m² chopped mat (RM2000 resin) + 2 layers of 450g/m² chopped mat (F010 resin) and 3/8 inch balsa wood + 3 layers of 450g/m² chopped mat (RM2000 resin)

 

The steps of mold making are as follows:

⑴. Application of release agent. Commonly used are release wax, liquid release agent and PVA

1. Paste-wiz release wax: After cleaning the surface of the original mold, start applying release wax, generally 6 times, 2 hours between each time. The specific operation method is as follows: first dip cotton cloth in wax, wipe the surface vigorously in a rotating manner, then use the same method to remove excess wax and scratches left by cotton cloth during waxing, and polish with clean cotton cloth after 2 hours. Repeat the same operation 6 times.

 

1. X-802 semi-permanent liquid release agent, it is recommended to use S-19B sealer before use. Operation method: Apply release agent 5 times. Dip clean pure cotton cloth in release agent but do not drip, wipe the release agent on the surface of the mold, form a thin and smooth coating, and then leave it for release agent to evaporate. Be careful not to wipe the operation area too much. After each layer is applied, leave it for 15 minutes to dry and solidify before applying the next layer. Use different clean cotton cloth for each layer of release agent. If streaks appear, replace the cotton cloth and make sure there is no excessive release agent attached to the cotton cloth. After the last layer is applied, it takes 30 minutes to cure. The longer the curing time, the better the demoulding effect.

 

1. If the original mold is made of acrylic material, we do not recommend using demoulding wax and liquid demoulding agent, but use PVA as the demoulding material. We use the method of spraying to spray it evenly on the surface of the original mold, which can also achieve a good demoulding effect. During the spraying process, pay attention to adjusting the atomization of the spray gun so that PVA can be attached to the surface of the original mold in a very thin layer and evenly, and pay special attention to the corners that are easily overlooked. Generally, it is recommended to spray twice, and the principle of controlling the interval time in the middle is that the previous layer must be completely dry.

 

• Spraying of Gel Coat

The amount of gel coat is generally controlled at 850g/m², the thickness at this time is between 0.6~0.8mm, and the gel time is controlled at about 2 hours. Geling too fast will lead to high porosity in the gel coat layer. The gel coat is sprayed in two times. The principle of controlling the interval between the two times is that the first layer of gel coat is completely cured, generally 2 to 3 hours. The pressure of the ES-100 spray gun is controlled at 70psi during spraying. Mold gel coat spraying procedure: First check whether the spraying equipment (ES-100) is in good condition, check whether all sealing conditions are good, and whether the pressure regulator is flexible.

 

1. Add 2% MEKP to the mold gel coat CCP071 and mix evenly.
2. Put the gel coat into the ES-100 paper cup and adjust the pressure to 70psi.
3. Keep the spray gun 300-500mm away from the mold surface, first pull the trigger with the gun head facing upwards, then aim the gun head at the mold surface to adjust the atomization pressure so that the spray line reaches the most ideal state. Pay attention to spraying the hard-to-reach positions first, such as the corners and right angles of the original mold surface, and then spray a large area. At the same time, the speed of the spray gun should be uniform. In the first spraying, the gel coat thickness of the entire surface is required to be relatively uniform. In the second spraying, the gel coat on the product part of the mold is required to be slightly thicker than the gel coat on the skirt part. When spraying, pay attention to the line shape of the later spray to press on the half of the previous position, and repeat this until the gel coat is sprayed. At the same time, the gel coat is required to cover the vertical part of the edge of the mold skirt. Clean the equipment immediately after spraying. And install the air source interface for pneumatic demoulding in a suitable position.

 

 

⑶ Covering of Surface Mat

The specification of surface mat is 30g/m², and the resin is vinyl F010 mold resin. When the second layer of gel coat is cured to the point where it is sticky but not gluey, the surface mat is laid. The advantage of laying the surface mat at this time is that it can not only improve the adhesion between the gel coat and the surface mat layer, but also better control the amount of resin.

 

The surface mat can be laid on the mold surface in advance. At this time, because the gel coat still has a certain adhesive ability, it can be laid very well. The docking part of the surface mat is required to remove the neat straight edges in order to achieve good docking. The weight ratio of vinyl F010 mold resin to surface mat is controlled at 9:1. Operation method: Dip a small amount of resin with a brush, apply force vertically downward to the surface, and spread it out from the middle of the mold to the surroundings, with the resin just soaking the surface mat as the standard. Be sure to eliminate bubbles when making paste. And pay attention to the vertical surface of the skirt edge also needs to be covered with surface mat, in order to avoid the mold itself from being separated from the mold due to shrinkage problems during the mold making process.

 

After solidification, use coarse sandpaper to remove burrs and bubbles, then wipe the surface clean with acetone and prepare for the next step.

 

• Laying of the first layer of Chopped Strand Mat

The specification of chopped strand mat is 450g/m², and the resin is vinyl F010 mold resin. Before pasting, the weight of the cut fiber should be weighed to control the amount of resin used. Generally, the weight ratio of F010 resin to chopped strand mat is controlled at 1.5:1, and the resin content is 40% at this time. When pasting chopped strand mat, the brush is a point brush to avoid affecting the glass fiber and causing bubbles and wrinkles. It is not allowed to brush the resin back and forth on the chopped strand mat. The bubbles are eliminated with a bristle roller, which spreads from the middle to the surroundings during rolling, and special attention is paid to the corners. When overlapping the chopped strand mat, try to tear it apart by hand to avoid local strength defects. In addition, after the pasting is completed, give enough time to eliminate bubbles with a bristle roller.

 

⑸Laying of five layers of 450g/m² Chopped Strand Mat

For this five-layer laying, we use RM2000 mold resin. The advantage of this resin is that it can be quickly laminated without worrying about shrinkage. The reason is that the resin system contains 35% filler, which makes its shrinkage rate very low. During the operation, the weight ratio of resin to fiber is controlled at 3:1, and the resin content is about 50% at this time.

 

The specific operation is as follows: First, divide the mold surface into parts of appropriate size, then cut the five layers of chopped strand mat required for this part and weigh the weight, then continuously soak the five layers of mat on a flat and clean operating table and remove bubbles, then lay the pre-impregnated fibers to their location, continue rolling, and remove all bubbles. Continue in sequence until all fibers are laid and wait for curing. Note that the joint part of the chopped strand mat must be handled well, and try to get a uniform thickness of the laminate.

 

⑹ Balsa Wood

Before balsa wood is applied, two layers of 450g/m² chopped mat with F010 resin are required. The operation is the same as the first layer of chopped mat. When the chopped mat is applied to the balsa wood, cut the outline board into small strips and apply them from the middle of the mold to the surrounding areas, with the standard of solid bonding. For the curved mold surface, there is no strict requirement for the front and back sides of balsa wood when applying it, and the principle is to facilitate operation. In addition, the balsa wood can be cut into appropriate sizes in different areas in advance, and the balsa wood can be directly bonded after the chopped mat is applied.

 

⑺Laying of the Subsequent Three Layers of Chopped Strands Mat

After the balsa wood is processed, the last three layers of chopped strands are laid, with resin RM2000, and the operation is as shown above.

 

⑻Reinforcement of the Mold

Since our injection is carried out under vacuum assistance, the pressure on the mold is not large, so it is only necessary to simply strengthen the mold to ensure the size of the mold itself. The reinforced material is a 20mm thick composite wood board with a width of 300mm. It is fixed with wood screws at the joint position, and then five layers of 450 g/m² chopped strands are pasted on it and wait for curing

 

⑼Demolding

At this point, the lower mold of the lightweight RTM mold is completed. After demolding, simple processing is performed to prepare for the production of the upper mold.

 

5. Apply wax sheet

After the lower mold is made, it is necessary to prepare for the upper mold. The most important process is the wax sheet covering. The thickness of the wax sheet is the thickness required for the product. Generally, the wax sheet needs to be covered in two layers. For example, a 5mm product is covered in 2mm and 3mm layers, first thin and then thick. The specific operation is as follows:

 

The wax sheet extends from the vacuum interface of the product to the surrounding areas. The position of the vacuum interface is generally determined at 1/3 of the entire product, and the distance from the injection port is 2/3 of the length of the product.

 

• Laying the first layer of wax sheet

Starting from the vacuum interface, cut the wax sheet into 4’’× 4’’ size squares. When laying, there is a gap of about 0.5mm between each block. The wax sheet must be close and neat, and all gaps must be connected smoothly. Lay the wax sheet about 2cm outside the edge of the product. After the first layer of laying is completed, use a scraper to level the surface and clean it.

 

• Laying the second layer of wax sheet

The difference between this layer of wax sheet and the previous layer of laying method is that the joints of all wax sheets must be tight, and try to use a whole sheet of wax sheet. The edge of the wax sheet should be scraped into the shape shown in Figure 1 with a tool. In this way, after all the wax sheets are docked, the surface can be scraped flat with a scraper without any concave areas, so as to ensure the thickness of the product and the production quality of the upper mold.

 

• Laying the wax sheet of the skirt part

The wax sheet of the skirt part will directly affect the subsequent mold closing process and whether the production is smooth, so it is a very critical process. The following takes a 5mm product as an example to illustrate the laying of the skirt wax sheet. As shown in Figure 2.

 

Description:

① Product thickness, 5mm. Product thickness 8mm

② Product edge extension, easy to operate during production. Width 20mm, thickness 3mm. (20mmx4mm)

③ Resin flow channel, width 15mm, thickness 5mm. (15×6)

④ T-shaped sealing strip position, width 15mm, thickness 3mm. (15×4)

⑤ T-shaped sealing strip groove, size 10.7mm×5mm. (8×5)

⑥ Air gap space, width 10cm, thickness 4mm, divided into two layers, the first layer also needs to leave a 0.5mm gap, and the latter layer is covered as a whole.

⑦ Outer sealing strip position, size 2.5cm×10mm.

⑧ Cover a layer of 1mm wax sheet on ②③④.

After the skirt wax sheet is covered, clay is needed to round the edges.

 

6. Making the Upper Mold

After laying the wax sheet, start making the positive mold. At the beginning, you need to set the position of the vacuum interface between the product part and the air gap. The specific steps are as follows:

① Spray PVA mold release agent on the wax sheet. The operation is as shown above.

② Spraying of gel coat. The gel coat is required to be a vinyl transparent gel coat.

The design of the structural layer is as follows: 1 layer of surface mat (30g/m²) + 1 layer of 450g/m² chopped mat + 3 layers of 450g/m² chopped mat + 3 layers of 450g/m² chopped mat

 

In the parts where the local mold is prone to deformation, it is necessary to use balsa wood to strengthen the sandwich core structure. After the balsa wood, add two layers of 450g/m² chopped mat.

 

③ During the operation, all vacuum interfaces and injection ports are placed in place after the gel coat spraying is completed. At the beginning of the curing of the second gel coat, the product and the skirt wax sheet are vacuumed, and the vacuum degree is very small (about 0.5inHg). As the layers gradually thicken, the vacuum degree needs to be continuously increased to ensure that the upper mold does not leave the wax sheet surface during curing and shrinkage, and at the same time, the wax sheet at the corners of the mold can be more compliant, so as to maintain the uniformity of the product size. The resin used in the upper mold is all F010 vinyl resin. The operation method is the same as described above.

 

7. Post-processing

At this point, the paste process of our mold is completed. Since the resin is not completely cured during the mold making process, if it is put into production immediately, it will seriously affect the quality and life of the mold. Therefore, the mold needs to be post-cured.

 

The method is as follows: heat treatment at a temperature 40-50℃ higher than the mold use temperature, generally 60-80℃ as the reference temperature, and cure for 3 hours to eliminate the internal stress of the mold and improve the curing degree of the resin, so that the mold can achieve the best performance. After the post-curing treatment, if there is enough time, the mold can be placed for a week before demolding and processing before putting it into production.

 

After the post-curing of the mold is completed, it can be demolded for post-processing.

 

⑴ Remove the mold and remove the wax flakes.

⑵ After removing the wax flakes, clean the mold with a mold cleaner (CW3000). Note that you need to wear gloves when operating. After washing three times, you can start water grinding.

⑶ Use 600-1000 mesh sandpaper to grind the mold according to product requirements. Note: When grinding, you must use a pad to achieve the desired finishing effect. Pads are generally made of plywood, wood, rubber sheets, etc., and are made appropriately according to the needs of the operation.

⑷ After the mold surface is polished to 1000 mesh, start polishing. Dip a cotton cloth in Aqua-Buff1000w polishing paste and apply it to the mold surface in a dot-coating manner, and moisten it with water. Then use a clean, damp wool wheel for grinding and polishing. During the polishing process, the polishing paste may dry out. You can spray water mist on its surface to re-moisten it and continue. When the grinding and polishing is done to an appropriate degree, wash the mold with water, and replace the wool wheel with Aqua-Buff2000 for polishing. The operation is similar to 1000w. After polishing, the mold can achieve a mirror effect. In order to achieve the best effect, it is recommended that the speed of the wool disc should not be less than 2500 rpm. After polishing, clean the surface of the mold and dry it naturally.

⑸After the mold is polished, the inner and outer sealing strips can be bonded in place, and the vacuum interface can be installed to prepare for the mold test.

 

8. Mold Trial

The process is as follows:

⑴ Before mold trial, be sure to ensure that the release agent is fully coated and do a demolding experiment.

⑵ Cut the mat according to the shape of the product, generally there are knitted chopped mat and composite mat. The number of layers covered is determined by the thickness of the product. 3M glue can be used to fix the fiber in the local non-adherent position.

⑶ Close the mold and apply a first-level vacuum (vacuum degree of 667 mmHg) to the mold skirt so that the upper and lower molds are tightly combined. The combined pressure can reach 1350 kg/m (along the skirt), so no clamping tools are required, and the internal and external seals play an airtight role.

⑷ Inject resin through the injection port located at the edge of the mold. The resin first flows along the peripheral resin channel, and then flows from the periphery to the center of the mold, and infiltrates the reinforcement material in turn. At this time, a second-level vacuum (vacuum degree of 376 mmHg) can be applied to reduce the internal pressure of the mold, which is conducive to the rapid flow of resin.

• Demold after the product is cured, check the entire mold and the product. Adjust when necessary until you are satisfied. At this point, the production of our entire mold is completed.