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树脂传递模塑 (R TM 工艺的发展及应用北京振兴科技文献服务中心曹运红文摘树脂传递模塑 (R TM 工艺是介于手铺法、喷射法和机械成形法之间的一种对模成形法。
文中叙述了 R TM 的发展过程和基本原理以及工艺装备、 , 并介绍了 R TM 的应用范围。
主题词 1引言 , 在美国已被广泛地用于汽车制造业的原始模型制造 , 并正在考虑生产复合材料结构零件。
船舶工业和小型导弹生产也采用了 R TM 工艺。
该工艺与传统的湿法铺层工艺相比 , 具有生产周期短、费用低及结构整体性好的优点。
飞机工业采用 R TM 工艺 , 可以生产出低费用和轻质量的飞机零件。
如小而复杂的控制面通常是用铝合金铸造而成。
这很可能用单一的 R TM 工艺所取代。
转枢、加强件等可以与连续纤维蒙皮一起模塑 , 大零部件 (如全翼也可以采用 R TM 工艺。
R TM 工艺的起源 , 可以追溯到四十年代末期 , 最初是为适用飞机雷达天线罩成形而发展起来的。
经过 30年的发展 , 英国航空航天公司在采用 R TM 工艺生产高整体性和高价结构如雷达天线罩方面拥有相当的经验。
手铺成型和喷射成型具有投资少等优点 , 但对环境污染 (苯乙烯较严重。
近年来 ,欧美等国家限制大气中苯乙烯含量 , 人们的兴趣也转移到 R TM 工艺上来。
因 R TM 工艺的掘起已使欧美发达国家产生了很大的变。
2基本原理及工艺装备 2. 1基本原理图 1 R TM 工艺原理图R TM 工艺的基本原理是 :在一个闭式的模具内预置纤维增强预型件 , 再用低压 (小于 0. 69M Pa 将树脂系统注入模具内 , 使之浸透纤维增强预型件 , 然后固化成两面光洁的零件 , 如图 1、 2所示。
图 2 R TM 工艺简图2. 2 R TM 工艺装备美国壳牌发展公司用作 R TM 工艺的装备包括注射系统、电热式加热器加热的 P -20钢模具、液压机、温度控制系统、真空泵、压力容器。
RTM成型工艺解析与生产注意事项RTM成型工艺与分类1.RTM所谓闭模成型工艺就是在阴、阳模闭合的情况下成型复合材料构件的工艺方法。
SMC、BMC模压、注射成型、RTM、VEC技术都属闭模成型工艺。
由于环境法的制定和对产品要求的提高使敞模成型复合材料日益受到限制，促使了闭模成型技术的应用，近年来尤其促进了RTM技术的革新和发展。
2.RTM的类型RTM工艺,即树脂传递模塑工艺,是一种新型的模压成型方法。
它具有模具造价低、生产周期短、劳动力成本低、环境污染少、制造尺寸精确、外形光滑、可制造复杂产品等优点。
40年代来，该工艺是为适应飞机雷达罩成型而发展起来的。
目前，RTM成型工艺己广泛应用于建筑、交通、电讯、卫生、航天航空等领域。
下面介绍几种RTM技术。
1）RTM，树脂传递模塑。
该技术源自聚氨酯技术，成型时关闭模具，向预制件中注入树脂，玻纤含量低，约20-45%。
2）VARIT，真空辅助树脂传递注塑。
该技术利用真空把树脂吸入预制件中，同时也可压入树脂，真空度约10-28英寸汞柱。
3）VARTM，真空辅助树脂传递注塑。
制品孔隙一般较少，玻纤含量可增高。
4）VRTM，真空树脂传递模塑。
5）VIP，真空浸渍法。
6）VIMP，可变浸渍塑法。
树脂借助真空或自重移动，压实浸渍。
7）TERTM，热膨胀RTM。
在预制件中插入世材，让树脂浸渍并对模具与成形品加热。
芯材受热膨胀，压实铺层。
利用这种压实作用，结合表面加压成型。
8）RARTM，橡胶辅助RTM。
在TERTM方法中不用芯材而用橡胶代之。
橡胶模具压紧成型品，使孔隙大大减少，玻纤含量可高达60-70%。
9）RIRM，树脂注射循环模塑。
真空与加压结合，向多个模具交替注入树脂，使树脂循环，直至预制件被充分浸透。
10）CIRTM，Co-Injection RTM。
共注射RTM，可注入几种不同的树脂，也可使用几种预制件，可利用真空袋和柔性表面的模具。
11）RLI，树脂液体浸（渗）渍。
轻型树脂传递模塑工艺(l-rtm)（Lightweight resin transfermolding process (l-rtm)）Lightweight resin transfer molding (L-RTM) - a rapidly developing low cost manufacturing technologyIntroduction of 1.L-RTM processThe traditional RTM technique, because it is a closed mold, with reduced volatile organic compounds (VOC) emissions (up to SPPm), the advantages of expanding available range of raw materials, reduce labor, environment friendly and can get two clean products etc.. But in RTM process, the injection of resin is carried out under higher pressure and velocity, so we must make the structure strength and stiffness of the mold sufficiently large enough to break and deform under the injection pressure. Usually, the sandwich composite material with steel tube support or aluminum die or steel mould processed by numerical control machine tool can make the manufacture cost increase, and the mould cost can be offset only when the product is big enough. In addition, in order to close the mold, it is necessary to make the peripheral sufficient clamping capacity or to use a closed die pressure system. All these factors limit the application of RTM technology to large products, otherwise the mold will become very heavy and the investment will be great.Lightweight resin transfer molding process (RTM, Light), also known as LRTM, ECO, VacuumMolding or VARTM. It is a low-cost manufacturing process developed in recent years. It has been used in the field of ship,automobile, industry and medical composite material more than RTM technology.The RTM Light process retains the die processing process of the RTM process, thus retaining almost all of the advantages of the RTM process. But the upper die for glass steel mould half rigid, thickness 6 8mm, usually do not need to use the steel reinforcement, the mold has a width of about 100mm by the rigid surrounding, double sealing belt constitutes an independent seal area, as long as a vacuum mold is closed and is very convenient and fast. Then the cavity is evacuated, and the resin is injected into the mold with the negative pressure in the mold and the lower injection pressure. The resin is infiltrated into the pre laid reinforcing fiber or preform. RTM - Light mold cost is low, and because the mold pressure reduction, its mold has close to the mold, it is easy to open mold from the process of transformation.The main equipment of RTM Light includes resin injection device, mold, vacuum pump and other auxiliary tools.2 light RTM compared with regular RTM(1) die;The mold is the biggest difference between the two processes. In the RTM investment, a considerable part of the cost is spent on the die and the clamping device because of the high injection pressure. This is not a good price for a product with little output. RTM process, mold life of up to 5000 or more, high production efficiency, suitable for an annual output of morethan 2000 products.The biggest advantage of RTM Light is the low cost of its mold production. The cost is only about half of the regular RTM mold, but the service life of the die is lower than that of the RTM mold. It is suitable for the products with an annual output of about 1000 pieces.The RTM Light process produces products that are larger in size than the traditional RTM, which is usually as small as a basketball cap, a length of 8m long hull (about 25m2), but this is not the ultimate limit of size. The product size is smaller than the basketball cap, the difficulty is to add fiber, and the product is greater than 8m, how to deal with the mold on the difficult.The disadvantage of glass fiber reinforced plastic mould is short service life of mould surface. In order to get good die life and product repeatability and dimensional accuracy, RTM -Both the Light and RTM processes must be of high quality and have an accurate cross section. In the composite molding process, the cost of surface requirements of the final product can reach 60% of the final product price. The composite mold can achieve the use of 500 times the surface quality of the car, and then the surface treatment of the mold. One way to increase life expectancy is to use a replaceable die surface(ex-changeablemoldSkins), such as the patent of JHm Technologies company, ZIPRTM technology,It can be used in RTM and RTM Light processes. Through the use of replaceable die surface to replace the vulnerable mold surface, thereby prolonging the life of the die and improving the quality of the die, the service life of the die can reach 8000, 10000 times. When the simultaneous use of several replaceable mold surface, due to the outside in the mold can be replaced directly on the mold surface coating and heating, thereby greatly improving the production efficiency.(2) injection pressure, flow rate and equipment;The injection pressure of RTM process is usually 0.1 0.4MPa, while the injection pressure of RTM Light process is not more than.1MPa, usually at 0.03-0.07MPa.The rate of resin injection varies with various factors such as resin viscosity, component size, fiber type and ply structure. The usual injection rate is 1.3 to 2 litres per minute.In order to prevent mold deformation or burst mode (especially in the position of the injection port), which requires a strict control of pressure. Injection equipment for the RTM Light process is usually equipped with a pressure feedback device that controls the pressure as a closed loop. RTM is also available in the standard equipment of a simple line pressure control design (mold protection system and a VMPC) and VMPC with POD electronic closed-loop system, can not lead to molddeformation and failure under the condition of using the original production equipment to get the best productivity.Equipment research is also developing toward low cost and multi use. The SSB injection equipment of Plastech adopts patented piston reforming precision metering pump. The minimum ratio of catalyst is up to 0.5%, which matches the industrial MPG (MouldPressureguard) the pump speed can be controlled by the machine itself. In 12 seconds and 15 seconds, the 1m2 reinforced material can be impregnated, and the wetting speed can be accurately controlled. Configure other options, also for hand gluing and brushing.(3) production efficiency and costRTM one Light process is a low-cost production technology. Compared with the traditional RTM technology, the die cost is low, and the complicated pressing device or pressure system is not needed, the investment is small, the operation is simple, and the manpower capital is saved, etc.. Compared with the opening process, it has the high precision of the product size, low porosity, production of styrene volatilization, environmental friendly, less waste materials (resin utilization rate of up to 95%), low rejection rate, high production efficiency.The injection pressure is low, the resin flow rate can not be accelerated to the optimum flow, before the RTM Light process the production speed of less than half of the RTM process, with each class 8 hours, for the use of the gel coat and non heatingmould process, RTM process in each class can produce 10 A 12 die, RTM-The Light process produces only 4 and 6 dies. For a 34 square foot product that needs to be heated and cured, the RTM process produces 40 molds per shift with the use of a hydraulic press, a heating die, and 5 replaceable dies. RTM in the same situation- Light process, can produce 20 die. But no water press is needed, and the mold price is also half lower.In recent years, through the improvement of mold design and process control, both production speed is approaching. Such as Xiraplas company in the use of RTM Light process alternative mold opening process, the workshop has become orderly, the use of the original 50 workers, and 3000m2 workshop area, making production increased by 25%. According to the company, production efficiency has been increased by 90% compared to the original mold opening process.(4) runner designThe flow design of the general RTM process is injected from the center and discharged from the periphery. But the RTM-Light process usually flows in from the perimeter and out of the center. We know that when the resin enters the mold cavity from the resin pipe and meets the fabric, the fabric will produce a counter pressure (resistance) to the resin. The magnitude of the reverse pressure is related to the permeability of thefabric, the viscosity of the resin, and the flow velocity of the resin, when the fabric and resin are selected,It is proportional to the flow velocity of the resin. Take an area of 3M2, thickness of 3mm products as an example, the general injection pressure is 0.05MPa, the injection time is 6min, the injection flow is 1.33L/min. If the injection from the center and maintain the flow unchanged, the anti pressure can be increased to more than 0.1MPa, resulting in the mold opening or mold phenomenon, and lead to resin flow forward out of control and the formation of dry spots and other issues. For this reason, the flow rate must be reduced, but this prolongs the injection time, so the injection from the center usually takes more than 6 minutes. When the surrounding resin injection, first into a gap about the surrounding flow 1mm almost no resistance, and then enter the fiber resin into the fiber increase due to pathway (from a point into a surrounding), relative resin in fabric flow slows down, back pressure decreases, the injection rate increase the injection time can be shortened. Tests show that for a 0.2m2 product, the time of injection from the periphery is 2.1 minutes, and the injection from the center to 9 minutes, the speed difference of four times. Of course, RTM process can also be injected from the surrounding resin, the pressure gradient is unchanged, but the highest point of the pressure from the original center point is moved to the periphery, which is beneficial to the deformation control of die, because the surrounding rigid die is better than that of the central area, but also on the periphery of the sealing requirements increased.The flow path design varies with the product, such as the 18mlong lamp post of Spectrayte company and the long runner. Brands's 6m2 floor, due to its asymmetrical structure, uses two outlets, each with a resin collector (Catchpot) at the center of each structure, with an injection time of 15 minutes. The Holland Royal Navy 13m2 hull manufacturing, due to larger products, using two diagonal arrangement of resin imports.(5) product accuracy, structure and otherThe size, viscosity, and repeatability of RTM and RTM Light products are affected by molding, resin, process control, and product curing. The product cross sectional accuracy is also affected by resin flow rate and injection pressure in the process. For the RTM process, when the mold is made according to the standard, without bending, the appropriate clamping device or press clamping, the parts of the dimensional accuracy repeatability is very good, the thickness deviation is not greater than 0.OlOmm. The RTM Light process usually has a certain deformation of the upper die, but the product size accuracy can also reach 0.020mm. Individual places are 4 0.030mm.Both RTM and RTM a Light process can suppress the sandwich material. The core can be made of balsa wood and foam. But the RTM process has a high injection pressure, limiting the use of low-density foam materials, the minimum density of foam is not less than 80Kg/m3, while RTM, Light and ZIPThe RTM process has a lower pressure, and the foam density he uses can be as small as 37Kg/m3. However, it is important to point out that the dimensional accuracy of core material meetsthe requirements of the mold in order to ensure the repeatability of the molding process and the quality of the product.The RTM and RTM Light processes also use preforms and inserts, which allow for high fiber volume products when using preforms.RTM-Light process can not gel, as long as the general release of wax, can release products. But do not release products such as RTM gel, more difficult.Compared with the die opening process, the investment of RTM Light is still relatively high, so it is necessary to consider the rationality of the cost of producing the necessary molds. In addition, the process is very professional and the daily maintenance task is heavy. It also affects the use of RTM Light for some manufacturers of hand ply composites.Compared to RTM, RTM Light has a low energy consumption, not too high on the mold rigidity requirement, but the viscosity of resin, resin and enhance the compatibility of materials, and the resin forward speeds demanding.3 light RTM process should pay attention to the problemRTM Light process is a highly specialized process, operators must be properly trained. If there is no reasonable fiber coating, good gas tightness and accurate mold installation, there is no consistent resin flow control, the product will be messy dry spots, radial bubbles, and resin enrichment and other issues. The following is a brief explanation of the relevantissues.(1) tightnessThe RTM Ligh process requires a higher level of detail, especially the tightness of the mold. The lower the vacuum of the vacuum trough used for the peripheral clamping, the better. The degree of vacuum in the lumen is generally controlled at about 15mm Hg. The periphery is clamped with a vacuum sealing groove and a flexible neoprene wing sealing ring (WingSeal profile) its bottom width is 20mm, the sealing ring joint should be vertical cut, with flexible adhesive glue, in order to ensure its elasticity. Outer ring and then 6mm wide silicone rubber edge.In the molding process, in addition to pay attention to the sealing of mold vacuum sealant, but also note the assembly of the mold, sealing ring and pipe connection, as well as the mold leakage caused by leakage. In fact, any seal or the entrance of the resin entrance, including the outlet of the vacuum zone, shall be checked strictly. A more hidden leak is due to cracks in the surface of the die panel, which are usually not found. The solution to this problem is that it is a very effective way to coat the outer surface of a mold with a resin that has been modified by a catalyst before it reaches the vacuum.Also, keep the cover clean and try not to clean it with solvent. The best release agent is free semi permanent release agent.(2) precise matching between upper and lower dies.The precise matching between the upper and lower dies contributes to the pressure balance in the cavity of the mold, and enables the resin to permeate evenly and helps to improve the quality of the products. Since the upper die is a semi rigid die, each die must be carefully calibrated.If the white spot appears continuously at the same location, this may be because the mold is closed inaccurate, resulting in inaccurate internal cavity, which led directly to the uneven thickness of the inner cavity. In this case, if the glass fiber layer is uniform, resin injection process flow is selective, it will choose the thickness (GAP) where relatively large, so in the region will lead to a relatively thin cavity of leukoplakia.Poor die positioning is an important cause of poor matching of dies. When the edge pin of the die is installed, the X and Y axes of the mold are naturally defined. If the location of the pin is not correct, it will cause unpredictable errors and change the injection characteristics.(3) reasonable paving and selection of raw materials,Due to the low pressure molding process on a RTM Light layer paving fabric requirements more stringent, laying unreasonable, especially the processing of the lap joint, will seriously affect the consistency of the resin flow, resulting in the lack of glue or resin products (dry spots) phenomenon.But with the help of glue fixed fabric in the layer, the layeris more smooth. But the spray and the resin must be good intermiscibility, spray too much or have a certain impact on the final performance of the product.Different fabrics and felt have a great influence on the process. It is necessary to use the enhanced material as much as possible. The resin flow rate of the O.c. closed felt or Hi Flow composite felt is twice as fast as that of the ordinary chopped felt.The appropriate resin system should be chosen according to the product requirements. Use low viscosity, low shrinkage resin as much as possible. Its standards are comparable to those required for vacuum resin diffusion processes.(4) surface crackCracks on the surface of the product will often be observed in the corner area. This is a common problem in the resin enrichment zone.This can also be traced back to the manufacture of the mold. If the 2.5 dies do not fit well with each other, a margin exceeding the expected thickness is produced. To solve this problem, in addition to the correction of the semi mold, the thickness of the glass can also be increased by adding additional glass fibers in these thicker areas to prevent cracks in the product.In the large flat area, cracks in the mold due to excessive thickness are found. This is due to the arbitrary increase in the speed at which the resin is injected. Injection speed toofast, it will make the mould cavity expansion, if the injection process is completed in a very short period of time. So, the cavity is no time to recover, so will lead to excessive resin mold crack. In extreme cases, the cracks on the surface of the mold can not be repaired.(5) overflow of resinIn order to receive the resin that is discharged before molding, many manufacturers feel the need to use a larger resin collector. This is the result of their lack of accurate control of mold filling. If the resin filling process is too fast, it is difficult to determine when to stop the injection. Because if you see the resin go to the resin collector and then stop the injection, then you'll see that too much of the resin will flow to the resin collector because the excess expansion mold has returned to its original size. To overcome this possibility, you can only replace a larger resin collector to prevent the spillage of the resin.The easy way to solve this problem is to calculate how much resin to use. But it is difficult to know exactly how much resin to use when molding large articles. Another method is to provide the operator with accurate pneumatic control to avoid the operator's blind judgment. The air pressure readings in the chamber provide more accurate mold filling information for operations, avoiding the need for larger resin receivers. Such a system ensures that the allowance of 10 to 100 milliliters is sufficient after each injection, which allows the resin to minimize waste and ensure an increase in profits.If there is a resin overflow in the vacuum zone at the edge of the mold, there are several reasons:Sealing of sealant is not goodWhen the sealant path is not in a horizontal position, will result in leakage of resin, in the mold on the panel if there is a convex part, it is necessary to ensure sufficient pressure on the part of the sealant that is completely sealed. A better method is to install a dynamic strip, this dynamic strip, in the edge of complex adaptive path on the sealing surface when the mold is closed this strip can be slightly expanded to seal.Improper placement of fibers in mouldsPlaced in the mold when the fiber is not fully sunburner or pruning, that cannot be placed in the fiber in the mould, and some fibers in the sealant path, which will directly lead to the leakage of resin, to do so before molding each time to carefully check the fiber layer.The injection pressure is too largeAnother common cause is the cause of leakage of resin sealant in the injection process, injection pressure in the pipeline is too large RTM Light mold is closed only by the action of atmospheric pressure, resin injection molding machine can produce more than the actual needs of the pressure, if there is no more sensitive and accurate pressure control, resin will leak into the vacuum zone, which will lead to the loss and mould around vacuum production failure.Loss of vacuum sealWhether it is a long-term or temporary edge vacuum loss, will lead to leakage of resin. Therefore, do not access several molds in the same vacuum system, as this will result in a reduction in the vacuum in the main vacuum zone.In fact, a simple automatic vacuum lock valve helps reduce the possibility of this vacuum loss.4 light RTM applicationsThere are not many reports about RTM Light technology and products in China, but the application development in foreign countries is very fast, and there are more than RTM application trends. At present, the common application areas are aerospace, military, transportation, construction, ships and energy, etc.. For example: the field of aerospace doors, fan blades, radome, aircraft engine hood: military field, torpedo shell tank, tubes and other areas; traffic light rail bus door, side panels, chassis, bumper, truck at the top of the baffle; the building area of street lamp pole, tubular wind generator hood decoration, doors, tables and chairs and the helmet; the field of ship hull, deck and other small boats.。
树脂传递模塑工艺（树脂压铸成型）属于复合材料的液体成型工艺
(Liquid composite molding)。
它是在20世纪70年代发展起来的复合材料成型新工艺，也有资料认为它是由20世纪30年代的浇铸冷模工艺演变而来的，在西欧RTM工艺也称"树脂注射"工艺。
RTM 工艺的基本原理示意如图-1(a)所示，在一定的温度、压力下，低黏度的液体树脂被注人铺有预成型坯（增强材料）的模具中，注人树脂，固化成型，然后脱模。
工艺过程图解如图- 1 (10所示，包括预成型坯的加工与树脂的注入和固化两步。
由于这两步可分开进行，所以说RTM工艺具有髙度的灵活性和组合性，便于实现"材料设计"，同时使操作工艺简单。
图-1RTM成型工艺
RTM工艺的注射操作一般要求在1/4 ~ 1/2树脂凝胶时间内完成，传递时间为2~15min，传递压力为0.3~0.7MPa。
为脱除模腔内的气泡,促进树脂的流动和改善浸渍性,还发展了一种在注入树脂的同时抽真空的新工艺——真空辅助RTM工艺。
