2019 Composite Material RTM Vacuum Closed Mold Process Practical Training Summary Report

 

Zhang Yanfei

 

Zhang Yanfei, associate professor at North University of China, mainly talked about the development and application of composite liquid molding technology. The content of the lecture is mainly divided into six parts:

 

Part 1, Overview of LCM Molding, the main contents include the definition of LCM, process principle, process composition, key process, main influencing factors of the process, development history, process advantages and disadvantages, and requirements of the resin system;

 

Part 2, Classification, characteristics and applications of LCM processes, the main contents are resin transfer molding RTM, vacuum assisted resin transfer molding VARTM, lightweight resin transfer molding L-RTM, resin infusion molding SCRIMP, resin film infiltration process RFI, structural reaction injection process SRIM, high pressure resin transfer molding HP-RTM, thermoplastic resin transfer molding T-RTM, surface resin transfer molding Surface-RTM, prepreg assisted resin transfer molding SQ-RTM, thermoplastic film assisted resin transfer molding Film-RTM, pultrusion-resin transfer molding Pultrusion-RTM, super resin transfer molding Ultra-RTM and other specific LCM processes. Characteristics, process principles, process, typical application parts;

 

Part 3, LCM Analysis of process preform preparation technology, the main contents include fiber preform technology overview (technical requirements), textile preforming technology (flat fabric, three-dimensional fabric) fabric form (flat-plain cloth, square fabric, twill, satin fabric, wrinkle-free fabric; three-dimensional-woven fabric, orthogonal fabric, 2D braided fabric, 3D braided fabric, 2D/3D stitching technology-single needle stitching technology, double needle, chemical stitching technology, VAT fiber variable angle traction machine paving preforming technology), advantages and disadvantages, application scenarios, typical application parts, setting agent setting technology, including short fiber jet preforming P4A technology, manual paving preforming, hot pressing preforming definition, process, process preparation, common problems, typical application parts;

 

Part 4, analysis of the development trend of mold filling flow control technology, the main contents include Darcy Law, resin system, permeability (single-direction saturated flow method, unsaturated radial method), thickness change measurement, injection method (edge ​​point/line injection, center injection, surrounding injection), working pressure, defect formation mechanism/control, corner effect, edge flow effect, process simulation (RTM-Worx, PAM-RTM);

 

Part V, LCM molding equipment technology development analysis, the main content is the fiber preform processing center, including equipment for short fiber injection preform, hot pressing preform, 2D weaving technology to prepare preform, 3D weaving technology to prepare preform, RTM injection system, including resin storage tank, heat exchange system, high-pressure metering pump, resin hedge mixing head, hydraulic press, including translatable work surface, reversible work surface, short-stroke hydraulic press, molding mold, clamping and transfer equipment, including fiber preform adsorption fixture, composite product adsorption fixture, machining equipment, including mechanical cutting, high-pressure water cutting, laser cutting, etc.;

 

Part VI, LCM of typical products Process examples mainly include Tailimo I-beam RTM molding,

 

Sikorsky UH-60 fuselage top cover SQRTM molding, UH-60 SARAP fuselage verification parts, soft mold auxiliary thrust cylinder RTM molding, and Torres Wing (dry fiber placement + VARI integral infusion molding).

 

Yu Mengbai

 

Yu Mengbai, General Manager of Shanghai Qichang New Materials Technology Co., Ltd. He mainly explained the process and precautions of L-RTM mold production.

L-RTM mold production mainly follows

① Read the drawings to see whether the product is suitable for L-RTM process, whether it needs to be modified, demoulding slope, embedded parts, local thickening, block division, etc., and increase the skirt and thickness of the L-RTM mold based on the original drawing;

② Model processing, you can choose block substitute wood, paste substitute wood, wood, high-density PU foam or PS Foam;

③ Model (wood processing), use the machining center to process the model, after processing, it is necessary to measure against the drawing. If the surface needs to be sealed, scrape the putty and then spray the easy-to-grind primer;

④ Model (easy-to-grind primer treatment), the recommended spraying amount is 300g/m2, spray first hard and then easy, and finally spray the large area of ​​the model. When grinding, determine the sandpaper mesh number and grind according to the product configuration;

⑤ Model (high-gloss gel coat treatment), the recommended spraying amount is 200g/m2, spray first hard and then easy, and finally spray the large area of ​​the model. When grinding, determine the sandpaper mesh number and grind according to the product configuration;

⑥ Demolding treatment, choose High-quality release agent, and ensure the cleanliness and appropriate temperature of the coating environment;

⑦ Mold gel coat spraying, recommended dosage 800g/m2 (small mold 1000g/m2), spray thin layers multiple times to avoid excessive thickening in local areas, spray first hard and then easy;

⑧ (fatigue-resistant layer) surface mat paste, make sure the surface mat is dry, and confirm the gel time of the resin, and paste the surface mat when the gel coat is sticky but not sticky, which can reduce the amount of resin;

⑨ (fatigue-resistant layer) chopped mat paste, the chopped mat must also be ensured to be dry, and the paste time close to the gel coat layer should be arranged during the day. Before pasting the chopped mat, make sure that the surface mat is completely cured and the bubbles have been removed. For molds with complex surfaces, choose 150-300gsm mat for the first two layers, and the mold reinforcement layer mostly chooses zero shrinkage resin, and its thickness is recommended to be 3mm Above;

⑩ (sandwich layer) production, pay attention to the fit, you can use special putty to stick it, or mix zero shrinkage resin and filler;

⑪ Wrapping layer production, first check whether the sandwich is firmly glued, make the corners smooth and polished, and then paste the wrapping layer;

⑫ Steel frame production, remove stress after the steel frame is welded, if there is no condition to remove stress, you can use silicone to bond the steel frame;

⑬ After the positive mold is completed, use high-grit water sandpaper for processing, and use pure cotton cloth to wipe in one direction when cleaning;

⑭ Mold cavity processing, the ambient temperature must be guaranteed for wax sheets. If the temperature is high, the wax sheets will become soft and deformed, and if the temperature is low, the wax sheets will become hard and have poor adhesion. Each wax sheet The sheet should be laid evenly with force, and there should be no air pockets underneath;

⑮ The key to making the air chamber is to ensure the sealing effect of the two subsequent layers. Reasonable design should be made before laying, and the internal and external sealing channels should be embedded during laying to ensure that they are not deformed and firmly adhered;

⑯ When designing the injection port and the exhaust port, the success rate should be considered first, and then the workload reduction and material saving should be considered;

⑰ When making the back mold, the resin used should consider the shrinkage effect, and the steps of pasting the sealing channel and the air chamber should be arranged reasonably to ensure that they cannot shrink or deform;

⑱ After the back mold is completed, the finish of the back mold is not required to be high, but the sealing of the injection port and the exhaust port is very important. As long as there is a slight air leak in the back mold, it will have a great impact on the product.

 

Ren Jian

Ren Jian, Chief Technical Engineer of Beijing Bonazhi Technology Co., Ltd. He mainly shared an operating manual for L-RTM products, covering the operation content, raw materials, tools and precautions of material preparation, mold preparation, gel coat spraying, fiber and preformed block laying, mold closing, exhaust pipe and injection hose installation and negative pressure measurement, RTM equipment debugging, resin injection, demolding, product cutting, product inspection and other processes.

 

September 7

 

On September 7, the main focus was on factory site demonstrations. They were L-RTM of flame-retardant vinyl ester resin from Nantong Fangxin, Changzhou Baisitong and Shanghai Huazheng Process demonstration, the product is a basin, mainly demonstrated the gel coat brushing, isolation mat, closed mold mat laying, mold closing, glue injection and demolding processes; Shanghai Saici demonstrated the vacuum introduction process of self-heating composite material molds, the product is a carbon fiber boat model, the resin used is Daosheng Tianhe’s epoxy resin, mainly demonstrated the spraying of transparent gel coat, surface carbon fiber laying, internal glass fiber laying, demolding cloth and guide net laying, glue injection pipeline and exhaust pipeline placement, bagging, resin introduction, heating and curing processes; Guangzhou Weipu demonstrated the vacuum introduction process and bonding process demonstration of carbon fiber modified car tail wing, the resin used is Fangxin and Beston’s flame-retardant resin, mainly demonstrated the brushing of transparent gel coat, surface carbon fiber laying, internal glass fiber laying, demolding cloth and guide net laying, glue injection pipeline and exhaust pipeline placement, bagging, resin introduction, curing processes; Taicang Hainuo’s dust-free grinding; Shanghai Kaiyuan’s fiberglass mold polishing.

 

September 8

 

On September 8, the main activities were factory demonstrations. They were the polyurethane resin L-RTM process demonstration of Nanjing Jufa, the product was a basin, mainly demonstrating the processes of gel coat brushing, isolation mat, closed mold mat laying, mold closing, glue injection and demolding; Shanghai Saici and Guangzhou Weipu product demolding; UV light-cured glass fiber prepreg flat plate curing demonstration.