The past decade has been a period of rapid development of SMC molded products in China, from a demand of several thousand tons to a demand of hundreds of thousands of tons now. The application fields of commodities have also expanded from traditional cars, building materials, and electrical to municipal, machine tools, engineering machinery, agricultural machinery, highway equipment, mining equipment, water conservancy equipment, and other aspects. The rapid pace of development has made us professionals feel delighted. The reason for this is:
One reason is that the Chinese market is too large, to the point where many products can only use technology with small initial equipment investment abroad, but in China, there is a large amount of available molding technology with large initial equipment investment;
Secondly, the rapid development of China's machinery and equipment manufacturing industry, especially hydraulic presses and molds, is not only due to their fast technological advancement and affordable pricing, but also results in a decrease in the breakeven point during the preliminary profit and loss analysis;
The third is the gradual improvement of domestic supporting materials, with professional grade products available for selection from resins, glass fibers, curing agents, release agents, and thickeners, ensuring quality and multiple functional options.
Fourth, the reform and opening up has brought new technologies, and has also cultivated a large number of SMC professional and technical personnel, opened up the thinking of Chinese professionals in the field of composite materials, and combined with the intelligence and innovation of Chinese people, the domestic SMC molding career has been carried out at a high speed in recent years.
The danger of professional development that we need to see together with the prosperous scene is also an objective law. Long term high-speed development is definitely not a merit, and there will be some doubts that need to be addressed.
1、 Many companies only focus on expanding the quantity rather than cultivating the quality. The company's development should be carried out in a healthy manner. Without reasonable profits and negotiated funding, it will only harm others and oneself. There have been bloody cases in the professional world.
2、 Professional competitions are not reasonable, but rather a combination of price and price tactics, resulting in low quality and low prices. Our products have certain advantages that allow customers to choose to replace metal parts, plastic parts, and other fiberglass parts. However, if the product's functionality is poor, customers can choose not to use SMC technology.
3、 Lack of knowledge about SMC as a whole. Although we all know how to make molds, SMC sheets, and molded products, we know very little about some basic principles, which exposes many questions to customers at the end of the product and affects the overall image of the SMC profession.
As a SMC sheet manufacturer, on the one hand, we need to strengthen internal management and improve the stability of product quality; On the other hand, we are strengthening research and development to provide impetus for the sustainable development of the company. But it's not enough to do our own homework well. No matter how good the SMC materials are, if the molds are poor or there are serious shortcomings in the product planning, we won't be able to do it. In recent years, I have done a lot of homework on my own, so I have become more aware of the importance of product layout and molds. There are many literature materials on SMC molding at home and abroad. If we carefully read and understand them, we can indeed make a lot of progress. Today, I have the opportunity to comment on some practical situations with us. Time is limited, so I choose some important questions to comment on.
1、 Mold parting layout and flash planning
Advocate for the use of a semi overflow straight parting layout for SMC molds, with the detailed layout as follows:
This layout allows the molding pressure to be effectively applied to the appearance of the product, ensuring the normal movement and polymerization reaction of SMC materials in the mold cavity, and together lifting the air as much as possible to obtain good product quality.
2、 Mold positioning and guiding equipment
SMC molds are different from injection molds. When the injection mold is closed, the mold temperature is not high, and the molding of the product is completed only after the mold is completely closed. This allows for accurate mold closure through the improvement of guide column accuracy. However, the normal operating temperature of SMC molds is around 150 ℃ (some can be higher), and high guide column accuracy will result in mold jamming (the shaft expands and the hole decreases when heated). This is especially true for large molds, so it is necessary to use other layouts to complete high-precision mold closure of SMC molds. A steel lock module with a certain slope and hardened appearance is a good choice (most foreign countries use brass and graphite with good wear resistance, but domestic presses have low precision, and the mold is subjected to large lateral forces during mold closing, resulting in simple damage)
Good positioning and guidance equipment is the guarantee of accurate mold closure, especially for the layout of the flying edge. If the mold cannot be closed accurately, it can cause wear and tear on the upper and lower molds at the flying edge, leading to damage to the product.
1. Molds with outstanding positioning, guidance, and flying edges:
2. Product defects caused by molds without outstanding positioning, guidance, and flying edge layout:
3、 Strengthening ribs and flanging
Usually, reinforcing ribs and flanging are used to improve the rigidity of the product, but poor planning can actually affect the quality of the product
1. Strengthen the muscles
Many materials about strengthening tendons will be introduced, so I won't go into more detail here.
2. Flanging (height less than 30mm)
The effect of flanging is also similar to that of reinforcing ribs. When we are all focusing on the effect of reinforcing ribs, we often overlook the effect of flanging.
This product is the upper cover of a bus air conditioner cover. It is considered that it may dry out with the internal air conditioner. The product has not been reinforced, and only relies on a 4mm thick flange to ensure rigidity. In practical production and use, the flange cracking is particularly severe, reaching more than 60%. After adding flange thickness and adding materials, the durability has improved a lot, but the cost has increased. This type of product did not consider the characteristics of SMC molded products at the beginning of planning: ① SMC products have poor resistance compared to metal stamping parts and injection molded parts, and can undergo less plastic deformation. ② The edge of the product is also the area where the glass fiber content is relatively low and where glass fiber orientation occurs briefly. The following improvements can be proposed:
If the layout agrees with the proposal, a composite layout with double panel bonding can be used to prevent the addition of product rigidity. At this time, the reinforcement planning of the outer panel can be relatively simple, and the inner panel can be made of SMC molding, metal stamping or other materials. The entire or part of the inner panel is bonded to the outer panel through layout bonding.
4、 Product opening
In the SMC molding process, the disorderly layout, feeding method, orientation, and data activities of the mold can affect the mechanical function and appearance quality of the opening. The ideal solution is secondary processing, which can choose drilling, punching, milling, or water cutting.
Of course, if the situation permits, it can also be completed through molds to reduce subsequent processing. Reasonable mold layout planning is crucial, usually using the so-called kneading area layout:
1. Kneading area planning (1) is suitable for small-scale opening areas, with simple molds and minimal SMC flash damage
2. Kneading area planning (II) is suitable for larger opening areas, where the mold is more messy than the previous one and SMC burrs are more wasteful
The two plans do not have too strict scale boundaries, and thoroughly consider product demand, mold quality, press pressure, and data activity.
Of course, if the opening scale is too large or there are too many openings, the kneading area planning (1) should still be selected, as it may affect the appearance quality due to the intense activity of SMC data in the kneading area.
If the opening area of the product is larger, such as the glass windows on the car door and rear lift door, consider planning straight cutting edges around the opening area. To prevent the occurrence of welding marks, it is necessary to take the paving material around the opening, and it is necessary to stack 30-50mm at the paving joint.
There is another way to plan the kneading area that can also be considered in the absence of pressure from the press
I used this plan on the radiator face shield of Xinming Heavy Duty Truck's Steyr King to prevent the problem of insufficient pressure in the kneading area due to lack of pressure.
The actual situation is that more than half of the molds are arranged with straight flying edges in the opening area, and the gaps at the cutting edges are not strictly controlled. The precision of the mold guidance positioning is also poor. In addition, the lack of precision of the press machine results in cumbersome material laying, large flying edge waste, poor appearance quality, weld marks, and product mold pulling marks.
5、 Product ejection and inserts
Most SMC products use methods such as ejector rods, ejector plates, and pneumatic ejector to ensure uniform ejector force and parallelism. These ejector methods can be used independently or in combination. The orientation of the protrusion should be planned as much as possible in areas with strong rigidity of the product, such as reinforcing ribs, reinforcing rib insertion protrusions, and embedded parts. If the convex platform is core type (i.e. hollow in the center), it is best to use the method of pushing out the tube. Another important effect of the ejector pin is to help release air from the mold during SMC data activity.
If there are inserts on the product, a ejector pin can be planned at the insert location, but a movable block should be used. After the product is pushed out, remove the live block from the product.
Many domestic manufacturers have simplified the planning by making the top rod head into a convex platform, or directly placing the embedded parts on it, or forming a core type convex platform on the molded product.
However, the results of this approach are not ideal. After the product is pushed out, the head of the ejector pin gets stuck on the product, requiring force to remove it. In severe cases, it needs to be pried with something, which can cause damage or cracking to some parts of the product, affecting its subsequent use.
Other SMC products are brittle and have poor self-lubricating properties. It is best not to use self tapping screws. If self tapping screws are necessary, try not to disassemble them.
1、 At the beginning of opening the mold, I had extensive discussions with product planners, production personnel, and mold planners to develop a reasonable product and mold planning plan.
This was once done well by BAIC Glass and Xienuo (now sole proprietorship changed to Quannai). The A-side digital model and B-side layout and digital model provided by the OEM are manufactured by the molding manufacturer. Such SMC products will have more advantages in the production and application process.
2、 The mold should be made by a manufacturer with good quality. Remember not to be greedy for cheap. Good layout, good materials, good processing techniques, and good surface treatment molds are sure to ensure the success of your product. Good molded products can be directly painted or spray painted, but in reality, molded products require a lot of follow-up disposal, which also affects customers' selection of SMC molded products. After all, the post-processing of injection molded and stamped parts is simple.
Specialized collaboration is necessary in the SMC molding industry chain, and it is important to remember that resin manufacturers produce SMC materials, SMC material manufacturers produce products, and product manufacturers produce SMC materials. Due to the close proximity, it is difficult to achieve precision in the end. I fully understand that when there is a problem with the product, both sides argue with each other, ultimately leading to a high resolution plan - to digest the poor resin and SMC materials on their own. And due to the ability to compete, it will affect the close collaboration between you and your clients.
 

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