What is the manufacturing process of SMC products? Today, let's take a closer look.

1、 Preparation before restriction

(1) SMC quality inspection

The quality of SMC sheets has a significant impact on the molding process and product quality. Therefore, it is necessary to understand the quality of the material before imposing restrictions, such as the resin paste formula, the thickening curve of the resin paste, the glass fiber content, and the type of glass fiber moisturizing agent. Single weight, film peelability, hardness, and quality uniformity.

(2) Make a choice

Based on the structure and shape of the product, the feeding direction, and the process, determine the shape and scale of the sheet material selection, manufacture a sample, and then cut the material according to the sample. The selected shapes are mostly square or circular, with scales ranging from 40% to 80% of the projected surface area of the product. To avoid contamination from external impurities, the upper and lower films are removed before loading.

(3) Preparation of equipment

① Understand the various operating parameters of the press, especially adjusting the working pressure, press operating speed, and table parallelism.

② The mold device must be level and positioned at the center of the press table. Before limiting, the mold must be thoroughly cleaned and coated with release agent. Before adding materials, wipe the release agent evenly with clean gauze to avoid affecting the appearance of the product. Regarding the new mold, it is necessary to remove the oil before use.

2、 Add ingredients

(1) Confirmation of feeding amount

The amount of material added to each product can be calculated according to the following formula at the initial limit: (g)=product volume (cm × 10 × 6) X 1.8 (g) (2) Confirmation of feeding area. The size of the feeding area directly affects the compactness of the product, the activity interval of the material, and the surface quality of the product. It is related to the activity and curing characteristics of SMC, product functional requirements, mold structure, etc. The general feeding area is 40% -80%, and if it is too small, it may cause glass fiber orientation due to the long process. Reduce intensity, add waviness, and even fail to fill the mold cavity. Excessive size is not conducive to exhaust and is prone to internal cracks in the product.

(3) Feeding direction and method

The direction and method of feeding directly affect the appearance, strength, and directionality of the product. Normally, the feeding direction of the material should be in the middle of the mold cavity. Regarding asymmetric and disordered products, it is necessary to ensure that the feeding direction reaches all ends of the mold cavity together during molding. The feeding method is necessary to facilitate exhaust. When stacking multiple layers of sheets, it is advisable to stack the blocks in a pagoda shape, with the top being smaller and the bottom being larger. Other than that, try not to separate the material blocks, otherwise air entrapment and fusion zones may occur, leading to a decrease in the strength of the product.

3、 Forming

After the material block enters the mold cavity, the press quickly descends. When the upper and lower molds match, slowly apply the required molding pressure, and after a certain curing time, the product is formed. During the molding process, it is necessary to reasonably select various molding process parameters and press operating conditions.

(1) Forming temperature

The unevenness of the molding temperature depends on the curing system of the resin paste, the thickness of the product, the production power, and the degree of disorder of the product structure. The molding temperature is necessary to ensure the smooth progress of the crosslinking reaction caused by the curing system and complete thorough curing.

Generally speaking, the molding temperature selected for thick products should be lower than that of thin-walled products, which can avoid excessive heat accumulation inside thick products due to high temperatures. If the thickness of the product is 25-32mm, the molding temperature is 135-145 ℃. Thinner products can be formed at 171 ℃.

The increase in molding temperature can shorten the corresponding curing time; On the contrary, when the molding temperature decreases, the corresponding curing time needs to be extended. The molding temperature should be selected by balancing high curing speed and optimal molding conditions. It is generally believed that the molding temperature of SMC is between 120-155 ℃.

(2) Forming pressure

The molding pressure of SMC varies with the structure, shape, scale, and degree of SMC thickening of the product. Products with simple shapes only require a molding pressure of 5-7MPa; Products with disordered shapes can be formed under a pressure of 7-15MPa. The higher the thickening degree of SMC, the greater the required molding pressure. The size of the molding pressure is also related to the mold structure. The forming pressure required for straight parting structure molds is lower than that for horizontal parting structure molds. Molds with smaller gaps require higher pressure than molds with larger gaps.

Overall, the confirmation of molding pressure should consider multiple factors. Generally speaking, the molding pressure of SMC is between 3-7MPa.

(3) Curing time

The curing time (also known as insulation time) of SMC at the molding temperature is related to its properties, curing system, molding temperature, product thickness, and color. The curing time is generally calculated at 40s/mm. For products with a thickness of 3mm or more, add 1min of curing time for every 4mm added.

4、 Press operation

Due to SMC being a fast curing system, the rapid closure of the press is crucial. If the press closes too slowly after adding materials, it is easy for pre curing spots to appear on the surface of the product, or for material shortage or excessive size to occur. At the end of the press stroke, the mold closing speed should be carefully adjusted to slow down the closing process and facilitate exhaust during the rapid closing process.

The article originates fromSMC molded products http://www.jmlicheng.com