Key Control Parameters Of SMC Compression Molding Dies
Jan 27, 2026
The core of SMC compression molding lies in the precise control of four key parameters, which directly determine the curing integrity, appearance accuracy and mechanical property stability of the products. The standard specifications and control points of each parameter are as follows:
1. Temperature Parameters
Temperature is the core prerequisite for the curing and cross-linking reaction of SMC materials. The surface temperature of the mold and the overall temperature difference must be strictly controlled to prevent abnormal temperatures from affecting the curing rate and causing performance defects or dimensional deviations in the products.
Standard temperature: Under normal working conditions, the upper mold temperature is controlled at 145°C, and the lower mold temperature is controlled at 140°C. For special types of resin formulations, the temperature range can be adjusted to 130-160°C, and the specific values need to be determined based on the material performance parameters.
Temperature difference control: The overall temperature difference on the mold surface must be strictly controlled within ±5℃. For large-sized or thick-walled products, zonal temperature control technology should be adopted to prevent local overheating that may cause the products to become brittle and crack, or local overcooling that may result in under-curing.
II. Pressure Parameters
The molding pressure must meet the requirements for the SMC material to flow fully and conform completely to the contour of the mold cavity. At the same time, it is necessary to avoid defects in the product caused by excessive or insufficient pressure. It should be precisely controlled according to the structural characteristics of the part in different scenarios.
Molding pressure: Gradually increase the pressure to 10-25 MPa within 30-60 seconds after closing the mold. For complex-shaped products with high material thickening degree, the pressure level should be appropriately increased to ensure that the material flows evenly and fills every corner of the cavity.
Pressure stability: Throughout the pressurization process, uniform and stable pressure must be maintained to avoid pressure fluctuations that could lead to uneven density of the product, and subsequently result in quality issues such as pores, shrinkage marks, and flash abnormalities.
III. Time Parameters
The core of time parameters is the curing time, which should be flexibly adjusted based on the thickness of the product and the type of material formula. Under the premise of ensuring complete curing of the product, the production efficiency should be optimized.
Conventional curing time: Based on the actual thickness of the product, the standard curing duration is 1-1.5 minutes per millimeter. This ensures that the material fully completes the cross-linking reaction and guarantees that the mechanical properties of the product meet the standards.
Special material curing time: The curing time for carbon fiber reinforced SMC products needs to be extended. It is usually controlled within 10 to 15 minutes to prevent insufficient curing from causing inadequate strength and rigidity of the products, which may affect their safety in use.
IV. Exhaust Parameters
During the curing process of SMC materials, a small amount of gas is released. It is necessary to timely exhaust it through scientific exhaust design; otherwise, it is easy to form air holes inside the products and cause scorch marks on the surface. The exhaust parameters need to be coordinated and matched with the temperature and pressure parameters.
Exhaust groove design: The depth of the exhaust grooves is strictly controlled within 0.01-0.03mm, and their positions should be precisely set in the areas where the material flow reaches last, at the corners of the cavity, and other air-trapping dead corners to ensure smooth exhaust without excessive flash formation.
Exhaust timing: It is necessary to perform short-term exhaust through the pressure release and mold loosening method when the material has reacted to the semi-cured stage (before complete crosslinking and curing). Exhausting too early will not achieve the desired effect, while exhausting too late will make it difficult to expel the gas as it will be encapsulated by the cured layer. At the same time, it is necessary to coordinate with the temperature control rhythm. An increase in temperature will accelerate the generation of gas, and it is necessary to ensure that the exhaust capacity is adapted accordingly.
The principle of parameter coordination: The four key parameters need to be mutually adapted and dynamically adjusted. For instance, when the temperature rises, the exhaust rate should be accelerated and the curing time slightly shortened. After the pressure increases, the curing cycle can be moderately compressed to ensure that the overall process remains in a balanced state, taking into account both product quality and production efficiency.
In summary, temperature, pressure, time and exhaust are the four core control parameters for SMC molding, which are interrelated and mutually restrictive, and none of them can be missing. Temperature determines the basic efficiency of the curing reaction, pressure ensures the material filling and the density of the product, time balances the curing quality and production efficiency, and exhaust avoids appearance and internal defects such as pores and charring. In actual production, it is necessary to take the standard parameters as the benchmark, and make dynamic adjustments based on the structure of the part, the material formula and the performance of the equipment. Strictly follow the principle of parameter coordination to continuously and stably produce SMC products that meet the quality requirements, and at the same time extend the service life of the mold and optimize the comprehensive production benefits.
