HOT PRESS MOLDING
Press molding is a molding method generally used in high-volume composite production such as the automotive industry. There are two types, cold and hot press molding.
In the hot press molding method, the material is placed in the hot mold and the mold is closed with a hydraulic press. In general, the press molding process is performed at a mold temperature of 150°C - 170°C and a mold pressure of 800-1000 kPa, with a curing time of 2-10 minutes depending on the wall thickness. Hot press molding is a low cost process and is capable of high volume production.
Hot press molding method is used for productions with thermoset matrix. The main thermoset molding components that we produce in our company are SMC (hot press molding pulp) and BMC (hot press molding paste).
Hot press molding method with SMC and BMC is one of the fastest production methods used in composite material production.
Within our company, we have 12 vertical presses in the range of 80 tons - 1200 tons, which we use only in the contract printing of our customers, as well as 2 Krauss Maffei Thermoset Injection Molding machines of 450 tons.
Comparison of Thermoset and Thermoplastic injection
In thermoset injection, the product is obtained by injecting cold Glass fiber reinforced polyester molding compound (BMC or SMC) into the mold heated at around 140-180 degrees.
In thermoplastic injection, the material is melted and injected into the mold at a temperature of around 80-100 degrees, and the part is cooled.
The areas where thermoset materials are used intensively are the places where the product will be exposed to high temperatures or where durability is sought. Medical applications can be given as a good example of this. In addition, the use of thermoset composite (GRP: Glass Fiber Reinforced Polyester) product is mostly preferred in high voltage applications, products with low shrinkage requirements such as automotive, and non-flammability applications.
Thermoplastic materials, on the other hand, will not be exposed to high temperatures and are suitable for use in areas where durability is not required.
Thermoset material is injected more slowly than thermoplastic materials and is kept in the mold for a longer time. In terms of price, although the thermoplastic material seems more economical than the thermoset material in terms of cost per piece, it is preferred as a good alternative due to its many advantages such as the thermoset material being more durable according to the suitability of the usage areas.
It is not possible to melt and recycle the product produced with thermoset material. However, it can be used as a filling material in the BMC process in certain proportions by breaking it down and micronizing it, or it can be broken down and used as an additive in asphalt or concrete.
In thermoplastic material, it is possible to granulate the products and mix them into fresh granules and reuse them as a second quality product.
As a result of the comparison, although thermoplastic seems to have both more economical, faster production and recyclability, thermoset material is preferred in usage areas where special (flameproof, dielectric, durability) products are desired.
For example, in the automotive industry, where thermoset material is frequently preferred, it is preferred in many parts from bumper to trunk lid, from hood to headlight bodies, thanks to its properties such as heat resistance, rigidity and paintability.
Thermoset materials add strength to the structure of the product, thanks to the cross-linking of the chemicals used in their production at the molecular level with the help of temperature.
Advantages of thermoset materials:
Chemical resistance: Thanks to its chemical combination in production, it is resistant to damage and abrasion of chemicals.
Thermal resistance: It has high thermal resistance since it does not melt.
High durability: Thanks to its chemical structure, it has high mechanical strength and is more stable in terms of dimensions.
Weight: With a density of 1.5-1.9 g/cm^3 (lower densities can be achieved with Light SMC).
Disadvantages of thermoset materials:
Mold design: Although it is similar to thermoplastic molds, there are critical points to be considered in terms of design. For example, when designing the mold, it requires specialized knowledge, such as leaving a bleed due to the structure of the product.
Non-recyclability: It is not possible to recycle the product produced with thermoset material by melting it. However, it can be used as a filling material in the BMC process in certain proportions by breaking it down and micronizing it, or it can be broken down and used as an additive in asphalt or concrete.
Low impact resistance: Despite its high strength, the product tends to break in bending and point impacts because it does not have a flexible structure like thermoplastic.
Advantages of thermoplastic materials:
Recycling: thermoplastic materials can be turned into granules and re-products can be produced, even if they are of second quality.
Production cost: Low wastage costs as the waste products can be broken down and reused in production.
Impact resistance: It has an unbreakable structure even though it is deformed thanks to its flexibility in bending and point impacts.
Disadvantages of thermoplastic materials:
Low thermal resistance: Since thermoplastics can be melted and recycled, they cannot be used in areas where thermal resistance is required.