Once the paste viscosity is sufficiently thickened to reach its forming plateau,the SMC can be compression molded inside a hot mold.For that purpose, hydraulic or mechan-ical presses can be used.Their loading capacity depends on the size of the part to be molded (presses with a maximal load up to 40,000 kN can be used for the largest parts). Dedicated molds are mounted on these presses. They are made of cast, forged,or machined metals (usually steel). Their surfaces are hardened, polished, and at times, treated (chrome plated) Side cores, requirements for inserts, and other refinements can be added.The molds can be heated byusing preferably, a thermal fluid (steam, oil) that cir-culates inside the mold. Compared to standard heating systems (e.g., electrical heating cartridges), this solution can heat the mold and the SMC but it can also extract the additional heat that is released during the exothermic SMC curing. Various successive operations are required for compression molding, the second and fundamental step of the SMC process. Depending on the complexity of the part to be produced, most of these operations can be robotized.
First, several sheets or charges are cut from the thick-ened SMC. Their carrier film is withdrawn, and sets of 2–10 charges are then stacked together. The surface of the stacked charges usually occupies 30–70% of the total surface of the mold (mold surface coverage). The time required for this operation is concurrent and not taken into account in the compression molding cycling time:it is generally achieved during the curing of the previous compression-molded part (see below). Special care must be taken to cut, ply, and weigh the stacks respectively to their prescribed shape and weight: their weights must equal those of the final parts (for that purpose, and because of the possible thickness irregularity of compounded sheets,small pieces of charges are sometimes cut from the stacks or added to them) and their geometrical shapes are usually designed for optimized mold-filling conditions. It is also important to notice that the charge stacking can induce air entrapment between the charges: if not properly eliminated during compression molding, the entrapped air can be a possible source of residual and unfavorable pores in produced parts.
Second, the stacked charges, initially and usually at room temperature, are then positioned onto the lower part of the compression-heated mold (130–160 ◦ C, depending on the resin to be cured). During this charge placement,which lasts approximately 10–20 s, particular attention must be paid to the positioning of the stacks in the mold:slight variations can induce drastic changes during mold filling.
Third, the heated mold is progressively closed at typical closing velocities usually ranging between 1 and 10mm/s.During the mold closing (duration: 1–10 s), the SMC charges are continuously heated and forced to flow within the mold cavity. Flow mechanisms occurring during this phase are closely related to the rheology and the ini-tial microstructure of SMC. They are very complex but they are essential, since they considerably affect the final microstructures of molded SMC parts (see the section titled ‘‘Mold-Filling Phase’’), and so their end properties.
Fourth, the mold is kept closed under high pressure (5–20MPa) for approximately 30 s–3min. Most of the curing reaction of the SMC paste occurs during this phase (see the section titled ‘‘Curing Phase’’).
After this curing, an in-mold coating (IMC) operation can be achieved  in order to erase surface defects that have been created during compression molding (sink marks, pores, etc.) and to form a primer-like surface before painting. This operation consists in opening the mold slightly and injecting and curing a coating compound onto the external surface of the SMC.(WE DON’T DO IN-MOLD COATING(IMC),we cam do coating after we get parts.)
Lastly, the mold is opened and the cured part is ejected.It is then often positioned onto a cooling jig in order to complete the cooling while maintaining its geometry to defined dimensions. Thereafter, subsequent finishing operations are usually performed: deburring, polishing,insert placement, bonding, painting, and so on