Compression molding is one of the primary processing methods for manufacturing plastic parts developed at the beginning of the plastics industry. It was generally utilized in the bakery kitchen industry for treat or cake forming before the presence of the plastic material. Generally, there are four types of compression molding. In this article, we will break down these common techniques along with the pros and cons of compression molding.
Although similar to thermoplastics, compression molding is more commonly used to manufacture thermoset plastic parts. The crude materials for pressure forming are usually in granules, clay-like masses, or preforms. They are first positioned in an open, warmed shape cavity. The shape is then shut, and a critical factor is applied to drive the material to fill the hole. Water-driven rams are frequently used to produce adequate power during the trim interaction. The warmth and critical factor are kept up until the plastic material is fixed. Then the molding compound is placed in an open, heated mold cavity. The mold is closed, and then pressure is applied to force the material to fill the entire mold cavity. Excess material is carried away by overflow grooves. The heat and pressure are maintained until the plastic material cures.
A variety of molding processes form the plastic into the desired shape, depending on the intended use of the plastic. Custom plastic parts assembly depends on various sorts of trim in a variety of sizes. Plastic is an engineered material that is delicate or semi-fluid when warmed. The soft plastic is set in molds, and afterward, the plastic is cooled or set. In the wake of the setting, the plastic is in the ideal shape, and whatever kind of embellishment was utilized to make it is taken out. Thermoplastics can be melted and reformatted if necessary, although thermoset plastics cannot be reheated.
Four Types of Compression Molding
1. Flash Type
This kind of shape is generally utilized in light of the fact that it is not difficult to produce and keeps the thickness and density of the part inside short proximity. As the form shuts, the overabundance material slimes off the ground, making a flimsy crest.
This feather hardens first, preventing mold charge from escaping. Flash-type molds can be loaded according to volume as excess material is allowed to flow out. The material lost through flashing is higher than other types of compression molds, but the original mold cost is relatively low.
2. Positive Type
A positive type of mold is a deep cavity and a plunger that compresses the compound at the bottom of the mold. Since there is very little material escape, it is essential to weigh the charge correctly if the portion size is to be controlled. This type of mold is used for high-impact materials and parts requiring deep draw.
3. Landed Positive Type
This type of mold is similar to positive mold, except that the ground is incorporated into the plastic design to prevent the plunger’s travel at a predetermined point. The density may vary depending on the charge. In this process, more loading space is provided, which makes the processing of heavy material possible.
4. Semi-positive Mold
It is a combination of flash type and landed mold. In addition to the flash ridge, the ground is incorporated to restrict the plunger’s travel, while some of the pressure is taken up by the land, with a lot of pressure being put on the part being molded.
The amount of clearance between the flash ridge controls the thickness of the flash and the density of the molded part to a great extent.
Oil and air-hardening tool steel is used for phenolic, urea, and melamine materials, and cast steel is used for polyester materials requiring low pressure. The flash parting lines on the die of these materials are usually flame hardened, and the cavities are hard chrome plated.
Advantages
Low-cost tooling
Given that the process doesn’t include an infusion or move cycle, tooling has fewer foundation prerequisites than tools intended for other embellishment strategies. Little else is required in the method of extra highlights, other than the unique qualities of the cavity that will deliver the shaped parts, which clearly need to imitate the detail required for the item. Tools can be made of aluminum or low-cost grades of steel which can reduce costs, although any device must be able to withstand the required molding pressures.
Disadvantages
Not suitable for complex molds
While complex parts can be made utilizing these types of compression molding, depending upon the material required and the plan of the item, it is, for the most part, more qualified for creating more significant, less complex articles. This is on the grounds that the restricted progression of material inside the cavity frequently makes it hard to dispense with voids, air traps, and weave lines when attempting to create more unpredictable parts. Due to its limitation for creating complex shapes, it is important to plan, design, then produce a plastic prototype to determine whether compression molding is suitable for the product.
