What is the difference between blow molding and injection molding?

What is the difference between blow molding and injection molding? 

Source: Looking for Plastics

Blow molded products are hollow; Injection molding has an injection port, so the molded product will have a small amount of unwanted parts, and it will be cut off by a process. However, if you look carefully, you can still find it. Injection molding is a method in which thermoplastic or thermosetting molding compound is first plasticized uniformly in a heating cylinder and then pushed into a mold cavity of a closed mold by a plunger or a moving screw. Injection molding is applicable to almost all thermoplastics. In recent years, injection molding has also been successfully used to mold some thermosetting plastics. Injection molding has a short molding period, and the quality of molded products can range from a few grams to tens of kilograms, and molded products with complex shapes, sizes and metal or nonmetal inserts can be molded at one time. Therefore, the method has strong adaptability and high production efficiency. Blow molding: a method of blowing a hot parison closed in a mold into a hollow product by means of gas pressure, or blowing a tube blank into a tube film without a mold. The method is mainly used for manufacturing various packaging containers and tubular films. All the hollow blow molding materials with melt index of 0.04~1.12 are relatively excellent, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin, among which polyethylene is much more widely used. Injection blow molding: plastic is first made into a bottomed parison by injection molding, and then the parison is moved into a blow mold and blown into a hollow product. Extrusion blow molding: plastic is first made into a bottomed parison by extrusion, and then the parison is moved into a blow mold to blow into a hollow product. Stretch Blow Molding: Stretch Blow Molding is a kind of blow molding with biaxial oriented stretching. Its method is to stretch the mold longitudinally first, and then inflate it with compressed air to achieve transverse stretching. Stretch blow molding can greatly improve the transparency, impact strength, surface hardness and rigidity of products, and is suitable for blow molding of polypropylene and polyethylene terephthalate. Blow film method: a method of forming thermoplastic films. The method comprises the following steps of: firstly extruding plastic into a tube by an extrusion method, then continuously expanding the plastic into a tubular film with a certain size by means of air blown into the tube, and folding and winding the tubular film into a double-layer flat film after cooling.