Blow Molding Vs Injection Molding – What’s The Difference Between Blow Molding & Injection Molding


Are you creating a product that requires molding plastic parts? There are several processes to choose from. Injection molding and blow molding are the two most popular ways to produce high quality, cost-effective plastic parts and products, but both are used for different applications and the processing conditions and processing raw material conditions are also different. Do you know the difference between them? Which one is better? Here we detail everything about injection molding Vs blow molding.


What Is Blow Molding?

Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in the opposite open die while it is hot (or heated to softening state). After the mold is closed, compressed air is injected into the parison immediately to make the plastic parison inflate and cling to the inner wall of the mold. After cooling and demoulding, various hollow products are obtained.


Advantages of blow molding include: 

● The cost of blow molding mold is low, and the production cost of products is also low.

● In blow molding, the parison is formed through the machine head under low pressure and inflated under low pressure. Therefore, the residual stress of the product is small, and the performance of various strains such as tension, impact, bending and environment is high, so it has good service performance.

● The relative molecular weight of blow molding grade plastics is relatively high. Therefore, blow molded products have high impact toughness and high resistance to environmental stress cracking, and are suitable for producing containers or barrels for packaging or transporting detergents and chemical reagents.

● Because the blow mold is only composed of female die, the wall thickness of the product can be changed by simply adjusting the mould gap or extrusion conditions, which is beneficial to the products that can not accurately calculate the required wall thickness in advance.

● Blow molding can produce products with very small wall thickness.

● Blow molding can produce complex, irregular and integral products.


What Is Injection Molding?

Injection molding, a kind of molding method of industrial products. Rubber injection molding and plastic injection molding are usually used for products. Injection molding can also be divided into injection molding technology and die casting method. Injection molding machine is the main molding equipment that makes thermoplastic or thermosetting materials into various shapes of plastic products by plastic molding mold. Injection molding is realized by injection molding machine and mold.

Advantages of plastic injection molding include:

● Precise, cost-effective production of large volumes of small parts.

● Better material use efficiency with little scrap or waste.

● Detailed, highly engineered tooling with multi-cavity mold options.

● Flexibility in being able to change the type of material or color that is being used.


What’s The Difference Between Blow Molding & Injection Molding?

Product Difference

Plastic blow molding is the use of gas to form products, the need for injection processing is generally used to do thicker products. Blow molding is different, because the product is thinner and more transparent, and a slight defect is obvious. Therefore, the requirements are higher, and blow molding has some requirements on the toughness and tensile properties of raw materials. The product of processing injection mold is thicker, and the requirements for raw materials are relatively low.

Structure Difference

Blow molding can only be used for products with simple structure, such as seats that can not be adjusted in any part, and detachable seats are basically blow molded.

The injection molding process can be used for the production of safety seat with complex structure, such as adjustable head support and wings on both sides, adjustable sitting and lying, folding and other functions.

Texture Difference

Blow molding products are hollow, and the color is mostly black, because black can cover up the defects such as burr and surface roughness caused by blow molding process. Because the blow molding mouth is hollow, the weight is light.

The surface of the injection molded products is smooth, the texture is better than that of blow molded products, and the flexibility and compression resistance of injection molded products are better than that of blow molding products. Of course, the cost is also high, and the price of injection molded products is higher than that of blow molded products.

Process Difference

The blow molding process begins by heating raw plastics materials to temperatures of 350-420 degrees F.  The material is then extruded from the head of the machine as a hollow tube aka parison.  The mold closes around the parison and roughly 80psi is blown into the parison causing it to balloon and take the shape of the mold.  The mold is then cooled, allowing the plastic to “set.”  Once the set time has been reached, the mold opens, and produces the product to the operation.  The part then goes through a degating process which allows inside of the part to be accessible.

The process of plastic injection mold is to melt the plastic material, and then inject it into the membrane cavity. Once the molten plastic enters the mold, it is cooled and molded into the desired shape according to the mold cavity. The resulting shape is often the final product, and no other processing is required before installation or use as the final product. In addition, in the process of injection molding, many details, such as bulge, rib and thread, can be molded in one-step operation of injection molding.


Which One To Choose, Blow Molding Or Injection Molding?

To find out which process is right for you, contact EX MOULD, one of the world’s largest industrial injection molded parts manufacturers and a leading provider of advanced injection molding technology. EX MOULD is known for their commitment to quality and customer satisfaction.