What is the difference between injection molding, blow molding, and extrusion molding

What is the difference between injection molding, blow molding, and extrusion molding
Injection molding, blow molding, and extrusion molding are the three major methods of product molding. Most of the common mass-produced plastic products are mostly produced by these three plastic molding methods. However, for companies that are exposed to plastic molding for the first time, they often confuse these three methods. Molding methods, we often encounter customers who don't know whether their products are suitable for injection molding, blow  molding or extrusion molding.  Which the technical method is the most time-saving and cost-effective? Today's article will help you understand what injection molding, blow molding and extrusion molding are. What is the difference between these three molding methods? What is it suitable for? Let's take a look.

What are the product molding methods?

Injection Molding

Injection molding is to melt granular raw materials in the barrel of the injection molding machine into a state of flowing liquid raw materials. Under the action of the screw and the machine, the flowing raw materials are injected into the mold at a certain speed. After a period of cooling, the mold is opened and then get the finished product. In the process, the raw materials will pass through various parts of the machine, so the mold, structure and pressure setting of the injection molding machine have a great relationship with the quality of the injection molding. The advantage of the injection molding machine is that in addition to making plastic products, it can also make ceramics, metal and silicone. The machine is set up by a professional injection machine manufacturer from the very beginning, and products with good quality can be produced stably.
〈Extended reading: 5 keys to the stability of injection molding products

Blow molding

Blow molding is also called hallow molding. The manufacturing method is to melt the plastic into a fluid state at the beginning, and then make the plastic into a small plastic blank in the middle, then put it in the mold, and put the plastic blank in the mold, so that it can be molded close to the mold, and the finished product can be obtained after cooling. The earliest blow injection was used to make glass bottles. Now in addition to glass bottles, plastic bottle makers can also pass through the blow molding machine. It is the most commonly used injection method for hollow plastic workpieces. The advantages are low production costs and stable product quality. The disadvantage is that the products can only be limited to blow products.

Extrusion molding

Extrusion molding is to melt the raw material particles into a fluid state followed by mixing with additives, and then squeeze it into the die hole to form a continuous shape tube. After the liquid is cooled, it can be molded, and the product can be directly segmented, packaged, and extruded. The shape of the steel mold through which the plastic passes will determine the cut surface shape of the produced tube. For example, if the mold hole shape is a straight shape, then the extrusion molding will be a flat tube; if the mold hole shape is round, The extrusion molding will be a long cylindrical body. The steps of extrusion molding are very similar to injection molding. The advantage is that the cost is lower than that of injection molding, and the pressure accuracy standard is relatively low. The disadvantage is that the product is limited to continuous shapes. 

Introduction of 3 molding methods ╴Mold requirements, costs, and uses

After introducing injection molding, blow molding and extrusion molding, we also summarized some of their respective requirements for molds, the cost of making each product, and which types of products are suitable for three molding methods. Let us continue to read!

Injection molding machine

If you want to use an injection molding machine to make products stably, the mold is very important. It is related to the stability of the finished product. Without a good mold and without first trying mold, a large amount of scrap products may be ocurred. Therefore, in these 3 moldings, , the cost of the injection mold is the most expensive. Because of the higher mold cost, it is the priority consideration when companies develop new products. The most recommended molding machine is injection, blow-out, and extrusion. The most versatile molding method in the world, from large auto parts to bottle caps, even ceramics, metal products and other materials, are all within the range that injection molding machines can produce. If you are not sure whether your products are suitable for production with injection molding machines, welcome to contact us any time.
〈Extended reading: What are injection molding machines? What are the types?

Blow molding machine

The mold used in blow molding has a low relation to the scrap of finished product, because the mold only accounts for about half of the key factors for the stability of the finished product, and the other half is set by other setting, such as the unevenness of the finished shell after blowing out, resulting in smallness. These are not problems that can be solved by mold improvement. The mold cost of the blow molding machine is not high. If your product is a plastic bottle, such as PET bottles, flower pots and other products, it is very recommended to choose a blow molding machine.

Extrusion molding machine

Extrusion molding molds (generally called die heads) need to have a certain understanding of the properties of plastics when they are made, because plastics often expand when they are extruded from the mold holes, and the coefficient of expansion will change with environmental factors, which is difficult to predict. Therefore, the mold hole needs to be professionally designed. For example, when you want to make a square tube, the mold hole must use the concave design to improve the plastic expansion characteristics. The cost of the extrusion molding die is low. If your product is long and has continuous shapes, such as plastic water pipes, wires, straws, etc. It is recommended that you choose an extrusion molding machine.


Whether it is injection molding, blow molding or extrusion molding, they have their own advantages, disadvantages and also different suitable products. If your company has a few products and specializes in hollow products or continuous-shaped products, it is recommended that you first inquire about the blow molding machine and extrusion molding machine.  You can provide us with your products and needs to evaluate whether these two models are suitable for production; if it is a company that develops more diverse products, then the injection molding machine is a product that can control the quality of the product and can also reply the most need of production. It is recommended that you find a professional injection molding machine manufacturer to make an inquiry. We are a professional injection molding machine expert who has been operating for many years. If you need more information, please feel free to contact us any time.
〈Extended reading: How to choose an injection machine? 8 key points let you choose the right injection molding machine!
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