injection molding?
The most common plastic product process is injection molding, which I believe we all know in structural design. From buttons to bumpers are made by injection molding. But each process has its limitations, and injection molding can not be invincible to eat all the plastic products in the world.
Most people know that the mouse shell is injection molded, and the drinking water pipe at home is extruded. But how are cables, slides in kindergartens, plastic bathtubs, wagons in front of shopping malls, dolls with unique shapes, plastic seats for buses, plastic handles for tool pliers, etc?
Please read on patiently, this article will be revealed slowly.
injection molding
Injection molding can be divided into horizontal injection molding, vertical injection molding, two-color injection molding, low-pressure injection molding, high-speed injection molding, etc
a) Common horizontal injection molding
b) The vertical injection molding machine mold is open and close in the up and down direction, the mold face up, the inserts are easy to be placed, and the inserts are easy to be formed. Usually used for connector, wire and other products processing.
c) Two color forming machine and two color forming die are needed for two color forming
d) Low pressure injection molding is a kind of molding method which can inject the packaging material into the mold with a very low injection pressure (2-20 bar) and cure it quickly (5-50 seconds). It is mainly used for packaging and protection of precision and sensitive electronic components, including printed circuit board (PCB), automotive electronic products, mobile phone batteries, wire harness, waterproof connector, antenna, etc.
e) High speed injection molding. Ordinary injection molding machines are all pure hydraulic injection molding machines, while the relative running speed of the hydraulic injection molding machine driven by hydraulic oil is relatively slow, while the high-speed injection molding machine uses servo motor to realize mold opening and closing, ejection, material injection and storage functions, etc., with fast injection speed, more precise position control, and better production efficiency.
Compared with ordinary injection molding, high-speed injection molding is more efficient and environmentally friendly. High speed injection molding can form parts with thinner wall thickness, which can greatly improve the shrinkage of the outer wall of the product at the corresponding bone position.
Blow molding (extrusion blowing, injection blowing, injection pull blowing)
Fang Gong thinks that blow molding is a magical existence for some large-scale products. Why do you say that? Let's see the following figure.
If such a large product is made by injection molding, it is inconceivable.
Many things in life are made by blow molding, such as small mineral water bottles, shampoo bottles, medicine bottles, large traffic barriers, ice cream cones, etc. Below are some applications of blow molding products
Most thermoplastics can be used for blow molding. The common materials are PE, PP, pet and PVC, among which HDPE is the most widely used and polycarbonate (PC) also has some applications. PP can be used to make vessels with high temperature of 80-100 ℃, but its physical properties will be poor at low temperature. Pet has outstanding transparency and air tightness, and is widely used in blow molded beverage bottles and drug packaging containers.
Blow molding can be divided into extrusion blowing, injection blowing and injection pull blowing according to different processes.
a) Extrusion blow, that is, extrusion blow molding method. This method is mainly used to produce plastic buckets and bottles. Most of the shampoo bottles we use are made by this process.
(a) Extrusion parison (b) closed mold blowing plastics (c) cooling (d) open mold taking out products
1 - extruder 2 - extrusion die mouth 3 - extrusion billet 4 - blow molding die 5 - air nozzle
(1) The molten plastics are extruded into tubular billets;
(2) The closed die clamps the blank, inserts the air nozzle into one end of the blank, and the other end of the blank is closed and cut off;
(3) Blow the parison with compressed air to form the product;
(4) Cooling blow molding products;
(5) Open the mold to take out the product and cut off the tail;
b) Note - blow molding. First, the plastic is made into a bottom parison by injection molding, and then the hot parison is put into a blow molding mold to blow and expand into a hollow product
Advantages: the product strength is relatively high and the precision is high. There is no joint on the container, no need to repair. The transparency and surface finish of blow molded parts are good. It is mainly used in hard plastic containers and wide mouth containers.
Disadvantages: the equipment cost of the machine is very high, and the energy consumption is large. Generally, only containers with small volume (below 500ml) are formed, and containers with complex shape cannot be formed, and it is difficult to form elliptical products.
c) Note - pull - blow, that is, injection stretch blow molding process. At present, the application of this technology is more extensive than injection blow. This blow molding method is actually injection blow molding, but with the increase of axial tension, the blow molding is easier and the energy consumption is reduced. The volume of the processed products can be larger by injection drawing blowing than by injection blowing. The volume of the blown container is 0.2 ~ 20L. The working process is as follows:
① First injection mold, the principle is the same as ordinary injection;
② Then the billet is transferred to the heating and temperature regulating process to make the billet soft;
③ Turn to the drawing blowing station and close the mold. At the same time, air blowing makes the parison close to the die wall and cool down;
④ Transfer to the demoulding station to pick up the parts.
Note drawing blowing process:
Injection molding parison → heating parison → closing, drawing and blowing → cooling and taking parts
Summary: whether injection blow molding or injection drawing blow molding or extrusion drawing blow molding, it is divided into one-time forming and two-time forming processes. The one-time forming process is highly automated, and the clamping and transposition system of parison requires high precision and high equipment cost. In general, most manufacturers use the two-step molding method, that is, molding the parison first through injection molding or extrusion, and then putting the parison into another machine (injection blower or injection drawing blower) to blow out the finished product
