What Is Injection Molding? 5 Unknown Facts
What is injection molding? Injection molding is a process in which thin-walled parts are made of non-ferrous metals, plastics, and steel using automated equipment. This technology characterizes by high performance. When creating parts, a liquid melt obtained from these materials is fed at high speed into a special mold, after which casting of a given configuration obtains under pressure.
Features of metal injection molding technology
This device is casting equipment, the design of which provides for movable and fixed parts. The first move along with the guide cylinders and the second is mounted on a stationary plate.
What is injection molding? Before the start of the technological process, the movable part of the mold was tightly fixed to the fixed parts with the help of a hydraulic cylinder. Then, to prevent the movement of these parts, the latter fastens with special locks.
After pouring and solidifying the molten material, the movable part of the device shifts to the side, and the workpiece obtained under high pressure removes from the equipment using mechanical pushers.
This composition is used to eliminate the negative impact of high temperatures on the steel parts of the equipment.
What is injection molding?
The main unit of this equipment is the chamber in which the material presses. This structural element is of two types: cold and hot. Structurally, the first chamber presents in the form of a horizontally laid cylinder, inside of which there is a funnel piston used for pouring the molten material.
Moreover, the process of manufacturing parts in such equipment is as follows: after filling the installation with metal, a piston starts, which, moving inside the cylinder, pumps the melt into the mold. After filling the latter, the pressure inside the chamber increases. This happens by increasing the force on the piston, which leads to the crystallization of the metal.
The function of Hot Chambers In Injection molding
What is injection molding? The hot chamber of the molds presents in the form of a bath located in a cast-iron crucible, which constantly heats during the creation of blanks. In such installations, a piston is also used, which pushes the melt out of the crucible while moving.
Further, the metal rises through a special channel with a heated mouthpiece (which prevents the solidification of the material), through which it enters the mold. At the end of the process, the remains of the melt return to the bath.
Moreover, hot chamber molds are used to create blanks from zinc and magnesium alloys.
What is injection molding? Material heating temperature
The temperature to which the material heats and is selected considers two parameters. The grade of the alloy and the geometric parameters of the part create. Failure to comply with this rule leads to serious consequences.
Moreover, due to overheating of the material during mold pouring, splashes fly out that block the ventilation holes, as a result of which gas removal disturbs, which leads to the appearance of pores in the workpiece after the latter has hardened.
Exceeding temperature increases the duration of metal crystallization
Exceeding the permissible temperature leads to an increase in the duration of metal crystallization, this is why it takes more time to complete the process.
What is injection molding? This leads to an increase in the load on the equipment, which increases the wear of the mold. In such conditions, the risks of welding metal to the inner walls increase. As a result, the probability of damage to the part during ejection increases.
Moreover, this technological process involves pressing at a minimum temperature. Non-ferrous metals heat 10-300 degrees above the point at which the alloy begins to solidify.
At the same time, if the technical task requires the manufacture of parts with a thin wall, the heating temperature increases. When creating castings of a simple configuration, the opposite approach uses. In such cases, the material heats to a temperature slightly above the melting point.
Manufacturing of high-strength parts
If high-strength parts are manufactured during this technological process, then the metal pours into the mold in a solid-liquid state. This approach achieves the following results:
- Eliminate the appearance of a shrinkage effect in the created workpiece;
- Reduce the negative impact of high temperature on equipment;
- Reduce the duration of the casting hardening process;
- Reduce the risks of welding metal to the inner walls.
Moreover, metal with hard phase inclusions is pressed exclusively in cold chamber machines. This explains by the fact that when manufacturing parts from this material in other equipment. What is injection molding? Then the risks of melt solidification in the supply channel increase.
In particular, during aluminum injection molding, the volume of solids should be 40-60%, providing that the molds are easily filled and the quality of the casting remains at a high level.
Molten material feed rate
The speed at which the piston compresses the molten material determines by taking into account the characteristics of the alloy and the geometry of the part to manufacture:
Detail of a complex geometric shape and with thin walls. When creating such a workpiece, the melt should be pressed at high speed. This requirement explains by the fact that the liquid material must have time to fill all the cavities before solidification begins.
Moreover, exceeding the permissible pressing speed leads to the fact that the supplied jet scatters into small drops, as a result of which air enters the melt. If the design provides for an insufficient number of channels intended for the removal of gases, or they clog, voids will remain in the cast billet.
In order to avoid such consequences, injection molding carries out in a vacuum in which the mold is placed.
The speed determines the quality of the casting
The speed at which the pressing carries out determines the quality of the castings and the life of the equipment. If the melt is fed too quickly, then because of this, the lubricant that the bath has been treated with is washed off. Because of this, the metal sticks to the inner walls, which, when pushed out, leads to damage to the workpiece.
If the speed is too slow, the quality of the part deteriorates. In this case, the metal begins to solidify before the pressure inside the equipment increases. A smaller parameter selects when creating blanks from steel and copper alloys. Molten tin and zinc fed at a faster rate.
Pressure on the melt during solidification
After filling the mold with metal, the pressure on the piston increases many times. The material experiences such an impact until it hardens. Through pressure:
- The density of the workpiece increases;
- Improved mechanical characteristics of the casting;
- The formation of shrinkage defects excludes;
- The quality of the casting improves;
- The risk of marriage reduces;
- The surface finish of the metal part increases.