Injection molding is a kind of molding process for mass production of products with complex shapes by injecting plastic materials molten by heat into an injection mold, and then solidifying them using some type of coolant. The method is especially suitable for manufacturing products in large volumes where the same part is being produced tons and tons of times in succession.
Injection molding machine consists of two parts: the fix mold and the moving mold. The fix mold is installed on the stationary plate of the injection molding machine, whereas the moving mold is mounted on the movable plate of the injection molding machine. During the injection molding process, both the fixed and moving molds are closed to form the cavity and prepare the pouring system. The fixed mold and moving mold are separated to take the products out when the mold is opened.
The structure of mold is subjected to differ based on the properties of materials, the type of injection molding machine, and the attributes of final products, but the fundamental structure is the same. The basic structure can be generally broken into four parts: the die frame, die core, auxiliary system, auxiliary parts, dead angle treatment mechanism and other components.
● Die Frame: This is a standard die that can easily be obtained from pretty much any die frame manufacturer. It is not a custom die which saves a lot of time from needing to design the mold. A die frame in plastic injection molding is often referred to as the standard plastic mold frame, which forms the most fundamental frame part of the plastic mold.
● Die Core: The kernel is the most important and fundamental part of the mold. The kernel in which parts of the final product are formed is where most of the processing time lies. However, injection mold with simpler structure may not have the mold kernel parts since the products can be created on the template directly.
● Auxiliary Parts: This includes components like the locating ring, injector bushing, thimble pin, grasping pin, ejector guide sleeve, garbage pin, support column and other supports parts. Most of these are easily attainable from the relative manufacturers, but some may require customization based on the mold requirement.
● Auxiliary Systems: Auxiliary system of an injection molding machine is made up for a casting system, ejection system, cooling system and exhaust system. It may also come with a heating system sometimes if the materials are required to be heated at a very high temperature.
● Dead Angle Treatment Mechanism: An injection molding machine will have one or multiple structures to cope with dead angles if the product has a dead angle. This may encompass the sliding block, inclined top, hydraulic cylinder or other parts that are used to deal with dead angles.
As aforementioned, the biggest advantage of the injection molding process is for mass production of parts. Aside from the upfront cost of implementing the injection molding process, the manufacturing cost is actually quite low. Other benefits include:
● Low scrap rate: Injection molding machines create relatively lower scrap rate compared to CNC machines which remove a substantial amount of an original sheet or block of material. On a note, additive manufacturing processes like 3D printing may have even lower scrap rates. It is also worth noting that the waste plastic from injection molding processes normally comes from the sprue, runners, gate locations and any overflow material that gets out of the part cavity itself consistently (i.e., the flash condition).
● Superior repeatability: Another key advantage of injection molding you can produce successively identical parts with the same, exact parameters. This is a very useful characteristic when you need to ascertain maximum consistency as well as the party reliability for the products of your company.
Some known disadvantages of injection molding machines include the high tooling cost and long lead times. Prior to actually being able to produce parts, you are typically required to design and prototype a part through 3D printing or CNC, in most cases. Then you are also required to design and prototype a mold tool to make sure the machine is capable of mass production based on those prototypes. And all of these can add to the cost and time incurred. It is however rare that you will need to prototype injection molding tools.
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