What is Plastic Injection Molding?
Injection molding is a molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity giving the article the desired shape. Injection molding is a manufacturing technique for making parts from plastic material. Molten plastic is injected at high pressure into a mold, which is the inverse of the desired shape. The mold is made by a mold maker from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection molding is very widely used for manufacturing a maxnext GmbH Nürnberg variety of parts, from the smallest component to entire body panels of cars.
The process of plastic injection molding
An injection molding machine consists of three basic parts, the mold plus the clamping and injection units. The clamping unit is what holds the mold under pressure during the injection and cooling. Basically, it holds the two halves of the injection mold together.
During the injection phase, plastic material, usually in the form of pellets, are loaded into a hopper on top of the injection unit. The pellets feed into the cylinder where they are heated until they reach molten form (think of how a hot glue gun works here). Within the heating cylinder there is a motorized screw that mixes the molten pellets and forces them to end of the cylinder. Once enough material has accumulated in front of the screw, the injection process begins. The molten plastic is inserted into the mold through a sprue, while the screw controls the pressure and speed.
The dwelling phase consists of a pause in the injection process. The molten plastic has been injected into the mold and the pressure is applied to make sure all of the mold cavities are filled.
Then the plastic is allowed to cool to its solid form within the mold. The clamping unit is then opened, which separates the two halves of the mold. An ejecting rod and plate eject the finished piece from the mold.
A machine used to extrude materials is very similar to the injection-molding machine explained above. A motor turns a thread, which feeds granules of plastic through a heater. The granules melt into a liquid, which is forced through a die, forming a long ‘tube like’ shape. The extrusion is then cooled and forms a solid shape. The shape of the die determines the shape of the tube.
Advantages of Injection Molding
- High tolerances are repeatable
- Wide range of materials can be used
- Low labor costs
- Minimal scrap losses
- Little need to finish parts after molding
Disadvantages of Injection Molding
- Expensive equipment investment
- Running costs may be high
- Parts must be designed with specific molding consideration.
Injection molding is a relatively new way to manufacture parts. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods. Injection molding is often used in mass-production and prototyping. It produces such small products as bottle tops, sink plugs, children’s toys, containers, model kits, disposable razors and parts of cameras. The process can even mould such large items as dingy hulls and kit car body shell parts.
Metal Injection Molding
What is Metal Injection Molding?
Metal injection molding is a powder metallurgy process used for manufacturing metal parts. Although metal injection molding uses powder metal, it is nothing like conventional powder metal processing. The metal powders used in metal injection molding are 10-100 times smaller than in powder metal processes. Also, the end product of metal injection molding is much higher in density. Metal injection molding offers the same benefits and features as plastic and rubber molding, but produces a much stronger end product. Applications for metal injection molding parts include surgical tools, automotive locks and actuators, firearm components, computer hard disk drives and electrical connectors.
Process of Metal Injection Molding
Metal injection molding is a fast growing manufacturing method that bridges the gap between the technology up gradation and costs involved. The metal injection molding process involves five steps, mixing, injection molding, de binding, sintering, and part finishing.
In the mixing step, metallic powders, selected for their strengths and inherent abilities such as impact strength, high and low temperature characteristics, wear resistance characteristics, machine ability, and hardness, are mixed, often with a binding agent. By mixing powders, the goal is to create a composite with the strengths and benefits of all the incorporated metals, while offsetting the independent weaknesses.
Once the powders are mixed, a “feedstock” is produced. This feedstock is injected into molds in the same way that plastic or rubber injection molding is performed. The part that emerges from the injection molding stage is referred to as a “green” part.
In the de binding stage of metal injection molding, the green part is immersed in a water bath to remove the binder, which has entered into the part matrix. In cross-linking, the de bound green part is exposed to ultraviolet light which thermo sets the binding agents used with the metal powders.
Once the de binding stage has been completed, the part is placed into a furnace and heated to over 2000 degree Fahrenheit. This process, called sintering, fuses the metal parts into a solid shape. Finally, the sintered piece is sent to a finished stage where burrs and surface imperfections are removed and the finished part can be shipped.
Advantages of Metal Injection Molding
- High Shape Complexity
- Low Cost
- Tight Tolerances
- High Density
- High Performance
Uses of Metal Injection Molding
The technology excels at applications that require shape complexity and high final properties, such as high strength and density, excellent magnetic permeability, high temperature strength, corrosion resistance, and thermal conductivity in applications that cannot be fulfilled by plastics or light metal alloys. Metal injection molding is thus maxnext GmbH Nürnberg best for some of the following uses viz. making of microelectronic packaging, automotive sensors and actuators, hand tools and hardware, computer heat dissipation devices, oil well drilling tools, aerospace and engine fuel components.
To Sum Up
Metal injection molding can provide a substantial cost savings over conventional metal machining options. Metal injection molding parts have high densities and mechanical properties approaching those of forged or machined components. Metal injection molding process can produce more complex parts than either investment casting or traditional press and sinter techniques.