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How To Choose The Suitable Plastic For Injection Molding

The injection molded mold injects the plastic material to be formed into a specific cavity.

After the mold cavity re-ejected, the product is formed after cooling. One of the most ideal methods for mass production of injection molding. Moreover, it can be mass-produced after the mold has been opened.

There are many types of products produced by injection molding, among which plastic casings, consumer electronics, automotive parts, household appliances and so on.

The period of injection molding is short, usually only 3-4 seconds. In other wards, a product can be formed in 7 seconds, which is the benefit of injection molding.

Basic Steps In Injection Molding

Step 1. The plastic resin comes in raw pellets. These are dried to the right moisture content, and then if necessary they can be blended with pigments or master batch colorants.

Step 2. The dried pellets are poured into the hopper of the molding machine. A reciprocating screw inside the barrel of the machine will transport these pellets towards the mold.

Step 3. Within the barrel, the pellets are mixed and heated until fully molten, forming the liquid resin.
Step 4. The heated mold closes automatically and resin, under great pressure, is injected through a gate and into the mold cavity.
Step 5. The mold is cooled to solidify the part inside.

Step 6. The mold opens and the part is ejected to begin a new cycle.

Injection Unit Assembly

Injection molding machines have many components, injection units, mold assemblies and clamping units to perform each stage of the process cycle.

Injection Mold Housing

Injection molding dies typically use a mold made of steel or aluminum as a custom tool. The mold has many components but can be divided into two halves. Each half is mounted inside the injection molding machine .The rear half can be slid so that the mold can be opened and closed along the parting line of the mold. The two main components of the mold are the mold core and the mold cavity. When the mold is closed, the space between the mold core and the mold cavity forms a part cavity that will be filled with molten plastic to form the desired part. Multi-cavity molds are sometimes used, where the two mold halves form several identical part cavities.

Materials For Injection Molding

There are many materials used in injection molding, including thermoplastic materials and thermosetting materials. The usual raw materials are raw granules that are melted into products after thermal processing. Here is a summary of some common materials:

Material

abbreviation

Material properties

application

Representative products

Acrylonitrile butadiene styrene

ABS

Robust, flexible, low mold shrinkage (tight tolerance),chemical resistance, plating ability, natural opacity, low cost / medium

Car (console, panel, trim, vent), box, instrument, housing, inhaler, toy

Acrylic

Polymethylmethacrylate

Rigidity,brittleness,scratch resistance, transparency, optical transparency, low/medium cost

Display stand, knob,lens, lampshade, panel,mirror, signage, shelf, tray

Polyphenylene sulfide

PPS

Extremely high strength, heat resistance, brown, very high cost

Bearings, covers,fuel system components, guides,switches and shrouds

Polypropylene

Polypropylene

Lightweight, heat resistant, highly chemical resistant, scratch resistant, natural waxy appearance, tough and rigid, low cost.

Car (bumper, lid, trim), bottle, lid, crates, handle, outer casing

Polypropylene

PP

Chemical,resistance,Elasticity and toughness,Fatigue resistance,Insulation,Transmittance

CNC machined sheet

Polyamide

Nylon

High strength,fatigue resistance,chemical resistance, low creep, low friction,almost opaque/white, medium/high cost

Bearings, bushings, gears, rollers, wheels

POM

POM

Highstiffness,low friction coefficient,hardness, highheat resistance,good electrical and dielectric properties, stability, more creep resistance, high gloss surface than nylon

applications include high-performance components such as gears and fasteners (screws, nuts, washers, gaskets, etc.)

Teflon

Teflon

Lowest friction coefficient

Reagents for chemicals and containers

Injection Cost Considerations

Before starting a new injection project, we need to konw the general costing of the injection molding process in detail. Injection molding costs are considered within these ranges, taking into account the complexity of the project, the design, and the choice of materials. Among them, we need to focus on the following:

Material costs

When considering an injection molding project, the first time is the choice of materials. Modern injection molding machines have used millions of injection molding materials.So the possibilities that can be offered is more.  The weight and nature of the material is the determining factor. In addition, it is necessary to understand the relationship between the volume, density and the like of the material in the cavity of the container.

Molding cost

The cost of mold opening is generally determined by the bottom of the mold and the cavity. Plastic injection molds are differentiated according to the processing unit. The larger the part, the larger the mold base and the larger the cavity.

Cost of production

Production costs here include time and work efficiency costs. Moreover, the clamping force tonnage controlled by the injection molding machine will affect the effect of injection molding. The larger the part, the greater the clamping force and the higher the production cost.

In summary, the factors that affect the cost of injection molding include:

Material costs

Cost of production

Processing cost

design

Product complexity

Number of parts

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