The Basic Facts Of Plastic Injection Molding Process

Published: 23rd February 2011
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Plastic injection molding process by definition may be the progression of injecting plastic-type right into a mold (or mould in European circles), cooling the plastic-type, ejecting it in the mold, and packing the completed item for sale on the consumer. This sounds easy and in it's fundamental form it is, however the procedure required with generating all this take place is in fact very complex.

A range of components are produced using plastic injection molding process which varies in the smallest component to an whole body component of a vehicle.

Plastic-type components applied for the plastic injection molding process are thermoplastics or thermosetting plastics. Each the thermoplastic and thermosetting plastic molding are polymers. Some broadly utilised thermoplastics are nylon, polyethylene, and polystyrene while bakelite, vulcanized rubber are the extensively utilized thermosetting plastic. At times a polymer with a quite excessive elasticity is also utilised. This type of polymer is known as elastomer

The Basic Steps of Plastic Injection Molding Process can be Described in Six Steps.
These include Heating, Plasticizing, Injecting, Packing , Cooling, and Ejecting are:
 Heating the plastic material resin for the required variety of the item getting used.
 Developing the shot size by way of use of a reciprocating screw which conveys the melted plastic-type for the front in the screw.
 Injecting the plastic-type to the mold beneath stress to fill the cavity of the mold.
 Packing the plastic-type to produce a total portion within the mold.
 Cooling the plastic in the mold by means of the usage of cooling channels most commonly with water.
 Ejecting the cooled component in the mold.
 Repeating the process more than and more than once more.

Troubleshooting on Plastic Injection Molding Process and How to Improve
 Flashing
Flashing is the excess material at the ends of the part or on the side of the parting line
Flashing on plastic injection molding process caused by the injection speed is too high or excessive volume of material so that material into the gap cavity, clamping force or power the press mold is less so material into the gap parting line, or mold condition defects.
Improve: decrease injection speed, review the position of a stroke and a holding position, raise the pressure mold clamping, check whether the mold is a problem.

 Silver-Strike
Silver-Strike is sign white / silver which appears in the direction of material flow injection
Silver-Strike on plastic injection molding process caused by resin material moisture is still high, the moisture content is transformed into a gas that is mixed with molten materials within the cylinder
Improve: needed a good drying material with time and temperature sufficient to remove moisture.

 Wrap
Wrap is product form bent / curved
Wrap on plastic injection molding process caused by common lack of pressure distribution of the product or differences in depreciation.
Improve: increase cooling time or decrease injection pressure, check for mold cooling system or correct the mold.

 Bubble-Blowhole
Bubble-Blowhole is hollow or air bubbles that occur in the product, but we can not see it unless the product is transparent or air bubbles that occur on the surface of the product.
Bubble-Blowhole on plastic injection molding process caused by the gas mixed with molten materials within the cylinder.
Improve: make sure materials have passed the drying process properly, raise the screw back pressure during the plasticizing process to force the gas out of the cylinder, improving gas ventilation systems in the mold so the gas is not trapped in the product, decrease injection speed to give time for the gas out through the ventilation systems.

 Whitening
Whitening is white marks / cracks / under cut on the product side of the tangent.
Whitening on plastic injection molding process caused by the different pressure of the inequality area of a product, mold design that makes uneven cooling products between one side with the other side, or the product over pack in some places as the material cools
Improve: polish on the mold cavity is happening whitening product, lower injection pressure to prevent over-pack in the product

 Burnmark
Burnmark is scorch mark on a product in the last section filled with material.
Burnmark on plastic injection molding process caused by the burning gas because the gas trapped, injection speed is too high, or a gas ventilation system in the mold is blocked
Improve: add scerw back pressure to reduce the gas content in liquid material, lower injection velocity and widen or create a gas ventilation system

 Short shoot
Short shoot is some of the product is lost or not filled materials during the process of injection
Short shoot on plastic injection molding process caused by the injection speed is too low so that the material to harden before they reach the last section filled with material, mold temperature is too low so blocking the flow of material, the volume of material is less or unstable.
Improve: increase injection speed and mold temperature, check the check-ring is worn or is normal to prevent backflow material from the front to the back, review the position of a stroke and a holding position.

 Sink-mark
Sink-mark is concave or hole on the surface of a product
Sink-mark on plastic injection molding process caused by the differences in viscosity between the material with normal temperature and materials that require a longer cooling time and gathered in one side.
Improve: in principle, very difficult to find solutions to this mold design, add a holding pressure or holding pressure time to maintain stable material pressure within the mold, extend the cooling time to reduce the depreciation rate, change the form of mold to reduce the level of viscosity differences (for example, by adding dummy-pin.)

 Flow Mark
Flow Mark is signs or wave lines on the surface of product.
Flow Mark on plastic injection molding process caused by too low injection speed, mold temperature is too low, or mold gate hole is blocked so that the material can not flow normally.
Improve, increase injection speed, mold temperature and check for mold gate holes

 Jetting line
Jetting line is line burst on the surface of the product, starting from the gate point
Jetting line on plastic injection molding process caused by the mold temperature is too low and the injection speed is too high that will occur in bursts mark on the surface of the product
Improve: raise the mold temperature and injection speed down.


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