Advantages and disadvantages of injection molding

R-C (1)

1.The advantages of injection molding process

(1) the use of injection mould for the parison wall thickness distribution for precise control, make the container wall thickness is relatively uniform, avoids the general blow molding products of the corner part thinned phenomenon, products can be controlled in a heavy + 0.1 g, the precision of the screw thread can be controlled within the scope of the soil is 100 microns, the mouth size precision, thin neck high precision molding, products;

(2) the products do not need to be processed E times, no seams, saving the finishing hours of products;

(3)The billet made by injection can all enter the blow molding mold, and there is no waste in the processing process, which reduces the waste of molding materials;

(4) can get smooth surface products, no scratch, surface text and design is clear;

(5) can be economically small batch production;

(6) wide range of application to plastic varieties;

(7) high degree of automation, can be multi-mode production, high production efficiency.

2.The disadvantages of injection molding process

  1. The shrink

Shrinkage generally occurs in the bone position, screw column and other glue position after the comparison of the area.

1) Structural design: uneven design of the workpiece wall thickness or too thick of the workpiece

The glue thickness is as uniform as possible, the uneven position should be smooth transition, and pay attention to the glue.

2) Mold design: the runner is too thin or the mold temperature is too high;

3) Injection design: insufficient pressure holding time, injection pressure is too small;

  1. Insufficient mold filling

1) Mold temperature, material temperature or injection pressure and speed are too low

2) Uneven plasticizing of raw materials

3) Poor exhaust

4) Insufficient liquidity of raw materials

5) the piece is too thin or the gate size is too small

  1. Crisp

1) The drying conditions are not suitable, and too much recycled material is used

2) The injection molding temperature setting is unreasonable

3) The gate and runner system are not properly designed

4) Weld mark strength is insufficient

Burned in 4.

1) The drying conditions are not suitable, and too much recycled material is used

2) High melt temperature leads to material degradation

3) The screw speed is too fast

4) Poor exhaust system

  1. Fly-edge or drape

Often occurs in parting surface, line clamp, inclined top or insert position.

1) Insufficient clamping force;

2) There is wear and tear of the mold, insufficient hardness of the mold, and poor matching of the parting surface;

3) Unreasonable forming conditions (temperature is too high, pressure)

4) Unreasonable exhaust system design;

5) the glue has doping, so that the fluidity of the glue increases or the viscosity decreases;

  1. Plastic deformation

Internal stress is generated by high pressure during injection molding, and bending or warping occurs after demoulding. The most prone to problems are tablet-style products.

1) Structure design: the product is too thin to cause insufficient strength or too flat;

In structural design, the bone position and glue thickness should be appropriately increased to avoid large area plate products;

2) Mold design: the water outlet setting is unreasonable; The ejection mechanism force is too large;

The deformation of rubber parts should be considered in the design of nozzle.

3) Injection design: long holding time; Large injection pressure;

  1. More or less glue

Glue position deviation, mainly occurs in the thimble position. Multiple glue to consider whether affect the appearance or assembly, there is no need to not change.

1) Mold design more or less;

2) insufficient thimble length;

~ (If the thimble is too long, the top white will occur, and the injection pressure is too large, the ejection speed or the injection speed is too fast.)

3) Insufficient injection pressure or poor exhaust in the mold cavity

  1. Strain

The product is caused by friction mold in the process of demoulding.

1) Structure design: the inclination of drawing die is insufficient;

2) Mold design: the surface accuracy is not enough, and the error is large;

3) Injection design: excessive use of release agent (coating for separating products and molds);

  1. Clamp water line or weld mark

1) Selection of raw materials: slow flow speed of raw materials and insufficient drying;

2) Mold design: the cold well is too small; The nozzle design is not reasonable; Poor exhaust;

In terms of structure design, bone position can be added in the area where weld marks are easy to be produced.

3) Injection design: mold temperature is too low; Material temperature is too low; Small injection pressure;

  1. Water mouth cut mark

Less common are the following:

  1. Peel in layers

The ability to peel off the surface of a piece layer by layer

1) Mix with other incompatible polymers

2) Too much release agent is used during molding

3) Resin temperature is not consistent

4) Too much water

  1. The flow mark

Refers to the wavy forming defect on the product surface. When the viscosity of melt is too large and the stagnation form of mold filling occurs, the front material will quickly condense and contract as soon as it touches the surface of the cavity, and the later molten material will expand and contract and the cold material will continue to advance alternately so that the molten material will form surface water grain in the advance.

1) Mold temperature or material temperature is too low

2) The injection speed and pressure are too low

3) The runner and gate size is too small

4) The melt fluidity of raw materials is poor

  1. The silver lines

The emission of moisture, air or carbide along the flow direction on the surface of the workpiece

1) The moisture content in the raw material is too high

2) The raw material is filled with air

3) Polymer degradation at high temperature