draft angle and wall thickness of injection molding

There is no certain criterion for the size of demoulding draft angle, and the most are determined by moldmakers experience and the deep draw of products. In addition, the molding method, wall thickness and plastic material should be also considered.

Generally , a certain amount of demoulding draft angle is required for any side of the molded product, so that the product can be smoothly ejected out of the mold. The draft angle is usually 0.5 ~ 1.

Rule of thumb,the following points need to be followed:

If the plastic part requires high dimensional accuracy and small shrinkage, a smaller draft angle should be selected , such as 0.5.

PICplastic materialcavity(a1)core (a2)
PA20~40′25~40′
PA(GF)20~50′20~40′
PE25~45′20~45′
POM35~1°30′30~1°
Polyetherchloride25~45′20~45′
PC35~1°30~50′
HIPS35~1°30′30~1°
PMMA35~1°30′30~1°
ABS40~1°20′30~1°

For deep draw and larger injection molded part, mold maker need take the smaller draft angle according to actual demand.

If the shrinkage is large, a larger draft angle should be selected.

When the plastic part wall thickness is thick, the molding shrinkage will increase, and the demoulding draft angle should be larger.

The demoulding draft angle of transparent parts should be increased to avoid scratching. Generally, the demoulding draft angle of PS materials should be no less than 2.5 ~ 3, and that of ABS and PC materials should be no less than 1.5 ~ 2.

The side wall of plastic parts with texture, sandblasting, etc. shall have a demoulding draft angle of 2 ~ 5 , depending on the specific texture depth.

The deeper the texture depth is, the greater the demoulding draft angle should be.

When the structure is designed to be shut-off, the draft angle of shut-off surface is generally 1 ~ 3.

direction of draft angle.Generally the inner hole is based on the small end, which conforms to the drawing, the draft angle is checked from the large end, the shape is based on the large end.

The demoulding draft angle is not included in the tolerance range of plastic parts as rule of thumb.

The demoulding draft angle of the shell profile plastic part is greater than or equal to 3. Except the shell surface, the demoulding draft angle of other features is 1 .

In particular, it can also be taken according to the following principles: the demoulding draft angle of reinforcing ribs:

  • < 3mm, draft angle is 0.5,
  • 3 ~ 5 mm, draft angle is 1, and
  • > 5mm,draft angle is 1.5;

The demoulding draft angle of draw depth:

  • <3mm, draft angle is 0.5,
  • 3 ~ 5 mm, draft angle is 1
  • >1.5mm, draft angle is 1.5

Wall thickness of plastic parts

It is very important to determine the wall thickness of plastic parts reasonably. The wall thickness first depends on the requirements of plastic parts, including the strength, quality , electrical performance, dimensional stability and assembly requirements. Generally, the wall thickness has fixed values as rule of thumb, which can be determined by referring to similar ones.

Engineering plasticsMinimum wall thicknessWall thickness of small productsWall thickness of medium productsWall thickness of large products
Nylon (PA)0.450.761.52.40~3.20
Polyethylene (PE)0.61.251.62.40~3.20
Polystyrene (PS)0.751.251.63.20~5.40
Modified polystyrene0.751.251.63.2~5.4
Organic glass (PMMA) (372)0.81.52.24.00~6.50
Polypropylene (PP)0.851.451.752.40~3.20
Polycarbonate (PC)0.951.82.33.00~4.50
Polyoxymethylene (POM)0.81.41.62.40~3.20
Polysulfone (PSU)0.951.82.33.00~4.50
ABS0.81.52.22.40~3.20
PC+ABS0.751.52.22.40~3.20
Polyvinyl chloride (hard)1.151.61.83.2~5.8
Polyvinyl chloride (soft)0.851.251.52.4~3.2
polyamide0.450.751.52.4~3.2
polyphenyl ether1.21.752.53.5~6.4
polysulfone0.951.82.33.0~4.5
Chlorinated polyether0.91.351.82.5~3.4
cellulose acetate0.71.251.93.2~4.8
ethyl cellulose0.91.251.62.4~3.2
Acrylic0.70.92.43.0~6.0

The wall thickness of plastic parts should be uniform as far as possible, avoiding too thin wall, too thick wall and sudden change of wall thickness.

If the wall thickness of plastic parts must be changed, gradual change or circular arc transition should be adopted, otherwise the plastic parts will be deformed due to uneven shrinkage, which will affect the strength of plastic parts and the fluidity during injection molding.

Thickness difference shall be controlled within 25% between each walls, and the minimum wall thickness of the part shall not be less than 0.4mm, and  the area shall not be greater than 100mm².

The wall thickness of plastic parts is generally in the range of 1 ~ 5 mm. The most common is 2 ~ 3 mm.

Try not to design ribs and boss too thick. It is recommended to take half of the body wall thickness , otherwise it will easily cause appearance problems such as sink marks.

Try not to design the part as a single flat plate with the very small size, otherwise the deformation will lead to unevenness of the part.

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