Plastic Production Classroom (3) – Understand the model design of injection molding

Plastic Production Classroom (3) – Understand the model design of injection molding
Injection molding is an effective and fast production method for the mass production of plastic products of different shapes.
However, to produce a perfect plastic product, good mold design is a key to determining the quality of the finished product.
As the saying goes, "seven parts of the mold, three parts of the process", for injection molding, both the mold and the injection machine have a great impact on the quality of the final product.
, even the mold has a greater impact on the finished product than the injection machine.

Injection mold design
The structure of the injection mold is determined by the type of injection machine and the molded product, and each mold is composed of a movable mold and a fixed mold.
The movable mold will be installed on the moving plate of the injection machine, while the fixed mold will be installed on the fixed plate of the injection machine.
When plastic is injected, the injection machine closes the movable mold and the fixed mold to form a complete mold cavity. After the plastic has cooled and formed, the mold will separate again.
The molded part is ejected from the demoulding structure, and the above process is repeated. The structure of each mold will vary depending on the shape of the product.
At this time, if you do not fully understand the product and mold design, it will be difficult to make excellent plastic products.
To create high-quality plastic products, the following points should be considered during design:

Mold draft angle
When manufacturing plastic products, every detail of the mold may become an important key to the success or failure of the product.
In order to smoothly extract the molded product from the mold, the draft angle is a detail that cannot be ignored in the design and manufacturing of the mold.
If there is no draft angle, there will be resistance when the molded product is demoulded, and even the demoulding cannot be successful. If the mold is deeper, a larger draft angle is required.
Basically add 1 degree of draft angle for every inch. When the draft angle is insufficient, it is very likely that the finished product will be scratched or have severe ejection pin marks during demoulding.

Rounded corners instead of sharp corners
In order to ensure that the finished product has a consistent meat thickness, the rounded corners will be taken into consideration when making the mold. Rounding the sharp corners can not only make the finished product easier to release from the mold, but also
It also allows the plastic to flow more smoothly during plastic molding. In addition, this design can also reduce the manufacturing cost of the product,
And due to the reduced stress, the product is less likely to crack during manufacturing, making it more durable.
In order to keep the finished product with the same thickness, the outer radius of the fillet design is usually about 3 times the inner radius.

Avoid dead corners and undercuts
If the mold has dead corners or undercuts during design or manufacturing, it will make it more difficult to demould the finished product.
It may also cause surface scratches and other effects, so when designing the mold, try to avoid dead corners and undercuts in the mold.
In addition, when manufacturing molds, we should also try to avoid in order to solve the problems of dead corners and undercuts.
Instead, it leads to increased costs in mold design and disassembly. If you need to design concave or convex corners when remanufacturing the product, you must match the mold design and slider for production.

Thin shell design can be used inside
Everyone must know the principle of thermal expansion and contraction, and you should also take this into consideration when designing plastic products.
The thin shell design inside the product can effectively avoid shrinkage or deformation caused by product cooling.
And compared with solid products, thin shell designs can save excess manufacturing costs. Also, when the desired shape is too long or too large,
The problem of easy breakage can be solved by adding strong ribs to provide additional support to the product.
When adding strong ribs, the draft angle and main meat thickness should be considered, and should not exceed 1/3 of the thickness of the connected main structure.

 

Use appropriate material thickness
When designing products, appropriate materials will be selected based on the needs of use and user preferences. These plastic materials are based on their flexibility, rigidity, solidity, brittleness and other characteristics.
And affect different flesh thickness designs. If the thickness of the meat is too thin or too thick, it may cause defects, collapse, or shrinkage marks in the finished product.
Suggestions for the thickness of various materials are provided here. You can avoid irreparable tragedies by referring to this table.

Plastic material

Recommended thickness (inches)

ABS

0.045-0.140

Acetal

0.030-0.120

Acrylic

0.025-0.500

Liquid Crystal Polymer

0.030-0.120

Long-fiber reinforced plastics

0.075-1.000

Nylon

0.030-0.115

Polycarbonate

0.040-0.150

Polyester

0.025 - 0.125

Polyethylene

0.030 - 0.200

Polypropylene Sulfide

0.020 - 0.180

Polypropylene

0.025-0.150

Polystyrene

0.035-0.150

Polyurethane

0.080-0.750

Product manufacturing details and improvements
When you use plastic products, you may find that there are usually parting lines, gate locations, and some traces of ejector pins on the surface of these products.
These are unavoidable situations during the manufacturing process. However, in order to make the product more beautiful, manufacturers usually cleverly hide these traces in less obvious locations.
Or perform secondary processing to remove it. When designing these positions, the plastic must flow evenly and fill the entire mold cavity.
And consider whether they affect the use of the product or other parts.

The final product can be improved by following these principles when designing molds. They are called design for manufacturability (DFM).
In addition to the methods listed here, there are still many factors that need to be considered in the design of plastic products.
For example, mold manufacturing costs, improving pouring methods, reducing demoulding time, etc. In addition, many manufacturers will use their many years of experience to
A variety of different design approaches have been developed. By recording and improving the checklist, you can also save unnecessary costs and time.