Mold Tech

Precision Plastic Injection Molding

• 2021-08-13

What is precision plastic injection molding?

Normally tolerance on the Plastic molding part is around 0.05-0.1mm, if the part tolerance requirement is about 0.01-0.03mm, that means this is precision plastic injection molding, to make high precision plastic injection molding parts, the first thing is making the precision injection mold, all of the mold components must have tolerance within 0.005-0.01mm, this is min requirement for high precision plastic injection mold after mold is completed finished, then take mold trial to verify the dimension according to 2D drawing requirement, to trial the mold and make stable tolerance, precision plastic injection mold is number one key point to making high precision molding parts, but not limited to this, you still need use high precision injection molding machine to produce the part, by this two min requirement we can make sure that we can make precision molding parts continually, there are few issues that we make still need to know for the precision plastic injection molding.

Question I:

The determination of the structure of the precision plastic mold is the key, and the overall structure is the embodiment of the final effect of the product: the determination of the overall structure of the mold, the determination of the gate system, the determination of the ejection system and the determination of the water transportation system, and others should be conducive to the post-processing orientation of the product.

Question II:

What about the feeding problem? First of all, we will choose a reasonable injection scheme according to the structure, weight, volume, and cost of the product, which can meet the requirements of customers as well as the requirements of quality. Second, we will design in strict accordance with the injection design standards: the layout of the runner should be uniform, especially the size of the cross load surface of the main and sub runner, the shape and size of the gate.

Question III:

What about the ejection problem? Firstly, we will determine the ejection mode according to product orientation and structure. Secondly, we will evaluate the ejection balance and coexist with other systems, such as interference with water transportation and recycling marks, date clock, etc.

Question IV:

The design of the water channel system is based on four requirements (the cooling line should be as balanced as possible. The water cooling line shall not interfere with other mechanisms. The water channel equipment shall meet the customer’s standards and be easy to install. Each water channel line shall be displayed with identification numbers or marks (in and out).

 Question V:

how to ensure the manufacturing accuracy of the mold and the accuracy of the molding products, this mainly depends on the manufacturing accuracy of the mold cavity, the insert, and the mold core size. The accuracy of the mold cavity number or the accuracy of the parting line will directly affect the size of the product. Firstly, we need to make the manufacturing process plan and flow chart. Each completed manufacturing process must be fully inspected and the data inspection list must be recorded in the datasheet. After the manufacturing is completed, the workpiece shall be processed and maintained.

The design of the parting line of plastic mold is also an important part. If the design is not reasonable, the part is not easy to demoulding or even damage the mold. Here are the design principles for the parting line of mold

It is convenient to eject out the plastic part and simplify the structure of the plastic mold. After the demoulding direction is selected, the position of the parting line should make the plastic part fall done without any interference, like sliders, etc.

For the plastic part with high coaxiality accuracy, the parting line should be selected at the position where two diameters can be placed on the lower mold or upper mold at the same time.

When the precision of the plastic part along the height direction is required to be high, the half overflow cavity should be used. If the transverse flash is formed at the parting line, it is easy to ensure the height precision, while the non-overflow cavity is not easy to ensure.

When the radial dimension accuracy is high, the influence of flash thickness on the accuracy of the plastic part should be considered, as shown in the figure. If the vertical parting of plastic parts is easy to ensure, the horizontal profile is difficult to control due to the thickness of the flash, which affects the accuracy of plastic parts.

Ensure the appearance of the plastic part, it shall be easy to clean the flash and not easy to damage the appearance. The flash produced by the parting surface as shown in the figure shall be easy to clean and not easy to damage the appearance of the plastic part.

It is convenient for the manufacture of plastic mold and the processing of forming parts. The improved parting surface makes the processing concentricity of plastic mold low, easy to manufacture and the flash does not damage the appearance of plastic parts.

Ensure the strength of the formed parts, for example, when determining the parting surface, avoid the thin wall and sharp corner of the formed parts.

In addition to the design elements of general molds, the following points should also be considered in the design of precision injection molds:

•  Adopt proper mold dimension tolerance;

•  Prevent forming shrinkage error;

•  Prevent deformation of injection part;

•  Prevent the deformation of demoulding;

•  The manufacturing error of the die/mold is minimized;

•  Prevent the error of mould precision;

•  Maintain mold accuracy.

Prevent the error of mold precision; classification of processing molds in plastic mold factory and requirements of various points for attention

There are many kinds of plastic injection molds, which can be roughly divided into ten categories. According to different requirements of a part material, physical and chemical properties, mechanical strength, dimensional accuracy, surface finish, service life, economy, etc, different types of injection mold are selected.

The plastic mould with high precision needs to be processed by a high precision CNC machine, and the material and molding process of the mould have strict requirements. Mould technology is also needed to design and analyze.

Some of the parts have special requirements during molding, so advanced technologies such as hot runner, gas-assisted injection molding, nitrogen cylinder, etc. are needed for plastic mold.

Plastic mold manufacturers shall have CNC machine tools, EDM machine tools, wire cutting machine tools, and CNC profiling milling equipment, high-precision grinder, high-precision three coordinate measuring instruments, computer design, and related software, etc.

In general, large metal stamping dies (such as automobile cover part die) should consider whether the machine tool has a blank holder mechanism, even edge lubricant, multi-position progressive, etc. In addition to the punching tonnage, the punching times, feeding device, machine tool and die protection device should be considered.

The plastic mold manufacturing capacity and process of the above are not possessed and mastered by every enterprise. When choosing a cooperative plastic mold manufacturer, we must know its processing ability, not only look at the hardware equipment, but also combine the management level, manufacturing experience, and technical force.

For the same set of mould, there is sometimes a big gap in the quotation of different mould manufacturers. You should not pay more than the value of the mold, but also should not be less than the cost of the mold. Plastic mold manufacturers, like you, want to make a reasonable profit in business, ordering a set of molds with a much lower price will be the beginning of trouble. You should start with your own requirements and measure them comprehensively.

If you have any requirement for precision mold manufacturing services, you are welcome to contact, Sincere Tech is a professional custom precision plastic injection molding and molding company in China, We offer precision injection mold/molding for the medical industry, electronic industry, automotive industry, and so on.

TAG：