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Injection molding is a manufacturing process used to make objects from plastic material. There are two main types of injection molding: precision and ordinary. In this blog post, we will discuss the differences between these two types of injection molding.
Compared with ordinary injection molding, precision injection molding is a process that requires high precision and surface quality of the molded parts, which has special requirements for injection molding machine, injection mold, molding process, and molding materials.
Concept of Precision Injection Molding
Precision injection molding refers to the injection molding method in which the dimensional repeatability of the molded products is so high that it is difficult to achieve the requirements by using general plastic injection molding machines and conventional injection molding processes.
The concept of &#;precision injection molding&#; is mainly different from &#;conventional injection molding&#;, which is based on the rapid development of polymer materials and the use of precision plastic parts to replace high-precision metal parts in the field of instrumentation and electronics.
At present, there are two indicators to define precision injection molding: one is the dimensional repeatability of the product, and the other is the repeatability of the product quality.
This paper focuses on precision injection molding in terms of the dimensional repeatability of products. However, the accuracy of plastic parts cannot be equated with the accuracy of metal parts due to the different nature of various materials and manufacturing processes.
Source: https://www.pinterest.com/pin//What is precision plastic injection molding?
Precision injection molding refers to a type of injection molding technology that can mold products with high requirements for intrinsic quality, dimensional accuracy, and surface quality.
The dimensional accuracy of the plastic products produced can reach 0.01mm or less, usually between 0.01 and 0.001mm.
The most important technical index for evaluating the products is the accuracy of the injection-molded products (dimensional tolerance, form tolerance, and surface finish of the products).
To produce precision plastic products, it is necessary to strictly control four major factors, such as precision molding materials selection, precision injection mold design,precision molding process, and operator&#;s technical level.
A precision injection molding machine requires the dimensional accuracy of the products to be within 0.01~0.001mm, and many precision injection molding machines also require high injection pressure and high injection speed.
Require the clamping system to have sufficiently large rigidity and sufficiently high clamping accuracy, the so-called clamping accuracy refers to the uniformity, adjustability, stability, and repeatability of the clamping force and high accuracy of the opening and closing position.
It is required that the pressure, flow rate, temperature, and metering can be precisely controlled to the corresponding accuracy, and multi-stage or stepless injection is used to ensure the reproduction conditions of the molding process and the repetition accuracy of the product size, etc.
Comparison of the injection pressure
Ordinary machine: 147 to 177MPa;
precision machine: 216 to 243MPa;
ultra-high-pressure machine: 243 to 392MPa.
Factors affecting the dimensional accuracy of products
(1) Mould precision
(2) Shrinkage rate of molding
(3) The temperature and humidity of the environment in which the product is used and the magnitude of fluctuations.
Specific requirements for precision injection molding
(1) First, the injection pressure should be greater than 25MPa;
(2) Injection speed should be greater than or equal to 300mm/s;
(3) Product dimensional accuracy 0.001mm;
(4) The standard deviation coefficient (rate of change) of product quality should be less than 0.1%;
(5) Accuracy of opening and closing position: open &#; 0.03mm close &#; 0.01;
(6) Injection position accuracy (holding pressure termination point) is less than 0.03mm;
(7) Tie rod force balance is less than 1%;
(8)The accuracy of the pre-molding position is less than 0.03mm;
(9) The balance of fixed and dynamic mold plate A: less than 0.03mm when the clamping force is zero B: less than 0.005mm when the clamping force is maximum;
(10) Barrel and screw temperature control accuracy is less than ±0.5&#;.
Source: https://www.pinterest.com/pin//Comparison of the characteristics between precision injection molding and general injection molding
Features of precision injection molding
(1) High dimensional accuracy and small tolerances of the products, i.e. there are high precision dimensional boundaries.
(2) High repeatability of product weight, requiring daily, monthly, and yearly dimensional stability.
Characteristics of general injection molding
General plastic injection molding does not require high dimensional accuracy of injection molded parts and is generally based on the standard of being able to be assembled.
The appearance requirements of injection molded parts are relatively high, and secondary processing (such as oil spraying) may be used to improve the appearance of defects when necessary.
General injection molding does not require a special precision injection molding machine, nor does it require a special specified material, generally common thermoplastics can be used to produce. Therefore, the common injection molding process is also widely used in the modern plastic industry.
Source: https://www.pinterest.com/pin//The conditions that must be met for precision injection molding
The precision molds of molded products are an important condition to decide whether the products can reach the dimensional tolerance required by the design, and the precision injection molding machine is the key equipment to ensure that the products are always molded within the required dimensional tolerance and to guarantee a very high yield.
(1) The material of the mold should be good, choose the alloy steel with high mechanical strength or high hardness (molding parts should reach about HRC52), good wear resistance, and strong corrosion resistance. Rigid enough, cavity size accuracy, finish and positioning accuracy between the template should be high.
(2) The materials used to make the cavity and sprue should be subjected to strict heat treatment.
(3) Precision injection molding machine should be used.
(4) To adopt a precision injection molding process
(5) To use materials suitable for the precision injection molding process
Source: https://www.pinterest.com/pin//Most of the commonly used precision injection molding materials are as follows
(1) POM and carbon fiber reinforced (CF) or glass-reinforced (GF). This material is characterized by good creep resistance, fatigue resistance, weathering resistance, good dielectric properties, non-combustible, and easy to release by adding lubricant.
(2) PA and glass-reinforced PA66 are characterized by strong impact resistance and abrasion resistance, good flowability, and can be molded into 0.4mm wall thickness products. Glass fiber reinforced PA66 has heat resistance (melting point 250 &#;), the disadvantage is that it has moisture absorption, generally after molding is to be processed by moisture conditioning.
(3) PBT reinforced polyester, molding time is short. Forming time comparison is as follows: PBT &#; POM &#; PA66 &#; PA6.
(4) PC and GFPC: good wear resistance, enhanced rigidity, good dimensional stability, weather resistance, flame retardant, and good molding processability.
Shrinkage in Precision Injection Molding
An important method to ensure the dimensional accuracy of injection molded parts in the precision injection molding process is to control the shrinkage of injection molded parts, among which are: thermal shrinkage of injection molded parts, disguised shrinkage, orientation shrinkage, and compression shrinkage, and elastic recovery.
Link to Yihua Mould
(1) Thermal shrinkage is a thermophysical property inherent to the molding material and the mold material. The precision mold temperature is high, the temperature of the product is also high, and the actual shrinkage rate will increase, so the temperature of the precision injection mold should not be too high.
(2) Phase change shrinkage is called phase change shrinkage due to the crystallization of polymer in the process of orientation of crystalline resin, which is caused by the reduction of specific volume.
High mold temperature, high crystallinity, large shrinkage; but on the other hand, the increase in crystallinity will increase the density of the product, reduce the coefficient of linear expansion, the shrinkage rate is reduced. Therefore, the actual shrinkage rate is determined by the combined effect of the two.
(3) Shrinkage in the direction of orientation, due to the forced stretching of molecular chains in the direction of flow, so that the macromolecules in the cooling tend to recoil and recover, in the direction of orientation will produce shrinkage.
The degree of molecular orientation is related to injection pressure, injection speed, resin temperature, and mold temperature. But the main one is the injection speed.
(4) Compression shrinkage and elastic restoration, general plastics are compressive. That is, the specific volume changes significantly under high pressure.
In general, temperature increases the pressure molding products specific volume will decrease, density will increase, expansion coefficient will decrease, shrinkage rate will be significantly reduced.
Corresponding to the compressibility, the molding material has an elastic reset effect so that the product shrinkage is reduced. The factors affecting the shrinkage of the products are related to the molding conditions and operating conditions.
Precision injection molding equipment
A precision injection molding machine is an injection machine with closed-loop injection control, usually, the injection pressure and injection speed of the injection machine is controlled by closed-loop control. The signal is consistent with the system requirements so that the output signal is closer to the desired value of the system output deviation is minimal.
Simply put, closed-loop control is closer to the desired value of the automatic adjustment control, injection molding machine due to the use of injection closed-loop control, greatly improving the repeatability and stability of injection molding, reducing the size of the parts fluctuations, but also to improve the size of the parts accuracy and dimensional stability, injection molding machine to achieve closed-loop control.
For hydraulic injection molding machine must use servo valves to achieve closed-loop control of hydraulic system pressure and flow, ultra-precision injection molding machine, in addition to the use of servo valves, but also with the use of servo control board with the computer control system, to further improve the hydraulic system output pressure and flow of repetitive accuracy to achieve ultra-precision injection molding.
Summary
Both precision injection molding and general injection molding need to meet the precision requirements, assembly requirements, and appearance requirements of the product.
Of course, the quality and cost of any product are closely related. When deciding to manufacture injection molding product, you need to first make a full understanding of the market positioning and cost assessment of the product to ensure that the project can be successfully realized.
Precision molding is the latest technology in the world of plastic injection molding. Precision molding is a type of plastics molding that is the most expensive and sophisticated process of mold design in the market.
Precision mold parts to assemble the precision mold-MEITUO
The process of precision molding is never used in the development of the entire product by the plastic injection molding companies. It is only used in the manufacturing process in small and infrequent occasions when product development calls for an unusually precise form of plastic injection molding.
As mentioned above, precision injection molding is a highly technical process and requires the use of precision molds and precision machines. The process of precision molding differs from conventional injection molding techniques. The process is required for the development of precise plastic parts with complex geometries that can replace high precision metal parts for various industrial applications.
The precision of a part is largely dependent on the precision injection mold and its suitability to meet the design engineering requirements.
The precision of the mold is a result of various factors including:
The process of molding plastic by CNC machining into an exceptional price and calculated shapes is known as polymer optics.
The process of precision molding is never used in the development of the entire product by the plastic injection molding companies. It is only used in the manufacturing process in small and infrequent occasions when product development calls for an unusually precise form of plastic injection molding.
As mentioned above, precision injection molding is a highly technical process and requires the use of precision molds and precision machines. The process of precision molding differs from conventional injection molding techniques. The process is required for the development of precise plastic parts with complex geometries that can replace high precision metal parts for various industrial applications.
The precision of a part is largely dependent on the precision injection mold and its suitability to meet the design engineering requirements.
The precision of the mold is a result of various factors including:
The process of molding plastic by CNC machining into an exceptional price and calculated shapes is known as polymer optics.
ABS is a thermoplastic polymer, which means it is can retain its elasticity through high temperatures. It has a reduced shrinkage of =/-.006. It is still considered not appropriate for precision molding, which usually requires a shrinkage of +/-002.
This shrinkage capacity is usually achieved through the addition of glass or another resin that is mixed with the plastic. The external material keeps the plastic in its place and absorbs the excessive heat, thereby reducing shrinkage.
It should be noted that the induction of this material into the product does not ensure that the product will not shrink. The resulting product will shrink in parallel to the induced resin.
Now that the product has more structure, shrinkage can be taken into account and a product development plan can be developed that will keep the product straight.
The process of precision molding requires that every piece of the product is developed identically and will be attached in an identical manner.
If a product is not identical to the mold design then the precision product will also not be accurate. A precise mold is the only way to ensure that there is no change in the design in any way.
When you are in need of a precision-molded product, make sure that the manufacturer understands this aspect of development.
Precision molding is a slow and steady process that requires time and focus. Do not choose injection molding companies who specializes in rapid tooling, as they are not too familiar with the precision molding process. The rapid tooling process finishes the mold design quickly.
This is the main idea of precision tooling and we hope to have covered all the basics.
There is not much information on the process available online so we decided to present the process through our experience.
If you ever require a precision modeling process for your products, it is best to truly understand the mechanics of the process as best as you can.
If the manufacturer can see that you know what you are talking about, they will be more motivated to deliver the product that you asked for.
Precision molding machines should preferably be high pressure. This helps improve the quality and the overall precision of the plastic parts.
An injection pressure of around 392 MPa reduces the shrinkage factor to zero. Additionally, the mechanical strength of the part increases significantly when the injection pressure is kept around 392MPa.
Further, the efficiency of the injection rate improves when maximum injection pressure is increased.
Following are the main structural features of precision molding machines:
Additionally, precision moulding machines should be able to manage the repeatability and accuracy of a product.
When planning to create a precision molded product, it is important to consider the following key criteria:
As mentioned earlier in the article, precision molding is way more sophisticated and expensive than conventional plastics molding. This is the reason why it is important to understand the different aspects of your custom plastic parts and determine the ones requiring high tolerances.
It is also important to understand whether those tolerances can be managed through conventional injection moulding techniques. A plastic part may be created using both- conventional plastic injection molding process as well as precision moulding. An electronic part, may, for example, require precision works only for a small section of the piece and not the entire part.
Hence, understanding and determining the precision requirements will ensure a cost-effective solution that will meet your needs. Additionally, it will also help ensure that your parts are prepared with high quality and meet the production deadlines.
Selecting the right plastic resins is an important factor for creating the right precision molded parts. The selection of material is one of the biggest determining factors in determining whether the plastic molded products will come out as desired.
Within the plastic material, shrinkage range is one of the most important criteria for creating parts with high precision. Narrow shrinkage ranges offer better chances of reaching tight tolerances.
Again, the requirement of shrinkage depends on the product being created. While a wider range of shrinkage is not preferable since it makes it hard to hit the right tolerance levels, it can still be used to create products that do not need to be of an exact size.
Polypropylene has a wider shrinkage range of +/- .014&#; to +/- .022&#;. Acrylonitrile butadiene styrene (ABS) on the other hand has a narrower range but is still not in the category that fits the need for precision molding.
Usually, the shrinkage ranges required for molding a precision part is around +/- .001&#; or +/- .002&#;
Choosing a plastic resin that offers low shrinkage is hence an easy way to get your materials right for precision moulding.
However, this may not always be a cost-effective option due to the high cost of the desired resins.
Various molders hence prefer to reach the high tolerance level by adding filler materials to the plastic resins. These include glass fibers, mica and other filler materials. The addition of fillers narrows down the shrinkage range and hence provides a better structure to the parts.
Choosing the right precision molding company is another important factor in creating quality molded products. The key requirements for creating precision molded plastic parts that have tight tolerances and are produced as exact replicas of each other is to have high precision molds and tools.
It is hence important to select a precision molding manufacturer who specializes in high precision tooling with a thorough understanding of the process. The availability of technology to create precise molds that produce identical parts is a very important criterion for manufacturing precision molded products.
Precision moulding is used in the development of a wide variety of products as stated earlier. But the technology truly revolutionized the development of lenses in various applications as it allowed for the contract manufacturing of glass free lenses that were cheaper and much stronger.
Glass lenses are highly delicate, harder to make, and expensive, but plastic optic lenses have truly revolutionized the optics industry.
Precise molding is used in the development and mass production of precise spherical, diffractive, freeform, aspheric and other types of lenses that are high-quality products and have perfect optical surface finishing.
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