What is precision injection molding?
Creates precise plastic components
Materials should have a low shrinkage capacity
Rely on the precision injection mold
A slow and steady process
Uses polymer optics
Many molding processes are known to mass produce products that are used in daily life. However, various industries have parts and pieces that are too complex to be made with ordinary plastic injection moldings. A process called precision injection molding is used for such processes.
But, what is precision injection molding? It is a highly technical process that makes use of precise molds. It is not used to develop whole products, instead, it develops more complex plastic parts.
It differs from convection modeling in many ways, from the materials used to the mold created to the machine used in creating the product. This article tackles all you need to know about this technical process. By the end, you can assess if this is the molding process that you need for your next project.
Compared to plastic injection molding, this method produces precise plastic parts. It does not mass produce whole parts. These products that are made in the process replace high-precision metal parts from different industrial appliances.
The plastic components produced in precision injection molding require a tight tolerance. That means that the requirements for the product have precise and accurate procedures. When not followed, it can break inside the mold.
Products that are produced in precise injection molding are also comprised of complex geometric parts. These items have specific shapes that are needed for certain items in automotive, pharmaceutical, information technology, and medical fields.
Precise injection molding can cause plastics to shrink during the manufacturing process. That&#;s why its materials are different from other injection molding materials.
When materials have a high shrinkage capacity, they melt as they undergo the precise injection molding process. It ruins the product in the end.
The materials used for this molding process need to have a low shrinkage capacity. The shrinkage required is around +/-0.01&#; or +/-0.02&#;. However, many materials can&#;t reach this range.
An example of this would be ABS, a thermoplastic polymer. This kind of plastic can retain its elasticity while going through high temperatures. However, its shrinkage of +/-0.06 is still not appropriate for precision molding. Glass and other resin can be added to reach the desired shrinkage. These help the material absorb the excess heat while keeping the plastic stable.
The precision made during this molding process is achieved through its mold. It needs to suit the design engineering requirements.
To craft the mold, it needs to undergo accurate study, design, and testing. Many elements need to be taken into account for the mold. Here are some of the elements that need attention:
The mold cavity size &#; its position and the number of cavities it has
The precision of the parting surface
The materials used for the mold (this can be made from steel alloys or cast irons)
The bottom plate&#;s thickness
The runner size
Precision injection models are made with tolerances between +/-0.02&#; and +/-0.01&#; or less. All elements mentioned are considered when considering the dimensions tolerance.
A high-precision model is required when creating plastic parts that have tight tolerances. Each part made in a precise injection model needs to be identical. This process can only be applied to plastic parts that are placed and connected with other parts in a fixed form.
Because of the precise products, the manufacturer should not rely on rapid tools for this method. Precise injection modeling is a slow and steady process that makes a high-precision tool.
Polymer optics are used in precise injection molding. This is when CNC machining is used to mold the plastics into precise and calculated shapes. The machines have high pressure that helps improve the quality and precision of the plastic parts. They also manage to repeatedly create an accurate product.
The entire process is automated and conducted through computers through an automatic handling system. It allows the producer to customize the process for the product needed to be molded.
This reduces the cost of labor while increasing production efficiency thanks to its automated process.
Now that you&#;ve answered what precision injection molding is, you can check if you can apply it to some of your products. As stated above, it can also develop a wide variety of complex products.
If you&#;re interested in this process or other molding processes, message Richfields today. We offer various tooling solutions including precision injection molding. Don&#;t hesitate to reach out to learn more about how our services can help your next project.
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
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(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.
(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.
If you are looking for more details, kindly visit Precision Molds And Molding.