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Precision injection moulding is a specialized process that offers unique benefits to various industries requiring high-precision parts. This comprehensive guide will explore the differences between conventional and precision injection molding, the challenges faced in this process, troubleshooting common problems, the importance of areas of precision, choosing the best manufacturer, maintaining quality control, industries that commonly use precision injection molding, factors to consider when selecting a precision machine, cost comparison.

What is the difference between conventional and precision injection molding?

Conventional injection molding is a common method for making different shaped, sized, and complex plastic pieces. In this method, melted plastic is put into a mold, and it becomes solid in the shape of the mold&#;s space as it cools down. In contrast, precision injection moulding focuses on producing parts with extremely tight tolerances and high levels of accuracy, and the mold material is of high quality and sturdy, with great accuracy in the cavity dimensions, a smooth finish, and precise alignment between the different mold parts. This process demands high precision molds, advanced machinery, and skilled operators to achieve the desired results.

The main difference between the two lies in the tolerance levels. Conventional injection molded parts typically have a tolerance of +/- .005&#;, whereas precision molded parts require tolerances between +/- .002&#; and +/- .001&#; or even less in some cases.

What are some of the challenges in precision injection molding?

Precision injection molding is a complex process that involves producing high-precision plastic products with close tolerances, intricate geometries, and intricate design features. While this technique has many advantages, it also faces several challenges, including:

1. Material selection and preparation: Choosing the correct material for a specific application is essential when working with precision injection molding. The features of materials, like thickness, ability to handle the heat, and how much they shrink, can really affect how well the process works and the final product&#;s quality. Material preparation, including drying and blending, must be done carefully to maintain consistency and avoid defects.

2. Tooling design and fabrication: Designing and making precision injection mold require advanced engineering skills and sophisticated machinery. The mold must be capable of producing parts with tight tolerances and intricate details consistently. Factors such as venting, cooling channels, and gate placements must be meticulously considered during mold design.
3. Machine calibration and process control: Precision injection molding machines need to be correctly calibrated and maintained to ensure consistent, reproducible results. Factors such as injection pressure, melt temperature, cooling rates, and part ejection must be tightly controlled throughout the process.
4. Shrinkage and warping: During the cooling process, the plastic material shrinks, which might result in dimensional inaccuracies or warping. It is crucial to account for these issues during mold design, material selection, and process control.
5. Process repeatability: It is vital to control and monitor the molding parameters to ensure repeated success in delivering high-quality parts with close tolerances. Variations in the process can lead to defects and inconsistencies.
6. Part inspection and quality control: With tight tolerances and intricate details, quality control and inspection for precision injection molding parts can be challenging. Advanced measuring and inspection techniques, such as coordinate measuring machines (CMM) or optical inspection systems, may be required to assess part quality accurately.
7. Cost and lead time: Precision injection molding can be more expensive and time-consuming due to the complexity of tooling design and fabrication, material preparation, and process optimization. Finding the right balance between cost efficiency and part quality is essential.
8. Skilled operators: The precision injection molding processes require a deep understanding of material behavior, machine capabilities, and process control. Skilled operators and engineers with the right expertise are crucial for achieving optimal results consistently.

Troubleshooting common problems in precision injection molding

Troubleshooting common problems in precision injection molding involves identifying the root causes and implementing appropriate corrective actions. Here are some common issues and potential solutions:

Common ProblemsCausesSolutionsShort shotsWhen a plastic part is not completely filled, it results in a short shot.
Causes include insufficient material, low injection pressure, or incorrect shot size.&#;&#;Increase injection pressure, and ensure the shot size is adequate.
&#;&#;Check for any obstructions in the mold or material flow.
&#;&#;Increase material temperature to improve flow properties.
&#;&#;Optimize the gate and runner design.FlashAn excess plastic material that flows beyond the parting line, resulting in undesired thin layers, is called a flash. Causes may include high injection pressure, worn or damaged mold, or insufficient clamping force.&#;&#;Reduce injection pressure.
&#;&#;Inspect and repair the mold if necessary.
&#;&#;Increase clamping force on the injection molding machine.Sink marksDepressions on the part surface are caused by uneven cooling or material shrinkage.&#;&#;Adjust the cooling rate and injection speed.
&#;&#;Modify gate location or part-wall thickness to improve material flow.
&#;&#;Optimize material selection or processing conditions.WarpingDistortion of the part, typically caused by uneven cooling, material shrinkage, or residual stress.&#;&#;Improve mold design to ensure uniform cooling.
&#;&#;Adjust packing pressure to reduce residual stress.
&#;&#;Check material moisture content and drying process.Weld linesVisible lines on the part where different material flows meet, usually caused by insufficient fusion or air entrapment.&#;&#;Increase injection pressure and speed.
&#;&#;Optimize gate placement and venting.
&#;&#;Ensure material temperature is within the proper range.Burn marksDiscolored or charred areas on the part, are typically caused by trapped air, overheating, or excessive residence time.&#;&#;Optimize venting and gate placement.
&#;&#;Adjust injection speed and pressure.
&#;&#;Ensure the material temperature is within a suitable rangeJettingWavy patterns in the part caused by a turbulent flow of material during filling.&#;&#;Increase injection pressure and speed.
&#;&#;Improve runner and gate design to ensure proper material flow.
&#;&#;Adjust material temperature.DelaminationSeparation of layers within the molded part, is usually caused by contamination or material incompatibility.&#;&#;Ensure material and additives are compatible.
&#;&#;Improve material preparation and drying process.
&#;&#;Thoroughly clean the mold and the injection molding machine.

Troubleshooting precision injection molding problems is a continuous process of monitoring, optimizing, and fine-tuning. Each problem may have multiple causes, and solutions may involve making adjustments to multiple variables. An experienced team of operators and engineers plays a crucial role in addressing these issues and maintaining a high-quality molding process.

Areas of Precision

Tolerance Issues

Precision injection moulding is necessary when a product requires tight tolerances, which means the dimensions of the part must be followed precisely and accurately. Identifying the areas that require precision molding ensures a cost-effective solution without compromising quality. In some cases, tolerances can be achieved through conventional injection molding, but precision molding provides a more reliable solution for critical components.

Materials

Choosing the right plastic material plays a significant role in achieving the desired level of precision in injection molded parts. Materials with low shrinkage properties are preferred for precision molding applications. In some cases, the addition of fillers or reinforcements, such as glass fibers or carbon fibers, can help improve the material&#;s dimensional stability and reduce shrinkage.

Technique

The technique used in precision injection moulding is crucial for ensuring the production of identical parts with tight tolerances. A high-precision mold, advanced machinery, and skilled operators are required for a successful precision molding process. The process should be slow, steady, and focused to produce consistent and accurate results.

What to Look for When Selecting The Injection Molding Manufacturer

Choosing the right precision injection molding company is essential for achieving high-quality, precise parts. When selecting a manufacturer, consider the following factors:

1. Expertise in precision molding: Look for a company with extensive experience and a proven track record in precision injection moulding.
2. High-precision mold and machine capabilities: Ensure the manufacturer uses advanced machinery and high-precision molds to produce accurate parts consistently.
3. Quality control measures: The manufacturer should have stringent quality control measures in place to ensure the production of consistent, high-quality parts.
4. Technical support and customer service: A reliable manufacturer like Seaskymedical, should provide excellent customer service, technical support, and assistance throughout the production process.

How can Quality Control be Maintained in Precision Injection Molding?

Maintaining quality control in precision injection moulding is critical for producing consistent, high-quality parts. The following steps can help ensure quality control:

• Use high precision of the mold and machines with advanced capabilities to produce precise plastic parts consistently.
• Implement strict injection molding process control measures, such as monitoring temperature, pressure, and cycle time, to maintain consistent part quality.
• Conduct regular inspections and testing of parts to ensure they meet the required tolerances and specifications.
• Train and educate operators on the importance of precision and accuracy in the molding process.

What Industries Commonly Use Precision Injection Molding?

Precision injection moulding is widely used across various industries requiring high-precision parts, including:

• Medical devices: Precision molded components are used in surgical instruments, diagnostic equipment, and implantable devices.
• Automotive: High-precision parts are critical for the performance and safety of vehicles, such as fuel injectors, sensors, and electronic components.
• Aerospace and defense: Precision injection molded parts are used in aircraft components, satellite systems, and military equipment.
• Electronics: Precision injection moulding is used to produce connectors, switches, and other components for electronic devices.
• Optics: The process is employed for the manufacturing of lenses and other optical components that demand high levels of precision.

What factors should be considered when selecting a precision injection molding machine?

When selecting a precision injection molding machine, consider the following factors:

1. Clamping system stiffness: The machine should have a stiff clamping system with a controlled movement between 0.05 to 0.08mm.
2. Dimensional tolerance capabilities: The machine should be able to maintain tight tolerances consistently throughout the production process.
3. Injection pressure: High pressure machines are preferred for precision molding, as they can improve part quality and reduce shrinkage.
4. Machine speed: The speed of the machine, including die opening and closing, should be optimized for precision molding applications.
5. Plasticizing components: The machine should have high-quality plasticizing components, such as the screw, screw head, and material barrel, to ensure consistent part quality.

What is the cost of precision injection molding compared to other manufacturing processes?

Precision injection molding usually costs more than regular injection molding because it needs special molds, better machines, and trained workers. But the good parts of precision molding, like making things exact, high-quality products, and having less waste, often make up for the extra costs. Sometimes, precision injection molding costs less than other methods, like using machines or adding materials, especially when making a lot of items at once.

Conclusion

Precision injection moulding is a specialized process that offers significant advantages for industries requiring high-precision parts.

By understanding the differences between conventional and precision molding, addressing common challenges, and implementing best practices, manufacturers can produce consistent, high-quality parts that meet the demanding requirements of various applications.

Selecting the right precision injection molding company, like Seaskymedical, materials, and machinery is crucial for ensuring a successful precision molding project. With proper planning and execution, precision injection moulding can be a cost-effective solution for producing high-quality, accurate parts across various industries.

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.

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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

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(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&#;.

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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.

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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

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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.

Contact us to discuss your requirements of precision mold parts. Our experienced sales team can help you identify the options that best suit your needs.