How to improve the precision of medical plastic injection molding parts?

• How to improve the precision of medical plastic injection molding parts?
  • What is precision injection molding?
  • How to achieve high-precision medical injection molding parts
  • Factors and solutions affecting the dimensional accuracy of medical plastic products
    • Three major factors affecting the tolerance of medical plastic products
  • Medical plastic product tolerance solutions
  • Other reasons affecting the tolerance of medical injection molding parts
  • Why are tolerances important for medical injection molded parts?
  • How to choose the right medical injection molding manufacturer?
  • Equipment required for medical injection mold processing
  • Conclusion
  • Get Started with Elimold

Injection molding is the most common manufacturing process for making plastic products composed of multiple parts that must be assembled in the final stage of production. Part assembly involves the correct alignment and connection of different parts. Here, tolerances are very important, and if they are not properly specified and controlled, the assembly will fail. Especially in the medical field, it is very important to maintain the tolerance of medical injection molded parts. As an important product that is related to human health and life safety, medical equipment requires extremely high precision and reliability in every link of its production process. Precision molds and precision injection molding technology, as the core tools and technologies for medical equipment manufacturing, directly affect the production efficiency, quality stability and cost control of products. By optimizing mold design, manufacturing process and intelligent management, the production efficiency and quality of medical equipment can be significantly improved. This article will discuss how to improve the precision of medical injection molded parts.

What is precision injection molding?

Precision injection molding refers to an injection molding method in which the size repetition accuracy of the molded injection molded products is very high, so that it is difficult to achieve the requirements using general injection molding machines and conventional injection molding processes. The concept of “precision injection molding” is mainly different from “conventional injection molding”. It is based on the rapid development of polymer materials and the use of precision plastic parts to replace high-precision metal parts in the fields of instruments and electronics. At present, there are two defining indicators for precision injection products: one is the repetitive accuracy of product size, and the other is the repetitive accuracy of product quality.

How to achieve high-precision medical injection molding parts

The precision injection mold of medical molded products is an important condition for determining whether the relevant precision medical products can meet the dimensional tolerance required by the design. In addition, the precision injection molding machine is a key equipment to ensure that the product is always molded within the required dimensional tolerance range and to ensure a very high yield rate. The most important technical indicator for evaluating medical injection molded parts is the accuracy of the product (dimensional tolerance, form and position tolerance and surface finish of the product). In order to produce precision medical plastic products, four major factors must be strictly controlled, including material selection, mold design, injection molding process, and operator’s technical level.

In medical injection molding projects, the product dimensional accuracy is usually required to be within 0.01 to 0.001 mm. Many medical products also require the injection molding machine to have high injection pressure and high injection speed; the clamping system is also required to have sufficient rigidity and high clamping accuracy. The so-called clamping accuracy refers to the uniformity, adjustability, stability and high repeatability of the clamping force, and high precision of the opening and closing positions; and the pressure, flow, temperature, metering, etc. can be accurately controlled to the corresponding accuracy. Multi-stage or stepless injection is used to ensure the reproducibility of the molding process of medical plastic products and the repetitive accuracy of the product size.

Factors and solutions affecting the dimensional accuracy of medical plastic products

To optimize the tolerance of medical injection molding products, it is necessary to use manufacturing-oriented design, use the correct injection molding materials, adjust the injection mold design and process control to optimize the product design. This section will explain the relevant factors of the dimensional accuracy of marketing medical plastic products and the solutions provided by Eimold based on experience so that you can obtain precise plastic injection molding products.

Three major factors affecting the tolerance of medical plastic products

Injection mold precision limit: The mold manufacturing precision requirements for medical precision injection molded parts are extremely high. If the mold processing equipment is not accurate enough, such as positioning errors of CNC machining machines, tool wear, etc., it will cause dimensional deviations of the mold cavity and core. For example, when manufacturing tiny medical implant molds, machining accuracy errors may cause the key dimensions of the product to not meet the design requirements. For example, if the wall thickness tolerance of the pacemaker housing exceeds the allowable range, it will affect its performance and safety.

Unstable material shrinkage: Different batches of medical injection molding materials, even for the same model, may have different shrinkage rates. This may be caused by changes in the composition, molecular weight distribution or additives of the material. For example, some plastics containing bioactive ingredients have fluctuations in the content of additives, which will cause changes in shrinkage, which in turn affects the dimensional accuracy of the injection molded parts.

Fluctuation of injection molding process parameters: Process parameters such as injection temperature, pressure and speed have a significant impact on dimensional accuracy. Temperature changes can cause thermal expansion and contraction of the material, thereby changing the size of the injection molded part. For example, if the barrel temperature is too high, the viscosity of the plastic melt will decrease, and the shrinkage will increase when cooling in the cavity, resulting in a smaller product size. The injection pressure is unstable. When the pressure is insufficient during the holding stage, the melt cannot be effectively compensated for shrinkage, which will cause shrinkage holes and dimensional deviations.

Medical plastic product tolerance solutions

• Improve mold manufacturing accuracy: Use high-precision mold processing equipment, such as ultra-precision five-axis cnc machining centers, to ensure that the dimensional accuracy of the mold cavity and core can reach the micron level or even submicron level. For key dimensions, the tolerance should be controlled within ±0.005mm. Regularly maintain and calibrate the processing equipment, and replace worn tools in time. In terms of mold design, optimize the cooling system to reduce the dimensional changes caused by thermal expansion and contraction of the mold.
• Stabilize material performance: Select a material supplier with stable quality and good reputation. Strictly inspect each batch of materials entering the factory, focusing on key performance indicators such as shrinkage rate and molecular weight. For special medical materials, suppliers are required to provide detailed composition and performance reports. Before the material is used, a trial mold can be carried out, and the injection molding process parameters can be adjusted according to the trial mold results to adapt to the shrinkage characteristics of the material.
• Precisely control process parameters: Determine the optimal injection molding process parameters through a combination of experiments and simulation analysis. For example, for polycarbonate (PC) materials, the barrel temperature is precisely controlled between 280-320°C, the nozzle temperature is slightly lower than the barrel temperature, and the mold temperature is adjusted between 80-120°C according to the structure and size of the injection molded part. Using advanced injection molding machine control systems, the process parameters are monitored and adjusted in real time to ensure the stability of the parameters throughout the injection molding process.

Other reasons affecting the tolerance of medical injection molding parts

During the entire medical injection molding process, special attention should be paid to the maintenance of a dust-free or low-microbial environment and the production environment temperature for the production of medical plastic products to ensure that the products meet the special requirements of the medical industry. This requires manufacturers to establish clean workshops that meet the production requirements of medical products and control the temperature, humidity and cleanliness of the workshops. For example, for the production of implantable medical devices, the workshop should reach a cleanliness level of 10,000 or even higher. During mold processing and injection molding, use medical-grade release agents and ensure the cleanliness of the mold. Before each injection molding, the mold is thoroughly cleaned and sterilized, such as by high-temperature high-pressure steam sterilization or ethylene oxide sterilization.

Why are tolerances important for medical injection molded parts?

Medical plastic products are mainly needed to deliver drug compounds to the target location. Therefore, they are essential to human health in daily life and must be guaranteed to be functional and achieve the desired therapeutic effect. To ensure correct production and meet various industry specifications, you must perform quality control on large quantities of products, process subtle features and non-standard geometries, and properly handle transparent, sensitive or easily bendable plastics.

However, the degree of variation in the manufacturing process of any medical injection molded part depends on its accuracy, and although injection molding is quite precise, there is still a small amount of variation. This variation makes it important to determine the allowable deviation range for the part to function effectively after assembly. Plastic molding tolerances are critical when assembling medical products with multiple injection molded parts. For example, if you want to connect two plastic molded parts using bolts, you need to drill a hole in both parts. Any error in the location and size of the hole can cause errors and loss of function during assembly, ultimately leading to medical product failure and even threatening patient health. Therefore, each medical injection molded part needs to maintain precise tolerances for maximum functionality.

How to choose the right medical injection molding manufacturer?

Elimold’s team of medical injection molding engineers have professional skills and rich manufacturing experience to ensure the smooth operation of medical injection molding projects and reduce the risks of all projects. When you want to find the right medical injection molding manufacturer, you can refer to the following multiple capabilities to analyze and select relevant manufacturers.

• Mold design: Medical injection mold engineers need to have rich experience and mold manufacturing technology. Generally, injection molds are designed with high precision by using advanced computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies to ensure that the shape, size and surface finish of the mold meet the strict requirements of medical devices.

• Plastic material knowledge: A deep understanding of the various plastics used in the medical field and their properties is required, which will ensure that the right plastic material can be selected according to the specific application.

• Familiarity with manufacturing processes: A deep understanding of manufacturing processes will ensure that the best mold structure can be designed to make it run smoothly.

• Design skills: Possess strong design skills, including creating complex 3D models, analyzing the strength and durability of designs, and developing efficient mold designs.

• Knowledge of mold materials and structures: In-depth understanding of the advantages and disadvantages of each mold material.

• Problem solving skills: Ability to identify potential problems in mold design and develop solutions to solve problems as quickly as possible.

• Communication skills: Good communication skills, able to work effectively with engineering team, production team, marketing team/customers.
• Project management skills: Ability to manage time effectively to ensure that projects are completed on time, and able to manage multiple projects at the same time.

• Continuous learning: They can be committed to keeping up with the latest developments in mold design and plastic material technology to maintain industry competitiveness, and continuously improve our service quality to provide better support to customers.

Equipment required for medical injection mold processing

Precision equipment is the main factor in ensuring that high-precision medical plastic products can be manufactured. No matter what kind of precision equipment, it must ultimately be able to stably control the dimensional repetition accuracy and quality repetition accuracy of medical plastic products. The following are the equipment commonly used by Eimold to manufacture medical injection molds and produce related products.

• High-speed CNC machine tools: Elimold introduced 14 new CNC machine tools NXV 600A from Taiwan in April 2020. All parts of the mold, such as cavity, core, insert, mold frame assembly, are CNC machined to ensure the accuracy of the parts.

• EDM machine: EDM is a common high-precision processing technology in mold manufacturing. Elimold uses two DM1470M-CNCEDM machines to improve work efficiency and accuracy. On the other hand, Elimold always uses copper to make electrodes, and all electrodes are measured by coordinate measuring machines (CMM) and can only be used after passing the test.

• Wire cutting machine: Wire cutting machine, Elimold uses low-speed wire cutting machine (WEDM) to improve the accuracy of mold parts, mainly for mold inserts, ejector holes, inclined ejector holes and inclined ejectors.

• Mold frame procurement: Elimold purchases mold frames from high-quality brands to ensure that their quality meets our precision requirements. At the same time, the accuracy of the mold is guaranteed, which is also crucial for us to obtain high-precision final plastic parts. Of course, this will cost some money, but in the end you will know that it is worth it.

• Experience of mold makers: Mold making is a professional skill that requires a combination of expertise, precision, creativity and attention to detail. Elimold’s mold makers have more than 20 years of mold making experience. They have rich experience and are able to handle high-demand, high-precision and complex mold structures. They are familiar with the characteristics of metal and plastic materials and the various processes of mold processing. They are able to troubleshoot and solve problems that arise during mold making and can creatively meet design and manufacturing challenges. Experienced mold makers can reduce the risk of irreversible errors, and good mold assembly skills will affect the final quality of plastic products.

• Quality Inspection: The Elimold team will use a coordinate measuring machine (CMM) to measure all mold components with an accuracy of less than 0.01 mm in key locations. In addition, the accuracy of all electrospark machining (EDM) electrodes will be measured with a coordinate measuring machine (CMM) with an accuracy of less than 0.01 mm. This helps control mold quality and improve accuracy. This is also one of the main processes to improve the accuracy of medical plastic parts or other industrial plastic parts.

• Injection molding technology and equipment: Elimold purchased 50 new injection molding machines in 2024. The injection molding engineers have more than 20 years of industry experience and are capable of handling different medical injection molding projects. They are proficient in various plastics and their characteristics, familiar with color matching, drying methods of raw materials before molding, and have rich experience in mold temperature, injection pressure, cooling time control, and can automatically set the robot to pick up the product, and can solve various product problems, such as shrinkage, warping, dimensional control, etc. After the mold test is successful, the Elimold production team will record the molding data and prepare quality control process information, such as SOP, SIP, CP, etc., which will be used for future mass production.

Conclusion

There is always a certain degree of variation in the injection molding process, so the allowable deviation range is important so that the parts can function effectively after assembly. Therefore, injection molding tolerances are crucial when assembling products with multiple injection molded parts. When controlling and optimizing injection molding tolerances, the allowable deviation range that helps medical products function to the maximum can be determined. Common methods to achieve this goal depend largely on DFM, material selection, and process control.

Get Started with Elimold

Producing high-performance and consistent products from multiple injection molded parts comes with the goal and reduction of injection molding variations. Through part optimization, reliable and high-quality medical parts can be manufactured. Partnering with Elimold Company may be your best decision to manufacture high-quality medical plastic parts. We are a professional injection molding company that is experienced in injection molding services and has the machines and experience required to achieve this goal. Our team consists of qualified individuals who are committed to delivering high-quality medical products at the right pace.