Tooling Material Selection

Micro injection molding has emerged as a pivotal manufacturing technique for producing highly precise and consistent intricate components, particularly in medical device, life science, and drug delivery industries. One of the fundamental aspects influencing the success of micro injection molding is the selection of appropriate tooling materials. PDC identifies the critical factors guiding tooling material selection in this technical post and provides an overview of materials suitable for micro injection molding applications. 

Factors Influencing Tooling Material Selection: 

  1. Mechanical Properties: The mechanical properties of the tooling material, including hardness, toughness, and wear resistance, are paramount. The material must withstand the high pressures and repeated cycles of micro injection molding without succumbing to deformation or premature wear. 
  2. Thermal Stability: Micro injection molding involves subjecting the tooling to elevated temperatures during the injection and cooling phases. Hence, the selected material should exhibit excellent thermal stability to prevent thermal degradation and maintain dimensional accuracy over prolonged production runs. 
  3. Surface Finish: The surface finish of the tooling directly impacts the quality and appearance of the molded parts. Tooling materials with superior polishability and corrosion resistance are preferred to achieve smooth, defect-free surfaces on the molded components. 
  4. Chemical Compatibility: Certain applications, particularly in the medical and pharmaceutical sectors, require compatibility with various chemicals, sterilization methods, and aggressive molding resins. The tooling material must resist chemical attack and maintain its integrity in harsh operating environments. 
  5. Cost and Lead Time: Material cost, availability, and ease of machining also influence the selection process. Balancing performance requirements with cost-effectiveness is crucial to optimizing the overall manufacturing process. 

Overview of Materials Suitable for Micro Injection Molding Tooling: 

  1. Tool Steel: Tool steels, such as P20, H13, and S7, are widely used in micro injection molding due to their excellent combination of hardness, toughness, and machinability. These materials offer good thermal conductivity and wear resistance, making them suitable for high-volume production. 
  2. Stainless Steel: Stainless steel alloys, such as 420 and 440C, are preferred for applications requiring corrosion resistance and high polishability. These materials exhibit good dimensional stability and can withstand prolonged exposure to aggressive molding resins and sterilization methods. 
  3. Powdered Metal: Powdered metals such as CPM S30V and CPM S90V are specialty steels formed by a sintering process for extremely precise control of the grain structure of the material. This allows for the machining of micro features so small that the consistency of the grain structure can have an impact. These materials also exhibit extremely high durability and corrosion resistance, making them excellent candidates for high wear or abrasive applications. 
  4. Aluminum: Aluminum alloys, including 7075 and 6061, are valued for their lightweight properties and high thermal conductivity. While not as hard as steel, aluminum tooling offers faster heat dissipation and shorter cycle times, making it ideal for prototyping and low-volume production. 
  5. Copper Alloy: Copper alloys, such as Ampcoloy, are renowned for their exceptional thermal conductivity while maintaining a safe work environment with the absence of Beryllium. These materials are well-suited for applications requiring rapid heat transfer, such as micro molding of high-temperature materials or small features prone to overheating. 

Conclusion: In micro injection molding, the choice of tooling material significantly influences product quality, production efficiency, and overall manufacturing costs. By carefully considering the critical factors discussed above and selecting the most suitable material for each application, manufacturers can optimize their processes and achieve consistent success in producing precision-engineered components. As technology advances and new materials emerge, continuous evaluation and adaptation of tooling material selection strategies will be essential to stay at the forefront of innovation in micro injection molding. 

Mastery in Precision Molding – Insights from Our Expertise:

Serving medical markets, we are particularly concerned with corrosion and contaminants in our molds at PDC. Our production tools are built with 420 stainless steel mold bases and hardened 420 stainless steel inserts by default. Specific tooling features that require specialty materials are carefully evaluated for wear condition, hardness differential to mating components, and corrosion resistance, and if necessary, are protected with plating or coating such as nickel, nickel-PTFE, or Diamond-Like Coating (DLC).