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Injection Mold Tooling: Comprehensive Guide

Injection mold tooling describes the molds used in the injection molding process to provide cavities within which polymers are molded. These molds consist of various movable elements including cavity and core plates that form the mold-space.

 

Injection mold tooling is crucial in that it defines the quality, precision and rapidity/cost of the molding process. Effective tooling ensures consistent product dimensions, reduces defects and benefits manufacturing speed and cost.

 

Key aspects of injection mold tooling include material selection, mold design, cooling systems, gate/runners, ejection and maintenance. Considerations such as complexity of the part, tolerance requirements, production volume, and material flow properties drive tooling design, to ensure optimal performance and longevity.

Injection mold tools are large, complex and expensive but highly cost effective

Tooling Design

Careful tooling design is crucial to injection molding outcomes, as it affects every aspect of the molding process. Well-designed tooling ensures consistent part production, low defects and high capacity tools.

Key factors to consider include:

  • Part complexity: Complex geometries require intricate mold designs and increased moving parts.
 
  • Material selection: Materials have varying flow and cooling characteristics that must be accommodated.
 
  • Part line: Part line placement affects molding appearance and functionality.
 
  • Cooling system: Efficient cooling reduces cycle-time and improves part quality/consistency.
 
  • Tolerances and surface finish: Tooling quality greatly affects molding precision and aesthetics.
 

Good quality tooling design delivers parts that are precise and have minimal defects, consistent quality and optimized productivity, meeting commercial demands of the industry and customer expectations.

Tooling Materials

Commonly used tooling materials include

  • Hardened steel: Maximum durability and wear-resistance, suitable for high-volume production. Requires refinishing after hardening and careful heat treatment to avoid distortion.
 
  • Pre-hardened steel: Requires spark machining processes such as wire cut and electrical discharge machining (EDM), increasing manufacture costs but avoiding heat-treatment risks after machining.
 
  • Stainless steel: Typically used for acidic-melt polymers such as POM/acetal.
 
  • Aluminum: Lightweight and faster to machine, suitable for prototyping and low-volume production. Lower durability and cost.
 
The choice of tooling material directly affects the mold’s lifespan, maintenance expectations and part precision. High-quality materials like hardened steel ensure longer-lasting, higher-performance molds. Aluminum is more suited for shorter runs and prototyping.
 

Runner System

Runners in injection mold tooling are the channels that guide/direct molten charge from the tooling injection point (the sprue bush) to the mold cavities. They are designed to ensure an even, laminar and efficient distribution of the material to the cavities.

Two types of runner systems should be considered

  • Cold runners: These are runners that fill as the tool is charged whose content then cools and is ejected with the parts, to be trimmed as waste. This approach is low cost and slower to operate, being better suited to low-moderate volumes and single cavity tools with minimal runner requirements.
 
  • Hot runners: This type integrates electrical heaters into the runner channels to keep the polymer molten between shots. This type of runner reduces waste and allows faster production, where volumes justify the extra cost. Some materials benefit from hot runner setups.

Ejector Pins

Ejector pins in injection mold tooling push out or eject the molded parts from the mold cavity. They are typically driven by the ejector plate and are pushed to demold the part, as an integrated function of the tool opening.

 

Careful ejector pin design and placement are key to ensuring smooth part ejection without causing damage or deformation and avoidance of ejector tell-tales in strategic cosmetic locations. Design considerations include pin size, number and placement relative to the part geometry to avoid cosmetic defects or part distortion during ejection. Ejector pins can have complex profiles at their tips, to conform to the part. They can also be embodied as a part line ejector plate or stripper plate that is used where ejection is less readily actioned by pins.

 

Effective ejector design is imperative in optimizing tool life, reducing maintenance costs and delivering acceptable part quality/aesthetics. Poorly designed ejection can stress-mark the product and cause rapid scuffing wear as parts drag..

Mold Build and Lead Time

The mold build process in injection molding involves five key steps

  • Design: The mold design stage is where quality and effectiveness are initiated – and where costs can be controlled considerably.
 
  • Material selection: The selection of materials often flows directly from the art, volume and cost requirements.
 
  • Machining: CNC and EDM machining of mold components, including cavities, cores and inserts, is time consuming and costly. However, this is central to tool quality, part line accuracy, blanking (sealing at closure) and part precision.
 
  • Assembly: Assembly of mold components and integration of features like cooling channels and ejector systems is critically important and requires patient expertise. Plate functionality and setup accuracy must be closely evaluated.
 
  • Tool trialing: With the tool put up onto a molding machine, tooling operational parameters must be trialed and optimized – melt temperature, tool temperature, injection speed/time, dwell time, cooling etc will require careful tuning.
 

Lead time in mold production is influenced by

  • Complexity: More complex molds require longer machining and assembly times, with component counts rising into the hundreds of moving parts.
 
  • Material availability: Delays in obtaining mold materials can impact lead time, particularly for exotic requirements or larger tools.
 
  • Design changes: Revisions or modifications to the mold design always blow-out the lead time. A well managed design process must work to avoid this with aggressive prototyping/validation procedures.
 
  • Capacity and workload: Mold manufacturer’s who deliver the best tooling outcomes are always in demand, so scheduling may require compromises.
 

Strategies to reduce tooling lead time, without sacrificing quality are

  • Efficient design: Streamlining mold design to minimize complexity is a great schedule improver, as is picking the most capable and experienced tool designer.
 
  • Material management: Ensuring timely availability of materials by, for example, ordering main blocks (bolsters) as soon as the cavity layouts have settled.
 
  • Parallel processing: Overlapping tasks like design, machining, and assembly. This can involve risk if it moves too fast, but the schedule savings can be significant.
 
  • Advanced manufacturing technologies: Utilizing rapid prototyping (metal 3D printing) and advanced machining techniques can accelerate production, typically without compromising quality if the supplier capabilities are sufficient.

Volume Production

Volume of parts planned for production is a critical driver of many design and manufacturing choices in injection mold tooling. The economies of scale are significant in their effect on per-unit costs, tooling life expectancy needs and meeting high demand efficiently. High volume demand equips the optimization of the production processes to minimize cycle times and drive towards consistent part quality over longer runs. Lower volumes dictate economies in tooling durability and production rate, but typically not in part quality.

Key considerations that relate to production volume include

  • Cycle time: Optimizing cycle times can maximize throughput and reduce manufacturing costs, but the effect on tooling costs can be high.
 
  • Multi-cavity tools: Using multi-cavity molds will greatly increase productivity per cycle – but tooling structure, runners and overall size/cost must increase.
 
  • Automation: Implementing automated systems for mold loading, part ejection, and quality inspection can increase productivity and reduce labor costs – but not for free.
 
  • Material selection: Opting for materials that balance cost-effectiveness with performance and durability is a way to moderate costs or improve the product, and a balance must be struck in this.
 
  • Tool maintenance: Ensuring regular maintenance will prevent downtime and maintain production efficiency. Higher cost tooling may allow longer periods/volume between interventions.
 

Challenges consequent on higher volumes include initial setup costs, accelerated tool wear, and maintaining part consistency. Higher-quality tooling, optimizing mold design for efficiency, adopting lean manufacturing principles and leveraging advanced technologies like robotics and real-time monitoring will enhance production reliability and minimize costs per unit.

Quality Injection Molding

Injection mold tooling quality plays a central role in ensuring high-quality parts by influencing precision, repeatability, surface finish and part stability. It serves in defining approaches to the mold cavity, cooling system, runners and gating, heavily impacting the molding production rate and final part quality.

Factors that influence the quality of molded parts are typically

  • Mold design: Precision in mold design and finesses in flow control/fill reduce defects like warping or sink marks.
 
  • Material selection: Choosing the optimum material for strength, durability, and finish will typically lift part quality and precision.
 
  • Process parameters: Optimizing parameters like temperature, pressure, and injection speed will directly influence part quality – balancing productivity benefits against quality is a live decision enacted at the molding machine in real time.
 
  • Tool maintenance: Regular upkeep is imperative in maintaining consistent performance, part line quality, precision and tool life.
 

Strategies to ensure quality of injected parts include

  • Design optimization: Utilizing experienced designers and good simulation software will improve part geometry.
 
  • Material testing: Evaluating material properties to match application requirements, while maintaining part quality is a decision matrix with various degrees of freedom.
 
  • Process monitoring: Implementing real-time monitoring and statistical monitoring over the longer terms enables adjustment of parameters for intra and inter batch part-consistency.

Prototype Tooling

Prototype tooling refers to the creation of molds specifically designed for fast trial and limited volume purposes. Its primary aim is to produce sample and early production parts quickly and cost-effectively. This can rapidly validate part design, product function and manufacturability prior to full-scale production.

Prototype tooling has various advantages and limitations. The advantages are typically considered to be

  • Speed: Prototype tooling should provide rapid production of prototype and early production parts for product and process validation and pre-or-early-production.
 
  • Cost: Lower initial investment is required, compared with full production molds, though overall tooling costs will be higher due to duplication.
 
  • Flexibility: The cost benefit in prototype tooling is typically the ability to iterate and refine designs based on early production results, without risking high-cost production tooling changes.
 

Prototype tools will not withstand high-volume production, so they must be phased out in a balanced handover to mass production.  They may also limit the choice of materials compared to mass production molds.

Cost Considerations

Cost-effective injection mold tooling balances CAPEX with part-quality production, to achieve competitive pricing and faster ROI. The options to alter this balance are too design optimization Material economics and standardization with off the shelf parts

 

Well-planned tooling design and material selection can greatly impact overall production costs by reducing scrap rates, improving cycle times and minimizing maintenance requirements.

Future Trends and Innovations

Near-term trends in injection mold tooling include additive manufacturing (metal 3D printing) for tooling inserts and cavities, simulation software and digital twins for predicting mold behavior and IoT sensors in molds enabling real-time monitoring of parameters, for faster tuning.

 

Various steps are revolutionizing tooling design and production by improving precision, reducing lead times and lowering costs. Digital design tools and simulations reduce iterations by validating mold performance earlier. Automation streamlines manufacturing processes, increases consistency, and enhances quality control.

 

Integration of AI empowers predictive maintenance and process optimization. Materials innovations create new material types and grades. Progress in sustainability will drive the adoption of eco-friendly materials and processes. Overall, these developments promise to make injection mold tooling more efficient, versatile, and environmentally friendly

Jon
Jon
Jon is a dynamic and accomplished professional with a rich and diverse background. He is an engineer, scientist, team leader, and writer with expertise in several fields. His educational background includes degrees in Mechanical Engineering and Smart Materials. With a career spanning over 30 years, Jon has worked in various sectors such as robotics, audio technology, marine instruments, machine tools, advanced sensors, and medical devices. His professional journey also includes experiences in oil and gas exploration and a stint as a high school teacher. Jon is actively involved in the growth of technology businesses and currently leads a family investment office. In addition to his business pursuits, he is a writer who shares his knowledge on engineering topics. Balancing his professional achievements, Jon is also a dedicated father to a young child. His story is a remarkable blend of passion, versatility, and a constant pursuit of new challenges.

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