Cold Runner vs Hot Runner Molds: How to Choose the Right Injection Molding System

For companies operating in the polycarbonate injection molding and ABS injection molding space, selecting the right mold setup is a crucial decision that impacts part quality, process efficiency, and production costs. A key choice is whether to use a cold runner or hot runner mold system. While bothmethods deliver plastic resin into cavities to form parts, they have distinct differences in their configurations and capabilities.

By comparing factors like upfront costs, production efficiency, part quality, flexibility, and applications, manufacturers can determine if a cold runner or hot runner system makes the most sense for their needs. Weighing the pros and cons of each option allows you to select an optimal injection molding setup aligned with your specific product goals, production environment, and business objectives. click for more

Cold Runner Mold Systems

A cold runner system is the more common and traditional method of multi-cavity ABS injection molding. This setup uses an open channel called a sprue to deliver plastic resin from the injection nozzle into the cavities.

Key attributes of cold runner molds include:

Simpler and More Affordable Initial Setup

• Cold runners have a relatively straightforward design with an open sprue feeding multiple part cavities. This makes initial fabrication simpler and more cost effective.
• Tooling is less complex than hot runner systems. Maintenance costs are also lower over the mold's lifetime.
• The simpler cold runner setup allows molds to be produced faster. This enables a quicker transition into full production.

Higher Scrap Rates During Operation

• After each cycle, the sprue and runners solidify, attaching to parts as scrap material that must be removed through degating.
• The scrap plastic adds waste and additional handling requirements that drive up operational costs over time.

Risk of Variations Between Parts

• As plastic flows through a cold runner into multiple cavities, variations in fill time, pressure, and temperature can occur.
• This may result in inconsistencies in part quality, dimensions, appearance, or performance across cavities.
• Balancing the runner system is critical to minimize discrepancies between parts produced in different cavities.

Frequent Purging Required During Color Changes

• With different colored resins flowing through a shared runner system, extensive purging is essential when changing colors to avoid contaminating future parts.
• Significant material waste and production downtime results from frequent color changeovers.

Limited Ability to Balance Filling For Optimal Quality

• The open cold sprue fills the cavities sequentially. This makes balancing fill rates and injection pressure difficult.
• Imbalanced filling can lead to part defects, dimensional variations, warpage, and sinks/voids.
• Overall, part quality is dependent on runner balancing expertise and process experience.

Better Suited for Lower Volume Production

• The added scrap, changeover times, and mold maintenance requirements are more easily absorbed in lower volume production scenarios.
• For higher volume production, hot runner systems often deliver better efficiency and part consistency.

Hot Runner Mold Systems

Hot runner molds use heated delivery channels to keep plastic melted as it flows directly into individual part cavities. This eliminates solid scrap sprues/runners and provides better consistency.

Key features of hot runner injection molding include:

Higher Initial Tooling Cost and Complexity

• Hot runners require complex heated manifold systems tailored to the mold and resin. This increases design, fabrication, testing, and validation time.
• The advanced tooling and control technology raises initial mold costs significantly over a cold runner.

No Scrap Sprue or Runners During Operation

• With plastic staying molten in heated delivery channels, no scrap is created during the injection process. This eliminates secondary trimming/degating steps.
• Lack of scrap reduces wasted material, handling, and downtime costs over the production run.

Improved Consistency Across Multiple Cavities

• In hot runners, each individual cavity is fed by a dedicated nozzle, eliminating variations between parts.
• This allows better control of fill rates, pressure, temperature, and cooling for consistent high quality output.

Quick Color Change Capability

• With no open runners to contaminate, purging requirements are minimized for color changes. This allows much faster changeovers.
• Scrap and downtime are reduced during color adjustments, improving flexibility and efficiency.

Balanced Filling For Superior Part Quality

• Dedicated nozzles filling each cavity simultaneously under precise control allows ideal fill rates and pressure profiles.
• This balances packing, minimizes stresses, and improves dimensional consistency. Result is high quality, consistent parts across cavities.

Higher Output Volumes For Maximum Efficiency

• The scrap reduction, fast changeovers, and consistency make hot runners ideal for higher volume production scenarios.
• In low to mid-range volumes, the added hot runner costs may not justify investment over a cold runner.

Key Differences Between Cold Runners and Hot Runners

Selecting Between Cold Runner vs Hot Runner Molds

Choosing between a cold runner vs hot runner system depends heavily on your specific production environment, product needs, volumes, and business objectives.

When selecting injection molding setup, key factors to consider include:

• Part size - Smaller parts cool faster, favoring cold runners. Larger parts benefit from hot runners.
• Annual volume - Higher volumes amortize hot runner costs over more parts. Lower volumes suit cold runners.
• Accuracy/consistency needs - Tighter tolerances and consistency require hot runners.
• Material used - Certain resins like PVC perform better in hot runners.
• Part complexity - More complex geometries and thin walls favor hot runner control.
• Color change frequency - Frequent color changes support hot runners.
• Expected lifetime - Long production runs favor hot runners. Short runs suit cold runners.
• Budget - Initial cost is lower for cold systems, but operational costs are lower for hot runners long-term in high volume scenarios.

Carefully weighing these factors and priorities will lead you to the optimal mold setup for your specific manufacturing needs and business objectives.

Leveraging the Right Injection Molding System

Determining whether to implement cold runner or hot runner technology requires a close analysis of your production environment, needs and business goals. While hot runners offer efficiency and quality gains, they also require higher initial investment which may not make sense for some low or mid-volume scenarios.

By realistically assessing your specific needs around volumes, changeovers, part requirements, budgets, and capabilities, processors can select the ideal injection molding system. Choosing the right setup from the outset prevents wasted time and cost implementing a system mismatched to your operations. With an injection molding system closely aligned to your situation, you can achieve high performance, quality, and value.