Have you ever wondered what makes your injection molding process so smooth and consistent? Behind every perfectly ejected plastic part lies a crucial component that often goes unnoticed—die springs. These hardworking mechanical heroes are the backbone of efficient mold operations, ensuring your ejector pins return precisely to their starting position, cycle after cycle, millions of times over.

In this comprehensive guide, we’ll dive deep into the world of injection mold springs, exploring everything from international standards to troubleshooting common failures. Whether you’re a mold designer, production engineer, or procurement specialist, understanding spring selection and maintenance can save you thousands of dollars in downtime and mold damage.

Why Springs Matter in Modern Injection Molding

Let’s start with a simple question: What happens when your die springs fail? The answer isn’t pretty. Ejector pins get stuck in the extended position, parts remain trapped in the mold, production stops, and you’re looking at expensive emergency repairs. In fact, studies show that spring-related failures account for approximately 15-20% of unplanned mold downtime in manufacturing facilities.

But here’s the good news: most spring failures are preventable. With proper selection, installation, and maintenance, your mold springs can deliver millions of reliable cycles. The key is understanding how these components work and what they need to perform optimally.

The economic impact is significant. A single hour of downtime in a high-volume molding operation can cost anywhere from $500 to $5,000, depending on your production scale. When you multiply that by the number of potential spring-related stoppages, the importance of getting this right becomes crystal clear.

Understanding Die Springs in Injection Mold Applications

What Are Die Springs and How Do They Work?

Unlike ordinary compression springs you might find in everyday applications, die springs are engineered for extreme duty. They’re manufactured using rectangular wire instead of round wire, which gives them a significant advantage: approximately 30% more load-bearing capacity in the same space.

Think of it this way—if a regular compression spring is like a standard car tire, a die spring is like a heavy-duty truck tire. Both serve the same basic purpose, but one is built to handle much more demanding conditions.

Here’s what makes die springs special:

  • Temperature Resistance: Die springs can withstand temperatures up to 200°C (392°F), which is crucial in injection molding where heat transfer from the mold is constant
  • Superior Load Capacity: The rectangular wire cross-section provides more material in a compact footprint
  • Longer Service Life: Made from hardened alloy steel, these springs resist fatigue failure even after millions of cycles
  • Precise Load Characteristics: Manufacturing tolerances typically within ±10% ensure consistent performance

At Cixi Dili Spring Co., Ltd., we’ve been manufacturing precision die springs since 1995, and we’ve seen firsthand how quality materials and manufacturing processes make the difference between a spring that lasts one year versus one that lasts five years or more.

The Ejector Pin Return System Explained

Let me walk you through what actually happens inside your mold during each cycle. Understanding this process will help you appreciate why spring selection is so critical.

Step 1: Mold Closing and Injection
When the mold closes, the ejector pins are in their retracted position, held back by the return springs. The springs are under compression—what we call “preload”—typically 10-15mm of deflection. This preload ensures the pins stay firmly retracted during injection.

Step 2: Cooling and Part Formation
As the plastic cools and solidifies, the springs maintain constant pressure, keeping the ejector plate assembly stable. This is where spring quality matters—inferior springs may lose load over time due to heat transfer from the mold.

Step 3: Mold Opening and Ejection
Here’s where the magic happens. The machine’s ejector system pushes the ejector plate forward, compressing the springs even further. The ejector pins push the molded part out of the cavity. In our production facility, we’ve captured this process on video, and you can see how smoothly the ejection occurs when springs are properly sized and maintained.

Step 4: Spring Return
Once the ejector system pressure releases, the compressed springs instantly pull the ejector plate back to its starting position. This return action must be fast enough to complete before the mold closes again, yet controlled enough to avoid impact damage. The spring force must overcome friction, the weight of the ejector assembly, and any residual adhesion.

Watch the complete ejection and spring return cycle in action. This video from our production facility shows how die springs instantly return the ejector plate to its starting position after part removal, demonstrating the precise, controlled motion that quality springs provide.

In the images from our facility, you can see a blue mold base assembly showing the die spring installation. Notice the blue-colored springs visible through the mold opening—these are medium-duty springs, the most commonly used type in injection molding applications.

Types and Standards: JIS, ISO, and ANSI Mold Springs

One of the most confusing aspects of specifying mold springs is navigating the different international standards. Don’t worry—I’ll break this down in plain language.

Color-Coded Load Classifications

Manufacturers use a color-coding system to help you quickly identify spring load ratings. However, here’s the catch: the color codes differ between standards! Let’s focus on the most common system used globally:

Yellow Springs – Extra Light Duty
These are the lightest duty springs, offering the most flexibility in compression—up to 50% maximum safe compression (40% for 1M cycles). Ideal for delicate part ejection where you need gentle force but significant stroke capability. You won’t see these often in heavy production molds, but they’re perfect for thin-walled parts, electronics components, and applications requiring high deflection with lower force.

Blue Springs – Light Duty (Most Common)
If you look at any molding facility, you’ll see that 70-80% of JIS die springs installed are blue. These offer an excellent balance of force and durability for standard injection mold applications. Maximum safe compression is 40% of free length, though for high-volume production targeting 1,000,000 cycles, limit compression to 32% for optimal service life.

Red Springs – Medium Duty
When you need more force than blue springs provide, red springs are your answer. Maximum safe compression is 32% (25.6% for 1M cycles). Common in larger molds or applications with higher friction ejection. Red springs provide significantly more force than blue springs of the same size while accepting lower compression ratios.

Green Springs – Heavy Duty
These are for demanding applications: large part ejection, high-friction geometries, or molds with extensive ejector pin layouts. Green springs provide substantial force but require conservative compression limits—maximum 24% safe compression (19.2% for 1M cycles). This lower compression limit is due to the higher stress levels in the heavier wire used in green springs.

Brown Springs – Extra Heavy Duty
The powerhouses of the spring world. If you’re working with die-casting molds or extremely large injection molds, brown springs provide maximum force capacity. However, they have the most restrictive compression limits—maximum 20% safe compression (16% for 1M cycles). These springs require careful design to ensure adequate free length for your required stroke while staying within these strict limits.

International Standards Comparison

Now let’s talk about the three major spring standards you’ll encounter:

JIS B 5012 (Japanese Industrial Standard)
This is the most widely adopted standard globally, particularly in Asia and North America. JIS springs use the color-coding system described above and are known for consistent quality and availability. At Dili Spring, we manufacture JIS-compliant springs to exact specifications, ensuring perfect interchangeability with major mold component brands.

ISO 10243 (International/European Standard)
Common in European mold shops, ISO springs are designated as 1S, 2S, 3S, 4S, and 5S, with the number indicating load capacity. They’re dimensionally similar to JIS springs but may have slightly different load specifications. Always verify compatibility when mixing standards.

ANSI/DME Standard (American Standard)
Popular in North American mold building, particularly with US die springs from DME and Progressive Components. The color-coding is similar but not identical to JIS. DME medium-duty blue springs are often specified as the baseline for American mold designs.

Pro Tip: Never mix different standards in the same mold assembly unless you’ve verified load compatibility. Using three JIS blue springs and one ISO 2S spring might seem equivalent, but slight load variations can cause uneven ejection and premature wear.

Critical Design Considerations for Mold Springs

Compression Rate and Preload Requirements

Here’s a critical rule established by JIS (Japanese Industrial Standard) spring specifications: compression limits vary by spring load class and are indicated by the color-coding system. This isn’t arbitrary—it’s engineering data derived from decades of testing and real-world application.

JIS Standard Maximum Safe Compression Limits by Color:

  • Yellow Springs (Extra Light Duty): Maximum safe compression 50% of free length
  • Blue Springs (Light Duty): Maximum safe compression 40% of free length
  • Red Springs (Medium Duty): Maximum safe compression 32% of free length
  • Green Springs (Heavy Duty): Maximum safe compression 24% of free length
  • Brown Springs (Extra Heavy Duty): Maximum safe compression 20% of free length

Important: Service Life vs. Compression Rate
While the above figures represent absolute maximum safe compression, achieving long service life requires operating at lower compression rates. For 1,000,000 cycle life (standard for high-volume production), the recommended compression limits are:

  • Yellow Springs: Maximum 40% compression for 300000 cycles
  • Blue Springs: Maximum 32% compression for 300000 cycles
  • Red Springs: Maximum 25.6% compression for 300000 cycles
  • Green Springs: Maximum 19.2% compression for 300000 cycles
  • Brown Springs: Maximum 16% compression for 300000 cycles

These limits are established by the JIS B 5012 standard based on material stress characteristics and fatigue testing. Exceeding these compression ratios causes stress levels that accelerate fatigue failure. The spring may work fine for a few thousand cycles, then suddenly break, often taking out ejector pins, damaging the mold base, and contaminating your parts with metal fragments.

Let’s do a quick calculation example using the most common spring type:

Example: You’re selecting a blue JIS spring (light duty) with a free length of 100mm for a high-volume production mold requiring 1,000,000 cycles.

  • Absolute maximum safe compression per JIS: 100mm × 0.40 = 40mm (blue spring absolute limit)
  • Recommended maximum for 1M cycles: 100mm × 0.32 = 32mm (for long service life)
  • Recommended preload: 10-15mm
  • Available working stroke for 1M cycle life: 32mm – 15mm = 17mm maximum

If your ejector stroke is 25mm, you have several options:

  • Option 1: Use a longer blue spring (125mm free length): 25mm ÷ 125mm = 20% compression ✓ (well within 32% limit for 1M cycles)
  • Option 2: Switch to yellow springs which allow up to 40% compression for 1M cycles: 25mm ÷ 100mm = 25% ✓ (within limit, but verify force is adequate)
  • Option 3: If you only need 300,000 cycles, blue springs at 25% compression are acceptable (limit is 43% for 300K cycles)
  • Option 4: Use multiple springs to distribute the load and reduce individual spring stroke

Why Preload Matters
Preload is the initial compression applied when the mold is fully closed. This serves several critical functions:

  1. Prevents Shock Loading: Without preload, the ejector plate would impact the spring suddenly, causing stress spikes that lead to early failure
  2. Maintains Pin Position: The preload force keeps ejector pins firmly seated during injection, preventing flash or part damage
  3. Compensates for Wear: As mold components wear slightly over time, preload ensures the spring remains engaged

During spring manufacturing at our facility, we test each spring batch to verify load characteristics at various compression points, ensuring they’ll perform reliably within the 10-35% working range.

Spring Buckling Prevention

Imagine pushing down on a tall, thin pencil standing on end. What happens? It bends sideways rather than compressing straight down. Springs can do the same thing—and when they buckle, failure is imminent.

The engineering guideline is simple: If the free length is more than four times the diameter, provide guidance.

For example:

  • Spring outside diameter: 25mm
  • Critical length: 25mm × 4 = 100mm
  • If your spring free length is 125mm, you need guidance

Guidance Solutions:

1. Spring Pockets
A bore in the mold base that the spring sits inside. The pocket diameter should allow for spring expansion (springs get wider as they compress) but prevent sideways movement. A good rule of thumb: pocket diameter = spring outside diameter + 2-3mm.

2. Guide Rods
A rod that passes through the center of the spring. This is common in larger springs or where space doesn’t permit deep pockets. The rod must be hard and smooth to prevent wear.

3. Spring Cups or Retainers
These components capture the spring ends and provide lateral support. They’re particularly useful in retrofit situations where you’re adding springs to an existing mold.

Close-up view of die spring installation in injection mold showing blue compression springs, ejector plate assembly, and precision machined spring pockets
Proper spring pocket design in mold base assembly. The machined pockets provide guidance to prevent buckling while allowing for diameter expansion during compression.

In the mold assembly shown in our facility images, you’ll notice the springs are installed in carefully machined pockets within the blue mold base. This pocket design prevents buckling even under maximum compression.

Installation Best Practices

Let’s talk about the practical aspects of getting springs into your mold correctly. I’ve seen countless spring failures that could have been prevented with proper installation.

Hole Sizing for Diameter Expansion
Here’s something many people don’t realize: springs increase in diameter as they compress. If your spring pocket is too tight, the spring will rub against the wall during compression, creating friction, heat, and wear. Eventually, the spring coating wears off, corrosion begins, and failure follows.

The math is straightforward:

  • Measure the spring’s maximum diameter at full compression (manufacturer data)
  • Add 2-3mm clearance
  • Machine your pocket to this diameter
  • Ensure the pocket depth is at least equal to the compressed spring height

Spring Cup Assembly Techniques
When using spring cups or retainers:

  1. Ensure the cup is seated squarely against the mounting surface
  2. Use the correct fastener torque—over-tightening can distort the cup
  3. Verify the spring sits concentrically in the cup before assembly
  4. Apply a light coating of mold grease to the cup interior to reduce friction

Alignment and Positioning
Misaligned springs create uneven forces on the ejector plate, leading to binding, wear, and potential mold damage. Use these alignment checks:

  • Verify all springs are the same height (free length) using a caliper
  • Check that spring pockets are perpendicular to the mounting surface
  • Ensure ejector plate moves smoothly through the entire stroke before final assembly
  • Test ejection force balance—the plate should lift evenly without tilting

After proper heat treatment and surface finishing, our springs undergo rigorous quality inspection to ensure they’ll install and perform correctly in your molds.

Common Problems and Troubleshooting Solutions

Spring Failure Causes

Let me share some real-world failure scenarios I’ve encountered over three decades in the spring manufacturing industry.

Problem #1: Compression Beyond JIS Limits
Symptom: Spring breaks suddenly, often after months of apparently normal operation, or fails to reach expected cycle life.
Cause: The spring was compressed beyond its JIS-specified limit during part of the cycle, perhaps due to mold adjustments or process changes. For example, a blue spring compressed beyond 40% (absolute maximum) or beyond 32% when 1M cycle life is required; a red spring beyond 32% maximum or beyond 25.6% for 1M cycles; a green spring beyond 24% maximum.
Solution: Measure actual spring compression at maximum ejector stroke. Use indicator pins or mark the ejector rod to verify travel. If compression exceeds the JIS limit for your spring color and target life, you have several options:

(1) install longer springs of the same type to reduce compression percentage,

(2) switch to a lighter-duty spring color that allows higher compression (e.g., blue to yellow, red to blue),

(3) accept shorter service life if cycle count requirements are lower (e.g., 300K vs 1M cycles), or

(4) add additional springs to share the load and reduce individual spring stroke.

Problem #2: Heat Transfer Issues
Symptom: Springs lose tension over time, ejector pins return slowly or incompletely.
Cause: Excessive heat from the mold (mold temperatures above 80°C for extended periods) degrades spring temper.
Solution: Increase cooling in the ejector side of the mold. Consider heat shields or insulating washers between hot mold components and springs. For very hot molds, specify springs with enhanced heat treatment.

Problem #3: Binding and Wear
Symptom: Springs develop shiny wear spots, coating flakes off, eventually the spring breaks.
Cause: Spring pocket too small, allowing the expanding spring to rub against the pocket walls.
Solution: Measure the compressed spring diameter (typically 3-5% larger than free diameter). Enlarge pockets if necessary. The hole should feel loose when the compressed spring is test-fit.

Performance Issues You Can Fix

Issue: Loss of Load Over Time
All springs experience some load loss over their lifetime—it’s normal. However, excessive loss (more than 15% in the first year) indicates a problem.

Diagnostic steps:

  1. Measure the free length of suspect springs—if they’ve shortened significantly, they’ve taken a “set” from over-compression
  2. Check mold temperatures—sustained temps above 100°C will accelerate load loss
  3. Verify spring specification—are you using the correct load class for your application?

Solution: Replace springs that have lost more than 10% of original load. Review compression ratios and consider upgrading to the next load class (blue to red, red to green) to reduce stress levels.

Issue: Uneven Ejection Problems
The part ejects on one side before the other, causing scuffing or gate problems.

Diagnostic steps:

  1. Verify all springs are the same specification (don’t mix brands or load classes)
  2. Measure free length of each spring—variation more than 0.5mm causes uneven forces
  3. Check for binding in ejector pins or wear in guide pins

Solution: Replace springs as a complete set, not individually. Even springs from the same manufacturer can vary slightly batch-to-batch. When you order springs from Cixi Dili, we provide matched sets from the same production lot for critical applications.

Issue: Mold Damage from Spring Malfunction
This is the nightmare scenario—a broken spring causes ejector pin jamming, damaged cores, or cracked mold plates.

Prevention is everything:

  • Implement preventive spring replacement based on cycle counts (typically every 1-2 million cycles)
  • During mold maintenance, inspect springs for cracks, corrosion, or deformation
  • Keep detailed records of spring installations and replacement dates
  • Never reuse springs when rebuilding or modifying a mold—they’re inexpensive compared to mold damage

Preventive Maintenance Tips

An ounce of prevention is worth a pound of cure—especially when that cure involves emergency mold repairs.

Inspection Intervals:

  • Daily: Visual inspection for obvious damage or missing springs
  • Weekly: Check ejection speed and consistency
  • Monthly: Measure ejector return force (should be consistent from month to month)
  • Quarterly: Remove and inspect springs for wear, corrosion, or load loss
  • Annually: Consider replacing springs in high-cycle molds (over 500,000 cycles/year)

Replacement Indicators:
Replace springs immediately if you observe:

  • Any visible cracks or breaks
  • More than 5% reduction in free length
  • Coating worn off exposing bare metal
  • Corrosion or rust spots
  • Permanent deformation (spring doesn’t return to original shape)

Record Keeping Best Practices:
Create a spring log for each mold including:

  • Spring specifications (standard, size, color/load class)
  • Installation date and cycle counter reading
  • Inspection dates and findings
  • Replacement dates and reasons
  • Any mold modifications affecting springs

This data becomes invaluable for predicting spring life in similar molds and optimizing your spare parts inventory.

Modern Trends: Are Springs Still Necessary in 2025?

This might surprise you, but there’s an ongoing debate in the molding industry: do we even need springs anymore?

Some modern injection molding machines offer adjustable ejector force control through servo-driven or hydraulic ejection systems. The theory is that you can control both the ejection stroke and return stroke electronically, eliminating springs entirely.

The Case Against Springs:

  • Eliminates spring maintenance and replacement costs
  • Prevents mold damage from broken springs
  • Allows variable ejection force for different processes
  • Reduces mold complexity

The Case For Springs (Still Strong):

  • Springs provide fail-safe return force independent of machine settings
  • Faster cycle times—springs return instantly when released
  • Works with any molding machine, not just modern equipment
  • Lower initial mold cost
  • Proven reliability over decades of use

My Professional Opinion?
After 30 years in this industry, I believe springs still have a vital role. Yes, spring-less designs work in specific applications, particularly with newer machines and simpler part geometries. However, for complex molds, high-volume production, and situations where mold portability matters (moving molds between different machines), springs remain the most reliable solution.

The key is using quality springs properly specified and maintained. When springs fail, it’s almost always due to poor selection, installation, or maintenance—not because springs are inherently unreliable.

At Cixi Dili Spring Co., Ltd., we’re investing in advanced spring manufacturing technology not because we’re ignoring industry trends, but because we believe quality springs will remain essential for the foreseeable future.

Choosing the Right Mold Spring Manufacturer

Not all springs are created equal. You can buy dirt-cheap springs from unknown suppliers, or you can invest in quality components that protect your expensive mold assets. Here’s what to look for:

Material Quality: The Foundation of Reliability
Premium die springs use hardened alloy steel—typically chrome silicon alloy steel (ASTM A401) or chrome vanadium alloy steel (ASTM A877). These materials provide:

  • High tensile strength (typically 1800-2000 MPa)
  • Excellent fatigue resistance
  • Thermal stability up to 200°C
  • Consistent performance over millions of cycles

Cheap springs often use inferior steel alloys that may look identical but fail prematurely under production conditions.

Tolerance Standards: Consistency Matters
Quality manufacturers maintain load variation within ±10% across the entire batch. This means if you buy 20 springs, they’ll all perform nearly identically. Lower-grade springs can vary by ±20% or more, causing the uneven ejection problems we discussed earlier.

Dimensional tolerances are equally important:

  • Free length: ±1% or better
  • Outside diameter: ±0.2mm or better
  • Squareness of ends: <0.5° deviation

Corrosion Resistance: Long-Term Protection
Die springs should feature E-coat (electrophoretic coating) or powder coating for superior corrosion resistance. This is especially critical in humid environments or when using water-based mold release agents.

E-coating provides uniform coverage, even in tight spaces between coils, offering better protection than spray painting or zinc plating.

Why Cixi Dili Spring Co., Ltd. Stands Out

Since our founding in 1995, Cixi Dili Spring Co., Ltd. has focused on one mission: delivering precision springs that exceed international standards. Here’s what sets us apart:

Three Decades of Manufacturing Excellence
With 30 years of continuous operation, we’ve refined our manufacturing processes to eliminate the common defects that plague cheaper springs. Our spring winding technology ensures consistent coil pitch and wire tension, critical factors in spring longevity.

Multi-Standard Compliance
We manufacture springs compliant with JIS B 5012, ISO 10243, and ANSI standards, giving you flexibility regardless of your mold design’s origin. Whether you need JIS standard die springs or US standard die springs, we maintain inventory for fast delivery.

Custom Solutions from Drawings or Samples
Have a unique application? We excel at custom spring manufacturing. Send us your drawing, a sample spring, or even just your requirements, and our engineering team will design the optimal solution. We’ve created custom springs for:

  • Oversized molds requiring non-standard spring dimensions
  • High-temperature applications needing special heat treatment
  • Corrosive environments requiring exotic coatings
  • Space-constrained designs needing maximum force in minimum volume

Complete Product Line
Beyond die springs, we manufacture the complete range of industrial springs:

Rigorous Quality Control
Every spring batch undergoes comprehensive testing:

  • Load testing at multiple compression points
  • Dimensional inspection using calibrated equipment
  • Surface quality examination
  • Material certification verification
  • Cycle life testing for critical applications

Our quality management system ensures traceability from raw material to finished product, giving you confidence in every spring we ship.

Global Export Quality
We export to customers worldwide, including demanding markets in North America, Europe, and Asia. Our products meet international safety and quality standards, and we provide full documentation for your quality assurance requirements.

Conclusion: Maximizing Mold Efficiency Through Proper Spring Selection

Let’s bring this all together. We’ve covered a lot of ground, from basic spring function to complex troubleshooting scenarios. Here are the key takeaways:

1. Springs Are Critical, Not Commodity Components
Don’t treat die springs as generic parts. The few dollars you save buying cheap springs will cost you thousands in downtime when they fail. Invest in quality springs from established manufacturers.

2. Follow JIS Compression Limits by Spring Color and Target Life
Understand that each spring color has two critical limits: (1) Absolute maximum safe compression: Yellow 50%, Blue 40%, Red 32%, Green 24%, Brown 20%; and (2) Compression limits for long service life (1M cycles): Yellow 40%, Blue 32%, Red 25.6%, Green 19.2%, Brown 16%. Always design for your target cycle life, not just the absolute maximum. If your application requires more stroke, use longer springs, choose a lighter-duty color that allows higher compression (like yellow vs. blue), or add additional springs. Following these standards will eliminate 80% of potential spring failures.

3. Standardize on One Spring System
Choose JIS, ISO, or ANSI and stick with it across your facility. This simplifies inventory management, ensures compatibility, and makes troubleshooting easier.

4. Implement Preventive Maintenance
Regular inspection and proactive replacement based on cycle counts will prevent surprise failures and protect your molds. The cost of scheduled spring replacement is trivial compared to emergency repairs.

5. Work with Experienced Suppliers
Partner with manufacturers who understand your applications and can provide technical support. At Cixi Dili Spring Co., Ltd., we’re not just selling springs—we’re helping you optimize your mold performance.

Whether you’re designing a new mold, troubleshooting ejection problems, or setting up a maintenance program, I hope this guide has given you the knowledge and confidence to make better decisions about your mold springs.

Remember, behind every successful production run are hundreds of small components working flawlessly together. Die springs might be small and often invisible, but they play an enormous role in your molding success.

Ready to Upgrade Your Mold Spring Quality?

Contact Cixi Dili Spring Co., Ltd. for expert guidance on your spring applications:

📧 Email: [email protected]
📱 WhatsApp: +86 13586942004

Our engineering team is ready to help you select the perfect springs for your application, troubleshoot existing problems, or design custom solutions for unique challenges. With 30 years of experience and millions of springs in service worldwide, we’re your partner for mold spring excellence.

Frequently Asked Questions (FAQs)

Q1: How often should I replace die springs in my injection molds?

A: The replacement interval depends on several factors, but here’s a practical guideline: for high-cycle production molds (running 24/7), consider replacing springs every 1-2 million cycles or annually, whichever comes first. For lower-volume molds, inspection-based replacement is more economical—replace springs when you observe any of these signs: visible wear or corrosion, more than 5% loss of free length, coating damage exposing bare metal, or any cracks or deformation. Always replace springs as a complete set, not individually, to maintain consistent ejection forces. Keep cycle counter records for each mold to track spring lifespan and predict future replacement needs. Many of our customers at Dili Spring implement a preventive maintenance schedule where springs are automatically replaced during major mold servicing, typically every 12-18 months for production molds.

Q2: Can I mix different brands or standards of die springs in the same mold?

A: This is strongly discouraged, even if the springs appear similar. Different manufacturers may have slight variations in load characteristics, material properties, and dimensional tolerances—even when conforming to the same standard (JIS, ISO, or ANSI). Mixing brands can result in uneven ejection forces, with some springs compressing more than others, leading to tilted ejector plates, binding, and premature wear. If you absolutely must mix brands, at minimum verify that:

(1) all springs have identical free lengths (within 0.5mm),

(2) load rates are within 5% of each other at your working compression, and

(3) you perform thorough ejection testing before production. However, the best practice is to replace all springs with a matched set from a single manufacturer and production batch. At Cixi Dili, we specifically provide matched spring sets for critical applications to eliminate this concern.

Q3: Why do my die springs keep breaking, and how can I prevent it?

A: Spring breakage typically results from one of four root causes:

(1) Over-compression—the springs are being compressed beyond 35% of free length, either during normal operation or due to mold interference. Solution: Measure actual compression at maximum stroke and install longer springs if needed.

(2) Buckling—springs with high length-to-diameter ratios (over 4:1) that lack proper guidance. Solution: Install spring pockets, guide rods, or spring cups to prevent lateral movement.

(3) Heat damage—excessive heat transfer from hot molds degrades spring temper over time. Solution: Improve cooling, add heat shields, or use springs with enhanced heat treatment for high-temperature applications.

(4) Poor quality springs—inferior materials or manufacturing defects. Solution: Source springs from reputable manufacturers like Cixi Dili Spring Co., Ltd. that use hardened alloy steel and maintain strict quality control. Additionally, ensure springs aren’t being side-loaded due to misaligned ejector systems, and verify that spring pockets are sized correctly to allow for diameter expansion during compression.

Q4: What’s the difference between JIS, ISO, and ANSI die springs, and which should I use?

A: While all three standards serve the same basic purpose, they differ in dimensions, load specifications, and color-coding systems. JIS (Japanese Industrial Standard B 5012) is the most widely adopted globally, especially in Asia and North America, using a color code where blue typically indicates medium duty—the most common type. ISO 10243 (European standard) uses numerical designations (1S, 2S, 3S, etc.) and is prevalent in European mold shops. ANSI/DME (American standard) is popular in North American mold building and uses similar color coding to JIS but with some load variations. For new mold designs, I recommend JIS standards because of their global acceptance, extensive availability, and consistent manufacturing quality across suppliers. However, if you’re working with existing molds or have a shop full of molds built to a specific standard, maintain consistency with that system. The most important factor isn’t which standard you choose, but that you stick with one standard throughout your facility to simplify inventory management and ensure compatibility. At Dili Spring, we manufacture to all three standards, giving you flexibility regardless of your choice.

Q5: How do I calculate the correct spring force and quantity needed for my mold’s ejector system?

A: This requires considering three key factors:

(1) Weight of the ejector assembly—measure or calculate the total mass of ejector plates, pins, and attachments, then multiply by gravitational acceleration (9.8 m/s²) to get the weight force.

(2) Friction forces—estimate friction between ejector pins and mold cavities plus friction from guide pins; this typically adds 30-50% to the required force.

(3) Part adhesion—some part geometries create significant adhesion to cores that must be overcome; this is application-specific but can be substantial. A simplified calculation: Total Required Spring Force = (Ejector Weight + Friction Force + Adhesion Force) × Safety Factor, where safety factor is typically 1.5-2.0. Once you have the total force requirement, divide by the number of springs you plan to install, considering space constraints. Then select springs where your working compression (typically 25-30% of free length) produces the needed force per spring. Important: Verify that maximum compression during ejection doesn’t exceed 35% of free length. If calculations seem complex, contact our engineering team at Dili Spring—we regularly assist customers with spring selection calculations and can optimize your design for reliability and cost-effectiveness.