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Is it possible to achieve ultra-long stroke mold opening on a plastic injection molding machine?

2026/01/06 By le zhan

plastic injection molding machine 5-6

When you need to injection mold a large, multi-part automotive housing, or a deep, multi-cavity cosmetic container, the two halves of the mold need to move an exceptionally long distance to clear complex cores, inserts, or multi-stage ejection systems. On traditional plastic injection molding machines, you either accept limited mold geometries or purchase larger, slower machines, sacrificing production cycle time. What if a plastic injection molding machine could simultaneously achieve ultra-long mold opening strokes, millimeter-level positioning accuracy, and fast, stable platen movement without compromising production speed or reliability? This combination is entirely possible with Topstar’s Ts series toggle plastic injection molding machine.

Why are ultra-long strokes important for plastic injection molding machine?

Ultra-long mold opening strokes are crucial in a variety of applications, including deep-drawn containers, inserts with high ejector pins and overmolding, multi-stage ejection, long-stroke core pulling, and molds requiring large interlocking or multi-layer demolding. Plastic injection molding machines that support long-stroke mold opening allow engineers to design parts with complex undercuts, telescopic cores, or multi-layer structures without time-consuming secondary processing.

Specific benefits include:

Single-shot production: Reducing assembly, secondary processing, or manual post-processing by providing the necessary geometry in the mold in a single cycle.

Higher automation: Long strokes allow for safe integration of injection molding robots, insert pick-and-place devices, or in-mold labeling equipment that requires extra clearance.

Faster product changeovers: Mold maintenance and changeovers become easier and less time-consuming due to longer mold opening times and precise platen control.

However, achieving long strokes without compromising platen parallelism and stability is a major engineering challenge. Long strokes amplify deflection, place higher demands on the guiding system, and increase the mechanical work that the drive system must perform. Therefore, Topstar has developed a new diagonal toggle mechanism layout, combined with modern control and guidance technologies, to enable ultra-long mold opening and achieve stable, precise mold opening.

TS170-Injection-Molding-Machine

Achieving Ultra-Long Stroke Mold Opening with a Diagonal Hinge Layout

Toggle mechanisms are a traditional solution that uses mechanical advantage to convert small actuator movements into large platen opening and closing strokes. However, the classic linear toggle mechanism layout is typically limited by its geometry: long strokes require longer toggle links and larger platen spacing, which increases inertia and reduces stiffness. Topstar’s innovation lies in adopting a diagonal toggle mechanism layout, readjusting the link geometry to achieve ultra-long strokes while improving stiffness and providing smoother kinematic characteristics.

The main advantage of the diagonal hinge layout is higher mechanical advantage within the effective range of motion, allowing for larger opening distances without the need for oversized actuators. This diagonal geometry enables medium-sized cylinders or servo actuators to drive longer platen strokes than equivalent-sized straight-link mechanisms. Simultaneously, the machine bed and frame distribute the link loads into more rigid load paths, reducing the deflection of the toggle links.

This enables ultra-long-stroke mold opening with large platen travel and robust structural support, reducing deformation and helping maintain mold opening accuracy to less than 1 mm.

New-oblique-hinge-layout

Achieving less than 1 mm mold positioning accuracy on plastic injection molding machine

Achieving mold opening positioning accuracy of less than 1 mm at ultra-long strokes depends on controlling three mechanical factors: platen stiffness, guiding accuracy, and balanced load distribution. Ultra-long-stroke injection molding machines must be carefully designed in every aspect.

  1. Platen Design and Reinforcement

The platen must resist bending throughout its entire stroke. Topstar uses thickened platen sections with internal reinforcing ribs and an optimized box-beam geometry to increase moment of inertia without adding excessive mass. This enhances the platen’s resistance to bending during long-stroke opening.

  1. High-Precision Guiding System

As the stroke increases, the importance of guide rail design becomes increasingly critical. Topstar uses preloaded linear guides or high-preload crossed-roller bearing structures to minimize clearance. Where applicable, multi-rail structures can distribute the load and prevent tilting.

  1. Toggle and Drive Stiffness

The link bearings and pivots of the diagonal support rods utilize high-grade spherical roller bearings and hardened pins. Low-clearance link joints reduce micro-movements that would otherwise accumulate over stroke and time. Servo or hydraulic actuators are installed using rigid couplings and anti-backlash devices. The actuator support structure transmits force directly to the machine base, preventing bending of the platen assembly.

Mold Design and Considerations

Achieving ultra-long strokes in a plastic injection molding machine is only part of the solution; the mold design must fully utilize the stroke advantage while avoiding damage and maintaining production cycles. Integration and commissioning are crucial.

Mold Design:

Balanced Load Distribution: Install and support heavy core components or long lifters to distribute the load near the platen’s center, reducing the tilting force arm that can occur during long strokes.

Lifters and Core Mechanisms: Long core lifters must have anti-buckling support, guide rails, and segmented movement to avoid sudden load changes that could affect platen parallelism.

Ejection and Demolding Sequence: Employ a multi-stage ejection sequence coordinated with the platen movement to avoid sudden shifts in the center of gravity. Phased movement reduces transient loads and enables faster, smoother long-stroke cycles.

Mold Cooling and Thermal Stability: Ensure that thermal gradients do not cause differential expansion, thus reducing mold opening accuracy during long production runs.

Practical, Precise Ultra-Long Stroke Mold Opening

By systematically optimizing the injection molding machine’s mechanism geometry, structural rigidity, guiding accuracy, and drive control, Topstar TS series injection molding machines have successfully overcome the traditional technical bottleneck: “the longer the stroke, the lower the accuracy and the slower the speed.” Using a diagonal hinge layout, it achieves ultra-long mold opening distances while maintaining high rigidity, high stability, and millimeter-level positioning accuracy, enabling complex core mechanisms, multi-stage demolding, and high-automation integration to be completed stably within a single molding cycle.

Frequently Asked Questions

1. What constitutes an “ultra-long” mold opening stroke on an injection molding machine?

While there is no single numerical standard, “ultra-long” typically refers to a platen stroke significantly exceeding the standard mold clearance. This is usually several hundred millimeters – necessary for deep ejection, high inserts, or multi-layer ejection. The specific definition depends on the mold sizes commonly used in your factory.

2. How does Topstar ensure mold opening position accuracy of less than 1 mm at such long strokes?

Topstar’s approach is multi-layered: a diagonal toggle mechanism reduces link deflection; reinforced molds and multiple guide rails minimize bending; and model-based closed-loop control applies feedforward and real-time compensation to correct predictable elastic deflection.

3. Will the extra-long stroke increase my cycle time?

Not necessarily. Through optimized toggle geometry and coordinated motion control, long strokes can be achieved with minimal increase in cycle time. In many Topstar systems, optimized acceleration/deceleration profiles and integrated motion blending features enable fast opening and closing without increasing cycle time.

 

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