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Unscrewing Injection Molds Case LP | Spark Mould
13 Injection Mold Case Studies
for Plastic Threaded Parts
From standard external threads to complex auto-unscrewing
and collapsible core mechanisms, discover how we overcome tooling
challenges with precision and efficiency.
Injection molding of threaded parts is one of the core challenges in mold design. Depending on the thread's position and structural characteristics, we showcase comprehensive, customized mold solutions and practical case studies for both External and Internal Threads.
Male Thread Mold Structures: Combining Efficiency and Precision
External threads generally do not create full-circumference undercuts, making demolding relatively straightforward. Depending on product appearance requirements and parting line allowances, we primarily utilize the following two mold structures:
1
Split Cavity Mold Structure (Half-Mold):
The threads can be released simply by separating the cavities. This eliminates the need for side-action core pulling mechanisms, resulting in a highly compact mold structure. This design is exceptionally well-suited for meeting the demands of ultra-high cavitation requirements.
2
Standard Flat Mold Structure:
This structure utilizes the thread's central axis as the parting line, allowing the product to be ejected simply by separating the A and B plates. In direct contrast to the split cavity mold, forming certain hollow features with this method requires the integration of side-action core pulling mechanisms. However, for hollow components featuring dual external threads (double male ends), this structure actually provides a much simpler and more streamlined solution.
Case 1: 8-Cavity Split Cavity Mold Structure for Small Thumb Screws
Case 2: Standard Flat Mold Structure with Sliders for Threaded Quick Couplings
Internal Thread Mold Structures: Overcoming "Full-Circumference Undercuts"
Forming internal threads creates a 360-degree undercut inside the part, requiring highly specialized ejection mechanisms. We offer industry-proven solutions categorized into Auto-Unscrewing Mechanisms and Collapsible Cores.
Case 3: Mold-Opening-Force-Driven Linear Gear Mechanism for Unscrewing Thread
Case 4: Cylinder-Controlled Linear Gear Unscrew Thread Mold Mechanism
Auto-Unscrewing Mechanisms
(By Drive Type)
Different production environments and product specifications dictate the optimal power transmission method:
1
Linear Gear (Rack and Pinion) Drive
Power Source: Driven directly by the injection molding machine's opening force or by external hydraulic cylinders.
Features: Exceptional structural stability; currently one of the most widely used unscrewing methods.
2
(Hydraulic/Servo) Motor Gear Drive
Power Source: Powered entirely by external hydraulic motors or servo motors.
Features: Delivers robust power with precise control over rotational speed and turns. Ideal for long threads or high-cavitation molds.
3
Lead Screw (Rifled Nut) Drive
Power Source: Relies entirely on the linear pulling force during mold opening, converted into rotational movement via a high-pitch lead screw.
Features: Highly integrated internal mold structure requiring no external power. Perfect for short threads and compact mold layouts.
Case 5: Hydraulic-motor-driven 16-cavity automatic unscrewing mechanism.
Case 6: Mold Solutions for Plastic Parts with Dual-Stage Internal and External Threads
Case 7: Lead Screw Drive automatic unscrew thread mechanism 4-cavity
Auto-Unscrewing Mechanisms
(By Core Movement)
During the unscrewing process, the relative movement between the core and the molded part falls into two categories:
1
Retracting Threaded Core:
The threaded core rotates and retracts simultaneously, pulling away from the part smoothly. The plastic part remains completely stationary during this phase.
2
Stationary Rotating Core:
The threaded core rotates in place without retracting, utilizing the thread's pitch to "push" the part off the core. Note: When using this method, the part's ejection movement direction must be perfectly aligned with the mold's parting direction.
Case 8: The product is ejected via an automatic thread-unscrewing mechanism -1
Case 9: The product is ejected via an automatic thread-unscrewing mechanism -2
Case 10: line strainer head Mold-Combining Auto-Unscrewing with Side-Action Mechanisms
Case 11: 4-Cavity Automatic Unscrewing Mold Mechanism for FPT × FPT 90-Degree Elbows
Advanced Application: Combining Auto-Unscrewing with Side-Action Mechanisms
When a product features a closed threaded cavity, or if the side-action mechanism (slider) must pass through the threaded port, we combine these two mechanisms into a complex composite core-pulling system.
1.The side-action slider first retracts a short, safe distance to clear space for the threaded core.
2.The auto-unscrewing mechanism activates, rotating and separating the threaded core from the part.
3.Finally, the entire slider assembly is fully extracted to complete the complex internal cavity ejection.
Collapsible Cores for Internal (Female) Threads
For certain specific applications, we utilize collapsible core technology to solve internal thread ejection challenges.
1
Technical Principle & Limitations:
Since internal threads are full-circumference undercuts, a collapsible core uses a mechanical design that allows the core segments to collapse inward during ejection. This reduces the overall outer diameter, allowing the core to be pulled safely from the part without any rotation.
2
Ideal Applications:
Excellent for caps, closures, and pipe fittings with internal threads, offering extremely fast cycle times.
3
Design Limitations:
Because the collapsing mechanism requires internal physical space to function, this structure is not suitable for small-diameter threaded ports.
Case 12: 4-Cavity Collapsible Thread Core Structure for Plastic Hex Nuts
Case 13: 8-Cavity Collapsible Thread Core Structure for Plastic Hex Nuts
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