Precision Positioning in Automotive Molds

In automotive injection mold design, to enhance the positioning accuracy during mold closing and reduce misalignment between the fixed and moving halves during the injection process, molds require robust locking and positioning mechanisms, commonly referred to as "three-level positioning."

Three-level positioning is critical for both standard molds and automotive injection molds. The design of the mold's guiding system must pay particular attention to three-level positioning, especially for high-precision automotive plastic parts. Poorly designed mold guidance and positioning can lead to issues such as improper mold movement, mold damage, misalignment between the fixed and moving halves, and dimensional mismatches (steps) on molded parts. This makes the mold's guiding system a crucial component.

Level 1 Positioning: Guide Pin Positioning

Level 1 positioning refers to the guide pin positioning, which serves as the primary positioning mechanism. It achieves alignment between the fixed and moving halves through the interaction of guide pins and bushings. The positioning accuracy depends on the machining precision of the mold base holes and the dimensional accuracy of the guide pins and bushings. Inaccurate machining of the mold base holes can cause the guide pins to seize. Additionally, guide pins are the main components that bear the weight of the mold base. During design, their strength and length must be considered; overly long or weak guide pins can lead to inaccurate positioning and seizing. Based on experience, the maximum length of guide pins should not exceed 10 times their diameter.

The functions of guide pins and bushings can be summarized into three points:

1. Accurate guidance and positioning of movable parts.

2. Support the weight of the mold.

3. Protect the mold's forming components.

The diameter of guide pins is typically selected according to the LKM standard, while non-standard mold guide pins can reference the LKM standard. The maximum diameter of round guide pins is generally limited to 80mm. The length of guide pins should extend at least 30mm above the highest surface of the mold. For molds with sliders, the guide pins should enter the bushings by at least 20mm before the inclined guide pins engage the sliders. Regular maintenance and lubrication of guide pins and bushings are essential during the injection molding process to avoid friction-related issues. Improper clamping of the mold and unevenness of the machine's front and rear plates can also cause inaccurate positioning and seizing of guide pins. In summary, Level 1 positioning is critical.

Level 2 Positioning: Mold Stop and Interlocking

Level 2 positioning involves the mold stop and the four-sided interlocking mechanism between the fixed and moving halves, primarily serving as the positioning for the mold base. Its positioning accuracy is higher than that of guide pins and bushings. The slots for wear-resistant blocks in the stops should be machined together to ensure precise alignment between the fixed and moving halves. The material for wear-resistant blocks is typically heat-treated CR12 steel, and oil grooves should be added to the friction surfaces for lubrication. Wear-resistant blocks effectively protect vulnerable insertion surfaces on the mold and are particularly important for precision molds and automotive molds. Misalignment between the fixed and moving halves can lead to wear on the mold's insertion surfaces and flash on the molded parts. Many surface scratches on plastic parts in actual production are related to poor Level 2 positioning design, which requires special attention.

Level 3 Positioning: Core Stop Positioning

Level 3 positioning refers to the stop positioning on the mold core, primarily protecting the precise alignment of the mold's insertion surfaces. The stop positioning on the mold core ensures accurate alignment between the fixed and moving core halves, effectively protecting the core's insertion surfaces while also withstanding lateral injection pressure. During design, stops should not be aligned in the same direction but should interlock to prevent the mold from tilting or slipping to one side. Stops are generally designed with angled insertion surfaces, with angles 0.5–1 degree smaller than the smallest insertion angle and textured surface angle on the mold core. This ensures effective protection of the mold core's insertion surfaces and prevents texture damage during mold opening and closing. When machining and assembling the stops, the insertion surfaces should fit tightly, with reasonable tolerances set to ensure precision. Manual fitting should be avoided, relying instead on machine tool accuracy. This is particularly important for automotive and precision molds. The height of the stops should be 5–10mm higher than the highest surface of the mold core to effectively protect the core surface.In automotive injection molds, the three levels of positioning progressively increase in accuracy, and they play a significant role in ensuring the quality of molded parts and the mold's guiding system. While other molds may also benefit from this approach, if the molded part has no insertion surfaces or textured surfaces, some positioning designs can be omitted. Otherwise, all three levels of positioning must be designed with high precision.

Types and Applications of Precision Positioning in Automotive Injection Molds

In automotive injection molds, the mold is divided into the front and rear halves, which frequently open and close. To ensure precise mold closure, precision positioning mechanisms are often added to the mold base. Let’s explore the types and applications of precision positioning in injection molds.

1. Types of Precision Positioning in Automotive Injection Molds

•Edge Locks: Suitable for medium and small automotive molds, widely used in automotive mirror, steering column, and door panel molds.

•Conical Precision Positioning Components: Suitable for small automotive molds, but less commonly used due to the risk of breakage.

•Angled Square Positioning Components: Suitable for medium and small molds, though less common in automotive molds.

•Top Locks: Suitable for medium and small molds, often used in automotive headlight and steering column molds.

•1-Degree Precision Positioning: Widely used in medium and large automotive injection molds, such as door panels, instrument panels, fenders, bumpers, etc.

1. Placement of Edge Locks and Top Locks

Typically, four sets of edge locks are added to a mold. The optimal placement is at the four middle positions, as shown in the diagram. Due to thermal expansion and contraction caused by temperature differences between the front and rear halves, placing the locks in the middle effectively prevents side burning during mold closure.

3. Placement of Conical Precision Positioning Locks If the middle positions are occupied by sliders, lifting holes, or other structures that interfere with the edge locks, the edge locks can be moved diagonally to avoid conflicts.

4. Placement of Precision Positioning Components

If there are sliders on all four sides of the mold base, leaving no space for edge locks, conical precision positioning components or angled square positioning components can be used.

5. Placement of 1-Degree Precision Positioning

For medium and large molds with four-sided enclosure, the optimal placement of 1-degree precision positioning is near the R-angle corners.