Key Points for Lifter Stroke Design in Mold Engineering

Key Points for Lifter Stroke Design in Mold Engineering

When a standard lifter cannot fully clear a product’s undercut due to remaining interference between the lifter and the product’s rib area during horizontal movement, a drop-down lifter (ejector-actuated lifter) structure can be considered.

1. Application Scenario:

Suitable for products with undercuts in both the ejection direction and along the parting line. In such cases, the lifter cannot be fully withdrawn in either horizontal (H) or vertical (V) directions relative to the product. Instead, it must move along an inclined path (Direction P), as shown in Figure 1.

Figure 1: Undercut Analysis of the Product

In such cases, a drop-down lifter (ejector-actuated lifter) structure can be considered.

Figure 2: Drop-down Lifter (Ejector-Actuated Lifter) Structure

2. Structural Design:

The drop-down lifter structure is shown in Figures 2 and 3 (only the larger lifter with a lifter pin is illustrated; smaller lifters without pins can be simplified):

Figure 3: Drop-down Lifter (Ejector-Actuated Lifter) Structure

3. Stroke Calculation:

Based on motion analysis, using the fixed base as the reference, the lifter block (connected to the ejector plate and ejector retainer plate, with its guiding surface aligned with the product’s movement direction) and the lifter slide (connected to the lifter pin or lifter) exhibit the following triangular relationship in their motion (as shown in Figure 4):

Figure 4: Geometric Model of the Drop-down Lifter

From the diagram, the designer can determine in advance:

• The horizontal stroke of the lifter (S)

• The sliding angle of the lifter (Y)

The lifter sliding stroke can then be calculated as:

S1 = S / sin(Y)When the designer further defines:

• The lifter angle (X)

The lifter ejection stroke is derived as:

H = S1 × cos(Y) + S / tan(X)Where:

• S: Horizontal stroke of the lifter

• S1: Sliding stroke of the lifter (distance the lifter slides along the lifter block’s inclined surface)

• X: Lifter angle

• Y: Lifter sliding angle

4. Design Considerations:

1. Y = Y1 – Ensure no undercut occurs during the lifter’s sliding along the lifter block’s guide surface.

2. S ≥ K + 3mm – Provide sufficient stroke with a safety margin.

3. L ≥ S1 + 3mm – Prevent interference between the lifter slide and the ejector plate during movement.

4. H1 ≥ H + 5mm – Avoid interference between the lifter spacer block and the B plate.

5. Provide adequate clearance for water line fittings when cooling lines are present.

6. All other requirements remain the same as for standard lifters.