In injection molding, the projected area is a crucial parameter that affects machine selection, clamping force, and mold design. It refers to the two-dimensional footprint of the molded part as viewed from the direction of the mold’s closing force. Understanding how to calculate the projected area in injection molding ensures that the molding machine operates efficiently and prevents defects such as flash and short shots.

Understanding Projected Area and Its Importance

The projected area plays a key role in determining the clamping force required during injection molding. When molten plastic is injected into the mold cavity, it exerts pressure on the mold’s surfaces. If the clamping force is insufficient, the mold may separate slightly, causing defects. The projected area helps in selecting a machine with adequate clamping force to maintain proper mold closure.

Additionally, the projected area influences mold design, cavity layout, and cooling efficiency. A larger area increases the force needed to keep the mold shut, impacting production costs and machine selection.

Methods to Calculate Projected Area

The projected area is calculated based on the largest outline of the part, as seen from the mold closing direction. For simple shapes, basic geometric formulas are used:

Rectangular part: Area = Length × Width

Circular part: Area = π × (Radius)²

For complex geometries, the part is divided into basic shapes, and their areas are summed. If the part contains cutouts or holes, their areas must be subtracted from the total projected area.

Example Calculation

Consider a injection molded plastic part with an 80 mm × 50 mm rectangular footprint and two circular cutouts, each with a diameter of 10 mm.

Calculate the rectangle's area:

80×50=400080 \times 50 = 400080×50=4000 mm²

Calculate the area of one circular cutout:

π×(10/2)2=78.54\pi \times (10/2)^2 = 78.54π×(10/2)2=78.54 mm²

Calculate the total cutout area:

2×78.54=157.082 \times 78.54 = 157.082×78.54=157.08 mm²

Determine the final projected area:

4000−157.08=3842.924000 - 157.08 = 3842.924000−157.08=3842.92 mm²

Conclusion

Calculating the projected area in injection molding is essential for machine selection, mold design, and quality control. It ensures that the mold remains closed under pressure, preventing defects and improving production efficiency. By accurately determining the projected area, manufacturers can optimize their molding processes and reduce production issues.