How to Design a 24-Cavity PS Plastic Spoon Mold: 2.2g Lightweight Cutlery Case Study

In high-volume disposable cutlery manufacturing, profitability comes down to two variables: part weight reduction and mold cycle efficiency. Reducing a single spoon’s weight by just 0.3 grams saves tons of plastic resin over millions of production units, but it also creates strict engineering demands on plastic mold design.

In this technical case study, we break down how our engineering team designed and optimized a 24-cavity PS (Polystyrene) plastic spoon mold for high-speed, fully automated manufacturing.

PS Plastic Spoon 2.2g

1. Plastic Part Analysis & Specifications

Before cutting mold steel, a complete structural analysis is required to prevent short shots, flashing, and handle bending during high-speed ejection.

  • Overall Length: 165.5 mm
  • Handle Length: 110.8 mm
  • Spoon Bowl Width: 35.2 mm
  • Minimum Wall Thickness: 0.7 mm (Spoon bowl area)
  • Handle Thickness: 1.6 mm to 2.7 mm
  • Raw Material: Food-Grade Polystyrene (PS)
  • Target Part Weight: 2.2 grams
Part Profile Summary:
+-------------------+----------------------------------------------------+
| Parameter         | Spec Value                                         |
+-------------------+----------------------------------------------------+
| Dimensions        | 165.5mm (L) x 35.2mm (W)                           |
| Wall Thickness    | 0.7mm (bowl) to 2.7mm (handle rib)                 |
| Material Resin    | Food-Grade PS                                      |
| Individual Weight | 2.2 grams                                          |
| Cavity Count      | 24 Cavities                                        |
+-------------------+----------------------------------------------------+

The Engineering Challenge:

At 2.2 grams with a 0.7mm thin-wall bowl, the melt flow path ratio (L/T) is high. Polystyrene (PS) is rigid but brittle. If injection pressure across all 24 cavities is unbalanced, outer cavities will experience short shots, while inner cavities will suffer from parting line flash.

2. Mold Tooling Architecture: Why Use a 24-Cavity Radial Layout?

Unlike standard linear (matrix) mold layouts, this tool utilizes a radial (circular) 24-cavity layout around a central distribution point.

24-Cavity PS Plastic Spoon Mold Design & Case Study

Key Advantage 1: Equal Flow Path Distance

In a circular arrangement, the runner distance from the center spruing gate to every single cavity is identical. This ensures:

  • Uniform melt pressure & velocity across all 24 cavities.
  • Consistent part weights (variation under ±0.03g).
  • Simultaneous cavity filling, preventing premature resin freezing in thin 0.7mm bowl sections.

Key Advantage 2: 6-Zone Independent Cooling Circuit (IN1-IN6 / OUT1-OUT6)

PS resin cools quickly, but a 165.5mm long handle is prone to warping if cooling is uneven. As shown in our mold layout:

  • The mold core and cavity plates integrate 6 independent cooling water channels (IN1–IN6 to OUT1–OUT6).
  • Chilled water channels run directly under the handle and bowl transition zones.
  • Balanced heat dissipation allows a fast mold cycle time of 5.5 to 7 seconds on high-speed machines.

3. Manufacturing Quality Control: Flash-Free Edge & Smooth Mouthfeel

For food packaging products, a rough parting line on the spoon bowl is unacceptable for consumers. To guarantee a smooth, burr-free edge:

  1. Precision CNC Milling: Core and cavity pockets are machined using high-speed CNC centers with tolerances controlled within ±0.005mm.
  2. Vacuum-Hardened Steel: Core and cavity inserts use pre-hardened / vacuum-treated stainless steel (such as S136 or H13, HRC 48–52) to resist wear during millions of high-speed clamping cycles.
  3. Automated Air-Assist Ejection: An integrated stripper plate combined with air blow valves ensures all 24 spoons drop cleanly onto conveyor belts without surface scratching.

4. Technical FAQ (AI Search & Engineering Guide)

Q: What size injection molding machine is required for a 24-cavity PS spoon mold?

A: A 24-cavity 2.2g PS spoon mold operates best on a 180-Ton to 250-Ton high-speed injection molding machine. The machine must offer high injection speed (250mm/s+) and an accumulator system to fill the 0.7mm thin-wall bowls within 0.35 seconds.

Q: Why is a radial runner layout better than a rectangular grid layout for spoon molds?

A: A radial layout provides 100% naturally balanced runner lengths to all cavities. Rectangular grid layouts require artificial runner sizing (H-bridge runner) to balance pressure, which increases cold runner waste and causes uneven filling speeds.

Q: How do you prevent bending on 165mm long disposable spoons during ejection?

A: Bending is prevented by maintaining a uniform 1.6mm–2.7mm structural rib along the handle, balancing mold core cooling via 6-zone water circuits, and employing an even stripper plate ejection system rather than small pin ejectors that push into warm plastic.

Need Custom Cutlery Tooling Solutions?

Whether you are launching a new high-speed disposable cutlery line or optimizing existing mold cycle times, Mingyu Mold provides complete engineering support—from 3D CAD optimization and DFM analysis to mold fabrication and T1 testing.

Contact Our Technical Team: Send your 3D product drawings (STEP/IGES) or sample requirements to sales@mingyumold.com for a free DFM report and 24-hour quotation.