Key Design Guidelines for Plastic Injection Molded Products

1. Wall Thickness (Cavity Thickness)

• General Range: 0.80–3.00 mm for overall casings. Large products require thicker walls, while small products can use thinner walls; 1.0–2.0 mm is common for most products.

• Uniformity Requirement: Maintain uniform wall thickness as much as possible. Gradual transitions are allowed for local thickness adjustments (avoid abrupt changes) to prevent shrinkage and ensure full filling.

• Minimum Thickness: Most plastics struggle to fill cavities with thickness <0.3 mm, but soft plastics and rubber can achieve full filling at 0.2–0.3 mm.

2. Reinforcing Ribs (Ribs)

• Thickness Control: Typically 0.5–0.7 times the overall wall thickness. Thickness >0.7 times the wall thickness easily causes shrinkage.

• Draft Angle: Add a 0.5–1° draft angle for tall ribs (to reduce demolding resistance); short ribs may omit draft angles.

3. Draft Angle

• General Range: 1–5°, with 2° as the common default. Adjust based on product size, height, and shape to ensure smooth demolding without affecting functionality.

• Mold-Specific Adjustment: The draft angle of the cavity (A-side) should be 0.5° larger than that of the core (B-side) to keep the product on the core during mold opening.

• Special Areas: Draft angles are required for pillows, through holes, and shut-off surfaces, with a single-side height difference (between large and small ends) >0.1 mm.

4. Fillets (R Angles)

• Minimum Size: The smallest fillet radius (R) should be >0.3 mm, as smaller radii are difficult to machine on molds.

5. Holes

• Shape and Size: Prefer simple, regular round holes over complex shaped holes. Avoid overly small diameters or excessive depth-to-diameter ratios (thin, long mold cores are prone to breakage and deformation).

• Spacing Requirements: The distance from a hole to the product edge should be >1.5 times the hole diameter; the distance between holes should be >2 times the hole diameter to maintain structural strength.

• Molding Methods: Holes parallel to the mold opening direction use cores (insertable or extendable), shut-offs, or through holes. Holes non-parallel to the opening direction require slides or lifters. Sidewall holes should use shut-offs or through holes where possible (without affecting product use and assembly).

6. Bosses

• Draft Angle: No draft angle is needed for short bosses ejected by sleeves. Tall bosses require cross ribs (with 1–2° draft angles), and bosses themselves may need draft angles based on height.

• Fit Clearance: A 0.05–0.10 mm single-side clearance is recommended for boss-shaft or boss-boss assembly to accommodate positional errors during processing.

• Self-Tapping Screw Compatibility: The inner hole diameter of bosses for self-tapping screws should be 0.1–0.2 mm smaller than the screw diameter (e.g., φ2.60–2.80 mm for M3.0 self-tapping screws) to ensure secure locking.

7. Inserts

• Positioning: Ensure inserts are fully, accurately, and reliably positioned in the mold.

• Bonding and Sealing: Guarantee strong bonding between the insert and the molded part (insufficient overmolding thickness reduces bond strength). Prevent plastic leakage during molding.

8. Surface Textures

• Draft Angle Adjustment: Deep or dense textures increase demolding resistance, requiring larger draft angles.

9. Text

• Processability: Raised text is easier to machine (via cavity recesses), while recessed text requires protruding cores and is more difficult to manufacture.

10. Threads

• Simplification: For low-precision threads, use forced demolding-compatible structures to simplify design.

11. Support Surfaces

• Rationale: Large flat plastic surfaces are prone to warpage and difficult to machine to absolute flatness.

12. Assembly Methods

12.1 Ultrasonic Welding

• Features: Easy mold implementation but requires specialized ultrasonic equipment (increased cost); non-detachable.

• Weld Line Design: Triangular cross-section (0.30 mm wide × 0.3 mm high), with 2 mm gaps every 5–10 mm along the length.

12.2 Self-Tapping Screw Assembly

• Features: Easy mold implementation but adds assembly steps (increased cost); cumbersome to disassemble.

12.3 Snap-Fit Assembly

• Features: Complex mold processing but convenient assembly and repeatable disassembly.

• Design Notes: Avoid excessive local wall thickness at snaps; ensure mold manufacturability. Snaps should have proper fit tightness and fitting surfaces with appropriate gaps on other sides.

12.4 Boss Shaft-Hole Assembly

• Features: Easy mold processing and assembly; convenient disassembly.

• Limitation: Less secure compared to other methods.

13. Matching Ribs (Tooth Openings)

• Depth: 0.8–2.5 mm.

• Clearance and Draft Angle: 0.1 mm side clearance. Add a 1–5° draft angle (2° common) for deep ribs; no draft angle needed for shallow ribs.

• Fitting Surface: Zero clearance for the top and bottom matching surfaces.

14. Aesthetic Lines

• Width: 0.2–1.0 mm, adjusted based on overall product size.

15. Surface Treatment Methods

16. Common Metal Materials

17. Rust Prevention for Metal Materials