Inner Tray Structure Design
Step-by-step guidance on structural support and custom internals.
🏗️ Basic Structural Categories
📐 Flat Insert
Structure:A flat base on which the product rests directly
Suitable Products:Books, tablets, photo frames and other flat items
Design Notes:
- • Base bearing calculation: σ = F/A ≤ [σ]
- • Edge protection: corner radius ≥2 mm
- • Anti-slip treatment: surface roughness Ra 1.6-3.2 μm
- • Thickness: 5-20 mm depending on product weight
🕳️ Recessed Insert
Structure:A recess shaped to the product, which sits inside it
Suitable Products:Phones, cosmetics, craft items and other regular geometries
Design Parameters:
- • Fit clearance: 0.5-2 mm per side
- • Recess depth: 60-80% of product height
- • Draft angle: 1-3° (for injection molding)
- • Radii: inner corner R ≥1 mm, outer corner R ≥0.5 mm
🔲 Compartmented Insert
Structure:Multiple separate cavities that stop products colliding
Suitable Products:Spirits, cosmetic sets, electronic accessories
Structural Calculation:
- • Divider thickness: t = √(3FL²/2Ebh³)
- • Number of compartments: n = √(box area / single-item footprint)
- • Spacing: maximum product dimension + 2 × safety clearance
🎐 Suspension Insert
Structure:The product is suspended in the center, clear on all sides
Suitable Products:Precision instruments, fragile glassware, optical components
Design Principles:
- • Vibration transmissibility: T = 1/√[(1-r²)² + (2ζr)²]
- • Suspension frequency: fn = (1/2π)√(k/m)
- • Damping ratio: ζ = c/(2√mk)
- • Material choice: high-damping material with loss factor η > 0.1
⚙️ Manufacturing Processes
🔧 Die-Cut Insert
Process:Flat material formed by die cutting and creasing
Materials:Corrugated board, EVA foam, EPE foam
Design Rules:
- • Crease depth: 50-70% of material thickness
- • Fold radius: ≥2× material thickness
- • Tab design: insertion depth ≥10 mm, insertion force 5-15 N
- • Tolerance: ±0.5 mm (standard die cutting), ±0.2 mm (precision die cutting)
💉 Injection-Molded Insert
Process:Melted plastic pellets injected into a mold
Materials:ABS, PC, PP, PE and other engineering plastics
Mold Design:
- • Parting line: at the largest cross-section or wherever ejection is easiest
- • Gating: choose between pin, side and submarine gates
- • Cooling: cooling time t = s²/(π²α) × ln(4/π² × ΔT₁/ΔT₂)
- • Ejection: combinations of ejector pins, stripper plates and air ejection
🌡️ Thermoformed Insert
Process:Thermoplastic sheet heated to soften, then vacuum formed
Materials:PET, PVC, PS, PP and other thermoplastics
Process Parameters:
- • Forming temperature: softening point + 20-40°C
- • Vacuum: -0.08 to -0.095 MPa
- • Draw depth: ≤50× material thickness
- • Wall thickness: thinnest at the top, medium on the sides, thickest at the base
🔥 Compression-Molded Insert
Process:Material formed and cured under heat and pressure
Materials:Molded pulp, thermosets, composites
Process Control:
- • Temperature: 180-220°C (pulp), 140-180°C (plastics)
- • Pressure: 2-8 MPa
- • Cycle time: 3-15 minutes
- • Cure check: gel content >85%
⚡ Classification by Function
🛡️ Cushioning Inserts
Design Principle:
Material Requirements:
- • Compressive strength: 0.05-0.5 MPa
- • Energy absorption: 0.5-5.0 J/cm³
- • Resilience: ≥40%
Structural Optimization:
- • Graded cushioning: soft surface, firm middle, soft base
- • Honeycomb structure: raises cushioning efficiency by 30-50%
- • Wave profile: increases deformation stroke
⚡ Conductive / Antistatic Inserts
Technical Targets:
- • Surface resistance: 10⁶-10⁹ Ω/sq (antistatic grade)
- • Volume resistivity: 10⁴-10⁸ Ω·cm
- • Static decay time:<2 s
- • Triboelectric voltage:<100V
Material Modification:
- • Conductive fillers: carbon black, carbon fiber, metal powder
- • Loading: 2-15% (by mass)
- • Dispersion: high-shear mixing, ultrasonic dispersion
🌿 Freshness-Preserving Inserts
How It Works:
- • Desiccants: silica gel, molecular sieve, quicklime
- • Oxygen scavengers: iron-based, enzyme-based, vitamin C based
- • Antimicrobials: silver ions, titanium dioxide, chitosan
- • Atmosphere control: porous films, selectively permeable membranes
Performance:
- • Moisture capacity: 10-300% RH
- • Oxygen scavenging rate: 0.1-50 ml/day
- • Antimicrobial rate: >99% (E. coli, Staphylococcus aureus)
- • Breathability: 0.1-1000 ml/(m²·day·atm)
✨ Presentation Inserts
Visual Design:
- • Golden ratio: aspect ratio 1:0.618
- • Color pairing: 60°-120° apart on the color wheel
- • Surface gloss: 20-80 GU at 60°
- • Texture: roughness Ra adjustable from 0.1 to 10 μm
Ergonomics:
- • Easy handling: finger clearance ≥15 mm
- • Viewing angle: optimal at 15-30°
- • Stable center of gravity: CoG height<1/3 of total height
- • Tactile feel: Shore A 20-60° (comfortable to touch)
🎯 Special Structure Case Studies
📚 Multi-Tier Stacked Structure
Use Cases:Jewelry boxes, cosmetic sets, tool cases
Design Notes:
- • Load calculation: σ = P/(A×n), where n is the number of tiers
- • Positioning accuracy: inter-tier misalignment<0.5mm
- • Ventilation: Ø6-10 mm vent holes on each tier
- • Opening mechanism: hinges, slides, magnetic location
📖 Flip-Lid Structure
Use Cases:Laptops, premium gifts, precision instruments
Mechanical Design:
- • Hinge choice: torque hinges hold an angle, damped hinges open slowly
- • Opening angle: adjustable from 90° to 180°
- • Support strength: load capacity when open ≥1.5× product weight
- • Latching: push, twist or magnetic latches
📤 Sliding / Drawer Structure
Use Cases:Drawer packaging, display boxes, storage boxes
Slide Design:
- • Sliding resistance: μN = 0.1-0.3 × product weight
- • Travel: 0.8-1.2× product length
- • End stops: mechanical stops, spring detents
- • Load capacity: ≥2× product weight as a safety factor
🔄 Foldable Structure
Use Cases:Temporary packaging, exhibition materials, seasonal products
Folding Mechanism:
- • Folding ratio: stored volume / in-use volume ≤1:3
- • Folding moment: M = F × L × cosθ
- • Elastic recovery: residual deformation<5%
- • Cycle life: ≥1000 fold/unfold cycles
🔢 Engineering Calculations for Structural Design
Load-Bearing Strength
Bending stress:
σ = M/(W×S)
M: bending moment (N·mm)
W: section modulus (mm³)
S: safety factor (1.5-3.0)
Shear stress:
τ = Q×S/(I×t)
Q: shear force (N)
S: first moment of area (mm³)
I: moment of inertia (mm⁴)
t: section thickness (mm)
Vibration Response Analysis
Natural frequency:
fn = (1/2π)√(k/m)
Magnification factor:
β = 1/√[(1-r²)² + (2ζr)²]
Transmissibility:
T = √[(1+(2ζr)²)]/[(1-r²)² + (2ζr)²]
Thermal Stress
Thermal stress:
σth = E×α×ΔT/(1-μ)
E: Young's modulus (MPa)
α: coefficient of linear expansion (1/°C)
ΔT: temperature difference (°C)
μ: Poisson's ratio
⚠️ Key Parameter Ranges:
• E: 0.1-200 GPa
• α: 1-200×10⁻⁶/°C
• μ: 0.1-0.5
🔍 Quality Control and Inspection Standards
Dimensional Accuracy
Measuring Tools
• Vernier caliper (±0.02 mm), micrometer (±0.001 mm), CMM (±0.001 mm)
Tolerance Grades
• IT12-IT16 (general accuracy), IT8-IT11 (higher accuracy)
Inspection Frequency
• First-article inspection, in-process checks (every 2 hours), final inspection
Performance Test Methods
Compression Test
• Standard: GB/T 8168-2008
• Specimen size: 50 × 50 × 25 mm
• Conditions: 2 mm/min compression speed, 50% compression
• Metrics: compressive strength, compression set
Drop Test
• Standard: GB/T 4857.5-1992
• Drop height: 760 mm (general products), 1200 mm (rugged products)
• Drop orientation: face, edge and corner
• Pass criteria: no product damage and no cracking of the insert
Vibration Test
• Standard: GB/T 4857.7-2005
• Frequency range: 5-200 Hz
• Acceleration: 1-10 g; duration: 30-120 minutes
• Sweep type: sine sweep, random vibration
Appearance Standards
Surface Defects
• Scratches: length<10 mm, depth <0.1 mm
• Bubbles: diameter<2 mm, count <5 per dm²
• Color difference: ΔE<3 (CIE Lab color space)
• Contamination: no visible stains, fingerprints or dust
Geometry
• Flatness: ≤0.5 mm/100 mm
• Squareness: ≤1°
• Symmetry: ≤1 mm
• Roundness: ≤0.2 mm
💡 Practical Selection Advice
Cost-Sensitive Products
- • First choice:Die cutting, compression molding
- • Materials:Corrugated board, EPE foam
- • Traits:Low cost, mature processes, well-developed supply chain
- • Best for:High-volume, standardized products
Precision-Protection Products
- • First choice:Injection molding, precision die cutting
- • Materials:EVA foam, engineering plastics
- • Traits:High accuracy with excellent protection
- • Best for:Electronics and precision instruments
Premium Display Products
- • First choice:Thermoforming, precision injection molding
- • Materials:Clear PET, premium EVA
- • Traits:Beautiful appearance with transparent presentation
- • Best for:Cosmetics, luxury goods, gifts
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