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:

G = (V₁-V₂)²/(2S×g)

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

Factory Direct Custom Packaging & Prototypes

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