Rubber prototypes—crafted from materials like silicone, TPE, TPU, and natural rubber—are critical for validating product functions like elasticity, sealing, and slip resistance. Unlike plastic or metal prototypes, their production requires specialized mold-making and molding processes to leverage rubber’s unique flexible properties. This article breaks down the full process from demand analysis to final testing, with comparisons, technical tips, and real-world examples to help you avoid common pitfalls and create high-quality rubber prototypes.
1. Pre-Production: Define Requirements & Plan Design
Before starting fabrication, clarify testing goals and design parameters to ensure the prototype aligns with your needs. This stage lays the foundation for material selection and process choice.
1.1 Clarify Core Requirements
Rubber prototypes serve three key validation purposes—focus on these to guide your design:
| Requirement Category | Key Test Goals | Real-World Example |
| Functional Validation | Test elasticity (e.g., “Can the waterproof ring bounce back after compression?”), sealing (e.g., “Does it prevent water leakage?”), and slip resistance (e.g., “Does the grip stay secure when wet?”). | A phone manufacturer tests a silicone waterproof ring prototype to ensure it seals the charging port during 30-minute water submersion. |
| Material Property Testing | Verify temperature resistance (e.g., “Will it withstand -30°C to 150°C for automotive use?”), wear resistance (e.g., “Does the tire tread avoid tearing?”), and hardness (30°–70° Shore). | An outdoor gear brand tests a TPE grip prototype to confirm it retains flexibility after 1,000 hours of UV exposure. |
| Structural Compatibility | Ensure rubber parts assemble with metal/plastic components (e.g., “Does the rubber slot fit the plastic housing?”) and optimize thickness/chamfers to prevent deformation. | A medical device team adjusts the thickness of a silicone tube prototype from 1mm to 1.5mm to avoid kinking when connected to a plastic connector. |
1.2 Design 3D Models with Rubber-Specific Rules
Use CAD software (SolidWorks, ProE, UG) to create a digital model, focusing on parameters unique to rubber:
| Design Parameter | Requirements & Tips | Reason |
| Shrinkage Rate | Account for rubber’s natural shrinkage (1.02–1.05%: silicone = 1.03%, polyurethane = 1.02%). | Prevents dimensional errors—e.g., a 100mm waterproof ring will shrink to 97mm if using silicone; model it as 103mm initially. |
| Thickness & Chamfers | Keep thickness 0.5–5mm (too thin = easy tearing; too thick = slow curing). Add 0.5–1mm chamfers to edges. | A silicone shock pad prototype with 0.8mm chamfers avoids cracking when compressed, unlike a sharp-edged version that breaks after 50 presses. |
| Anti-Slip Patterns & Holes | Mark anti-slip textures (e.g., grid patterns for grips) and assembly holes (e.g., 2mm diameter for screws) with clear coordinates. | A power tool handle prototype with 0.5mm-deep grid patterns passes slip tests—users report 40% less hand fatigue than a smooth-surface version. |
1.3 Split Complex Parts (If Needed)
For curved or thin-walled rubber parts (e.g., a U-shaped sealing strip), split the 3D model into sections. This simplifies mold machining and prevents deformation during demolding. For example:
- A curved silicone earbud prototype is split into “ear tip” and “body” sections—each fits into a smaller mold, reducing the risk of air bubbles compared to a single large mold.
2. Mold Making: Choose the Right Method for Your Batch & Precision
Rubber prototypes require custom molds—select between CNC-machined and 3D-printed molds based on precision needs and production volume.
| Mold Type | Process Details | Advantages | Disadvantages | Ideal For |
| CNC Machined Mold | Use CNC to engrave steel or aluminum blocks; polish the surface to Ra0.8–Ra1.6 to reduce demolding friction. | High precision (±0.05mm), reusable (500+ cycles), suitable for hard rubbers like EPDM. | High cost (\(500–\)2,000 per mold), slow lead time (3–5 days). | Small batches (10–100 units) of high-precision parts (e.g., medical device seals). |
| 3D Printed Mold | Print resin (SLA) or nylon (SLS) molds; post-process with sanding to smooth surfaces. | Fast lead time (1–2 days), low cost (\(100–\)300 per mold), easy to modify for complex shapes. | Low durability (20–50 cycles), limited to soft rubbers like liquid silicone. | Single or small batches (1–10 units) of complex parts (e.g., irregular-shaped TPU overlays). |
Key Tip: For prototyping, start with a 3D-printed mold if you need to test 1–5 units quickly. Switch to a CNC mold if you require 20+ identical prototypes (e.g., for user testing).
3. Molding Process: Select Based on Rubber Type & Part Size
The molding method determines the prototype’s precision, elasticity, and cost. Choose from three common processes based on your material and application:
3.1 Liquid Silicone Injection Molding (LSR)
- Applicable Materials: Liquid silicone (30°–70° Shore hardness).
- Process Steps:
- Mix liquid silicone (Part A + Part B) in a 1:1 ratio.
- Inject the mixture into a preheated mold (150°C–200°C).
- Cure for 5–15 minutes (depending on thickness).
- Demold and trim excess material.
- Advantages: High precision (ideal for micro-parts like phone waterproof rings), excellent elasticity, and no post-curing needed.
- Ideal For: Transparent medical parts (e.g., infusion tube fittings) and high-precision seals.
3.2 Solid Rubber Pressing
- Applicable Materials: Natural rubber, EPDM, and silicone rubber sheets.
- Process Steps:
- Cut rubber sheets into the approximate shape of the mold cavity.
- Heat the sheets to 120°C–180°C to soften them.
- Press the softened rubber into the mold with 10–20 MPa pressure.
- Cool for 10–20 minutes, then demold.
- Advantages: Low cost, fast for large parts (e.g., automotive shock absorbing pads), and suitable for aging-resistant materials like EPDM.
- Ideal For: Sealing strips (e.g., door gaskets) and large slip-resistant mats.
3.3 Polyurethane Casting (UR)
- Applicable Materials: Polyurethane elastomers (TPU, TPE).
- Process Steps:
- Mix AB components (resin + hardener) in a 1:1 ratio.
- Degas the mixture under vacuum (-0.1MPa) to remove air bubbles.
- Pour the mixture into the mold slowly to avoid eddy currents.
- Cure at room temperature (24 hours) or heat (80°C for 2 hours).
- Advantages: Mimics rubber’s flexibility, perfect for cladding metal/plastic parts (e.g., power tool handles with metal cores).
- Ideal For: Overmolded prototypes (e.g., silicone-coated plastic buttons).
Comparison Table: Molding Process Selection Guide
| Part Type | Recommended Process | Material Example | Lead Time |
| Micro-seals (≤5mm) | LSR | Liquid silicone | 1–2 days |
| Large shock pads (≥200mm) | Solid Rubber Pressing | EPDM | 2–3 days |
| Overmolded grips | Polyurethane Casting | TPU | 1–3 days |
4. Post-Processing: Refine & Enhance Prototype Quality
Rubber prototypes require targeted post-processing to fix defects, improve performance, and add functional details.
4.1 Basic Trimming & Deburring
- Use a sharp blade or grinding wheel to remove excess rubber burrs (common around mold edges). For small parts like silicone earbuds, use tweezers to peel off tiny burrs—avoid sanding (it can damage soft rubber surfaces).
4.2 Secondary Vulcanization (For Silicone)
- Bake silicone prototypes at 150°C–200°C for 2–4 hours. This step improves temperature resistance (by 30%) and aging resistance (extends lifespan by 50%), critical for automotive or outdoor use. For example:
A silicone automotive seal prototype, after secondary vulcanization, withstands 150°C for 1,000 hours without hardening—vs. 500 hours for an unprocessed version.
4.3 Surface Treatment
Add functional or decorative finishes based on your needs:
- Anti-Slip Coating: Spray epoxy-based anti-slip paint on grips to boost friction (reduces slip by 60% for wet surfaces).
- Silk Screen Printing: Apply logos, hardness labels (e.g., “50° Shore”), or warning text (e.g., “Medical Grade”).
- Material Bonding: Use rubber-specific adhesives to attach rubber to metal/plastic (e.g., a nylon + rubber overlay for a tool handle).
5. Testing & Optimization: Validate Performance & Fix Issues
Test the prototype against your initial requirements, and address common problems like bubbles or deformation.
5.1 Key Test Items
| Test Type | How to Perform | Pass/Fail Criteria |
| Elasticity Test | Compress the prototype to 50% of its thickness, release, and measure recovery time. | Recovers to original shape in ≤1 second (e.g., a shock pad prototype passes this test). |
| Sealing Test | Submerge the prototype in water (for waterproof parts) or apply air pressure (for airtight seals). | No water leakage/air loss after 30 minutes. |
| Dimensional Accuracy | Use a caliper to measure key dimensions (e.g., diameter of a waterproof ring). | Error within ±0.1mm (meets most industrial standards). |
5.2 Solve Common Defects
| Defect | Causes | Fixes |
| Demolding Difficulty | High rubber elasticity, rough mold surface (Ra >1.6), no draft slope. | Polish mold to Ra ≤0.8; add 1°–3° draft slope; use silicone-specific release oil. |
| Bubbles | Air trapped in liquid rubber, fast pouring, no degassing. | Degas rubber under -0.1MPa vacuum; pour mixture slowly (≤5ml/second); use a mold with air vents. |
| Dimensional Deformation | Uneven mold temperature (±>5°C), incorrect shrinkage rate. | Heat mold evenly (use a temperature-controlled oven); adjust 3D model size based on material shrinkage (e.g., add 3% for silicone). |
6. Yigu Technology’s Perspective on Rubber Prototype Production
At Yigu Technology, we’ve found that the biggest challenge in rubber prototype making is balancing flexibility with precision—many clients rush to choose LSR for high precision but overlook cost for small batches. Our approach is to match processes to needs: for 1–5 units of complex parts, we recommend 3D-printed molds + polyurethane casting (fast and cheap); for 10+ high-precision parts, CNC molds + LSR (durable and accurate). For example, a medical client initially chose LSR for a single silicone tube prototype (cost \(300), but we switched to 3D-printed molds + casting (cost \)80) without sacrificing quality. We also emphasize pre-testing material compatibility—e.g., ensuring TPE bonds well with ABS before overmolding—to avoid rework. Rubber prototypes thrive on attention to detail; small adjustments (like adding a 2° draft slope) can save days of troubleshooting.
7. FAQ: Common Questions About Making Rubber Prototypes
Q1: Can I use 3D printing directly to make rubber prototypes (without molds)?
A1: Rarely—most 3D-printed “rubber-like” parts (e.g., TPU filaments) lack the elasticity and sealing performance of true rubber. Molding processes (LSR, casting) are needed to leverage rubber’s natural properties. For simple concept tests, 3D-printed TPU can work, but for functional validation, use mold-made rubber prototypes.
Q2: How do I choose between silicone and TPE for my prototype?
A2: Choose silicone for high temperature resistance (up to 200°C) and transparency (e.g., medical devices, phone waterproof rings). Choose TPE for better wear resistance and lower cost (e.g., grips, toy parts). For example, a baby bottle nipple prototype uses silicone (non-toxic, heat-resistant), while a toy car tire prototype uses TPE (cheaper, durable).
Q3: Why does my rubber prototype have a sticky surface?
A3: Sticky surfaces are usually caused by incomplete curing (e.g., LSR cured at 140°C instead of 160°C) or excess release oil. Fixes: Re-cure the prototype at 160°C for 1 hour; wipe excess oil with a lint-free cloth. For silicone, secondary vulcanization also eliminates stickiness by removing residual low-molecular-weight compounds.