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- TPU is a flexible, abrasion-resistant thermoplastic elastomer processed at 180–230°C on standard injection molding machines.
- Shore A hardness spans 60A–98A, covering everything from soft grips to semi-rigid structural parts.
- Pre-drying at 80–100°C for 2–4 hours is mandatory — moisture above 0.02% causes splay and chain scission.
- TPU outperforms TPE in tensile strength (25–55 MPa) and abrasion resistance, making it ideal for demanding applications.
- Design for TPU requires generous draft angles (2–3° for soft grades) and gate diameters ≥1.5 mm.
What Is TPU Injection Molding?
TPU 사출 성형1 is the process of injecting melted thermoplastic polyurethane into a steel mold to produce flexible, abrasion-resistant parts. The material combines rubber-like elasticity with thermoplastic processability, making it ideal for overmolding, seals, and wear components. For a broader view, see our 사출 성형 guide and the 사출 금형2 overview.
For a broader view, our injection molding complete guide covers process fundamentals, material behavior, and production decisions.
For broader context, compare this topic with supplier sourcing guide.
In our Shanghai factory, we run 47 injection molding machines from 90T to 1850T, so we treat every tooling decision as a process-window question, not just a quoted price.
TPU injection molding is melting thermoplastic polyurethane pellets and injecting them into a mold to make flexible, rubber-like parts. It runs on the same machines used for ABS, PP, or nylon.
In our factory, TPU has become one of the most requested elastomeric materials over the past five years. Customers come to us when they need parts that combine rubber-like flexibility with thermoplastic recyclability — think cable overmolds, wearable device skins, and industrial seals. The chemistry behind TPU consists of alternating hard segments (from diisocyanate and chain extender) and soft segments (from polyol), which create its signature combination of strength and elasticity at the molecular level.
TPU 사출 성형: 엔지니어를 위한 완벽 가이드
““TPU can be injection molded on the same machines used for ABS, PP, and nylon.””True
Standard reciprocating-screw injection molding machines process TPU effectively. The key differences are parameter settings (lower barrel temperatures of 180–230°C, slower injection speeds) and the mandatory pre-drying step — not the equipment itself.
““You need specialized rubber-processing equipment to mold TPU parts.””False
TPU is a thermoplastic elastomer, not a thermoset rubber. It melts and flows like a thermoplastic, so it can be processed on any standard injection molding machine without special rubber-processing attachments or vulcanization ovens.
What Are the Key Material Properties of TPU?
TPU’s key properties are Shore A hardness of 60A–98A, tensile strength of 25–55 MPa, and abrasion loss of 20–80 mm3. These are set at synthesis via hard/soft segment ratio.
| 속성 | Typical Value | Significance |
|---|---|---|
| Shore Hardness | 60A–98A / 40D–80D | Soft grips to semi-rigid housings |
| 인장 강도 | 25–55 MPa | Higher than most TPEs |
| 휴식 시 신장 | 300–700% | Excellent flexibility |
| Operating Temp. | –40°C to +100°C | Outdoor and refrigerated use |
| 내마모성 | 20–80 mm3 DIN loss | Superior to rubbers and TPEs |
| 수분 흡수 | 0.5–2.0% (24 hr) | Mandatory pre-drying |
Polyester-based TPU grades offer superior oil resistance and abrasion performance, while polyether-based grades excel in hydrolysis resistance and low-temperature flexibility. For marine or humid-environment parts, we always specify polyether TPU. For automotive underhood components exposed to hydraulic fluid, polyester grades perform better.
TPU process parameters are barrel temp 180–230°C, mold temp 20–50°C, slow injection speed, and 2–4 hour pre-drying at 80–100°C. Moisture below 0.02% is mandatory.
| 매개변수 | Range | 참고 |
|---|---|---|
| Pre-drying Temp. | 80–100°C | 2–4 hours; dehumidifying dryer |
| Barrel Temp. (Rear) | 170–190°C | Prevents premature melting |
| Barrel Temp. (Front) | 190–230°C | Avoid exceeding 240°C |
| 금형 온도 | 20–50°C | Higher = better surface |
| 사출 압력 | 50–120 MPa | Softer grades need less |
| 유지 압력 | 60–80% of peak | Prevents sink marks |
| 냉각 시간 | 15–60 seconds | Flexible parts need longer |
| 나사 속도 | –50 ~ +80°C | Slow prevents shear damage |
In our experience, TPU’s sensitivity to residence time is one of the trickiest parameters to manage. If TPU sits in the barrel at processing temperature for more than 5–10 minutes, it begins to degrade — you’ll see yellowing and a sharp drop in tensile properties. We always purge the machine between runs and minimize shot-to-cycle intervals during production startup.
What Are Common Defects in TPU Injection Molding and How Can You Prevent Them?
The most common TPU defects are splay marks (moisture), mold sticking (high tack), short shots (low pressure), and yellowing (thermal degradation). Each has a specific root cause and a practical fix.
| 결함 | Root Cause | Prevention |
|---|---|---|
| Splay / Silver Streaks | Moisture in material | Dry at 90°C for 3–4 hours |
| Part Sticking | High elasticity, low draft | Increase draft to 2–3° |
| Bubbles / Voids | Thermal degradation | Reduce barrel temp; improve venting |
| 쇼트 샷 | Insufficient fill pressure | Raise injection pressure 10–20% |
| 플래시 | Overpacking; worn parting line | Reduce holding pressure |
| Yellowing | Excessive temp or residence | Keep barrel below 240°C; purge |
We’ve found that part sticking is the single biggest production bottleneck for soft TPU grades. In one project for a wearable fitness device, we were running Shore 75A TPU with a complex undercut geometry. The fix wasn’t more release agent — it was increasing the draft angle from 1° to 2.5° on the sidewalls and redesigning the ejector pin locations. Cycle time dropped from 45 seconds to 28 seconds after the mold modification.
““TPU must be dried at 80–100°C for 2–4 hours before every production run.””True
Pre-drying is non-negotiable. Moisture content above 0.02% causes hydrolytic chain scission during the melt phase, producing splay marks, surface bubbles, and significant reduction in tensile strength.
““If TPU pellets are stored in a sealed bag, they don’t need drying.””False
TPU is highly hygroscopic — it can absorb enough moisture in 30–60 minutes of open-air exposure to cause splay marks and chain scission. Pre-drying is mandatory regardless of storage conditions.
What Industries Rely on TPU Injection Molded Parts?
TPU is widely used across automotive, footwear, medical, consumer electronics, and industrial applications. Its combination of flexibility, abrasion resistance, and chemical tolerance makes it the go-to elastomer for demanding environments.
자동차: Door seals, gearshift boots, cable grommets, and vibration-damping mounts. Polyester-based TPU grades offer the fuel and oil resistance required for underhood applications. We’ve produced TPU cable harness guides for EV battery packs where dimensional stability at –30°C was a hard requirement.
Footwear: Midsoles, outsoles, and toe caps use TPU for exceptional abrasion resistance (20–40 mm3 DIN loss) and flex fatigue endurance. Injection molded TPU outsoles withstand millions of flex cycles without cracking.
의료 기기: Medical-grade TPU formulations are used for surgical tubing, catheter components, and wearable sensor housings. Polyether TPU’s hydrolysis resistance and biocompatibility (ISO 10993) make it suitable for body-contact applications. We produce flexible TPU housings for continuous glucose monitoring devices.
““TPU can accommodate minor undercuts by flexing during demolding.””True
TPU’s elasticity allows it to stretch over minor undercuts without damage, reducing tooling complexity by eliminating sliders or lifters.
““TPU parts are too expensive for high-volume consumer products.””False
TPU costs more per kilogram than commodity TPE, but its longer mold life (300K+ shots), lower scrap rate, and runner recyclability often make it cheaper per-part in volumes above 10,000 units.
소비자 가전: Phone cases, cable overmolds, earphone tips, and smartwatch bands. TPU’s chemical resistance to sweat, cleaning solvents, and UV light makes it durable in daily consumer environments.
Industrial: Hydraulic hose couplings, conveyor components, roll covers, and protective boots from harder TPU grades (Shore 90A–60D). Abrasion and tear resistance exceeds natural rubber by 3–5× in high-speed conveyor applications.
How Does TPU Compare to TPE, Silicone, and Rubber?
TPU is stronger and more abrasion-resistant than standard thermoplastic elastomers (TPEs), with tensile strength of 25–55 MPa versus 8–20 MPa for TPE. It also offers recyclability that vulcanized rubber and LSR cannot match.
| 속성 | TPU | TPE | 실리콘 | Rubber |
|---|---|---|---|---|
| 인장 강도 | 25–55 MPa | 8–20 MPa | 6–12 MPa | 10–30 MPa |
| Abrasion | 우수 | Good | Poor | Very Good |
| Temp. Range | –40 to +100°C | –50 to +80°C | 빨간색 TPU 플라스틱 사출 성형 부품 | –40 to +100°C |
| Recyclable | Yes | Yes | 아니요 | 아니요 |
| Pre-drying | Mandatory | Sometimes | 아니요 | N/A |
We’ve run direct comparison projects for clients choosing between TPU and TPE for phone case applications. TPE (SEBS-based) costs 20–30% less per kilogram and processes more easily, but drop test results were consistently 15–25% worse with TPE versus a comparable Shore 85A TPU grade. When mechanical performance under repeated impact is critical, TPU wins.
What Design Guidelines Should You Follow for TPU Parts?
TPU parts are best designed with 1.5–4.0 mm walls, 2–3° draft for soft grades, gate diameter ≥1.5 mm, and gradual transitions. TPU flexes enough to demold 3–5% undercuts without sliders.
벽 두께: Very thin walls (6 mm) produce long cooling times and potential voids. Uniform wall thickness is especially important with TPU — sudden changes cause differential shrinkage that creates warpage.
초안 각도: This is where we see the most design revisions. Shore 60A–75A grades need 2–3° minimum, and 3–5° for textured surfaces. TPU grips the mold core during cooling, so generous draft is essential for reliable ejection.
언더컷: Unlike rigid plastics, TPU can accommodate minor undercuts (3–5% of part diameter) by flexing during demolding. This reduces tooling complexity — many features that would require sliders in ABS can be directly demolded with TPU.
게이트 디자인: Submarine gates are popular for TPU because they self-degate. Gate diameter must be 1.5–2.5 mm minimum — undersized gates cause excessive shear. Avoid pin gates smaller than 1.0 mm with soft grades.
| Checkpoint 1 area | Checkpoint 1 verification |
|---|---|
| 레진 특성 | Confirm how mold design affects TPU Injection Molding: Complete Processing Guide for Engineers. |
| 재료 | Check resin behavior, shrinkage, heat, and cosmetic risks. |
| 품질 | Ask for inspection evidence before production approval. |
오버몰딩: TPU is one of the most versatile materials for overmolding onto rigid substrates (ABS, PC, PC/ABS, nylon). We’ve successfully overmolded Shore 85A TPU onto PC/ABS housings, achieving bond strength exceeding 5 MPa in peel tests. For more on 사출 금형 설계 design principles, see our complete guide.
Key checks before an RFQ are confirming resin grade, tolerances, cosmetic zones, and annual volume. Tool life, cavity count, and automation level also change the unit price.
The RFQ should also ask for manufacturing assumptions. Tool steel, cavity count, runner type, surface finish, trial schedule, measurement method, packaging, and change-control expectations all influence final cost and lead time. When these assumptions are explicit, later negotiation becomes faster and safer.
A strong, detailed technical reply will always identify missing inputs instead of hiding uncertainty. If the supplier asks about tolerance stack-up, gate vestige limits, resin certification, color matching, or annual demand variation, that usually means the engineering team is evaluating the project at production depth rather than quoting blindly.
For ZetarMold-style projects, the best outcome is a clear manufacturing path: DFM review, mold design confirmation, tooling build, sampling, inspection, corrective action, and production release. That sequence provides practical authority and gives buyers a useful checklist for their next supplier conversation.
What Production Evidence Should You Review Before Approving a TPU Supplier?
Key production evidence records are molding trials, dimensional reports, and resin certificates. Before approving any TPU supplier for production, first-article data should list measured values for every critical dimension, not just pass/fail stamps alone.
When a project involves cosmetic or tight-tolerance 플라스틱3 parts, the evidence should also include sample approval rules agreed before volume production begins. Boundary samples, measurement fixtures, color standards, and defect classification boards must be established and clearly documented before the production release to prevent subjective acceptance disputes later.
Frequently Asked Questions About TPU Injection Molding
What is the minimum order quantity for TPU injection molded parts?
There is no universal minimum — it depends on tooling amortization. For a simple mold costing $3,000–5,000, quantities of 500–2,000 parts can be economical. For high-volume TPU parts (100,000+ units/year), multi-cavity molds with 4–8 cavities are standard.
Can I use recycled TPU (rTPU) for injection molding?
Yes, but with limitations. Recycled TPU typically has 10–20% lower tensile strength and reduced elongation. For non-structural applications, rTPU works well. For load-bearing parts, mixing 10–20% rTPU with virgin resin is a common compromise.
How long does a TPU injection mold typically last?
A production-grade P20 steel mold for TPU typically lasts 300,000–500,000 shots. TPU is gentler on mold steel than abrasive-filled materials, so mold life is primarily driven by shot count.
Why does my TPU part turn yellow after molding?
Yellowing is almost always caused by thermal degradation — barrel temperature too high (above 240°C), excessive residence time, or moisture-induced hydrolysis. Check your barrel temperature profile first and purge the machine before production.
What is the typical shrinkage rate for TPU?
TPU shrinkage ranges from 0.8–2.0% depending on hardness. Softer grades (Shore 60A–75A) shrink 1.5–2.0%, while harder grades (Shore 90A–60D) shrink 0.8–1.2%. Always consult the material datasheet and run test shots before finalizing mold dimensions.
Is TPU safe for food contact applications?
Some TPU grades are FDA-compliant for food contact under 21 CFR regulations, but the specific grade must be verified. Not all formulations are food-safe — colorants and additives may disqualify a grade.
What is the difference between polyester and polyether TPU?
Polyester TPU offers better oil resistance and abrasion performance; polyether TPU provides superior hydrolysis resistance and low-temperature flexibility. For marine or humid environments, specify polyether. For automotive underhood applications, choose polyester.
Get Expert TPU Injection Molding Support
The biggest cost driver in TPU molding is not material price — it is getting drying, draft angles, and gate design right the first time. In our 20 years of running TPU tools at ZetarMold, our 8 senior engineers use mold flow simulation on every TPU project before steel is cut, catching fill imbalances and weld-line risks early.
With 47 injection molding machines (90T–1850T), 400+ material options, and ISO 9001/13485 certified quality systems, we have the equipment and experience to handle TPU projects from prototype through volume production. Contact us to discuss your TPU project — our English-speaking engineering team responds within 24 hours.
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