Injection molding is a traditional manufacturing technology with a history of over 100 years. Its core principle is to heat and melt plastic materials, then inject them into pre-designed molds under high pressure, and obtain plastic parts after cooling and solidification.
- Key Process Indicators:
- Molding cycle: Generally 10-60 seconds/piece (varies by part size and complexity)
- Tolerance control: Can reach ±0.02mm for precision parts
- Material utilization rate: Over 95% (with reasonable design)
3D printing, or additive manufacturing, constructs objects by stacking materials layer by layer according to 3D model data. Common technical types include FDM (Fused Deposition Modeling), SLA (Stereolithography), and SLS (Selective Laser Sintering), each with unique characteristics:
| Technology Type |
Material Range |
Precision |
Surface Roughness |
Typical Application |
| FDM |
PLA, ABS, PETG |
±0.1mm |
50-200μm |
Prototyping, low-load parts |
| SLA |
Photopolymer resin |
±0.05mm |
10-50μm |
High-precision prototypes |
| SLS |
Nylon, PA12 |
±0.15mm |
30-80μm |
Functional parts, wear-resistant components |
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Economies of Scale: Once molds are completed, the unit cost decreases significantly with increased production volume. For example, a plastic gear with an initial mold cost of 50,000 yuan will have a unit cost of only 1.2 yuan when production reaches 100,000 pieces (mold amortization included).
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Material Versatility: Compatible with over 80% of engineering plastics, including PP (polypropylene) for food containers, ABS (acrylonitrile butadiene styrene) for electronic housings, and POM (polyoxymethylene) for high-wear parts like gears.
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Surface Quality: Can achieve Ra 0.8-1.6μm surface roughness without post-processing, meeting the requirements of automotive interior parts and consumer electronics.
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Design Freedom: Enables the manufacturing of structures that are difficult or impossible with injection molding, such as:
- Lattice structures for lightweighting (e.g., aerospace brackets with 40% weight reduction)
- Internal flow channels with complex curves (e.g., medical device manifolds)
- Integrated assemblies that eliminate assembly steps (e.g., multi-part mechanisms printed as a single piece)
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Rapid Iteration: Shortens the product development cycle from design to physical verification. For instance, a consumer electronics company reduced the prototype verification cycle from 8 weeks (using traditional methods) to 3 days by adopting SLA 3D printing.
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Customization Capability: Maintains stable unit costs even when producing personalized products. A dental laboratory, for example, produces 50 custom orthodontic aligners daily with consistent quality and cost.
- High Initial Investment: Precision molds for complex parts (e.g., automotive dashboard frames) can cost 200,000-500,000 yuan, with a production cycle of 8-12 weeks.
- Design Restrictions: Undercuts and complex internal cavities often require split molds, increasing costs and reducing structural strength. For example, a water pump housing with a spiral internal channel would require a 5-part mold, increasing production complexity.
- High Modification Costs: A slight change in product dimensions (e.g., a 0.5mm adjustment in a mobile phone case) may require reworking the mold, costing 30%-50% of the original mold price.
- Material Performance Gaps: Most 3D printing materials have lower mechanical properties than their injection-molded counterparts. For example, 3D-printed ABS has a tensile strength of 25-30MPa, while injection-molded ABS reaches 40-45MPa.
- Production Efficiency: A 10cm×10cm×10cm part takes 4-6 hours to print with FDM, while injection molding can produce 50-100 pieces in the same time.
- Post-Processing Requirements: SLA-printed parts require resin cleaning and UV curing, and FDM parts need layer line polishing to achieve a smooth surface, adding 20%-30% to the total production time.
A new energy vehicle manufacturer faced the following challenge: developing a battery cooling manifold with a complex internal flow channel (requiring 12 curved channels) and planning for mass production of 50,000 units/year.
- Development Phase: Used SLS 3D printing (nylon material) to produce 10 prototypes, verifying the flow efficiency and structural strength in 1 week, avoiding the risk of mold modification.
- Mass Production Phase: After design finalization, switched to injection molding (PA6+GF30 material), reducing the unit cost from 50 USD (3D printing) to 7 USD, meeting the mass production demand.
A manufacturer of orthopedic implants needed to produce 200 custom femoral stems, each matching the patient's bone structure (based on CT scans).
- 3D Printing Solution: Adopted SLM (Selective Laser Melting) technology with titanium alloy Ti6Al4V, directly manufacturing implants from 3D models. Each implant took 12 hours to print, with a unit cost of 8,000 yuan, and the total project was completed in 3 weeks.
- Injection Molding Infeasibility: Custom molds for each implant would cost 50,000 yuan/set, resulting in a total cost of over 10 million yuan, which is economically unfeasible.
A smartphone brand launched a new earbud case, with an annual production plan of 1 million units, requiring high surface finish (Ra <0.8μm) and impact resistance.
- Injection Molding Solution: Used PC/ABS material with a 2-cavity mold (cost 180,000 yuan). The molding cycle was 30 seconds, with a unit cost of 8 yuan, and mass production was achieved 10 weeks after mold completion.
- 3D Printing Comparison: Using SLA technology would result in a unit cost of 65 yuan and a production time of 2 hours per piece, making it impossible to meet the annual output demand.
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