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Views: 0 Author: Site Editor Publish Time: 2025-02-20 Origin: Site
| Table of Contents |
1. Introduction |
| 2. Key Considerations for Selecting Injection Molding Materials 2.1 Final Usage Environment of the Product 2.2 Mechanical Performance Requirements 2.3 Processing Characteristics 2.4 Appearance Requirements |
| 3. Common Categories of Injection Molding Materials and Their Characteristics |
| 4. Economic Considerations in Material Selection |
| 5. Considerations for Special Requirements |
| 6. Conclusion |
1. Introduction
"The same mold, but changing the material caused the yield rate to plummet from 95% to 62%." This was a real lesson we learned while debugging a new project for a home appliance client. The choice of material is not simply about "plastic" versus "more expensive plastic"; it directly determines the product's lifespan, safety, and production costs. Statistics show that 60% of injection molding defects (such as cracking, deformation, and color differences) are related to material misuse, and the wear rate of molds can increase 2-3 times due to differences in material flowability. With 23 years of experience in injection molding technology, we deeply understand that scientific material selection equals 50% assurance of product performance plus 30% control over costs.
When selecting injection molding materials, multiple key factors must be considered to ensure that the final product not only meets design requirements but also performs stably in actual usage scenarios. The following are several core dimensions of consideration.
2.1 Final Usage Environment of the Product
Temperature Tolerance Range
High-Temperature Scenarios: If the product needs to be exposed to temperatures above 80°C for long periods (such as components around a car engine), standard ABS will soften and deform (HDT only 95°C). It needs to be upgraded to PA66 (HDT 250°C) or high-temperature-resistant LCP (HDT 280°C).
Low-Temperature Scenarios: In environments below -30°C (such as cold chain logistics boxes), HDPE's impact strength is three times higher than that of PP, avoiding low-temperature brittleness.
Chemical Exposure
Strong Corrosive Media: Chemical valves in contact with concentrated sulfuric acid must use PTFE, which has far superior acid and alkali resistance compared to PP/PE.
Oil Environments: Fluoroelastomer (FKM) is recommended for automotive oil hoses; standard NBR will swell 10%-15% after prolonged oil immersion.
Outdoor/Indoor Use
UV-Sensitive Areas: If outdoor lighting fixtures use unmodified ABS, they will yellow and powder within a year; ASA with added UV stabilizers can maintain color for five years without significant change.
Humidity Impact: Nylon (PA6/PA66) can absorb moisture, causing dimensional changes of up to 1.5%, requiring glass fiber reinforcement or surface coating (like automotive wiper supports).
2.2 Mechanical Performance Requirements
Strength and Rigidity
High-Load Structural Components: For components like drone arms, 30% glass fiber-reinforced PA6 (tensile strength > 180MPa) should be selected instead of unreinforced PC (only 65MPa).
Case of Insufficient Rigidity: A base for home appliances using HIPS (bending modulus 2.3GPa) led to deformation; switching to 20% mineral-filled PP (modulus 3.8GPa) increased costs by only 5%.
Impact Resistance
Low-Temperature Impact Resistance: The preferred choice is PC/ABS alloy (notched impact strength 50kJ/m²), which is more suitable for automotive dashboards than pure ABS (20kJ/m²).
Warning: PC is prone to hydrolysis and embrittlement in humid environments and must be dried to a moisture content of <0.02% (like medical device housings).
Wear Resistance
Friction Parts like Gears and Bearings: Prioritize POM, which has a dynamic friction coefficient of only 0.15-0.25, 40% lower than PA66.
Wear-Resistant Modification: Adding 15% PTFE or molybdenum disulfide (MoS₂) can reduce wear rates by more than 50% (e.g., printer sliders).
2.3 Processing Characteristics
Flowability (Melt Flow Index, MFI)
Thin-Walled Parts (thickness < 0.5mm): Must use high-flow materials (like LCP, MFI > 200g/10min) to avoid an 80% increase in short-shot risk.
Cost of Insufficient Flowability: A certain electronic connector using standard PA66 (MFI 15g/10min) had a yield of only 65%; switching to high-speed injection-grade PA66 (MFI 60g/10min) increased it to 92%.
Molding Cycle
Fast Crystallizing Materials (like PBT): Cooling time is 30% shorter than that of ABS, making it suitable for large-scale production (like connectors).
Cost Association: If the material molding cycle is extended by 5 seconds, a 100,000-piece order will incur an additional 28 hours of machine time costs.
Shrinkage Rate
High-Precision Gears: Should use low-shrinkage materials (like POM with a shrinkage rate of 1.8%-2.5%), and mold designs need to allow for a compensation amount of 0.5%-1.2%.
Case of Uncontrolled Shrinkage: A certain precision gear had poor meshing due to excessive shrinkage of PP (1.6%-2.2%); switching to POM controlled the tolerance within ±0.02mm.
2.4 Appearance Requirements
Surface Gloss
High-Gloss Surfaces (like high-end cosmetic packaging): Should use ABS (gloss > 95GU), avoiding HIPS (gloss < 80GU).
Spray Compatibility: The adhesion of PC/ABS alloys is three times higher than that of pure PC, making it more suitable for automotive grilles that require secondary spraying.
Color Requirements
Dark Products (like black appliance housings): Can add 2%-5% carbon black masterbatch, but note that carbon black can reduce material toughness (impact strength decreases by 15%-20%).
Caution with Light/White Parts: A certain toy manufacturer used 30% recycled PP, leading to a color difference ΔE > 5 (standard requires ΔE < 2).
Transparency
Optical Grade PC: Light transmittance > 90% (3mm thickness), haze < 1%, suitable for goggles and LED lampshades.
Processing Warning: Transparent materials must control mold temperature (±3°C fluctuation can cause streaking), and molds need to be mirror-polished (Ra < 0.01μm).
In injection molding, different categories of materials are widely used due to their performance and application differences. According to performance and usage, injection molding materials can generally be divided into four main categories: general plastics, engineering plastics, high-performance plastics, and specialty plastics. Below are the main characteristics and applicable scenarios of these materials:
(1) General Plastics: The preferred choice for low-cost, high-volume production
PP (Polypropylene)
Core Characteristics: Low density (0.9g/cm³), resistant to acids and alkalis, food-grade certification easily passed.
Advantages: Lowest cost (about 12-15 yuan/kg), suitable for disposable packaging and daily necessities (like storage boxes, cups).
Limitations: Temperature resistance < 100°C, poor impact resistance (notched impact strength only 3kJ/m²).
PE (Polyethylene)
Subcategory Choices:
HDPE (High-Density): High rigidity, suitable for bottle caps and chemical barrels;
LDPE (Low-Density): High flexibility, used for hoses and cling film.
Critical Weakness: Poor resistance to environmental stress cracking (prone to cracking when in contact with detergents).
PS (Polystyrene)
Transparent Version (GPPS): Light transmittance > 90%, but very brittle (impact strength 2kJ/m²), used only for disposable cutlery and CD cases.
Toughened Version (HIPS): Adds rubber particles to enhance toughness (impact strength 8kJ/m²), suitable for refrigerator liners and toy housings.
(2) Engineering Plastics: The balance point between performance and cost
ABS (Acrylonitrile-Butadiene-Styrene Copolymer)
Performance Tag: Excellent overall mechanical properties (tensile strength 40MPa, impact strength 20kJ/m²), easy to electroplate/spray.
Typical Applications: Appliance housings (air conditioner panels, vacuum cleaners), automotive interiors.
Pain Point: Poor weather resistance (needs ASA blend for outdoor use).
PC (Polycarbonate)
High-Point: High transparency and impact resistance (notched impact strength 60kJ/m²), suitable for safety helmets and riot shields.
Critical Flaw: Prone to hydrolysis (bubbles easily with humidity > 0.02% during high-temperature processing), must be pre-dried for 4 hours (120°C).
Alternative Solution: PC/ABS alloy (20% cost reduction, 30% improved flowability).
PA (Nylon, Polyamide)
PA6 vs PA66:
Index | PA6 | PA66 |
Melting Point | 220°C | 265°C |
Moisture Absorption | 2.7% | 2.5% |
| Applicable Scenarios | Gears, fishing lines | Automotive oil pans, zip ties |
Glass Fiber Reinforcement: PA66 + 30% GF tensile strength > 200MPa, but increases mold wear (every 10% glass fiber content reduces mold life by 15%).
(3) High-Performance Plastics: The ultimate solution in extreme environments
POM (Polyoxymethylene, Acetal)
King of Friction: Dynamic friction coefficient of only 0.15, self-lubricating, used for gears and bearings.
Shrinkage Trap: Shrinkage rate can reach 2.2%, requiring mold compensation design for high-precision components.
PEEK (Polyether Ether Ketone)
Performance Ceiling: Temperature resistance of 260°C, flame retardant V-0 grade, radiation-resistant, certified for medical implants (like spinal fusion devices).
Cost Warning: Price around 800-1200 yuan/kg, requires specialized high-temperature molds (resistant to 380°C).
LCP (Liquid Crystal Polymer)
King of Thin Walls: Excellent flowability (MFI > 200g/10min), yield rate > 95% for 0.2mm thick mobile phone SIM card trays.
Anisotropy Warning: Molecular chain orientation leads to transverse strength being only 50% of longitudinal strength (requires structural design optimization).
(4) Specialty Plastics: Customized choices for functional needs
TPE/TPU (Thermoplastic Elastomers)
Flexibility Champion: Hardness range 60A-95A, used for non-slip handles and seals.
Mold Adhesion Challenge: High-viscosity materials require molds coated with Teflon (reducing demolding force by 50%).
PMMA (Acrylic)
Optical Benchmark: Light transmittance 92% (better than PC), but very brittle (impact strength only 1.5kJ/m²), used only for lamp covers and signs.
Scratch-Resistant Modification: Adding nano SiO₂ coating (surface hardness improved from 2H to 4H).
When selecting injection molding materials, it is essential to pay attention not only to the performance and applicability of the materials but also to fully consider economic factors to maximize cost-effectiveness while meeting performance requirements. The following are three core aspects of economic consideration:
(1) Raw Material Costs: Unit Price ≠ Total Costs
Material Type | Unit Price (yuan/kg) | Savings Strategies | Typical Case |
General Plastics (PP) | 12-15 | Wall thickness optimization (from 2.5mm to 1.8mm, reducing costs by 28%) | A daily chemical bottle structure optimization saves 1.2 million yuan annually |
Engineering Plastics (ABS) | 20-25 | Use ABS in load-bearing areas, mix HIPS in non-load areas | Printer casing mixed-use scheme reduces total costs by 15% |
High-Performance Plastics (PEEK) | 800-1200 | Use only for critical components (like implant screw heads) | A certain orthopedic instrument uses PEEK + titanium alloy composite structure reduces costs by 40% |
Glass fiber-reinforced materials (like PA66 + 30% GF) have a unit price 10-15% higher, but due to strength improvements, material usage can be reduced by 20%-30%, keeping total costs balanced;
Caution with recycled materials: 30% recycled PP reduces unit price by 25%, but increases color difference scrap rate by 12%, raising overall costs by 8%.
(2) Processing Costs: The Game of Yield and Efficiency
Cost Factor | Impact Magnitude | Optimization Scheme | Data Support |
Molding Cycle | Cycle extension of 1 second → 10,000 pieces increases cost by 7% | Use fast crystallizing materials (like PBT is 30% faster than PA66) | A connector factory switched to PBT, saving 850,000 yuan annually in processing fees |
Mold Wear | Every 10% increase in glass fiber content → mold life decreases by 15% | Surface chrome/ceramic coating (extends life by 3-5 times) | A certain automotive parts factory reduced mold repair costs by 60% |
Energy Consumption | High-temperature materials (like PEEK) consume 220% more energy than ABS | Use servo motor + hot runner system (35% energy savings) | A medical factory reduced electricity costs from 18% to 12% |
High-flow materials (like LCP) can reduce short-shot risk, increasing yields to 95%, offsetting the disadvantage of being 20% more expensive;
Materials with a shrinkage rate > 1.5% require secondary processing (like CNC trimming), increasing costs by 0.3-0.8 yuan per piece.
(3) Product Lifecycle Costs: The Invisible Iceberg
Cost Type | Hidden Cost Scenarios | Material Selection Strategy | Empirical Case |
Repair Costs | Outdoor equipment has a 23% annual return repair rate due to material aging | Use ASA instead of ABS (weather resistance improved by 5 times) | A streetlight housing reduced repair costs from 500,000 yuan/year to 80,000 yuan/year |
Replacement Costs | Appliance gear wear leads to entire unit replacement | POM replaces HDPE (lifespan increases from 2 years to 8 years) | A certain brand of rice cooker reduced warranty claims by 70% |
Recycling Costs | EU EPR regulations impose a fee of 300 euros/ton on non-recyclable materials | Use single-material PP (100% recyclable) | A certain export enterprise avoided paying 1.2 million yuan in environmental fines annually |
Total Cost = Material Cost × Quantity + Processing Cost × Output + (Repair + Recycling Costs) × Lifespan
Classic Example:
Material Selection Comparison for Automotive Engine Mount (10-year cycle):
· Option A: Standard PA66, initial cost 3.8 yuan/piece, but replaced every 2 years (total cost 3.8 × 5 = 19 yuan)
· Option B: PA66 + 50% GF, initial cost 6.5 yuan/piece, lifespan 10 years (total cost 6.5 yuan)
→ Option B total cost is reduced by 65%.
In certain specific industries or application scenarios, the selection of injection molding materials must meet special requirements to ensure that products achieve standards in functionality, safety, and regulatory compliance. Below are several common special requirements and their corresponding considerations:
Food Contact Level Requirements
For products that come into direct contact with food (such as food containers, utensils, and packaging materials), materials must comply with food safety regulations.
Compliance with Food-Grade Certification: Materials must pass certifications such as FDA or EFSA to ensure they do not release harmful substances when in contact with food.
Safety and Stability: Choose non-toxic, tasteless, and chemically stable materials, such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). These materials maintain stable performance in high or low-temperature environments without affecting food safety.
High-Temperature Resistance: For food containers that require microwave heating or high-temperature sterilization, materials must possess good heat resistance, such as high-density polyethylene (HDPE) or polysulfone (PPSU).
Flame Retardant Requirements
For applications such as electronic products, appliance housings, and construction materials, flame retardant performance is a crucial safety indicator.
Compliance with Flame Retardant Level Certification: Choose materials that meet UL 94 certification, such as V-0 grade materials, which can self-extinguish quickly in open flames and prevent fire spread.
Common Flame Retardant Materials: Such as flame-retardant polycarbonate (PC) with added flame retardants, flame-retardant ABS, and polyamide (PA). These materials maintain mechanical performance while possessing excellent flame retardant properties.
Environmental Requirements: The selection of modern flame retardant materials must also consider environmental regulations, such as the EU's RoHS and REACH standards. Halogen-free flame retardant materials (like halogen-free PC/ABS) are becoming the choice for more enterprises, meeting both flame retardant and environmental trends.
The requirements for materials in medical devices and equipment are particularly stringent, necessitating a balance between biocompatibility, safety, and durability.
Compliance with Medical Certifications: Medical-grade materials must meet ISO 10993 or USP Class VI standards to ensure they are non-toxic to the human body.
High-Temperature and Sterilization Resistance: Medical devices often require high-temperature sterilization or chemical disinfection, so materials must possess good resistance to high temperatures and chemical corrosion, such as polyether ether ketone (PEEK), polysulfone (PSU), and medical-grade polypropylene (PP).
Transparency and Impact Resistance: For medical devices that require observation or precise operation (such as syringes and blood filters), materials must have high transparency and impact resistance, such as polycarbonate (PC) or polymethyl methacrylate (PMMA).
Choosing the right injection molding materials is an important decision that requires specialized knowledge and extensive experience. At Alpine Mold, we have over 20 years of experience in the design and manufacturing of injection molds, and we deeply understand the characteristics and applications of various materials. Our technical team is not only proficient in the performance characteristics of different injection molding materials but also adept at weighing various factors based on our clients' specific needs to provide the optimal material selection options.
We emphasize the importance of professional consulting and adhere to the service philosophy of "professional orientation, cost optimization." Through in-depth technical exchanges and demand analysis in the early stages, we can assist clients in selecting the most cost-effective material solutions while ensuring product performance. Our professional advice covers not only material selection but also mold design optimization and production process improvements, helping clients achieve the best balance between product quality and production costs.
If you have any questions regarding the selection of injection molding materials, please feel free to contact our technical team. Let Alpine Mold become your trusted technical partner, working together to create high-quality and competitive injection-molded products.
