The selection of injection molding materials in Dalian directly affects product performance, production efficiency, and cost, and the following key factors need to be comprehensively considered:

1、 Product performance requirements

Mechanical properties

Strength and stiffness: Materials are selected based on the product's stress conditions, such as high-strength nylon (PA) and polycarbonate (PC) for structural components, while lightweight components can be made of polypropylene (PP) or modified polypropylene.

Resilience and impact resistance: For products that require drop or impact resistance (such as home appliance casings), PC, ABS, or PC/ABS alloys can be selected, avoiding the use of brittle polystyrene (PS).

Wear resistance: Moving parts such as gears and bearings should be made of materials with good wear resistance, such as polyoxymethylene (POM), reinforced nylon (PA+fiberglass), or polytetrafluoroethylene (PTFE) filling materials.

physical property 

Heat resistance: Select materials according to the usage temperature. For example, PC and nylon (PA66 has a temperature resistance of about 150 ℃) can be selected for long-term temperature resistance above 100 ℃. Engineering plastics such as polyphenylene sulfide (PPS) and polyether ether ketone (PEEK) are required for higher temperature scenarios (such as automotive engine components).

Chemical resistance: For products that come into contact with solvents, acids, and bases (such as chemical containers), polyethylene (PE), polypropylene (PP), or fluoroplastics (such as PTFE) should be selected. Avoid using easily corrosive ABS or polyurethane (PU).

Insulation and conductivity: Electronic components require high insulation materials (such as polyphenylene oxide (PPO), epoxy resin), while anti-static or conductive components can choose modified plastics with added carbon black and metal fibers.

Appearance and performance

Surface smoothness: Transparent products (such as optical lenses) are mainly made of optical grade PMMA or PC, while matte surface products can be made of PP or ABS with added matte agents.

Color stability: Products for long-term outdoor use should be made of materials that are resistant to ultraviolet (UV) radiation (such as ABS or ASA with added antioxidants and light stabilizers) to avoid fading or aging.

2、 Adaptability of molding process

melt fluidity

The melt flow rate (MFR) of materials directly affects the filling ability: thin-walled or complex structural parts require high flowability materials (such as injection grade PS, polypropylene (PP) low melt index grades), while thick walled parts can choose grades with slightly lower flowability but lower cost.

For small sprues or long process molds, priority should be given to materials with high MFR values (such as ABS, whose MFR is usually 5-20g/10min, and the higher the value, the better the flowability) to avoid insufficient filling or obvious weld lines.

Thermal stability and processing temperature

Materials that are prone to decomposition at high temperatures, such as polyvinyl chloride (PVC) and polyoxymethylene (POM), require strict control of the barrel temperature and residence time to avoid the formation of bubbles or discoloration during degradation.

The material processing temperature needs to be matched with the injection molding machine: for example, the processing temperature of PC is about 280~320 ℃, while PE only needs 180~250 ℃. If the equipment has insufficient high temperature, it cannot process high-temperature materials.

Shrinkage and deformation control

Crystalline plastics (such as PE, PP, PA) have a high shrinkage rate (1%~2.5%), requiring the design of a larger mold demolding slope and cooling system to avoid product size deviation or warping; Amorphous plastics (such as PS, PC, ABS) have a lower shrinkage rate (0.3%~0.8%) and are more suitable for high-precision parts.

The shrinkage rate of glass fiber reinforced materials (such as PA+30% GF) decreases along the direction of glass fiber orientation, and attention should be paid to the design of mold flow channels to reduce anisotropic deformation.

3、 Cost and environmental requirements

material cost

General plastics (such as PE, PP, PS, ABS) have lower costs and are suitable for large quantities of low-priced products; Engineering plastics (such as PA, PC, POM) and specialty plastics (such as PEEK, PPS) have high costs and are often used in high-performance scenarios.

Consider the proportion of recycled materials: Some products can use a certain proportion of recycled materials (such as industrial packaging) to reduce costs, but attention should be paid to the performance degradation of recycled materials (such as a decrease in impact strength).

Environmental Protection and Regulatory Compliance

Food contact products must comply with FDA, GB4806 and other standards. Food grade PP, PE, and PC (BPA content must meet the standard) can be selected, and materials containing halogens or heavy metals should be avoided.

EU regulations such as RoHS and REACH restrict certain substances (such as phthalates and polybrominated biphenyls), and electronic and electrical products must choose halogen-free flame retardant materials (such as halogen-free flame retardant PC/ABS).

Biodegradable materials such as polylactic acid (PLA) and poly (adipic acid/butylene terephthalate) (PBAT) should be selected for disposable tableware.

4、 Subsequent processing and usage scenarios

Post processing requirements

Products that require electroplating or spraying should be made of materials with good surface adhesion (such as ABS, which is easy to electroplate after surface treatment with chromic acid), while PP needs to undergo flame treatment or primer coating before spraying.

Components that require welding (such as ultrasonic welding) must have a matching melting point, for example, PC and PC parts are easy to weld, while PC and ABS are difficult to weld.

Adaptability to the usage environment

Outdoor products require materials with strong weather resistance (such as ASA and PMMA with added UV absorbers) to avoid cracking or discoloration caused by light and rain.

Products in humid environments (such as bathroom components) should be made of materials with low water absorption rates (such as PP, POM, PA with high water absorption rates that need to be dried in advance).

5、 Suppliers and Supply Chain

Material stability

Choose the brands of mainstream suppliers (such as BASF, DuPont, SABIC) to ensure consistent performance of materials from different batches and avoid molding defects (such as insufficient weld strength) caused by fluctuations in resin molecular weight.

Supply cycle and inventory

For urgent orders, priority should be given to locally sourced materials that are easy to purchase, such as general plastics; Special engineering plastics may require advance booking and supply chain risk assessment.

The selection of injection molding materials should follow the principle of "performance first, considering cost and process", and verify whether the selected materials meet the requirements through sample testing (such as mold testing and mechanical performance testing). For complex products, mold flow analysis (such as Moldflow) can be used to simulate material flow and cooling processes, optimizing material selection and mold design in advance.