Plastic materials are the most widely used materials in home appliance manufacturing industry.
Master plastic materials commonly used by modern enterprises and learn how to reasonably select materials in design to improve structure, processing technology and reduce manufacturing costs, etc.
Cultivate structural design talents favored by enterprises.
American wire specifications

 

EC standard (applicable in Europe)

 

GB standard (China)

 

What is a standard?

 

Various terminal pulling forces:
1).U-shaped terminal: pulling force for welding is >8kgf, and pulling force for spot welding is >8kgf. Displacement cannot exceed 15cm/sec
A: Requirements for connecting double U-shaped terminals: Small U-shaped rear end needs to be punched on wiring insulation layer and cannot be punched on wire core.
B: Single U-shaped terminal wiring requirements: At least 1.5mm of terminal must be connected to wiring insulation layer. The entire part of terminal cannot be connected to wire core.
C: When connecting terminals, pressure of terminal machine cannot be adjusted too high, and terminals must not crush or break wire core. Terminal needs to completely cover wire core.
2) Pulling force of large and small switch terminals:
A: Connection pulling force of large switch terminals is >8kgf. Connection requirements are same as double U-shaped ends. Terminal insertion pulling force is >5kgf.
B: Connection pulling force of small switch terminals is >8kgf, connection requirements are same as double U-shaped ends, and terminal insertion pulling force is >3kgf.
C: When switch terminal is plugged in, use a force of about 300g to shake it until it becomes loose.
D: SHARP and Zojirushi customers’ closed-end terminal bonding pull force is >10kgf.
3) Bonding pull force of closed-end terminals is >5kgf. Currently, all closed-end terminals of company are of same model. Bonding force of closed-end terminals of SHARP and Zojirushi customers is >10kgf.
A: When connecting closed-end terminals, wiring and power cord cores must be fully inserted into terminals, and no cores should be exposed.
B: Insulation layer on the surface of terminal cannot be damaged.
Power cord tension
1) TUV specification power cord pull force test: pull with a force of 6kgf, once every 1 second, a total of 25 times, and wire core displacement cannot be >1mm.
Displacement between double-covered insulation skins cannot be >2 mm.
2). UL specification power cord should be pulled with a force of 16 kgf for 1 minute. Core displacement of power cord should not be >1 mm.
3) JQA specification power cord tension test: 9kgf tension test, pull for 15 seconds, do not touch internal connections.
4) During TUV/UL specification power cord tension test, inner connection of power cord needs to be removed.
Solder pull
Solder pulling force is >5kgf. When soldering, tin wire must be completely melted and penetrated into wire core and copper foil.
"Restriction of use of certain hazardous substances in electrical and electronic equipment"
Table 2 Six types of hazardous substances restricted by RoHS Directive

Corresponding to EU directive, at present, China's Ministry of Information Industry has formulated "Measures for Management of Pollution Prevention and Control of Electronic Information Products" in accordance with relevant provisions of "Law on Promotion of Clean Production" and "Law on Prevention and Control of Environmental Pollution by Solid Matter", and it will be implemented on January 1, 2005. Producers of my country's electronic information products (electronic radar products, electronic communication products, radio and television products, computer products, household electronic products, electronic measuring instruments, electronic special products, electronic components, electronic application products, electronic materials products) shall take measures to gradually reduce and eliminate content of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl (PBB), polybrominated diphenyl ether (PBDE) and other toxic and harmful substances in electronic information products; for those that cannot be completely eliminated, content of toxic and harmful substances shall not exceed relevant provisions of national standards.
Regarding content of toxic and harmful substances in environmentally friendly materials, General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China has issued ten national mandatory standards for limit of harmful substances in indoor decoration materials. Standards for limit of harmful substances in wallpapers of indoor decoration materials are of reference significance to electronic information products:

 

Find required materials by yellow card number

 

Plastic materials can be divided into two categories: thermoplastics and thermosetting plastics.
Thermoplastics can be divided into three types based on their conformation (different forms): amorphous polymers (PS, PC, PMMA), semi-cured polymers (PE, PPPA), and liquid crystal polymers (LCPs)
Thermoplastics soften and flow when heated, solidify and harden after cooling to become solid. Thermoplastics are composed of curved polymers. When heated, they only undergo physical changes. Groups on their molecular chains are stable, and no chemical reactions occur between molecules. Most thermoplastics can be dissolved by chemical solvents. They are less resistant to chemicals than thermosetting plastics, their use temperature is lower than that of thermosetting plastics. Their mechanical properties and hardness are also relatively low. Due to its mature production process, wide source, and recyclability, it is currently widely used.
Common engineering plastics: PA polyamide, POM polyoxymethylene, PC polycarbonate, PPO modified polyphenylene ether, PET/PBT polyester

 

It has good mechanical strength and wear resistance, but no self-lubricating effect. It has good low temperature performance, still shows good toughness at -40 degrees, and is easy to color.
Material humidity should be guaranteed to be less than 0.1%. Melting temperature: 210~280℃; recommended temperature: 245℃. Mold temperature: 25~70℃.
Heat deformation temperature of ABS is 65~70 degrees. Shrinkage: 0.4~0.7%, 0.6%.

Transparency can reach 90%, rigid and tough, high impact strength, operating temperature can reach more than 120 degrees, but poor stress resistance and cracking resistance.
Typical application range: electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry (vehicle front and rear lights, dashboards, etc.).
Melting temperature: 260~340℃.
Mold temperature: 70~120℃.
Injection pressure: Use high injection pressure as much as possible.
Injection speed: Use low speed injection for smaller gates and high speed injection for other types of gates.

PC/ABS has combined properties of both PC and ABS. For example, easy processing properties of ABS, excellent mechanical properties and thermal stability of PC.
Ratio of the two will affect thermal stability of PC/ABS materials. PC/ABS blends also show excellent flow properties.

Yield strength, tensile strength, compressive strength and hardness are better than PE. It has a particularly high bending fatigue strength and can be used to make dumpling chains. It has good heat resistance and can only be used at low temperatures of -15 degrees, but it will crack when it is below -35 degrees. It is easy to age and does not absorb water (good high-frequency insulation performance).
Melting temperature: 220~275℃, be careful not to exceed 275℃.
Mold temperature: 40~80℃, 50 degrees is recommended. Degree of crystallization is mainly determined by mold temperature.
Shrinkage rate is quite high, generally 1.0~2.5%.

Abrasion-resistant, high-strength, good toughness, self-lubricating, can be used for a long time at -40~100 degrees. High water absorption makes product size change greatly, and it must be dried in hot air before molding.
Melting temperature: 230~280℃, 250~280℃ for reinforced varieties.
Mold temperature: 80~90℃
Shrinkage rate of PA6 is between 1% and 1.5%

Melt temperature: 225~275℃. For products with glass additives, it is 275~280℃. Melting temperature should be avoided above 300℃.
Mold temperature: 80℃ is recommended
Shrinkage rate of PA66 is between 1% and 2%

POM has a very low friction coefficient and good geometric stability, is particularly suitable for making gears and bearings. Because it is also resistant to high temperatures, it is also used in pipeline devices (pipeline valves, pump housings), lawn equipment, etc.
POM is a tough and elastic material that has good creep resistance, geometric stability and impact resistance even at low temperatures
Melting temperature: 190~230℃ for homopolymer materials; 190~210℃ for copolymer materials.
Mold temperature: 80~105℃. In order to reduce shrinkage rate after molding, a higher mold temperature can be selected.
Injection pressure: 700~1200bar
Injection speed: medium or high injection speed.
High degree of product formation of POM leads to a relatively high shrinkage rate, which can be as high as 2%~3.5%. Different shrinkage rates for different reinforced materials.

It is white waxy at room temperature, translucent particles, soft and tough, easy to deform, lighter than water, and non-toxic.
Melting temperature: 220~260℃. For materials with larger molecules, recommended melting temperature range is between 200~250℃.
Mold temperature: 50~95C. Plastic parts with wall thickness below 6mm should use higher mold temperature, plastic parts with wall thickness above 6mm should use lower mold temperature. Cooling temperature of plastic parts should be uniform to reduce difference in shrinkage rate. For optimal processing cycle time, cooling channel diameter should be no less than 8mm, and distance from mold surface should be within 1.3d (here "d" is diameter of cooling channel).

Melt temperature: 180~280℃
Mold temperature: 20~40℃
In order to achieve uniform cooling and more economical heat removal, it is recommended that cooling cavity diameter is at least 8mm, and distance from cooling cavity to mold surface should not exceed 1.5 times cooling cavity diameter.
Injection pressure: up to 1500bar.
Holding pressure: up to 750bar.

Has good electrical properties, good arc resistance, no moisture absorption, and good molding processability. Commonly used in instrument housings, junction boxes, toys, etc.
Melting temperature: 180~280℃. For flame-retardant materials, upper limit is 250℃.
Mold temperature: 40~50℃.
Injection pressure: 200~600bar.
Shrinkage is between 0.2~0.7%, usually 0.4%

Typical application range: wire sheathing, water supply pipes, household pipes, house wall panels, commercial machine housings, electronic product packaging, medical equipment, food packaging, etc.
Melting temperature: 185~205℃.
Mold temperature: 20~50℃.
Shrinkage rate of PVC is quite low, generally 0.2~0.6% (hard)

PMMA Polymethyl methacrylate is commonly known as "plexiglass"
PMMA is used to make transparent parts.
Penetration of white light is as high as 92%
Melting temperature: 240~270℃.
Mold temperature: 35~70℃.
Shrinkage is between 0.2~0.9%

1. Versatility
2. Easy to mold into complex special-shaped parts
3. Low relative density
4. A certain degree of light transmittance
5. Coloring-integrality
6. Lower processing energy requirements
7. Chemical resistance
8. Mechanical properties: Plastic materials can be elastic or hard rigid materials, and their mechanical properties have a certain range of variation.
9. Good insulation
10. Flammability
11. Poor weather resistance
12. Higher coefficient of thermal expansion (CTE)

Physical properties of materials: density, relative density, elasticity, plasticity, toughness, rigidity, brittleness, notch sensitivity, isotropy, anisotropy, water absorption and molding shrinkage, etc.
Elasticity: It is ability of a material to partially or completely recover to its original size and shape after deformation.
Plasticity: It is ability of a material to maintain its deformed shape and size after being deformed by force.
Toughness: It is ability of a polymer material to absorb mechanical energy through elastic deformation or plastic deformation without being damaged.
Ductility: Elongation of a material that is not damaged by stretching or calendering is called ductility.
Brittleness: It is property of a polymer material that is prone to fracture when absorbing mechanical energy.
Notch sensitivity: Property of a material that cracks from an existing notch, crack or sharp angle, and crack quickly penetrates the entire material is called notch sensitivity.
Isotropy: Isotropic materials are thermoplastic or thermosetting materials with same physical properties in any direction.
Anisotropy: Properties of anisotropic materials are related to test direction. Reinforced plastics have higher properties in direction of arrangement of fiber reinforcements.
Water absorption: Water absorption is expressed as percentage of mass increase after material absorbs water.
Molding shrinkage: Molding shrinkage refers to shrinkage of size of part relative to mold size after it is removed from mold and cooled to room temperature.
Ball pressure test conditions: weight 20N, steel ball diameter 5mm, indentation diameter less than 2mm after 1 hour. Above conditions must be met at test temperature.
Experimental conditions for heat deformation temperature of plastic materials: 45N/cm2 (0.45MPa) or 180N/cm2 (1.8MPa) deformation is 0.25mm. Temperature when deformation is greater than 0.25mm.
Polymers prone to stress cracking include: acrylic, polycarbonate, polystyrene, SAN, polysulfone, ABS, and PPO.

When designing general products, performance and cost should be considered comprehensively. Following is a typical material selection process
(1) Conception of parts: Conduct preliminary functional design, that is, shape of part and shape of its functional elements, and consider selection of basic processing methods
(2) Material selection: Screen candidate materials based on engineering properties and processability of plastics related to performance under stress, which are applied to product when part is working.
(3) Preliminary analysis and design: Use engineering design properties to calculate wall thickness and other dimensions of part. Design product and mold according to characteristics of plastic.
(4) Trial samples: Test and evaluate under actual use conditions of part or under simulated use conditions of part.
(5) Redesign and retest: When it is found that performance does not meet requirements of use, re-screen material or redesign and test.
(6) Determine final design and material selection based on test results of trial samples and cost of processing parts.
(7) Determine technical specifications and inspection methods of materials.
Sometimes above steps can be shortened, especially when requirements for parts are simple or difference between new parts and old parts is small. However, sometimes material selection step is more complicated, especially when developing new applications or when stresses to which plastic is subjected are very complex. A systematic and comprehensive analysis method is not only a reliable way to succeed, but also a way to save development costs.
2. General material selection for plastics
When designers start designing components or draw part drawings, they should list the use conditions and important material selection factors for components, then select materials reasonably. It includes following three steps:
(1) According to application purpose, list all functional requirements of components (not performance of material) and quantify them as much as possible. For example:
① Maximum deformation allowed under rated continuous load;
② Type and size of stress during use and transportation; whether it is subjected to long-term stress, dynamic or static stress;
③ Maximum operating temperature
④ Allowable dimensional changes at operating temperature;
⑤ Allowable dimensional tolerances of parts;
⑥ Performance requirements for parts:
⑦ Whether parts require coloring, bonding, electroplating, etc.
⑧ How long is required storage period, whether it is used outdoors;
⑨ Whether there are flame retardant requirements, etc.
2) According to functional requirements of components, consider performance values (engineering performance) and design data, propose performance values of target material (component material), and select material based on these performance requirements. Even if these performance estimates are rough, it will greatly facilitate screening of candidate materials and provide a useful basis for final material selection.
Selecting appropriate material performance is critical and complex, because a certain function of a component often includes several properties. For example, in requirements of dimensional stability, in addition to dimensional accuracy, linear expansion coefficient, molding shrinkage, water absorption, creep, etc. must also be considered. In addition to considering material properties, strength and stiffness of parts must also be considered from product structure design (such as thickness and reinforcement). Molding processability, durability, and economy of material are also factors that should be considered when selecting materials. Sometimes, certain usage requirements may not clearly state quantitative requirements for material performance. For example, electroplating properties often need to be screened through actual tests or existing experience. Another example is plastic artillery shell belts. Material is required to withstand complex external forces such as high-speed impact, compression, twisting, shearing, and influence of high-speed, high-temperature, and high-pressure airflow. It is difficult to directly propose quantitative performance requirements for material. Therefore, in addition to mechanical calculations, simulation tests and exploratory tests can also be used to deduce stress conditions and propose rough performance requirements.
(3) Finally, candidate materials are determined by comparing engineering performance requirements of components with material properties.
Following issues should be noted when selecting plastics:
① You must have a comprehensive understanding of performance of selected plastics, then consider formulation, process and product design according to conditions of use.
②) Plastics generally have low thermal conductivity, so full attention should be paid when selecting and designing.
③ Linear expansion coefficient of plastics is generally larger than that of metals, and some are easy to absorb water, so size changes greatly. When selecting and designing, appropriate gap and tolerance range should be considered.
④ Some plastics have a tendency to stress cracking. When selecting and designing, stress should be minimized as much as possible. Product design should avoid stress concentration, or appropriate post-processing should be performed, and processing technology should be strictly controlled.
⑤ Some plastics have a tendency to creep and shrink or deform afterward. Full attention should be paid when selecting and designing.
⑥ Various plastics have a certain range of use strength and media allowed to contact, as well as pressure and speed limits that can be tolerated, which should be considered when selecting and designing.
(1) Based on application purpose, such as product's load conditions, operating environment, temperature, electrical performance, etc.
2) Based on functional requirements of component, such as product's dimensional stability, shrinkage (caused surface defects), water absorption, creep, temperature resistance, moving parts or stationary parts, external force conditions, etc.
(3) Finally, determine candidate materials by comparing component's engineering performance requirements with material properties.
Material selection must comply with safety standards.

Product development plan (decided by upper level).
Conduct market research and collect customer information.
- Target consumer groups, product usage patterns and environmental requirements.
- Basic parameters and performance range of products.
- Determination of product design task book: product name (follow company's naming rules and do not change it at will), materials used for components, regions where product is sold, safety standards used, development cycle, etc.
Design appearance of product. Appearance is designed according to development task book or customer information. Only after appearance proposal is confirmed can structure be fully designed.
- Ergonomic.
- Appearance should be novel to customer.
- Whether it can accommodate all functional structures.
Product structural design, appearance can be adjusted for structure.
①Determine material used for product.
②Determine mold opening direction and parting line.
③Understand role of each structure, make structure tight and reasonable. Only after understanding its role can structure be improved and reasonably designed.
④Consider draft angle while making structure (impact on structural size)
⑤Try to use standard parts and general parts to simplify structure and reduce costs.
⑥Matching relationship between components and determine reserved clearance value.
⑦Consider principle of product series. (Appearance should be similar to series, structure should be general to reduce costs and shorten development cycle)
⑧Indicate mold making method of certain structures on mold opening drawing. ((Leave a way for yourself)
⑨Propose a product development proposal. (Confirm mold opening)

Design of molded plastic parts or products should take into account factors such as aesthetic requirements, processing performance and various performance characteristics.
① Dimensional stability and ability to withstand stress and strain induced by external factors.
② Stress and strain generated during product manufacturing and assembly.
→ It is necessary to conduct a structural reliability assessment of proposed design to ensure that product can remain normal during assembly and use.
Definition of structural design (summarized by limit state principle): Purpose of structural design is to obtain a practical and reliable solution so that designed structure can meet its use requirements, leave room for improvement, that is, it cannot reach limit state.
Task of structural design is to design a component that can withstand loads and imposed deformations, because component is likely to encounter these two external forces when in use. → Load conditions that can represent normal use conditions; → Or can represent what is considered to be the worst case.
Fundamentals are goal of structural designers, but failure analysis of a specific plastic part design is very difficult because performance of plastic materials is strongly affected by use environment and processing conditions, two factors that are far beyond complete control of product designers.
Design method (solution)
Design based on previous experience (as a well-founded assumption or applying empirical rules).
There is no substitute for design experience, and rapid development of current plastics industry has led to a shortage of experienced plastic product designers. Designing plastic parts based on past experience has been widely used in plastic product design.
→Under-safe design: product is damaged during use or assembly.
→Over-safe design: product must be good to use. Disadvantages are as follows:
①More complex than actually needed.
②More material than actually needed.
③Excessive wall thickness leads to production cycle and quality problems
④High design costs for products.
→Although experience is irreplaceable, possibility of obtaining the best structural design using only empirical methods is small (complex structure).
A reliability design is carried out by using experimental methods and sample analysis.
The most likely way to obtain a reliable design is through sample analysis and repeated design of structure, but conditions are:
① Quality of sample can represent quality of product;
② Expected experimental conditions can be simulated or estimated.
③ This method is very expensive, and the more important problem is that design takes too long, especially when evaluating long-term effects such as creep behavior or environmental stability.
An analytical approach to strain engineering relevance is employed.

 

Part wall thickness: h
Slope of each side (θ): 0.5°~1.5°
Rib height (L): <5h, (typically 2.5~3.5h)
Rib spacing (center): ≥2~3h
Root fillet radius (R): 0.25~0.40h
Rib thickness (t): 0.4~0.8h (generally 0.6)
Specific size of rib varies with material.

 

For plastic materials with large shrinkage rates, rib thickness is 0.5t; for plastic materials with small shrinkage rates, maximum rib thickness can be 0.75t.