"Material Selection and Performance Optimization Techniques for Mechanical Design"

Material selection in mechanical design is a key link in determining product performance, cost, reliability and life. This is a complex decision-making process involving multiple factors. The following is a systematic material selection consideration framework and an introduction to common materials:

Common mechanical engineering materials and their typical applications

Steel materials (most widely used):

Carbon structural steel (Q235, 20, 45): general structural parts, shafts, gears, bolts and nuts, etc. Low cost, good processability, and decent overall performance. 45 steel is often used as shafts after quenching.

Alloy structural steel (40Cr, 20CrMnTi, 42CrMo): Important parts that require higher strength, toughness or hardenability. Such as gears, drive shafts, connecting rods, and high-strength bolts. 20CrMnTi is often used as automotive transmission gears (carburizing and quenching).

Tool steel (T8, T10, Cr12MoV, W18Cr4V): Cutting tools, molds, and measuring tools. High hardness, wear resistance, and hot hardness (high-speed steel).

Stainless steel (304, 316, 420, 17-4PH): For occasions requiring corrosion resistance or hygiene requirements. Food machinery, chemical equipment, medical equipment, decorative parts. 304 is general purpose, 316 has better corrosion resistance, 420 can be hardened to make tools/bearings, and 17-4PH is precipitation hardened stainless steel (high strength + corrosion resistance).

Bearing steel (GCr15): Balls and raceways of rolling bearings. Extremely high hardness, wear resistance, and contact fatigue strength.

Spring steel (65Mn, 60Si2Mn): Springs. High elastic limit and fatigue strength.

Wear-resistant steel (such as Hardox): Engineering machinery buckets, crusher liners, etc. Extremely high hardness and wear resistance.

Non-ferrous metals and their alloys:

Aluminum alloys

Advantages: low density, high specific strength, good electrical and thermal conductivity, atmospheric corrosion resistance, and easy processing and molding.

Applications: Aerospace structural parts, automobile body/wheel/engine parts, electronic product housing, radiator, lightweight structural parts.

Copper alloy (brass H62, bronze QSn6.5-0.1, beryllium bronze):

Advantages: excellent electrical and thermal conductivity (pure copper), corrosion resistance, wear resistance (bronze), easy cutting (brass), non-magnetic.

Applications: conductive parts (wires, terminals), radiators, bearings/sleeves (bronze), gears, springs (beryllium bronze), corrosion-resistant parts (marine), decorative parts.

Titanium alloy (TC4):

Advantages: extremely high specific strength, excellent corrosion resistance (especially seawater/chemical), good biocompatibility, heat resistance.

Disadvantages: high cost and difficult to process.

Applications: aerospace engine/structural parts, high-performance racing parts, chemical equipment, medical equipment (implants), seawater desalination equipment.

Magnesium alloy:

Advantages: the lowest density metal structural material, high specific strength/specific stiffness, good shock absorption.

Disadvantages: poor corrosion resistance, flammable, high cost.

Application: extremely weight-sensitive occasions (racing cars, aerospace, portable device housings).

Zinc alloy (die-cast zinc alloy ZA3, ZA8):

Advantages: excellent casting fluidity, can manufacture complex thin-walled parts, low cost, good surface treatment.

Application: a large number of small structural parts, housings, decorative parts, toys, locks used in die-casting.

Engineering plastics:

General plastics (ABS, PP, PE, PVC): housings, containers, pipes, daily necessities. Low cost and easy processing.

Engineering plastics:

Nylon (PA6, PA66, PA12): wear-resistant, self-lubricating, good toughness. Gears, bearings, pulleys, ropes, automotive parts.

Polycarbonate (PC): high transparency, high impact toughness, dimensional stability. Safety glass, lampshades, electronic housings, medical devices.

Polyoxymethylene (POM): high rigidity, low friction, dimensional stability, fatigue resistance. Precision gears, bearings, buckles, zippers.

Polyester (PBT, PET): Good strength and stiffness, heat resistance, electrical insulation. Electrical connectors, switches, automotive parts.

Polyphenylene ether (PPO/PPE): Dimensionally stable, heat resistant, low water absorption. Electrical components, hot water pipes, automotive dashboards.

High-performance plastics (PPS, PEEK, PTFE):

Advantages: extremely high heat resistance, chemical resistance, strength, flame retardancy.

Disadvantages: very high cost.

Applications: aerospace, semiconductors, chemicals, seals, bearings, gears in harsh environments.

Composite materials:

Fiber reinforced plastics (FRP): such as glass fiber reinforced plastics (GFRP/glass fiber reinforced plastics), carbon fiber reinforced plastics (CFRP), Kevlar fiber reinforced plastics.

Advantages: high strength/weight ratio (especially CFRP), strong designability (anisotropy), corrosion resistance, good fatigue performance.

Disadvantages: high cost (especially CFRP), anisotropy requires special design, difficult recycling, difficult damage detection.

Applications: aerospace main structural parts, high-performance automobile/racing car body parts, sports equipment (rackets, bicycles), wind turbine blades, pressure vessels, ships.

Metal matrix composites (MMC): such as SiC particle reinforced aluminum.

Advantages: high specific strength/specific stiffness, wear resistance, good thermal conductivity, improved high temperature performance.

Disadvantages: high cost, difficult processing.

Applications: aerospace, precision instruments, automotive pistons/brake discs (high performance).

Ceramics:

Advantages: extremely high hardness, wear resistance, high temperature resistance, corrosion resistance, insulation.

Disadvantages: extremely brittle, difficult to process, poor impact resistance.

Applications: cutting tools, wear-resistant parts (nozzles, sealing rings), high temperature parts (engine spark plugs, turbine blade coatings), insulators, bioceramics (artificial joints).

Others:

Rubber/elastomers: seals, shock absorbers, tires, hoses. Provide elasticity and sealing.

Wood: traditional structures, models, specific decorative/functional parts. Renewable resources.

Functional materials: piezoelectric ceramics, shape memory alloys, superconducting materials, etc. are used for specific sensors and actuators.

Typical steps for material selection

Clearly define design requirements and working conditions: Detailed analysis of part functions, loads (size, type, direction, static/dynamic/impact), motion forms, working environment (temperature, humidity, medium), life requirements, dimensional accuracy, weight limits, safety requirements, cost targets, etc.

Determine key performance indicators: According to the working conditions, select the most critical 1-3 performance requirements (such as high strength, high wear resistance, corrosion resistance, low density, conductivity).

Preliminary screening of candidate materials: According to the key performance indicators, consult the material manual/database, exclude materials that obviously do not meet the requirements, and select several candidate materials (such as: high-strength steel, titanium alloy, certain engineering plastics or composite materials under high strength requirements).

Evaluate candidate materials: For each candidate material, systematically evaluate its performance in all considerations (mechanics, physics, chemistry, process, cost, reliability, etc.). Make a comparison table.

Consider the manufacturing process: Can the selected material achieve the designed shape and accuracy through the expected manufacturing process (casting, forging, machining, welding, injection molding, etc.) economically and efficiently? The impact of the process on the final performance of the material?

Cost accounting: Estimate the material cost and processing cost (including heat treatment, surface treatment).

Risk assessment: Evaluate the possible modes of material failure (fracture, wear, corrosion, fatigue, deformation) and their consequences. Is a safety factor required? Are there alternatives to reduce risks?

Final decision and verification: Weigh all factors comprehensively and select the best material. If necessary, conduct sample trial production, performance testing or simulation analysis for verification. Consider the stability of the material supply chain.

Documentation: Clearly record the reasons for material selection, material brand, specifications, standards, heat treatment status, surface treatment requirements, etc.

Practical suggestions

Make good use of standards and manuals: ASTM, ISO, DIN, GB and other standards provide a large number of material specifications, performance and test methods. Material manuals are a tool for quick inquiries.

Utilize material databases: Many commercial software (such as Granta CES Selector, Ansys Granta MI) and online databases provide powerful material screening and comparison functions.

Consider maturity and experience: Under the premise of meeting the requirements, give priority to mature and familiar materials in the industry to reduce risks.

Focus on surface treatment: Surface treatment (electroplating, spraying, carburizing/nitriding, anodizing, PVD/CVD coating) can significantly improve the surface properties of materials (wear resistance, corrosion resistance, and aesthetics), and is sometimes more cost-effective than replacing the base material.

Consult suppliers: Material suppliers usually have a deep understanding of the performance, processing and application of their products and can provide valuable suggestions.

Life cycle thinking: Consider the environmental impact of the entire life cycle of materials from mining, manufacturing, use to recycling/disposal (sustainable design).

Core considerations

Mechanical properties (core):

Strength: yield strength, tensile strength, compressive strength (bearing load without failure).

Stiffness: elastic modulus (ability to resist elastic deformation).

Toughness: impact toughness, fracture toughness (ability to resist impact load and crack propagation).

Hardness: The ability of the surface to resist local plastic deformation (such as indentation, scratches, and wear).

Fatigue strength: The ability to resist fatigue fracture under alternating loads.

Creep strength: The ability to resist slow plastic deformation at high temperatures.

Wear resistance: The ability to resist the loss of friction surface material.

Physical properties:

Density: Affects weight (key to lightweight design).

Thermal properties: Thermal expansion coefficient (dimensional stability), thermal conductivity (heat dissipation), specific heat capacity, melting point/heat resistance.

Electrical properties: Conductivity, insulation (key to electrical equipment).

Magnetic properties: Ferromagnetic, paramagnetic, antimagnetic (key to motors and sensors).

Chemical properties (environmental resistance):

Corrosion resistance: The ability to resist environmental (atmosphere, water, acid, alkali, salt, etc.) erosion.

Oxidation resistance: The ability to resist oxidation (rust, peeling) at high temperatures.

Chemical solvent resistance: The ability to resist erosion by specific chemicals.

Biocompatibility: Key to medical devices).

Processability:

Casting properties: fluidity, shrinkage, segregation tendency.

Forging/formability: plastic deformation ability, cold/hot forming performance.

Machinability: machinability, tool wear, surface quality.

Weldability: weld joint quality, crack sensitivity.

Heat treatability: potential for improving performance through heat treatment (hardenability, etc.).

Surface treatment: adaptability to electroplating, spraying, carburizing/nitriding, etc.

Economical:

Material cost: unit price of raw materials.

Processing cost: manufacturing, heat treatment, surface treatment and other costs.

Procurement difficulty: whether the material is easy to obtain, delivery cycle.

Overall cost: consider material utilization, waste recovery value, product life cycle cost.

Reliability, safety and life: for parts with serious failure consequences (such as pressure vessels, aviation components), the material must have extremely high reliability and predictability.

Safety factor needs to be considered.

Estimate performance degradation (wear, corrosion, fatigue) within the design life.

Other special requirements:

Weight limit (aerospace, automotive lightweight).

Appearance requirements (decorative parts).

Non-magnetic requirements (certain precision instruments).

Vibration and noise reduction requirements.

Summary: Material selection for mechanical design is a decision-making process that balances art and science. There is no "best" material, only the "most suitable" material. In-depth understanding of part requirements, material properties and manufacturing processes, and finding the best balance between cost, performance, reliability and sustainability are the keys to successful material selection. If you have specific parts or application scenarios, I can provide more targeted material selection suggestions.