I. Three Rules of Material Selection
There are three golden rules for material selection. Industry experience dictates that mechanical material selection follows three principles: first, select based on performance to ensure the material meets functional requirements (such as load type, wear resistance, and corrosion resistance);
second, select based on manufacturability to ensure the material can be processed (considering machinability, weldability, and heat-treatability); and third, select based on cost-effectiveness to control expenses while satisfying the first two criteria. These three factors collectively determine the final material choice.
II. Steel Materials
Selecting steel materials.
Industry data indicates that 45 steel is an all-rounder with excellent comprehensive properties and good hardenability, making it suitable for shafts, gears, and connectors;
its performance can be further enhanced through quenching and tempering or surface hardening, with a price range of approximately 4.5 to 7 RMB per kilogram. Q235 carbon steel is prone to rust and is suitable for sheet metal weldments that will undergo baking varnish or powder coating, costing about 3.5 to 6.5 RMB per kilogram. For heavy-duty, wear-resistant applications, choose 40Cr high-strength alloy steel; for high-impact loads, choose 20CrMnTi; and for rolling elements in bearings, choose GCr15 bearing steel—essentially, the steel grade is determined by the load requirements.
III.
Lightweighting with Aluminum Alloys
Aluminum alloys and lightweighting.
According to industry data, 6061 aluminum alloy offers medium strength (tensile strength approx. 260–310 MPa, yield strength approx. 240–275 MPa) and good corrosion resistance and machinability; it is suitable for structural components, machine frames, robotic tool plates, and lightweight fixtures, and supports anodizing. 6063 aluminum alloy features excellent extrudability and an attractive anodized finish, making it ideal for decorative parts and heat sinks. 7075 aluminum alloy offers higher strength (tensile strength approx. 572 MPa) and is used for aerospace-grade load-bearing applications—it is the preferred choice for lightweighting.
IV. Stainless Steel and Corrosion Resistance
Stainless steel and corrosion-resistant applications.
Industry experience suggests using 304 stainless steel (containing 18% chromium and 8% nickel) for general rust resistance;
it is corrosion-resistant and food-grade, making it suitable for humid environments, food processing equipment, medical devices, and areas exposed to corrosive gases. For highly corrosive environments, use 316 stainless steel, which includes 2%–3% molybdenum for resistance to saltwater and chemical media. Note that 304 cannot be hardened by quenching and relies on work hardening; do not expect to harden 304 shafts via quenching, and be aware of poor machinability and a tendency for the material to stick to cutting tools—exercise caution when selecting stainless steel for machined parts.
V.
Plastics and Surface Treatment
Engineering plastics and surface treatment.
Industry experience indicates that POM (polyoxymethylene) and ABS are suitable engineering plastics for lightweighting and self-lubricating applications, offering insulation, wear resistance, and low cost. For guide shafts, the standard cost-effective solution is quenched and chrome-plated 45 steel; switch to GCr15 bearing steel for high-precision, heavy-load, and wear-resistant applications, or to 304/316 stainless steel for humid, food-grade, medical, or corrosive environments. Carburizing or nitriding gear tooth surfaces can significantly enhance contact strength—material selection is merely the foundation; heat treatment and surface treatment determine service life.
Conclusion
When selecting materials for automation equipment components, the rule of thumb is: “Analyze operating conditions first, determine the material next, and then specify the treatment.” Use 45 steel (with quench-and-temper and chrome plating for the best cost-performance ratio) for standard structural parts and drive shafts; 40Cr for wear-resistant parts; 20CrMnTi for heavy-impact/high-load applications; and GCr15 for rolling bearing elements. Opt for 6061 aluminum (anodized) for lightweight structural components and 6063 for extruded profiles. Use 304 stainless steel for corrosion-resistant applications (such as in humid environments or the food and pharmaceutical industries) and 316 for highly corrosive environments (noting, however, that it cannot be hardened and has poor machinability); use POM or ABS plastics for lightweight, self-lubricating applications.
Industry practice dictates a three-way balance among load requirements (static, impact, fatigue, and wear resistance), manufacturing processes (machining, welding, heat treatment), and cost-effectiveness. For reference, Q235 costs approximately 3.5–6.5 RMB/kg, while 45 steel costs about 4.5–7 RMB/kg. Ultimately, the material determines the baseline performance, while heat treatment and surface finishing determine the upper limit of service life;
a proper match between these factors constitutes a sound material selection.
