Materials and Processes
Steels and heat treatment, non-ferrous alloys, welding, corrosion, casting and forging, sheet metal, injection molding, composites, and material selection, testing and failure, with worked numbers.
Every engineered part is a choice of material and of the process that shapes it, and the two cannot be separated: a steel that cannot be welded, an aluminum that will not bend without cracking and a plastic that warps in the mold are all good materials used the wrong way. This guide covers the metals and how heat treatment changes them (steels, aluminum, copper, titanium), the main processes (welding, casting, forging, sheet metal forming, injection molding, composites), corrosion and protection, and the selection, testing and failure analysis that tie them together. One hydraulic press, with its 4140 piston rod, welded S355 frame, cast block, sheet guard and molded cover, runs through the pages, and every number is computed. The strength and fatigue side is in Structures and Strength of Materials, and the machining in CNC Machining.
Start here: what do you need?
| I need to… | Go to |
|---|---|
| harden, temper or case-harden a steel | Steels and Heat Treatment |
| choose between aluminum, copper, titanium or magnesium | Aluminum, Copper, Titanium and Other Alloys |
| weld a joint, size a fillet or decide on preheat | Welding Processes and Weld Design |
| stop corrosion, choose stainless or a coating | Corrosion and Protection |
| design a casting or decide between casting and forging | Casting, Forging and Powder Metallurgy |
| bend sheet, compute the flat length or the press force | Sheet Metal Forming |
| design a molded plastic part or estimate cost and cycle time | Injection Molding and Plastics Processing |
| use glass or carbon fiber composites | Composites and Fiber-Reinforced Plastics |
| compare materials, check toughness or analyze a failure | Material Selection, Testing and Failure |
A suggested order
Start with the metals: Steels and Heat Treatment and Aluminum, Copper, Titanium and Other Alloys. Then the ways of making and joining them: Welding Processes and Weld Design, Casting, Forging and Powder Metallurgy and Sheet Metal Forming. Corrosion and Protection applies to all of them. The non-metals follow in Injection Molding and Plastics Processing and Composites and Fiber-Reinforced Plastics, and Material Selection, Testing and Failure puts the choice together.
- Steels and Heat Treatment: Carbon and alloy steels, quenching and tempering, hardenability, case hardening and the numbers that go with them.
- Aluminum, Copper, Titanium and Other Alloys: Aluminum tempers, copper and brass, titanium, magnesium and zinc: properties, strength-to-weight and thermal expansion.
- Welding Processes and Weld Design: Arc processes, heat input, carbon equivalent and preheat, fillet weld sizing, distortion and inspection.
- Corrosion and Protection: Galvanic corrosion, corrosion rate, stainless steel, coatings, galvanizing and cathodic protection with worked numbers.
- Casting, Forging and Powder Metallurgy: Solidification time, risers, shrinkage, forging force and when to cast, forge or machine from bar.
- Sheet Metal Forming: Bend allowance and K-factor, springback, minimum bend radius, blanking force and deep drawing.
- Injection Molding and Plastics Processing: Clamp force, cooling time, shrinkage, wall thickness rules, cost per part and other plastic processes.
- Composites and Fiber-Reinforced Plastics: Rule of mixtures, laminates, sandwich panels, manufacturing and design rules for glass and carbon fiber parts.
- Material Selection, Testing and Failure: Ashby indices, weighted selection, toughness and fracture, tests, failure analysis and a worked selection.
One press, nine processes
Worked example: the parts of the hydraulic press
- The piston rod (Steels and Heat Treatment): 4140, oil-quenched and tempered at 540 °C: 36 HRC, about 1 160 MPa tensile.
- The frame (Welding Processes and Weld Design): S355 with a carbon equivalent of 0.42; a 4 mm throat fillet carries 5 times the cylinder load.
- The cylinder block (Casting, Forging and Powder Metallurgy): cast iron, 200 × 200 × 60 mm, solidifying in about 9 minutes, fed by a riser of 1.25 times its solidification time.
- The guard (Sheet Metal Forming): 3 mm steel, bend allowance 6.6 mm, flat length 189.2 mm; a glass-fiber alternative (Composites and Fiber-Reinforced Plastics) is about 40 percent lighter for equal stiffness.
- The cover (Injection Molding and Plastics Processing): ABS, 2.5 mm wall, a 23-second cycle, about 0.93 each at 50 000 parts.
- The finish (Corrosion and Protection): an 85 µm galvanized frame lasts about 60 years in an urban atmosphere.
Quick reference: the equations
| What you need | Equation |
|---|---|
| Martensite hardness | HRC ≈ 20 + 60 √C (percent carbon) |
| Tempering parameter | P = T (20 + log10 t), T in K, t in hours |
| Hardness to strength | UTS (MPa) ≈ 3.45 × HB for steel |
| Carbon equivalent | CE = C + Mn ÷ 6 + (Cr + Mo + V) ÷ 5 + (Ni + Cu) ÷ 15 |
| Weld heat input | kJ/mm = η V I × 60 ÷ (1 000 × speed in mm/min) |
| Corrosion rate | mm/yr = 3.27 × 10⁻³ icorr EW ÷ ρ |
| Solidification time | t = B (V ÷ A)² |
| Bend allowance | BA = (π ÷ 180) θ (R + K t) |
| Blanking force | F = L t τ, τ ≈ 0.8 UTS |
| Cooling time (molding) | t = h² ÷ (π² α) × ln[(4 ÷ π)(Tm − Tw) ÷ (Te − Tw)] |
| Rule of mixtures | E1 = Vf Ef + (1 − Vf) Em |
| Critical crack | ac = (1 ÷ π) (KIC ÷ (Y σ))² |
Related guides and tools
- Structures and Strength of Materials, Fatigue and Failure and the Material Properties Table.
- Sheet-Metal Bend Allowance Calculator, Steel and Plate Weight Calculator and Weld Size Calculator.
- CNC Machining, Laser Cutting, 3D Printing and Speeds and Feeds.
- Hydraulics and Pneumatics for the press.
- The Downloads library (a welding formula sheet and the sheet-steel gauge table).
Safety first
- Heat treatment and casting involve molten metal, hot oil and furnaces: burns, fire, steam explosions and toxic fume. Train, wear proper PPE and never let water touch molten metal.
- Welding: arc eye, burns, fume, fire and electric shock (see the welding page and Workshop Safety).
- Presses, shears and brakes crush: guard and interlock them, and never reach into the die.
- Plastics, resins and composites: sensitizing resins and hardeners, dust and fume, flammable solvents: ventilate and protect skin and lungs.
- Metal dusts and fines (magnesium, titanium, aluminum) burn or explode; use Class D extinguishers and dry the swarf.
- The numbers here are for study and preliminary design. Critical parts need the specification, the supplier’s data, the standard and testing.
FAQ
Where do I start?
Read Steels and Heat Treatment for the metal you will use most, or Material Selection if the question is which one.
Which is the cheapest way to make one part?
Machining from bar or plate, or fabrication or 3D printing: no tooling. Casting, forging and molding pay back only at volume (Casting has a break-even example).
Where can I find material properties?
In the Material Properties Table, the Material Properties page in the Structures guide, handbooks such as Machinery’s Handbook and the ASM Handbooks, and the supplier’s data sheet.
Where is machine design?
It is the next guide in this series.
References
- ASM Handbooks (Heat Treating, Welding, Casting, Corrosion, Failure Analysis); Callister, W. D., Rethwisch, D. G., Materials Science and Engineering, Wiley; Ashby, M. F., Materials Selection in Mechanical Design.
- Kalpakjian, S., Schmid, S. R., Manufacturing Engineering and Technology, Pearson; Groover, M. P., Fundamentals of Modern Manufacturing, Wiley; Machinery’s Handbook, Industrial Press.
- ISO, ASTM, EN and AWS standards for materials, tests, welding and coatings (cited on each page).
Last reviewed: November 2026. Values are typical; check the standard, the supplier’s data and the requirements that apply to your part.