Molds are a vital component in modern manufacturing, widely used across various fields, including automotive, aerospace, electronics, and medical devices. They determine a product’s shape, dimensional accuracy, surface quality, and production efficiency. Different material properties, part complexity, production volume, and cost considerations drive engineers to select the most suitable mold forming process. This report will focus on three common metal forming mold technologies: forging, extrusion, and die casting, and explain how Computer Numerical Control (CNC) technology is revolutionizing mold design and manufacturing.
I. Basic Introduction to Mold Technologies
Forging Molds
Forging is a process that uses pressure (impact or compression) to induce plastic deformation in a metal material, thereby achieving the desired shape and mechanical properties. The forging mold is the tool that shapes the preform into a forged part, making it a critical piece of process equipment in the die forging process.
Principle
Pressure is applied to the metal, causing its internal grain structure to rearrange, which in turn enhances the material’s strength, toughness, and fatigue life. The formation of this grain flow is a key characteristic that makes forged parts superior to cast parts.
Classification
- Hot Forging Molds: Performed above the metal’s recrystallization temperature, suitable for large, complex parts.
- Warm Forging Molds: Performed below the recrystallization temperature but above room temperature.
- Cold Forging Molds: Performed at room temperature, offering high accuracy and good surface quality, suitable for small, precision parts.
- Open-Die Forging: The mold does not completely enclose the workpiece, suitable for simpler or larger parts.
- Closed-Die Forging: The mold completely encloses the workpiece, resulting in no or minimal flash, high material utilization, and high precision; suitable for complex, precision parts.
Applications: Automotive crankshafts, connecting rods, gears, aerospace structural components, turbine blades, heavy machinery parts, etc.
Extrusion Molds
Extrusion is a continuous forming process where metal material (usually aluminum alloy) is forced under pressure through a die opening to obtain a specific cross-sectional shape. Extrusion molds are typically made of high-strength tool steel and must withstand the high pressure and temperature of the extrusion process.
Principle
A heated metal billet is placed in an extrusion container, and pressure is applied by a ram to force the metal through the die opening, creating a profile with the same shape as the die hole[cite: 24]. [cite_start]This is an efficient method for producing long, hollow, or complex cross-section parts.
Classification
- Solid Extrusion Molds: Used to produce solid profiles, such as rods and bars.
- Hollow Extrusion Molds: Used to produce hollow profiles, such as various tubes and shaped pipes.
- Semi-Hollow Extrusion Molds: Intermediate between solid and hollow, possessing a partially hollow structure.
Applications: Architectural profiles (doors, windows, curtain walls), automotive parts (radiators, body structures), electronic product casings (mobile phones, laptops), furniture, rail transportation, etc.
Die Casting Molds
Die casting is a versatile and highly efficient metal casting process that produces geometrically complex metal parts by forcing molten metal under high pressure into reusable molds (called die casting molds).
Principle
Molten metal (such as aluminum, zinc, or magnesium alloys) rapidly fills the mold cavity under high pressure and solidifies under pressure. This process produces parts with high dimensional accuracy, excellent surface finish, and high production efficiency.
Classification
- Hot-Chamber Die Casting Molds: The furnace and injection mechanism are integrated, suitable for lower-melting-point alloys (e.g., zinc, magnesium).
- Cold-Chamber Die Casting Molds: The furnace and injection mechanism are separate, suitable for higher-melting-point alloys (e.g., aluminum, copper).
Applications: Automotive parts (engine blocks, transmission housings), electronic product casings, appliance components, communication equipment, medical devices, etc.
II. Part Selection Criteria
The choice among different mold technologies depends on various factors, including the part’s **material, shape complexity, dimensional accuracy requirements, mechanical properties, production volume, and cost budget.
| Characteristic/Technology | Forging | Extrusion | Die Casting |
|---|---|---|---|
| Material | Steel, Aluminum, Titanium, Copper alloys | Aluminum alloys, Copper alloys | Aluminum, Zinc, Magnesium, Copper alloys |
| Shape Complexity | Medium to complex, but usually with some limitations | Complex cross-sections, long profiles | Highly complex, thin walls, fine structures |
| Dimensional Accuracy | Medium to high | Medium to high | High |
| Surface Finish | Good, may require post-processing | Good, may require post-processing | Excellent, usually no post-processing required |
| Mechanical Properties | Excellent (grain flow), high strength | Good, directional | Good, but porosity may be present |
| Production Volume | Medium to high volume | High volume | Very high volume |
| Mold Cost | High | Medium | High |
| Per-Part Cost | Medium | Low | Low |
| Typical Parts | Crankshafts, connecting rods, gears, turbine blades | Door/window profiles, heat sinks, electronic casings | Automotive engine blocks, electronic casings, appliance components |
Specifically, Forging is suitable for critical load-bearing parts requiring high strength, high toughness, and high reliability. Extrusion is best suited for producing long profiles with a constant cross-sectional shape, especially aluminum alloy profiles. Die Casting is the ideal choice for producing high-volume parts with thin walls, complex shapes, high dimensional accuracy, and strict surface quality requirements.