Material Processing: Sintering, Casting, and Molding Methods
Material Processing Techniques
Heat Treatments
Sintering
A process that consists of applying pressure and high temperature, below the melting point.
Hardening (Temple)
Heating the material to a temperature between 800-1000°C and then cooling it rapidly. Achieves maximum possible hardness.
Tempering (Revenido)
Heating to 200-500°C to achieve desired characteristics of elasticity, tenacity, and toughness.
Casting and Molding Processes
Metals Casting
Metals, melted with heat, are poured into a mold containing cavities.
Ceramics Casting
Involves casting a slurry (lechado) of clay (arcilla) and water into a porous mold. The mold draws moisture (atrae humedad) from the mix, producing a slip of uncooked clay.
Plastics Injection Molding
Plastic material is introduced under pressure into a metallic mold where it is either cooled (refrigerado) for thermoplastics or cured for thermosets.
Material Preparation for Molding
General Principle
Liquid material flows into a mold. The mold device provides (suministra) the cavity where the material solidifies.
Metals
Furnaces (Hornos) are used to melt the metal. For small quantities of non-reactive metals, a blowtorch (soplete) and crucible (Crisol) may be used.
Thermoplastics
In an injection molder, the barrel melts the polymer. Melting occurs through friction, aided (asistido) by heat generated by electric resistances.
Thermosets
Formed by two separate components, one of which is liquid. Crosslinks (Enlaces cruzados) are formed inside the mold.
Ceramics
Clay particles are put into a suspension with water and then fired at high temperatures.
Mold Types
Permanent Molds
Used multiple times. Made of several parts. Created by machining metal blocks.
Non-permanent Molds
Used only once. Broken to extract the finished part. Typically made with ceramics.
Mold Components and Terminology
- Cope: Upper half of the mold, helps form the cavity where material is poured.
- Riser (Mazar): Supplies additional metal to compensate for material contraction (contracción) during cooling. Helps avoid defects like air inclusions and shrinkage cavities. Designed to solidify last.
- Sprue Core (Núcleo de cono de flujo): Channels the metal from the feeding channel to the mold cavity.
- Cavity (Cavidad): Defines the exterior shape of the object. Filled with molten material.
- Drag (Yunque o Base): Lower half of the mold.
- Gate (Canal de entrada): Connects the feeding system. Allows molten material to flow from the runner into the cavity.
- Runner (Corredor): Channels material from the feeding system to the mold cavity. Distributes metal across multiple cavities if necessary.
- Flask (Caja de moldeo): Structure that holds the casting mold during the pouring process.
- Chaplet (Perno de apoyo): Supports cores in their position within the mold during pouring (la Colada).
- Core Point Pouring Cup: A cup placed on top of a core in the mold, allowing molten metal to be poured directly onto the core’s central point to improve metal distribution and reduce turbulence.
Fundamental Manufacturing Concepts
Solidification Factors
Solidification time depends on temperature, density, surface area, and volume.
Manufacturing Definition
The process of transforming materials into usable objects through physical means.
Process Categories
- Consolidation: Solidification of material, e.g., Casting (Vaciado), Sintering (Sinterizado).
- Machining: Removal of material, creating chips (viruta).
- Forming: Shaping material without removal, e.g., Rolling.
- Joining: Combining parts to create complex shapes.
- Finishing: Surface treatment processes (Acabado).
Sand Mold Composition
- Dry Sand: Silica + thermosetting polymer.
- Green Sand: Silica + clay + water + charcoal.