Manufacturing Technology: An Overview

Manufacturing Technology Overview

• Manufacturing technology is a branch of Mechanical Engineering
• Focused on industrial production of goods via advanced machine tools
• Transforms raw materials into final products
• Aims to improve manufacturing processes, techniques, efficiency, reliability, cost, and safety

Systematics of Manufacturing Technology

• Divided into three fundamental clusters based on geometry

Formative Manufacturing Technology

• Achieves desired geometry by applying external force or heat
• Includes casting and forging

Subtractive Manufacturing Technology

• Achieves desired geometry by removing material

Additive Manufacturing Technology

• Achieves desired shape by adding material
• Often uses staggering contoured layers, known as layer or layered technology

Casting Process Basics

• Casting involves molten metal flowing into a mold
• The metal solidifies to match the mold cavity's shape
• Metal is heated to a liquid state before pouring into the mold
• Can be carried out in a foundry, equipped for mold making, melting, handling, and cleaning
• Molds contain a cavity that shapes the cast part
• Molds are often designed oversized to compensate for metal shrinkage during solidification/cooling

Types of Molds

• Can be made of sand, plaster, ceramic, or metal
• Open molds are filled directly by pouring metal into the cavity
• Closed molds utilize a gating system to guide molten metal flow

Solidification, Cooling, and Processing

• Solidification starts when molten metal cools to its freezing point
• The metal takes the solid shape of the mold cavity during solidification
• After cooling, the casting is removed
• Additional processing may be required such as surface cleaning, heat treatment, and machining for tight tolerances

Expendable Mold Casting

• The mold is destroyed to remove the casting
• Sand casting is an example, where molten metal is poured into a sand mold, and the mold is then sacrificed
• Well-suited for intricate geometries and low-volume, custom designs

Permanent Mold Casting

• Molds are reusable for multiple castings
• Die casting utilizes intricate mold designs and is suitable for high-volume, repetitive production
• Economical for high-production operations, but has mold opening limits

Heat and the Casting Process

• Furnaces heat the metal to a molten temperature for casting

Heat Energy

• Needed to raise temperature to the melting point, convert from solid to liquid (heat of fusion), and reaching desired pouring temperature

Bernoulli's Theorem Principle

• States that the total energy in a flowing liquid is constant at any two points, including head, pressure, kinetic energy, and friction losses

Simplified Equation

• v = √2gh: Applies when friction losses and pressure changes are ignored
• v is the velocity of liquid metal at the sprue base (cm/s)
• g is 981 cm/s
• h is the sprue's height CM

Continuity Law

• States that the fluid volume throughout flow space should remain constant

Passageways

• Sprue: Casting mold passageway to flow molten metal to the mold cavity

Tapered Sprue

• Designed to prevent air aspiration by matching cross-sectional area to velocity

Molds

• Must ensure constant Q (volumetric flow rate) at the top and bottom of the sprue Q = VA

Mold Filling Time Equation

• TMF = V/Q, gives the minimum time

Fluidity

• Refers to molten metal's ability to flow and fill the mold before freezing
• Is Inversely proportional to viscosity, high viscosity means low fluidity, and low viscosity means high fluidity
• Fluidity can be assessed with the Spiral Mold Test by measuring the length of the solidified metal in a spiral channel - the longer the spiral, the higher the fluidity

Temperature Effects of Casting

• Higher pouring temperature (relative to freezing point) improves fluidity
• Oxide formation, gas porosity, and sand penetration are risks
• Alloys with partially solidified portions have reduced fluidity
• A higher heat of fusion increases fluidity
• A faster rate of heat can reduce fluidity

Sand Casting

• Also known as sand-mold casting
• A process involving pouring molten metal into a sand mold and breaking the mold to remove the casting
• A cavity is created in the sand mold by packing sand around a pattern
• Consists of an approximate duplicate or replica of the part or casting component
• Incorporates a gating and riser system
• Internal surfaces often add a core
• A new mold must be made each time the mold is scarified
• Fabrication considers the pattern and mold

Patterns

• Patterns replicate the object to be cast
• Patterns are often embedded in molding sand
• Generating cavities in molding sand means the patterns are withdrawn
• the Mold cavity becomes filled with molten metal which then solidifies for casting

Type of Pattern Materials

• Wood (Shisham, Kail, Deodar, Teak, Mahogany)
  • Easy to work
  • Lightweight
  • Good surface finish
  • Wooden laminated patterns, strong and reliable
  • Susceptible to moisture
  • Wears out upon sand abrasion
• Metal (Cast Iron, Steel, Brass, Bronze, Aluminum Alloys)
  • Cast Iron
    • strong, brittle
  • Brass
    • Good surface finish, costly, heavy, corrosion
  • Aluminum Allous
    • Lightweight
    • Good machinability
    • Corrosion resistance
• Plastic
  • Thermosetting resin
    • needs a metal reinforcement
• Foam
  • Benzene
  • Ethyl Benzene

Pattern types

• One piece/ Solid Pattern
• Two piece/ Split Pattern
• Cope and drag patterns
• Three or multi piece pattern
• Loose Piece pattern
• Match Plate Pattern
• Follow board pattern
• Gated Pattern
• Sweep Pattern
• Skeleton Pattern
• Segmental or part pattern

Solid Patterns

• A single piece without joints, partings, lines, or loose pieces

Two Piece Patterns

• Must be split if solid patterns are difficult to withdraw from the mold cavity with two pieces joined at the parting line using dowel pins

Three/ Multi-Piece Patterns

• Complicated in shape and difficult to make with one or two pieces, these patterns need multi-molding flasks

Loose-Piece Patterns

• Used when the pattern is difficult to withdraw, these patterns contain loose pieces provided on the pattern, intricate molds, which are removed and withdrawn

Mold Materials

• Must be a suitable and workable material with high refractoriness of natural source
• Metallic and Non Metallic materials are options for creation
  • Metallic consists of cast iron
  • Non Metallic include
    • molding sands
    • plaster of paris
    • graphite
    • silicon carbide
    • ceramics

Various Sands

• Most commonly a non-metallic molding material
  • Inherent properties such as refractoriness, chemical, thermal stability, high permeability, workability and strength
• Types of sands for molds are Natural, Synthetic and Chemically coated

Natural Sands for Molds

• Sourced from natural deposits and require additives and water for molding
• Clay content is slightly higher, so new sand can be added to reduce it

Synthetic Sands for Molds

• Prepared by mixing clay free sand, clay binder and water

Chemically Coated Sands for Molds

• Silica grains coated with a non-thermosetting hydrocarbon resin
• Additional clay binder is OK
• Keeps the moisture content above 3% usually
• Resin carbon helps to keep the molten materials from reacting

Inorganic Binders

• Clay binders found from Fireclay and volcanic rock sources