تصنيع 5

    Cards (13)

    • Forging
      A deformation process in which the work is compressed between two dies, using either impact or gradual pressure to form the part
    • Forging
      • A workpiece is compressed between two opposing dies, so that the die shapes are imparted to the work
      • Forgeability is the capability of a material to undergo deformation without cracking
      • Forging is traditionally a hot working process, but many types of forging are performed cold
      • A forging machine that applies an impact load is called a forging hammer, while one that applies gradual pressure is called a forging press
      • Part sizes may range from very small parts to very large (up to 23 m) long shafts
    • Forged parts
      • Gears
      • Bolts and rivets
      • Hand tools
      • Numerous structural components for machinery, aircraft, railroads
      • A variety of other transportation equipment
    • Classification of Forming Processes (by temperature)
      • Cold Forging
      • Hot and Warm Forging
    • Cold Forging
      • Requires higher forces due to the higher strength of the workpiece material
      • Workpiece material must possess sufficient ductility at room temperature to undergo the necessary deformation without cracking
      • Advantage is the increased strength that results from strain hardening of the component
      • Cold-forged parts have a good surface finish and dimensional accuracy
    • Hot and Warm Forging
      • Most forging operations are performed hot or warm, owing to the significant deformation demanded by the process and the need to reduce strength and increase ductility of the work metal
      • Requires lower forces, but the dimensional accuracy and surface finish of the parts are not as high as in cold forging
    • Classification of Forming Processes (by die type)
      • Open die forging
      • Impression-die forging (Closed-die forging)
      • Flashless forging (True closed-die forging)
    • Open die forging
      • The simplest forging operation for producing simple shapes
      • Also called upsetting or flat-die forging
      • Two dies having simple geometric shapes (e.g., parallel flat, semicircular) are employed, normally on large workpieces
      • Forged parts have good strength and toughness, and very reliable for highly stressed and critical applications
    • Impression-die forging (Closed-die forging)
      • The die surfaces contain a shape or impression that is imparted to the work during compression
      • Usually carried out at elevated temperatures for enhancing the ductility of the metals and to lower the forces
      • During deformation, some of the material flows outward and forms a flash
    • Flashless forging (True closed-die forging)
      • The work is completely constrained within the die and no excess flash is produced
      • The volume of the starting workpiece must be controlled very closely so that it matches the volume of the die cavity
    • Analysis of Open-Die Forging
      1. Compression of a workpart of cylindrical cross section between two flat dies
      2. Reduces the height of the work and increases its diameter
      3. True strain experienced by the work during the process can be determined by: ε = ln (h0/h)
      4. Force required to continue the compression at any given height h during the process can be obtained by: F = Yf A
    • Barreling effect
      • Occurs in actual upsetting operations due to friction opposing the flow of workmetal at the die surfaces
      • More pronounced in hot working due to higher coefficient of friction and heat transfer at the die surfaces
      • Can be reduced by using an effective lubricant and/or heated dies
      • More significant as the diameter-to-height ratio (D/h) of the workpart increases
    • Lubricants in forging
      • A wide variety of metalworking fluids can be used
      • Greatly influence friction and wear, affecting the forces required and the manner in which the material flows into the die cavities
      • Act as a thermal barrier between the hot workpiece and the relatively cool dies, slowing the rate of cooling of the workpiece and improving metal flow
      • Act as a parting agent, preventing the forging from sticking to the dies and helping in its release from the die