Materials & Processes in Manufacturing

Transcription

1 Materials & Processes in Manufacturing ME 151 Chapter 18 Hot Working Processes 1 Introduction Forming of materials their recrystallization temperature Higher temperatures weaken the metal making it more ductile Massive deformation without exhausting the materials plasticity Often an economical means of producing a desired shape Major Hot-Working Processes Pipe Welding Piercing 2 Production of Pig Iron and Steel Secondary Processes Primary Processes 3

2 4 > Hot Process Usually the first process used to convert material into a finished product Products Produced: Continuous Casters Slabs Blooms Plate Sheet Strip Structural Shapes Bar Rails Input Materials for Other Processes Ingots Primary Mills Billets Bar Rod Figure 18-1 Page 383 Basic Hot Process Heated metal passed between two rolls rotating in opposite directions Metal is squeezed and elongated resulting in a decrease in cross sectional area control is crucial to the success of the process Figure 18-2 Page Mill Configurations Figure 18-3 Page 385 6

3 7 Producing Structural Shapes Figure 18-5 Page 386 Hot Rolled Product Characteristics Products are rolled and finished above the recrystallization temperature Products are normally of uniform & dependable quality Properties are usually not directional Relatively free of residual stresses Characteristics can vary with thickness & complex shapes Thin sheets (<0.8) have directional characteristics Complex shapes have directional characteristics Surfaces are covered with an oxide known as 8 Thermomechanical Processing Controlled consist of performing both deformation and heat treatment in one operation Result is the control of both and properties Benefits: Improved product properties Energy savings Possible material substitution 9

4 10 > Process Plastic working by means of localized compressive forces 3 Basic types of forging processes: - Increase in length with reduced cross section - Decrease in length with increase in cross section in Impression Dies - Produces multidirectional flow Common Processes - Open-Die Drop Hammer - Automatic Hot - Impression-Die Drop Hammer - Roll - Press - Swaging - Upset Open-Die Drop Hammer Metal is heated to a uniform temperature then shaped using a moving hammer against a stationary anvil Metal flow is not confined Multiple strikes to create part Most often used to pre-shape metal for a secondary operation Dependent on skill of operator 11 Impression-Die Drop Hammer Metal is shaped using dies to control the flow of metal Also called Closed-Die Higher strength to weight ratios than cast or machined parts Multiple strikes to create part Multiple die cavities to create a part Good dimensional accuracy Figure Page

5 13 Press Hot metal is slowly squeezed in heated dies to form part Generally used for larger parts or thicker cross sections Energy is mechanical or hydraulic Parts formed with a single closing of the die Slow squeezing action produces a more uniform metal flow Good dimensional accuracy Upset Metal is compressed to a final shape through a successive set of dies Diameter is increased by compressing the length Most widely used of all forging processes Heated bar stock or coil feed Usually small parts Multiple step process using split multi-stage dies Figure Page Automatic Hot Automatic upset forging of parts with mill length bars heated in the machine High production rates Hollow and solid parts Low cost materials and operation No scrap Good dimensional accuracy Can control material structure Figure Page

6 16 > Process Heated metal is forced through a shaped die to form a product with a constant cross section Commonly used with, low yield point metals Can either be a hot or cold process Characteristics Produce products with complex shapes, reentrant angles, and longitudinal holes No draft angles, thus reduced material and weight Single step cross section reduction Inexpensive die cost Low production run capability Good dimensional tolerance Strong directional properties Figure Page 399 Hot Direct Indirect Cold (Chapter 19) Impact Continuous Hydrostatic Methods Hollow Shape Internal Mandrel (Figure Page 401) Spider Mandrel (Figure Page 402) Figure Page > Process Flat sheet or plate is formed to produce a three dimensional part with a depth several times the material thickness Generally used to form thick-walled parts of simple geometry Figure Page

7 19 > Process 2 Basic hot forming processes used to create steel pipe Pipe Butt-Welded Pipe (1/8 to 3 inch diameter seamless pipe) Lap-Welded Pipe (2 to 14 inch diameter pipe) Piercing (Seamless tubing up to 12 inches in diameter) Chapter 18 - Hot-Working Processes Definition of hot-working processes Basic knowledge of the major hot-working processes and examples of products produced General understanding of hot rolling and controlled rolling process General understanding of forging and the different types of forging processes General understanding of extrusion and the different methods Review Questions: 20