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Deformation

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Deformation

1. 1. Deformation – Bulk = Significant change in surface area, thickness and cross section reduced, and overall geometry changed. l Deformation is a change in the shape or size of an object due to an applied force (the deformation energy in this case is transferred through work) or a change in – Sheet = Some deforming of material, but initial material thickness temperature (the deformation energy in this case is transferred through heat).Can remains the same be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). Forming ProcessesDeformation Process l Permanent (plastic) deformation of a material under tension, compression, shear or a combination of loads. l Deformation processes transform solid materials from one shape into another. The initial shape is usually simple and is plastically deformed between tools, or dies, to obtain the desired final geometry and tolerances with required properties.Types of Deformation Process l Types of Deformation – Bulk flow in (3) dimensions – Simple shearing of material – Compound to simple bending – Combination of aboveDeformation Process l Stresses used to produce change – Tension – Compression – Shear – Combination in multiple axis l (2) Classifications 1
2. 2. – Dependent » Process determines outcome – Independent / Dependent l Figure 15-1 Schematic representation of a metalforming system showing independent variables, dependent variables, and the various means of linking the two. Work Ranges l (2) Types of mechanical work where material undergoes plastic deformation l Hot Working (HW) l Cold Working (CW) Definition of HW vs. CWProcess Variables l HW is performed above the recrystallization temp of the material and CW is done below the recryllization temp of the material. l (3) Classification l Recystallization Temp- “The approximate minimum temp at which complete – Independent recyrallization of a cold worked metal occurs within a specified time.” » Controlled by the engineer » -Heat Treaters’s Guide, American Society for Metals 2
3. 3. Definition of HW vs. CW l Approximate temperature ranges – HW - .6 melt temp. of the material – WW - .3 to .6 melt temp of the material – CW - less than .3 of the material » Example - 1020 CRS 950 - 1300F Figure 15-3 Cross section of a 4-in.-diameter case copper bar polished and etched to show the as-cast grain structure.Hot Working l When HW a metal is in a plastic state and is easily formed. The forces required to deform the metal are less than CW. Some mechanical properties of the metal are improved due to process characteristics. l At elevated temperatures, metal microstructures are rebuilding continually through the recrystallization process which allows for much higher deformation.Advantages to HW l Porosity in metal is largely eliminated Figure 15-4 Flow structure of a hot-forged gear blank. Note how flow is parallel to all critical surfaces. (Courtesy of Bethlehem Steel Corporation, l Impurities (inclusions) are broken up and distributed through the metal Bethlehem, PA.) l Course grains are refined Advantages to HW l Due to grain refinement, the physical properties are generally improved l Amount of energy necessary to change the shape of the raw material in a plastic state is far less than if the material was “cold.” » Ductility and resistance to impact are improved l Economical compared to CW » Strength is increased Disadvantages to HWAdvantages to HW l High working temp. can result in rapid oxidation/scaling of surface = poor surface finish l Generally, close tolerances are hard to control l Equipment and tool maintenance costs are high Primary HW Processes 3
4. 4. l Rolling l Forging l Extrusion l Pipe & tube manufacturing l DrawingRolling l Heated metal is passed between rotating rolls to reduce the cross-section. Forging l The plastic deformation of metals, typically at elevated temperatures, using compressive forces exerted through a die to conform the metal to a desired shape. l Process advantages: – Closing of voids in the metal – Reduced machining time – Improve the physical properties of the starting metal l Process disadvantages:Rolling – Possible scale inclusions in forging l One of the primary first process to convert raw material into finished product. – Tooling cost can be high l Starting material (Ingots) are rolled into blooms, billets, or slabs by feeding material – Usually not used for short production runs through successive pairs of rolls. Forging Methods » Bloom - square or rectangular cross section with a thickness greater than 6” and a width no greater than 2x’s the thickness l Open-Die Drop Hammer - heated metal is placed between dies—a force is delivered with a steam hammer. » Billets - square or circular cross section - - smaller than a bloom – Accuracy is not good » Slabs - rectangular in shape(width is greater than 2x’s the thickness), slabs are rolled into plate, sheet, and strips. – Complicated shapes are difficult to produce 4
5. 5. Forging Methods l Impression Die Drop Hammer Forging - Hot pliable metal is forces into the shape of closed impression dies. This process is typically performed in a progressive method through a series of dies to control the flow. – 2 Types of drop forge hammers » Steam » Gravity l Press Forging – Large….thick work – Slow Squeezing action penetrates entire work piece producing uniform deformation – Dies are typically heated to: » Assist surface flow » Reduce surface heat loss » Assist in obtaining close tolerances and surface finish – Two types of presses -- mechanical and hydraulic » Hydraulic - up to 50,000 tons Hot Extrusion l A plastic deformation process in which metal is forces under pressure to flow through a single, or series of dies until the desired shape is produced. l Advantages l Upset forging – Wide variety of shapes – Grip a bar—heat the end—forge into desired shape – High production rates » Product examples – Improved microstructure and physical properties l Bolts – Close tolerances are possible l Engine valves 5
6. 6. – Economical l Advantages – Design flexibility l No heat requiredPipe, Tube, and Wire Manufacturing l Better surface finish • Tube - Butt or electric welding and Piercing l Superior dimensional control---little or no secondary operations l Strength, fatigue, and wear properties are improved l Improved machinability l Disadvantages Increased stress in material—strain hard Roll Alignment  Roll Alignment, specifically, is the alignment and measurement of roll parallelism in plant machinery that is typically used to feed sheet materials. Typical industrial applications include:  Paper and Pulp manufacture  Printing Works  Textile Mills  All types of Sheet ManufacturingDrawing l Flat sheet or a plate of metal is forced into a recess with a depth more than several  Problems associated with the misalignment of Rolls include: times the starting materials thickness.  Drift and tracking of sheet materials during feed  Wrinkling and Breakages in paper / materialCold Working  Uneven gloss rate in paper manufacture  High scrap rates of material l CW is done below the recrystallization point of the material. In CW, greater forces are required to transform the raw metal into the desired shape. Roll Alignment Process Industrial Applications for Roll Alignment l One major advantage…..as the grain deformation proceeds greater resistance to  The Headbox: the action is building resulting in improved strength and hardness (strain hardness).  The Foil Section:  The Press Section: l CW is a high volume production process.  The Dryer Section: l Similar processes as HW—major differences include  The Winder: The Coating Section: l Forces required Roll Alignment - Head Box  It is important that the breast roll is parallel to the apron board. If the air gap l Temperature range differs, it will cause problems with the consistency of the paper. It is also important that the apron board is straight and the slice gap is correct in order to get a uniform l Equipment specifications output of paper pulp on to the forming table. 6
7. 7.  Benefits:  Increased production capacity  Uniform paper structure and thickness  Reduced rate of scrap paper Roll Alignment - Finishing Calendars  Increased efficiency in the dewatering process and possibility to increase  The parallelism is important in the calendar, both vertically and horizontally, or the production speed roll nip will differ over the roll length. In some calendars, there is a nip offset that  Reduced risk of breaking the slice tip has to be considered.  Benefits:Roll Alignment - Dryer Section  Uniform gloss  In this section, the problems are similar to the press sections, although we would  Reduced scrap production like to point out the problem with wrinkles and breakages in the paper sheets. The  Increased time between roll replacement amount of rolls in the web path is large in the dryer section and increases the  Possibility to increase production speed importance of roll parallelism. Turret Punching  Benefits:  Increased uptime  is a process, where work piece are punched to make a desired hole of a metal sheet.  Increased time between felt changes  it is a CNC machine used for performing punching (a turret puncher) to a material such  Reduced scrap production us sheet of metal or plastic .  Increased product quality  Turret punching is a cold work process. This entails that material properties remain  Possibility to increase production speed unchanged as they are not exposed to thermal impact during machining.Roll Alignment - Forming Table Process  In this section, parallelism between the breast roll and the drive rolls is important, process produces shapes by selectively removing material from sheet metals. These sheets or the drift and wear of the wire will be affected. The surface of the paper sheet is are clamped into the machine on a table that is programmed to move to a specific affected if the dandy roll is not parallel to the forming table. The pick up roll and X/Y location within the matrix of the machine. The correct punch shape and size is the couch roll may cause breakages and wrinkles if they are not kept parallel, and selected at the turret and the machine actuates the punch to produce the desired the suction process may be affected. The levelling of the forming table is another hole. important factor in this section, that will especially affect the de-watering pro-cess and the deterioration of the foils.  Benefits: Punching Characteristics  Efficient de-watering process and uniform fibre structure will improve the paper quality  Increased de-watering capability gives possibility to  Increase production speed  Increased lifetime of the wire  Reduced energy consumption for the vacuum pumps Roll Alignment – Winders  Poor parallelism between the calendar rolls, the reel drum and spool may create problems with a high rate of scrap paper as a result. Also the paper may drift sideways during the reeling, creating problems with wrinkles and difficulties when cutting the paper.  Benefits:  Less scrap paper 7