Transforming Processes PDF

Plastically modify the shape of solid body in controlled manner, maintaining its material consistency and mass. Plastic deformation and formability can be done by using the stress-strain diagram (tensile test). There are three types of transformation which are cold forming, semi-warm transforming an...

Plastically modify the shape of solid body in controlled manner, maintaining its material consistency and mass. Plastic deformation and formability can be done by using the stress-strain diagram (tensile test). There are three types of transformation which are cold forming, semi-warm transforming and hot transforming. **Transformability** Depends on degree which material can undergo deformations without disturbing its cohesion, combined with degree of effort and precaution necessary to achieve the desired plastic shape change. **Ductility** Amount of deformation a material can undergo until cohesion is lost **Breaking strain** Amount of strain at which coherence is lost **Processing plastics** 1^st^ state is called '**[Glass state']** which means material is solid and put to **[machining]**. 2^nd^ state is '**[Softened state']** which means material is plastic and can be put to **roto molding**, **blow molding** or **thermoforming**. Last state is called '**Viscous state**' since material is liquid. Material is put to **[extrusion]** or Injection **[molding]**. **Blow molding plastics** Process: a hollow form in rubber (softened) state is inflated to take the shape of mold or free (drop) form. When blowing the original shape is transformed since blowing stretches the shape further and will reduce the wall thickness. After the blown mold has cooled sufficiently (to limit of the glass phase) it will retain its predetermined shape. **Mold blown** (muotti) *Extrusion-blowing process* or *Injection blow molding* process. **Free form blowing** Foil blowing **Extrusion blowing** An extrusion machine continuously extrudes pipes and after certain **process** extruded length is obtained, an air inlet valve and two mold halves are (ekstruusio) positioned around the extruded (soft) tube. Mold halves are closed so that the extruded pipe is pinched off and the end pressed against the valve (venttiili). Air is blown in the mold and in the process the airtight viscous material stretches to die. Meanwhile, the extrusion process continues. Therefore, the mold moves along during blowing to avoid collision. Finally, the mold opens, and the formed bottle is ejected, after which the cycle is repeated. **Injection blow** First a preform is made using an injection molding machine. This is **Molding** formed, after blowing the wall thickness is almost constant. After that the preformed sleeve is then blown in soft stage against the inner wall of blow Ruiskupuhallus mold using compressed air and cooled. Lastly, the blown bottle is ejected. muovaus (airtight) **Blown film**(pussit) An extruder with vertical extrusion extrudes a thin-walled tube and then (puhalluskalvo) large internal pressure inflates this tube to a multitude of its original **process** diameter forming a large balloon. In the process the tube stretches into a very thin tubular film. It's rolled up by guide rollers and a winding reel into plastic film (carrier bags). In this state film can still be perforated where necessary. **Thermoforming** Sheet material is heated to the rubber phase (an oven or light radiation) (lämpömuovaus) and then transformed on mold or free form and cooled in this shape. ***Key parameters*** First step is **softening** which happens when plastic sheet is heated to workable temperature using either radiation heating (direct application of heat using infrared radiation) or convection heating (heat distributed by blowing hot air over the surface). Also important is temperature and duration since these factors vary based on type/thickness of material. Second is **wall thickness** since thickness distribution across the molded product can be uneven (e.g. complex shapes). **Materials used** PVC, polystyrene(PS), Plexiglas(PMMA), ABS **Products** Packaging blisters, disposables (plates/cups), skylight windows, kitchen sink units, bathtubs. **Mold** Cheap and no need for structurally strong materials. **Thermoforming techniques:** **Vacuum Forming** Heated plastic is pulled against a mold using vacuum suction to create shape. **Plug-assisted forming** A mechanical plug helps pre-stretch the heated plastic before vacuum or pressure forming, improving material distribution. **[Metal transforming]** **Solid metal transforming** Happens by rolling process whereby the cross-section of relatively long workpiece is rolled out with rollers. Pressure forces using one or more pairs of rollers on size/shape changed. Usually it involves thickness reduction (flat rolling). **Hot rolling** Starts with Ingot with nonuniform grains. during hot rolling recrystallization occurs and new metal grains replaces deformed ones (internal stress relieve). Rough surface /limited dimensional accuracy. **Finishing via cold rolling** Cold hardening so crystals become longer (longitudinal) and they're highly compacted according to force direction. Has high dimensional accuracy, smoother surface. Continuous transition elastic to plastic area. **Extrusion** Starting material billet is pressed through a die using a RAM (press). **Solid metal** Procedure produces staff (long solid rods,), tubes, profiles (frames). Process is semi-continuous. **Direct extrusion** Extruded material and ram move in the same direction. 1. extrusion of staff 2. tube 3. extrusion of hollow profiles using a die with bridges. **Indirect extrusion** Extruded material and ram move in opposite directions, die is part of the ram. **Hollow extrusion** Indirect extrusion in which the non-extruded remainder of the billet becomes the bottom of the product. Cyclical process (as opposed to semi-continuous). (tölkit, pullot) Metal drawing A forming process in which the cross-sectional area of solid rod, wire or tube is reduced changed in shape by pulling the starting material through a die or drawing die. Reinforcement is essential for proper process operation since the tensile forces applied to the smallest material cross-section and no wire breakage should occur. **Forging** (solid) A collection of cyclical processes, in which the workpiece is transformed by compressive forces. Forged material is stronger and tougher compared to cast material due to significantly better homogeneity and finer structure. Suitable for manufacturing highly stressed structural components. **Hot forging** Work piece is heated up to red temperature. Needs relatively low process Most common forces and moderate dimensional accuracy and surface quality. Usually followed by mechanical finishing. **Cold forging/pressing** High process forces (sufficient ductility at room temp.). Good dimensional accuracy and surface quality. No post-processing required. **Open die forging** Form is not or only partially defined in tool or form and is obtained by manipulation of the workpiece. **Closed die forging** Billet takes form of die. **Bending/Folding** Forming process in which material will stretch on one side and compress on the other under the influence of a bending moment. **Materials** Sheet, strip, wire, tube and profile **Tension in neutral layer** When a material bends, the surface on the outside of the bend **under bending** experiences tensile stresses (stretched).The surface on the inside of the bend experiences compressive stresses (squished).**Transition Zone (Elastic Area**): There\'s an area between the tensile and compressive zones called the neutral layer, where there is no tension or compression. This layer is considered tension-free because the material neither stretches nor compresses there. **Location of the Neutral Layer**: For a small bending angle and large bending radius (rb): The neutral layer is at the center of the material. **For a larger bending angle and small bending radius:** The neutral layer shifts inward, closer to the center of the material. **Limitations of radius** Zone of elastic deformation are very large and the zone of plastic deformation very small. It results in a large rebound and small permanent flexure. Strain in the outer layer increases and this may cause necking and/or cracking. **Rebounding after** When the bending moment is removed, the material will rebound **bending** elastically to restore internal moment equilibrium.