Materials and Manufacturing Processes Exam 3

Flat Rolling

used to reduce thickness of a rectangular cross section

Shape Rolling

the rolling and roll forming of structural shapes by passing them through a rolling mill to bend or deform the workpiece to a desired shape while maintaining a constant cross-section

Thread Rolling

used to form threads on cylindrical parts by rolling them between two dies. The preferred method for producing strong, smooth, precise, and uniform external thread forms

Open Die Forging

workpiece is compressed between two flat dies, allowing metal to flow laterally with minimum constraint

Impression Die Forging

die contains a cavity or impression that is imparted to the work part. The metal flow is constrained so that flash (unwanted metal flow between dies) is created. It can create more intricate/precise patterns

Flashless Forging

the workpart is completely constrained in the die, which means that no excess flash is created and the exact volume of material is needed to fill the die cavity

Upset Forging

locally deforming a portion of a metal bar via forging, typically to create the head on a bolt, screw, or nail

Explain the advantages and disadvantages of hot forging

an advantage of hot forging is that it is easier to form pieces due to reduced strength and increased ductility in metal. Some disadvantages are that there’s a potential for warping and less precise tolerances compared to cold forging

Explain the advantages and disadvantages of cold forging

an advantage of cold forging is that there is increased end strength of the part due to work hardening. Some disadvantages are that there’s a potential for residual stress, limited formability, and suitability for certain materials and shapes

Direct extrusion

ram motion and material flow are in the same direction. There’s simpler tooling, higher rigidity of the ram, and a better surface finish on the final product. However, there’s a higher friction force as the billet slides along the container walls that must be overcome and there’s inconsistent cooling during the extrusion process that results in inconsistent grain sizes within the finished part. Also known as forward extrusion

Indirect extrusion

ram motion and material flow are in opposite directions. There's lower friction force, ease to produce hollow cross-sections, and more consistent cooling which leads to consistent grain sizes in the part. However, there’s lower rigidity of the hollow ram and difficulty in supporting the extruded product as it exits the die. Also known as backward extrusion and reverse extrusion.

Wire/bar drawing

cross section of a bar, rod, or wire is reduced by pulling it through a die opening. Drawing is often used for very long, thin products, where it would be difficult to push them through a die for extrusion

Turning

a machining process performed on a lathe. Shapes materials by means of a rotating drive which turns the workpiece against changeable cutting tools

Milling

the machining process of using rotary cutters to remove material from a workpiece by advancing (or feeding) in a direction at an angle with  the axis of the tool

Drilling

used to create a round hole. It is accomplished by a rotating tool that typically has two or four helical cutting edges

Boring

the process of enlarging a hole that has already been drilled (or cast) by means of a single-point cutting tool

Cutting Speed

defined as the speed at which the work moves with respect to the tool

Feed Rate

the amount of material removed per revolution

Depth of Cut

in turning is the distance the tools plunged into the surface

Blanking

when a piece of sheet metal is removed from a larger piece of stock by applying a large enough shearing force. The removed piece is called a blank, and it is not scrap but rather the desired part

Punching

when material is removed from a piece of sheet metal by applying a large enough shearing force. Punching is very similar to blanking except the removed material, called a slug, is scrap and leaves behind the desired feature in the sheet. It can be used to produce holes and cutouts of various shapes and sizes

Sheet Metal Drawing

a forming process which occurs under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body open on one side, or a hollow body is formed into a hollow body with a smaller cross-section

Green Strength

strength of the green compact. It’s okay for handling but not for actual structural use. The full strength is achieved after sintering.

Compaction

compression of powder in a die to create the desired geometric shape (green compact). The green compact is the work part after the pressing operation.

Sintering

heat treatment to bond the metallic particles, thereby increasing the strength and hardness

Infiltration

operation in which the pores of the powder metallurgy, or PM, part are filled with a molten metal of a lower melting temperature than the PM part metal. It is used to improve the strength/toughness, seal pores/make gas- or liquid-tight, improve machinability, or corrosion resistance.

Impregnation

the term used when oil or other fluid is permeated into the pores of a sintered PM part. It provides lubrication over the operational lifetime

Arc Welding

requires a high voltage electrical energy source, either alternating or direct current, to create an electrical arc between an electrode and the work

Resistance Welding

a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current. The melting and fusion of surfaces occurs due to heat generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding.

Solid State Welding

a group of welding processes which produces coalescence at temperatures below the melting point of the base materials being joined. It creates welds without any melting of workpiece or filler material. It usually utilizes high pressure or fast motion to create joining of surfaces.

What advantage does using spherical powder particles have, and by what processes are such particles made?

An advantage of spherical particles is that they have the lowest interparticle friction, which allows for particles to easily flow and fill all regions of the die cavity. Spherical powder particles are produced through atomization with rotating consumable electrodes. The metal of interest is formed into a solid electrode and then rotated at high speed and an electric current is used to melt the electrode, causing droplets to fly off and solidify. Slow cooling allows for the particles to be more spherical.

What advantages does using irregular shaped powder particles have, and by what processes are such particles made?

An advantage of irregular shaped powder particles is that they result in higher green strength, which allows for more surface area in contact with one another after pressing when compared to spherical particles. These are formed through water atomization where high pressure water is used instead of gas. This produces irregular shaped products because using water instead of gas causes fast cooling, so the particles have less time to form as they solidify very quickly.

It is determined that a gas atomization process results in powders with a mean diameter of 75 μm. If it is desired to produce powder particles with a smaller diameter, what are three changes to the production process that can be made to accomplish this?

Three changes to the production process to result in powder particles with a smaller diameter is to use a less viscous metal, use a smaller water spray nozzle, and increase the water pressure. Using a less viscous metal makes it easier for it to separate into smaller droplets/particles, a smaller nozzle increases the fluid velocity which results in smaller particles, and a higher pressure is able to fragment metal into smaller droplets.

Additive Manufacturing

the consolidation of feedstock materials (powder, wire, sheets) into a dense metallic part by selective melting and solidification of the feedstock materials. It requires a high energy source such as laser, electron beam, or electric arc in order to melt feedstock material. It also requires materials that can undergo this selective melting/solidification process and still result in good mechanical properties. These parts tend to have higher mechanical strength and lower fatigue strength compared to wrought material counterparts due to high residual stresses and porosity/defects.

Subtractive Manufacturing

controlled material removal. Any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process.

Keyhole defect

if power density of laser/electron beam is too high, material doesn’t just melt but also some of the metal vaporizes. The vaporized metal gases expands and pushes outward, forming a keyhole or tunnel from the surface down to the depths of the weld.

Lack of fusion defect

inadequate laser power/melting of the metal and penetration of the molten pool of an upper layer into the previous lower layers. New material doesn’t properly melt and fuse to previous layers, leaving behind a gap or pore.

Hatch Spacing

an additive manufacturing process parameter. Known as the distance between the center lines of two adjacent laser passes or scan tracks within a single layer of material

Layer Spacing

the vertical distance between successive layers of material deposited during the printing process

Scan speed

an additive manufacturing process parameter. The speed at which the laser beam moves across the powder bed while melting and fusing the material. As the scan speed increases, the lack of fusion defects also increases.

Crystalline ceramic

atoms arranged in a crystal lattice structure. It is more complicated than in metals, since it often has to accommodate atoms of significantly different sizes. These do not soften at elevated temperatures,  but creep deformation can occur. Ionic and covalent bonds do not allow easy slip/dislocation motion, even at elevated temperatures.

Amorphous ceramic

also known as non-crystalline ceramics and glasses. Has an amorphous arrangement of atoms. There’s no specific point when glass melts/solidifies, it simply continuously decreases in viscosity.

Glass

non-crystalline silicates, containing other oxides which influence the properties

Glass-ceramic

transformation of inorganic glass from amorphous to crystalline state by a high-temperature heat treatment. A nucleating agent is added to promote crystallization. The cooling rate will affect the final grain size, similar to in metals. The relative ease of fabrication allows for mass production of high quality products.

Clay ceramic

naturally found clay is mixed with water to create an easy-to-shape plastic mass, which is then dried and fired

Refractory ceramic

these have the capacity to withstand high temperatures without melting or decomposing. They remain stable and inert at high temperatures, and provide thermal insulation.

Abrasive ceramics

high hardness and melting point of ceramics make them desirable as abrasives used to wear, grind, and cut away others. Common abrasives are silicon, carbide, tungsten carbide, aluminum oxide, and silica sand. Diamonds are also utilized but are more expensive.

Cements

characteristic feature is that when mixed with water they form a paste that then sets and hardens. Portland cement is used extensively in construction as a binder for mortar and concrete and to bind aggregate particles into a cohesive mass.

Float Process

modern method to create large sheets or plates of glass. Molten glass is transferred using rollers onto a bath of liquid tin, where it floats on the surface. Gravity and surface tension forces cause the faces of the molten glass sheet to become perfectly flat and parallel. The glass is slowly cooled as it moves along the liquid tin bath to form the solid glass plate.

Hydroplastic forming

deformation of a hydroplastic mass of clay-water mixture to form the desired shape. Most common method is extrusion, where the hydroplastic mass is forced through a die with the desired cross-sectional geometry.

Slip casting

a slip is poured into a porous mold, and the water is absorbed into the mold leaving behind a layer of clay on the mold wall.

Powder pressing

a solid ceramic piece is formed through the compaction of ceramic powder particles, followed by sintering during a high temperature firing operation. It is similar to powder metallurgy, except there is no plastic deformation of ceramic powder particles like there is with metal particles. The ceramic component will have some porosity, which is reduced during the firing process.

Injection molding

a ceramic powder is mixed with a binder, then injected into a mold. The part is then removed from the mold, the binder is removed, and the part is fired to create the solid homogeneous part. It’s capable of producing relatively complex ceramic parts that cannot be fabricated using other methods.

Monomer

a single unit molecule

Polymer

multiple monomers bonded together

Cross-link

bonds that occur between two polymer chains, linking them together

Thermoplastic

soften when heated and eventually liquify and they harden and solidify upon cooling. This process is reversible and may be repeated numerous times. As the temperature increases, secondary bonding forces between adjacent chains are diminished due to the increased molecular motion, allowing easier motion of adjacent chains relative to one another when stress is applied. Manufactured by injection molding, extrusion, and thermoforming processes.

Thermoset

a polymer obtained by heating a soft solid or viscous liquid pre-polymer and irreversibly hardening and curing it by creating new polymer cross-links. Thermosets cannot be re-heated and re-molded. The shape and structure is permanently set. They are typically manufactured by injection/transfer of resin to a mold, then heating of the mold to cure and set the permanent shape.

Glass transition temperature

temperature at which polymer reversibly transitions from a softer, more ductile state to a more brittle, glass-like state.

Injection molding

pellets of polymer are fed into a cylinder, melted, and injected into a mold cavity and pressure is held until the polymer has solidified. This is the most widely used technique for fabricating thermoplastic materials.

Name the 4 main stages required in a powder metallurgy fabrication process

1. Powder Production

2. Blending

3. Compaction

4. Sintering

Powder production

create powder particles of desired size, shape, and chemical composition

Blending

mixing of different powders to create alloys, or adding lubricants/binders

Finishing Operation

operations such as machining to add final details to part

What is springback and what process is it primarily a problem in

elastic recovery results in a decrease in bend angle and an increase in bend radius after the force is removed. Primarily a problem with bending operations

What are the two major categories of polymer materials

1. Thermoset

2. Thermoplastic

Name 3 types of ceramic materials discussed in class

1. Refractory ceramics

2. Clay ceramics

3. Abrasive ceramics