ME251 exam 4

Selective Laser Sintering/Melting (SLS/SLM)

*essentially the same thing but sintering used for ceramics and melting used for metals and other materials -powder delivery section has elevator starting at the bottom and moving up -fabrication section has elevator starting at the top and moving down -roller pushes material from delivery to fabrication section -laser melts particles Many material options: plastics, waxes, metals, ceramics, particulate composites Very good material properties: high strength and toughness, particularly with post processing treatments -poor surface finish and dimensional accuracy

Advantages of NTM

*good for small details/complex geometry -tight tolerances -often very good surface finish -little or no burring or residual stresses -materials with high strength or hardness can be machined

Supports in Additive Processes

-Base: used in most curing type processes to keep the part form welding itself to the platform -Supports: used in many processes when overhanging parts would bend/break under their own weight during fabrication -sometimes made from different type of material than what is being printed -base and supports made with part then sanded off or broken off during post processing

Electrochemical Machining Processes

-ECM removes material by anodic dissolution with a rapidly flowing electrolyte -the tool is the cathode -work piece is the anode -separated by electrolyte, which helps sweep away by-products of reaction

Thermal Machining: Electron, Ion, and Laser Machining

-Electron beam machining (EBM) uses a beam of high energy electrons focused on the work piece to melt and vaporize a metal -ion beam machining (IBM) or focused ion beam (FIB) is a similar method that uses a focused beam of charged ions (usually gallium) to remove material on the surface of a work piece -laser beam machining (LBM) uses an intensely focused coherent stream of light to vaporize or chemically ablate materials

Mechanics of Machining

-Free Vibration (least bad) response to initial condition or sudden change -Forced Vibration (worse than free vibration) response to periodic (repeating with time) input -Self Excited Vibration (worst vibration) response of the system to a constant input, vibration may grow in amplitude over time

Disadvantages of NTM

-NTM processes typically have low feed rates and high power consumption (slow) -the feed rate is often independent of the material being processed (depending on materials mechanical properties) (some NTM processes can machine the entire surface at once)

Design Factors in Chemical Machining

-areas that are exposed longer will have more metal removed from them ~Etch factor (E) and Anisotropy (A) can be found in tables and used to predict what your mask width needs to be E= u/d A= d/u =1/E *many of these etchants are strong acids or highly caustic- need to make sure the work piece material etches faster than the mask material "etch selectivity"

Laminated Object Manufacturing

-bonds and cuts out shape in solid material sheets -typical materials: coated paper or ceramic tapes, metal -paper laminants behave like wood -ceramics and metals can have good mechanical properties, but require post processing firing steps

Laser Engineering Net Shaping and Direct Metal Deposition

-both methods add powdered material locally to a part: -laser engineering net shaping (LENS) uses a nozzle to deposit powdered material and then melts the powder with a laser to hold in place -direct metal deposition (DMD) melts the surface of the part locally with a laser, and then deposits the powder -both methods usually performed with metals -very good material properties -can be used to make multi-material components -can be used to repair previously manufactured parts

3D Printing

-can be used with any material but mostly used with ceramics and metals -can be used to make molds -can be make intricate, complex molds

Chip Formations

-continuous -discontinuous (best option) -continuous w/ BUE (built up edges) (worst option) *use coolants to keep temp down *use free machining steels to reduce coefficient of friction & make discontinuous chips

Inkjet Deposition

-deposits liquid material using inkjet printing technology -material solidifies upon impact -mow melting temperature materials

Considerations for EDM

-electrode tool material: the choice of electrode material depends on its machinability and cost as well as the desired MRR, surface finish, and tool wear **higher melting temp >> better (for tool) The dielectric fluid has four main functions: -electrical insulation -spark conductor -flushing medium -coolant

Nontraditional Machining

-etching -electro-polishing -electro-discharge machining -water jet -laser beam

Fused Deposition Process

-extrudes and fuses thermoplastic filament together using local melting -equipment is compact and low cost -material is relatively expensive and build times are long compared to other methods -limited to relatively low strength plastics and wax

Process Input Parameters

-general guidelines are available in many types of reference handbooks (machinists handbook) -factors that must be considered to machine a given material: -cutting speed, depth of cut, feed rate -process -material type and hardness -cutting tool material and geometry

Free Abrasives (mechanical NTM)

-many mechanical NTM methods use fine grains of abrasive to chip away at the surface; especially good for machining hard, brittle materials -typical abrasives: aluminum oxide, diamond, cubic boron nitride, silicon carbide (all ceramics) *abrasives need high hardness, friability (opposite of toughness) (ability for something to break or chip into smaller, sharp pieces)

Chemical Machining Processes

-material is removed form a work piece by exposing it to a chemical etchant -chemical reaction occurs everywhere the etchant contacts the work piece in order to create patterns: -use gel milling~ thick gel is applied to the work piece only in areas we want to etch (use very viscous etchant, paint it onto the surface) -use a masking material~ selected areas are covered and the remaining surfaces are exposed to the etchant -variety of metals, ceramics, and glasses may be etched

Nontraditional Machining Processes

-material removal using something other than mechanical cutting/scraping -four basic groups of material removal using NTM processes: -chemical (relies on chemical reaction to remove material) -electro-chemical (also chemical reactions but requires electricity for reaction to proceed) -thermal (use energy to vaporize or melt material) -mechanical (use mechanical force, but tool and work piece never come in contact with each other)

Sintermask

-modified version of selective laser sintering -sinter material together using a laser, but instead of writing the laser over the surface, entire surface is exposed to laser through rewritable photo-mask, similar to that used in solid ground processing

Solid Ground Curing

-most complicated -similar to Masked Lamp SLA, but "writes" mask at each step -also incorporates wax back-filling and milling steps -mask plotter cycle and model grower cycle 1. elevator platform w thin layer of polymer 2. write photo-mask for that particular layer 3. apply toner to glass layer 4. blast the surface of glass with UV light. light doesn't go through toner 5. remove liquid resin, solidifies only where there was no toner 6. top surface wobbly, apply a layer of wax to flatten it 7. use milling cutter to take material down to uniform thickness 8. rewrite photo mask for new layer and repeat

Additive Processes

-originally developed for creating prototype parts during product development cycles (1980'w) -"rapid prototyping" "tool free" or "free form' processes -usually cheaper and faster than making single components -early materials were poor quality -modern processes can be used to produce parts with a variety of material types: polymers, ceramics, metals, composites, even living cells

Stairstepping

-problem with process depending on the resolution of that process -surfaces not perpendicular to slice plane are approximated by layered geometry -layer thickness can be reduced to reduce this effect, but generally increases processing time -minimum and maximum layer thickness are dependent on specific process and mahcine -post processing can also be used to remove stairstepping geometry

Traditional Machining Limitations

-residual stresses and/or unwanted distortion of final part -burrs -delicate or complex geometries may be difficult or impossible many materials are difficult to machine (especially high strength, high hardness materials)

Resolution vs Accuracy

-resolution: smallest feature that can be created using a given process (voxel size: the spot size of the laser) -accuracy: how close the final geometry is to the intended geometry (large combination of factors determines accuracy, depending on the process) -accuracy issues can come from thermal expansion from laser beams

Chemical Machining Steps

-several different methods to make a masking layer: -cut and eel -scribe and peel -screen printing -photo-patterning -etch rates are slow (depth/time) in comparison to other NTM processes, but process happens over entire surface simultaneously

Electron Beam Melting Process

-similar to SLS but uses electron beam instead of laser -E beam usage means material must be electrically conductive and process must be performed in vacuum (mostly used for metals) -e beam has higher power than laser, producing denser metals, better mechanical properties than SLS -vacuum means cleaner environment

Ultrasonic Consolidation

-similar to laminated object manufacturing but uses ultrasonic vibration to fuse the layers together -usually uses metal foil -makes very dense final materials **great mechanical properties (especially if you use sintering or heat treatment step at the end) -short build times -wasteful

Machining

-the process of removing unwanted material from work-piece in the from of chips to obtain a finished product of the desired shape, size, and finish -capable of producing a wide variety of precision, surface finishes and speeds -most products require machining at some stage of production

Build Time vs Thickness

-thinner layers look better but take much more time to build -thick layers also take more time than medium layer thickness b/c laser takes a longer time to cure each layer

Defects in Etching

-typically occur due to dirt or something being on the surface or products pf the chemical reaction building up -overhang: deep cuts with improper agitation -islands: isolated high spots from dirt, residual maskant, or work material in-homogeneity -dishing: thinning in center due to improper agitation or stacking of parts in tank

Thermal Machining: Thermal Deburring

-used to remove burrs and fins by exposing the work piece to hot corrosive gases for a short period of time -technically a "thermo-chemical" process -thermo deburring can remove burrs or fins from almost any material but is especially effective with materials of low thermal conductivity

Thermal Machining: Plasma Arc Cutting (PAC)

-uses a super heated stream of electrically ionized gas (plasma) to melt and remove material -PAC can be used on exotic materials at high machining rates -material has to be electrically conductive

Cutting Parameters - Turning Processes

1. Cutting Speed (V) -primary cutting motion -velocity of work piece relative to the cutting tool (units: feet per minute fpm) 2. Feed Rate (f) -amount of material removed per revolution or per pass of tool over work piece 3. Depth of Cut (d) -distance tool engages work piece * can control all 3 * as V increases, surface finish gets better * as f increases, surface finish gets worse * higher d >> process goes quicker, but requires more force

Deposition Based Processes

1. Fused Deposition Modeling (FDM) 2. Laminated Object Manufacturing (LOM)/ Ultrasonic Consolidation 3. Laser Engineering Net Shaping (LENS)/ Direct Metal Deposition (DMD) -instead of curing locally in a uniform layer of raw material, the raw material is only deposited where needed -some methods fuse together plastic filament (FDM) or solid layers of material (laminated, ultrasonic) to form the final product.Others fuse powder or wire to the solid product via localized melting (LENS, DMD)

Powder Based Processes

1. Selective Laser Sintering (SLS)/ Selective Laser Melting (SLM) 2. Sintermask 3. Electron Beam Melting (EBM) 4. Three Dimensional (3D) Printing -all use some form of powder that is joined by melting/sintering particles together (SLS, EBM, SLM) or by the addition of a liquid under material (3D) **All produce very little waste -solid powder provides mechanical support >> no support structures needed

Liquid Based Processes

1. Stereolithography 2. Solid round Curing (SGC) 3. Inkjet Deposition (ID) or Droplet Deposition Manufacturing (DDM) -rely on selective exposure of photo-polymer (SLA & SGC) or meting/solidification of low melting point material (ID & DMM)

Assuming the descending platform (elevator platform) has just been moved down, place the following steps of the Solid Ground Curing process in the order in which they would occur.

1. a thin layer of uncured resin is spread on the elevator platform 2. material is exposed to UV radiation through a rewritable photo-mask 3. Uncured liquid resin is removed from the platform 4. A layer of liquid wax is applied and solidified 5. A milling operation is performed to planarize (flatten) the surface

Basic Process Steps

1. create digital model 2. process geometry into layers 3. deposit material, layer by layer 4. (optional) post processing -sintering, firing, additional curing -finishing or polishing -removing uncured resin -removing supports/ posts

4 basic physical components of any machining process

1. machine tool or machining center 2. work-piece 3. work-holding device 4. cutting tool -these components plus cutting parameters determine final quality

7 basic chip formation processes

1. turning 2. sawing 3. grinding 4. milling (most broadly applied and flexible) 5. broaching (least common) 6. drilling 7. shaping or planing (depends whether the tool or work piece is held stationary

Material Removal

1.Mechanical Machining: -turning -milling -drilling -boring -sawing 2. Nontraditional Machining -etching -electroplating -electrodishcharge machining -water jet -laser beam

Forces and Power in Machining

3D force in cutting can be thought of as three forces in three directions: 1. Direction of the cut (Fc) 2. Direction of the tool speed (Ff) 3. Direction perpendicular to the surface (Fr) % of Total Force Power Required Fc 58% 99% Ff 28% <1% Fr 14% <1%

Which of the following are typical advantages of nontraditional machining processes?

Able to machine with very tight tolerances Able to create complex or delicate geometry Able to machine brittle, strong, and hard materials Little to no residual stresses

Which of the following methods are used to create free-machining metals (in order to reduce the friction generated during cutting)?

Adding alloying agents that produce smaller cutting chips Adding alloying agents that serve as lubricants (such as lead)

advantages and disadvantages of electrochemical machining

Advantages: -ECM is well suited for the machining of complex two-dimensional shapes -delciate parts may be made -poorly machinable materials may be processed (even very strong, brittle or tough materials) -little or no tool wear Disadvantages: -initial tooling can be expensive -environmentally harmful by-products -control of electrolyte flow can be difficult -current densities tend to concentrate at sharp edges or features (causing extra material removal near corners)

advantages and disadvantages of EDM

Advantages: -applicable to all materials that are fairly good electrical conductors -hardness, toughness, or brittleness of the material imposes no limitations -fragile and delicate parts, complex geometries Disadvantages -slow compared to conventional machining -produces a hard recast surface -surface may contain fine cracks caused by thermal stress -fumes can be toxic -tool wear **material has to be conductive, not great for ceramics **often used in making tools and dies

advantages and disadvantages of chemical machining

Advantages: -induces *no stress* or cold working in the work piece -can be applied to almost any material -large areas can be etched simultaneously -can be applied to virtually unlimited shapes -possible to make thin sections and very small features Disadvantages: -requires the handling of dangerous chemicals -disposal of potentially harmful byproducts -material removal rate is slow

Which of these nontraditional machining methods is commonly used in the making of circuit boards?

Chemical Machining

Classification of Additive Processes

Classified by raw material used: 1. Liquid Material 2. Powder Based 3. Deposition Based

Stereolithography

Cures photo-polymer using UV radiation: 1. Traditional method- scan focused laser over surface, write geometry into polymer 2. Masked Lamp method- exposes entire layer at a time, using unique photo-masks. faster than traditional method but requires masks to be made for each layer

Which of the following are disadvantages of Electrochemical Machining?

Difficult to create sharp corners Environmentally harmful by-products Expensive tooling

Thermal Machining: EDM

Electrical Discharge machining (EDM) removes metals by discharging electric current from a pulsating DC power supply across a thin inter-electrode gap -the gap is filled by a dielectric fluid (electric insulator) which becomes locally ionized

Mechanical NTM Processes

Four major forms of mechanical nontraditional machining: 1. Ultrasonic- abrasives mixed in a slurry, ultrasonic transducers provide mechanical agitation to remove the material *good for glass cutting* 2. Water jet cutting (WJW)- water at 60,000 psi and 3000 ft/s erode the material 3. Abrasive waterjet cutting (AWC)- abrasives are added to a waterjet to improve the efficency 4. Abrasive Jet Cutting (AJC)- abrasives are mixed in a high velocity air stream at 1000 ft/s

Effects of Workpiece Material Properties

High strength and hardness materials require larger cutting forces, which increase: -deflection -friction (generates heat) -power required -tool wear *Ductility is important in determining type of chips produced

Which of the following methods is used to pattern live cells during bioprinting (also called tissue printing or organ printing)?

Inkjet deposition

Which of the following is considered to be a major disadvantage of Laminated Object Manufacturing?

Low density final materials

Material Removal Principle in EDM Processes

MRR= (C*I)/Tm C = constant I = current Tm = melting temp

The poor surface finish in products produced using Selective Laser Sintering or Electron Beam Sintering is caused by:

Particle size of the powdered material

Which of the following are typically considered to be disadvantages of additive processes?

Poor dimensional accuracy Slow production rates per part Poor surface finish Difficult to make large parts

Heat in Metal Cutting

Power put into cutting is largely converted to heat** which elevates the temp of all components -Three main locations of heat generation: 1. Shear Zone (where plastic deformation takes place) 2. Tool/Chip Interference (plastic deformation and friction) (waste energy) 3. Tool Flank (friction)

Pros and Cons of Additive Processes

Pros -often relatively inexpensive for single/few parts -handles complex geometry well -short lead time -no tooling necessary Cons -poor surface finish -poor dimensional accuracy (depends on process) -slow production rate per part -difficult to make large parts **mechanical properties better if made by other processes

Additive Processes: Applications

Rapid Prototyping (RP) -full size of scale models Direct Digital Manufacturing (DDM) -direct printing or fabrication of actual product Rapid Tooling (RT) -create items used in fabrication process of actual parts (cores/molds for casting, etc)

Which of the following are typically considered to be major disadvantages of the Fused Deposition Modeling process?

Relatively long build times Limited to low strength materials High material cost

"chatter"

Screeching noise created by tool bouncing with respect to work piece -looks like waves on the surface of the material

Which of the following processes use rewritable photomasks? (select all that apply)

Sintermask Solid Ground Curing

Original Additive Process

Stereolithography -platform starts at the top of the UV curable polymer layer -computer takes geometry and writes them out using UV laser beam -platform moves down so new liquid layer comes over top of it and laser writes out the next slice plane - builds layers up to create prototype

EDM Processes

Two major types: 1. Sinker EDM- tool is lowered down and vaporizes material away as it comes close to work piece, they never actually touch, makes interesting 3D geometry 2. Wire EDM- tool is a bit of wire, charge between wire and surrounding work piece, wire vaporizes nearby material as it moves along a path, only capable of producing 2D parts, creates very unique surface finish

Uses and Applications

Usually most appropriate when economics of scale don't apply: -when geometry is custom, or for small builds, additive processes can be very cost effective -traditional manufacturing is often faster/cheaper per part when many identical parts are needed Advantageous when time from design to build is critical: -getting prototypes in hours instead of weeks; healthcare applications Also appropriate when geometry would be very difficult to build in other ways -very complex or hollow geometry

Ductile material

Very long cutting chips

Abrasive particles used in many non-traditional mechanical machining processes are usually made of which type of material?

ceramics

_________ is the term for self-excited vibration during machining; it causes distinct unwanted lines on the cut surface of the machined part.

chatter

"Stack of Cards" Model

chips stack like a deck of cards

The largest amount of power required in machining processes is in the __________.

cutting direction (Fc)

The four basic physical components of any machining process are: the machining center, the workpiece, the workholding device and the ___________.

cutting tool

There are three major categories of vibration in machining; the amplitude of free vibrations tend to _________ with time, the amplitude of forced vibrations tend to _______ with time, and the amplitude of self-excited vibrations tend to ________ with time.

decrease stay the same increase

Which of the following are functions of the dielectric fluid in Electrical Discharge Machining?

electrical insulator flushing away debris coolant local spark conductor

The ________ is defined as the amount of material removed per revolution or per pass of the tool over the workpiece.

feed rate

The Electron Beam used in Electron Beam Melting has ________ power than the laser used in Selective Laser Sintering (SLS), producing _______________ mechanical properties, but ___________ accuracy than SLS.

higher better worse

The main difference between Electrochemical Machining and Electrical Discharge Machining (EDM)

in Electrochemical Machining, electricity is used to produce a chemical (etching) reaction, but in EDM electricity is used to produce a thermal (vaporization/melting) reaction.

Turning Process vs Milling Operations

in turning process, the work piece rotates about axis and tool fed into it, in milling operation tool rotates about axis and work piece is fed linearly into it

Etchant

liquid or gas that will react with a solid in away that will dissolve the solid

The seven basic mechanical machining or "chip formation" processes are: turning, _________, drilling, shaping/planing, sawing, grinding and broaching.

milling

Power in Cutting Direction

power = force x velocity ~power is so high in Fc because it has the highest velocity -there is almost no velocity in Ff or Fr directions

Brittle material

small cutting chips

Ways to Stop Chatter

speed up, slow down, or change the depth of cut