ME251 Exam 4
Defects in Etching
(a) overhang: deep cuts with improper agitation (b) islands: isolated high spots from dirt, residual maskant, or work material inhomogeneity (c) dishing: thinning in center due to improper agitation or stacking of parts in tank.
Which of the following are typical advantages of nontraditional machining processes?
-Able to create complex or delicate geometry -Little to no residual stresses -Able to machine with very tight tolerances -Able to machine brittle, strong, and hard materials
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 serve as lubricants (such as lead) -Adding alloying agents that produce smaller cutting chips
Typical abrasives:
-Al2O3 (Aluminum Oxide) -Diamond, -CBN (Cubic Boron Nitride) -SiC (Silicon Carbide)
Laminated Object Manufacturing
-Bonds and cuts out shape in solid material sheets -pretty good material properties -a lot of waste
Thermal Machining
-Electrical Discharge Machining (EDM) -Electron beam machining (EBM) -Ion beam machining (IBM) or Focused ion beam (FIB) -Laser-beam machining (LBM) -Plasma Arc Cutting (PAC) -Thermal Deburring -
Which of the following are disadvantages of Electrochemical Machining?
-Environmentally harmful by-products -Difficult to create sharp corners -Expensive tooling
Mechanics of Machining (Dynamics)
-Free vibration -Forced vibration -Self-Excited vibration
Supports in Additive Processes
-base -support
Typical material for Laminated Object Manufacturing:
-coated paper -ceramic tapes -metal -Paper laminates behave like wood -Ceramics and metals can have good mechanical properties, but require postprocessing firing steps
Which of the following are functions of the dielectric fluid in Electrical Discharge Machining?
-coolant -flushing away debris -local spark conductor -electrical insulator
Chip formation in mechanical machining
-discontinuous (good) -continuous -continuous with BUE (bad)
Three-Dimensional Printing
-for any material type -to make mold
Which of the following are typically considered to be major disadvantages of the Fused Deposition Modeling process?
-high material cost -relatively long build times -limited to low strength materials
Very good material properties for Selective Laser Sintering / Melting:
-high strength -toughness (particularly with post-processing treatments)
Materials that can be etched
-metals -ceramics -glasses -etched anything
Many material options for Selective Laser Sintering / Melting:
-plastics -waxes -metals -ceramics -particulate composites
Material types for modern additive process
-polymers -ceramics -metals -composites -living cells
Which of the following are typically considered to be disadvantages of additive processes?
-poor dimensional accuracy -difficult to make large parts -slow production rates per part -poor surface finish
Electrical Discharge Machining (EDM) process
-sinker EDM -wire EDM
Which of the following processes use rewritable photomasks?
-sintermask -solid ground curing
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 liquid resin is spread on the elevator platform 2. Material is exposed to UV radiation through a rewritable photomask 3. Uncured 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
Three major methods for Deposition-Based Processes:
1. Fused Deposition Modeling (FDM) 2. Laminated-Object Manufacturing (LOM) / Ultrasonic Consolidation 3. Laser Engineered Net Shaping (LENS) / Direct Metal Deposition (DMD)
Three major classifications for additive manufacturing, based on nature of raw material used:
1. Liquid-based 2. Powder-based 3. Deposition-based
Four basic physical components of any machining process:
1. Machine Tool or Machining Center 2. Workpiece 3. Workholding Device 4. Cutting Tool
Four major methods for Powder Based Processes:
1. Selective Laser Sintering (SLS) / Selective Laser Melting (SLM) 2. Sintermask 3. Electron Beam Melting (EBM) 4. Three-Dimensional (3D) Printing
Three primary methods for liquid-based processes:
1. Stereolithography (SLA) 2. Solid Ground Curing (SGC) 3. Inkjet Deposition (ID) or Droplet Deposition Manufacturing (DDM)
Stereolithography: Cures photopolymer using UV radiation:
1. Traditional method - scan focused laser over surface, "writes" geometry into polymer. 2. Masked-lamp method - exposes entire layer at a time, using unique photomasks. Faster, but requires masks to be made for each layer
Basic process steps
1. create digital model 2. process geometry into layers 3. deposit material, layer-by-layer (stereolithography) 4. postprocessing
Abrasive Waterjet Cutting (AWC)
Abrasives are added to a Waterjet to improve the efficiency
Abrasive Jet Cutting (AJC)
Abrasives are mixed in a high velocity air stream at 1000 ft/s
Ultrasonic
Abrasives are mixed in a slurry, ultrasonic transducers provide mechanical agitation to remove the material
Usually cheaper/faster than making single components using traditional manufacturing methods
Additive Processes
Powder-Based Processes
All use some form of powder that is joined by melting/sintering particles together (SLS, SLM, EBM, Sintermask) or by the addition of a liquid binder material (3D Printing)
Feed Rate
Amount of material removed per revolution or per pass of tool over workpiece
Which of these nontraditional machining methods is commonly used in the making of circuit boards?
Chemical Machining
Rapid tooling (RT)
Create items used in fabrication process of actual parts (cores/molds for casting, etc)
Direct digital manufacturing (DDM)
Direct printing or fabrication of actual product
Depth of Cut
Distance tool engages workpiece
__________ is important in determining type of chips produced
Ductility
Similar to SLS, but uses electron beam instead of a laser
Electron Beam Melting Process
__________ are slow (depth/time) in comparison to other NTM processes, but process happens over entire surface simultaneously
Etch rates
Continuous chips are the most desirable type during machining because they minimize tool wear and friction.
False
The primary difference between Abrasive Waterjet Cutting (AWC) and Abrasive Jet Cutting (AJC) is the type of abrasive particles used in the process.
False
Direction of the cut
Fc
Power distribution in mechanical machining
Fc ~99% Ff >1% Fr >1%
Force distribution in mechanical machining
Fc- 58% Ff- 28% Fr- 14%
Direction of tool feed
Ff
Direction perpendicular to the surface
Fr
Rapid prototyping (RP)
Full-size or scale models
machinist's handbook
General guidelines are available in many types of reference handbooks
Advantageous when time from design-to-build is critical
Getting prototypes in hours instead of weeks; healthcare applications
Material Removal Principles in EDM Processes
MRR= (C*I)/Tm
Chemical Machining Processes
Material is removed from a workpiece by exposing it to a chemical etchant
Nontraditional Machining (NTM) Processes
Material removal using something other than mechanical cutting/scraping
A lot of thin layers
Minimizes stairstepping but requires VERY long build times
_______________ are dependent on specific process and machine
Minimum and maximum layer thickness
Electrical Discharge Machining
Often used in making tools and dies
Additive Processes
Originally developed for creating prototype parts during product development cycles (1980's)
Cons for Selective Laser Sintering / Melting
Poor surface finish and dimensional accuracy
__________ can also be used to remove stairstepping geometry
Postprocessing
Liquid-Based Processes
Rely on selective exposure of photopolymer(photosensitive polymer) (SLA & SGC) or melting/solidification of low-melting point material (ID & DMM)
Few(ish) layers
Shortest build times. Each layer cures quickly. Moderately bad stairstepping problems
Solid-Ground Curing
Similar to Masked-Lamp SLA, but "writes" mask at each step. Also incorporates wax backfilling and milling steps
Modified version of selective-laser sintering (SLS)
Sintermask
Sintermask
Sinters material together using a laser, but instead of writing the laser over a surface, entire surface is exposed to laser through rewritable photomask, similar to that used in solid-ground curing process
Layer thickness can be reduced to reduce this effect, but generally increases processing time
Stairstepping
Self-Excited Vibration (worst)
The periodic response of the system to a constant input. The vibration may grow in amplitude (unstable) and occurs near the natural frequency of the system regardless of the input. Chatter due to the regeneration of surface waviness is the most common metal cutting example.
Free Vibration (Least bad)
The response to an initial condition or sudden change. The amplitude of the vibration decreases with time and occurs at the natural frequency of the system often produced by interrupted machining. Often appears as lines or shadows following a surface discontinuity.
can remove burrs or fins from almost any material but is especially effective with materials of low thermal conductivity
Thermal deburring
Electron Beam Machining, Ion Beam Machining, Laser Machining, and Plasma Arc Cutting are all thermal machining processes that rely on a focused beam or stream of energy to locally melt or vaporize material on a workpiece.
True
The main difference between Electrochemical Machining and Electrical Discharge Machining (EDM) is that 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.
True
Thermal Deburring
Used to remove burrs and fins by exposing the workpiece to hot corrosive gases for a short period of time
Plasma Arc Cutting (PAC)
Uses a superheated stream of electrically ionized gas (plasma) to melt and remove material
Few, very thick layers
Very bad stairstepping problems. Moderately long build times because each layer takes a long time to cure
Also appropriate when geometry would be very difficult to build in other ways
Very complex or hollow geometry
Waterjet cutting (WJC)
Water at 60,000 psi and 3000 ft/s erode the material
Many mechanical NTM methods use fine grains of ________ to chip away at the surface; especially good for machining hard, brittle materials
abrasive
Large combination of factors determines _________; varies from process to process
accuracy
Vacuum means cleaner environment
accuracy decrease
Plasma Arc Cutting
can be used on exotic materials at high machining rates
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
Process of removing unwanted material from workpiece in the form of _________ to obtain a finished product of the desired shape, size, and finish
chips
The largest amount of power required in machining processes is in the __________.
cutting direction (same direction as Fc)
High strength and hardness materials require larger_________
cutting force
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
Electrode (tool) material
depends on its machinability and cost as well as the desired MRR, surface finish, and tool wear
Many of these ______ are strong acids or highly caustic - need to make sure workpiece material etches faster than mask material
etchants (etch selectivity)
Machining is rarely used in the modern manufacturing of most products.
false
Powder-based processes are typically considered to be the most wasteful of the additive manufacturing methods.
false
The majority of the power put into machining processes is converted into shear and sound.
false
The ________ is defined as the amount of material removed per revolution or per pass of the tool over the workpiece.
feed rate
E-beam
has higher power than laser, producing denser metals, better mechanical properties than SLS
Power put into cutting is largely converted to__________
heat
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
Accuracy
how close the final geometry is to the intended geometry
Which of the following methods is used to pattern live cells during bioprinting (also called tissue printing or organ printing)?
inkjet depositon
Which of the following is considered to be a major disadvantage of Laminated Object Manufacturing?
large amount of material waste
Early parts made with these methods were good visual representations, but not structural
material for additive process
Capable of producing a wide variety of precision, surface finishes and speeds
mechanical machining
Direct Metal Deposition (DMD)
melts the surface of the part locally with a laser, and then deposits the powder
The seven basic mechanical machining or "chip formation" processes are: turning, _________, drilling, shaping/planing, sawing, grinding and broaching.
milling
Electron Beam Melting Process materials
must be electrically conductive and process must be performed in vacuum (limited to metals)
Solid powder provides mechanical support
no support structures needed (less waste)
The poor surface finish in products produced using Selective Laser Sintering or Electron Beam Sintering is caused by:
particle size of the powdered material
Electrochemical machining process
removes material by anodic dissolution with a rapidly flowing electrolyte
Electrical Discharge Machining (EDM)
removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap
impacted by the thickness of the cut plane, as wee'll see in the next slide
resolution
Resolution
smallest feature that can be created using a given process
Forced Vibration (median bad)
the respond to a periodic (repeating with time) input. The response and input occur at the same frequency. The amplitude of the vibration remains constant for a set input condition and is nonlinearly related to speed. Unbalance, misalignment, tooth impacts, and resonance of rotating systems are the most common examples.
One of the advantages of chemical machining is that it can be used to machine very large surfaces simultaneously.
true
The first additive process was invented in the 1980's and was limited to creating parts from a brittle photocurable polymer.
true
Supports
used in many processes when overhanging parts would bend/break under their own weight during fab
Base
used in most "curing" type processes to keep the part from welding itself to the platform
Electron beam machining (EBM)
uses a beam of high-energy electrons focused on the workpiece to melt and vaporize a metal
Ion beam machining (IBM) or Focused ion beam (FIB)
uses a focused beam of charged ions (usually gallium) to remove material on the surface of a workpiece
Laser-Engineered Net Shaping (LENS)
uses a nozzle to deposit powdered material and then melts the powder with a laser to hold in place
Laser-beam machining (LBM)
uses an intensely focused coherent stream of light to vaporize or chemically ablate materials
In laser curing, ________ size determines resolution
voxel
Advantages of Electrical Discharge Machining (EDM)
• 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
Laser-Engineered Net Shaping and Direct Metal Deposition
• 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
Advantages of NTM
• Capable of making complex, delicate, and very small (<<1mm) features • Tight tolerances • Often very good surface finish • Little or no burring or residual stresses • Materials with high strength or hardness can be machined
Four basic groups of material removal using NTM processes:
• Chemical • Electrochemical • Thermal • Mechanical
Several different methods to make a masking layer for chemical machining:
• Cut-and-peel • Scribe-and-peel • Screen printing • Photopatterning
Factors that must be considered to machine a given material:
• Cutting Speed, Depth of Cut, Feed Rate • Process • Material Type & Hardness • Cutting Tool Material & Geometry
High strength and hardness materials require larger cutting forces, which increase:
• Deflection • Friction (heat) • Power required • Tool wear
Inkjet Deposition
• Deposits liquid material using inkjet printing technology • Material solidifies upon impact • Low-melting temperature materials • good for low melting material • print tissue
3D force in cutting can be thought of as three forces in three orthogonal directions:
• Direction of the cut • Direction of tool feed • Direction perpendicular to the surface
Advantage of Electrochemical Machining
• ECM is well suited for the machining of complex twodimensional shapes • Delicate parts may be made • Poorly machinable materials may be processed (even very strong, brittle or tough materials) • Little or no tool wear
The dielectric fluid has four main functions:
• Electrical insulation • Spark conductor • Flushing medium • Coolant
Fused Deposition Process
• Extrudes and fuses thermoplastic filament together using local melting • Equipment is compact and low cost (currently marketed to individuals/small companies) • Material is relatively expensive and build times are long compared to other methods • Limited to relatively low strength plastics and wax
Advantages of chemical machining
• Induces no stress or cold working in the workpiece • 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 (< 1μm) features
Disadvantages of Electrochemical Machining
• 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)
Deposition-Based Processes
• 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)
Disadvantages of NTM
• NTM processes typically have lower feed rates and require more power consumption ($$$$$) • The feed rate in NTM is often independent of the material being processed • Some NTM processes can machine the entire surface at once
Pros for additive manufacturing
• Often relatively inexpensive for single/few parts • Handles complex geometry well • Short lead-time • No tooling necessary
Cons for additive manufacturing
• Poor surface finish • Poor dimensional accuracy (depends on process) • Slow production rate per part • Difficult to make large parts • bad mechanical property
Cutting Speed
• Primary cutting motion • Velocity of workpiece relative to cutting tool
Additive Processes: Applications
• Rapid prototyping (RP) • Direct digital manufacturing (DDM) • Rapid tooling (RT)
Disadvantages of chemical machining
• Requires the handling of dangerous chemicals • Disposal of potentially harmful byproducts • Material removal rate is slow
Machining processes that involve chip formation (traditional machining) have a number of 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)
Three main locations of heat generation in mechanical machining:
• Shear Zone - Plastic deformation • Tool/Chip Interface - Plastic deformation & friction • Tool Flank - Friction (friction= waste energy)
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! -short build time -wasteful
Postprocessing for additive process
• Sintering, firing, or additional curing • Finishing or polishing • Removing uncured resin • Removing supports/posts
Disadvantages of Electrical Discharge Machining (EDM)
• 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
Electrochemical machining (ECM)
• The tool is the cathode • Workpiece is the anode • Separated by electrolyte, which helps sweep away by-products of reaction
There are four major forms of mechanical nontraditional machining:
• Ultrasonic • Waterjet cutting (WJC) • Abrasive Waterjet Cutting (AWC) • Abrasive Jet Cutting (AJC)
Chemical reaction occurs everywhere the etchant contacts the workpiece. In order to create patterns:
• Use gel milling: thick gel is applied to the workpiece only in areas we want to etch • Use a masking material: selected areas are covered and the remaining surfaces are exposed to the etchant
Uses and Applications for addictive processes
• Usually most appropriate when economics of scale don't apply • Advantageous when time from design-to-build is critical • Also appropriate when geometry would be very difficult to build in other ways
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
