DML Final Exam
What is the smallest usable tool size
#6 or M4
Radial clearance
(1/2) (drill size - major diameter)
Tolerance for reaming
+/- 0.5 to 2 thou
Tolerance for boring
+/- 1 to 5 thou
Tolerance for drilling
+/- 2 to 10 thou
Tolerance for turning and milling
+/- 2 to 10 thou
Tolerance for free hand grinding
+/- 50 to 100 thou
Tolerance for free hand plasma cutting
+/- 50 to 100 thou
Tolerance range for bandsaw cutting
+/- 60 to 120 thou
Tolerance range for sheetmetal bending
+/- 60 to 120 thou
Tolerance range for sheetmetal shearing
+/- 60 to 120 thou
Line fit
0 clearance, or the same size hole as shaft
What is the max allowable material which can be removed in a single pass on the mill or lathe
0.100" (100 thou)
Pitch
1 / threads per inch
How many axes of motion do manual lathes in the lab have
2
Tolerances for Milling, Drilling, and Turning
2-10 thou
What is an AWJ used for?
2D CNC cutting of almost any material, regardless of STRENGTH
What is a waterjet used for?
2D CNC cutting of soft materials
How many axes does the mill have
3
How many threads carry an entire load
5
Definition of horse power
550 ft-lb / sec
Never bring anything within _________ of the cutting zone while the spindle is running
6"
Water cutting pressure and cutting jet velocities of Modern AWJ
80,000 psi and 2,000 mph
Sheets
<= 1/4" in thickness
Plates
> 1/4" in thickness
Clearance fit
A fit in which one part fits easily into another with a resulting clearance gap
Turning
A metal cutting process used mainly for the generation of cylindrical surfaces
Milling
A metal cutting process used primarily for the generation of rectangular surfaces
Overturning moment
A moment that puts a bending load on the support shaft of the motor
Interference fit
A very tight fit where the parts need to be forced together
When should the lathe chuck key be removed from the spindle
After clamping the work piece
When should you switch spindle directions
After the machine is completely stopped
Bending
Also known as breaking. Outer fibers are in tension inner fibers are in compression
Never cut any material except ___________ on the Marvel bandsaw.
Aluminum
Understand what 3 metals and their order of most manufacturable to least manufacturable
Aluminum Steel Titanium
What are 3 considerations when designing wheel hubs
Attaching hub to motor, attaching wheel or other transmission device to hub, transmitting power through hub
Die casting
Automated machine to inject molten metal under high pressure into intricately machined alloy steel mold halves
Why are matrix objectives weighted?
Because not all objectives are of equal importance
When should the HI/LOW range on the mills or lathes be set
Before turning on the machine
Accuracy
Being close to the correct actual value
Precision
Being close to the other values
Benefits of rolled threads
Better surface finish means lower stress risers, improved material properties means higher fatigue resistance
Functional difference between a bolt and a screw
Bolt mates with a nut, screw mates with the workpiece
What direction should the spindle be rotating on a lathe
CCW
Type of metals in order of strength weakest to strongest
Casting metal billet metal Forged metal
2 part features CNC machines can make but manual machines can't (at least not easily)
Chamfers/fillets Angled line
When turning on the milling machine
Check speed range Check tool clearance Check tool direction
Never pull _______ off the machines using your hands.
Chips
What gets clamped in the lathe's chuck and tailstock
Chuck = workpiece, tailstock = drill bit
Never leave the _______ in the chuck
Chuck key
What are 3 common work holding methods on a lathe
Chuck, between centers, collet
Never reach over the rotating __________ on the lathe for any reason because of the dangerously proturding ___________
Chuck; chuck jaws
Fasteners are primarily designed to do what?
Clamp parts together
What type of holes are bolt holes
Clearance holes
What are 4 key elements to decision matrices
Clearly defined/weighted objectives, justified magnitude assignments with traceable supporting data, always try to use linear score assignments, highest scoring concept wins
2 varieties of fastener threads
Coarse and fine
What type of internal thread is better for softer materials and why
Coarse threads because they have smaller minor diameters which gives the soft material higher static strength and fatigue resistance.
2 types of parts casting is good for
Complex or hollow parts and mass production
What are 2 types of parts CNC machines are better suited for making than manual machines
Complex parts requiring multiple axes of simultaneous motion Parts that need to be mass produced
CNC stands for
Computer numeric controlled
Is cone-bottomed or flat-bottomed holes cheaper and why?
Cone-bottomed because that is the shape of the drill bit.
Define what is meant by the phrase design for manufacturability (DFM)
Consciously trying to design parts that can be manufactured for the lowest cost while meeting the required design intent and service factors
2 common methods of programming CNC machines
Conversational programming and CAM programming
Define milling
Create a surface by removing material a little bit at a time by moving the workpiece forward at a slow speed to meet the cutter which is rotating at a high speed
Finishing cuts
Creates an attractive surface finish. Tool life is more important for finishing cuts.
Define end milling
Cutting a flat workpiece at a right angle to the axis of rotation of the cutter however it is allowed to go in all directions instead of just the x direction
Define face milling
Cutting a flat workpiece in the x direction at a right angle to the axis of rotation of the cutter
3 controllable parameters that influence the metal removal rate when turning
Cutting speed, depth of cut, feed rate
What is the limiting factor for how deep to cut (per pass) with an endmill in a particular material
Cutting tool / workpiece / machine stiffness
What are 2 types of edge finders used in the lab
Cylindrical and conical
Always take time to _________ each workpiece after cutting to remove the sharp edges.
Deburr
Basic size
Denotes theoretical exact size
Calculation of required fastener tightening torque depends on what two variables
Desired preload and fastener diameter
10 items a proper detail drawing should contain
Dimensions for every feature Tolerances for every dim Units specifications Material specs Quantity of parts Surface finish specs for every surface Appropriate hole/thread notes for every hole Unique part name and/or number Designer/drawer's names Additional info about breaking sharp corners, etc.
When operating a lathe, where should the tool bit typically be positioned
Directly on the spindle center line
Physical difference and functional difference between drill bits and reamers
Drill bit has 2 flutes and a reamer has more than 2; drill bits are used to create a hole and reamers are used to finish a hole/improve tolerance
Benefits of 80/20
Easy to add attachments Free movement along the shaft Assemblies are quick to build Adjustable Reusable Light weight Durable Abundant Requires little machining Versatile
Advantages of set screws
Easy to design, easy to machine, provides reliable power transmission in moderate torque applications when used with flatted shafts (i.e. positive mechanical engagement)
What are 5 features a CNC machine posses that allow increased productivity
Electronic high speed probing Automatically changing tools High pressure coolant Stiffer structures More powerful motors
1 physical difference between endmills and drill bits
Endmills have more cutting flutes that allow them to cut laterally into material Endmills are stiffer
Conversational programming
Enter in the parameters
T/F Manufacturing time is an example of a qualitative assessment
False
T/F Pulling, pushing, and stretching are the most common sheet metal operations
False
What is the #1 cause of mechanical failures in industry
Fastener failures
What info is required to properly denote fasteners in assembly BOMs for this course
Fasteners thread specs Fastener head type Overall fastener length
List the easiest mistake to make when changing tools on a milling machine
Forgetting to raise and lock the spindle in the uppermost position
What process produces the strongest metals
Forging
GTAW
Gas tungsten arc welding (TIG)
GMAW
Gast metal arc welding (MIG)
Always engage the workpiece ______ to avoid chipping the fragile cutting inserts/edges
Gently
Always wear ______ when working with sheetmetal, except when using ____________.
Gloves; powered equipment
What is the limiting factor for how fast a drill or endmill can rotate in a particular material?
Head generated in the cutting zone
What are 4 common components of an engine lathe
Headstock, cross slide, tool post, tailstock
Always check the milling machines and lathes are in _______ range before turning them on.
High
HSS
High Speed Steel
CAM programming
Import part model into a program then define parameters
What is the most common work holding method on a mill
In a vise
What are three things that can cause calipers to measure inaccurately
Incorrect zero Dropping/damage Improper pressure Jaws not normal to surface of work piece Improper calibration
Why is size of a tap drill important
It will determine the hole callout
The common types of milling machines are_____
Knee and column mills and bed mills
What hand should you file with
Left hand
Limit tolerance
Lists the maximum and minimum sizes
3 advantages of MIG welding
Low operator skill Fastest method Cost effective
Primary difference between MIG and TIG welding
MIG welding automatically feeds the filler wire into the weld pool whereas TIG uses a tungsten electrode to conduct the electricity and provide the heat source, and the actual filler wire is fed manually into the molten pool
Steps to change tools on the mill
Machine is off Over plastic Raise/lock the spindle to the uppermost position using the quill handle Depth stop is thumb tight
Limiting factor for how deep you can cut per pass with an endmill
Machine stiffness, cutting tool stiffness, work piece stiffness
3 Disadvantages of AWJ process?
Machines are expensive; machines require frequent maintenance; messy
Stress
Measure of how much tensile load is placed on a fastener
Strain
Measure of the fastener's change in length (stretch)
Billets
Metal that has not been forged
What type of fasteners are used for most lab motors
Metric
How to reduce part cost?
OTS parts Larger feature tolerances Coarser surface finish Fewer finished surfaces Fewer dim datums Weaker material Thru-bolted holes Thru holes Cone-bottomed holes Nominal part dims Smaller parts Min raw-stock removal Fewer fillets Standard cutter sizes Avoid mirror image (v. identical) parts Make great detail drawings
15 dimensioning mistakes that cause us to look like we don't know what we are doing
Omitting necessary dimensions Omitting tolerances for any dim Dimensioning to hidden lines Showing hidden lines or dims in iso views Duplicating dims in multiple part views Dimensioning which requires the manufacturer to perform calculations Dimensioning a hole by its radius or an arc by its diameter Specify metric threads callouts as UNC/UNF Specifying metric thread lengths in inches Poor print quality Dims placed carelessly over part views Shading in iso or ortho views Inconsistent line weights across dims Disproportionately scaled dims Too many views on one page
2 types of forging
Open die and closed die
Gearing can be used to increase motor torque at the expense of what?
Output speed
Power of a motor equation
P = V * I * n_motor V = Voltage I = current n_motor = electrical efficiency of the motor
What are 4 things that should be present in assembly BOMs created for this course
Part numbers Part quantities Part descriptions Unique item numbers matching the balloon numbers on the assembly drawing
Is a tap drill physically different from any other drill
Physically different
Casting
Pouring molten liquid into a mold where it is subsequently allowed to cool and solidify to produce a part that is near net (final) shape
What keeps a fastener tight
Proper installation torque
Always ______ and _________ the milling machine spindles before changing tools over the plastic ______________.
Raise; lock; table covers
6 related drilling operations
Reaming-used to make a hole bigger/increase tolerance Tapping-adding threads to a preexisting hole Counterboring- create a step for the head of a bolt to sit in Countersinking- create an angular step for the head of a flat head screw to sit in Centering-locating a hole, used before drilling Spotfacing-creating a flat surface on a part so that you have somewhere to drill
First 4 steps of the design process
Recognize the need Define the problem Do research Generate concepts
What are 4 reasons aluminum is a popular material choice
Relatively cheap Relatively low density Relatively strong Possesses a high machinability
Difference between relay and proportional control
Relay control has two settings: on or off. Proportional control allows the motor to operate at varying speeds
After clamping the work piece in the vise....
Remove parallels
4 drawbacks of a CNC machine
Requires programming skills Expensive Require more frequent and more costly maintenance Often slower for making one simple part/feature
When should you use slower cutting speeds?
Roughing cuts Stronger materials Flexible workpieces When trying to maximize tool life
Are round or square pockets/slots/holes cheaper and why?
Round because cutting tools are round
3 most common types of electric arc welding in order of increasing quality
SMAW, GMAW, GTAW
3 most common types of casting
Sand casting, investment casting, die casting
Why do female threads fail?
Shear along the major diameter
What sheet metal capabilities does the lab have?
Shear, brake (bending) , punch press (round holes)
SMAW
Shielded metal arc welding
For what type of parts are manual machines a better choice than CNC machines
Simple parts in low quantity
What is the limiting factor for how fast a drill or endmill can feed thru any material?
Size / strength of cutting edges / lips
Unilateral tolerance
Size differs in only on direction. Uses either a + or -
3 things you should check before/when turning on a milling machine
Speed range Clearance between cutting tool and everything else Direction
Always adjust _________ with the mills, lathes, and drill presses running
Spindle speeds
List the 4 common ways to transmit torque through a hub from strongest to weakest
Splines, keyways and pin joints, set screws, press fit
Investment casting
Start with a wax pattern made by a die mounted on a "tree" which is covered in stucco. Wax is removed with steam and fired to cure it
What are six factors that affect optimum cutting speed for drilling and milling?
Strength and thermal conductivity of material Depth of hole Presence and efficiency of cutting fluid Type, condition and stiffness of cutting machine Stiffness of workpiece, fixture and tooling Quality of holes desired
3 advantages of TIG welding
Strongest weld No cleanup Can weld virtually any conductive metal
What are gears used for
Switching between torque and speed
Fastener Torque equation
T = .2 * F_i * d F_i = desired preload (installed tensile force) d = nominal bolt diameter
Equation to calculate the required fastener torque
T = 0.2* F_i* D
Why do male threads fail?
Tensile loading along thread root
What rotates on a lathe
The chuck and the material/workpiece in it
What rotates on a milling machine
The cutting tool and the spindle
Shank
The cylindrical part of a fastener that extends from the underside of the head to the starting thread
Why should fasteners never be placed in shear
The fastener can loosen, it reduces load capacity and fatigue resistance, the thread can remove material from hole wall
Tolerance
The maximum amount a part can differ from the ideal size
Yield strength
The point above which the material permanently deforms
Fit
The range of how tightly two parts fit together
What is the structural benefit of bending sheet metal edges and flanges
The sheet metal becomes stronger/stiffer
Nominal size
The size used for identifying and describing the part
Allowance
The tightest fit, or minimum clearance
Closed die forging
The use of custom made, specialized dies with the desired final shape that enclose the heated metal during the forging process, forging the metal into a desired final shape.
What happens if chips collect inside a hole while drilling?
They cause the drill bit to overheat, seize, and break
Purpose of a fastener
To clamp parts together
What is the purpose of a clearance drill
To create a clearance hole
What is the purpose of an edge finder
To establish zeros of the x and y axes
What are ECNs used for
To formally track design changes and corrections through the project prototyping and life cycling phase
What is the purpose of peck drilling?
To help chips evacuate so they don't collect inside the hole.
Why are separate evaluation matrices created for separate functional subunits of a design?
To pick the best subunit to create one final design with all the best ideas, free of bias
What is the purpose of flux or shielding gas
To prevent rapid oxidation by preventing oxygen/air from coming into contact with the molten metal
What is the purpose of a countersink
To remove any burrs caused by drilling or tapping or to allow the head of a bolt or screw to lay flush with the surface of the workpiece
Why are decision matrices used
To unbiasedly evaluate different ideas based on a weighted set of objectives the design team decides are important for solving the problem
Bilateral tolerance
Tolerance using +/- The size can differ above and below ideal size
What is the purpose of tolerances and when should they be used
Tolerances note the allowable margin of error for each dimension; they should always be used on final part drawings because manufacturing dims without tolerances are useless
T/F AWJ machines can cut at different speeds depending on the desired finish?
True
T/F The electrode used when MIG welding is consumed as the weld is made.
True
T/F the suitability of parts for the forging process is independent of desired quantity
True
T/F`Suitability of parts for the casting process is independent of desired quantity.
True
Define lathe turning
Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material
Inspect the workpiece on the lathe after .....
Turning off the spindle
9 common lathe operations
Turning-cutting parallel to the axis of rotation Facing-cutting perpendicular to the axis of rotatioin Profiling-cutting at an angle to the axis of rotation Chamfering-the feed is used to create an angle at the edge of the cylindrical surface Parting-the feed moves radially to cut off the end of a surface Threading-tool moves linearly along a cylindrical surface to create grooves in a spiral pattern Boring-the tool moves along the axis of rotation to create or enlarge a preexisting hole Drilling-create a hole Knurling-a crosshatch pattern is formed on a part
Physical/ functional differences between and engine lathe and a turret lathe
Turret lathes are used for multiple-production jobs and engine lathes are used for single-production jobs. Turret lathe has a turret where an engine lathe has a tailstock
6 factors that determine cutting speed and feed rate when milling
Type of material to be cut How rigid is the setup The cutter's physical strength Material of the cutter The spindle's power Type of finish
How does a material's machinability affect material choice
Use softer/weaker materials
Purpose of a tap drill
Used to create a hole that will be tapped (last tool used before the tap)
Roughing cuts
Used to remove the maximum amount of stock in the minimum amount of time. Uses a heavy feed and a slow speed
Purpose of a center drill
Used to start a hole before drilling
Electric Arc Welding process
Using an electric arc to heat separate pieces of similar material to be joined to a temp high enough to cause melting and coalescing
Maximum Peripheral tool velocity equation
V = (pi) D N
Velocity with a load equation
V = .75 * pi * D * N = .75 * V_noload
What type of milling machines do we have in the lab
Vertical column and knee
6 Advantages of AWJ process?
Virtually any material can be cut; quality, satin-like finish; no heat in the machining process; environmentally responsible; no tool changing; can create almost any 2D shape
When do you change the spindle speeds on the milling machine
While the spindle is running
When should you adjust the spindle speed of a mill
While the spindle is running
How are threads on all fasteners made and why are they made this way
With sliding or rolling dies because they produce better surface finish and higher fatigue resistance
Sheet metal
Workpieces with a high ratio of surface area to thickness
What axes are on the mill
X, Y, and Z
Which axis is aligned with the spindle
Z
What keeps a bolted joint tight
adequate torquing/stretching of the bolt
Disadvantages of press fits
always slip when used with soft materials (like plastic) except where very low torque transfer is required; pressing parts together can damage electric motors or other precision components; press fits are also difficult to disassemble without damaging components
Shearing
cutting sheet metal by subjecting it to shear stresses
Disadvantages of set screws
does not provide reliable power transmission when used purely as a friction interface with no machined flat or recess except where very low torque transfer is required
Feed rate for a drill equation
f = N * f_r N = spindle speed f_r = feed per revolution of the drill
Linear feed rate of an endmill equation
f = N * f_t * m N = spindle speed F_t = feed per tooth / cutter m = number of teeth on endmill / cutter
Type of parts forging is good for:
high strength parts requiring high ductility
Disadvantages of key ways and pin joints
keyways are a little more difficult and costly to machine than pin joints because they require additional equipment and tooling (beyond simple drills and reamers); both keyways and pin joints are permanent once machined into the (motor) shaft and hub
Torque v. speed curves for electric motors are___ (trend)
linear
Before changing tools on a mill...
lock the quill in the upmost position
Advantages of key ways and pin joints
provide positive mechanical engagement in all cases; pin joints are easy to design and machine (because they are cylindrical); keyways and pin joints allow disassembly without damaging components
Advantages of press fits
simple to design and fabricate; work well for permanent assemblies using strong/hard materials like steels
Fasteners should always be loaded in _________ and never loaded in _________
tension, shear
Forging
the repeated deformation of heated solid metal to refine the grain structure and improve part strength without adversely affecting material ductility
Open die forging
the use of hammers, punches, and accessories to forge the metal into billets for subsequent machining to final size
Sand casting
uses 2 mold haves formed around wooden or metal part patterns
Based on the over- versus under-tightening example, properly torqued fasteners can withstand how many more force application cycles before failure?
~ 1,000 times