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