DML AI FLASHCARDS

Comprehensive Q&A flashcards covering casting, forging, CNC machining, DFM, fasteners, welding, sheet-metal forming, AWJ, and key manufacturing calculations to aid exam preparation.

What is the fundamental definition of casting?

Pouring molten metal into a mold, allowing it to cool and solidify to produce a near-net-shape part.

Which casting method most commonly uses two green-sand mold halves formed around patterns?

Sand casting.

In sand casting, what are the names of the bottom and top mold halves?

Drag (bottom) and cope (top).

What purpose do risers serve in a sand-cast mold?

They provide extra molten metal to compensate for shrinkage during solidification ("over-fill").

Name the six key factors that must be satisfied for a successful casting process.

1) Produce a mold cavity of correct shape & shrink allowance; 2) Provide means to melt metal; 3) Fill mold & vent gases; 4) Allow for metal shrinkage; 5) Permit part removal; 6) Provide for finishing operations.

Which casting process begins with a wax pattern tree that is coated in ceramic slurry?

Investment casting (lost-wax process).

What is the primary advantage of die casting over sand or investment casting?

High-pressure injection reduces porosity, giving better strength, surface finish and dimensional accuracy.

Why are cast parts generally weaker than wrought (billet) parts?

Random grain orientation and potential voids/inclusions formed during solidification.

Rank forging, billet, and casting on the relative strength scale provided in the notes.

Forging 10/10 (strongest), Billet 7/10, Casting 4/10 (weakest).

What is forging?

Repeated plastic deformation of heated solid metal to refine grain structure and increase strength without harming ductility.

Differentiate open-die and closed-die forging.

Open-die uses flat dies/hammers to make general forged billets; closed-die uses custom dies that fully enclose the work to create near-net final shapes for mass production.

Why does forging create stronger parts than machining from billet?

Compressive forces align the microstructure along part geometry, improving strength and toughness.

Define CNC.

Computer Numeric Control

– a machine tool whose axis motions, spindle speeds, tool changes, etc. are directed by computer code.

List two major advantages of CNC technology.

1) Simultaneous multi-axis motion enables 2-D/3-D contouring; 2) High repeatability for efficient mass production once a good program is proven.

Name two common disadvantages of CNC versus manual machining.

Higher capital/tooling cost and the need for skilled programming/setup (also larger space, more maintenance).

What are the two primary methods of CNC programming discussed?

Conversational programming and CAM (Computer-Aided Manufacturing) programming.

In conversational CNC programming, what does a G90 command indicate?

Absolute coordinate positioning.

Give the six typical CAM setup steps after importing the 3-D model.

1) Input stock size & origin; 2) Define tool library; 3) Choose tool for each feature; 4) Enter cutting parameters (speed, feed, depth, pattern); 5) Simulate/verify toolpaths; 6) Post-process to CNC code.

What misconception about CNC accuracy is highlighted in the notes?

CNC does not inherently ensure higher accuracy; machine condition and operator skill matter.

Anderson’s Law in DFM states what regarding part design?

Never design a part you can buy off-the-shelf unless a clear justification exists.

Provide the simplified torque equation for tightening a bolt to a desired preload.

T

0.2

Fi

d (Torque

0.2

preload force

bolt diameter).

Why is under-tightening a critical bolt often worse than slight over-tightening?

Insufficient preload allows cyclic loading to cause fatigue failure far sooner than a correctly (or slightly higher) preloaded joint.

Explain why fastener threads should not carry shear loads.

Threads are smaller diameter, provide low bearing area, loosen quickly, and the threads act like a file, enlarging the hole.

Define the difference between a bolt and a screw in proper terminology.

Bolt: external thread used with a nut (requires two tools). Screw: external thread mated directly into a tapped workpiece (one tool).

Why are rolled threads superior to cut threads?

Better surface finish, compressive residual stresses, continuous grain flow, and 30-75 % higher fatigue strength.

When should coarse threads be chosen over fine threads?

When the female material is weaker than the male fastener (e.g., steel bolt in aluminum casting).

What is a tap drill?

The specific drill size used before tapping internal threads so that threads are formed to correct depth and strength.

What are the two standard clearance hole classes on a tap chart?

Close-fit and free-fit clearance holes.

State the minimum number of full threads that should engage in a properly designed tapped joint.

At least five full threads of engagement.

Name two benefits of using dowel pins in an assembly.

Accurate positioning/locating of parts and resisting shear loads so bolts only provide clamping.

Provide one rule of thumb for placing bolt holes relative to an edge.

Keep the hole center at least one major fastener diameter from the edge for adequate bearing area.

What shielding mechanism is common to SMAW?

Flux coating on the electrode produces shielding gases and slag.

List one main advantage and one main disadvantage of SMAW (‘stick’ welding).

Advantage: Very portable & inexpensive. Disadvantage: Slow with significant post-weld slag cleanup and spatter.

Which arc-welding method feeds a continuous consumable wire and uses an external shielding gas?

GMAW (MIG) welding.

Give two reasons GMAW is popular in industry.

High deposition rate (fast), minimal post-weld cleanup, and relatively easy operator training.

What non-consumable electrode is used in GTAW (TIG) welding?

Tungsten.

Why is GTAW prized for aerospace applications?

Produces the highest quality, strongest, and cleanest welds with no spatter or slag.

What is springback in sheet-metal bending?

Elastic recovery after unloading that makes the final bend angle smaller and bend radius larger than the tooling.

State the general formula for punch force in shearing sheet metal.

P

0.7

UTS

thickness

total length of cut (P = 0.7 UTS t L).

Differentiate punching and blanking.

Punching discards the slug; blanking keeps the slug as the desired part.

In sheet-metal design, what is a typical minimum bend radius expressed as?

A multiple of material thickness, e.g., 2 T, 3 T, etc.

Define roll forming.

Progressively bending continuous strip through successive roller dies to create long profiles like channels or gutters.

What is deep drawing?

Forming a flat blank into a cup or box shape by pushing it into a die cavity with a punch (e.g., beverage cans).

Explain the main advantage of Abrasive Waterjet (AWJ) machining over thermal cutting methods.

No heat-affected zone; it can cut virtually any material without altering properties.

How does cutting speed vary with material thickness in AWJ according to the notes?

Cutting speed

1 / (Thickness^1.15); thin parts cut much faster than thick ones.

State two common reasons CNC machines achieve higher productivity than manual machines.

Automatic tool changers and high-pressure coolant flushing chips/heat, plus electronic probing and stiffer structures.

Give the typical tolerance band for non-critical hole locations in project parts according to the course guidelines.

±0.005″ to ±0.020″.

What surface finish note is acceptable when edges only need to be safe to handle?

“Debur all edges.”

Why should square holes generally be avoided in conventional machining designs?

Traditional rotating tools create round features; square holes require expensive secondary processes (EDM, broaching, etc.).

What is the recommended L:D ratio limit for drilling to maintain tool stiffness?

Preferably under 8:1; smaller is always better.

When dimensioning bolt circles, what extra information should be provided for machinists?

Cartesian X-Y coordinates of each hole center along with circle diameter.

What are the two primary columns that every Bill of Materials (BOM) must include beyond item number?

Part name and quantity (also description/part spec).

In welding symbol notation, where is the fillet weld symbol placed if the weld is required on the arrow side?

Below the reference line.

Name one common environmental advantage of AWJ machining.

Uses inert garnet abrasive and water – no toxic fumes or oils.

Why is over-bending often necessary in press-brake work?

To compensate for springback so the part finishes at the intended angle.

What term describes bending a sheet edge over itself to remove sharp edges and add stiffness?

Hemming (or seaming if joining two sheets).

List the seven major casting processes identified in the lecture notes.

1) Sand casting 2) Shell-mold 3) Permanent-mold 4) Die casting 5) Centrifugal 6) Plaster-mold 7) Investment casting.

Which casting method uses only gravity to fill permanent metallic molds?

Permanent-mold casting.

What machining process limitation is addressed by specifying cone-bottomed holes rather than flat-bottomed ones?

Drills naturally make cone-bottomed holes; specifying them avoids slower end-milling operations.

At what percentage of ultimate tensile strength (UTS) did the properly torqued 3/8-in bolt survive ~6 million cycles?

About 60 % of UTS preload.

What is the purpose of a pattern in sand casting?

To create the mold cavity; it is a duplicate of the desired part made oversize for shrinkage.

Give the typical shrink allowance per foot for gray cast iron patterns.

Approximately 1/10″ to 1/8″ per foot.

What is a match-plate pattern?

A combined cope and drag pattern mounted on opposite sides of a single plate for faster molding.

In a CNC pocket toolpath, which parameter controls how much tool engages material laterally each pass?

Stepover (expressed as distance or % of tool diameter).

What key parameter should be reduced up to 50 % when drilling holes deeper than three drill diameters?

Both speed (rpm) and feed (ipm) to reduce heat and chip clogging.

Provide the equation to convert recommended surface speed (sfm) to spindle speed in rpm.

N (rpm) = (12 × V*sfm) / (\n\n× D*in).

What machining feed formula is used for milling (feed per tooth)?

Feed (ipm) = N (rpm) × ft (in/tooth) × number of teeth.

Why should through-bolted holes be favored over tapped holes when possible?

Faster to make (just drilled) and avoid thread strength issues; only one part needs threads (nut).

What is the first design rule before detailing a part drawing?

Finish designing the part – ensure mounting, assembly access and size justification are resolved.

Explain why specifying "finish all over" on drawings is discouraged.

Unnecessary finishing greatly increases cost; only specify finishes where functionally required.

What three pieces of information must a threaded hole note include?

Tap drill size/depth, thread specification/depth, and quantity if more than one identical hole.

Which welding process is typically the fastest for carbon-steel sheet fabrication with minimal post-weld cleanup?

GMAW (MIG).

During SMAW, what becomes of the electrode coating?

It burns, creating shielding gases and leaving a slag layer over the weld bead.

Name two factors that influence the choice of a welding process for a job.

Material type/thickness and required weld quality (also equipment availability, production rate, operator skill, etc.).

What is a plug weld?

A circular weld filling a hole in one member to attach it to another underlying member.

In sheet-metal shearing, how does increasing punch-die clearance affect the cut edge?

Edge becomes rougher with larger burrs.

Why are flanges or tabs often added to thin sheet-metal parts instead of threading them?

Sheet thickness insufficient for

5 thread engagements; flanges allow riveting, welding, or screw/nut fastening.

State one key advantage of roll-forming versus discrete brake bends.

Continuous, high-speed forming of long parts with consistent profiles (channels, gutters, etc.).

What typical rolling speed is given for roll-forming lines?

About 1.5 m/s (

300 ft/min).

How does forging influence ductility?

Proper forging refines grain without reducing ductility; strength increases while ductility is largely retained.

What term describes CNC probing used to locate part zeroes automatically?

High-speed electronic probing.

Why should tolerance values be as large as functionally possible?

Tighter tolerances require more machining time and cost; larger tolerances reduce expense.

Explain "peck drilling" and its purpose.

Intermittently retracting the drill to break chips and allow coolant in, preventing clogging and heat build-up in deep holes.

For a ¼″ HSS drill in soft cast iron, what starting speed and feed were calculated (before 60 % lab reduction)?

1500 rpm and 6 in/min; adjusted to 900 rpm and 3.6 in/min for hand-oiled lab conditions.

Give one reason why permanent-mold casting produces better surface finish than sand casting.

Metal molds are smoother and don’t erode like sand, yielding finer surface texture.

What is the primary function of the sprue in a sand-casting mold?

Vertical passage through which molten metal is poured into the runners and cavity.

Describe the effect of high pressure in die casting?

Forces metal into fine features, reduces gas porosity, and improves mechanical properties.

What CNC code is typically used to turn the spindle on clockwise?

M03 (or M3).

How can springback be compensated when designing bending tooling?

Over-bend by an amount based on material and thickness so final angle matches spec.

Why should mirror-image parts be avoided unless necessary?

Increase design/drawing effort and manufacturing cost; identical parts reduce inventory and simplify assembly.

State the typical hardness range (Rockwell C) for Grade 8 steel bolts.

Approximately 32–38 HRC.

What is a "match-plate" pattern’s main production advantage?

Speeds up molding by aligning cope/drag halves precisely in a single operation.

In GMAW, what are two common shielding gases?

Argon and carbon dioxide (or Ar/CO₂ mixtures).

Identify two safety advantages of AWJ compared with laser cutting?

No hazardous fumes or intense light requiring special eye protection; relatively cool process.

Which welding process usually requires the highest operator skill but gives the finest control?

GTAW (TIG).

When calculating drill feeds, what symbol represents feed per revolution?

f\_r (fr).

How many threads per inch does a ¼-20 UNC fastener have?

20 threads per inch.

What is the rule of thumb for blind tapped hole drill depth relative to desired thread depth?

Drill at least one extra fastener diameter deeper than the usable thread length.

Give one guideline for designing parts around nominal raw-material sizes?

Specify dimensions slightly below stock size to avoid excessive material removal and save machining time.

What practical benefit does automatic chip-flushing coolant provide in CNC machining?

Removes heat and chips, enabling higher cutting speeds and better surface finish.