Metal Exam Part 2 Flashcards
True or False: The diacro bender can bend heavier stock than sheet metal benders.
True.
(Hopefully James won’t put this part on the exam but who knows with him…)
Material limits for the BCIT diacro bender:
* round mild steel bar1”
* square mild steel bar 3/4”
* steel tubing (16 gauge) 1-1/4”
* standard iron bar 1” OD
* flat bar (bend on side) 3/8”x 4”
* flat bat (bend on edge) 1/4” x 1”
* mild steel angle iron 3/16” x 1” x 1”
* mild steel channel 3/16” x 1/2” x 1”
What shapes can the diacro bender produce?
- circles
- eyelets
- zero-radius bends (tight corners)
- scrolls
- squares
- springs
When scoring of the material during forming is a problem on the diacro bender, what should you do?
lubricate the forming nose or using a
forming roller instead
What materials can you use with the hossfeld bender?
- Flat and round stock:
~ radius bends
~ square bends - Angle iron:
~ internal bends (after relief cuts
made)
~ external bends (relief cuts needed) - Tubing bends
- Scrolls
What can happen if you attempt to bend brittle materials?
The material may shatter - do not attempt
What are the 4 characteristics Foundry Sand must exhibit?
- Permeability - to allow gasses produced during pouring of molten metal to pass or vent through the mold. Permeability is inversely related to the percentage of clay content.
- Green Compressive Strength - the structural integrity of the sand grains held together by the clay. This determines how the mold will withstand handling and the forces of molten metal entering the mold cavity. Green Compressive Strength is directly related to the percentage of clay content and moisture.
- Dry Strength - upon contact with molten metal the mold dries rapidly. The sand must resist the forces of the metal to prevent erosion, cracking, and other deterioration of the mold cavity.
- Flowability - the ability to conform to the shape of the pattern as the mold is made. This is governed by the size and shape of sand grains and clay content.
Foundry sand is really a mixture of what two components?
Sand and Clay
What are the most common clays used in Foundry sand?
Bentonite and Fire Clay
What type of sand is usually used for aluminium casting? (in combination with clay)
Silica Sand
________ a process which mixes the sand and clay with a heavy roller with a kneading action.
_________ helps maintain high green compressive
strength.
Mulling
What are the Two Broad categories of Foundry Sand?
- Natural Bonded Sand
is used just as it is dug from the ground, making it inexpensive. It doesn’t produce smoke and fumes when metal is poured, is widely available, and may function over a wider range of moisture content (natural sands require 6-8% moisture content).
- Synthetic Sand
is produced through the blending of various types of sands and
clays to offer greater control of permeability, green compressive strength, and moisture content. Most synthetic sands require a 3% moisture content, resulting in less steam generation and greater permeability.
What is ‘Tempering’ foundry sand?
The process of adding an appropriate amount of water, for natural
bonded sands or oil for synthetic sands to allow the clay to hold the grains of sand together.
When tempering Foundry sand what occurs with too little moisture and what occurs with too much moisture?
too little moisture = mould will be weak and fall apart
too much moisture = generation of steam and reduced
permeability
both problems produce faulty castings
True or False: Oil-Tempered Synthetic Sands (Petrobond) require water when tempering.
FALSE
What is used to temper Oil-Tempered Synthetic Sands (Petrobond)?
-Special flour-like binder material (Petrobond)
-non-detergent oil (10 weight)
-a catalyst (P-1 or Methyl Alcohol will work)
Petrobond requires periodic rejuvination through the addition of small amounts of 3 things:
Binder, Oil, Catalyst
What is the procedure for Mulling Foundry sand?
- shovel the old oil base sand into the Muller (or cement mixer)
- add 1lb. of binder to every 100 lb. of sand – mull for 1 min.
- slowly pour in 1lb. of 40-weight oil – mull 10 min.
- add 1 ounce of P1 catalyst – mull for 5 min.
What is the procedure for making a sand mold for casting?
- place the drag on the molding board with the alignment pins down
- place the mold in the centre of the drag (small side up)
-
lightly dust the pattern with parting compound
4.riddle facing sand onto the pattern, covering 2” above the pattern - fill the drag with unriddled backing sand
- use the peening end of the bench rammer to ram sand around the pattern (one pass all over with wedge, one pass with flat end)
- add additional unriddled sand to allow the drag to be fully packed
- use the butt (flat) end of the bench rammer to complete packing
- strike off the excess sand with the strike-off bar
- place the bottom board on top of the drag & turn it over
- remove the molding board
- use the slick & oval or trowel to smooth & level the sand if necessary
- press the sprue & riser pins into the sand about 1” away from the pattern
- dust the pattern with parting compound (use sparingly)
- riddle, ram & strike-off the sand in the cope as you did before
- carefully lift the cope from the drag & place it on the edge
- remove the sprue & riser pins
- cut a gate from the mould to the sprue & the riser gate should be ≈ 1/2” X 1/2”
- place a screw into the pattern & tap the screw lightly
- carefully lift the pattern straight up from the mould
- use your finger or the slick & oval to smooth the resulting
surfaces in the gates - remove any loose particles using moulder’s bellows
- carefully reinstall the cope on the drag
- use your fingers to smooth the resulting holes into a funnel
shape
-ready to cast
5 steps to water-tempering foundry sand:
- Spread the sand a few inches deep on the floor. If new sand or clay is to be added,
distribute it evenly over the old sand and then mix by shoveling. - Sprinkle tempering water over the entire surface of the sand. Mix the sand and
water by shoveling. Err on the side of caution - don’t add too much water. Molding
sand is strongest when it appears to be slightly dry. Too much water gives the
impression of suitable tempering but results in low strength when the mold is used. - Test water content by grasping a handful of sand (palm facing down) and squeezing
firmly. Turn your hand over, relax the grip, and allow the sample to roll forward so
the sharp edges roll to the top side. Flowability is indicated by sharp edges, a clean
contour, and smooth surface. If the sand tends to crumble or is rough, it’s too dry -
add water sparingly and try again. - Grasp the sample by the ends and bend it. Good green compressive strength is
shown by a sharp break and toughness (resistance to breaking). - Riddle the sand to remove impurities and to aerate it to improve flowability around
the pattern.
What are the 5 basic steps to sand casting? (simplified)
- Prepare the Mould
a) Make the Pattern
b) Make the mould cavity
2) Prepare material for casting
3) Pour metal into mould: metal of proper temperature is introduced rapidly so the sprue is kept full.
4) Metal is allowed to solidify.
5) Mould is broken up to remove the casting, and sand is reclaimed for reuse
Name AT LEAST 5 things needed to cast aluminum
*pattern
*flask
*bottom & molding boards
*sand
*shovel
*rammer
*sprue & riser pins
*parting sand
*riddle
*draw spike
*striking bar
*crucible
*aluminum
*furnace
*skimmer
*degasser rod &tablets
*lifting & pouring tongs
*slick/spoon
What sand is easiest to work with when aluminum casting?
Synthetic sand
True or False: when aluminum casting the metal is poured at over 1300ºF (740ºC).
True
What is the minimum you should fill a crucible when melting?
Do not melt less than half a crucible full as this is hard on it
What is the maximum you should fill a crucible when melting and why?
Fill the crucible loosely to the top lip only. The metal must be able to rattle if shaken.
Pieces which are jammed in can expand when heated and break the crucible.
What safety precautions should you take before pouring melted aluminum?
Put on safety gear: leather shoes, leggings or pants, jacket, mitts, and helmet
with screened face shield. Turn ventilation fan on.
What is the procedure for heating and pouring aluminum?
- Weigh out aluminum to suit the crucible. Do not melt less than half a crucible full as this is hard on it.
- Fill the crucible loosely to the top lip only.
- Centre the base block and put a piece of cardboard on it to prevent its sticking to the
crucible. If the furnace is hot, first dampen the cardboard so it doesn’t burst into flame. - Place the charged crucible centered on the base block.
- Close the lid and confirm that it seats properly all around its circumference. Remove any obstruction which prevents proper seating. Open the lid and leave it to the side.
- Arrange the pouring area for safety and efficiency. Consider access to the flasks, ingot molds, etc. Be sure there are no tripping hazards present. Confirm that the lifting tongs, pouring shank, degassing plunger, skimmer, and garbage container are present and conveniently located.
- Put on safety gear
- With lid left to the side, light the furnace – follow posted directions.
- After a minute of warm up, close lid. Fine tune the flame.
- Using tongs, put the remaining metal around the lid of the furnace, but not covering the hole in any way. This will drive any moisture off the ingots.
- At first sign of melting, add about 2 tablespoons of Coveral flux (pink powder). Wrap in aluminum foil and throw in.
- As a molten heel develops, slowly and carefully add the rest of the preheated metal with preheated tongs. No moisture! No splashing.
- When the metal is all melted, add the rest of the flux (2 Tbs.).
- Monitor the metal for a shut off temperature of 1300º-1350ºF (705º-732ºC).
- Shut off furnace (including gas valve), open lid, briefly heat the skimmer and plunger over the furnace (not metal) to preheat and dry.
- Monitor temperature. As soon as the temperature peaks, degas with 1/3 to 1/2 tablet.
Hold down with plunger until bubbles stop, then move up and down without breaking
surface of metal (to stir the metal). - Carefully remove the crucible and place in pouring shank. Be sure the crucible is secure in the lifting tongs and move slowly.
- Skim with preheated skimmer. Place waste in metal garbage can.
19.Check temperature. Pour at about 1320º-1375ºF (715º-745ºC). - Pig any remaining aluminum - do not leave in the crucible unless you intend to place it back into the furnace to immediately melt more metal for casting. If the aluminum is allowed to solidify in the crucible it will likely expand and crack the crucible when it is next heated.
Explain what a misrun is and how it is caused.
A casting which was not successful because the mold was not filled entirely with metal.
- metal poured too slowly or too cold.
- Sprue too short or small, gating too small.
- Natural sand contained too much water, resulting in fast cooling of metal
What causes sand holes in aluminum casting?
- loose sand not removed from mold before closing
- thin sections of sand (in pattern area or gating) broken out during pouring
- sand too dry
- sand not rammed adequately during mold making
- sand requires mulling
What causes a rough surface on your aluminum cast?
sand not rammed adequately during mold making
* too much parting agent used (dries sand)
* pattern has rough surface
Explain what shrink is and how it is caused.
a depression or sunken cavity in the casting surface. The sunken area often has a
rough or granular appearance.
* Gates feed thin sections of the casting
* Riser should be used
* Riser too small or improperly located
* Metal was too hot when poured
* Metal alloy is wrong type to cast
Explain what drops are when aluminum casting and what causes them.
part of the sand mold falls into the cavity below, thus preventing the metal from filling
the mold.
* sand too dry
* sand not rammed tightly enough
* closed mold handled roughly
Explain what dross or slag is when aluminum casting and what causes it.
material other than that intended makes up part of the casting.
Proper sprue and gating practice will help prevent this problem.
* metal not skimmed adequately before pouring
* improper gating - runners in drag (bottom) and gates in cope (top)
* pouring basin not provided
Explain how to setup a 4 jaw chuck.
with a dial indicator, read the run-out
* move the jaw closest to the high in the proper direction
* 1/4 turn of the jaw will be ≈ .010”
* back the jaw out this amount and tighten the opposite
jaw.
Why a 4 jaw chuck? (three main reasons)
- Dial-in to perfect accuracy
10 - Hold odd shapes
- Machine off-centre
What is the cutting speed for aluminum?
500-1000 sfpm
What is the cutting speed for brass?
250-650 sfpm
What is the cutting speed for low carbon steel?
100 – 300 sfpm
What is the formula for Spindle RPM for Milling machines?
CSx4/D (Diameter of the milling cuttre in inches)
What is the Feed formula for Milling? (inches per minute)
(Number of cutter teeth) x (Feed per Tooth) x (RPM)
Example:
0.5” Diameter 2 flute end mill cutting
Aluminum
Spindle RPM = 500 x 4 /0.5 = 4000 RPM 0.5
Feed Rate = 2 x 0.011 x 4000 = 88 Inches/min
What color should you heat the metal to when forging?
cherry red
What type of steel should be used for forging?
mild steel
True or False: when forging you know the metal is up to temperature when sparks start flying off of it
False. Never allow the metal to become so hot that sparks fly from it
What are the 5 main hand-forging operations?
- Tapering
- Drawing out
- Bending
- Twisting
- Upsetting
What is tapering and what is the procedure for it?
Tapering is a shaping process for forming the ends of many projects, including cold
chisels & center punches
* Heat the end
* Hold the opposite end firmly with tongs
* Place the heated end on the face of the anvil
o Use an angle equal to half the amount of taper you want
* Strike the heated portion with the flat of the hammer
o Keep turning the metal to keep the tapering even
* Keep the metal at forging temperature
o Reheat the metal to dull cherry red as required
What are you doing when drawing out metal and how is it done?
Drawing out is done to make a piece longer and thinner
* Heat the area
* For round stock - hammer the metal to a square shape
o Use heavy blows that come straight down and are square to the work
* Heat the metal again
* Form it into an octagon
* Round the metal off, by turning steadily
* If you are drawing out square stock, round it first and finish by re-squaring it
“Bending” in forging can be done in various ways:
-For a sharp bend, heat the area at the bend line
-Place the heated bend area over the edge of the vice and strike the extended portion with the hammer
OR
-Place the hot metal in the hardy hole and pull or bend with tongs
OR
-Make a right-angle bend by placing the heated metal in a vice * Curved shapes are formed over the horn of the anvil
“Twisting” in forging is done by:
Heating the area and then bending the stock in a vice
“Upsetting” in forging is the opposite of:
Drawing out
What is “Upsetting” when forging?
- It increases the area of the metal by decreasing its length
- Heat the section to the proper temperature
- For short pieces – hold them over the end of the anvil and strike the end to flatten it out
- For longer pieces – clamp them in a vice, with the heated end extending above and strike the end with the hammer
What are some surface types that can be milled?
Flat surfaces (vertical, horizontal, angular), shoulders, grooves, T-slots, dovetails, keyways, irregular, and curved surfaces
What does the diving head allow the mill to do?
Allows the milling of equally spaced gear teeth, surfaces
or grooves on cylindrical parts. By linking the dividing head to the table longitudinal
feed, spirals may be machined
What are the 2 types of milling machines?
Bed-type (mostly large industrial
machines) and the knee-and-column type (has a table which is able to be raised up &
down)
What are the 3 axis of a milling machine?
- vertical (up & down) Z Axis
- longitudinal (left & right) X Axis
- cross or transverse (in & out) Y Axis
What is knee elevation on the mill?
establishes the correct tool-to-work piece clearance (depth of cut).
On the vertical mill the depth of cut may also be set using the vertical handwheel to set
the quill position. Adjustment is usually possible to the nearest .001”. May be manual or
power feed.
What is the knee clamp on the mill?
locks the knee position. Must be released before any knee elevation
adjustment is made. Should be locked during machining operations
What is Transverse (cross) table movement on the mill?
in and out adjustment with the cross feed
handwheel. Usually is not powered, but can be set to an accuracy of .001”
What is the Saddle or transverse clamp on the mill?
locks the transverse movement to help reduce vibration
during milling operations. Must be released before transverse adjustments.
What is Longitudinal table movement on the mill?
left and right movement of the table, which may be
manual or powered feed.
What is the Table clamp on the mill?
Locks the table in the longitudinal feed direction. Is usually tightened
during hole-machining operations
What is Rapid traverse on the mill?
allows rapid knee or table movement with power. Must be used with
caution!
What is conventional milling?
the workpiece is fed against the rotation of the cutter. Requires a tightly held workpiece as the cutting action tends to lift the work out of the vice or clamps
What is climb milling?
work is fed in the same direction as the cutter rotation. The cutting action tends to pull the workpiece under the cutter so any backlash will cause vibration, chatter, and possible cutter breakage. It produces a smoother surface and also allows the machining of small parts as cutter action tends to push parts into the table. On some
materials the cutters dull more rapidly.
What does a milling machine have to be equipped with in order to climb cut?
An anti-backlash device. Do not attempt on any machine unless you are certain of its proper
operation! Machine and cutter damage are almost a certainty
What are the 5 holding devices for a mill?
- Vise - most common method of holding the workpiece. Is often used with parallels to
align the work. - Jigs - utilize clamps, bolts and studs to correctly align the workpiece.
- Hold-downs use bolts and various fixtures to secure work.
- Angle plate - used with bolts and clamps.
- Dividing head - may be used with a chuck or between centers like a lathe set-up.
On the mill, how do you set a workpiece in the vice?
1) lay paper strips under the workpiece
2) tighten the vice handle
3) hit the workpiece with a deadblow hammer
this will seat the work
4) try removing the strip of paper
* when tightening a plain type milling machine vise it is not
necessary to strike the handle of the vise
What are parallels and what do they do?
- parallels are pieces of steel bar stock accurately machines
so that the opposing sides are parallel to each other - parallels are provided in sets of two with identic
What are v blocks and what do they do?
V-Blocks hold and support round work for milling or
drilling
* V-Blocks are typically clamped directly to the table as in
the picture on the right using a strap clamp
What is an end mill cutter?
end mills cut on their ends & their sides (unlike a drill bit)
* 2 flute & multi-flute end mills
* multi-flute end mill will produce a better finish than the 2
flute end mill at the same RPM and feed but it will have
less chip clearance space and therefore will be less
convenient in a heavy cut of soft material
What is a face mill cutter?
- face mills are used to cut with the ends of the cutter
rather than their sides - they create a face or flat surface
- they usually have a larger diameter than the width of the
work piece and the whole surface is processed in one pass
What diameter does RPM depend on on the lathe vs the mill?
Lathe cutting speed:
turn the work a certain number of rpm depending on
the work’s diameter
* milling machine cutting speed:
turn the cutter a certain number of rpm depending on
cutter diameter
Parts of the mill! You may want to go over this. Diagram is in week 16 Milling Machines presentation page 34 - 36
Good luck!
