VACUUM DIE CASTING MACHINES

1
VACUUM DIE CASTING MACHINES

• SOME AIR ENTRAPPED IN ORDINARY DIE CASTING
  MACHINES
• THIS PRODUCES BLOW HOLES
• IN VACUUM DIE CASTING TYPE, VACUUM PUMP CREATES
  VACUUM IN DIE CAVITY, A SEAL CUTS OFF THE PIPE
  CONNECTION AFTER EVACUATING
• THIS PREVENTS FLOW OF METAL FROM DIE TO VACUUM
  PIPE
• FLOW OF MOLTEN QUICK AND AUTOMATIC
• FINISHES
• ALL DIE CASTINGS SUSCEPTIBLE TO CORROSION, HENCE
  SUBJECTED TO FINISHING OPERATIONS OR PLATING

NITC
2
(No Transcript)
3
DESIGN CONSIDERATIONS

• USE OF RIBS, HUBS, BOSSES MUST BE TO REDUCE
  WEIGHT, STRENGTHEN THE PART, IMPROVE THE
  APPEARANCE
• THICK SECTIONS MAKE DIE HOTTER AND THUS LESSEN
  DIE LIFE
• LARGE SECTIONS TO BE COOLED MAY CAUSE POROSITY
• EXCESSIVE SECTIONAL CHANGES TO BE AVOIDED
• AVOID UNDERCUTS
• FILLETS DESIRABLE OVER SHARP EDGES
• DRAFTS NEEDED ON ALL CASTINGS
• EJECTOR PINS AT BACK TO AVOID VISIBILITY OF MARKS
• FLASH NECESSARY , TO BE REMOVED LATER BY TRIMMING

NITC
4
DIE MATERIALS
CASTING ALLOYS DIE MATERIAL
TIN, LEAD ALLOY CAST STEEL WITHOUT HEAT TREATMENT
ZINC, Al HEAT TREATED LOW ALLOY STEEL
COPPER BASE ALLOYS HEAT TREATED SPECIAL ALLOY STEEL
NITC
5
DIE CASTING ALLOYS

• MAINLY NON-FERROUS CASTINGS WITH PROPERTIES
  COMPARABLE WITH FORGINGS
• ZINC ALLOYS- WIDELY USED ( ? 70)- Al 4.1 Cu
  MAX 1, Mg 0.4 BALANCE ZINC
• -- PERMITS LONGER DIE LIFE, SINCE TEMP. IS LOW
• GOOD STRENGTH, Tensile Strength 300 Kg/cm2
• VERY GOOD FLUIDITY, THUS THIN SECTIONS POSSIBLE
• USES AUTOMOBILES, OIL BURNERS, FRIDGES, RADIO,
  TV COMPONENTS, MACHINE TOOLS, OFFICE MACHINERIES

NITC
6

• ALUMINIUM ALLOYS
• BY COLD CHAMBER PROCESS-
• Cu 3 to 3.5, Si 5 to 11 , BALANCE Al.
• LIGHTEST ALLOYS, GOOD CORROSION RESISTANCE, FINE
  GRAINED STRUCTURE DUE TO CHILLING EFFECT
• Tensile Strength 1250 to 2500 Kg/cm2
• GOOD MACHINABILITY, SURFACE FINISH
• USES MACHINE PARTS, AUTOMOTIVE, HOUSE HOLD
  APPLIANCES ETC.

NITC
7

• COPPER BASED ALLOYS
• Cu 57 to 81Zn 15 to 40 SMALL QUANTITIES OF
  Si, Pb, Sn
• VERY HIGH TENSILE STRENGTH 3700 to 6700Kg/cm2
• GOOD CORROSION RESISTANCE WEAR RESISTANCE
• LOW FLUIDITY, HENCE REDUCED DIE LIFE
• USES ELECTRICAL MACHINERY PARTS, SMALLGEARS,
  MARINE, AUTOMOTIVE AND AIR CRAFT FITTINGS,
  HARDWARES

NITC
8

• MAGNESIUM BASED ALLOYS
• LIGHTEST IN DIE CASTING, PRODUCTION COST SLIGHTLY
  HIGH, Al 9 Zn 0.5 Mn 0.5 Si 0.5,
  Cu0.3 REMAINING Mg.
• USES IN AIRCRAFT INDUSTRY, MOTOR ISTRUMENT
  PARTS, PORTABLE TOOLS, HOUSE HOLD APPLIANCES
• LEAD TIN BASED ALLOYS
• Lead base 80 Pb Tin base 75
  tin,
• antimony, copper
• LIMITED APPLICATIONS. LIGHT DUTY BEARINGS,
  BATTERY PARTS, X-RAY SHIELDS, LOW COST JEWELLERY,
  NON-CORROSIVE APPLICATIONS

NITC
9
SQUEEZE CASTING

• DEVELOPED IN 1960S (also called liquid forging)
• SOLIDIFICATION OF MOLTEN METAL UNDER HIGH
  PRESSURE (pressure application when liquid
  partially solidifies 70 to 140 MPa)
• A COMBINATION OF CASTING FORGING
• DIE, PUNCH, EJECTOR PIN
• PUNCH KEEPS ENTRAPPED GASES IN SOLUTION, RAPID
  COOLING DUE TO HIGH PRESSURE DIE- METAL INTERFACE
• PARTS OF NEAR-NET SHAPE MADE, COMPLEX AND FINE
  SURFACE DETAILS OBTAINED. No riser needed
• FOR FERROUS NON FERROUS
• AUTOMOTIVE WHEELS, SHORT BARRELED CANNONS ETC.

10
(No Transcript)
11
(No Transcript)
12
V-Process
1. Pattern (with vent holes) is placed on hollow
carrier plate. 2. A heater softens the .003" to
.007" plastic film. Plastic has good elasticity
and high plastic deformation ratio. 3. Softened
film drapes over the pattern with 300 to 600 mm
Hg vacuum acting through the pattern vents to
draw it tightly around pattern. 4. Flask is
placed on the film-coated pattern. Flask walls
are also a vacuum chamber with outlet shown. 5.
Flask is filled with fine, dry unbonded sand.
Slight vibration compacts sand to maximum bulk
density. 6. Sprue cup is formed and the mold
surface leveled. The back of the mold is covered
with unheated plastic film. 7. Vacuum is applied
to flask. Atmospheric pressure then hardens the
sand. When the vacuum is released on the pattern
carrier plate, the mold strips easily. 8. Cope
and drag assembly form a plastic-lined cavity.
During pouring, molds are kept under vacuum. 9.
After cooling, the vacuum is released and
free-flowing sand drops away leaving a clean
casting, with no sand lumps. Sand is cooled for
reuse.
NITC
13

• Benefits Of Using The V-Process
• Very Smooth Surface Finish
• 125-150 RMS is the norm. Cast surface of 200 or
  better, based on The Aluminum Association of
  America STD AA-C5-E18.
• Excellent Dimensional Accuracy
• Typically /-.010 up to 1 inch plus /-.002 per
  additional inch. Certain details can be held
  closer.
• /-.010 across the parting line.
• Cored areas may require additional tolerances.
• Zero Draft
• Eliminates the need for machining off draft to
  provide clearance for mating parts and assembly.
• Provides consistent wall thickness for weight
  reduction and aesthetic appeal.
• Allows for simple fixturing for machining and
  inspection.

NITC
14

•  Pattern construction becomes more accurate and
  efficient.
• Total tolerance range becomes more accurate and
  efficient.
• Geometry/tolerance of part is at its simplest
  form. Draft does not use up tolerance.
• Design/drafting is less complex. Calculations and
  depictions related to draft are eliminated.
• Thin Wall Sections
• Walls as low as .100 in some applications are
  possible.
• Excellent Reproduction Of Details
• Very small features and lettering are possible.
• Consistent Quality
• All molding is semi-automatic. Variable "human
  factor" has been reduced.
• Superior Machining
• Sound metal and no hidden sand in the castings
  means fewer setups, reduced scrap and longer tool
  life.
• Low Tooling Costs
•  

NITC
15

• All patterns are made from epoxy, machined
  plastics, SLA or LDM. There is no need to retool
  for production quantities.
• Unlimited Pattern Life
• Patterns are protected by plastic film during
  each sand molding cycle.
• Easy Revisions To Patterns
• No metal tooling to weld or mill. Great for
  prototypes.
• Short-Run Production Capability
• Excellent for short-run production while waiting
  for hard tooling. The V-PROCESS method can
  outproduce traditional prototype methods such as
  plaster or investment castings.
• Fast Turnaround
• From placement of order to sample casting in as
  little as two to four weeks.

NITC
16
CENTRIFUGAL CASTING AN OVERVIEW

• Known for several hundred years.
• But its evolution into a sophisticated production
  method for other than simple shapes has taken
  place only in this century.
• Today, very high quality castings of considerable
  complexity are produced using this technique.

NITC
17

• To make a centrifugal casting, molten metal is
  poured into a spinning mold.
• The mold may be oriented horizontally or
  vertically, depending on the casting's aspect
  ratio.
• Short, square products are cast vertically while
  long tubular shapes are cast horizontally. In
  either case, centrifugal force holds the molten
  metal against the mold wall until it solidifies.
• Carefully weighed charges ensure that just enough
  metal freezes in the mold to yield the desired
  wall thickness.
• In some cases, dissimilar alloys can be cast
  sequentially to produce a composite structure.

NITC
18
CENTRIFUGAL CASTINGTRUE- C.I. PIPES,
LINERS, BUSHES, CYLINDER BARRELS ETC.SEMI-
CENTRE CORE FOR INNER SURFACE- SHAPE BY
MOULD AND CORE, MAINLY NOT BY
CENRTRIFUGAL ACTION-
EgFLYWHEELSPRESSURE OR CENTRIFUGAL CASTING-
ALSO TERMED AS CENTRIFUGINGFOR NON
SYMMETRICAL SHAPES
MOULD WITH ANY SHAPE PLACED
AT CERTAIN DISTANCE FROM AXIS
19

• SEMI-
• CENTRE CORE FOR INNER SURFACE-
• SHAPE BY MOULD AND CORE,
• MAINLY NOT BY CENRTRIFUGAL ACTION-
  
• EgFLYWHEELS
•  
• SPEED OF ROTATION-
• 60 TO 70 TIMES GRAVITY FOR HORIZONTAL AND
  INCLINED TYPES
•   ABOVE 100 FOR VERTICAL TYPES.
•  

NITC
20
CENTRIFUGING PROPERTIES OF CASTING DEPEND ON
DISTANCE FROM AXIS
SQUEEZE CASTING
DIE, PUNCH, EJECTOR PIN
PARTS OF NEAR-NET SHAPE MADE, COMPLEX AND FINE
SURFACE DETAILS OBTAINED
FOR FERROUS NON FERROUS
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
CENTRIFUGAL CASTING

• points
• Denser structure, cleaner, foreign elements
  segregated (inner surface)
• Mass production with less rejection
• Runners, risers, cores avoided
• Improved mechanical properties
• Closer dimensions possible, less machining
• Thinner sections possible
• Any metal can be cast

NITC
28

• points
• Only for cylindrical and annular parts with
  limited range of sizes
• High initial cost
• Skilled labour needed
• Too high speed leads to surface cracks- (high
  stresses in the mould )

NITC
29

• For copper alloy castings, moulds are usually
  made from carbon steel coated with a suitable
  refractory mold wash.
• Molds can be costly if ordered to custom
  dimensions, but the larger centrifugal foundries
  maintain sizeable stocks of molds in diameters
  ranging from a few centimetres to several
  metres.
• The inherent quality of centrifugal castings is
  based on the fact that most nonmetallic
  impurities in castings are less dense than the
  metal itself. Centrifugal force causes impurities
  (dross, oxides) to concentrate at the casting's
  inner surface. This is usually machined away,
  leaving only clean metal in the finished product.
  
• Because freezing is rapid and completely
  directional, centrifugal castings are inherently
  sound and pressure tight.
• Mechanical properties can be somewhat higher than
  those of statically cast products.

NITC
30

• Centrifugal castings are made in sizes ranging
  from approximately 50 mm to 4 m in diameter and
  from a few inches to many yards in length.
• Size limitations, if any, are likely as not based
  on the foundry's melt shop capacity.
• Simple-shaped centrifugal castings are used for
  items such as pipe flanges and valve components,
  while complex shapes can be cast by using cores
  and shaped molds.
• Pressure-retaining centrifugal castings have been
  found to be mechanically equivalent to more
  costly forgings and extrusions.

NITC
31
NITC