advanced welding ,casting , forming processes pdf by [email protected]
TRANSCRIPT
UNIT 2.
ADVANCED MANUFACTURING PROCESS
Advanced Welding , casting and forging processes
Semester VII – Mechanical Engineering
SPPU
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II Shri Swami Samarth II
Unit. 2
9673714743
Advanced Welding, Casting and Forging processes
AMP
Unit.2
Syllabus
Friction Stir Welding – Introduction, Tooling, Temperature distribution and resulting melt
flow Advanced Die Casting - Vacuum Die casting, Squeeze Casting.
Welding :-
Welding is the process of joining together pieces of metal or metallic parts by bringing
them into intimate proximity and heating the place of content to a state of fusion or plasticity.
1. Key features of welding:-
The welding structures are normally lighter than riveted or bolted structures.
The welding joints provide maximum efficiency, which is not possible in other type of
joints.
The addition and alterations can be easily made in the existing structure.
A welded joint has a great strength.
The welding provides very rigid joints.
The process of welding takes less time than other type of joints.
2. Largely used in the following fields of engineering:-
Manufacturing of machine tools, auto parts, cycle parts, etc.
Fabrication of farm machinery & equipment.
Fabrication of buildings, bridges & ships.
Construction of boilers, furnaces, railways, cars, aeroplanes, rockets and missiles.
Manufacturing of television sets, refrigerators, kitchen cabinets, etc.
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Friction Stir Welding (FSW) was invented by Wayne Thomas at TWI (The Welding Institute),
and the first patent applications were filed in the UK in December 1991. Initially, the process was
regarded as a “laboratory” curiosity, but it soon became clear that FSW offers numerous benefits
in the fabrication of aluminium products. Friction Stir Welding is a solid-state process, which
means that the objects are joined without reaching melting point. This opens up whole new areas
1. Friction Stir Welding
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in welding technology. Using FSW, rapid and high quality welds of 2xxx and 7xxx series alloys,
traditionally considered unweldable, are now possible.
Friction stir welding (FSW), illustrated in Figure. 1, is a solid state welding process in
which a rotating tool is fed along the joint line between two workpieces, generating friction heat
and mechanically stirring the metal to form the weld seam. The process derives its name from this
stirring or mixing action. FSW is distinguished from conventional FRW by the fact that friction
heat is generated by a separate wear-resistant tool rather than by the parts themselves.
The rotating tool is stepped, consisting of a cylindrical shoulder and a smaller probe
projecting beneath it. During welding, the shoulder rubs against the top surfaces of the two parts,
developing much of the friction heat, while the probe generates additional heat by mechanically
mixing the metal along the butt surfaces. The probe has a geometry designed to facilitate the
mixing action. The heat produced by the combination of friction and mixing does not melt the
metal but softens it to a highly plastic condition.
Figure 1. Friction stir welding (FSW): (1) rotating tool just prior to feeding into
joint and (2) partially completed weld seam. N=tool rotation, f=tool feed.
Rotation Speed N
W.P
Thic
kness
Retreating side Advancing Side
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As the tool is fed forward along the joint, the leading surface of the rotating probe forces the metal
around it and into its wake, developing forces that forge the metal into a weld seam. The shoulder
serves to constrain the plasticized metal flowing around the probe.
Friction Stir Welding can be used to join aluminium sheets and plates without filler wire
or shielding gas. Material thicknesses ranging from 0.5 to 65 mm can be welded from one side at
full penetration, without porosity or internal voids. In terms of materials, the focus has traditionally
been on non-ferrous alloys, but recent advances have challenged this assumption, enabling FSW
to be applied to a broad range of materials.
To assure high repeatability and quality when using FSW, the equipment must possess
certain features. Most simple welds can be performed with a conventional CNC machine, but as
material thickness increases and “arc-time” is extended, purpose-built FSW equipment becomes
essential.
Process characteristics The FSW process involves joint formation below the base material’s melting temperature.
The heat generated in the joint area is typically about 80-90% of the melting temperature.
With arc welding, calculating heat input is critically important when preparing welding
procedure specifications (WPS) for the production process. With FSW, the traditional
components current and voltage are not present as the heat input is purely mechanical and thereby
replaced by force, friction, and rotation. Several studies have been conducted to identify the way
heat is generated and transferred to the joint area. A simplified model is described in the following
equation:
Q = µωFK
in which the heat (Q) is the result of friction (μ), tool rotation speed (ω) down force (F) and a tool
geometry constant (K).
The quality of an FSW joint is always superior to conventional fusion-welded joints. A
number of properties support this claim, including FSW’s superior fatigue characteristics.
Welding parameters
In providing proper contact and thereby ensuring a high quality weld, the most important
control feature is down force (Z-axis). This guarantees high quality even where tolerance errors in
the materials to be joined may arise. It also enables robust control during higher welding speeds,
as the down force will ensure the generation of frictional heat to soften the material.
When using FSW, the following parameters must be controlled: down force, welding
speed, the rotation speed of the welding tool and tilting angle. Only four main parameters need to
be mastered, making FSW ideal for mechanised welding.
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Advantages
(1) Good mechanical properties of the weld joint,
(2) Avoidance of toxic fumes, warping, shielding issues, and other problems associated with arc
welding,
(3) Little distortion or shrinkage,
(4) Good weld appearance.
(5) Less post-treatment and impact on the environment
(6) Energy saving FSW process
(7) Less weld-seam preparation
(8) Improved joint efficiency, Improved energy efficiency
(9) Less distortion – low heat input
(10) Increased fatigue life
Disadvantages
(1) an exit hole is produced when the tool is withdrawn from the work, and
(2) Heavy-duty clamping of the parts is required.
(3) Large Force required
Application
It is used in aerospace, automotive, Civil aviation , railway, and shipbuilding industries.
Automotive applications
In principle, all aluminium components in a car can be friction stir welded: bumper beams, rear
spoilers, crash boxes, alloy wheels, air suspension systems, rear axles, drive shafts, intake
manifolds, stiffening frames, water coolers, engine blocks, cylinder heads, dashboards, roll-over
beams, pistons, etc.
In larger road transport vehicles, the scope for applications is even wider and easier to adapt
– long, straight or curved welds: trailer beams, cabins and doors, spoilers, front walls, closed body
or curtains, dropside walls, frames, rear doors and tail lifts, floors, sides, front and rear bumpers,
chassis ,fuel and air containers, toolboxes, wheels, engine parts, etc.
Typical applications are butt joints on large aluminum parts. Other metals, including steel,
copper, and titanium, as well as polymers and composites have also been joined using FSW.
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The word tooling refers to the hardware necessary to produce a particular product. The most
common classification of tooling is as follows:
1. Sheet metal press working tools.
2. Molds and tools for plastic molding and die casting.
3. Jigs and fixtures for guiding the tool and holding the work piece.
4. Forging tools for hot and cold forging.
5. Gauges and measuring instruments.
6. Cutting tools such as drills, reamers, milling cutters broaches, taps, etc.
2.1. Sheet metal press working tools.
Sheet metal press working tools are custom built to produce a component mainly out of
sheet metal. Press tool is of stampings including cutting operations like shearing, blanking,
piercing etc. and forming operations like bending, drawing etc. Sheet metal items such as
automobile parts (roofs, fenders, caps, etc.) components of aircrafts parts of business machines,
household appliances, sheet metal parts of electronic equipments, Precision parts required for
horlogical industry etc, are manufactured by press tools.
2.2. Molds and tools for plastic molding and die casting.
The primary function of a mould or the die casting die is to shape the finished product. In
other words, it is imparting the desired shape to the plasticized polymer or molten metal and
cooling it to get the part. It is basically made up of two sets of components. i) The cavity & core
ii) The base in which the cavity & core are mounted. Different mould construction methods are
used in the industry. The mould is loaded on to a machine where the plastic material or molten
material can be plasticized or melted, injected and ejected.
2.3. Jigs and fixtures for guiding the tool and holding the work piece.
To produce products and components in large quantities with a high degree of accuracy
and Interchangeability, at a competitive cost, specially designed tooling is to be used. Jigs and
fixtures are manufacturing equipments, which make hand or machine work easier. By using such
tooling, we can reduce the fatigue of the operator (operations such as marking) and shall give
accuracy and increases the production. Further the use of specially designed tooling will lead to
an improvement of accuracy, quality of the product and to the satisfaction of the consumer and
community. A jig is a device in which a work piece/component is held and located for a specific
operation in such a way, that it will guide one or more cutting tools. A fixture is a work holding
2. Introduction to Tooling
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device used to locate accurately and to hold securely one or more work pieces so that the required
machining operations can be performed.
2.4 Press tools Press working is used as general term to cover all press working operations on sheet metal.
The stamping of parts from sheet metal is shaped or cur through deformation by shearing,
punching, drawing, stretching, bending, coining etc. Production rates are high and secondary
machining is not required to produce finished parts with in tolerance. A pressed part may be
produce by one or a combination of three fundamental press operations. They include:
1. Cutting (blanking, piercing, lancing etc) to a predetermined configuration by exceeding
the shear strength of the material.
2. Forming (drawing or bending) whereby the desired part shape is achieved by
overcoming the tensile resistance of the material.
3. Coining (compression, squeezing, or forging) which accomplishes surface
displacement by overcoming the compressive strength of the material.
Whether applied to blanking or forming the under laying principle of stamping process
may be desired as the use of force and pressure to cut a piece of sheet metal in to the desired shape.
Part shape is produced by the punch and die, which are positioned in the stamping press. In most
production operations the sheet metal is placed on the die and the descending punch is forced into
the work piece by the press. Inherent characteristics of the stamping process make it versatile and
foster wide usage. Costs tend to be low, since complex parts can be made in few operations at high
production rates.
Blanking
When a component is produced with one single punch and die with entire perifery is cut is
called Blanking. Stampings having an irregular contour must be blanked from the strip. Piercing,
embossing, and various other operations may be performed on the strip prior to the blanking
station.
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Piercing
Piercing involves cutting of clean holes with resulting scrape slug. The operation is often called
piercing, although piercing is properly used to identify the operation for the producing by tearing
action, which is not typical of cutting operation. In general the term piercing is used to describe
die cut holes regardless of size and shape. Piecing is performed in a press with the die.
Cut-off
Cut off operations are those in which strip of suitable width is cut to lengthen single.
Preliminary operations before cutting off include piercing, notching, and embossing. Although
they are relatively simple, cut-off tools can produce many parts.
Parting off
Parting off is an operation involve two cut off operations to produce blank from the strip.
During parting some scrape is produced. Therefore parting is the next best method for cutting
blanks. It is used when blanks will not rest perfectly. It is similar to cut off operation except the
cut is in double line. This is done for components with two straight surfaces and two profile
surfaces.
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Perforating:
Perforating is also called as piercing operation. It is used to pierce many holes in a
component at one shot with specific pattern.
Trimming
When cups and shells are drawn from flat sheet metal the edge is left wavy and irregular,
due to uneven flow of metal. This irregular edge is trimmed in a trimming die. Shown is flanged
shell, as well as the trimmed ring removed from around the edge. While a small amount of Material
is removed from the side of a component or strip is also called as trimming.
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Shaving
Shaving removes a small amount of material around the edges of a previously blanked
stampings or piercing. A straight, smooth edge is provided and therefore shaving is frequently
performed on instrument parts, watch and clock parts and the like. Shaving is accomplished in
shaving tools especially designed for the purpose.
Broaching
Figure shows serrations applied in the edges of a stamping. These would be broached in a
broaching tool. Broaching operations are similar to shaving operations. A series of teeth removes
metal instead of just one tooth’s in shaving. Broaching must be used when more material is to be
removed than could effectively done in with one tooth.
Side piercing (cam operations)
Piercing a number of holes simultaneously around a shells done in a side cam tool; side
cams convert the up and down motion of the press ram into horizontal or angular motion when it
is required in the nature of the work.
Dinking
To cut paper, leather, cloth, rubber and other soft materials a dinking tool is used. The cutting
edges penetrate the material and cuts. The die will be usually a plane material like wood or hard
rubber.
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Lancing
Lancing is cutting along a line in a product without feeling the scrape from the product.
Lancing cuts are necessary to create lovers, which are formed in sheet metal for venting function.
Bending Bending tools apply simple bends to stampings. A simple bend is done in which the line of
bend is straight. One or more bends may be involved, and bending tools are a large important class
of pres tools.
Forming
Forming tools apply more complex forms to work pieces. The line of bend is curved
instead of straight and the metal is subjected to plastic flow or deformation.
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Drawing
Drawing tools transform flat sheets of metal into cups, shells or other drawn shapes by
subjecting the material to severe plastic deformation. Shown in fig is a rather deep shell that has
been drawn from a flat sheet.
Curling
Curling tools curl the edges of a drawn shell to provide strength and rigidity. The curl
may be applied over aware ring for increased strength. You may have seen the tops of the sheet
metal piece curled in this manner. Flat parts may be curled also. A good example would be a
hinge in which both members are curled to provide a hole for the hinge pin.
Bulging
Bulging tools expand the bottom of the previously drawn shells. The bulged bottoms of
some types of coffee pots are formed in bulging tools.
Swaging
In swaging operations, drawn shells or tubes are reduced in diameter for a portion of their
lengths.
Extruding
Extruding tools cause metal to be extruded or squeezed out, much as toothpaste is extruded
from its tube when pressure is applied. Figure shows a collapsible tool formed and extruded from
a solid slug of metal.
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Cold forming
In cold forming operations, metal is subjected to high-pressure and caused to and flow into
a pre determined form. In coining, the metal is caused to flow into the shape of the die cavity Coins
such as nickels, dimes and quarters are produced in coining tools.
Flaring, lugging or collar drawing
Flanging or collar drawing is a operation in which a collar is formed so that more number
of threads can be provided. The collar wall can also be used as rivet when two sheets are to be
fastened together.
Planishing
Planishing tool is used to straighten, blanked components. Very fine serration points
penetrate all around the surface of the component
Assembly tools
Represented is an assembly tool operation where two studs are riveted at the end of a link.
Assembly tools assemble the parts with great speed and they are being used more and more.
Combination tool
In combination tool two or more operations such as forming, drawing, extruding,
embossing may be combined on the component with various cutting operations like blanking,
piercing, broaching and cut off
The type of tooling depends on the type of manufacturing process. Table.1, lists examples
of special tooling used in various operations
Table 1. Production equipment and tooling used for various manufacturing processes.
Process Tooling
(Function)
Equipment Special Tooling (Function)
Casting Various types of casting
setups and equipment
Mold (cavity for molten metal)
Molding Molding machine Mold (cavity for hot polymer)
Rolling Rolling mill Roll (reduce work thickness)
Forging Forge hammer or press Die (squeeze work to shape)
Extrusion Press Extrusion die (reduce cross-section)
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Stamping Press Die (shearing, forming sheet metal)
Machining Machine tool Cutting tool (material removal)
Fixture (hold workpart)
Jig (hold part and guide tool)
Grinding Grinding machine Grinding wheel (material removal)
Welding Welding machine Electrode (fusion of work metal)
Fixture (hold parts during welding)
Die casting is a permanent-mold casting process in which the molten metal is injected into
the mold cavity under high pressure. Typical pressures are 7 to 350 MPa (1015–50,763 lb/in2).
The pressure is maintained during solidification, after which the mold is opened and the part is
removed. Molds in this casting operation are called dies; hence the name die casting.
Two basic conventional die casting processes exist: the hot- chamber process and the
cold-chamber process. These descriptions stem from the design of the metal injection systems
utilized.
A schematic of a hot-chamber die casting machine is shown in Figure 1.2. A significant
portion of the metal injection system is immersed in the molten metal at all times. This helps keep
cycle times to a minimum, as molten metal needs to travel only a very short distance for each
cycle. Hot-chamber machines are rapid in operation with cycle times varying from less than 1 sec
for small components weighing less than a few grams to 30 sec for castings of several kilograms.
Dies are normally filled between 5 and 40 msec. Hot-chamber die casting is traditionally used for
low melting point metals, such as lead or zinc alloys. Higher melting point metals, including
aluminum alloys, cause rapid degradation of the metal injection system.
3. Die Casting
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Cold-chamber die casting machines are typically used to con- ventionally die cast
components using brass and aluminum alloys. An illustration of a cold-chamber die casting
machine is presented in Figure 1.3. Unlike the hot-chamber machine, the metal injection system is
only in contact with the molten metal for a short period of time. Liquid metal is ladled (or metered
by some other method) into the shot sleeve for each cycle.
To provide further protection, the die cavity and plunger tip normally are sprayed with an oil or
lubricant. This increases die material life and reduces the adhesion of the solidified component.
Conventional die casting is an efficient and economical process. When used to its
maximum potential, a die cast component may replace an assembly composed of a variety of parts
produced by various manufacturing processes. Consolidation into a single die casting can
significantly reduce cost and labor.
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In conventional die casting, high gate velocities result in atomized metal flow within the
die cavity, as shown in Figures 2.8 and 2.9. Entrapped gas is unavoidable. This phenomenon is
also present in vacuum die casting, as the process parameters are virtually iden- tical to that of
conventional die casting.
4. METAL FLOW IN VACUUM DIE CASTING
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Due to larger gate cross sections and longer fill times in comparison to conventional die casting,
atomization of the liquid metal is avoided when squeeze casting. Both planar and nonplanar flows
occur in squeeze casting. Achieving planar flow, however, is dependent on the die design and
optimization of the process para- meters. Figure 2.10 is a picture showing two short shots of
identical castings. In Figure 2.10a planar filling occurred within the die, while nonplanar filling
occurred in Figure 2.10 b.
These differences in metal flow were made possible by adjusting machine-controlled process
parameters. Be that as it may, for complex component geometries, nonplanar fill may be
unavoidable.
5. METAL FLOW IN SQUEEZE CASTING
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Die-casting is a method that produces a product by pouring melt into a mold followed by
punch-pressing, which allows a complicated shape to be fabricated. However, because die- casting
injects melt at a high velocity, gases and air remaining in the melt may cause internal defects;
therefore, the product’s mechanical properties are degraded. An enhanced die-casting method,
vacuum die-casting, has been developed by adding a vacuum device. Because vacuum die casting
creates a vacuum inside the mold cavity during casting, gases or air in the melt is removed,
decreasing the volume of gas pockets and improving the mechanical properties and smoothness of
the resulting surface. Using an aluminum or magnesium alloy made by vacuum die-casting, aircraft
and automotive parts in bulk shapes have been manufactured. The mold is encapsulated in a
housing that is sealed and placed above the furnace of molten metal. The sprue or gating, or some
form of spout, which is located at the bottom of the mold in the housing, is submerged into the
metal. A vacuum is then applied to the housing, which evacuates the atmosphere in the housing to
create differential pressure between atmosphere pressure above the melt and inside the mold. This
differential pressure is what forces the molten metal from below the surface into the mold cavity.
While gravity pouring has its advantages, within some geometries it can result in a
turbulent metal flow that can lead to entrained gas. The objective of vacuum casting is to control
the metal flow as much as possible for a tranquil mold fill. For metal castings that call for a sound,
consistent integrity, vacuum casting may deliver. The following advantages of vacuum casting
lend the process to precision applications:
6. Vacuum Die
Casting
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1. flow rate of molten metal into the mold cavity can be accurately controlled,
2. improving overall metalcasting soundness;
3. flow rate of the molten metal can be increased to fill the mold cavity more quickly than
with gravity pouring, resulting in the fillout of thinner casting sections; metal drawn into
the mold cavity is from below the surface of the molten metal bath,
4. Avoiding slag and inclusions;
5 . Critical metal temperature variations can be more consistently controlled since the mold is
taken to the furnace rather than vice versa;
6. good surface finish;
7. Excellent dimensional tolerances;
8. It is often easier to automate than gravity pouring.
9. Prolongs die life, eliminates debarring operation and increases up time of casting machine.
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Porosity often limits the use of the conventional die casting pro- cess in favor of products
fabricated by other means. Several efforts have successfully stretched the capabilities of
conventional die casting while preserving its economic benefits. In these efforts, squeeze casting
utilizes two strategies :
1. eliminating or reducing the amount of entrapped gases and
2. eliminating or reducing the amount of solidification shrinkage.
Squeeze casting is a Combination of casting and forging in which a molten metal is poured into a
preheated lower die, and the upper die is closed to create the mold cavity after solidification begins.
This differs from the usual permanent-mold casting process in which the die halves are closed
prior to pouring or injection. Owing to the hybrid nature of the process, it is also known as liquid
metal forging.
Squeeze casting as liquid-metal forging, is a process by which molten metal solidifies
under pressure within closed dies positioned between the plates of a hydraulic press. The applied
7. Squeeze casting
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pressure and instant contact of the molten metal with the die surface produce a rapid heat transfer
condition that yields a pore-free fine-grain casting with mechanical properties approaching those
of a wrought product. The squeeze casting process is easily automated to produce near-net to net
shape high-quality components.
The process was introduced in the United States in 1960 and has since gained widespread
acceptance within the nonferrous casting industry. Aluminum, magnesium, and copper alloy
components are readily manufactured using this process. Several ferrous components with
relatively simple geometry for example, nickel hard-crusher wheel inserts-have also been
manufactured by the squeeze casting process.
The squeeze casting process, combining the advantages of the casting and forging
processes, has been widely used to produce quality castings. Because of the high pressure applied
during solidification, porosities caused by both gas and shrinkage can be prevented or eliminated.
The cooling rate of the casting can be increased by applying high pressure during solidification,
since that contact between the casting and the die is improved by pressurization, which results in
the foundation of fine-grained structures.
Macro segregation has been known to be easily founded in most squeeze castings, which
leads to non-uniform macrostructures and mechanical properties. It is generally considered that
pressurization during solidification prevents the foundation of shrinkage defects. However, it
enhances the foundation of macro segregates in squeeze castings of aluminum alloys. Foundation
of macro segregates in castings or ingots has been reported to be caused by interdendritic fluid
flow, which is driven by solidification contraction, differences in density, etc.
Squeeze casting is simple and economical, efficient in its use of raw material, and has
excellent potential for automated operation at high rates of production. The process generates the
highest mechanical properties attainable in a cast product. The microstructural refinement and
integrity of squeeze cast products are desirable for many critical applications.
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As shown in Fig., squeeze casting consists of entering liquid metal into a preheated,
lubricated die and forging the metal while it solidifies. The load is applied shortly after the metal
begins to freeze and is maintained until the entire casting has solidified. Casting ejection and
handling are done in much the same way as in closed die forging. There are a number of variables
that are generally controlled for the soundness and quality of the castings.
Casting Parameters
Casting temperatures depend on the alloy and the part geometry. The starting point is normally 6
to 55°C above the liquids temperature. Tooling temperatures ranging from 190 to 315°C are
normally used. Time delay is the duration between the actual pouring of the metal and the instant
the punch contacts the molten pool and starts the pressurization of thin webs that are incorporated
into the die cavity. Pressure levels of 50 to 140 MPa are normally used. Pressure duration varying
from 30 to 120s has been found to be satisfactory for castings weighing 9 kg. Lubrication. For
aluminum, magnesium, and copper alloys, a good grade of colloidal graphite spray lubricant has
proved satisfactory when sprayed on the warm dies prior to casting.
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* Advantages
1. Offers a broader range of shapes and components than other manufacturing methods
2. Little or no machining required post casting process
3. Low levels of porosity
4. Good surface texture
5. Fine micro-structures with higher strength components
6. No waste material, 100% utilization
7.No blow hole.
8.Heat treatable
* Limitations
1. Costs are very high due to complex tooling
2. No flexibility as tooling is dedicated to specific components
3. Process needs to be accurately controlled which slows the cycle time down and increases process
costs.
4. High costs mean high production volumes are necessary to justify equipment investment
Application
Fuel pipe, Scroll, Rack housing, Wheel, Suspension arm, Brake caliper, No Shrinkage porosity, Cross
member node, Engine block, Brake disc, Piston.
********** Thank You ***********