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II Shri Swami Samarth II
Unit. 2 AMP
Advanced Welding, Casting and Forging processes
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Content
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.
1. Friction Stir Welding :-
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
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means that the objects are joined without reaching melting point. This opens up whole new areas
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.
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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.
1.0 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.
1.1 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.
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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.
1.2 Tools for welding
Welding tool design is critical in FSW. Optimising tool geometry to produce more heat
or achieve more efficient “stirring” offers two main benefits: improved breaking and mixing of
the oxide layer and more efficient heat generation, yielding higher welding speeds and, of course,
enhanced quality.
The simplest tool can be machined from an M20 bolt with very little effort. It has proved
feasible to weld thin aluminium plates, even with tooling as simple as this, although at very slow
welding speeds. However, tool materials should feature relatively high hardness at elevated
temperatures, and should retain this hardness for an extended period. The combination of tool
material and base material is therefore always crucial to the tool’s operational lifetime.
1.3 Tools for steels
To apply FSW in steel or other high-temperature materials, the difficulty is mainly
associated with finding proper tool material; a material that can withstand the high temperatures
that are experienced during the process. Resistance to wear (durability) is one important aspect,
especially as many of the intended applications are considered critical; hence there can be no traces
of the tool left in the seam. One of the most promising tool materials so far is the so called PCBN
(polycrystalline cubic boron nitride), which is manufactured by MegaStir.
1.4 Retractable pin tool
The Retractable Pin Tool (RPT) or Adjustable Probe Tool is a machine feature in which the pin
of the FSW tool may be moved independently of the tool’s shoulder. This permits adjustments of
the pin length to be made during welding, to compensate for known material thickness variations
or to close the exit hole of the weld.
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,
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(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.
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.
2. Introduction to Tooling 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.
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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
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
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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.
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.
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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
Processes
Other production machines include presses for stamping operations, forge hammers for
forging, rolling mills for rolling sheet metal, welding machines for welding, and insertion
machines for inserting electronic components into printed circuit boards. The name of the
equipment usually follows from the name of the process.
The type of tooling depends on the type of manufacturing process. Table.1, lists examples
of special tooling used in various operations
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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)
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)
Production machinery usually requires tooling that customizes the equipment for the particular
part or product. In many cases, the tooling must be designed specifically for the part or product
configuration. When used with general purpose equipment, it is designed to be exchanged. For
each work part type, the tooling is fastened to the machine and the production run is made. When
the run is completed, the tooling is changed for the next workpart type. When used with special
purpose machines, the tooling is often designed as an integral part of the machine. Because the
special purpose machine is likely being used for mass production, the tooling may never need
changing except for replacement of worn components or for repair of worn surfaces.
3. Die Casting
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.
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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.
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.
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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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3.1 METAL FLOW IN VACUUM DIE CASTING
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.
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3.2 METAL FLOW IN SQUEEZE CASTING
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.
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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.
4. VACUUM DIE CASTING
Entrapped gas is a major source of porosity in conventional die castings. Vacuum die
casting is characterized by the use of a con- trolled vacuum to extract gases from the die cavities,
runner sys- tem, and shot sleeve during processing.
Numerous metal casting processes have utilized vacuum systems to assist in the removal of
unwanted gases. These processes include permanent-mold casting, lost-foam casting, plaster mold
casting, and investment casting. The constraint in the evolution of vacuum die casting has been
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the development of a reliable vacuum shut-off valve. Vacuum die casting is compatible with other
high integrity processes, including squeeze casting.
Fig.4.1 Layout of early developed vacuum process
The vacuum die casting process minimizes gas entrapment by removing gases from the cavity
generated by two of these mechanisms. Both air in the die cavity and gases generated by the
decomposition of lubricants can be removed using the vacuum die casting process. In conventional
die casting, gases are typically vented from the die. However, the amount of gas that must vent
from the dies is much greater than that of just the die cavity. All gases in the runner system must
be vented as well as any volume of the shot sleeve not filled with metal. When examining the
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volume of gas that must be evacuated from the die combined with the short cycle times of
conventional die casting, one finds that it is virtually impossible for all gases to exit the die before
die fill is complete.
Fig.4.2 Schematic drawing of vacuum die casting process
The vacuum die casting process utilizes a conventional die casting machine coupled with a
vacuum system. This system is composed of a vacuum pump, a vacuum shut-off valve, a vacuum
control system, and an unvented die.
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Vacuum die casting builds upon conventional die casting practices by minimizing the
effects of a major contributor to porosity. The cycle time and economics of vacuum die casting are
equivalent to conventional die casting. The only economic penalty in using vacuum die casting is
the capital cost of the vacuum system and its operation. These additional costs, however, are minor
in comparison to increased component integrity. In converting conventional die castings to vacuum
die castings, one must consider the benefits that are sought. If porosity from gas entrapment is a
problem, vacuum die casting can offer improvements. If shrinkage porosity is an issue, other high
integrity die casting processes should be utilized.
4.1 Characteristics of vacuum die casting process
Vacuum process has been recognized as an efficient die-casting process to eliminate defects, such
as blowhole, cold shut, flow line and misrun. At casting site, reduction of shot speed and metal
pressure prevents burrs remarkably, and it also prolongs die life, eliminates deburring operation
and increases up time of casting machine. In starting up new parts, good parts can be easily
obtained. Modification process of die tooling can be reduced, and totally new product can be
introduced into mass production in a relatively short period of time. But there are some
disadvantages. One of them is that aluminum melt can intrude into vacuum line when aluminum
dreg stuck at shutting valve sheet during last shot.
5. Squeeze casting
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.
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Squeeze casting is characterized by the use of a large gate area (in comparison to
conventional die casting) and planar filling of the metal front within the die cavity. Squeeze casting
works to minimize both solidification shrinkage and gas entrapment. Planar filling allows gases to
escape from the die, as vents remain open throughout metal injection. Moreover, the large gate
area allows metal intensification pressure to be maintained throughout solidification.
The origins of the squeeze casting process can be traced back to a process known as squeeze
forming. A schematic showing the progressive cycle of the squeeze forming process is shown in
Figure 5. Initially, liquid metal is poured into an open die, as shown in Figure 5,a. The die is
closed (Figure 5,b) and the metal flows within the die, filling the cavity.
Figure 5. Schematic of the squeeze forming process.
During solidification, an intensification pressure is applied to the metal by the dies. After
solidification is complete, the component is ejected, as presented in Figure 5, c.
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Squeeze casting process parameters are very similar to conventional die casting in that the liquid
metal is pressurized during solidification. The major difference between squeeze casting and
conventional die casting is with regards to the gate velocity. Gate velocities are often achieved
during squeeze casting that are orders of magnitude slower than in conventional die casting. The
gate velocities in squeeze casting can be as low as those characteristic to permanent-mold casting.
Cycles times for squeeze casting are longer than those of conventional die casting. This is due to
both the slower metal injection speeds and the longer solidification times. The resulting
microstructures are much different. The microstructure in the squeeze casting is not as fine as that
observed in conventional die casting, and the dendrites are much more pronounced. The
mechanical properties of squeeze castings are much improved due to reduced levels of porosity
and the formation of micro- structures not possible in conventionally die cast components.
5.1 ELEMENTS OF SQUEEZE CASTING MANUFACTURING EQUIPMENT
Both horizontal and vertical conventional die casting machines can be used in conjunction
with the squeeze casting process. The differences in squeeze casting are attributed to the die design
and process parameters.
In comparison to conventional die casting, squeeze casting dies have larger gate areas.
Gates are no less than 3 mm in thickness to avoid premature solidification during intensification.
Some manufacturers utilize classical fan gating such as that used in conventional die casting. Other
producers have found large single- point gates ideal.
As squeeze castings have thicker gates, trimming is not a viable option to removing
components from their runner systems. Sawing is typically required. Automated sawing systems
are available for high volume production. However, automated systems require customer fixtures.
Although sawing may be necessary for removing components from their respective runner
systems, trimming often is not avoided. The removal of overflows and flash is still accomplished
using traditional trimming techniques.
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As with any die casting process, shot control is essential. Often the shot control systems
currently available on conventional die casting machines may be used with the squeeze casting
process. Process parameters, however, must be adjusted to allow for slower fill of the die cavity
and longer intensification times. Key process characteristics of squeeze casting include metal
temperature, melt cleanliness, cavity pressure, and gate velocities.
5.2 Difference Between CDE & Squeeze
Squeeze casting is a high integrity die casting process that builds upon conventional die
casting practices and is compatible with aluminum, magnesium, zinc, and copper alloy systems.
Cycle times are longer in comparison to conventional die casting due to longer metal injection
durations. Component integrity is improved by minimizing entrapped air and reducing
solidification shrinkage. Most squeeze casting components can be heat treated without blis-tering
defects to improve mechanical properties.
Conventional die casting is lower cost in the areas of capital equipment. Squeeze casting
has addi- tional costs associated with automated sawing for separating the runner system from
squeeze cast components. A saw must be purchased, operated, and maintained along with fixturing.
These additional costs, however, are often offset with benefits in the areas of porosity
reduction related to solidification shrink- age, which improves mechanical properties. Moreover,
the reduc- tion in entrapped gas results in a heat-treatable casting.
In converting conventional die castings to squeeze castings, one must consider the benefits
sought. If porosity from gas entrapment and solidification is a problem, squeeze casting can offer
improve- ments. If only entrapped gas is an issue, vacuum die casting may be sufficient. Moreover,
squeeze casting can be combined with vacuum die casting. The use of a vacuum system during
squeeze casting can further reduce entrapped gas beyond that normally achieved when squeeze
casting.
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A qualitative comparison of these two processes is shown in Figure 5.2.
+ = indicates favorable rating
Figure 5.2. Comparisons of conventional die casting and squeeze casting
Advantages
No Blow Hole
Heat treatable
Weld-able
No Shrinkage porosity
Infiltration of preformed insert (MMC)
Application
Fuel pipe, Scroll, Rack housing, Wheel, Suspension arm, Brake caliper, No Shrinkage porosity,
Cross member node, Engine block, Brake disc, Piston.
********** Thank You ***********
