BTM4723_Lect 2 Adv Casting new_3.pptx

BTM4723 Advanced Manufacturing Processes by Mas Ayu H.
BTM4723 Advanced Manufacturing
Processes
Advanced Metal Casting Process
by
Ts Dr Mas Ayu Bt Hassan
Faculty of Manufacturing & Mechatronic
Engineering Technology
masszee@ump.edu.my

Chapter Information
Lesson Objectives:
Advanced Metal Casting/Molding
Lesson Objective:
At the end of this lecture, students should be able to
understand and explain the following:
 Understand the various types of advanced metal-casting
processes & equipment
 Characteristics of each advanced casting processes

Introduction
The major categories are:
1. Expendable molds – mold destroyed/broken,
materials: sand, plaster, ceramics and binders.
2. Permanent molds – molds are used
repeatedly, materials: metals high strength at high
temperatures.
3. Composite molds – have both expendable &
permanent mold, materials: made of two or more
different materials (sand, graphite & metals)

Expandable Mold,
expendable-pattern
Casting Processes

Expendable mold, permanent-pattern
• Expendable mold processes are using an expendable
mould that need be destroyed in order to remove
the casting part
• Mould materials - sand, plaster, and binders
• Two types of expandable mold processes
1. Investment casting (lost-wax casting)
2. Lost foam casting (evaporative foam casting)

1. Investment
Casting

Investment Casting
• Also called lost-wax process
• Used to make office equipment, and
mechanical components such as gears
• Pattern is invested (surrounded) with the
refractory material
• Mould is heated up to drive off the water of
crystallization and to burn off any residual
wax
• Process is capable of producing intricate
shapes from ferrous and nonferrous metals
and alloys

Investment Casting
• Also known as the lost-wax process
• The pattern is made of wax or a plastic (e.g.
polystyrene by injection moulding)
• Careful handling of wax pattern during moulding is
important due to they are not strong unlike plastics.
• The term investment derives from the fact that the
pattern is invested with refractory material.
• However, wax can be recovered and reused.
• This is a type of precision casting process.

Steps in Investment Casting Process
(1) The pattern is made by injecting molten wax or plastic into a metal
die in the shape of desired pattern
(2) When the pattern solidified, it is then removed from the injection mould
(3) A number of pattern will be assembled in the form of pattern tree to
make one mould, significantly increase the production rate
Source by Kalpakjian Book, 2014

(4) (5) (6) The assemble pattern tree is then dipped into a slurry of
refractory material (very fine silica and binders, water, ethyl silicate, and
acids).
After initial coating has dried, the pattern will be coated repeatedly to
increase the desired mold thickness until it is completed.
(continue)

(7) The mold will be dried and heated to a temperature 90 – 175°C. It is held for
about 12 hours to melt out the wax. After that it is fired to 650 – 1050°C for about 4
hours to remove the water and burn off any residual wax.
(8) Then the molten metal will be poured and left to solidify.
(9) (10) The mold is shake-out and casting will be removed.
(continue)

Advantages and Disadvantages of
Investment Casting
• Advantages:
– Products with great complexity and intricacy can
be cast
– Closed dimensional tolerance with very good
surface finish
– Wax usually can be recovered for reuse
– Not required any additional machining because it
is a net shape process
• Disadvantages
– Required many processing steps
– Involved with expensive process due to involve
with the making of die mold

Advantages of investment casting
• Excellent surface finish.
• Tight dimensional tolerances.
• Complex and intricate shapes may be produced.
• Capability to cast thin walls.
• Wide variety of metals and alloys (ferrous and non-ferrous) may be cast.
• Low material waste.
https://www.milwaukeeprec.com/blog.html/2018/02/13/6-advantages-of-investment-castings/

Investment-cast Superalloy
Components for Gas Turbines
Copyright © 2010 Pearson Education South Asia Pte Ltd
Figure shows a cross section and microstructure of two
rotors:
1. (Top) Investment cast
2. (Bottom) Conventionally cast
Investment casting produce microstructure with
finer grains, because of the fine, uniform
equiaxed grains throughout the rotor cross
section.
In contrast, note the coarse-grained structure in
the lower half of the figure, showing the same
type of rotor cast conventionally; this rotor has
inferior properties compared with fine-grained
rotor.

Investment Casting of Total Knee
Replacements
Figure above: Manufacture of total knee replacements. (a) The Zimmer NexGen mobile-bearing
knee (MBK); the femoral portion of the total knee replacement is the subject of this case study. (b)
Assembly of patterns onto a central tree. (c) Dipping of the tree into slurry to develop a mold from
investment. (d) Pouring of metal into a mold.

TKR from Cobalt-based
alloy
Process begins with
injection molding then
hand assembled onto
trees. The trees contains
12 knee implants arranged
in 4 rows. The completed
trees are then form a
queue and taken in order
by industrial robot. The
trees then follow the
investment casting
process.

Video on Investment Casting Process

2. Lost-foam process
@ Evaporative
Pattern Casting

Evaporative-pattern casting process uses a polystyrene pattern, which
evaporates upon contact with molten metal to form a cavity for the casting
The most common evaporative-pattern material used is polystyrene foam.
http://www.investmentcastchina.com/lost-foam-casting/

Applications
Evaporative pattern casting is widely used for aluminum casting.
It is also used for steel casting, and for iron parts like water pipe and pump parts.
The difference between evaporative casting process and sand casting method is that, in
evaporative casting the pattern is not remove from the mould.
Used for ferrous and nonferrous metals which is applicable to automotive / marine industry.
The advantages are:
• Simple
• Inexpensive flasks and polystyrene
• Minimal finishing and cleaning operations
• Process can be automated
Evaporative Pattern/Lost-foam
Casting of Engine Blocks

(a) Molten metal was poured into the mold for lost-foam casting to produce 60-hp. 3-cylinder
marine engine; (b) Finished engine block. Source: Courtesy of Mercury Marine.
(b)
(a)
Example of Lost-foam Casting Product

Lost-foam Casting
• Quite same to investment casting process
(precision casting)
• Uses polystyrene pattern which evaporates once
the molten metal poured into the mold to form
the casting.
• It is unique in that a mold and a pattern must be
produced for every casting, whereas the patterns
in the processes described thus far are reusable.
• It is important casting process for ferrous and
non-ferrous metal especially in automotive
industry.

Lost-foam Casting
• The working principle of evaporative pattern casting is achieved by producing a
foam pattern, which is the replica of item to be cast.
• This pattern is brushed with refractory substances in order to add extra life to the
pattern when molten metal is poured or to make it resistant to high temperature.
• The pattern is then attached with sprues and gates using adhesives. It is placed
into a mould surrounded and packed by sand.
• Another way of doing this is by dipping the pattern into a ceramic slurry, just as
investment casting. it forms a shell around it when it dries
• The mould is kept at a specific temperature in order to allow the liquid metal to
easily flow and reach all parts and cuts of the pattern.
• After this, molten metal is poured into the mould and the pattern foaming
material vanish out of the mould as molten metal reaches it.
• As the pattern vanishes, the molten metal takes its shape and solidifies. After it
solidified, the casting is removed from the mould.

Lost-foam Casting
Schematic of the expandable-pattern casting process, also known as lost-foam
or evaporative casting. Source by Kalpakjian Book, 2014.

1. Raw material (expandable polystyrene, EPS) is placed in a preheated die (usually
aluminium). Once heated, the polystyrene expands and takes the shape of the die cavity.
2. After cooled, the die will be opened and the polystyrene pattern removed. They
may be arranged in cluster assembly.
Steps in Lost-foam Casting

BMM 3643 Page 26
3. The pattern will be coated with refractory slurry, dried and placed in a flask.
4. The flask filled with loose, fine sand that supports the pattern. The pattern is then
compacted inside it.
(continue)

(continue)
5. The molten metal will be poured into the mold. This immediately will vaporizes the
pattern and molten metal fills the mold cavity. The heat degrades polystyrene and the
products will be vented into surrounding sand.
6. Once cooled, the parts are shakeout to get the final products.

BMM 3643 Page 28
• Advantages:
– No parting lines, cores, risers etc.
– Inexpensive flasks are satisfactory.
– Polystyrenes are in expensive
– Net shape process (no secondary work)
• Disadvantages:
– The pattern handling requires great care and the
coating process is time-consuming.
– Good process control is very important as a scrapped
casting needs replacement not only the mold but the
pattern as well.
Advantages and Disadvantages of
Lost-foam Casting

Hybrid Evaporative Pattern Casting
• Hybrid casting process is introduced with an
aim to achieve better performance of the
advanced casting processes.
• The reason for developing hybrid-casting
processes is to make use of combined or
mutually enhanced advantages and to avoid
or reduce some adverse effects (if any) of the
constituent processes when they are
individually applied.

Expendable mold,
permanent-pattern casting
processes

1. Vacuum Sealed Moulding @
V process

V Process
• The pattern is covered tightly with a thin sheet of plastic.
• A flask is placed over the covered pattern and is filled with dry, binderless sand.
• A second sheet of plastic then is placed on top of the sand and a vacuum action
compacts the sand, the pattern can then be removed.
• Both halves of the mold are made in this manner and subsequently assembled.
During pouring of the molten metal, the mold remains under vacuum, but the
casting cavity does not.
• When the metal has solidified, the vacuum is turned off and sand falls away,
releasing the casting.
• Vacuum molding does not require a draft in the part, and can be very economical
because of the low tooling costs, long pattern life, and absence of binders in the sand
(which also simplifies sand recovery and reuse).
• Vacuum molding produces castings with high-quality detail and dimensional
accuracy; it suited especially well for large, relatively flat (plane) castings.

Copyright ©2014 by Pearson Education
South Asia Pte Ltd. All rights reserved.
FIGURE Below: The vacuum molding process. (a) A plastic sheet is thermoformed (see Section 19.6) over a
pattern; (b) a vacuum flask is placed over the pattern, a pouring basin/sprue insert is located, and the flask is
filled with sand. A second sheet is located on the top of the sand mold, and vacuum is applied to tightly compact
the sand against the pattern. (c) A drag is also produced, along with cheeks, cores, etc., as in conventional sand
casting; the cope and drag can be carefully transported without vacuum applied. (d) After the mold halves are
joined, vacuum is applied to ensure mold strength, and molten metal is poured into the mold.

Advantages:
• An alternative to “conventional” sand casting processes, with the advantage of a
cleaner working environment.
• Suitable for either “jobbing”, or fully automated production, although ideally the
foundry should be specifically designed for the process.
• Uses dry, unbonded silica sand which requires little compaction and is almost fully
reclaimable; a major economic advantage.
Products that have been produced include manhole covers and tractor sprockets.

2. Shell Molding

Shell Molding (cont.)
The shell mold casting process consists of the following steps:
• Pattern creation - A two-piece metal pattern is created in the shape of the desired part, typically from iron
or steel. Other materials are sometimes used, such as aluminum for low volume production or graphite for
casting reactive materials.
• Mold creation - First, each pattern half is heated to 175-370°C (350-700°F) and coated with a lubricant to
facilitate removal. Next, the heated pattern is clamped to a dump box, which contains a mixture of sand
and a resin binder. The dump box is inverted, allowing this sand-resin mixture to coat the pattern. The
heated pattern partially cures the mixture, which now forms a shell around the pattern. Each pattern half
and surrounding shell is cured to completion in an oven and then the shell is ejected from the pattern.
• Mold assembly - The two shell halves are joined together and securely clamped to form the complete
shell mold. If any cores are required, they are inserted prior to closing the mold. The shell mold is then
placed into a flask and supported by a backing material.
• Pouring - The mold is securely clamped together while the molten metal is poured from a ladle into the
gating system and fills the mold cavity.
• Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of
the final casting.
• Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed.
Trimming and cleaning processes are required to remove any excess metal from the feed system and any
sand from the mold.

Shell moulding
1. Shell mold casting is a metal casting process similar to sand casting, in that
molten metal is poured into an expendable mold.
2. In shell mold casting, the mold is a thin-walled shell created from applying a sand-
resin mixture around a pattern.
3. The pattern, a metal piece in the shape of the desired part, is reused to form multiple
shell molds.
4. A reusable pattern allows for higher production rates, while the disposable
molds enable complex geometries to be cast.

Shell Molding (cont.)
5. Shell mold casting requires the use of a metal pattern, oven,
sand-resin mixture, dump box, and molten metal.
6. Shell mold casting allows the use of both ferrous and non-
ferrous metals, most commonly using cast iron, carbon steel,
alloy steel, stainless steel, aluminum alloys, and copper
alloys.
7. Typical parts are small-to-medium in size and require high
accuracy, such as gear housings, cylinder heads, connecting
rods, and lever arms.

Shell moulding

Advantages of shell mould casting:
• Shell moulding can produce many types of castings with close
dimensional tolerances
and a good surface finish at low cost
• Applications include small mechanical parts requiring high
precision such as gear housings
• Shell sand has lower permeability than sand used for green-
sand moulding
• Complex shapes can be produced with less labour since it can
be automated easily

https://www.sydensen.com/Shell-mould-Sand-Casting.html
Products made using shell mould casting, include bracket, casing and other engine spare
parts.

Video on Shell Mold Casting

3. Ceramic mould casting @
Cope-and-drag investment
casting

Ceramic mould casting
• It uses refractory mold materials that suitable for high-temperature
exposure.
• Typical parts made are impellers, cutters for machining operations, dies
for metalworking and molds for making plastic and rubber components.
Parts weighing as much as 700kg have been cast by this process.
• The slurry is a mixture of fine-grained zircon (ZrSiO4), aluminium oxide
and fused silica, which are mixed with bonding agents and poured over
the pattern which has been in a flask. The pattern may be made of wood
or metal.
• After setting, the molds (ceramic facings) are removed, dried, ignited to
burn off volatile matter and baked. The molds are clamped firmly and
used as all-ceramic molds.

Ceramic mould casting (cont.)
• The ceramic facings are backed by fireclay (which
resists high temperatures) to give strength to the mold.
The facings are then assembled into a complete mold,
ready to be poured.
• The high temperature resistance of refractory molding
materials allows these molds to be used for casting
ferrous and other high-temperature alloys, stainless
steel and tool steel.
• Although the process is somewhat expensive, the
castings have good dimensional accuracy and surface
finish over a wide range of sizes and intricate shapes.

Copyright ©2014 by Pearson Education
South Asia Pte Ltd. All rights reserved.
FIGURE above Sequence of operations in making a ceramic mold.
Source: Metals Handbook, Vol. 5, 8th ed., ASM International, 1970.

Ceramic-shell Investment Casting
• Process is economical and is used for the precision casting of steels and
high-temperature alloys

Permanent-mold casting
processes

Permanent Mold Casting
• Permanent mould also called hard-mold casting – using
permanent mould that can be used for many times to make
finished parts
• The mold is made of metal (or a ceramic refractory material)
• Part shapes are limited by the need to allow removal from die
cavity
• Permanent mould processes are more economic for mass
production rate
• The process is used mostly for aluminium, magnesium, copper
alloys & gray iron due to lower melting points
• Steel also can be cast using graphite or heat-resistant metal
molds.

Vacuum Casting
• Also called countergravity low-pressure (CL)
process.
• Alternative to investment, shell-mold & green-
sand casting.
• Suitable for thin-walled (~0.5mm) complex shapes
with uniform properties.

Steps in Vacuum Casting
1. Mixture of fine sand and urethane is molded
over metal dies and cured with amine vapor.
2. The mold held with robot arm and immersed
partially into molten metal in induction furnace.
3. The molten metal can be melted in air (CLA
process) or in vacuum (CLV process).
4. The vacuum reduces the air pressure inside the
mold cavities, thus drawing the molten metal
into the mold cavities through a gate in the
bottom of the mold.

5. The process can be automated with cost
production similar to green-sand casting.
6. Carbon, low – high alloy and stainless steel
parts can be cast.
7. CLA casting can be made easily at high
volume and relatively low cost.
8. CLV casting usually involved with reactive
metals such as aluminium, titanium,
zirconium and hafnium.

FIGURE ABOVE Schematic illustration of the vacuum-casting process; note that the mold has a bottom gate.
(a) Before and (b) after immersion of the mold into the molten metal. Source: After R. Blackburn.

Other permanent castings
• Slush casting, pressure casting, centrifugal
casting, squeeze casting & composite-mold
casting.

TABLE 11.1 Summary of Casting Processes

In class activity
1. If you need only a few units of a particular casting, which
process(es) would you use? Why?
2. In shell-mold casting, the curing process is critical to the
quality of the finished mold. In this part of the process, the
shell-mold assembly and cores are placed in an oven for a
short period of time to complete the curing of the resin
binder. List probable causes of unevenly cured cores or of
uneven core thicknesses.
3. What are the benefits and drawbacks to heating the mold in
investment casting before pouring in the molten metal?
4. Rank the casting processes described in this chapter in terms
of their solidification rate. That is, which processes extract
heat the fastest from the given volume of metal?
56
Review Questions

Thank you

BTM4723_Lect 2 Adv Casting new_3.pptx

Recommended

Recommended

More Related Content

Similar to BTM4723_Lect 2 Adv Casting new_3.pptx

Similar to BTM4723_Lect 2 Adv Casting new_3.pptx (20)

Recently uploaded

Recently uploaded (20)

BTM4723_Lect 2 Adv Casting new_3.pptx