Home for Aluminum, Bronze, and Alloy Castings
THE CASTING PROCESSES
by Wynn Danzur Marketing
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This Section is very large and designed as Educational Tool. Not every Casting Process is listed, only the most commonly used. If there is a topic of Interested NOT presented in the entire Website, please submit a request through the Webmaster, what it is you are looking for. The best efforts will be given to accommodate requests for "Additional Sources," by return e-mail.
The Casting Processes that are explained, are done so in a format that only Introduces the reader to that Casting Topic. It is the reader's responsibility to go beyond what this Website has initiated.
If a reader requires further in depth information on a Casting Process, or topic, this information can be obtained from the local Library, the Internet, AFS, and the Organizations supporting that particular Casting Process.
The Origin of Metal Castings
According to biblical records, Casting technology reaches back almost 5,500 years BC. Gold, pure in nature, most likely caught Prehistoric man’s fancy…as he probably hammered gold ornaments out of the gold nuggets he found. Silver would have been treated similarly. Mankind next found copper, because it appeared in the ash of his camp fires from copper-bearing ore that he lined his fire pits with. Man soon found that copper was harder than gold or silver. Copper did not bend up when used. So copper, found a ‘nitch’ in man’s early tools, and then marched it’s way into Weaponry. But, long, long before all this…man found clay. He used clay and made pottery, now he had something to eat from.
Time passed ...
Then Man thought, "now…what else can I do with this clay mud stuff …". Early man thought about it, "I’ll use this pottery stuff, ( the first patterns ), to shape my metal into bowls ". Man had discovered the Casting Industry.
A casting, is the essential foundation of civilization. With it, man unlocked his future, placing him on the path toward conquering his environment. History tells us this happened in Mesopotamia, today's modern Iraq. The oldest casting in existence today is believed to be a frog, cast in copper. The frog’s complexity indicates that it was preceded by other simpler casting efforts. Things went slow back then. Tin, came around in the 16th Century, but man used earth's ores for 4500 years prior. The Chinese get the nod for iron castings around 1000 BC. India made steel about 500 BC. Civilization in general, was casting brass by then, ( brass = copper / plus zinc ) , which was many centuries before the Christian era. All along this path all the techniques for …" CASTING AND MOLDING PROCESSES " … were being discovered, and recorded into history. All of these processes would be pictured forever in time through the labors of early man.
Listings of the Casting Processes Groups
I. CONVENTIONAL - CASTING PROCESSES
II. PRECISION - CASTING PROCESSES
III. SPECIALIZED - CASTING PROCESSES
Broken down further:
The Individual Castings Processes / by their Groups
1. Conventional Castings Processes Groups are:
I. The CONVENTIONAL CASTING PROCESSES:
1A.) SAND CASTING ( also called, GREEN- SAND MOLDING ) – is the most commonly used casting platform throughout the entire Casting Industry, World Wide. Simply put, there is a top, a bottom, and a middle to a mold. The pattern, or impression device, sits in the middle of the mold, and later is surrounded with sand . These are the basic, universal casting components, which can be applied to all casting processes.
The top and the bottom of the pieces of the mold form the flask. The flask assembly, the top and bottom, "holds the whole thing together". The upper or topmost section of the flask of the mold (flask) is called the cope, while the bottom of the mold (flask) is called the drag. The impression device, in the middle, is called the pattern. The sand around the pattern is called the, holding medium. The mold maker uses the pattern to make the impression in the sand. He then sets the pattern aside. At that point, the molder closes the cope and drag, forming the mold. What the mold maker wants is the void left from the impression of the pattern, in middle of the sand, inside the mold. So, he fills that void with a molten material.
Basic casting like this, is also called, "Green Sand Molding, or Green Sand Casting". These are the most basic molding methods, currently used in today’s casting practices, regardless of the metal alloy, or any molten - liquid material being poured. Like was said in the Preface, Man has been casting things since before Biblical times, using these very concepts.
All casting techniques employed in the rest of the Casting and Molding Processes are in many ways, just like sand casting, or green sand molding. With some thought and imagination, you can always see the cope and drag principle of casting we already discussed. The different techniques or casting and molding processes are used to achieve a desired end product, which has a special need in the market place. This special need prompted man to develop special processes.
Examples of usage would be: Air movement components ( fan blades), hubs, shafts, tubes, rectangles, squares, holes, no holes, the list is endless.
1B.) GREY IRON CASTINGS – This process is very much like sand casting and green sand casting processes. It can be done as flask-less molding. The difference being that the molten material is gray iron.
Grey Iron is white iron to which 2% to 3% carbon has been added to reduce the hardness and brittleness of iron. See GREY IRON in Glossary.
Examples of usage would be: pump bodies, housings, impellers, sewer covers, gears, blanks, bases, pads, motor mounts etc.
2.) FLASKLESS, MOLDING – This process is a sand casting, or a green sand molding variation, that has been automated for speed and high volume out-put, of identical castings. Despite any misconceptions, a flask-less molding does use flasks. The flasks, " holds the whole thing together ". A Flask must be used on all sand molding for the containment of the sand, while the sand is firmed about the pattern. In flask-less molding, in either a vertical or a horizontal stance, a sand filled flask is rebuilt and used over and over, in this totally mechanized, and automated sand molding process. In sand casting or green sand casting, a tight fitting, individual – most likely sand filled flask – is used for each mold produced.
The Industry has sand molders, use machines named "Hunter" or "B&P", to identify the makes and models of their flask-less molding equipment. The benefits of these systems are very impressive … uniformity, high density molds, high out put of products, elimination of mold shift, just to mention a few, all of which drastically reduce labor expense.
Flask-less Molding provides a mold hardness that is consistent though out the mold. The operator can adjust to different cope, drag heights and total squeeze pressure to accommodate different mold densities and mold hardness to meet the molding application. The operator can adjust the sand fill allowing the adjustment for variations in each pattern. It is possible produce complex molds and mold with deep pockets, which are difficult with traditional, normal sand casting procedures
Rapid core setting, easy inspection of cores used, utilization of existing tooling, high casting quality, reduced finishing time, quick pattern change, exceptional mold to mold consistency, high productivity are some of the many reasons to use flask-less molding.
Examples of usage would be: Any thing you can make in a sand mold, but you want it made for high volume, high production type out lets.
To see an animation about how an automated molding machine operates, visit the Hunter Automated Molding Corporation link: http://www.hunterauto.com/seq/index.htm
3.) DRY SAND MOLDING – large components are very difficult to cast to exact size and dimensions. Hence, some foundries use dry sand molds to produce such parts. Dry sand molding is the green sand process modified by baking the mold at prescribed temperature. Engine blocks, large gears, big housings, construction parts, are examples of dry sand process candidates. Ferrous and non-ferrous metals are cast in this method. The key to this process is the proper baking time in relation to the binder and the moisture content. The other factors are the size, weight, and mass, of the component being cast. Wynn Danzur can explain the profitable advantages of this process to you. Some good examples are, the great strength of the part cast, exactness in dimension, much smoother finish, etc., but most important is how these processes will benefit your casting jobs.
Examples of usage would be: engine blocks, transmission housings, big gear boxes, etc.
4.) SAND SLINGING – is the rapid process of mechanically filling the flasks with sand. The sand is propelled into the flask, like a sling-shot. This yet, just another method for compacting the sand into the cope and drag of the flask. Some sand slingers are stationary, some portable, and are some moveable. The big plus with this process, is the elimination of sand waste, which is the universal sand foundry problem.
Examples of usage would be: large pump bodies, gear boxes, boat engine blocks, gears, Large valve bodies, etc.
5.) STACK MOLDING – is another high production, sand casting, or green sand molding process. The piston ring people know this method well. Simply explained, the bottom of a given flask in a stack provides the cope of the flask below, while the top, provides the drag of the next layer…"pan caked- casting ".
Examples of usage would be: piston rings
6.) DRY OR BAKED "SAND CORE" MOLDING – very intricate automotive and agricultural castings are formed with this process. Accuracy, is the key word here along with close tolerances. A binder is mixed with un-bonded sand, it is then formed to the mold or pattern and baked. This is an expensive process, that achieves high level accuracy, in all dimensions..) DRY OR BAKED "SAND CORE" MOLDING – very intricate automotive and agricultural castings are formed with this process. Accuracy, is the key word here along with close tolerances. A binder is mixed with un-bonded sand, it is then formed to the mold or pattern and baked. This is an expensive process, that achieves high level accuracy, in all dimensions.
Examples of usage would be: engine blocks, transmission housings, gear housings, pump housings etc.
7.) SHELL CORE MOLDS - are the earliest, most automated, and most rapid of mold, and core making processes. This technique is also called the " C " Process or, Croning. Found in Germany after WW II, from a patent issued to Johannes C. A. Croning. The " C "Process uses a fluidized, harden-able sand – synthetic resin mixture to do shell molding and shell core making. Some big advantages are closer tolerances, increased productivity, excellent casting surface finishing, almost "as cast quality ". Wynn Danzur, can work with you to determine how best this process may fit your operation. the earliest, most automated, and most rapid of mold, and core making processes.
Examples of usage would be: engines valve heads, transmission cases, valve bodies, etc.
8.) OTHER CONVENTIONAL PROCESSES - Loam Molds, Chamotte Molds, Compo Molds, Cement-Bonded Molds, Floor and Pit Molds, Sweep Molds( like loam molds), Open Sand Molds, Waterless Bonded Sand Molds, are some of the lesser used, but also very important processes.
8.1) Oil Based Sand Casting - is very similar to regular sand casting and green sand casting, but a oil based mixture of sand is employed, instead of earth and sands and clays. This concept, provides Die Cast like finish, at a fraction of the cost, because no expensive die casting tools are required. When long life span, and high out put required for the application, a Die Casting is best option.
Sand Castings / Green Sand Molding
Dry Sand Molding
Dry or Baked "Sand Core" Molding
Shell Core Molds
Other Conventional Processes
2. Precision Casting Processes Groups are:
II. PRECISION CASTING PROCESSES
Investment casting is also known as the lost wax process. This process is one of the oldest Casting processes dated backed to the Egyptian Age.
The Egyptian Pharaohs used forms of Investment Casting to make gold jewelry (and hence rumor has it came the name Investment) some 5,000 years ago.
Others say this, that Lost Wax Casting method is also known as Investment Casting in the modern industrial world. This is a very ancient method used for casting small bronze sculptures, but today it is used to make many different artifacts and the process varies from foundry to foundry.
The Process Names are interchangeable.
Using Investment Casting, intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process.
Investment Casting can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures.
How it all Works Graphic
How it all Works in Text Format
The investment mold, is made by making a pattern using wax or some other material that can be melted away.
This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved.
After this, the entire pattern is placed in an oven and the wax is melted away.
This leads to a mold that can be filled with the molten metal.
The mold is formed around a one-piece pattern, (which does not have to be pulled out from the mold as in a traditional sand casting process), this way very intricate parts and undercuts can be made.
The actual Wax Pattern itself is made by duplication process, using a stereo lithography or similar model-which has been fabricated using a computer solid model master. Then wax is poured into this pattern, making the wax patterns, that are a fixed to the Investment Casting Tree.
The materials used for the slurry are a mixture of plaster of Paris, a binder and powdered silica, a refractory, for low temperature melts.
Just before the pouring of molten metal, the mold is pre-heated to about 1000 ºC (1832 ºF) to remove any residues of wax, harden the binder.
The pouring of molten metal into a pre-heated mold also ensures that the mold will fill completely, eliminating chances for Porosity.
The Molten Metal Pouring can be done using gravity, pressure or vacuum conditions.
Extremely Close Tolerances are Achieved
Tolerances of 0.5 % of length are routinely possible, and as low as 0.15 % is possible for small dimensions.
Castings can weigh from a few grams to 35 kg (0.1 oz to 80 lb), although the normal size ranges from 200 g to about 8 kg (7 oz to 15 lb).
Normal minimum wall thicknesses are about 1 mm to about 0.5 mm (0.040-0.020 in) for alloys that can be cast easily.
The types of materials that can be Investment Cast are:
Aluminum alloys, Bronzes, tool steels, stainless steels, Steel-lite, Hastelloys, and precious metals.
Parts made with investment castings often do not require any further machining, because of the close tolerances that can be achieved.
B.) Noel Shaw invented the Process that bares his name in the 1940's. Heavy demand for war products, influenced the invention.
Before Shaw, castings have been made for centuries using the traditional "Lost Wax" or sand mould process. All these Processes have their own "nitch" just as the Shaw Process, has found it audience.
Shaw's new ceramic process offered several advantages over the old system, notably high quality, remarkably accurate castings, as well as significant cost savings.
The Shaw Process uses a very pure, strong gel to bond ceramic refractory powders to form a mould suitable for molten steel.
The exceptional permeability of the fired mould not only minimizes shock, but also allows free passage of air, eliminating the need for venting. High temperature thermal stability also minimizes mould distortion after pouring, resulting in extremely accurate castings.
Because a "split-mould" technique is used, pattern equipment is less expensive than for the expendable pattern process.
The unique feature of the Shaw Process is the "micro-crazing" that is created when the casting solution is burned off to dry the mould. This enables the Shaw Process mould to retain its original volume and dimensional accuracy.
The major advantages of Shaw Process Castings include:
Dimensional accuracy to 0.25mm tolerance.
Reduced machining costs by eliminating preliminary machining.
Increased output by reducing machining time.
Extremely fine surface detail.
Increased design possibilities, even for high alloy steels.
High integrity castings.
Relatively low pattern costs
Fired Shaw Molds
C.) REPLICA CASTING – can be made from any material that can be burned away, burnt out, or incinerated …leaving a pattern chamber free of ash and residue. Examples would be…plants, seedpods, insects, etc. This method is for very intricate designs, costume jewelry, precious metal replica.
D.) RUBBER MOLDS – is made of silicone or vulcanized rubber. It is a form containing the impression of an original mold. It is then filled with wax to duplicate identical molds of the original. A slurry is dipped around the wax, the wax burnt out and the molten metal poured into the void left by the burnt away wax. A simple example would be a mouth piece for dental work.
E.) SPIN CASTING – this bridges the gap between die casting and sand casting by incorporating the some of the important advantages of both of those processes.
E.1) Centrifugal Casting - is another name for this same Process.
Production of prototype castings, in high or low volumes, with low tooling costs and short lead times, yielding die cast quality parts known for the close tolerances.
How it all works:
" ...Imagine a star inside a circle both made of rubber. At the ends of the points of the star are the patterns…the arms of the star are the sprues for the molten material to flow out to the patterns. The circle is spun and the molten material is poured into the center of the star… the spinning motion casts the part.
Instead of using sand as the mold material, a metal is used as a mold. Typically cast iron or Meehanite (a dense cast iron) is used as the mold material and the cores are made from metal or sand. Cavity surfaces are coated with a thin layer of heat resistant material such as clay or sodium silicate.
The molds are pre-heated upto 200 ºC (392 ºF) before the metal is poured into the cavity. The cavity design for these molds does not follow the same rules for shrinkage as in sand casting molds, due to the fact that the metal molds heat up and expand during the pour, so the cavity does not need to be expanded as much as in the sand castings. However, care has to be taken to ensure proper thermal balance, by using external water cooling or appropriate radiation techniques.
Permanent mold castings, while not as flexible as sand castings in allowing the use of different patterns (different part designs), lower the cost of producing a part. At a production run of 1000 or more parts, permanent mold castings produce a lower piece cost part. Of course, the break-even point depends on the complexity of the part. More complex parts being favored by the use of permanent molds.
The usual considerations of minimum wall thicknesses (such as 3mm for lengths under 75 mm), radius (inside radius = nominal wall thickness, outside radius = 3 x nominal wall thickness), draft angles (1 to 3º on outside surfaces, 2 to 5º on inside surfaces) etc all apply. Typical tolerances are 2 % of linear dimensions. Surface finish ranges from 2.5 µm to 7.5 µm (100 µin to 250 µin).
Typical part sizes range from 50 g to 70 kg (1.5 ounces to 150 lb). Typical materials used are small and medium sized parts made from aluminum, magnesium and brass and their alloys.
Typical parts include gears, blades, props, hubs, splines, wheels, gear housings, pipe fittings, fuel injection housings, and automotive engine pistons.
Permanent Mold Castings
Illustration 1 How it works
Molten metal is gravity poured into cast iron molds, or graphite molds coated with a ceramic mold wash. Cores can be metal, sand, sand shell, or other.
Molds open and castings are ejected. The Low Pressure Permanent Mold method pressure-pours up to 15 p.s.i.
See Illustrations of Permanent Mold parts below.
Molten metal is gravity poured into cast iron molds, or graphite molds coated with a ceramic mold wash. Cores can be metal, sand, sand shell, or other. Molds open and castings are ejected. The Low Pressure Permanent Mold method pressure-pours up to 15 p.s.i.
Aluminum, Zinc, some Brass, Bronze, H.C. Copper, Lead and Gray Iron.
Limitation mainly foundry capabilities. Aluminum and Copper base: ounces to 100 lbs. Ferrous: 60 lbs. max.
Aluminum: Basic ± .015"
Add ± .002"/in.
If across parting line add
± .010" to ± .030" depending on size
Copper Base: Similar to Investment
Iron: ± .03" Basic.
Copper Base: 125-200RMS
Minimum Draft Requirements:
Outside: 2° Min (3° desirable)
Inside: 2° Min (4° desirable)
Ferrous: Outside: 1° Inside: 5°
Normal Minimum Section Thickness:
Aluminum: .100" for small areas, up to 3/16" or more for large areas.
Copper Base: .060"
Ferrous: 3/16" for small areas, 1/4" normal.
Illustration 4- Permanent Mold in action
Suitable for high volume casting
Quality of heavier casting improves with better use of tooling's and equipment
Casted products have better tensile strength and elongation than sand castings
Mass productions can be done is a single production run, which reduces the manufacturing cost
Products have excellent mechanical properties.
High tooling cost
Short mold life; higher the pouring temperature, shorter the mold life.
Limited to low-melting-point metals
G.) Die Casting- Is the process of making a casting by forcing molten metal into a metallic mold, or die, under great pressure.
A method of casting in which molten metal is poured, sometimes under pressure, into a mold or die. The die is made of metal and immediately after solidification of the casting the die opens and the casting is ejected
Method of mass-producing, under great pressure, molten zinc and white-metal alloys into permanent molds. Sharp clean detail can be achieved. Die-cast toys were very inexpensive and generally found in the five-and-dime emporiums
The forming of parts by forcing molten metal into metal molds. Castings made with this process can be made to very exacting tolerance. Zinc and aluminum are most commonly used.
Advantages and Benefits
Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.
High-speed production - Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical castings can be produced before additional tooling is required.
Dimensional accuracy and stability - Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.
Strength and weight - Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process.
Multiple finishing techniques - Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.
Simplified Assembly - Die castings provide integral fastening elements, such as bosses and studs. Holes can be cored and made to tap drill sizes, or external threads can be cast.
Die castings, pressure die castings, and vacuum die castings are processes by which foundries can rapidly create thin wall complex shapes, with high dimensional accuracy, and a very smooth attractive surface finish. The advantage to the die casting process is the ability to make large quantities of well defined castings quickly and cheaply that will require few secondary operations to obtain a finished part.
The disadvantage to the die casting process is that the initial die casting tooling cost is normally very expensive and the die casting process is limited to low temperature alloys, such as aluminum, brass, magnesium, and zinc.
Die castings are made by pouring, injecting, or pulling by vacuum melted alloys into the cavities of a hardened metal mold, called a die. Normally this is done in an automated die casting machine. Most dies have several cavities, making several parts with each casting cycle.
Die casting begins by making a steel die, which will be capable of making tens of thousands of castings. The dies are made in at least two sections. The die casting cycle begins by clamping the die sections together. Liquid alloy is then poured, injected, or pulled by vacuum into the die cavities. When it solidifies, the die opens and the castings are ejected. Once removed from the die, the die castings normally require a few secondary operations, usually just flash trimming, buffing, perhaps holes tapped or machined to a final tolerance and then anodized, painted, or plated.
Once again the best way to explain Casting Processes, is with visual illustrations...There are variations to die casting, but having the concept detailed in these Illustrations, you understand the basic idea to die casting process.
Illustration 1 - a gif. showing die casting machine animation, in operation
Illustration 2 - diagram of die casting machine in operation
Die Casting compared to other Processes
Die Casting vs. plastic molding - Die casting produces stronger parts with closer tolerances that have greater stability and durability. Die cast parts have greater resistance to temperature extremes and superior electrical properties.
Die Casting vs. sand casting - Die casting produces parts with thinner walls, closer dimensional limits and smoother surfaces. Production is faster and labor costs per casting are lower. Finishing costs are also less.
Die Casting vs. permanent mold - Die casting offers the same advantages versus permanent molding as it does compared with sand casting.
Die Casting vs. forging - Die casting produces more complex shapes with closer tolerances, thinner walls and lower finishing costs. Cast coring holes are not available with forging.
Die Casting vs. stamping - Die casting produces complex shapes with variations possible in section thickness. One casting may replace several stampings, resulting in reduced assembly time.
Die Casting vs. screw machine products - Die casting produces shapes that are difficult or impossible from bar or tubular stock, while maintaining tolerances without tooling adjustments. Die casting requires fewer operations and reduces waste and scrap.
Illustration 3 - removing flash, drilling holes, with trim die
Because of the excellent dimensional accuracy and the smooth surfaces, most high pressure die castings require no machining except the removal of flash around the edge and possible drilling and tapping holes. High pressure die casting production is fast and inexpensive relative to other casting processes.
H.) Powdered Metal Parts are made by mixing carefully selected metal powders and compacting them at room temperature in a precision die.
The parts are then heated, a process called sintering, to complete the metallurgical bond between powder particles.
After sintering, parts usually have the required close tolerances, mechanical properties and surface finish specified in the part blue prints.
This virtual no-waste process allows for nearly 100% raw material use with reduced manufacturing steps and reduced overall costs.
Additional processes, including machining, heat treating and forging, provide even greater precision and strength.
PM Parts are found in: Lock Hardware, Lawn and Garden, Firearms, Plumbing Parts, Business Machines, Computer Equipment, Printers, Copy Machine, Consumer Products, Automotive Industry, Hand and Power tool, just about everywhere.
Advantages of PM
Powder metal parts are not shape sensitive.
Near net shape production uses more than 97% of the starting raw material.
Powder metal is an energy and material saving process.
Intricate shapes are less expensively produced by powder metallurgy compared to machining.
Powder metal also competes favorably with zinc die-casting.
Less material waste, and fewer processing steps are some of the advantages of using the Powdered Metal Process.
Using Powdered Metal Parts is an excellent way to help do your part for the environment.
The production of these parts uses almost all raw materials to make them. This means there will be little waste created from their production.
You can sleep well knowing that you have chosen an excellent option for you and the environment.
Examples of some PM Parts
Examples of some PM Parts Equipment
Powdered Metal Parts ( PM ) are produced by mixing carefully selected metal powders, then compacting them at room temperature in a precision sized die. The PM Parts are then heated ( called sintering).
This produces the resulting shapes and completes the metallurgical bond between the powder particles.
After sintering, parts usually have the required tolerances, mechanical properties and surface finish specified in the drawing of the parts. Thus raw materials utilization is nearly 100% and manufacturing steps and costs are kept to a minimum.
If necessary, the parts may be machined, heat-treated, forged or otherwise processed further for even greater precision or strength.
I.) OTHER PRECISION MOLDING AND CASTING PROCESSES
Are some of the other processes
Powdered Metal Casting
Other Percision Molding and Casting Processes
3. Special Casting Processes Groups are:
III. Special Casting Processes
A.) Vacuum molding process, popularly known as V-process, is a sand molding process, in which un-bonded sand is held in place in the mold by a vacuum.
In this process the pattern is covered by a tightly conforming thin sheet of plastic film which is applied with vacuum after being heated.
The film, conforming to the shape of the pattern, may have a refractory coating applied which is dried before filling the flask with sand.
A flask is placed over the plastic coated pattern, and is filled with free-flowing sand, with vibration for compaction. Another sheet of plastic is placed over the top of the sand in the flask and the flask is evacuated.
The vacuum "hardens" (compacts) the sand so the pattern can be withdrawn, the vacuum holding the film to the pattern being released at this time. The other half of the mold is made the same way.
After cores are set in place, the mold is closed and poured while still under vacuum.
When the metal has solidified, the vacuum is turned off and the sand runs out freely, releasing the casting.
The V-process is known for the high dimensional tolerances and good surface finish of the castings. Due to multiplicity of operations it is suitable for low to medium production volumes, depending on the amount of conveyor-ized equipment within the foundry.
Because the sand never touches the pattern itself, there is almost no pattern wear. Minimal or zero draft allowance can be used on vertical surfaces.
Once again, this V-Process can be best explained and understood by text below, and a series of Illustrations and pictures we have collected:
The V-Process was invented in Japan in 1971 as an improvement on conventional sand casting. In this process, a thin preheated sheet of plastic film material is placed over a pattern and a vacuum is applied to draw the sheet to the pattern contours. The flask containing the mold is then filled with dry un-bonded silica sand which is compacted by vibration. A second plastic sheet is placed at the back of the flask and the mold is further compacted under vacuum. With the vacuum process maintained, the pattern is then removed and the two halves of the mold are joined and secured for pouring. After the metal has solidified, the vacuum is removed and the casting is released.
One big advantage to the V-Process is, pattern life is longer because there is no contact between the sand and the pattern.
V-Process Pattern 1 /Drag Side
V-Process Pattern 2/Drag Side
First the Foundry heats a thin plastic film and place it over a pattern. A vacuum tightly draws the film over the pattern, which is then surrounded by a flask. We fill the flask with dry, un-bonded, extremely fine sand and vibrate the sand so that it tightly packs the pattern. After a second sheet of film is placed on the flask, a vacuum draws out the air, and the completed mold is then stripped from the pattern.
Each half of the mold is made in a similar fashion, then aluminum is poured directly from the furnace into the closed halves. The mold is held under vacuum to retain its shape. After the mold cools, the vacuum is released and the sand and completed castings fall free.
Simple in concept and far reaching in impact, V-PROCESS produces quick turn-around, high-value castings. In order to provide the highest quality product, we continually strive to improve our systems and raise the level of our performance. To achieve these standards, we maintain ongoing training programs that teach our employees to accept responsibility and to act on their knowledge. The caliber of our people and the quality of our V-PROCESS make it possible for us to create a vision for the future, and to establish our company as a leader in the casting industry.
use this text to understand both Illustrations 1 and 2
B.) STYRA FOAM MOLDING – think of permanent molding, or sand casting, green sand molding. But, instead of sand, a permanent molding tool, STYRO-FOAM is used as the pattern material. Most times the styro-foam pattern is laid out by a computer, then air cut to the shapes needed, or many shapes fastened together to form pattern.
During the casting process, which would be just like sand casting, with the pouring of molten metal into pattern cavity, which in this process is styro-foam, sometimes the styro-foam is burned away, and sometimes it is not. This depends on the application of the actual component being cast.
See Lost Foam Casting above, and visit the exploded drawings or views Sections.
Examples of usage would be: large tooling for aircraft, bridge decking, highway barrier components, elevator components, to mention a few applications.
Centrifugal Casting- Is a method for casting metals or forming thermoplastic resins, in which the molten material solidifies in and conforms to the shape of the inner surface of a heated, and rapidly rotating container.
Simply put, melted metals or plastics are some way or how put into to a spinning mold or pattern.
Advantages and Benefits
1. Improved physical properties ______________
Formed under pressures many times that of gravity combined with directional solidification, two unique characteristics of the centrifugal casting process, parts made from centrifugals exhibit a denser, closer grained structure with vastly improved physical properties. Because of high structural uniformity, physical properties such as tensile strength, yield strength, elongation, reduction of area, and other desirable properties are improved by up to 30% over conventional gravity or static casting methods.
2. Longer Life ______________
Parts made from centrifugals, with the castings’ finer grained, denser structure provide increased service life and withstand greater overloads and impact without fracturing.
3. Reduced Rejects ______________
As the molten metal is poured, centrifugal forces distribute the molten metal against the walls of the mold with tremendous force, thereby displacing the lighter oxides and impurities, causing them to surface on the inside diameter of the hollow cylinder being cast. The trapped oxides and impurities are easily removed in the machining process.
4. Pattern Expense Eliminated ______________
The extensive inventory of molds available eliminate the customer’s expense of buying, storing, maintaining and insuring patterns.
5. Reduction of Manufacturing Costs ______________
As a result of the uniformity and other desirable characteristics of centrifugal castings, machining time and material waste are significantly reduced. Hard spots, sand residue, cavities, blowholes and porosity are virtually eliminated.
6. Production Flexibility______________
The centrifugal process allows economical production of a diversified range of sizes, shapes and quantities.
7. Faster Delivery ______________
Due to the short mold set up and preparation time required for centrifugal castings, delivery can be scheduled to meet the customer’s needs. The customer benefits from reduced manufacturing lead time and avoids the high cost of maintaining inventory.
A technique in which an ingot, billet, tube, or other shape is continuously solidified and withdrawn while it is being poured, so that its length is not determined by mold dimensions.
Continuous casting, also called strand casting, is the process whereby molten steel is solidified into a "semi-finished" billet, bloom, or slab for subsequent rolling in the finishing mills. Prior to the introduction of continuous casting in the 1950s, steel was poured into stationary molds to form ingots. Since then, "continuous casting" has evolved to achieve improved yield, quality, and cost efficiency. It allows lower-cost production of metal sections with better quality, due to the inherently lower costs of continuous, standardized production of a product, as well as providing increased control over the process through automation.
This Process is more often used for high volumes of repetitively shaped, Industrial type Products, and is used most frequently to cast steel (in terms of tonnage cast).
Aluminum and copper are also continuously cast.
Continuous Casting can best be explained and understood, by reviewing the assortment of images we have collected and posted below:
1. Ladle 2. Stopper 3. Tundish 4. Shroud 5. Mold 6. Roll support 7. Turning zone 8. Shroud 9. Bath level 10. Meniscus 11. Withdrawal unit 12. Slab
A. Liquid metal B. Solidified metal C. Slag D. Water-cooled copper plates E. Refractory material
Producing a hollow casting without a core in the mold by rotating a liquid alloy in a hollow metal mold until a solid layer chills onto the mold, and then pouring off the remaining liquid.
Slush casting is a method of making hollow castings without the complexity of using cores, particularly where the profile or surface finish of the inside is relatively unimportant.
This makes it an ideal method for reducing the weight of a handle or other attachment to a main article without upsetting the balance or feel.
The No-Bake Sand Casting process consists of sand molds created using a wood, metal or plastic pattern.
The Casting Sand is mixed with a urethane binder and deposited into a box containing the pattern (and all necessary formers and inserts) for pouring.
The sand mixture sets hard in a short time, and the mold is then removed from the pattern. Cores for forming internal passages in the castings are made using the same process.
The No-Bake casting technique creates molds with excellent dimensional stability. The casting surface finish is also improved over other sand casting processes.
No-Bake is one of the most efficient and advanced sand casting techniques currently available.
No- Baked molds
Squeeze casting, also known as liquid metal forging, is a combination of casting and forging process.
The molten metal is poured into the bottom half of the pre-heated die.
As the metal starts solidifying, the upper half closes the die and applies pressure during the solidification process.
The amount of pressure thus applied is significantly less than used in forging, and parts of great detail can be produced.
Coring can be used with this process to form holes and recesses.
The porosity is low and the mechanical properties are improved.
Both ferrous and non-ferrous materials can be produced using this method.
Illustrations below will help explain Process:
The "V" Process
Continuous Casting Process
Slush Casting Process
No-Bake Casting Process
Squeeze Casting Process
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