CASTING PROCESS (PROCES PENGECORAN LOGAM) SAND CASTING, INVESTMENT CASTING, PERMANENT MOLDING

Disini saya menjelaskan tentang process pengecoran logam yang di lakukan oleh suatu perusahaan.

Maka dapat dilihat dalam disain process sangatlah penting untuk itu bagi yang tertarik dalam pemodelan maka penggunaan software desain modeling bahakan sekarang ini disain surface sangatlah penting.

CASTING PROCESS

Casting is old way to manufacturing of part which known in 645 B.C. and a popular manufacturing process for casting metal products. Casting processes exploit the fluidity of liquid as it flows, assume the shape of prepared container, and solidifies up cooling. There are two main die casting process types and several variations in process design.  When molten metal is forced into mold cavities at high pressure, it is known as die casting. The process is best suited for speedy production of bulk metallic parts that require minimal post-production machining.

With technological advances, metal casting is playing a greater role in our everyday lives and is more essential than it has ever been.

Basic Requirement of Casting Processes

There are six basic requirements with most casting processes:

1.      A mold cavity, having the desired shape and size, must be produce with due allowance for shrinkage of solidifying material.

2.      A Melting process must be capable of providing molten material not only at the proper temperature, but also in desired quantity, and competitiveness cost.

3.      A Pouring Technique must be devised the molten metal into the mold.

4.      The solidification process should be properly designed and controlled.

5.      It must be remove the casting from the mold.

6.      After the casting is removed from the mold, various cleaning, finishing, and inspection operations may be required.

The Metal Casting or just Casting process may be divided into two groups:

Hot Forming Process

Examples are Centrifugal casting, Extrusion, Forging, Full mold casting, Investment casting, Permanent or Gravity Die casting, Plaster mold casting, Sand Casting, Shell Mold casting. The method to be used depends upon the nature of the products to be cast.

Cold Forming Process

Examples are Squeeze casting, Pressure die casting, Gravity die casting, Burnishing, Coining, Cold forging, Hubbing, Impact Extrusion, Peening, Sizing, Thread rolling.

Industrial Process Description

The metal casting process has been divided into the following five major operations:

• Obtaining the Casting Geometry :

The process is referred as the study of the geometry of parts and plans, so as to improve the life and quality of casting.

• Casting Patternmaking :

In pattern making, a physical model of casting, i.e. a pattern is used to make the mold. The mold is made by packing some readily formed aggregated materials, like molding sand, around the pattern. After the pattern is withdrawn, its imprint leaves the mold cavity that is ultimately filled with metal to become the casting.

In case, the castings is required to be hollow, such as in the case of pipe fittings, additional patterns, known as cores, are used to develop these cavities.

• Coremaking & Molding :

In core making, cores are formed, (usually of sand) that are placed into a mold cavity to form the interior surface of the casting. Thus the annul space between the mold-cavity surface and the core is what finally becomes the casting.

Molding is a process that consists of different operations essential to develop a mold for receiving molten metal.

• Alloy Melting and Pouring :

Melting is a process of preparing the molten material for casting. It is generally done in a specifically designated part of foundry, and the molten metal is transported to the pouring area wherein the molds are filled.

• Casting Cleaning :

Cleaning is a process that refers to the different activities performed for the removal of sand, scale, and excess metal from the casting. However, all the operations may not apply to each casting method but such processes play an important role to comply with environmental guidelines.

Figure 1. Simplified flow diagram of the basic operations for producing a casting process

There is some step should be seen in the casting process, namely;

1.      Pattern Equipment

The dimensional accuracy of a steel casting is dependent on the type and quality of the pattern. The foundry should be responsible for determining the type of pattern which will produce the highest quality part on their equipment.

Types of Patterns

Pattern equipment can be made of wood, metal, wax, plastic, foam, etc. The selection depends on the quantity and size of parts, molding method, casting tolerances required, and cost.

Each of pattern material have advantages and disadvantages depends on what the owner want.

a.      Wood patterns are less costly than other materials, but are suited only for prototypes and limited production. They can easily be converted to plastic if production requirements increase.

b.      Metal patterns are the most costly, but they are required for high volume production. The material can be aluminum, iron, brass, bronze, etc. Cast aluminum is the most commonly used material for medium volume requirements. Metal patterns are also required for both cores and molds produced by the shell process.

c.       Wax patterns are used in the investment, or lost wax, molding process. These processes use dies to form the patterns. The wax patterns are coated with a ceramic slurry to form a shell. The wax is then removed by heat. Pattern costs will vary considerably depending on material, volume required and tolerance requirements. Consultation with the foundry during the design stage will ensure that the type of pattern equipment necessary will be obtained at the lowest cost.

d.      Foam patterns may be used in the ceramic or bonded sand molding systems. In the ceramic systems they may be substitutes for wax and in the bonded systems inexpensive substitutes for other stronger materials. 

                

               Figure 2. Typical steps involved in making a casting from a green sand mold

1.      Molding Processes

The molding process is the ways we want make a mold, and what process we make that mold. There is some type of mold process, namely ;

a.        Green sand molding is the most widely used system and due to mechanization in many green sand foundries, the least expensive process. Water and clay in the sand allows molds to be produced with a high degree of hardness and an accurate mold cavity. 

                                        Figure 3. Sand Casting Process

a.        Shell molding uses resin bonded sand and a heated pattern to produce a fused sand mold with excellent detail and dimensional accuracy. Energy and material costs are higher than green sand. This process is not suitable for larger castings.

b.       Chemically bonded molding uses sand and various chemicals or gases to form a dry hard mold. Dimensional accuracy is good, and the process is suited to all sizes of parts; however, sand reclamation costs are high, and the process is more expensive than green sand.

c.   Vacuum molding uses dry un-bonded sand. The mold relies on the vacuum for its hardness; the vacuum must be maintained during pouring and cooling. All sizes of parts can be made by this process; accuracy and surface appearance are good.

d.       Investment casting (also called "Lost Wax") uses a wax or foam pattern formed by a very precise metal mold. Several patterns are fixed to a "tree" and then dipped into a ceramic slurry. Successive dipping and drying produces a thick shell of ceramic which becomes the mold. The wax or foam is removed by heat prior to pouring. This process is limited to smaller castings and is generally not competitive unless some machining can be eliminated.

Figure 4. Invesment Casting Process

f.     Expendable pattern casting is also called Lost Foam or Full Mold process and uses a pattern of polystyrene which can be cut from stock or formed in a metal die, depending on volume requirements. The patterns are coated with a ceramic wash. The pattern and polystyrene gating system are embedded in dry sand, and when poured, the polystyrene melts and evaporates. Cores are not required, and capital requirements are low. Dry sand is easily reclaimed compared to other processes. This process produces a clean, tightly tolerance casting. This process is currently in the development phase for steel castings.

g.     Graphite molding utilizes graphite molds which are semi-permanent. Dimensional control and surface appearance are excellent. This is a highly specialized process suited mainly to parts like railroad wheels.

h,  Permanent mold castings poured into molybdenum molds are severely limited in size. 

                                               Figure 5. Permanent Molding

i.   Centrifugal molding produces parts from molten metal poured into rotating molds. Rotation of the mold causes the metal to be held to the inside diameter of the mold. It is ideally suited for pipe and symmetrical configurations.

j.      Ceramic molding employs a mixture of refractory materials, hydrolyzed ethyl silicate, and a catalyst which is poured over a pattern. The ceramic shell is stripped before fully setting, then fired, and assembled for pouring. This process produces excellent surface appearance and accuracy and is particularly adapted to turbine blades and manifolds.

1.      Melting and Pouring Operations

Several types of melting furnaces are used in the production of steel castings.

a.      Electric arc furnaces (EAF) are responsible for the production of the majority (84%) of steel castings. These units are composed of a steel shell, refractory lining, and a refractory lined roof with three openings for graphite electrodes. Melting is accomplished by the heat from the electric arc. The EAF is the most flexible unit for melting steel in that the charge material can be varied and the steel can be refined in the furnace before tapping.

b.      Electric induction furnaces are the most common unit for smaller production quantities. The furnace consists of a steel shell with a refractory lining surrounded by a copper coil. Heat is generated by an electric current in the coil.

2.      Finishing and Heat Treating

When a casting has cooled, it is shaken out of the mold. Before it can be shipped, it must be finished or cleaned. The first step is an abrasive blast which cleans the surface of all residue of the mold. Then the extraneous metal of the gating system and fins are removed by torch cutting, sawing or grinding. Welding of discontinuities is a common practice in the steel casting industry.

Heat treatment processes may be used to enhance the properties of specific alloys. The scale formed on casting surfaces during heat treatment is removed by abrasive blasting.

Steel castings can be straightened by pressing if warpage occurs during processing. This operation ensures dimensional accuracy of the finished part.

a.      Pre-machining or rough machining has become very common in steel foundries. When the customer requires very precise location of finish stock or reduced finish stock the foundry can perform a rough machining operation to provide the desired characteristics.

Many foundries can also supply parts in the finish machined condition.

b.      Process capability and tolerances are dependent on many factors. As mentioned earlier, pattern quality, mold material, pre-machining, straightening, etc., can all affect tolerances. The ability to control the casting process is of extreme importance to today's foundry-man, and the supplier of choice can document his programs for the buyer.

Material of Casting;

There are some material can be done by casting, it can be divided into three big type material of casting, namely;

-          Non-ferrous alloys have excellent machinability, and most are lighter than the iron family, but they do not have the strength and toughness required for many severe applications.

-          Gray Iron is produced more than any other iron alloy. It offers excellent castability and machinability, but it is essentially a brittle material. It is the least expensive of the iron alloys, and the dominant user is the automotive industry.

-          Ductile Iron, also referred to as nodular iron (or S.G. iron in Europe), is a cast iron which does have some ductility. Applications for this material have grown dramatically in the past 30 years, and it has supplanted malleable iron in most cases. Ductile iron has been used for steel applications where weldability and toughness are not required.

The Industrial Which Use Casting Process

The industries who are major users of steel castings and the applications that require the unique properties of cast steel. The generic term "steel" covers a wide range of grades of materials, however, for simplicity two alloy groups are normally considered: Carbon and Low Alloy (C&LA) and High Alloy. High Alloy grades include stainless steels and nickel-base alloys. Austenitic Manganese steels and all other non-stainless steels are usually included in the C&LA group.

These parts are used in severe applications such as couplers, draft gears, side frames, bolsters, and wheels. Construction machinery manufacturers use about 15% of the steel castings produced each year. The applications here are as varied as the equipment produced. Parts range from end caps on hydraulic cylinders for a small backhoe to transmission housings on large earth-moving machinery.

Valves and fittings of cast steel account for about 5% of production and are used for the drilling, recovery, transportation, and refining of natural gas and crude oil both on land and offshore. These parts vary in size from a few pounds to many tons. Applications are very severe requiring performance in corrosive liquids at both subzero and elevated temperatures. Operating pressures can reach many thousands of p.s.i. in valves and blowout preventers.

Heavy trucks—both on and off-highway—use about 5% of industry production. Some applications include: axle housings, suspension brackets, wheels, brake parts, axle spindles, differential housings, and fifth wheels.

Mining industry makes extensive use of steel castings for their extreme requirements of toughness and abrasion resistance both for ore recovery equipment and crushing mills. Both high manganese and other alloy steels are widely used, and these materials can only be produced as castings.

Numerous other industries use steel castings. These range from food processing and electronics to oil and gas, defense and pulp and paper industries. In fact, castings touch every aspect of our lives.

Example Company:

Company using casting process is like A Cast Alloy Steel Casting Foundry (CASCF) in India. It provides Stainless Steel Casting, sand casting, Alloy Steels Casting, High alloy steel casting, Wear resistance steel casting, Heat resistance steel casting, High chrome steel casting for various industries. This company offers pattern making to finished Steel Casting & Alloy Steel Casting and can perform in-house or outsource for virtually any needed secondary operations.

A-Cast Alloy is promoted by qualified and experienced entrepreneurs having 6 years experience with great technical expertise to provide Quality Stainless Steel Casting. This company also manufactures Steel Castings by CO2 Silicate Moulding and no bake Moulding Process for Steel Casting & Alloy Steel Casting and Super Alloy metal grades depending on the requirements of the customer and job; with the capacity to manufacture 200 MT of casting per month

Figure 6. One of product Cast Alloy Steel Casting Foundry is Yoke

Process of Casting of CASCF

PATTERN SHOP

At our Steel Casting Foundry we have following in-house Alloy Steel Casting, Stainless Steel Casting Manufacturing Process facilities.

Pattern shop : Inhouse pattern shop with full time pattern maker. Machines : 6nos of lathes, Drill machine and all instruments for wood and   alluminium work. Benefits : High production patterns are on match plate for quality assured castings.

SAND MOULDING

Sand Moulding : Manual Moulding by CO2-Silicate with patterns on match plates. Single piece casting : 30Kg to 650Kg single piece. Bed size : 35”X35”. Process time : 36hours. Production : Castings in huge quantities.

MELTING

Control panel : 2nos of control panel 600kw and 250kw. Both can run at a time simultaneously. Crucible : 3nos of crucibles 1000kg, 750kg and 300kg.

POURING

Ladles : Different size of ladles from 50kg to 1000kg. Pouring : Metal is poured both the way by crane and manual.

FETTLING

Cutting : Stainless cutting by 2-nos of high ampere rectifiers. Mild steel cutting by Oxy-LPG. Heavy Grinding : 3nos of Swing grinder and 1no 5HP bench grinder. Medium grinding : 15nos of Flexibe shaft grinders. Shot Blasting : Tumble and Hanger type shotblasting machine

	MACHINE SHOP
	Manual Lathe : 2nos center height 24” Manual Lathe : 4nos center height less than 20” Milling Machine : 1no. Keyaway Machine : 1no. Drill Machine : 1no. Buffing Machined : 1no. Welding Machine : 1no.

References:

1.      J T. Black, Ronald A, 2008, Kohser Materials and Processes in Manufacturing, John Wiley & Sons, Inc

2. Malcolm Blair, Thomas L. Stevens Editor(s):  1995, Steel Castings Handbook, 6th Edition., ASM International ,www.asminternational.org.
3. ….., http://www.themetalcasting.com/casting-mold-making.html, retrieved October 30^th, 2013
4. ….., http://www.thomasnet.com/articles/custom-manufacturing-fabricating/die-casting-types,  retrieved October 30^th, 2013
5. ……, http://www.engineershandbook.com/MfgMethods/casting.htm,  retrieved October 30^th, 2013
6. ……., http://www.a-castalloy.com/process.html, retrieved October 30^th, 2013