Parul Institute of Engineering & Technology

Mechanical Engineering

A PROJECT REPORT ON “DIE CASTING”

SUBMITTED BY: Shrimali Yagnesh (05 ME 114) Patel Dixit (05 ME 87)
GUIDED BY: Professor Adil Khan DEPARTMENT OF MECHANICAL Murajmalani Lalit (06 ME 79)

Parul Institute of Engineering & Technology
Mechanical Engineering
ACADEMIC YEAR-20009-2010

CERTIFICATE
TO WHOM SO EVER IT MAY CONCERN This is to certify that following students of B.E.8th Semester (Mechanical Engineering) have satisfactorily completed their project on “DIE CASTING” Sr. No 01 02 03 Name of Student Shrimali Yagnesh Dixit Patel Murajmalani Lalit Roll No. 05 ME 114 05 ME 87 06 ME 79

Guided By:

Adil Khan Lecturer (Mechanical Engg.)

Prof. Hitesh Bhargav H.O.D (Mechanical Engg.)

PARUL INSTITTUTE OF ENGINEERING & TECHNOLOGY P.O. Limda, Ta: Waghodia, Dist: Vadodara

CHAPTER 1 INTRODUCTION

HISTORY: □ Casting or founding is one of the oldest manufacturing processes which date back to approximately 4000 B.C. □ The manufacture and use of castings can be traced both in ancient and modern history. □ The first foundry centre came into existence in the China. □ Earliear to that founding was an Art and a craft with all its secrets confined to certain families. □ The middle part of the 20th century saw marked developments in founding. Newer techniques came into existence, the casting phenome none could be understood better, more and more young men took intrest and got trained in this field and eventually many Engineering Institutes teaching metal casting as an independent subject.

PRINCIPLE OF CASTING
□ Casting is the metal shaping process serving the society since civilization. A wide variety of sizes and shapes of simple and intricate nature can be produced in different metals. □ Casting is the process of producing metal/alloy component part of desired shapes by pouring metal into a prepared mould and then allowing the meta/alloy to cool and solidify.The solidify piece of metal is known as CASTING. □ Casting is a solidification process, which means the solidification phenomenon controls most of the properties of the casting. Moreover, most of the casting defects occur during solidification, such as gas porosity and solidification shrinkage.

FUNDAMENTALS OF CASTING
Casting is a process in which a solid is melted by heating to a proper temperature, and the molten metal is then poured into a mould or cavity, which helps it to get a proper shape during its solidification. In this process, simple or complex shapes can be formed using any metal that can be melted. The finished components can have virtually any shape and configuration depending on the design. Moreover, in metal casting process one can improve the resistance to working stresses of the components. You can also control the directional properties and a pleasing appearance of the output can also be achieved.Size of cast parts varies from a fraction of an inch and a fraction of an ounce to over 30 feet (10 meters) and many tons, depending on its application. Metal casting has its advantages over other processes in the production components, where: Parts are having hollow sections or internal cavities Parts that contain irregular curved surfaces Parts made from metals that are difficult to machine. Metal casting is widely used and one of the most popular manufacturing processes, because of the advantages mentioned above.

THEORY OF CASTING
Solidification occurs in two steps: nucleation and crystal growth In the nucleation stage solid particles form within the liquid. When these particles form their internal energy is lower than the surrounded liquid, which creates an energy interface between the two. The formation of the surface at this interface requires energy, so as nucleation occurs the material actually undercools, that is it cools below its freezing temperature, because of the extra energy required to form the interface surfaces. It then recalescences, or heats back up to its freezing temperature, for the crystal growth stage. Note that nucleation occurs on a pre-existing solid surface, because not as much energy is required for a partial interface surface, as is for a complete spherical interface surface. This can be advantageous because fine-grained castings possess better properties than coarse-grained castings. A fine grain structure can be induced by grain refinement or inoculation, which is the process of adding impurities to induce nucleation. All of the nucleations represent a crystal, which grows as the heat of fusion is extracted from the liquid until there is no liquid left. The direction, rate, and type of growth can be controlled to maximize the properties of the casting. Directional solidification is when the material solidifies at one end and proceeds to solidify to the other end; this is the most ideal type of grain growth because it allows liquid material to compensate for shrinkage. Cooling curves are important in controlling the quality of a casting. The most important part of the cooling curve is the cooling rate which affects the microstructure and properties. Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure. Below is an example cooling curve of a pure metal or eutectic alloy, with defining terminology.Note that before the thermal arrest the material is a liquid and after it the material is a solid; during the thermal arrest the material is converting from a liquid to a solid. Also, note that the greater the superheat the more time there is for the liquid material to flow into intricate details. The cooling rate is largely controlled by the mold material. When the liquid material is poured into the mold, the cooling begins. This happens because the heat within the molten metal flows into the relatively cooler parts of the mold. Molding materials transfer heat from the casting into the mold at different rates. For example, some molds made of plaster may transfer heat very slowly, while steel would transfer the heat quickly. Where heat should be removed quickly, the engineer will plan the mold to include special heat sinks to the mold, called chills. Fins may also be designed on a casting to extract heat, which are later removed in the cleaning (also called fettling) process.

TERMINOLOGY OF CASTING
The casting process uses the following specialized terminology: □ Pattern: An approximate duplicate of the final casting used to form the mold cavity. □ Molding material: The material that is packed around the pattern and then the pattern is removed to leave the cavity where the casting material will be poured. □ Flask: The rigid wood or metal frame that holds the molding material. □ Cope: The top half of the pattern, flask, mold, or core. □ Drag: The bottom half of the pattern, flask, mold, or core. □ Core: An insert in the mold that produces internal features in the casting, such as holes. □ Core print: The region added to the pattern, core, or mold used to locate and support the core. □ Mold cavity: The combined open area of the molding material and core, there the metal is poured to produce the casting. □ Riser: An extra void in the mold that fills with molten material to compensate for shrinkage during solidification. □ Gating system: The network of connected channels that deliver the molten material to the mold cavities. □ Pouring cup or pouring basin: The part of the gating system that receives the molten material from the pouring vessel. □ Sprue: The pouring cup attaches to the sprue, which is the vertical part of the gating system. The other end of the sprue attaches to the runners. □ Runners: The horizontal portion of the gating system that connects the sprues to the gates. Gates: The controlled entrances from the runners into the mold cavities. □ Vents: Additional channels that provide an escape for gases generated during the pour. □ Parting line or parting surface: The interface between the cope and drag halves of the mold, flask, or pattern. □ Draft: The taper on the casting or pattern that allow it to be withdrawn from the mold □ Core box: The mold or die used to produce the cores.

CHAPTER 2 CASTING PROCEDURE

Basic Steps in Making Castings
There are six basic steps in making castings:
Obtaining the casting geometry Patternmaking Core making Molding Melting and pouring Cleaning Other procedures may be performed before delivery
The various steps in the production of castings are briefly summarized for the benefit of those who may be unfamiliar with foundries and the casting process.
Obtaining the casting geometry
The traditional method of obtaining the casting geometry is by sending blueprint drawings to the foundry. This is usually done during the request for quotation process. However, more and more customers and foundries are exchanging part geometry via the exchange of computer aided design files.
Patternmaking
The pattern is a physical model of the casting used to make the mold. The mold is made by packing some readily formed aggregate material, such as molding sand, around the pattern. When the pattern is withdrawn, its imprint provides the mold cavity, which is ultimately filled with metal to become the casting.If the casting is to be hollow, as in the case of pipe fittings, additional patterns, referred to as cores, and are used to form these cavities.
Core making
Cores are forms, usually made of sand, which are placed into a mold cavity to form the interior surfaces of castings. Thus the void space between the core and mold-cavity surface is what eventually the casting becomes.
Molding
Molding consists of all operations necessary to prepare a mold for receiving molten metal. Molding usually involves placing a molding aggregate around a pattern held with a supporting frame, withdrawing the pattern to leave the mold cavity, setting the cores in the mold cavity and finishing and closing the mold.
Melting and Pouring
The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry, and the molten metal is transferred to the pouring area where the molds are filled.

Cleaning
Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal from the casting. The casting is separated from the mold and transported to the cleaning department. Burnedon sand and scale are removed to improved the surface appearance of the casting. Excess metal, in the form of fins, wires, parting line fins, and gates, is removed. Castings may be upgraded by welding or other procedures. Inspection of the casting for defects and general quality is performed.
Other processes
Before shipment, further processing such as heat-treatment, surface treatment, additional inspection, or machining may be performed as required by the customer's specifications.

ADVANTAGES OF METAL CASTING
□ Casting is one of the most versatile manufacturing processes. □ Casting provides the greatest freedom of design in terms of shape, size and product quantity. □ Casting imparts uniform directional properties and better vibration damping capacity to the cast parts. □ Casting produces machinable parts. □ Shapes difficult and uneconomic to obtain otherwise may be achieved through casting process. □ Very heavy and Bulky parts which are otherwise difficult to get fabricated may be cast. □ Metals difficult to be shaped by other manufacturing processes may be cast.

APPLICATIONS
The growing demand of high precision castings and of intricate designs at lower costs has helped considerably in the development of Foundry Industry. Hardly there is any product, today, which does not have one or more cast components.
Transportation vehicles Machine tools structures
Turbine vanes Power generators Railway crossings Aircraft jet engine blades Agricultural parts Communication, Construction and Atomic Energy

CHAPTER 3 ELEMENTS OF CASTING
The gating system
A simple gating system for a horizontal parting mold. The gating system serves many purposes, the most important being conveying the liquid material to the mold, but also controlling shrinkage, the speed of the liquid, turbulence, and trapping dross. The gates are usually attached to the thickest part of the casting to assist in controlling shrinkage. In especially large castings multiple gates or runners may be required to introduce metal to more than one point in the mold cavity. The speed of the material is important because if the material is traveling too slowly it can cool before completely filling; leading to misruns and cold shuts. If the material is moving too fast then the liquid material can erode the mold and contaminate the final casting. The shape and length of the gating system can also control how quickly the material cools; short round or square channels minimize heat loss. The gating system may be designed to minimize turbulence, depending on the material being cast. For example, steel, cast iron, and most copper alloys are turbulent insensitive, but aluminum and magnesium alloys are turbulent sensitive. The turbulent insensitive materials usually have a short and open gating system to fill the mold as quickly as possible. However, for turbulent sensitive materials short sprues are used to minimize the distance the material must fall when entering the mold. Rectangular pouring cups and tapered sprues are used to prevent the formation of a vortex as the material flows into the mold; these vortices tend to suck gas and oxides into the mold. A large sprue well is used to dissipate the kinetic energy of the liquid material as it falls down the sprue, decreasing turbulence. The choke, which is the smallest cross-sectional area in the gating system used to control flow, can be placed near the sprue well to slow down and smooth out the flow. Note that on some molds the choke is still placed on the gates to make separation of the part easier, but induces extreme turbulence. The gates are usually attached to the bottom of the casting to minimize turbulence and splashing. The gating system may also be designed to trap dross. One method is to take advantage of the fact that some dross has a lower density than the base material so it floats to the top of the gating system. Therefore long flat runners with gates that exit from the bottom of the runners can trap dross in the runners; note that long flat runners will cool the material more rapidly than round or square runners. For materials where the dross is a similar density to the base material, such as aluminium, runner extensions and runner wells can be advantageous. These take advantage of the fact that the dross is usually located at the beginning of the pour, therefore the runner is extended past the last gate(s) and the contaminates are contained in the wells. Screens or filters may also be used to trap contaminates It is important to keep the size of the gating system small, because it all must be cut from the casting and remelted to be reused. The efficiency, or yield, of a casting system can be calculated by dividing the weight of the casting by the weight of the metal poured. Therefore, the higher the number the more efficient the gating system/risers
Shrinkage
There are three types of shrinkage: shrinkage of the liquid, solidification shrinkage and patternmaker's shrinkage. The shrinkage of the liquid is rarely a problem because more material is flowing into the mold behind it. Solidification shrinkage occurs because metals are less dense as a liquid than a solid, so during solidification the metal density dramatically increases. Patternmaker's shrinkage refers to the shrinkage Solidification shrinkage Solidification shrinkage of various metals Metal Aluminium Percentage 6.6 Copper Magnesium Zinc Low carbon steel High carbon steel White cast iron Gray cast iron Ductile cast iron 4.9 4.0 or 4.2 3.7 or 6.5 2.5–3.0 4.0 4.0–5.5 −2.5–1.6 −4.5–2.7 Most materials shrink as they solidify, but, as the table to the right shows, a few materials do not, such as gray CI. For the materials that do shrink upon solidification the type of shrinkage depends on how wide the freezing range is for the material. For materials with a narrow freezing range, less than 50 °C (122 °F) a pipe type cavity forms in the center of the cavity, because the outer shell freezes first and progressively solidifies to the center. Pure and eutectic metals usually have narrow solidification ranges. These materials tend to form a skin in open air molds, therefore they are known as skin forming alloys. For materials with a wide freezing range, greater than 110 °C (230 °F),much more of the casting occupies the mushy or slushy zone (the temperature range between the solidus and the liquidus), which leads to small pockets of liquid trapped throughout and ultimately porosity. These castings tend to have poor toughness, and fatigue resistance. Moreover, for these types of materials to be fluid-tight a secondary operation is required to impregnate the casting with a lower melting point metal. For the materials that have narrow solidification ranges pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies towards the gate. This allows a continuous feed of liquid material to be present at the point of solidification to compensate for the shrinkage. Note that there is still a shrinkage void where the final material solidifies, but if designed properly this will be in the gating system.

Risers and riser aids
Risers, also known as feeders, are the most common way of providing directional solidification. It supplies liquid metal to the solidifying casting to compensate for solidification shrinkage. For a riser to work properly the riser must solidify after the casting, otherwise it cannot supply liquid metal to shrinkage within the casting. Risers add cost to the casting because it lowers the yield of each casting; i.e. more metal is lost as scrap for each casting. Another way to promote directional solidification is by adding chills to the mold. A chill is any material which will conduct heat away from the casting more rapidly that the material used for molding. Risers are classified by three criteria. The first is if the riser is open to the atmosphere, if it is then its called an open riser, otherwise its known as a blind type. The second criterion is where the riser is located; if it is located on the casting then it is known as a top riser and if it is located next to the casting it is known as a side riser. Finally, if riser is located on the gating system so that it fills after the molding cavity, it is known as a live riser or hot riser, but if the riser fills with materials that's already flowed through the molding cavity it is known as a dead riser or cold riser Riser aids are items used to assist risers in creating directional solidification or reducing the number of risers required. One of these items are chills which accelerate cooling in a certain part of the mold. There are two types: external and internal chills. External chills are masses of high-heat-capacity and high-thermal-conductivity material that are placed on an edge of the molding cavity. Internal chills are pieces of the same metal that is being poured, which are placed inside the mold cavity and become part of the casting. Insulating sleeves and toppings may also be installed around the riser cavity to slow the solidification of the riser. Heater coils may also be installed around or above the riser cavity to slow solidification.

Mold cavity
The mold cavity of a casting does not reflect the exact dimensions of the finished part due to a number of reasons. These modifications to the mold cavity are known as allowances and account for patternmaker's shrinkage, draft, machining, and distortion. In non-expendable processes, these allowances are imparted directly into the permanent mold, but in expendable mold processes they are imparted into the patterns, which later form the mold cavity. Note that for non-expendable molds an allowance is required for the dimensional change of the mold due to heating to operating temperatures. For surfaces of the casting that are perpendicular to the parting line of the mold a draft must be included. This is so that the casting can be release in non-expendable processes or the pattern can be released from the mold without destroying the mold in expendable processes. The required draft angle depends on the size and shape of the feature, the depth of the mold cavity, how the part or pattern is being removed from the mold, the pattern or part material, the mold material, and the process type. Usually the draft is not less than 1%. The machining allowance varies drastically from one process to another. Sand castings generally have a rough surface finish; therefore need a greater machining allowance, whereas die casting has a very fine surface finish, which may not need any machining tolerance. Also, the draft may provide enough of a machining allowance to begin with. The distortion allowance is only necessary for certain geometries. For instance, U-shaped castings will tend to distort with the legs splaying outward, because the base of the shape can contract while the legs are constrained by the mold. This can be overcome by designing the mold cavity to slope the leg inward to begin with. Also, long horizontal sections tend to sag in the middle if ribs are not incorporated, so a distortion allowance may be required Cores may be used in expendable mold processes to produce internal features. The core can be of metal but it is usually done in sand.

Filling
Schematic of the low-pressure permanent mold casting process

Macrostructure
The grain macrostructure in ingots and most castings have three distinct regions or zones: the chill zone, columnar zone, and equated zone. The image below depicts these zones. The chill zone is named so because it occurs at the walls of the mold where the wall chills the material. Here is where the nucleation phase of the solidification process takes place. As more heat is removed the grains grow towards the center of the casting. These are thin, long columns that are perpendicular to the casting surface, which are undesirable because they have anisotropic properties. Finally, in the center the equiaxed zone contains spherical, randomly oriented crystals. These are desirable because they have isotropic properties. The creation of this zone can be promoted by using a low pouring temperature, alloy inclusions, or inoculants.

CHAPTER 4 TYPES OF CASTING PROCESSES

Expendable mold casting
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds.

Waste molding of plaster
A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand, the expensive work of bronze casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist. In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting.

Sand casting
Sand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at low cost, but there are other benefits to sand casting, such as very small size operations. From castings that fit in the palm of your hand to train beds (one casting can create the entire bed for one rail car), it can all be done with sand casting. Sand casting also allows most metals to be cast depending on the type of sand used for the molds.

Plaster mold casting
Plaster casting is similar to sand casting except that plaster of Paris is substituted for sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1– 10 units/hr-mold is achieved, with items as massive as 45 kg (99 lb) and as small as 30 g (1 oz) with very good surface finish and close tolerances. Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce near net shape castings. The biggest disadvantage is that it can only be used with low melting point nonferrous materials, such as aluminium, copper, magnesium, and zinc.

Shell molding
Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of flask filled with sand. The sand is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and hardens into a shell around the pattern. Because of the resin it gives a much finer surface finish. The process is easily automated and more precise than sand casting. Common metals that are cast include cast iron, aluminium, magnesium, and copper alloys. This process is ideal for complex items that are small to medium sized.

Investment casting
Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity. Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting, it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast.

Evaporative-pattern casting
This is a class of casting processes that use pattern materials that evaporate during the pour, which means there is no need to remove the pattern material from the mold before casting. The two main processes are lost-foam casting and full-mold casting.

Non-expendable mold casting
The permanent molding process
Non-expendable mold casting differs from expendable processes in that the mold need not be reformed after each production cycle. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting.

Permanent mold casting
Permanent mold casting is metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold, however gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting more than one casting still have a limited life before wearing out.

Die casting
Die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium sized parts are needed with good detail, a fine surface quality and dimensional consistency.

Centrifugal casting
Centrifugal casting is both gravity- and pressure-independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 900 N. Lead time varies with the application. Semi- and true-centrifugal processing permit 30-50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3-4.5 kg. Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting.

Continuous casting
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Molten metal is poured into an open-ended, watercooled copper mold, which allows a 'skin' of solid metal to form over the still-liquid centre. The strand, as it is now called, is withdrawn from the mold and passed into a chamber of rollers and water sprays; the rollers support the thin skin of the strand while the sprays remove heat from the strand, gradually solidifying the strand from the outside in. After solidification, predetermined lengths of the strand are cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five meters wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut. Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increases the quality of the final product. Metals such as steel, copper and aluminium are continuously cast, with steel being the metal with the greatest tonnages cast using this method.

CHAPTER 5 DIE CASTING

A precision casting technique, die casting uses a permanent die or mould, into which molten metal is directly discharged. Along with gravity feed system, metal is consistently forced into the mould under high pressure. As per the cost incurred in the designing of dies, tooling and other capital costs are relatively high as compared to other operational costs. The operative costs are low due to the high level of industrialization and the small number of fabrication steps which includes the process of direct pouring of metal into a permanent mould. The major die casting alloys are zinc, aluminium, and magnesium, copper.

Die Casting Process
The basic die casting process consists of injecting molten metal under high pressure into a steel mold called a die. Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 400 tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to twoto-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.

Design: Perfect for bulk and mass production, die casting technique is most appropriate for non-ferrous metals with relatively low melting point of approx 870oC such as lead, zinc, aluminum, magnesium and some copper alloys. The casting metals having high melting point like steel, iron and ferrous metals lowers die life. Dies are fabricated from two blocks of steel, each including part of cavity, locked and attached together during the casting process.

Die Casting vs. 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.

Choosing the Proper Alloy
Each of the metal alloys available for die casting offer particular advantages for the completed part. Zinc - The easiest alloy to cast, it offers high ductility, high impact strength and is easily plated. Zinc is economical for small parts, has a low melting point and promotes long die life.

Aluminum - This alloy is lightweight, while possessing high dimensional stability for complex shapes and thin walls. Aluminum has good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures. Magnesium - The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast. Copper - This alloy possesses high hardness, high corrosion resistance and the highest mechanical properties of alloys cast. It offers excellent wear resistance and dimensional stability, with strength approaching that of steel parts. Lead and Tin - These alloys offer high density and are capable of producing parts with extremely close dimensions. They are also used for special forms of corrosion resistance.

Die Construction
Dies, or die casting tooling, are made of alloy tool steels in at least two sections, the fixed die half, or cover half, and the ejector die half, to permit removal of castings. Modern dies also may have moveable slides, cores or other sections to produce holes, threads and other desired shapes in the casting. Sprue holes in the fixed die half allow molten metal to enter the die and fill the cavity. The ejector half usually contains the runners (passageways) and gates (inlets) that route molten metal to the cavity. Dies also include locking pins to secure the two halves, ejector pins to help remove the cast part, and openings for coolant and lubricant. When the die casting machine closes, the two die halves are locked and held together by the machine’s hydraulic pressure. The surface where the ejector and fixed halves of the die meet and lock is referred to as the "die parting line." The total projected surface area of the part being cast, measured at the die parting line, and the pressure required of the machine to inject metal into the die cavity governs the clamping force of the machine.
There are four types of dies
1. Single cavity to produce one component
2. Multiple cavities to produce a number of identical parts
3. Unit dies to produce different parts at one time
4. Combination dies to produce several different parts for an assembly.

CHAPTER 6 GRAVITY DIE CASTING OR PERMANENT DIE CASTING

Gravity die casting is a process wherein the liquid metal is poured into metallic moulds without application of any external pressure. The liquid metal enters the cavity by gravity. Gravity die casting (GDC) is different from High Pressure Die Casting (HPDC), where the liquid metal is injected into the metal mould under very high pressures for production of thin walled smaller castings. Gravity die casting is a manufacturing process for producing accurately dimensioned, sharply defined, smooth or textured-surface metal parts. It is accomplished by gently pouring molten metal into reusable metal dies under the force of gravity. The term, "die casting," is also used to describe the finished part.To begin the process, a cast iron mould capable of producing tens of thousands of castings must be made in at least two sections to permit removal of castings. These sections are mounted securely to solid base and are arranged so that one is stationary (fixed die half) while the other is moveable.
To begin the casting cycle, the die caster clamps the two die halves tightly together. Molten metal is poured into the die cavity where it solidifies quickly. The die halves are drawn apart and the casting is ejected. Die casting dies can be simple or complex, having moveable slides, cores, or other sections depending on the complexity of the casting.The main advantage of gravity die casting over sand casting is the high speed of production. The reusable die tooling allows for many hundreds of castings to be produced in a day. High definition parts reduce machining costs and superior surface finish reduces finishing costs. Although die-castings are in most cases cheaper than sand castings, die tooling is considerably more expensive than sand tooling so an optimum number of castings need to be produced to make the process cost effective in the long run.

COMPARISION OF PERMANENT MOLD CASTING WITH SAND CASTING
Closer dimensional tolerance and accuracy can be achieved Permanent mold casting possesses smoother surfaces and better appearances. It is possible to obtain surface smoothness of 100 to 125 micro inches root-mean-square. Chilling effect of the metal mold help producing a fine grained metal structure Metal cores employed in permanent mold can produce holes of much smaller diameter than sand cores. Inserts can be usefully employed and readily cast in place. Mass production of castings is more economical. Less floor space is needed. The cycle of operation consumer much less time than that of sand casting.
Permanent mold casting involves low overhead charges. Structurally superior and stronger casting can be produced. Locally heavy section can, with suitable casting and die design, be produced sound and free from porosity.

ADVANTAGES OF DIE CASTING
Same dies are used again and again to produce casting. Dies are capable of retaining their accurancy and usefulness for long period of production. High production rates can be achieved with die casting technique. It is possible to hold close dimensional tolerance. Very thin sections can be cast without any difficulty. Threads and other fine surface details can be easily obtained on die-cast surface. Quite intricate shapes can be die-cast. Surface smoothness of 1250 micro-mm root-mean-square can be obtained. Inserts can be readily cast in place. Die casting technique can be mechanized and used in mass production. Machining cost of die-casting are very small.

LIMITATIONS OF DIE CASTING
Ferrous alloys are not cast and moreover a limited number of non-ferrous alloys can be economically die-cast. The maximum size of the casting which can be made by die casting technique is restricted. Maximum sizes are about 100kg for zinc and 35kg for aluminium die casting. Since die casting machine and dies involve high costs, the die casting process prove uneconomical for small scale production. Die casting have been found to contain some porosity; this necessities the evacuation of air from the die cavity. Die casting technique require comparatively a longer period of time for going in to production. Die casting technique requires special skills on the part of maintenance and supervisory personal
In certain cases, dies may produce an undesirable chilling effect on the die-casting.

APPLICATIONS
Carburetors bodies. Hydraulic brake cylinder. Refrigeration casting. Washing machine gears and gear covers. Connecting rods and automotive pistons. Oil pumps bodies. Typewriter segments. Aircraft and missile castings

CHAPTER 7 INVESTMENT CASTING PROCESS

Investment casting or 'lost wax process' is an industrial process which employs in-process control at every point. Highly refined on-line process control methods are backed up with laboratory skill. Every casting shipped--and this applies equally to orders for a dozen castings or half a million--can be relied on to meet the designer's performance specification. Below is a graphical step-by-step representation of the Investment casting process.

PATTERN PRODUCTION - The process begins with production of a One-piece heat-disposable pattern. This pattern is made by injecting Wax into a metal die. A pattern is required for each casting. These Disposable patterns have the exact geometry of the required finished Part, but they are made slightly larger, to compensate for volumetric Shrinkage in the pattern production state and during solidification of Metal in the ceramic mold.

PATTERN ASSEMBLY - Patterns are fastened on to one or more Runners and the runners are attached to the pouring cup. Patterns, Runners and pouring cups comprise the cluster or tree, which is needed to produce the ceramic mold. The number of runners per section and their arrangement on the pouring cup can vary considerably, depending On alloy type, size, and configuration of the casting.

CERAMIC SHELL MOLD PROCESS - The ceramic shell mold technique Involves dipping the entire cluster into a ceramic slurry, draining it, Then coating it with fine ceramic sand. After drying, this process is Repeated again and again, using progressively coarser grades of Ceramic material, until a self-supporting shell has been formed.

REMOVING THE WAX - The coated cluster is placed in a high temperature furnace where the pattern melts and runs out through the gates, runners and pouring cup. This leaves a ceramic shell containing cavities Of the casting shape desired with passages leading to them.48.7511

CASTING - The ceramic shell molds must be fired to burn out the last Traces of pattern material and to preheat the mold in preparation for Casting usually in the range of 1600 to 2000 degrees Fahrenheit. The Hot molds may be poured with the assistance of vacuum, pressure And/or centrifugal force. This enables reproduction of the most intricate details and extremely thin walls of an original wax pattern.

CLEANING - After the poured molds have cooled, the mold material is Removed from the casting cluster. This is done by mechanical vibration, abrasive blasting and chemical cleaning.

CASTING REMOVAL - Individual castings are then removed from the Cluster by means of cut-off wheels and any remaining protrusions left by Gates or runners are removed by belt-grinding.

FINISHING - The castings are then ready for secondary operations Such as: heat treating, straightening, machining, finishing, inspection, Non-destructive testing, and then shipment to the customer.
Challenges Pattern assembly is the most important and most challenging step in the process because: (1) There must be sufficient strength at the point of attachment to keep the branches from falling off when the cluster is jostled during subsequent steps; (2) The angle of attachment is critical for proper flow of wax from the tips of the branches downhill and out the rootbase opening during the autoclave step, and flow of molten metal from the tree trunk into the branches and downhill all the way out to their tips during the metal pouring stage; (3) A high-quality weld/glue site (a smooth fillet weld; no glue drips are desired) is necessary to avoid a potential “inclusion” defect in the cast metal part, which can otherwise occur if a jagged lip of ceramic exists at the location where the molten metal flows from the tree trunk into the branch – the flow of metal can snap off a chip of ceramic and engulf it; (4) A more-densely packed number of branches improves yield of product parts per unit of tree trunk, (which must be re-melted to reclaim the metal); (6) Uniform spacing between patterns is necessary to ensure each metal part cools at the same rate to prevent premature fracture of the shell.

Advantages and disadvantages of investment casting
Advantages
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. Draft is not required in the molds design. Low material waste.

Disadvantages
Individual pattern is required for each casting. Limited casting dimensions. Relatively high cost (tooling cost, labor cost).

Applications
Investment casting is used in the aerospace and power generation industries to produce turbine blades with complex shapes or cooling systems. Blades produced by investment casting can include single-crystal (SX), directionally solidified (DS), or conventional equiaxed blades. Investment casting is also widely used by firearms manufacturers to fabricate firearm receivers, triggers, hammers, and other precision parts at low cost. Other industries that use standard investment-cast parts include military, medical, commercial and automotive.

The Future
Refinements continue in both the alloys used in die casting and the process itself, expanding die casting applications into almost every known market. Once limited to simple lead type, today’s die casters can produce castings in a variety of sizes, shapes and wall thicknesses that are strong, durable and dimensionally precise.A magnesium seat

CHAPTER 7 EXPERIMENTAL PROCEDURE OF WAX DIE CASTING

This is only a conceptual design based casting process.
Wax is the material, from which costing of washer & coin are prepared. The wax is of paraffin type Having a melting point of 60-70 degree centigrade.
From the bottom of the stainless steel pot. The heat source of pumping stove is given a proper way that don’t cause any hazards or problem for us .
After the passes, the wax material getting stored melting.After a sufficient molten wax is accumulated in the stainless steel furnace.Wax is allowed to the ladle of Mild Steel.through The operating knob or kock of copper material.
The molten wax then slowly passes through the die cavity here two dies of MS are fitted.The molten wax passes & poured in the mold cavity of two dies simultaneously.The molten wax takes some time to solidify into the mold cavity.
The charge is then allowed to solidify (5 to 7 minutes) in the die. Then after some time, the die is taken out from the die stand & slowly the one part of die or upper (removable part) of the die is removed. Then the solidified piece is our resulting casting product like weaker & coin. Then the casting is inspected whether it is having a good surface finish or not.
The time taken during melting, pouring & solidifying processes are recorded & analysed how quickly this process take time to make a complete casting product.

USEFULNESS OF PROJECT
It is esiear to use wax material use wax material for casting process as no harmful in the laboratory.
Less costlier as compared to the other material.
Easily melted as compared to other metal/alloy takes longer time to meet & solidify in the laboratory.
In less time, more products can be occupied with die casting.
Helpful in mass production of componants.
Good surface finish is achieved.
Intricate shaped casting can be achieved.
By wax /casting or we can say that from wax pattern further mold cavity is achieved by pouring the wax pattern into the Silica+Mg mixture and then allowing it to soidify.
In this method, coating is done on the wax pattern smoothly heat is given from the outside that the wax pattern is removed from the mold & thus cavity is formed into it
By. We can pour the alloy/metal into the mold cavity. This process is called as lost wax process or Investment casting process.

PROBLEMS ASSOCIATED WITH THIS CASTING PROCESS
The die casting processes(gravity and pressure) will not be favouerd because of the slowness of operation , and the difficulties of automating production as requirement of servomechanism to operate ladle and control the cavity from furnace
Also this design is just only for small foundry.
Required more accuracy for pouring the molten metal into the die cavity. Gravity die casting is also not easily dealt with in terms of effluent control if chemically bonded cores are used,since the dies are arranged around the shop in order to which changes from day to day in a jobing shop.

FUTURE SCOPE OF CASTING

Parul Institute of Engineering & Technology

Mechanical Engineering

Parul Institute of Engineering & Technology

Mechanical Engineering

Parul Institute of Engineering & Technology

Mechanical Engineering

Parul Institute of Engineering & Technology

Mechanical Engineering