Die Casting History, Future and advantages

History of Die Casting

The earliest examples of die casting by pressure injection - as opposed to casting by gravity pressure occurred in the mid-1800s. By 1892, commercial applications included parts for phonographs and cash registers, and mass production of many types of parts began in the early 1900s.
The first die casting alloys were various compositions of tin and lead, but their use declined
with the introduction of zinc and aluminum alloys in 1914. Magnesium and copper alloys quickly followed, and by the 1930s, many of the modern alloys still in use today became available.
The die casting process has evolved from the original low-pressure injection method to techniques including high-pressure casting at forces exceeding 4500 pounds per square inch squeeze casting and semi-solid die casting. These modern processes are capable of producing high integrity, near net-shape castings with excellent surface finishes.

Future of Die Casting

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 complex shapes and sizes.

Advantages of die Casting

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 diecastings 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.

High pressure Die Casting Process

High pressure die casting is a manufacturing process in which molten metal (aluminum) is injected with a die casting machine under force using high speed and considerable pressure into a steel mold or die to form products. 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 two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts. 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.

There are several aluminum alloys with different mechanical properties and chemical breakdowns. Aluminium is used in 80-90% of the high pressure die casting alloys available in the world today. In many cases aluminum high pressure die casting can replace steel, increasing strength and reducing part weight. high pressure die casting parts are produced in small sizes of less than 30 gms up to large sizes.

This equipment consists of two vertical platens on which bolsters are located which hold the die halves. One platen is fixed and the other can move so that the die can be opened and
closed. A measured amount of metal is poured into the shot sleeve and then introduced into the mould cavity using a hydraulically-driven piston. Once the metal has solidified, the die is opened and the casting removed.In this process, special precautions must be taken to avoid too many gas inclusions which cause blistering during subsequent heat-treatment or welding of the casting product. Both the machine and its dies are very expensive, and for this reason pressure die casting is economical only for high-volume production.Thousands of high pressure die casting parts can be produced in a single day with the right die casting tooling and proper high pressure die casting part design. Production of quantities of 20,000 to 30,000 high pressure die casting parts a week in some cases. Most of the casting manufacturers are capable to design or work with buyer's designer to develop high volume high pressure die casting tooling.

High pressure die casting (HPDC) is a widely used manufacturing process for mass production of components of aluminium and magnesium alloys, such as automotive transmission housings and gearbox parts. Molten metal is injected at high speed (50 to 100 metres/sec) and under very high pressures into a die through a complex gate and runner system. The geometrical complexity of the die leads to strongly three-dimensional fluid flow. Within the die cavity, jetting and splashing results in liquid droplet and possibly atomised spray formation. Crucial to the production of homogeneous cast components with minimal entrapped voids
is the order in which the various parts of the die fill and the positioning of the gas exits. This is determined by the design of the gate configuration and the geometry of the die.

Basic functions of Die Casting

Hold molten metal in the shape of the desired casting. Provide a means for molten metal to get to a space where itwill be held to the desired shape. Remove heat from the molten metal and to allow the metal to solidify To provide for the removal of the casting.

Hot and Cold Chamber Die casting

Hot and Cold Chamber Die casting Die casting is one of the most common manufacturing processes. The basic idea is to force metal into a permanent mold using high pressure. The metal then cools (often assisted by water cooling of the die). The mold is then opened, and the casting ejected.
Molds for die casting are quite elaborate. They are usually constructed of alloy steel in two pieces (called the cover and the ejector). The die must withstand high temperature and pressure, so the die is typically made for chromium or tungsten steel alloys. In order to increase die life, and improve throughput, the die is usually cooled with water, air or nitrogen.

Materials:

Materials best suited for die castings are zinc, aluminum, magnesium, copper, lead and tin. High pressure die casting is generally limited to non-ferrous metals because of the difficulty in making refractory molds capable of withstanding the high temperature and pressure.

Applications:

- automotive parts
- appliances
- office machines
- bathroom fixtures
- outboard motors

Hot chamber machines are:

- good for low temperature zinc alloys (approx. 400°C)
- faster than cold chamber machines
- cycle times must be short to minimize metal contamination
- metal starts in a heated cylinder
- a piston forces metal into the die
- the piston retracts, and draws metal in

Cold chamber machines:

- casts high melting point metals (>600°C)
- high pressures used
- metal is heated in a separate crucible
- metal is ladled into a cold chamber
- the metal is rapidly forced into the mold before it cools

Advantages:

• intricate parts possible
• short cycles
• inserts feasible
• cycles less than 1 minute
• minimum finishing operations
• thin sections, high tolerances, good surface finish

Disadvantages:

• metal die is costly
• porous parts
• not suited to large parts
• long setup times
• $5000-200,000 for machine
• metal melting point temperature must be lower than die

Hot and Cold Chamber Die casting

Hot and Cold Chamber Die casting Die casting is one of the most common manufacturing processes. The basic idea is to force metal into a permanent mold using high pressure. The metal then cools (often assisted by water cooling of the die). The mold is then opened, and the casting ejected.
Molds for die casting are quite elaborate. They are usually constructed of alloy steel in two pieces (called the cover and the ejector). The die must withstand high temperature and pressure, so the die is typically made for chromium or tungsten steel alloys. In order to increase die life, and improve throughput, the die is usually cooled with water, air or nitrogen.

Materials:

Materials best suited for die castings are zinc, aluminum, magnesium, copper, lead and tin. High pressure die casting is generally limited to non-ferrous metals because of the difficulty in making refractory molds capable of withstanding the high temperature and pressure.

Applications:

- automotive parts
- appliances
- office machines
- bathroom fixtures
- outboard motors

Hot chamber machines are:

- good for low temperature zinc alloys (approx. 400°C)
- faster than cold chamber machines
- cycle times must be short to minimize metal contamination
- metal starts in a heated cylinder
- a piston forces metal into the die
- the piston retracts, and draws metal in

Cold chamber machines:

- casts high melting point metals (>600°C)
- high pressures used
- metal is heated in a separate crucible
- metal is ladled into a cold chamber
- the metal is rapidly forced into the mold before it cools

Advantages:

• intricate parts possible
• short cycles
• inserts feasible
• cycles less than 1 minute
• minimum finishing operations
• thin sections, high tolerances, good surface finish

Disadvantages:

• metal die is costly
• porous parts
• not suited to large parts
• long setup times
• $5000-200,000 for machine
• metal melting point temperature must be lower than die

Sand casting

Sand casting

In spite of its innocuous name, sand casting is one of the most major industrial metal casting processes. Sand casting accounts for over 90% of all metal poured for casting.

The process of sand casting begins by fabricating a pattern for the final object. The pattern is often two piece due to the construction of the mold. The pattern can be made from virtually any substance including wood, foam, clay and plastic.

The mold which contains the sand is called a flask. It consists of two pieces, the top or cope and the bottom or drag. The centerline divides the cope from the drag. Holes called sprues feed molten metal into the flask and holes called risers allow air bubbles to escape.

To begin the casting process, the flask is broken into its two pieces. The pattern is inserted into the flask and the flask reassembled. Sand is packed tightly around the pattern. Then the flask is opened and the pattern removed. The sand imprint is checked carefully, and appropriate risers and sprues added (if not contained on the original pattern). Then the flask is closed and molten metal poured into the sprues until it emerges from the risers.

After the metal has cooled, the flask is broken open and the cast part removed. The sand is cleaned and recycled back for the next casting operation. The sprues and risers are removed and the part is cleaned.

Tricks:

Either "green" sand (actually black) or dry sand is used for casting. In green sand casting, the sand binder is kept moist with water. The part is cast as soon as possible after the pattern is removed. In dry sand casting, an organic binder is used -- and the mold is baked after the pattern is removed. Green sand casting is more economical, dry sand casting has better dimensional tolerances.

To create a hole in the middle of a casting, a baked sand part called a core is inserted in the mold after the pattern has been removed. The core will be removed destructively after the casting is complete -- leaving a hole in the middle of the part.

Polystyrene or Styrofoam can be used to create a one-time pattern for a specialty casting. In this process, the pattern is inserted into the flask and left there. When the molten metal is poured over the pattern, it vaporizes and the vapor escapes from the riser holes.

Materials:

Any metal that can be melted. Common metals include cast iron, steel, brass, bronze, aluminum alloys, and magnesium alloys.
Advantages:
• Exceptionally economical
• Virtually no materials waste, as leftovers can be remelted and used again
• The castings can range from a few ounces to thousands of pounds
• The castings are isotropic
• Virtually unlimited freedom of shape
Disadvantages:
• Dimensional tolerances of 1/16" are typical -- this is large for many applications
• The castings have a work hardened (chilled) surface and cause significant tool wear in post casting machining.

Sand casting

Sand casting

In spite of its innocuous name, sand casting is one of the most major industrial metal casting processes. Sand casting accounts for over 90% of all metal poured for casting.

The process of sand casting begins by fabricating a pattern for the final object. The pattern is often two piece due to the construction of the mold. The pattern can be made from virtually any substance including wood, foam, clay and plastic.

The mold which contains the sand is called a flask. It consists of two pieces, the top or cope and the bottom or drag. The centerline divides the cope from the drag. Holes called sprues feed molten metal into the flask and holes called risers allow air bubbles to escape.

To begin the casting process, the flask is broken into its two pieces. The pattern is inserted into the flask and the flask reassembled. Sand is packed tightly around the pattern. Then the flask is opened and the pattern removed. The sand imprint is checked carefully, and appropriate risers and sprues added (if not contained on the original pattern). Then the flask is closed and molten metal poured into the sprues until it emerges from the risers.

After the metal has cooled, the flask is broken open and the cast part removed. The sand is cleaned and recycled back for the next casting operation. The sprues and risers are removed and the part is cleaned.

Tricks:

Either "green" sand (actually black) or dry sand is used for casting. In green sand casting, the sand binder is kept moist with water. The part is cast as soon as possible after the pattern is removed. In dry sand casting, an organic binder is used -- and the mold is baked after the pattern is removed. Green sand casting is more economical, dry sand casting has better dimensional tolerances.

To create a hole in the middle of a casting, a baked sand part called a core is inserted in the mold after the pattern has been removed. The core will be removed destructively after the casting is complete -- leaving a hole in the middle of the part.

Polystyrene or Styrofoam can be used to create a one-time pattern for a specialty casting. In this process, the pattern is inserted into the flask and left there. When the molten metal is poured over the pattern, it vaporizes and the vapor escapes from the riser holes.

Materials:

Any metal that can be melted. Common metals include cast iron, steel, brass, bronze, aluminum alloys, and magnesium alloys.
Advantages:
• Exceptionally economical
• Virtually no materials waste, as leftovers can be remelted and used again
• The castings can range from a few ounces to thousands of pounds
• The castings are isotropic
• Virtually unlimited freedom of shape
Disadvantages:
• Dimensional tolerances of 1/16" are typical -- this is large for many applications
• The castings have a work hardened (chilled) surface and cause significant tool wear in post casting machining.

Die CONSTRUCTION in Die Casitng

Die CONSTRUCTION in Die Casitng

In the simplest case a die consists of two halves into which the impression of the part to be moulded is cut. The mating surfaces of the die halves are accurately machined so that no leakage can occur at the split line. It may by seen that in order to facilitate mounting the mould in the machine and cooling and ejection of the moulding, several additions are made to the basic mould halves. Firstly, backing plates permit the mould to be bolted on to the machine platens. Secondly, channels are machined into the mould to allow the mould temperature to be controlled. Thirdly, ejector pins are included to that the moulded part can be freed from the mould. In most cases the ejector pins are operated by the shoulder screw hitting a stop when the mould opens. Two side cores are incorporated in fixed half as each component requires it. Two finger cams are provided in fixed half for the actuation of these side cores. The mould cavity is joined to the machine nozzle by means of the sprue. The sprue anchor pin then has the function of pulling the sprue away from the nozzle and ensuring that the moulded part remains on the moving half of the mould, when the mould opens. The impressions are joined to the sprue by runners - channels cut in core insert of the mould through which the plastic will flow without restriction. A narrow constriction between the runner and the impressions allows the moulding to be easily separated from the runner and sprue. This constriction is called the gate.

Fixed half and moving half

The various mould parts fall naturally into two section or halves. Hence that half attached to the stationary platen of the machine is termed the fixed half. The other half of the mould attached to the moving platen of the machine is known simply as the moving half.

Generally the core is situated in moving half and the overriding reason is, the molding, as it cools, will shrink on to the core and remain with it as the mould opens. This will occur irrespective of whether the core is in the fixed half or the moving half. However, this shrinkage on to the core means that some form of ejector system is almost certainly necessary. Motivation for this ejector system is provided if the core is in moving half. Moreover, in the case of single-impression basic mould, where a direct sprue feed to the underside of the molding is desired the cavity must be in the fixed half and core in the moving half.

Die CONSTRUCTION in Die Casitng

Die CONSTRUCTION in Die Casitng

In the simplest case a die consists of two halves into which the impression of the part to be moulded is cut. The mating surfaces of the die halves are accurately machined so that no leakage can occur at the split line. It may by seen that in order to facilitate mounting the mould in the machine and cooling and ejection of the moulding, several additions are made to the basic mould halves. Firstly, backing plates permit the mould to be bolted on to the machine platens. Secondly, channels are machined into the mould to allow the mould temperature to be controlled. Thirdly, ejector pins are included to that the moulded part can be freed from the mould. In most cases the ejector pins are operated by the shoulder screw hitting a stop when the mould opens. Two side cores are incorporated in fixed half as each component requires it. Two finger cams are provided in fixed half for the actuation of these side cores. The mould cavity is joined to the machine nozzle by means of the sprue. The sprue anchor pin then has the function of pulling the sprue away from the nozzle and ensuring that the moulded part remains on the moving half of the mould, when the mould opens. The impressions are joined to the sprue by runners - channels cut in core insert of the mould through which the plastic will flow without restriction. A narrow constriction between the runner and the impressions allows the moulding to be easily separated from the runner and sprue. This constriction is called the gate.

Fixed half and moving half

The various mould parts fall naturally into two section or halves. Hence that half attached to the stationary platen of the machine is termed the fixed half. The other half of the mould attached to the moving platen of the machine is known simply as the moving half.

Generally the core is situated in moving half and the overriding reason is, the molding, as it cools, will shrink on to the core and remain with it as the mould opens. This will occur irrespective of whether the core is in the fixed half or the moving half. However, this shrinkage on to the core means that some form of ejector system is almost certainly necessary. Motivation for this ejector system is provided if the core is in moving half. Moreover, in the case of single-impression basic mould, where a direct sprue feed to the underside of the molding is desired the cavity must be in the fixed half and core in the moving half.

DIFFERENT DIE CASTING ALLOYS in Die Casting

DIFFERENT DIE CASTING ALLOYS in Die Casting

Aluminum Alloy

Aluminum or aluminum is a silvery and ductile metal widely used for manufacturing components and parts in diverse industries. The metal is found primarily in bauxite ore and is known for its light weight and resistance to corrosion. Aluminum castings are used in the aerospace industry and very important in other areas of transportation and building.

Properties of Aluminum Alloy

Aluminum has a number of properties, which makes it suitable for being casted into unique

and complex shapes components and spare parts, which are further used in a number of industries. Some of the properties are:

• Low density: The metal is only one-third the weight of steel.
• Corrosion resistant: Aluminum and its alloys are generally resistant to corrosion, the natural aluminum oxide coating acts as an effective barrier to moisture, air, and various chemicals.
• Good conductor of electricity: This property has made the metal useful for manufacturing various components and spare parts in electrical equipments etc.
• Non combustible and Non Magnetic: These two properties have made the metal invaluable in industries including electronics etc
• Non - Toxic: This property has made aluminium of use in food and packaging industries
• Malleable: This helps the metal for use in common manufacturing and shaping processes . The metal is also ductile and hence can be easily machined and cast

Cobalt Alloy

Cobalt is a hard, lustrous, silver-gray metal, found in different ores. It is also used for preparing magnetic, wear-resistant, and high-strength alloys. The metal compounds are used in the production of inks, paints and varnishes.

The metal alloys are easily castable and the compositions are characterized with high carbon content & minimum silicon, both providing fluidity. Cobalt and its alloys have been used in demanding applications since a very long time and have contributed significantly to industrial products and processes.

Copper Alloy

Copper is a popularly used ductile metal with excellent electrical conductivity, and also finds extensive use as a thermal and electrical conductor, as a building material, and as an important component of various alloys.

There are numerous alloys of copper with important historical and contemporary uses. Casted copper alloys have high tensile and compressive strength, have good wear qualities when subjected to metal-to-metal contact, are easily machined, have good thermal and electrical conductivity, and high corrosion resistance for maximizing product performance. Some of the widely used alloys are:

· Bronze: An alloy of copper and tin

· Brass: An alloy of copper and zinc.

· Monel/ Cupronickel: An alloy of copper and nickel.

Properties of Copper

Copper has numerous properties, which makes it useful in various industrial applications. Some of the properties are:

Ø Malleable

Ø Ductile

Ø Good conductor of heat

Ø Good conductor of electricity-in pure state

Lead Alloy

Lead is a soft, heavy, toxic metal, bluish white in color when freshly cut but tarnishes to dull gray when exposed to air. The stable and heavy metal has a dull luster and is a dense, ductile, very soft, highly malleable, with poor electrical conductivity. This metal is highly corrosion resistant and this property, makes it useful for carrying corrosive liquids (e.g. sulfuric acid).

The metal is used in wide variety of industries as it can be easily casted or molded into different shapes & used as solder.

Magnesium Alloy

Magnesium is an abundantly found metal, silvery white in appearance, fairly strong and light in weight. The metal is protected by a thin layer of oxide which is hard to remove and it tarnishes slightly when exposed to air.

Magnesium alloys find applications in various industries as they meet the requirements for lightweight materials to operate under increasingly demanding conditions. These metal alloys have always been demanded by designers due to their low density, only two thirds that of aluminum. This has been a significant factor in the widespread use of casted and wrought magnesium alloy.

There have been quite a few developments in the recent years to improve the performance of these alloys used in different casting processes. Improvements in mechanical properties has made these alloys more in demand for specialty application areas like aerospace.

Magnesium Alloy Designation System

A standard system of alloy and temper designations, as given by the American Society for Testing and Materials (ASTM B 275) is explained in the following table:

• For the convenience of buyers we explain the designation system with the help of an example, considering the magnesium alloy AZ81A-T4.
• The first part of the designation, AZ, indicates that aluminum and zinc are the two principal alloying elements.
• The second part of the designation, 81, indicates the rounded-off percentages of aluminum and zinc (8 and 1, respectively).
• The third part, A, indicates that it is the fifth alloy standardized with 8% Al and 1% Zn as the principal alloying additions.
• The fourth part, T4, indicates that the alloy is solution heat-treated.

Nickel Alloy

Nickel is an alloy metal, silvery white in color that takes on a high polish. It belongs to the class of transition metals, and is hard and ductile. The metal is found combined with sulphur in millerite, with arsenic in the mineral niccolite, and with arsenic and sulphur in nickel glance.

It is pre-eminently an alloy metal, and its main use is in the nickel steels and nickel cast irons, of which there are large number of varieties. The metal is also widely used for many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminum, lead, cobalt, silver, and gold.

The metal is magnetic in nature, and is very frequently accompanied by cobalt, both being found in meteoric iron.

Refractory Alloy

Refractory metals belong to a special class of metals that highly and exceptionally resistant to heat, wear, and corrosion. These properties make these reactive metals of use in various industrial applications.

Popular Refractory Metals:

• Tungsten (W)
• Molybdenum (Mo)
• Niobium (Nb)
• Tantalum (Ta)
• Rhenium (Re)

Since these metals have a high melting point, the components are never fabricated by casting. Powder metallurgy process is used wherein the pure metal is compacted, heated using electric current, and further fabricated by cold working with annealing steps. Refractory metals can be molded and formed into wire, bars, ingots, sheets or foil.

Tin Alloy

Tin is one of the earliest metals discovered by human being. Tin is known for a low-melting point (450°F) and its fluidity. It's very easy to form tin alloy with other metals because of its softness and formability. The metal has a high boiling point and is nontoxic and solderable. The difference of temperature between melting and boiling points, which is important for castings, is greater than all other metals.



Different casting methods used for tin alloy casting are gravity die casting, pressure die casting, and centrifugal casting. As there is little or no shrinkage occurs on solidification, components produced by tin-alloy castings are sound and dimensionally accurate. The design of molds should be such that sufficient amount of metal is fed to inside corners of the mold cavity. Carbon-steel or rubber molds can be used as tin alloys have low-melting points.

Though, little bit expensive, tin is considered to be the perfect metal for casting. As the melting temperature is fairly low, simple molds, even molds made of special rubber can be used. Unlike lead, tin is non-toxic and it's shiny and doesn't tarnish.

Zinc Alloy

Zinc alloys are nonferrous alloys and most commonly used in the manufacturing of die cast components. These components are produced with various compositions and grades. Zinc alloy components come with different shapes, dimensions, and features. There are very less amount of alloying elements in commercially pure, very low alloy or unalloyed zinc. Commercially, these (pure or unalloyed) zinc are used to galvanize metals and for other non-structural applications. Galvanizing iron to make it corrosion resistance is one classic example of this kind of use.

Dimensions and production processes are two things that should be analyzed properly before selecting zinc and zinc alloys.