Casting is the manufacturing way to form metal parts by using all kinds of casting processes. In casting, meIted metal will be pouring or injected into the prepared mold. Then solidified into solid metal shape while cooling under room temperature, finally sand or shot blasted to net shape product.
History of Casting
The melting ovens of the early Iron Age can partly be traced back to ceramic burning ovens. The model and mould building was mastered very well from the beginning. Lost moulds made of loam and clay, wax models, single piece-work as well as permanent moulds made of stone and metal for the serial production of casting parts were already used. The production of hollow spaces by using cores, has already been proved by the oldest casting parts discovered.
After the great performances in the field of casting during antiquity, it took a long time to match the former level in the occidental Middle Ages. However, whereas there is hardly any continuous documentation about casting technology during the antiquity, the German monk Thophilus already examined the forming and casting very intensively around 1140. The “fireworks books”–especially the book by Italian Biringuccio – were written after 1500 AD should also be mentioned in this context. Loam, plaster and wax were the most important working materials. Crucible and later flame ovens were available for the melting of copper, tin and lead alloys. Casting by means of forming sand was common for small parts; permanent moulds were of great importance for the serial casting of lead and tin materials. In the beginning, the casting of bells and other clerical equipment was the main focus. Relief casting matched the artistic quality of the antique casting at the beginning of modern times.
The China casting had mastered the melting of iron since 500 BC, 2.000 years before the Europeans. New excavations proved that they succeeded in the mass production of cast tools and farm equipment after the development of iron casting.
From the early beginning to present day, casting has been used to create lots of metal components for all industries.
Types of Casting
Modern casting has become a cost-effective metalworking method to produce metal components in cast steel, cast iron and cast aluminum, ect. Here, we would like to introduce the common casting methods according to different cast metals.
Types of Casting for Steel
Investment Casting, also know as precision casting, type of casting using an expendable pattern of wax, which is “invested” or surrounded by a molding medium in slurry or liquid form. After the molding medium has solidified, the pattern is removed by subjecting the mold to heat, leaving a cavity for reception of molten metal.
Water glass casting is the investment casting process to produce small and medium type carbon and alloy steel castings with smooth surface and tight tolerances. It is the cheapest casting method to produce precision steel castings.
Silica sol casting is the other investment casting process which is open to all types of precision steel castings, but more widely used to produce stainless steel castings. Compared with water glass investment casting, the cost is much higher, but better surface finish and dimension accuracy.
In conclusion, for steel castings weighting less than 60kg, investment casting is the right solution.
For large steel castings, sand casting is used.
Types of Casting for Iron
There are also two types of casting processes to produce iron castings. Well known casting type to produce iron castings is sand casting.
Sand casting, also known as sand molded casting, is the casting process that uses sand as the mold material. Molds made of sand are relatively cheap, and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mold cavities and gate system are created by compacting the sand around models called patterns, by carving directly into the sand.
Sand casting is available to produce all types of iron castings. More often made iron castings by sand castings are grey iron castings and ductile iron castings.
Types of Casting for Aluminum
Aluminum is one of the popular metals to be applied in different industies for its light weight. Even if casting, there also contains several types: High pressure die casting and gravity casting.
High temperature die casting is the casting method that produce aluminum and zinc alloys by injecting liquid metals into molds under high temperature. Common aluminum alloys produced in die casting method are: A356, A380 and ADC-12. Due to the high cost of die casting molds, it is more cost effective for large production runs. Die casting is the ideal casting process for aluminum castings in thin wall thickness.
Gravity casting is another casting type to make thick aluminum castings. Compared with aluminum die casting method, the surface will be rougher, but lower cost. And machining is usually operated when there is a high requirement on dimensional accuracy and surface roughness.
Casting Quality
Mainly includes the surface quality, internal quality. Surface quality refers to the casting surface roughness, surface defect, size deviation, deviation of shape, and weight deviation. Inner quality mainly refers to the chemical composition, physical properties, mechanical properties of castings, inner casting defects like sand hole, gas hole, crack, inclusion, segregation, and so on.
Casting quality has a great influence on the performance of mechanical products.For example, the wear resistance and dimensional stability of machine tool castings, directly affect the precision of the machine tool to keep life; The size accuracy and surafce roughness of all kinds of pump impellers, housings and other cast components shell, directly affect the working efficiency of the pump and the hydraulic system; The strength and heat shock resistance of internal combustion engine cylinder block, cylinder head, cylinder liner directly affect the working life of the engine.
There are many factors affecting the quality of castings. The first is the design of the casting component. During design, in addition to the working condition and the metal material performance, designer should also consider the design from the characteristic of casting process and casting alloys, in order to avoid or reduce the casting composition segregation, deformation, cracking and other defects. The second is reasonable casting process. Namely select a casting type according to the structure, weight and dimensions. The third is the quality of materials used in casting process. Refractory materials, sand binder, and the quality of coating materials will also have an effect on the casting quality. Fourth is process operations, foundries need to control casting quality by making reasonable operation procedures and improving the technical level of workers.
Quality Inspection of Castings
Casting testing mainly includes dimensional inspection, the appearance and visual inspection, chemical composition analysis and mechanical property test. For some important castings with strict requirement, we still need to conduct nondestructive testing.
Surface Inspection
Liquid penetrant testing
Liquid penetrant testing is used to check the various open defects of casting surface, such as surface crack, surface pinhole, which are difficult tested by the naked eye. Commonly used penetrant testing is shading detection, which sprays high permeability colored liquid on the casting surface, penetrating into the open defects, then quick wipes surface infiltration liquid layer, and then spray imaging agent on the surface. Finally it can reflect the shape, size and distribution of defects. It should be pointed out that, the accuracy of the penetrant testing will get decreased with the increasing surface roughness of checked castings.
Magnetic particle testing
Magnetic particle testing is suitable for detecting defects in surface defects and below the surface. It requires direct magnetization equipment and magnetic powder (or magnetic suspension) to conduct the detection operation. Magnetizing equipment is used to produce magnetic field around castings. Magnetic powder or magnetic suspension is used display defects on the surface of
castings.
Inner Inspection
For internal defects, the commonly used nondestructive testing methods are ray detection and ultrasonic testing. The effect of ray detection effect is the best, it can reflect the type, shape, size and distribution of internal defects. But large castings with large thickness, ultrasonic testing is more effective. It can measure the position, equivalent size and distribution of the internal defects more accurately.
After inspection of castings, we can divide castings to three levels: qualified castings, repaired casting and scrapped castings.
Qualified castings are the castings whose surface and inner quality shall meet the requirements of the relevant standards or the technical conditions of delivery and acceptance.
Repaired castings refer to the castings whose appearance quality and internal quality not fully conform to the standard and acceptance conditions, but are allowed to be repaired to meet the standard and casting acceptance technical requirements.
Scrapped castings refer to castings whose surface quality and internal quality are not qualified, also are not allowed to repair.
Advantages & Disadvantages of Casting
Advantages of Casting:
- Casting is the process that molten metal flows into mold to form desired shape. Hence any complex shape can be easily produced.
- Practically any material can be casted.
- Ideal method is by producing small quantities
- Due to small cooling rate from all directions, the properties of casting are same in all directions.
- Any size of casting can be produced up to 200 tons.
- Casting is the often cheapest and most direct way of producing a shape with certain desired mechanical properties.
- Certain metals and alloys such as highly creep resistant metal-based alloys for gas turbines cannot be worked mechanically and can be cast only.
- Heavy equipment like machine leads, ship’s propeller, etc. can be thrown easily in the required size rather than fabricating them by joining several small pieces.
- Casting is best suited for composite components requiring different properties in various direction. These are made by incorporating preferable inserts in a casting. For example, aluminum conductors into slots in iron armature for electric motors, wear resistant skins onto shock resistant components.
Disadvantages of Casting:
- Defects are unavoidable.
- When there is a high requirement on strength, forging is more reliable, see more on casting vs forging…
Applications of Castings
Castings are used virtually every where. The transport sector and heavy equipment is the predominant consumer (for farming, construction and mining) taking up over 50% of castings produced.
A sector wise casting consumption is given below which highlights the importance of casting in any industrial set up.
- Transport: Automobile, aerospace, railways and shipping
- Heavy Equipment: Construction, farming and mining
- Machine Tools: Machining, casting, plastics molding, forging, extrusion and forming
- Plant Machinery: Chemical, petroleum, paper, sugar, textile, steel and thermal plants
- Defence: Vehicles, artillery, munitions, storage and supporting equipment
- Electrical Equipment Machines: Motors, generators, pumps and compressors
- Hardware: Plumbing industry pipes, joints, valves and fittings
- Household: Appliances, kitchen and gardening equipment, furniture and fittings
- Art Objects: Sculptures, idols, furniture, lamp stands and decorative items
CFS foundry is the casting foundry in China, we can supply all types of castings to companies from America, Canada, UK, Australia, etc. Request a free inquiry? Contact us now!