Dynamic Diagram of Various Casting Processes

2019-12-12

What is casting?

Liquid metal is poured into the mold cavity corresponding to the shape and size of the part, and then it is cooled and solidified to obtain the production method of blank or part, which is usually called liquid metal forming or casting.
Casting is a kind of metal hot working technology which has been mastered by human beings for about 6000 years. China has entered the heyday of bronze casting from about 1700 BC to 1000 BC, and its technology has reached a quite high level. Casting is a method of casting liquid metal into a casting cavity which is suitable for the shape of the part. After it is cooled and solidified, the part or blank can be obtained. Most of the cast materials are originally solid but heated to liquid metal (e.g. copper, iron, aluminum, tin, lead, etc.), while the materials of the mold can be sand, metal or even ceramics. According to different requirements, different methods will be used.

Process flow: liquid metal → filling → solidification shrinkage → casting

Process characteristics:

1. It can produce any complex parts, especially the parts with complex inner cavity shape.
2. It has strong adaptability, unlimited alloy types and almost unlimited casting size.
3. The material source is wide, the waste products can be remelted, and the equipment investment is low.
4. High scrap rate, low surface quality and poor working conditions.

With the development of science and technology and the vigorous development of foundry industry, different foundry methods have different mold preparation contents. Taking the most widely used sand casting as an example, mold preparation includes two major tasks: molding material preparation, molding and core making. In sand casting, all kinds of raw materials used for molding and core making, such as casting raw sand, molding sand binder and other auxiliary materials, as well as molding sand, core sand and coating prepared from them, are collectively referred to as molding materials. The task of preparing molding materials is to select appropriate raw sand, binder and auxiliary materials according to the requirements of castings and the properties of metals, and then mix them into tools according to a certain proportion Molding sand and core sand with certain properties. The commonly used sand mixing equipment includes wheel mixer, counter current mixer and continuous mixer. The latter is specially designed for mixing chemical self hardening sand, which is continuously mixed and has high mixing speed.
Molding and core making are carried out on the basis of determining the molding method and preparing the molding materials according to the casting process requirements. The accuracy of castings and the economic effect of the whole production process mainly depend on this process. In many modern casting workshops, the molding and core making are mechanized or automated. The commonly used sand molding and core making equipment includes high, medium and low pressure molding machine, air impact molding machine, non box injection molding machine, cold box core making machine, hot box core making machine, film coated sand core making machine, etc.
After the casting is taken out from the casting mold cooled by pouring, there are gates, risers, metal burrs and draping seams. The casting of sand casting also adheres to sand, so it must go through the cleaning process. The equipment for this kind of work includes polishing machine, shot blasting machine, pouring and riser cutting machine, etc. Sand casting cleaning is a process with poor working conditions, so when choosing the molding method, we should try to create convenient conditions for sand cleaning. Some castings need to be treated after casting due to special requirements, such as heat treatment, reshaping, antirust treatment, rough machining, etc.
The casting process can be divided into three basic parts: the preparation of casting metal, the preparation of casting mold and the treatment of casting. Cast metal refers to the metal material used for casting in casting production. It is an alloy composed of a metal element as the main component and other metal or non-metal elements. It is commonly known as cast alloy, mainly including cast iron, cast steel and cast non-ferrous alloy.
After the casting is taken out from the casting mold cooled by pouring, there are gates, risers and metal burrs. The casting of sand casting also adheres to sand, so it must go through the cleaning process. The equipment for this kind of work includes shot blasting machine, gate riser cutting machine, etc. Sand casting cleaning is a process with poor working conditions, so when choosing the molding method, we should try to create convenient conditions for sand cleaning. Some castings need to be treated after casting due to special requirements, such as heat treatment, reshaping, antirust treatment, rough machining, etc.
Casting is a relatively economic method of blank forming, which can show its economy for the parts with complex shape. Such as the cylinder block and cylinder head of automobile engine, ship propeller and exquisite works of art. Some parts that are difficult to cut, such as nickel base alloy parts of gas turbine, cannot be formed without casting.
In addition, the size and weight of casting parts are widely used, and the metal types are almost unlimited; while the parts have general mechanical properties, they also have comprehensive properties such as wear resistance, corrosion resistance, shock absorption, etc., which other metal forming methods such as forging, rolling, welding, punching, etc. cannot do. Therefore, in the machine manufacturing industry, the number and tonnage of rough parts produced by casting method is still the largest.
The materials often used in foundry production include various metals, coke, wood, plastics, gas and liquid fuels, molding materials, etc. The required equipment includes various furnaces for smelting metal, various sand mixers for sand mixing, various molding machines and core making machines for molding and core making, sand dropping machines and shot blasting machines for cleaning castings, etc. There are also machines and equipment for special casting as well as many transportation and material handling equipment.
Casting production has different characteristics from other processes, such as wide adaptability, more materials and equipment, and environmental pollution. Foundry production will produce dust, harmful gas and noise pollution to the environment, which is more serious than other mechanical manufacturing processes, and measures need to be taken to control.
The development trend of casting products requires better comprehensive properties, higher precision, less allowance and cleaner surface. In addition, the demand for energy conservation and the demand of society for the restoration of the natural environment are also growing. In order to meet these requirements, new cast alloys will be developed, and new smelting processes and equipment will appear accordingly.
At the same time, the degree of mechanization and automation of foundry production is increasing, and it will develop to flexible production, so as to expand the adaptability to different batches and varieties of production. New technologies for saving energy and raw materials will be given priority, and new processes and equipment with little or no pollution will be given priority. The quality control technology will have a new development in the detection, nondestructive testing and stress measurement of each process.

Types of casting:

Die casting
Sand mold casting
Investment casting
Die forging
Die cutting
Die cutting process – cutter die
Forging
Rolling
Pressure casting
Low pressure casting
Centrifugal casting
Lost foam casting
Squeeze casting
Continuous casting
Drawing
Stamping
Metal Injection Molding
Turning process
Milling process
Planing
Grinding process
Selective laser melting
Selective laser sintering
Metal deposition
Roll forming

Die casting (note that die casting is not the abbreviation of pressure casting)

It is a kind of metal casting process, which is characterized by applying high pressure to molten metal by using mold cavity. The mold is usually made of alloy with higher strength. This process is similar to injection molding

Sand mold casting

It’s making molds out of sand. In sand mold casting, the finished part model or wooden model (pattern) shall be put into the sand, and then the sand shall be filled at the end of the pattern. After the pattern is taken out of the box, the sand shall form the mold.
In order to take out the mold before casting metal, the mold should be made into two or more parts; in the mold making process, the holes for casting metal into the mold and the vent holes must be reserved to synthesize the pouring system.
After pouring the metal liquid into the mold, keep it for a proper time until the metal solidifies. After taking out the parts, the mold is destroyed, so a new mold must be made for each casting.

Investment casting

It is also called lost wax casting, including pressing wax, repairing wax, tree assembly, sizing, melting wax, casting liquid metal and post-treatment. Lost wax casting is to use wax to make the wax mold of the parts to be cast, and then the wax mold is coated with mud, which is the mud mold. After the clay mould is dried, it is roasted into a pottery mould.
Once roasted, all the wax molds melted and lost, leaving only pottery molds. Generally, the casting port is left when making the mud mold, and then the molten metal is poured into the pouring port. After cooling, the required parts are made.

Die forging

It is a forging method of forging by using die to form blank on special forging equipment. According to different equipment, die forging can be divided into hammer forging, crank press forging, flat forging, friction press forging, etc.

Die cutting

That is to say, the blanking process is to locate the film formed in the former process on the die, close the die to remove the redundant materials, retain the 3D shape of the product, and match with the die cavity.

Die cutting process – cutter die

The cutting process of knife die is to locate the membrane panel or line on the bottom plate, fix the knife die on the machine template, and use the force provided by the machine to control the blade to cut off the material. What distinguishes him from the punching die is that the incision is smoother; at the same time, by adjusting the cutting pressure and depth, the indentation, half break and other effects can be punched out. At the same time, the low cost operation of the mold is more convenient, safe and fast.

Forging

It is a kind of processing method that uses forging machine to exert pressure on metal blank to produce plastic deformation to obtain forgings with certain mechanical properties, certain shape and size. It is one of the two parts of forging (forging and stamping).
Through forging, the defects of loose as cast metal produced in smelting process can be eliminated, and the microstructure can be optimized. At the same time, the mechanical properties of forgings are generally better than those of castings of the same material because of the intact metal streamline.
For the important parts with high load and severe working conditions in the related machinery, except for the simple shape of rolled plates, profiles or weldments, forgings are often used.

Rolling

Also known as calendering, refers to the process of shaping the metal ingot through a pair of rollers. If the temperature of the metal during rolling exceeds its recrystallization temperature, this process is called “hot rolling”, otherwise it is called “cold rolling“. Calendering is the most commonly used means in metal processing.

Pressure casting

The essence of the method is to make liquid or semi liquid metal fill the cavity of the die casting mold (die casting mold) at a higher speed under the action of high pressure, and then mold and solidify under pressure to obtain the casting.

Low pressure casting

A casting process in which liquid metal is filled and solidified into a casting under the action of low pressure gas. Low pressure casting was mainly used in the production of aluminum alloy castings at first, and then expanded its application to produce copper castings, iron castings and steel castings with high melting point.

Centrifugal casting

It is a technology and method that liquid metal is injected into a high-speed rotating mold to fill the mold and form the casting under the action of centrifugal force. According to the shape, size and production batch of castings, the mold used in centrifugal casting can be non-metallic mold (such as sand mold, shell mold or investment mold shell mold), metal mold or mold with coating layer or resin sand layer in the metal mold.

Lost foam casting

It is a combination of paraffin or foam models that are similar to the size and shape of the casting to form a model cluster. The fire-resistant coating is then painted and dried and embedded in the dry quartz sand for vibration modeling. Under the negative pressure, the model is vaporized, the liquid metal occupies the model position, and the new casting method is formed after solidification and cooling.
Lost Foam Casting (EPC) is a new technology of near no allowance and precise molding. It does not need to take mold, no parting surface and no sand core, so there is no flash, burr and draft angle in the casting, and the size error caused by core combination is reduced.

Squeeze casting

It is also called liquid die forging, which makes molten metal or semi-solid alloy directly injected into the open die, then closes the die to generate filling flow, reaches the external shape of the part, and then applies high pressure,
To make the solidified metal (shell) produce plastic deformation, while the non solidified metal bears isostatic pressure, while high-pressure solidification occurs, and finally obtain the workpiece or blank. The above is direct squeeze casting;
Indirect squeeze casting is a method of injecting molten metal or semi-solid alloy into a closed mold cavity through a punch, applying high pressure to make it crystallize and solidify under pressure, and finally obtaining a workpiece or blank.

Continuous casting

It is a casting method that the liquid metal is continuously poured into one end of a through mold and the molding material is continuously pulled out from the other end.

Drawing

It is a kind of plastic processing method that the metal blank is pulled out from the die hole which is smaller than the section of the blank by the external force acting on the front end of the metal to obtain the corresponding shape and size of the product. Because drawing is usually carried out in cold state, it is also called cold drawing.

Stamping

It is a forming processing method that presses and dies exert external forces on plates, strips, pipes and profiles to produce plastic deformation or separation, so as to obtain the required shape and size of workpieces (stamping parts).

Metal Injection Molding

Metal injection molding (MIM) is a new type of near net powder metallurgy forming technology extended from the plastic injection molding industry. As we all know, plastic injection molding technology can produce all kinds of complex shape products at low price, but the strength of plastic products is not high. In order to improve its performance, metal or ceramic powder can be added to plastic to obtain high strength and wear resistance Good products.
In recent years, the idea has evolved to maximize the content of solid particles and to completely remove the binder and densify the preform during the subsequent sintering process. This new powder metallurgy forming method is called metal injection molding.

Turning process

It means that lathe processing is a part of machining. Lathe machining mainly uses turning tools to turn the rotating workpiece. The lathe is mainly used for processing shafts, discs, sets and other workpieces with rotating surfaces. It is the most widely used machine tool in machinery manufacturing and repair factories.
Turning is a method of cutting workpiece by using workpiece rotation relative to cutter on lathe. The cutting energy of turning is mainly provided by workpiece rather than tool. Turning is the most basic and common cutting method, which plays an important role in production.
Turning is suitable for machining the rotating surface. Most of the workpieces with the rotating surface can be machined by turning methods, such as the inner and outer cylindrical surface, the inner and outer conical surface, the end face, the groove, the thread and the rotating forming surface, etc. the tools used are mainly turning tools.

Milling process

Milling is to fix the blank and use a high-speed milling cutter to cut out the required shape and features. Traditional milling is mostly used for milling simple shapes / features such as profiles and grooves. CNC milling machine can process complex shape and features.
Milling and boring machining center can be used for three-axis or multi axis milling and boring machining, for machining, mold, inspection tool, mould, thin-walled complex surface, artificial prosthesis, blade, etc. When choosing the content of NC milling, we should give full play to the advantage and key role of NC milling machine.

Planing

It is a kind of machining method that the planer is used to make the horizontal relative linear reciprocating motion of the workpiece, which is mainly used for the shape machining of parts. The precision of planing is it9 ~ it7, and the surface roughness Ra is 6.3 ~ 1.6um.

Grinding process

Grinding refers to the processing method of cutting off redundant materials on the workpiece with abrasive and abrasive tools. Grinding is one of the widely used cutting methods.

Selective laser melting

In a tank filled with metal powder, the computer controls a high-power CO2 laser to selectively sweep the metal powder surface. At the place where the laser goes, the metal powder on the surface is completely melted and combined, while the place where the laser doesn’t shine remains in the powder state. The whole process needs to be carried out in a sealed chamber filled with inert gas.

Selective laser sintering

SLS uses infrared laser as energy source, and most of the molding materials are powder materials. During processing, the powder is preheated to a temperature slightly lower than its melting point, and then the powder is leveled under the action of a scraping stick; the laser beam is selectively sintered under the control of a computer according to the information of the layered section,

After one layer is completed, the next layer is sintered, and after all sintering is completed, the surplus powder is removed, then a sintered part can be obtained. At present, the mature process materials are wax powder and plastic powder. The sintering process with metal powder or ceramic powder is still under study.

Metal deposition

It is similar to the “milking oil” type of molten deposition, but the metal powder is ejected. In addition to spraying metal powder materials, the nozzle also provides high-power laser and inert gas protection. In this way, it will not be limited by the size of the metal powder box, and can directly produce larger parts, and it is also very suitable for the repair of local damaged precision parts.

Roll forming

The roll forming method uses a group of continuous stands to roll stainless steel into complex shapes. The order of the rollers is designed so that the roll shape of each frame continuously deforms the metal until the desired final shape is obtained. If the shape of components is complex, up to 36 racks can be used, but for components with simple shape, three or four racks can be used.

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]
Please notice that you might be interested in the other technical articles we’ve published:

+86-18267732328

[email protected]

Dynamic Diagram of Various Casting Processes