High pressure and high speed filling die casting mold is the two main characteristics of die casting. It is commonly used compression injection pressure is from thousands to tens of thousands of kPa, and even up to 2 × 105kPa. filling speed of about 10 ~ 50m / s, and some times even up to 100m / s or more. The filling time is very short, generally within the range of 0.01~0.2s.
Casting dimensional accuracy is high, generally equivalent to 6 ~ 7, and even up to level 4; surface finish is good, generally equivalent to die casting workshop
in 5 ~ 8; strength and hardness is high, strength is generally higher than the sand casting 25 ~ 30%, but elongation decreased by about 70%; dimensional stability, interchangeability is good; die-casting thin-walled complex castings. For example, the current zinc alloy die casting minimum wall thickness of up to 0.3mm; aluminum alloy castings up to 0.5mm; the minimum casting hole diameter of 0.7m die casting although there are many advantages, but there are some shortcomings, yet to be resolved. Such as: 1). Die casting due to the liquid metal filling cavity speed is high, the flow state is not stable, so the use of general die-casting method, castings are easy to produce porosity, can not be heat treatment; 2). Complex castings of concave, die casting is more difficult; 3). High melting point alloys (such as copper, ferrous metals), die casting type life is low; 4). Not suitable for small batch production, the main reason is the high cost of manufacturing die casting, die casting machine production efficiency, small batch production is not economical. 2, die casting application scope and development trend die casting is one of the most advanced metal molding method, is to realize less chips, no chips effective way, application is very wide, development is very fast. At present, the die-casting alloy is no longer limited to non-ferrous metals of zinc, aluminum, magnesium and copper, and also gradually expand to die-casting cast iron and cast steel parts. Die casting size and weight, depends on the power of the die-casting machine. As the power of the die-casting machine is increasing, the casting shape size can be from a few millimeters to 1 ~ 2m; Weight can be from a few grams to dozens of kilograms. Foreign countries can die-casting diameter of 2m, weight of 50kg aluminum castings. Die casting is no longer limited to the automobile industry and instrumentation industry, gradually expanding to other industrial sectors, such as agricultural machinery, machine tool industry, electronics industry, national defense industry, computers, medical equipment, clocks and watches, cameras and daily-use hardware and so on dozens of industries. In the die-casting technology and the emergence of vacuum die-casting, oxygen die-casting, fine speed dense die-casting and the application of soluble core and other new technology.
Edit this paragraph die casting machine
Types of die casting machine
Die casting machine is generally divided into two major categories of hot pressure chamber die casting machine and cold pressure chamber die casting machine. Cold compression chamber die casting machine according to its compression chamber structure and arrangement is divided into horizontal die casting machine and vertical die casting machine (including full vertical die casting machine) two kinds. Hot compression chamber die casting machine (referred to as hot air die casting machine) pressure room immersed in the heat preservation melting crucible liquid metal, injection parts are not directly connected with the base, but installed in the crucible above. The advantages of this kind of die-casting machine is the production process is simple, high efficiency; Metal consumption is less, process stability. But the pressure room, ejection punch long-term immersion in liquid metal, affecting the service life. And easy to increase the iron content of the alloy. Hot compression chamber die casting machine is mostly used for die casting zinc alloy and other low melting point alloy castings, but also used for die casting small aluminum, magnesium alloy die casting. Cold room die casting machine pressure room and heat preservation furnace is separate. Die casting, from the holding furnace to take out the liquid metal poured into the pressure chamber after die casting.
Die casting machine selection
Actual production is not every die-casting machine can meet the needs of die-casting a variety of products, and must be selected according to the specific circumstances, generally should be considered from the following two aspects: (1) according to the different varieties and batch selection in the organization of many varieties, small batch production, generally want to choose the hydraulic system is simple, adaptable, and can be quickly adjusted to the die-casting machine. In the organization of few varieties of mass production, to choose to be equipped with a variety of mechanization and automation control institutions of high efficiency die-casting machine; for a single variety of mass production of castings can choose special die-casting machine. (2) according to the casting structure and process parameters selection casting shape inch, weight, wall thickness and other parameters on the selection of die-casting machine has an important impact. Castings weight (including pouring system and overflow tank) should not exceed the rated capacity of the die-casting machine pressure set, but not too small, so as not to cause the waste of die-casting machine power string. General rated capacity of the die-casting machine can check the manual. Die-casting machine have a certain maximum and minimum distance, so the thickness of the pressure type and casting height to have a certain limit, if the thickness of the pressure casting type or casting height is too big may not be able to take the casting.
Edit paragraph die casting process
In the die casting production, die casting machine, die casting alloy and die casting type is three big elements. Die casting process is the three elements for the right combination and use the process. Make all kinds of process parameters to meet the needs of die casting production.
Pressure and speed selection
The selection of the pressure of the injection ratio should be determined according to different alloys and casting structure characteristics. The choice of filling speed, generally for thick-walled or internal quality requirements of high castings, should choose lower filling speed and high pressure boosting; For thin-walled or surface quality requirements of high castings and complex castings, should choose higher than the calendar and high filling speed.
Pouring temperature
Pouring temperature refers to the average temperature of the liquid metal from the pressure set into the cavity, due to the pressure chamber of the liquid metal temperature measurement is inconvenient, generally use the temperature inside the holding furnace. Pouring temperature is too high, shrinkage, so that the casting is prone to cracks, grain size, but also can cause sticking type; pouring source is too low, easy to produce cold segregation, surface pattern and pouring defects such as insufficient. Therefore, the pouring temperature should be considered at the same time with the pressure, pressure casting temperature and filling speed.
The temperature of the die-casting mold
The casting mold should be preheated to a certain temperature before use, usually with gas, torch, electrical or induction heating. In continuous production, die casting temperature tends to rise, especially die casting high melting point alloy, rise very quickly. The temperature is too high in addition to make the liquid metal produce sticky type, casting cooling slow, make grain coarseness. Therefore, in the die casting temperature is too high, should take period cooling measures. Usually with compressed air, water or chemical medium for cooling.
Filling, holding pressure and open time
1) filling time since the liquid metal began to enter the cavity to fill the cavity stop, the time required is called filling time. Filling time depends on the size and complexity of the volume of the casting. For large and simple castings, the filling time should be relatively long, and for complex and thin-walled castings, the filling time should be shorter. Filling time is closely related to the cross-section area size of the inner gate or the width and thickness of the inner gate, and must be determined correctly. (2) Holding pressure and open time from the liquid metal filling cavity to the inner gate completely solidified, continue to be under the action of the compression injection punch duration, known as holding pressure time. The length of holding time depends on the material and wall thickness of the casting. After holding pressure should be opened to remove the casting. From the end of the ejection to die casting open time, known as the open time, open time should be controlled accurately. Open time is too short, due to the alloy strength is still low, may be in the casting top out and from the die casting fall caused by deformation; But open time is too long, the casting temperature is too low, shrinkage is big, on the core and top out of the casting resistance is also big. General open time according to the casting wall thickness of 1 mm need 3 seconds to calculate, and then adjusted by the test of any.
Die casting paint
Die casting process, in order to avoid casting and die casting mold welding, reduce the casting top out of the friction resistance and to avoid the die casting mold excessive heat and the use of paint. Requirements for the coating: 1) in high temperature, has good lubricity; 2) low volatility point, in 100 ~ 150 ℃, the diluent can be quickly evaporated; 3) no corrosive effect on the die casting mold and die casting; 4) stable performance in the air diluent should not be volatilized over the decision to thickening; 5) at high temperatures will not precipitate harmful gases; 6) will not be produced in the die casting cavity surface scale accumulation.
Castings cleanup
Castings cleanup is very heavy work, its workload is often die casting workload of 10 to 15 times. Therefore, with the die-casting machine productivity, the increase in production, casting cleanup work to achieve mechanization and automation is very important. (1) cut off the sprues and fly edge cut off the sprues and fly edge used equipment is mainly punch, hydraulic machine and friction press, in a large number of production pieces, according to the casting structure and shape of the design of special molds, in the punch to complete the cleanup task at a time. (2) surface cleaning and polishing surface cleaning using ordinary multi-angle roller and vibration buried cleaning device. For the batch is not big simple small pieces, can be used to clean up the angle of the roller, the surface requirements of high decorative items, can be used to cloth or leather polishing wheel polishing. For mass production of castings can be used screw shell type vibration cleaning machine. Cleaned castings in accordance with the requirements of use, but also surface treatment and impregnation to increase the luster, prevent corrosion, improve airtightness. m; Minimum pitch of 0.75mm.