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Die Casting Process defination and application
Die-casting process is the use of the three elements of machines, molds and alloys, pressure, speed and time of the process of reunification.
Pressure casting is a special casting method in modern metal processing technology developed rapidly in a small non-cutting. It is the process of molten metal at high speed under high pressure mold filling, solidification and formed at high pressure casting. High-speed high-pressure casting pressure is the main feature. Commonly several tens of MPa pressure, filled velocity (ingate speed) of 16 to 80 m / s, the liquid metal filling the mold cavity is very short, about 0.01 to 0.2 seconds.
Since the products produced by this method has a high production efficiency, simple process, high grade casting tolerance, good surface roughness, high mechanical strength, can save a lot of machining processes and equipment, conservation of raw materials, etc., it has become the foundry industry in China is an important part.
Die-casting process is the three elements of die casting machine, die casting mold and alloy combinations to be organically integrated use of the process. The die-cast metal process by filling the cavity is pressure, speed, temperature, and time and other process factors to obtain a uniform procedure. At the same time, these processes and factors that influence each other, mutual restraint, and complement each other. Proper selection and adjustment of these factors make it coherent, in order to obtain the desired results. Therefore, in the die casting process not only pay attention to the process of casting structure, die-casting mold progressiveness, die-casting machine performance and excellent structural resistance, adaptability and die-casting alloy smelting process chosen normative; should pay attention to the pressure, temperature and time and other parameters important role casting quality. In the die casting process should focus on effective control of these parameters

Edit pressure
For pressure die casting process are the main features distinguish other casting methods.
Injection force

Injection force is a die-casting machine injection mechanism pushing force of the piston motion shot. It is a reflection of die casting machine features
One of the main parameters.
Shot size of the force by the pressure sleeve and the cross-sectional area of ​​the working fluid is determined injection pressure is calculated as follows:
P = P injection pressure injection cylinder × π × D2 / 4
Where: P injection pressure - injection pressure (N- cow)
P cylinder injection - the injection pressure of the working fluid within the cylinder (Pa- Pa)
D- injection cylinder diameter (m- m)
π = 3.1416
Specific pressure

Indoor molten metal pressure in the unit area called the pressure on specific pressure. Injection pressure than the pressure and also pressure chamber
The ratio in terms of the relationship between the results of cross-sectional area is calculated as follows:
Than the pressure P = P injection pressure / F-pressure chamber cross-sectional area
Where: P ratio of pressure - pressure ratio (Pa- Pa)
P injection pressure - injection pressure (N- cow)
F-pressure chamber cross-sectional area - sectional area of ​​the pressure chamber (m2- m 2)
That is the cross-sectional area of ​​the pressure chamber F = πD2 / 4 where D (m- m) diameter of the pressure chamber
π = 3.1416
The effect of pressure

Effect of (1) specific pressure on the mechanical properties of castings
Than the pressure increases, fine crystal, fine-grained layer thickness, due to improved fill characteristics, improve the surface quality, porosity
Mitigate the impact, thereby improving the tensile strength, but the elongation decreased.
(2) the impact of filling conditions
Alloy melt under high pressure effect than to fill the cavity, the alloy temperature, improved liquidity, beneficial casting
Improve the quality of parts.
Than the pressure of selection

(1) according to the strength of the casting consider requesting
Casting will be divided into two types of strength requirements and general requirements, for there is strength requirements, should have
Good density. This should be high pressure ratio compression.
(2) According to the thickness of the casting considerations
In general, when casting thin-walled castings, a larger flow resistance in the cavity, the gate also uses a smaller thickness, thus having a large resistance, so that there must be larger than the filling pressure, in order to guarantee the achievement of required . ingate speed for thick-walled castings, on the one hand a lower ingate selected speed, and longer solidification time for the metal, allowing smaller than the filling pressure; the other hand, in order to make the casting has a certain density, also need to have
Boost pressure than enough to meet the requirements for complex shape castings, fill higher than the pressure should be used. Further, as the alloy category, size ingate speed die casting machine power capacity and mold strength should be properly taken into account. filling pressure than the size calculated according to the selected main ingate speed. as supercharging pressure than the size of the alloy according to the category, refer to the following value selection table when the exhaust cavity under favorable conditions, the ratio of the thickness of the gate with the appropriate thickness of the casting, the choice of a low pressure ratio pressure, while exhaust conditions worse, the thickness of the gate and the casting wall thickness of more hours, the pressure ratio pressure should be higher.
Boost pressure than the recommended use range table
Part Type Aluminum zinc alloy brass
Bear the light load parts 30 ~ 40MPa 13 ~ 20MPa 30 ~ 40MPa
Bear a greater load of parts 40 ~ 80MPa 20 ~ 30MPa 40 ~ 60MPa
Airtight surface of the large thin wall parts 80 ~ 120MPa25 ~ 40MPa 80 ~ 100MPa
Forces associated editor
definition

Die-casting process, and the end of the filling into pressurized stage, acting on the solidifying metal than the pressure (supercharging pressure ratio), passing through a metal wall cavity (casting gating system, overflow discharge system), said the pressure expansion of the type of force (also known as anti-stress).
Clamping force (ie clamping force) is an important parameter when first selected die casting machine to be determined.
Calculation Method

When the expansion-type force is exerted on the parting, it is parting surface expansion-type force, acting upon the respective side walls of the cavity, it is called a side type expansion force expansion-type force
It can be expressed as:
P-type expansion than the pressure force = P × A projected area
Where: P-type expansion force expansion represents the type of force (unit: N- cow)
P represents the pressure ratio supercharging pressure (Unit: Pa- Pa)
A represents the projected area subjected to expansion-type force projection area (m 2 unit m2-)
Clamping force must be greater than the calculated expansion-type force normally. Otherwise, when the hydraulic metal shot, mold parting surface will swell to open, resulting splatter, and the pressure in the cavity can not be established, resulting in casting dimensional tolerances difficult to guarantee, even difficult to mold.
Clamping force shall meet the requirements of the following general formula:
P clamping force ≥ K × P-type expansion force
Where: P clamping force - die casting machine clamping force (N- cow)
K- safety factor (usually take K = 1.3)
P-type force expansion - expansion-type force (N- cow)
Injection speed editing
1, generally at a rate of speed of two punches and the gate, 2), the slow speed of injection of molten metal punch to push the gate 0.3 m / s, 3), the gate quickly fill the cavity 4- 9 m / s, fast action shot of influence, improve injection speed, functionality into heat energy, mobility, and help eliminate the flow marks, cold shuts and other defects, to improve the mechanical properties and surface quality Jane, injection speed options Optional and considerations:
1) thermal conductivity and specific heat of a solidification temperature range.
2) low-speed or low mold temperature, high speed and vice versa.
3) complex castings using high-pressure injection speed.
Ingate speed 15-70 m / s, (liquid metal) 4, punch injection speed and the speed of the gate of the relationship:
Austrian radio ram pressure higher speed, the higher the speed of the liquid metal orally.
Speed ​​Select Edit
1, sprue 15-25 m / s,
2, runner 20-35 m / s, in the pouring reputation contained Road 30 large 70 m / s, 3 mm so as not to cast a thin selection ingate speed 38-46 m / s, within 5 mm thick casting poured selection port speed 46-40 m / s, more than 5 mm thick casting choice ingate speed 47-27 mm / sec, the whole regulator method: regulators entire injection plunger speed, replace the pressure chamber diameter, inner gate change cross-sectional area,
Determination and Analysis editor
1, die-casting parameters tester, primary, secondary and boost conversion point in time,
2, pressure die-casting quality start on:
After the initial filling level 80%, for the second time and boost starting point conversion, and finally holding pressure, otherwise it will affect the quality.
3, injection plunger wear blocked shot on poor die-casting parameters;
4, injection chamber and the punch wear causal analysis:
With the degree of the injection chamber and punch a gap of less than 0.1 mm, the punch and the pressure chamber back and forth wearing high temperature generated by friction, pressure chamber larger diameter, smaller punch, punch aluminum shavings stuck impact pressure chamber to pass speed and pressure and refuses to accept the force to punch so you want to use high-temperature lubricants, plunger will open cooling water, but also to choose the punch material, generally used in ductile iron or bronze, etc..

 

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