Basic Theory Of Copper, Aluminum, Magnesium and Zinc Alloy Die Casting

In this guide, we cover everything about copper, aluminum, magnesium and zinc alloy die casting. 

Basic Knowledge Of Die Casting

1. What is die casting?

Pressure casting is called die casting for short. Die casting is a process in which metal liquid rapidly fills the mold cavity under pressure by using die-casting molds and machinery and equipment, and changes from liquid state to solid state to form required products.

2. What are the types of die casting?

The injection chamber is divided into hot chamber die casting and cold chamber die casting. The pressure can be divided into low-pressure casting and pressure casting. The exhaust mode can be divided into ordinary die casting and vacuum die casting.

3. What are the die casting alloy materials? What are their characteristics?

The commonly used materials suitable for die casting are: zinc alloy, aluminum alloy, magnesium alloy and copper alloy. They have the following characteristics: good fluidity in liquid state, relatively fixed melting and freezing points, small shrinkage, certain high-temperature strength, good processability and corrosion resistance.

4. What are the main components of aluminum alloy die casting? What are the impurities?

– The main ingredients are: aluminum, silicon, copper, magnesium, manganese, zinc, etc.

– Impurities include iron, zinc, copper, tin, aluminum, sulfur, phosphorus, etc.

Different alloy brands have different requirements for their main components and impurities.

5. What are the main defects of die castings?

There are undercasting, cracks, deformation, cold shut, cold lines, shrinkage, air holes (sand holes), mechanical strain, die sticking strain, delamination, mold staggering, slag inclusion, surface cavitation, blistering, fleshy, lack of meat, etc.

6. What is the temperature of aluminum alloy liquid suitable for die casting production?

650 ℃ ~720 ℃

7. What are the characteristics of die casting production?

– High production efficiency, which can realize mechanized or automated production.

– Good product quality: A. high dimensional accuracy and surface finish. B. Good mechanical properties. C. Good interchangeability. D. The contour is clear, the casting wall is thin and complex, and the pattern, pattern and text can obtain high definition.

– Good economic effect: A. excellent economic indicators. B. Low cost of die castings. C. It can be used as part assembly.

– The investment cost of die-casting equipment and molds is high, which is not suitable for small batch production.

Die Casting Machine

1. What are the main parts of the die casting machine?

The die casting machine is mainly composed of closing mechanism, injection mechanism, ejection mechanism, power (hydraulic) system, control system, lubrication system, cooling system, etc.

2. What is the tonnage of the die casting machine named after?

The tonnage of the die-casting machine is named after the maximum clamping force (clamping force). For example, the 180t die-casting machine has a maximum clamping force of 180 tons.

3. What is the function of the closing mechanism of the die casting machine?

The function of the closing mechanism is to install and fix the die casting mold and drive the opening or closing of the moving die of the die casting mold.

4. What is the nominal pressure of the hydraulic system of the die casting machine?

It is 12 MPa (or 120 kg / cm2).

5. What is the function of the injection mechanism?

The injection mechanism is a key part of the die-casting process, which enables the metal liquid to fill the mold cavity at a certain speed and pressure from the injection chamber.

6. What process parameters can be adjusted during die casting production?

– Mold thickness

– Mold closing speed

– Mold opening speed

– Mold closing time

– Slow injection speed

– Fast injection speed

– Slow injection stroke

– Fast injection stroke

– Injection pressure

– Tracking stroke

– Tracking delay

– Ejection stroke

– Ejection speed

– Ejection delay

– Cycle time

– Aluminum temperature 

– Die casting mold temperature

9. What role does the nitrogen bottle of the die casting machine play?

It plays the role of energy accumulation. When rapid injection is required, the accumulator quickly releases a large amount of hydraulic oil to accelerate the injection head. When pressurization is required, the accumulator instantly releases pressure to pressurize the injection head.

10. What is the function of the lubrication system of the die casting machine?

The lubrication system of the die casting machine is generally an independent system. It plays a key role in ensuring the normal operation and service life of the machine by setting the automatic oiling for each sliding and rotating part of the closing mechanism at a certain interval.

11. What is the function of the hydraulic system of the die casting machine and what are its main components?

It provides power for the die casting machine to complete various actions. It is mainly composed of motor, oil pump, oil cylinder, various control valves and pipelines.

12. What is the function of the cooler?

It can cool and protect the hydraulic system.

13. Why should the ejector rod and ejector head be cooled with cooling water?

Because the cooling water installed in the ejector head of the ejector rod has the following functions:

– The insulation heat is transferred from the ejector rod to the hydraulic system.

– Reduce the wear of the injection head at temperature.

– Speed up the cooling of the remaining materials to prevent the remaining materials from sticking to the injection head and blowing up due to insufficient cooling of the remaining materials.

14. What is the harm of high hydraulic oil temperature of die casting machine?

– The oil temperature is too high (more than 50 ℃) and the characteristics of the hydraulic oil are reduced, making the working pressure of the system abnormal (low).

– High oil temperature intensifies the internal leakage of oil cylinder and valve, resulting in unstable process parameters.

– High oil temperature accelerates the aging of sealing ring.

– The oil temperature is too high, which makes the hydraulic oil prone to deterioration, leakage and loss.

Die Casting Mold

1. What are the components of the die casting mold?

The structure of the die-casting mold can be divided into the following parts according to its functions:

(1) Molding part (dynamic and fixed mold core, molding insert, core pulling, etc.)

(2) Mold base part (movable and fixed mold clamping plate, AB plate, supporting plate and mold foot).

(3) Bypass system (sprue sleeve, splitter cone, runner, inlet bypass).

(4) Overflow system (overflow tank, steam exhaust tank).

(5) Ejector mechanism (ejector pin, ejector pin fixing plate, ejector plate, reset lever).

(6) Guide parts (guide post, guide sleeve, middle guide post, middle guide sleeve).

(7) Core pulling mechanism (core pulling slider, inclined guide post, clamping block, spring, etc).

(8) Others (cooling system, heating system, reinforcing column, etc).

2. What is the material of the die casting mold?

The die-casting mold shall be made of the following steels:

(1) H13 (heat-resistant steel) as front and rear mold cores, core pulling cores, sprue sleeves, shunting cones, etc).

(2) 45 # steel (as a and B plates, sliding blocks, inclined guide posts, etc).

(3) T8, T10 (guide post, guide sleeve, thimble, reset rod, etc).

(4) A3 steel (front and rear formwork clamping plate, supporting plate, thimble plate, formwork foot, etc).

3. What is the heat treatment hardness of die casting mold core? What are the consequences of being too soft and too hard?

The maximum hardness of mold core after heat treatment is hrc45 ~ 48. The treatment is too soft (lower than hrc43), and the mold core is easy to collapse, deform and stick during die casting production. If the treatment is too hard (higher than HRC50), the mold core is easy to crack. After nitriding, the hardness of some parts will reach hrc58-60.

4. What are the factors to consider when selecting a die casting machine for a die casting mold?

(1) installation of the die-casting mold.

(2) Pouring amount of molten metal.

(3) Clamping force.

(4) Injection specific pressure.

(5) Mold opening stroke.

Aluminum Alloy Melting

1. What are the commonly used aluminum alloy melting furnaces?

The common melting furnaces now include resistance crucible furnace, medium frequency induction furnace, fuel oil reverberatory furnace, fuel oil crucible furnace and coke crucible furnace. Our company uses coke crucible furnace.

2. What are the characteristics of coke crucible furnace?

– Low furnace construction cost.

– Low fuel cost.

– Fast melting speed.

– The furnace temperature is difficult to control. 

– Short service life of crucible.

– Large amount of exhaust gas and smoke emission, and poor working environment.

3. What are the characteristics of oil fired crucible furnace?

The fuel oil furnace has the characteristics of simple structure, easy manufacture, simple operation, convenient maintenance, easy control of furnace temperature compared with coke oven, but low thermal efficiency, large fuel consumption and high cost.

4. What types of crucibles are there?

The crucible is divided into graphite crucible and metal crucible, and the metal crucible is divided into cast iron crucible and cast steel crucible. Our company uses graphite crucible for ground furnace and cast iron crucible for die casting melting furnace.

5. Why must a new crucible be preheated and roasted before use?

Because the new crucible can be roasted before use to improve the service life of the crucible. During the preheating process of the metal crucible, the inner wall of the crucible is coated with crucible coating, which forms a separation layer between the metal liquid and the crucible wall to prevent the metal liquid from directly contacting the crucible wall and corroding the inner wall. 

6. What must be done with aluminum scoops and slag scoops before use?

Before new use, the dirt on the surface of the aluminum spoon should be removed, and the place directly in contact with the molten metal should be preheated and rinsed with a layer of paint.

7. Why is it difficult to use aluminum alloy with longer melting time?

Because the longer the melting time is, the higher the overheating degree of molten metal is, and the more serious the alloy suction and oxidation are, the castings are prone to hydrogen embrittlement, pinholes, pores, cracks, slag inclusions and other defects during die-casting production.

8. Why should the slag from aluminum alloy smelting be treated with “rubbing ash”?

Usually, the slag fished out of the crucible will contain a large amount of fine aluminum alloy particles. By adding flux through “rubbing ash”, the slag and flux will react chemically to produce high temperature, so that the aluminum alloy particles will converge into droplets in the liquid and be folded out, which can be recycled to reduce the loss of aluminum alloy.