High-pressure zinc die casting is a challenging process without the right information.
A reason this guide explores everything you need to know about high-pressure die casting.
Keep reading to learn more.
What Is High-Pressure Zinc Die Casting?
High-pressure zinc die casting is a very efficient fabrication technique for making different kinds of products.
The process will force molten zinc metal at high velocities and pressure levels within a sealed die cavity.
Besides, the die contains moving and stationary halves that you will mount to the platens of the die casting machine.
high pressure die casting
The die casting machine contains injection ends that utilize hydraulic systems and pressurized gas to relay the piston forward.
High-pressure zinc die casting machines can turn the molten zinc metal into solid form within seconds.
Which Systems Can You Use To Inject Molten Zinc Metal Into Moulds Within A High Pressure Die Casting?
There are two processes that you can employ, and they include:
Hot Chamber Die Casting
This process entails automatically supplying molten zinc metal through goosenecks inside the molten zinc metal furnace to the die casting machine.
At the start of the process, the piston retracts enabling the gooseneck to fill with molten zinc metal.
molten zinc metal
Once you activate the piston, the metal plunges via the gooseneck and inside the die.
Some benefits of hot chamber die casting entail the following:
- Sophisticated cast-in details
- A fast-cycling production
- The design of the dies are efficient thus minimizing waste
- It minimizes porosity
- Durable die-casting units because of low melting points
Cold Chamber Die Casting
In this process, you will relay molten zinc metal to the containing furnace of the machine from a melting furnace.
For every cycle, you will transfer a specific amount of molten zinc metal to the shot chamber of the high-pressure die casting machine.
Also, you will use automatic ladles to assist with the transfer mechanism.
Programmable hydraulic valves will actuate plungers that will force the molten zinc metal within the die at high pressure and velocities.
After the molten zinc metal solidifies, you will release the plunger and eject the solid zinc component.
high pressure die casting
What Are The Benefits Of High-Pressure Zinc Die Casting?
High-pressure zinc die casting will offer you the following benefits:
- It will allow you to attain tight tolerance levels
- The surfaces of the zinc components from this process are smooth
- It enables you as the manufacturer to make sophisticated zinc components in large amounts
- Since it can last for several cycles, you will fabricate several zinc components before conducting replacement services
- In the process of making zinc components in large quantities, you will save on the production costs
- High-pressure zinc die casting allows you to produce similar zinc components
- The process enables you to make zinc parts that have thin walls and are lightweight
- High-pressure zinc die casting enables you to solidify the molten zinc metal within seconds due to its short casting cycles
What Are Some Limitations Of High-Pressure Zinc Die Casting?
The limitations of high-pressure zinc die casting should not deter you from employing the process.
These limitations include the following:
Some of the disadvantages include:
- The initial capital you need before starting production is high
- Also, high-pressure zinc die casting requires expensive and complex tools
- This process is not cost-effective when making single or conducting small production processes
- High-pressure zinc die casting is inflexible when you compare it to gravity die casting
- The process of heat treatment may generate surface blisters due to the porosity of the zinc component that contains gasses within it
How Do High Pressure And Low-Pressure Zinc Die Casting Compare?
Low-pressure zinc die casting occurs as you gently fill the molten zinc metal into the die cavity via tubes located on holding surfaces.
Also, the filling process of the mold in low-pressure zinc die casting happens in a vertical position.
low pressure die casting
Low-pressure zinc die casting has the following benefits:
- It is suitable for complex geometries and designs
- The process produces components with high strength features
- Automation works well with this process
- The process is affordable when handling small production runs
- Low-pressure zinc die castings are good for configurations that have a considerable wall thickness
- The process is accurate and provides high accuracy of the dimensions
High-pressure zinc dies casting occurs after you force molten zinc metal inside the die.
Also, this process tends to occur in a horizontal plane.
High-pressure zinc dies casting can happen in either hot or cold chamber die casting processes.
There are benefits to using high-pressure zinc die casting and they entail the following:
- The process will effectively handle the production of thin-walled zinc components
- Also, the process occurs rapidly since the casting cycles are short
- The final product will show a smooth surface
- It is cost-effective when performing large production processes
- The process functions well with large zinc alloy components
How Will You Conduct The Process Cycle Of A High-Pressure Zinc Die Casting?
The process cycle for high-pressure zinc die casting entails the following:
Clamping
Here, you will clamp together both halves of the die.
Also, you need to clean the die from the previous injection and then lubricate it to make the next ejection process easy.
The time for lubrication is higher with the component size, aide-cores, and cavity number.
Furthermore, you may not need to lubricate the die after each cycle, but you can perform it after 2 to 3 cycles.
All this depends on the material you are using.
The next step entails closing and securing the two clamped halves together.
Also, you need to apply sufficient force when clamping the die to ensure they are securely closed during the molten metal injection process.
The time you need to secure and clamp the die relies on the machine as large machines need more clamping forces thus, taking more time.
Injection
Here, you will transfer the molten zinc metal which is at a specific temperature within the furnace.
It goes into the chamber where you will inject it into the die.
The injection process can either be a cold chamber or a hot chamber process.
After the transfer process, you will inject the molten zinc at high pressures of around 1000 PSI to 20000 PSI.
This pressure will ensure the molten zinc metal during the solidification process.
The injection time usually lasts 0.1 seconds to inhibit one part of the zinc metal to solidify early.
Some factors that will influence the injection time include the following:
- Material thermodynamic properties
- Casting wall thickness
The larger the wall thickness, the longer the injection time.
Also, injection time in cold chamber die casting includes the time you will use to manually ladle molten zinc metal inside the shot chamber.
Cooling
After the molten zinc metal enters inside the die cavity, it will start to solidify following the injection process.
The final zinc shape of the cast forms after you fill the whole die cavity and it solidifies.
Besides, you cannot open the die until after the time for cooling elapses and the zinc cast solidifies.
To estimate the cooling time, you will consider the following:
- Thermodynamic properties of zinc metal
- Maximum thickness of the wall casting
- Die complexity
Also, you will require more cooling time if you need a large wall thickness.
Ejection
Here, you will open the die halves and use an ejection system to remove the cast from the die cavity after cooling time elapses.
Ejection mechanisms will apply a force to remove the zinc component.
This is because the cooling process causes the part to shrink and stick to the die.
After ejection, you will clamp the die readying it for the next cycle.
Trimming
During the cooling process, zinc materials within the die solidify and attaches to the casting.
Therefore, it is important to trim this excess material together with a flash that may have happened.
Trimming can happen manually using saws or using trimming presses.
Also, you can dispose of or recycle the scrap material you trim from the zinc component.
Which Zinc Alloys Can You Use In High Pressure Die Casting?
Zinc alloys available for use in this process include the following:
Zamak Alloys
This version so zinc alloy has around 4% of aluminum and they offer suitable strength and castability.
They have been widely used for several years.
zamak alloy
ZA alloys
This type of zinc alloy is suitable for components needing high strength.
Besides, they have high strength since they contain a high amount of aluminum material.
ZA Alloys
What Should You Consider When Selecting Zinc Alloys For High-Pressure Zinc Die Casting?
These include the following:
Cost
Zinc alloy cost is vital in the whole product price in high-pressure zinc die casting.
The price fluctuates depending on the market conditions and the weight of the material.
Process Cost
Zinc alloys that you can perform hot chamber die casting need small die casting machines.
These machines also operate at higher rates than the same size as cold chamber die casting machines.
Maintenance and replacement cost for zinc alloys is low since they do not attack the steel dies.
Also, they cast at low-temperature values.
However, the cost will increase with ZA alloys.
Zinc alloys may also minimize finishing machine operations when you need precision like zero drafts.
Structural Traits
ZA alloys have high yields strength, elasticity modulus is a good choice when you need maximum strength within a specific area.
Also, consider the creep characteristics of zinc alloys when you are planning to load them for a long time as they have a visco-elastic behavior.
Weight
Different alloys possess different weight levels and you should consider this factor for your application.
Impact Strength
Zinc alloys have the highest strength impact but start to lessen when temperatures are sub-zero degrees Celsius.
Also, these alloys contain low yield strengths but store a lot of elastic energy due to their non-linear modulus of elasticity.
Surface Finish
Zinc alloys allow you to maintain a high-quality finish in the long run as they are compatible with steel dies.
Corrosion Resistance
The corrosion resistance varies with the alloy you are using, so factor this in depending on the application.
Machinability
Zinc alloys provide suitable machining traits when you need them in machining operations.
Besides, the level of machinability varies on the alloy you are using in the die casting process.
What Tooling Will You Use In High-Pressure Zinc Die Casting?
The die which you will inject molten zinc metal is customized for the process.
Besides, the dies have two halves that are the cover die and the ejector die.
The cover die sits on a stationary platen while the ejector dies is on a movable die.
This design enables the die to open and shut along the parting line.
The die cavity has two inserts that are the core insert that you will fit in ejector dies and cavity inserts that fit into the cover die.
Furthermore, cover dies to enable molten zinc metal to flow to the part cavity through the opening from the injection unit.
Ejector dies have ejector boxes and support plates which mount on the platens while the inside has the ejection unit.
Once the die opens, clamping bars push ejector plates forward within the ejector boxes.
This motion pushes ejector pins to the molded zinc parts, thus removing them from the insert core.
What Are Some Of The Machine Specifications For A High-Pressure Zinc Die Casting?
Hot chamber and cold chamber high-pressure zinc die casting machines are categorized by the clamp tonnage they offer.
To determine the needed clamp force, you will consider the area of the component within the die and the injection pressure of the molten metal.
This means that a large zinc component will need a large clamping force.
Also, other materials that need higher injection pressures may need high tonnage equipment.
Furthermore, the component size should complement other machine specifications like:
- Clamp stroke
- Platen size
- Maximum shot volume
- Minimum mold thickness
High-pressure zinc dies casting parts to vary in size this you need these specifications to cater for large ranges.
What Is The Purpose Of Die Channels In High-Pressure Zinc Die Casting?
Molten zinc metal needs to flow inside part cavities that need many channels within the die.
Besides, these channels vary slightly for both cold chamber and hot chamber machines.
In hot chamber systems, molten zinc enters via sprue bushings then flows in sprue spreaders.
The sprue is the main channel that molten metals use to enter the die.
In cold chambers, molten metal enters the die via injection sleeves after flowing via several runners.
It then passes through gates into the part cavities which will direct the flow of the molten metal.
Cavities may contain overflow wells that offer extra molten metal sources during solidification.
Furthermore, you may find small channels running to the external part of the die from the cavities.
They act as ventilation pores that enable air from the die cavity to escape.
Molten metal flowing through these dies solidify and attach to the cast, hence, you must trim them after the ejection process.
Also, they enable the flow of oil or water in the die, parallel to the cavity, and eliminate heat from the die.
What Will Cause Defects In High-Pressure Zinc Die Casting?
Here are the possible defects you will encounter in high-pressure zinc die casting, and their causes:
- Flash
The causes include low clamping force and high injection pressure.
- Hot tearing
This happens when the cooling rate happens non-uniformly.
- Unfilled parts
This occurs due to low injection temperature, slow injection, or insufficient amount of shot.
- Ejector marks
This occurs when you apply a high ejection force or perform a short cooling time.
- Bubbles
This happens when you have an extremely high injection temperature or if the cooling rate is non-uniform
What Design Rules Should You Consider During High-Pressure Die Casting?
Some design rules to factor in entail the following:
- Apply round corners since they minimize the concentration of stress and fractures
- Use minimum external undercuts since they require side cores that add to the cost of the tooling
- Ensure you have a uniform wall thickness as it enhances a uniform cooling process
- Employ draft angles on every wall running parallel to the parting as it eases the ejection process
How Should You Design The Die That You Will Use In High-Pressure Zinc Die Casting?
The die should allow the easy flow of molten zinc metal into the cavities.
Also, apply draft angles as it enhances the removal of cast parts from the die.
Furthermore, include complex add-ons like undercuts in the die that need extra die pieces.
Also, ensure you use high-quality material when designing the die.
For instance, high-grade steel allows for between 100000 and 150000 cycles while low carbon steel can reach up to 1000000 cycles.
What Determines That Cost Of High-Pressure Zinc Die Casting?
Some of these factors include the following:
- Production cost
- Material cost
- Tooling cost
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