Замисляли ли сте се някога как се произвеждат сложни компоненти на автомобил, като двигателни блокове или силови влакове? What may be said about these heavy parts is that they are similar to light surgical tools that are used in the medical industry. High-pressure die casting is ideal for producing strong and fragile parts at the same time.
What makes HPDC a favored process with myriad uses? This article discusses the features of the HPDC process in terms of the process technicalities and uses. Knowing these factors will enable you to decide whether this manufacturing technique will suit your needs or not.
Леене под високо налягане: Общ преглед
In the High-pressure die-casting technique, the parts are formed by injecting red-hot metal into a mold. The process involves a high pressure normally hydraulic to force the metal into a die shape. A strong press has to keep the die sealed during the injection. When the metal has set, the die releases the casting. After ejection the die locks for the next cycle consequently. The tooling is composed of two steel blocks that together make the die cavity.
High Pressure Die Casting Process Step By Step
Here are frequent steps normally involved in high-pressure die casting:
стъпка 01: Preparation of the Die
На първо място, it’s recommended that the surface of the cooperating parts of the steel die be cleaned and checked for potential contaminants. It should be tightly fixed for the formation of a precise cavity with many exacting standards having a tolerance level of about ±0.005 inches.
стъпка 02: Heating the Die
The die should be heated to range between 300°F and 500°F or 150°C to 260°C. This temperature range ensures the efficient flow of metals and minimizes thermal shock during injection.
стъпка 03: Molten Metal Production
The metal alloys usually used are aluminum or zinc. Нормално, these are melt around 1200°F to 1300°F (650°C to 700°C). To achieve the correct viscosity and flow characteristic, it is necessary to maintain this temperature.
стъпка 04: Injection of Molten Metal
Pour the molten metal into the die cavity at high pressure, this usually varies from 1,500 да се 30,000 psi or 10 да се 200 MPa. This high pressure guarantees the mold to be filled right to the brim to reduce the chances of enclosed air and thereby produce close-to-net shape components.
стъпка 05: Holding Pressure
The pressure is then kept on for several seconds (3 да се 10 seconds) so as to compensate for the contraction that metal undergoes when it cools. This holding phase provides a considerable improvement to the mechanical properties of the final part due to the decrease in porosity.
стъпка 06: Охлаждане и втвърдяване
Let the molten metal crystallize inside the die. Coalescence times can be longer and usually take from 10 да се 30 seconds depending on the part thickness and material.
стъпка 07: Ejection of the Casting
After the mixture has been set, the die is then opened and the casting is recovered using ejector pins which apply a pull of about 10 tons. This way it is easier to remove the material without affecting the part, and thus maintaining its dimensions.
стъпка 08: Trimming and Finishing
Remove unwanted material from the casting by incorporating appropriate mechanical trimming tools or die cutters. The final operations in a workpiece may be done through machining, surface treatment, or polishing, which may be defined by the surface roughness average or Ra.
стъпка 09: Гарантиране на качеството
Perform strict and comprehensive tests on the outline of the finished casting for porosity or dimensional error. Ultrasonic or X-ray tests are used to check the quality of all the parts before selling them on the market.
Advantages of High-Pressure Die Casting
Леене под високо налягане (HPDC) is highly appreciated for its benefits compared to conventional approaches. Here are the common benefits of this process:
Increased Speed of Production
Compared to gravity or low-pressure casting, HPDC increases production efficiency by a large margin. High-speed injection takes a short time to fill the die and in the process leads to low cycle times. Следователно, it is ideal for industries that need many parts, and HPDC is the preferred method for quantity production.
High Quality of Parts
Products made through HPDC are characterized by high accuracy and quality of the components. High dimensional accuracy and improved surface finishes mean less post-processing is required hence reducing time and expense. It also makes plating and coating easier because it provides a smooth surface on which to apply the finishes. въпреки това, HPDC offers a uniformity of the mechanical characteristics of the produced components, thus providing reliability in use.
Capability for Thin-Walled Products
From the design perspective, HPDC offers the advantage of thin-walled structures. Wall thicknesses of less than 0.4mm can be realized depending on the design requirements. This capability results in a large amount of weight savings that are essential in industries such as automotive and aerospace. освен това, the method can include inserts that can be cast in the first place thus reducing the number of parts going to be assembled.
Adaptive Design of the Building Complexity
The die shapes of HPDC allow the development of complex designs because of the nature of the process. With this technique, manufacturers can create complex geometries that may be difficult to use with other technologies. This flexibility is amenable to different assemblies and it further improves the functionality of the finished product.
Longevity of Tooling
HPDC (high-pressure die casting) allows for the efficient production of parts using dies that are designed to endure multiple production runs. This durability cuts per unit cost, thus allowing manufacturers to spread initial tooling costs over many parts. High-quality die designs make it possible to achieve high-quality production even after several numbers of production runs.
Disadvantages of High-Pressure Die Casting
въпреки това, there are some drawbacks of using High-Pressure Die Casting (HPDC) that can make it unsuitable under some conditions.
High initial cost and operating cost
Sunk and initial costs are high for the implementation of HPDC. The making of dies is expensive, more so than other techniques. Като цяло, these costs are justified only for mass production of goods.
Few Advantages for Thicker Castings
While HPDC gives very short production cycles, the advantage decreases as the casting thickness is increased. More thickness of the wall prolongs the time taken for solidification negating the benefits of the quick injection.
Risk of Porosity in Castings
Porosity in cast parts occurs due to the presence of air pockets. Several factors contribute to this issue, включително; alloy choice, cooling shrinkage, and the rate at which the mold fills up with molten metal. Porous castings are bad for structures and their performance as they hold weak mechanical properties.
Problems with Heat Treatment and Welding
Like any other casting process, microcracks in porous castings can be caused by welding or heat treatment. During these processes, air trapped in the pores expands causing failure of the various components. If the material requires heat treatment, then you may require special methods of avoiding porosity.
Applicable only to High Fluidity Metals
The applications of HPDC are restricted to metals that exhibit high fluidity. The most appropriate materials for use in the production of metallic-based coatings include aluminum, цинк, и магнезий. This limitation limits the applicability of HPDC for other types of metal.
High-Pressure Die-Casting: Hot and Cold Chamber Systems
High-pressure die casting employs two distinct systems for injecting molten metal into molds:
- Hot Chamber System
- Cold Chamber System
Laying it down to these systems, let us discuss deeper for good understanding;
Hot Chamber System
The system is well applicable for metals such as zinc, магнезий, олово, и т.н. The injection mechanism still stays submerged in the liquid metal. В експлоатация, a piston forces the molten metal through the nozzle into the die.
Cold Chamber System
For high melting point metals, the cold chamber system is usually exploited. Some of the metal examples include aluminum and copper. Each system is capable of producing magnesium parts, but small parts frequently use hot chambers, while large parts require cold chambers because of size factors.
Cold chamber systems work at higher pressure as compared to hot chamber systems. The pouring process is faster and that is why production rates are normally higher in hot chambers.
Injection Systems in Cold Chamber
The cold chamber system employs two types of injection methods:
- Horizontal Injection
- Vertical Injection
The molten metal is channeled directly into a feed channel which supplies the cold chamber. This pouring can be done automatically or manually.
The piston is activated hydraulically and comes down through a steel-made channel. This action prevents light from entering and forces the molten metal to enter the mold with pressure and at high speed.
В последствие, the piston returns to its initial position, and the mold is released for the solidified product. The casting is then ejected, and the molding assembly returns to the position for the reception of another batch.
What are the Most Common Metals Used in High-Pressure Die Casting?
The most common types of metals employed for high-pressure die casting include:
Алуминиево леене под налягане
Aluminum die casting entails forcing molten aluminum into a mold at high pressure of up to (1,500 да се 25,000 psi). The process results in intricate and narrow cross-sectional geometries with a polished surface. Common products comprise motor vehicle components, side channel blowers, electronic equipment housing, and manufacturing items.
Zinc Die casting
Zinc Die casting is a high-pressure technique. It involves forcing molten zinc into molds to produce accurate parts. It yields intricate forms with superior surface features. The process is most frequently applied in car parts and electrical connectors. В процеса, pressure ranges between 1000 да се 30000 psi).
Magnesium Die casting
Magnesium die casting is a lightweight material-forming process in which high pressure is used to force molten magnesium into molds. This method also generates tough and rigid components that are suitable for automotive and aerospace applications. Magnesium die casting works at moderate pressures of around 1500 да се 20000 psi and this results in high levels of accuracy in terms of dimension as well as surface finish. Допълнително, the lightweight nature of magnesium has positive implications for the fuel efficiency of vehicles.
Applications of High-Pressure Die Casting
The high quality attained with HPDC makes it more preferred in various industries. Key applications include:
Автомобилен сектор
In automotive manufacturing, HPDC is used to manufacture significant structural parts made of light metals such as aluminum and magnesium. Examples of common parts are engine blocks, transmission housings, and oil pans. These components need light durable structures to improve vehicle performance and efficiency in terms of fuel consumption.
Медицинско поле
HPDC can be considered an optimum technique in the production of lightweight surgical instruments. Medical devices including imaging equipment and infusion pumps are produced through this process. As medical applications require high-quality reliable components because of the precision and performance needed.
Аерокосмическа индустрия
The aerospace manufacturing sector turns to HPDC as a technique that suits complex geometries. Examples are aluminum, цинк, and magnesium which are used in the production of parts for automobile engines and other structures used in aircraft. The mechanical properties of the components created through HPDC align with the safety and performance requirements required for aerospace components.
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General FAQ’s
Q1. What is the normal cycle time of high-pressure die casting?
Cycle times for high-pressure die casting are between 15 и 60 seconds depending on the part design and size. Заради този бърз обрат, системата е много подходяща за производство в голям обем.
Q2. What is the common wall thickness when using this process?
Използване на леене под високо налягане, възможно е да се постигне дебелина на стената до толкова ниска 0.5 мм, при запазване на високата якост на компонента.
Q3. How does high-pressure die casting impact mechanical properties?
Механичните свойства на частите, отляти под високо налягане, са по-добри от тези на частите, отлети с пясък; якостта на провлачване варира от 200 да се 300 MPa и якостта на опън варира от 250 да се 400 MPa в зависимост от вида на използваната сплав.
Q4. What percentage of waste is normally produced in high-pressure die casting?
Производственият процес също е много ефективен, с отпадъци от по-малко от 5%, главно поради подрязване и излишък на материал, които могат да бъдат върнати в производствения цикъл.
Q5. How does mold temperature affect the casting process?
Важно е температурите на формата да се поддържат в диапазона от 180 да се 300 C за по-добри резултати. Времето за охлаждане е по-дълго при по-ниски температури, и повърхностното покритие е по-добро при по-високи скорости на охлаждане. However excessive heat can be problematic for dimensional accuracy.
Q6. High Pressure Die Casting Pressure Range
High-pressure die casting typically operates at pressures ranging from 1,500 да се 30,000 psi. This high pressure allows molten metal to fill the mold quickly and evenly.
