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When it comes to how die cast pins are created there are many questions that you might have in regards to its construction.
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The process starts in acquiring a mold for the die casting process. These molds/ dies are usually engineered to produce tens of thousands of castings in rapid succession especially for small parts like pins. The design of the desired pins should reflect accurately in the mold created. Typically, the construction of these molds is at least two sections to permit the removal of castings. These halves are securely mounted in a machine differently from each other. One half is stationary(fixed die) while the other half is movable (injector die half). The halves of the dies are clamped tightly together by the die casting machine at a given pressure. After this, molten metal is injected into the die cavity and is left to solidify. Once the metal has solidified, the dies are separated and the casting is released. The types of molds/ dies used in die casting can vary from simple to complex geometry (e.g., moveable slides, cores, or other sections depending on the desired finished part).
The die casting process is one of the fastest fabrication methods known for producing small parts like pins. Thus, this casting method is more advantageous than sand casting, which has non-reusable molds for each casting process. Some casting methods are not as precise as die casting.
There are two main methods of die casting; these are hot and cold chambers. These processes would depend on the type of metal and the part. The metals processed in the cold chamber method are metals with high melting points (e.g., aluminum, brass, or copper alloys). The metals processed in hot chambers won’t dissolve when heated (e.g., zinc, lead, and magnesium alloys).
Planning for the different factors that may affect the die casting process will greatly dictate a finished pin’s quality. Before contacting a contract manufacturer or before fabricating through Die casting, the common factors to consider are the quantity, Type of Alloy, Type of Components, type of finish, and product design.
The desired intricacy of the finished product is a very important factor that will influence the choice of material used in the process. Typically, aluminum is an excellent material choice because of its lightweight and non-corrosive properties. On the other hand, Stainless steel is the most common material used for more pins requiring extreme accuracy because of its high precision and non-corrosive properties.
Aside from the most common materials mentioned above, the most common metals used in die casting are Aluminum, Zinc, Brass, Bronze, Tin, Lead, Magnesium, Silicon Tombac, Stainless steel, Carbon steel, and many more. These metals should be able to maintain their mechanical properties and structural characteristics during and after the melting process.
Zinc is the most convenient metal to work on when it comes to die casting. It boasts the characteristics of having a high ductility, toughness (high impact strength), and wide variety of plating options. Zinc can be alloyed with different metals to improve its strength. Furthermore, alloyed zinc parts have an improved impact resistance compared to that of the cast aluminum and grey cast iron. Zinc die cast parts can work with requirements having very tight tolerances.
One zinc alloy that has an exceptional casting fluidity are ZAMAK alloys. ZAMAK is an alloy composed of the right amounts of zinc, aluminum, magnesium, and copper. These alloys are very capable of casting thin-walled parts with a thickness of .025 inches or .65 mm. ZAMAK components can be smaller, lighter, and low cost.
Zinc has a lower casting temperature, which means it has a lesser and minimal thermal shock. Minimized thermal shock extends the life of casting tools to 10 times more than that of aluminum dies.
Zinc alloys have impressive elastic moduli. This property makes zinc alloys more rigid than aluminum, magnesium alloys, and engineering plastics.
Zinc outperforms Bronze in heavy-duty industrial applications because of its impressive bearing properties.
Some disadvantages related to zinc are having issues with flow marks, cold lattice, porosity, shrinkage, cracking, and burn mold. Due to these issues, the melting temperatures in zinc materials have to be closely monitored.
Aluminum metal takes minimal energy to melt, which makes this material very cost-effective and convenient. This material is lightweight, corrosion-resistant. In addition to these, Aluminum has high dimensional stability, high strength, and can stand high temperatures.
Aluminum materials can experience a notable shrinkage during the cooling process. Pure aluminum has a shrinkage percentage of 6.5% during the solidification process.
Brass has high conductivity and high corrosion resistance, which makes this more advantageous than other materials. Also, brass is resistant to temperature changes and has a low melting temperature (900 degrees Celsius). Using brass for die casting enables parts to be formed quickly in large quantities.
One disadvantage of using brass is its complex and laborious process of melting. Brass has to be monitored continuously to avoid undesired results. The most common issues related to brass die casting are burnt part, scaling, porosity, and die defects.
The geometry of the die casting molds will determine how the molten material fills and cools. The way material flows in a die affects the stress, grain, and porosity of a finished product. Having the right geometry for a specified application prevents poor fluid flow, part shrinkage, solidification problems, hot cracking, post-casting checks, and poor surface finish.
Below are the Geometric features that affect the die casting mold.
A draft is a crucial design requirement for the smoothness of ejecting the part from its mold. The draft angle will vary depending on the wall type, surface requirement, depth of surface, and the selected metal.
Fillet radii make the structure of a product stronger by reducing the stress concentration on a sharp part. Incorporating radii distributes stress over a broader fillet volume, which lessens weak points on die casted parts. Thus, this prevents shearing on the sharp edges of the parts.
A parting line is one of the first factors to be defined in designing a mold. This line will be the driver in designing molds (inside and outside surfaces or the cover or the ejector).
Bosses are mounting points, standoffs, and are designed to maintain uniform wall thicknesses to eliminate after casting machining.
Bosses are strategically located on mold designs to maintain uniform wall thickness. These features serve as stand-offs and mounting points for parts.
Ribs are incorporated in the mold designs to fill all the die casting parts and avoid weak parts. These are commonly used to provide a path for molten materials and speed up the ejection process.
When designing for holes and windows, it is important to consider a higher draft on these parts. These features have a significant connection with the surface of the die, contributing to the possibility of blocking the flow of the molten material.
Porosity is inevitable in die-cast components. The main factors that affect porosity in a die cast part are the improper mold design, purity of the metal used, pressure and shot speed and shrinkage of the material.
What manufacturers do usually is to optimize their tooling design to minimize the voids and redirect it to the non-critical areas.
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