Common Quality Defects on Zinc and Aluminum Casting

Die casting is a process of casting metal and involves heating metal to the melting point, which is then poured into a cast. Zinc is a common alloy used in the die casting process.

Die casting is the most effective way to shape metal for components. This process is used worldwide to make mechanical, electronic, and automotive products.

There are some common defects, however, that can occur with die casting. In some cases, the defects are severe, which could have a negative effect on the finished product, while at other times there is only slight damage, which doesn’t affect the product and its use.

The main die casting defects which occur during die casting can be divided in categories related to different phases of the production process: die casting, pre-finishing, machining operations and surface finishing.

It is important to remember that not every defect can be avoided during the die casting phase, but it is necessary to focus on mold design. This is because during the production phase it is only possible to act on a limited number of parameters, and sometimes the only thing that the designer can do to solve a problem is to modify mold design.

The following are the most common defects in die casting production:

Shrinkage

Shrinkage porosity defects are created during the solidification and cooling phases of casting. They are created due to material shrinking and for this reason are a common defect when die casting large parts.

During the solidification phase, the material tends to move near colder zones, and as a result, due to differences in temperature between the casting surface and core, cavities are concentrated inside the part.

Cracks

Cracks can appear on the surface of the product if during the process the temperature is too high or too low. Severe cracks may damage the integrity of the component and can even cause the product to break apart.

Shot Over

This zinc defect can happen if any metal is left behind in the mold from a previous batch. This can cause a shot over to take place, and if it does, there will be a piece of zinc that has attached itself to the new mold. Fortunately, this defect doesn’t affect the overall strength of the finished product.

Common Aluminum Casting Defects

Aluminum is commonly used in the casting process since this metal is a low cost option. It can also be recycled and remolded, which saves both energy and resources. For these reasons, there has been a lot of research and development into the science of die casting aluminum over the years.

Aluminum castings are more likely to suffer from internal defects like shrinkage, looseness, and problems with porosity. When the castings are machined, the internal defects show up after the dense layers on the surface have been removed.

Here are some of the most common quality defects that may appear when die casting aluminum:

Cracks From Heat Treatments – These cracks are caused by overheating or when there is a lot of stress on the metal from pulling it too much.

Casting Cracks – These cracks develop along the boundary of the grain and are more likely to appear when specialty molds are used for complex shaping of the aluminum.

Shrinkage – Aluminum castings often shrink due to overheating, a fast pouring speed, or too much moisture in the sand mold.

Causes of Casting Defects

Here are some of the most common causes of defects that may appear during the casting process:

• Castings are removed from the mold too early
• The sand mold produces a poor yield
• The heat treatment is excessive, causing overheating
• Excessive rate of cooling
• The structural design of the casting is not reasonable (variances in the wall thickness, sharp corners, etc.)

Dioxide Slag

Molds with corners may not receive enough ventilation, causing slag to oxidize. This causes a fracture that may be yellow or off-white and it can be found when anodizing, pickling, or during alkaline washing. The fracture can also be discovered by using mechanical processing, fluoroscopy, or by x-ray.

This is commonly caused by a pouring system with a poor design or when the alloy liquid slag isn’t removed. It can also occur when there is inadequate standing time allowed following the refining treatment.

Stomata Bubbles

The wall pores in the castings are usually oval or round and have a smooth surface. Surface bubbles in pours are often discovered by sandblasting. They can also be found using an x-ray, mechanical processing, or a fluoroscopy. If using an x-ray, the bubbles appear as black spots.

This type of defect can be caused by poor ventilation of the sand core and the mold or when impurities like grassroots or coal dust are mixed into the sand. This defect may also be due to a pouring system with a poor design. The pouring speed must be exact so that no gas is involved in the process.

Effects of Zinc and Aluminum Defects

When a severe defect is noticed the die casting must be done all over again. A severe defect can result in breakage in the component, which can lead to a catastrophic situation. As a company that is ordering parts, you need to have trust in the business you are using for the casting. You must work with a reputable company that provides high-quality zinc and aluminum custom designed parts to preserve the reputation of your own business.

Never settle for second best. At ADHECOGEN we offer high-quality, designed parts for office furniture and patio and window hardware industries. You can count on our commitment to quality and on our impeccable customer service. Whether you have a large order to place or a small one, we’ll work with you to get the parts you need on budget and on time.

Visit www.adhecogen.com for more information or feel free to contact us directly to talk to one of our team members at (905) 282-0881.