Die Casting Supplier-Die Casting Tolerance Standards

Tolerance standards for die castings depend on the type of metal alloy used and the specific elements of the object being cast, such as size and length. When manufacturing a part, the whole part must be considered. However, other parts (such as the proximity of features within a part and the proximity of those features to other parts) are also important.

Depending on the tolerance level, the part may exceed the tolerance range and still work effectively. Tight tolerances can produce more precise products, but they have some problems of their own, which can pose challenges when manufacturing extremely special components. Following the die-casting industry standards and making adjustments from there is always the best tolerance.

Tolerances are not only used in die casting, but also in other production processes such as sand casting, investment casting and machining. The process you choose will depend on many factors, including the tolerance standard for each factor. Which one is best for your next manufacturing project, and how do tolerances measure each other? This guide can help you decide which process is most effective for your facility.

Standard and precision tolerances
Standard tolerances include a series of applications related to function, fit and shape, and their accuracy is not as good as precision tolerances. Both are expressed in units of one thousandth of an inch and one hundredth of a millimeter. However, the acceptable range of accuracy tolerances in design-specific values ​​is small. Precision tolerances can provide higher accuracy when producing parts, but they can also cause setbacks, such as frequent mold inspection and maintenance and shortened mold life cycles.

Precision tolerances may also cost more, because the mold must be stiffer and more tested than the standard type. Standard tolerances provide you with parts that are out of tolerance and ensure a more predictable service-while accuracy often requires specific specifications. Both types cover some common dimension categories, they are:

draft
Mobile mold components
Flatness
Concentricity
Linear dimension
Perspective
Parting line
Core hole

 

 

1. Dimensional tolerance standards for die castings

The die-casting industry standard is jointly defined by the North American Die-casting Association (NADCA) and the international ISO series. The dimensional tolerance includes the size of a half-mold and the parting line. These guidelines cover metals such as aluminum, copper, zinc, and magnesium, and are classified according to standards or accuracy. At Premier Die Casting, we specialize in aluminum and zinc die castings, which are the two materials we will introduce here.

aluminum
Aluminum die casting has higher productivity than many other metal alloys. The technology also tends to be lower in cost. It produces light but durable parts that can be used in any application. The NADCA dimensional tolerances for half of an aluminum mold are as follows:

Standard: every 1 inch +/- 0.010 inch-then every additional inch +/- 0.001 inch
Accuracy: +/- 0.002 inches per 1 inch-then +/- 0.001 inches per additional inch
In addition, NADCA provides a set of tolerance standards for casting parts on the parting line dimensions. These measurements are determined by the projected area of ​​the die casting and are expressed in square inches. The standard tolerances for aluminum are:

Up to 10 in2: + 0.0055 inches
11 square inches to 20 square inches: + 0.0065 inches
21 square inches to 50 square inches: + 0.0075 inches
51 square inches to 100 square inches: +0.012 inches
101 square inches to 200 square inches: +0.018 inches
Over 201 square inches to 300 square inches: +0.024 inches
The precision tolerance of the projected area of ​​die castings is defined by the following units:

Up to 10 in2: + 0.0035 inches
11 square inches to 20 square inches: + 0.004 inches
21 square inches to 50 square inches: + 0.005 inches
51 square inches to 100 square inches: + 0.008 inches
101 square inches to 200 square inches: +0.012 inches
201 square inches to 300 square inches: +0.016 inches
Zinc zinc
Many manufacturing experts believe that zinc is the easiest metal to cast. Because of this versatility, it provides a range of benefits. Some advantages include maximum strength and hardness, corrosion resistance, and higher dimensional stability than other metals. According to NADCA, the half-mold tolerance is:

Standard: every 1 inch +/- 0.010 inch-then every additional inch +/- 0.001 inch
Accuracy: +/- 0.002 inches per 1 inch-then +/- 0.001 inches per additional inch
The tolerance standards for zinc die-casting in the United States include standard tolerances for parting lines of objects. These standards are:

Up to 10 in2: + 0.0045 inches
11 square inches to 20 square inches: + 0.005 inches
21 square inches to 50 square inches: + 0.006 inches
51 square inches to 100 square inches: + 0.009 inches
101 square inches to 200 square inches: +0.012 inches
Over 201 square inches to 300 square inches: +0.018 inches
The following are the tolerances of zinc die-casting precision parting lines:

Up to 10 in2: + 0.003 inches
11 square inches to 20 square inches: + 0.0035 inches
Between 21 square inches and 50 square inches: + 0.004 inches
51 square inches to 100 square inches: + 0.006 inches
101 square inches to 200 square inches: + 0.008 inches
201 square inches to 300 square inches: +0.012 inches
Die Casting Tolerance and Mechanical Parts Tolerance

Due to its speed, die-casting parts are very suitable for high-volume applications. In addition, the amount of finishing and machining required after the part comes out is also less. Due to the complex nature of commonly used molds, it produces tighter tolerances.

When you need extremely high-precision parts, it is usually best to choose computer numerical control (CNC) processing. Without the help of CNC machine tools, it can be difficult to produce tens of thousands of parts that require the same details. Industries such as telecommunications and electrical enclosures use high-precision, complex parts, which can usually only be produced by machining. You can also use this technique to add features to existing parts, such as parts formed by die casting.

It is important to remember that materials are also important when manufacturing parts by CNC machining. If you follow very tight tolerances, but the type of material is soft (such as plastic), it may bend during cutting. This factor may make it difficult to process plastic parts without leaving room for special mold considerations.

If you only produce a small number of detailed parts, machining with blanks may be cost-effective, but the cost increases as the workload increases. Compared with die casting, this method also requires more time-the process itself and the action of setting the milling or turning center. Although it can produce high-precision designs, not all designs can be made of strong blanks, which is not cost-effective.

ISO 2768 covers tolerances for parts made by machining sheet metal or removing metal. Tolerance casting names are divided into four categories-fine, medium, rough and very rough. Taking "fine" as an example, this is the allowable machining deviation when following the linear dimension standard:

 

0.02 inches to 0.12 inches: +/- 0.002 inches
Over 0.12 inches to 0.24 inches: +/- 0.002 inches
Over 0.24 inches to 1.18 inches: +/- 0.004 inches
Over 1.18 inches to 4.72 inches: +/- 0.006 inches
Over 4.72 inches to 15.75 inches: +/- 0.008 inches
Over 15.75 inches to 39.37 inches: +/- 0.012 inches
Over 39.37 inches to 78.74 inches: +/- 0.020 inches

 

 

2. Die casting tolerance standard and sand casting tolerance standard

Like die casting, sand casting can be adapted to complex designs and is compatible with many metal alloys. The size of parts created by this process can be a few ounces or a few tons-sand casting provides a lot of versatility in part manufacturing. Because the mold has the ability to withstand high temperatures, it can be used with metals such as titanium and nickel.

Compared with die casting, this method does have several disadvantages. Sand casting requires that you create a new mold every time you create a part, which can become time-consuming and expensive. Although you can recycle and reuse sand, it is more efficient to use a steel mold that has been formed and is ready for the next set of parts. Using sand also means you need to spend time cleaning the castings. Generally, sand casting often requires more labor.

This method can perform high-precision processing, but because it uses loose materials instead of metal, its accuracy is not as good as that of the mold. When dealing with die castings, you will also get higher tolerances, which is why it is cheaper than sand. Although precise tolerances may result in more expenditure, loose tolerances will also result in more expenditure. If your parts are of poor quality, you will spend more time and money to manufacture new parts with higher tolerances.

To understand the true dimensions of die casting and sand casting, you need to be familiar with the tolerances of sand casting. There are different tolerances, depending on whether you are making a feature film or a short film. Within these tolerance ranges, the specific conditions you want to use determine the acceptable tolerance levels.

 

 

3. Die casting tolerance standard and precision casting tolerance standard

Investment casting involves the use of hot wax and heat to manufacture components with highly detailed internal cavities. People also call this method lost wax casting. Engineers use this method by making a mold using a wax mold and applying it to a slurry composed of ceramic refractories. Once dry, they remove the wax by heating, leaving ceramic or plastic molds.

Because investment casting involves multiple detailed steps, it takes more time than many other processes. Due to the complexity and the amount of labor, you can expect the same cost level as foundry sand. Similar to sand casting, precision castings require the use of new materials after each part is produced. Since the technology does not involve recycling-the materials used in the mold are not reusable, so it may consume more resources.

Changes that exceed approved investment casting tolerance standards are usually caused by shrinkage, tooling, and process changes. The tolerance range for precision casting is +/- 0.005 inches to 1 inch, and every subsequent inch is +/- 0.005 inches. Compared with die casting, investment casting has a larger tolerance range (+/- 0.002 inches to 1 inch), which means that if you are looking for higher accuracy, the die casting method may be your better choice.

 

 

 

4. Die casting tolerance standard and vacuum process tolerance standard

Vacuum casting (also known as V-casting) also involves sand, but the process is different from the usual sand casting techniques. Manufacturers use vacuum to shape sand into the shape of the parts to be cast. By placing a plastic film on the pattern, they used a vacuum sealing material and then encapsulated it with a flask. Then, they filled the flask with fine sand, placed a second sheet of paper on the flask and sealed it in vacuum. The result is to fix the complete mold with the vacuum seal.

This method does not require sand mixers or other types of equipment for hardening the sand, because it does not use any pressure compaction strategy. This factor can reduce some of the costs associated with conventional sand casting.

Vertical casting allows you to manufacture parts by repeatedly using the same pattern. Since then, there is less waste left, which makes the technology more efficient and very sensitive to waste. The size range is up to 150 pounds, and the tolerance range is +/- 0.010 inches to 1 inch, and every inch thereafter is +/- 0.002 inches. Similar to investment casting, it provides a larger range of tolerances compared to die casting, which may be disadvantageous or more desirable depending on your manufacturing needs.

 

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