Tolerance Criteria for Die Casting

Tolerance criteria for die casting depend on the type of metal alloy used and the specific elements of the object being cast, such as dimensions and length. When manufacturing a part, the part must be considered as a whole. However, additional components (such as the proximity of features within the part and the proximity of these features to other components) are equally important.

Depending on the tolerance level, a part may be out of tolerance and still work effectively. Tighter tolerances produce more accurate products, but they come with their own set of issues and can present challenges when creating extremely specific components. It's always best to follow industry standards for die casting and make adjustments from there.

Tolerances are not just used in die casting - these measurements are also found in other production processes such as sand casting, investment casting and machining. The process you choose will depend on many factors, including the tolerance criteria for each factor. Which one is best for your next manufacturing project, and how do the tolerances measure up against each other? This guide can help you determine which process will work best for your facility.

 

Standard and Precision Tolerances

Standard tolerances cover a range of applications related to function, fit and shape - they are not as precise as precision tolerances. Both are expressed in units such as thousandths of an inch and hundredths of a millimeter. However, precision tolerances have a smaller range of acceptable variation in design specified values. Precision tolerances allow for greater accuracy when producing parts, but they can also cause frustrations, such as frequent mold inspections and repairs and shortened mold life cycles.

Precision tolerances can also be more expensive to use, as the tooling must be more rigid and undergo more testing than standard types. Standard tolerances provide a greater range for out-of-tolerance parts and ensure more predictable service - while accuracy often requires specific specifications. Both types cover a number of common dimensional categories, which are

● Draft

● Dynamic Die Components

● Flatness

● Concentricity

● Linearity dimensions

● Angle

● Parting line

● Hollow hole

 

 

Die casting dimensional tolerance standard

Die casting industry standards are defined by the international ISO series. Dimensional tolerances encompass both the dimensions for one die half and dimensions over the parting line. These guidelines cover metals like aluminum, copper, zinc and magnesium and are categorized by being either standard or precision. At HEBEI YOGEM, we specialize in aluminum die casting, which is the material we’ll cover here.

 

Aluminum

Aluminum die casting enables a higher manufacturing rate than many other metal alloys. This technique also tends to be less costly. It yields lightweight but durable parts ready for any application. Dimensional tolerances for one aluminum die half are as follows:

● Standard: +/- 0.010 inch per 1 inch — then +/- 0.001 inch for each additional inch

● Precision: +/- 0.002 inch per 1 inch — then +/- 0.001 inch for each additional inch

Additionally, NADCA provides a set of cast component tolerance standards regarding dimensions over the parting line. These measurements are determined by the projected area of the die casting and expressed in inches squared. The standard tolerances for aluminum are:

● Up to 10 in2: + 0.0055 inch

● Over 11 in2 to 20 in2: + 0.0065 inch

● Over 21 in2 to 50 in2: + 0.0075 inch

● Over 51 in2 to 100 in2: + 0.012 inch

● Over 101 in2 to 200 in2: + 0.018 inch

● Over 201 in2 to 300 in2: + 0.024 inch

The precision tolerances for the projected area of the die casting are defined by these units:

● Up to 10 in2: + 0.0035 inch

● Over 11 in2 to 20 in2: + 0.004 inch

● Over 21 in2 to 50 in2: + 0.005 inch

● Over 51 in2 to 100 in2: + 0.008 inch

● Over 101 in2 to 200 in2:+ 0.012 inch

● Over 201 in2 to 300 in2: + 0.016 inch

 

Die Casting Tolerance vs. Machined Part Tolerance

Die casting is excellent for high-volume applications because of its speed, plus it requires less finishing and machining after the part comes out. It yields tighter tolerances because of the intricate nature of the molds commonly used.

When you need a part with extreme precision, it’s often best to choose computer numerical control (CNC) machining. Producing thousands of detailed parts that need to be identical can be difficult without the help of a CNC machine. Industries like telecommunications and electrical housing use high-precision, complex parts that can usually only be produced with machining. You can also use this technique to add features to an already existing piece, such as one formed from die casting.

It’s essential to keep in mind that material also matters when manufacturing a part with CNC machining. If you’re following very tight tolerances but the material is of a softer variety — like plastic — it may flex while it’s being cut. This factor can make it difficult to machine a plastic part without making room for specific tooling considerations. 

Machining with billet materials can be cost-effective if you’re only producing a low quantity of detailed components, but expenses increase as the amount of work does. This method also requires more time than die casting — both the process itself and the act of setting up the milling or turning center. And though it yields high-precision designs, not all designs can be created from solid billet, nor is it cost-effective to do so.

ISO 2768 covers tolerances for pieces made by machining sheet metal or removing metal. The tolerance cast designation is split into four categories — fine, medium, coarse and very coarse. Using the “fine” designation as an example, here are the permissible deviations for machining when following the standards for linear dimensions:

● 0.02 inch to 0.12 inch: +/- 0.002 inch

● Over 0.12 inch to 0.24 inch: +/- 0.002 inch

● Over 0.24 inch to 1.18 inch: +/- 0.004 inch

● Over 1.18 inches to 4.72 inches: +/- 0.006 inch

● Over 4.72 inches to 15.75 inches: +/- 0.008 inch

● Over 15.75 inches to 39.37 inches: +/- 0.012 inch

● Over 39.37 inches to 78.74 inches: +/- 0.020 inch

 

Die Casting Tolerance Standards vs. Investment Casting Tolerance Standards

Investment casting involves the use of hot wax and heat to create components with highly detailed inner cavities. People also refer to this method as lost wax casting. Engineers employ this method by creating molds from wax patterns and coating them in a slurry consisting of ceramic refractory material. Once this dries, they remove the wax by applying heat, leaving the ceramic or plastic mold behind.

Because investment casting consists of multiple detailed steps, it takes more time than many other processes. You can expect a similar level of expenses like what you’d see with sand casting because of the complexity and amount of labor. Also similar to sand casting, investment casting requires new materials after producing each part. This technique can be even more resource-intensive because it doesn’t involve recycling — the materials used for the mold aren’t reusable.

Variations outside of the approved investment casting tolerance standards usually result from shrinkage, tooling and process variation. Tolerances for investment casting range from +/- 0.005 inch to 1 inch, with every inch after that being an additional +/- 0.005 inch. Investment casting offers a broader tolerance range than die casting — which is +/- 0.002 inch to 1 inch — which means the die casting method may be the better choice for you if you’re looking for higher accuracy.

 

Contact HEBEI YOGEM Your Die Casting Needs

If you’re seeking casting services to produce the highest-quality parts, HEBEI YOGEM can help. Our Quality Policy and ISO 9001 certification keep us accountable for the work we do. We strive to bring you only the best parts and services each time. Whether you’re in the medical, automotive or lighting industry, you can find a solution to your die casting needs at HEBEI YOGEM. Contact us today with the casting project you have in mind, and we’ll work with you to create a top-class, long-lasting end product.