Sheet metal tolerances

Tolerances Guideline for Sheet Metal Fabrication

Sheet metal tolerances mainly include dimensional tolerances and form and position tolerances, and the specific requirements are as follows:

Dimensional tolerances

Linear dimensional tolerances:

Nominal size ≤ 400mm, tolerance is ± 0.8mm;
400mm < nominal size ≤ 1000mm, tolerance is ± 1.2mm; Nominal size > 1000mm, tolerance is ± 2.0mm.
Plate thickness dimensional tolerances:

Plate thickness ≥ 0.5 ~ 1.5mm, tolerance is ± 0.08mm;
1.5 ~ 3.0mm, tolerance is ± 0.17mm;
Plate thickness > 3.0mm, tolerance is ± 0.20mm.
Angle tolerances:

Shear angle tolerance is ± 1.5°;
When the bending angle is not 90°, the angle tolerance is ± 1.5°;
When the bending angle is other angles, the angle tolerance is ± 3.0°.

Form and position tolerances

Shape and position tolerances: should comply with the provisions of the design drawings. The unmarked shape and position tolerances are Class K of GB/T1184-1996.

Limit deviation and basic size

Limit deviation: The limit deviation of holes and internal dimensions is preceded by a “+” sign as the upper deviation, and the lower deviation is 0; the limit deviation of shafts and external dimensions is preceded by a “-” sign as the lower deviation, and the upper deviation is 0; the limit deviation of hole center distance, hole edge distance, length, height and unmarked tolerance dimensions is preceded by a “±” sign as the upper deviation and lower deviation respectively.
These standards and requirements ensure the accuracy and consistency of sheet metal parts during the manufacturing process and meet the needs of different application scenarios. Detailed sheet metal tolerance chart shows:

What Factors Impact Tolerance During Sheet Metal Fabrication?

The actual tolerance in sheet metal processing will be affected by various factors, so early communication with manufacturers and feedback during the manufacturing process are very important. So what specific factors will affect it? At present, there are several categories summarized in the industry:

1. Material selection:

The type and thickness of the selected metal material have original tolerances. These inherent tolerances play a vital role in completing the overall tolerance of the finished component.

2. Process complexity:

The number of operations that metal parts need to do directly affects the tolerance. As each operation process is performed, the tolerance will also increase, complicating the accuracy.

3. Equipment accuracy:

Different tools and machines used in manufacturing have different accuracy levels. The accuracy capability of the equipment is the determining factor in achieving a specific tolerance level.

4. Manufacturing company capabilities:

Each metal parts custom manufacturing and assembly company has its own equipment and process level. Different process levels also affect the company’s ability to control the tolerance of the sheet metal parts produced. Therefore, here, long-term and stable communication with the manufacturer is very important, and tolerance issues need to be repeatedly confirmed and supervised before and after the cooperation relationship is determined.

Here is a detailed introduction to the two points of material and process:

The impact of materials on sheet metal design
Material tolerance is a natural tolerance problem of sheet metal parts, which is characterized by the original tolerance caused by factors such as material properties and manufacturing processes. These tolerances are particularly affected by material thickness, with each thickness category exhibiting different tolerance levels.

Material Tolerances – Thickness

Choosing the right sheet thickness is a major factor in sheet metal manufacturing, including overall part strength, weight, and overall design features such as minimum bend radius, hole and slot size, and flange length. Ensuring uniform thickness across the entire sheet metal part is critical to final product quality and performance.

Of course, different materials have different original tolerance levels. It is recommended to proactively communicate and confirm with the sheet metal manufacturer when selecting metal materials.
Sheet Metal Process Selection & Tolerances

Sheet Metal Bending Process

Sheet metal bending requires the use of a bend sheet metal tool to process the sheet metal into the desired shape. Of course, not all bending forming requires the use of custom molds. Without the use of molds, the engineer’s manual operation level needs to be considered. Personal ability plays a decisive role. Usually, metal bending will have the following tolerance issues:

1. Corner formation:

Usually sheet metal bending tolerances cannot achieve a true 90° corner; the corner will have a radius.

2. Bending angle:

The standard tolerance of the bending angle is ± 0.5°, ensuring accuracy while allowing for minimal differences.

3. Bending length:

The tolerance of the bending length is usually ± 0.20 mm (0.010 inches) per bend, balancing the accuracy and flexibility of the bending process

Stamping process

Stamping tolerance refers to the tolerance range of size and shape in stamped metal parts. This process involves using a die to stamp a metal sheet into a specific shape. Of course, the accuracy of stamping is also affected by many factors, such as material type, thickness, and complexity of the die. There are several tolerance issues for stamping tolerances:

1. Material behavior:

Different materials react differently to stamping, affecting the accuracy of the final product.

2. Die accuracy:

The complexity and accuracy of the die used directly affect the achievable tolerances.

3. Process speed:

The speed of the stamping process affects heat generation and material deformation, which further affects tolerances.

Punching process

Punching tolerance is the tolerance range allowed for punching, during which the hydraulic press forms a hole or shape in the metal sheet. The accuracy of the punching is critical to ensure the functional and structural integrity of the final product. There are several tolerance issues for punching tolerances:

1. Tool wear:

The condition and wear of the punching tool will affect the accuracy of the punched hole or shape.

2. Material thickness:

Thicker materials can pose challenges in maintaining tight tolerances.

3. Machine calibration:

The calibration and maintenance of the punching machine plays a vital role in achieving the required tolerances.

Of course, the above is a simple summary of sheet metal tolerances. In fact, choosing a professional sheet metal manufacturer is the primary key point, because in the modern sheet metal processing industry, there are basically not many differences in materials and equipment. Only professional sheet metal companies determine the ability to control tolerances in terms of engineers and process levels. If you need custom metal components or are a trader, you can choose the help of Mulan Group. As a professional Chinese sheet metal manufacturer, it has 18 years of experience in the fabrication of sheet metal parts. Its cooperative customers are all over the world, and it can meet various sheet metal processing needs and cooperation needs.

Here is our Sheet metal forming sample display：

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