Understanding Tolerances in Metal Stamping
What Engineers and Manufacturers Need to Know
In metal stamping, precision is often critical to how a component performs in the finished assembly. A stamped metal part may need to fit around another component, maintain a precise electrical connection, accommodate a press-fit bushing, or meet specific dimensional requirements throughout high-volume production.
Metal stamping tolerances define how much a finished part is allowed to vary from its specified dimensions while still meeting the requirements of the application.
For engineers and manufacturers, establishing the right tolerances is an important part of designing a cost-effective, manufacturable component. Tolerances that are unnecessarily tight can increase tooling, inspection, and production costs, while tolerances that are too loose can create assembly or performance problems.
Acro Metal Stamping specializes in tight-tolerance and complex metal components, with capabilities that include progressive and compound dies, deep drawing, in-house tooling, and precision production stamping.
Not every feature on a stamped part requires the same tolerance. A hole used for a press fit may require significantly tighter control than an exterior edge where a small amount of dimensional variation has no effect on assembly or performance.
This is why engineers should evaluate tolerances according to the function of each feature rather than automatically applying the tightest possible specification to every dimension.
Why Are Stamping Tolerances Important?
Tolerances directly affect part fit, function, manufacturability, and cost.
Consider a stamped electrical terminal. The position of a contact feature may determine whether the terminal properly mates with another component. A small dimensional variation could affect the connection.
Similarly, a drawn metal component may require precise dimensions to accommodate a bushing, shaft, housing, or other mating component.
Acro has produced components with highly demanding requirements. One example is a deep-drawn steel component requiring side-wall tolerances of ±0.0005" for a press-fit bushing, along with a flatness requirement of 0.005" after seven drawing operations.
These examples demonstrate why tolerance requirements should be evaluated in the context of the finished part and its application.
Common Types of Metal Stamping Tolerances
Several different types of tolerances may be specified on a stamped metal component.
Dimensional Tolerances
Dimensional tolerances control measurements such as:
- Length
- Width
- Height
- Diameter
- Distance between features
- Overall part dimensions
The required tolerance depends on the function of the dimension. A mounting hole location, for example, may require tighter control than a non-functional exterior dimension.
Hole and Feature Tolerances
Hole diameter and location can be critical for fasteners, shafts, bushings, bearings, electrical components, and press-fit applications.
Tooling design, punch-to-die clearance, material properties, and press operation can all influence the final geometry of a stamped hole.
Bend and Form Tolerances
Bending and forming introduce additional variables. Material springback, thickness, bend radius, tooling, and material characteristics can all affect the final position of a formed feature.
A part can meet its individual linear dimensions while still creating an assembly issue if a bend angle or formed feature is outside its functional requirement.
Flatness and Profile Tolerances
Flatness can be important when a stamped component must sit against another surface or maintain a precise relationship with a mating component.
Forming operations can introduce stresses and deformation that influence flatness. For this reason, flatness requirements should be considered during both part design and tooling development.
What Affects Metal Stamping Tolerances?
The achievable tolerance for a stamped component depends on several factors.
Material
Different metals respond differently to stamping and forming. Acro works with materials including copper, tin, nickel, brass, phosphor bronze, stainless steel, and specialty alloys.
Material properties can influence springback, deformation, forming behavior, and dimensional stability.
Material Thickness
Material thickness and thickness variation can affect forming, clearances, hole geometry, and finished dimensions.
For example, Acro's published specifications for certain deep-drawn components establish different thickness tolerances based on material thickness.
Part Geometry
Simple flat stampings may be easier to control than components containing multiple bends, formed features, or deep draws.
As geometry becomes more complex, tooling design and process control become increasingly important.
Tooling
Tool design has a direct influence on repeatability and dimensional control.
Acro designs, builds, and maintains progressive and compound stamping dies in its in-house toolroom. This vertical integration provides control over tooling development, maintenance, and modifications.
Press Technology
The stamping press and production process also influence dimensional consistency. Acro utilizes servo press technology for precision stamping and forming applications.
Secondary Operations
Deburring, plating, heat treating, tapping, drilling, riveting, and other secondary operations can affect final dimensions.
When a component undergoes multiple manufacturing processes, the complete process needs to be considered when establishing final tolerances.
Metal Stamping Tolerance Chart
There is no single tolerance that applies to every stamped metal part. Requirements depend on material, thickness, geometry, tooling, process, and application.
As a general reference, Acro's published sales terms specify that, when no tolerances are shown, its standard dimensional tolerances are ±0.010" on decimal dimensions, ±0.025" on fractional dimensions, ±3° on angles, and ±0.003"/−0.003" on hole sizes. The same terms address flatness, burrs, and other conditions.
These published standards should not be treated as a universal metal stamping tolerance chart. Critical dimensions should be specified on the engineering drawing and reviewed with the stamping manufacturer.
Tight Tolerance Metal Stamping
Some applications require considerably tighter tolerances than standard commercial stamping specifications.
Tight-tolerance stamping may be necessary for:
- Press-fit components
- Electrical connectors and terminals
- Precision shims
- Bearings and bearing components
- Drawn cups and housings
- Components with critical mating surfaces
- High-volume assemblies with limited dimensional variation
Acro identifies tight-tolerance components as a core production capability and manufactures parts including electrical connectors and terminals, shims, bearings, washers, drawn cups, and discs.
Modern servo press technology and carefully controlled tooling can also make it possible to stamp parts that historically may have required additional machining or cutting operations.
Tolerance Stack-Up in Stamped Parts
Tolerance stack-up occurs when the variation of multiple dimensions accumulates across a component or assembly.
For example, a stamped bracket may contain several holes, bends, and mounting surfaces. Even when each individual dimension falls within its specified tolerance, the combined variation can affect the relationship between the final features.
For critical assemblies, engineers should evaluate the complete dimensional chain rather than considering individual tolerances in isolation.
A stamping manufacturer can help identify which dimensions are functionally critical and where tolerances may be safely adjusted to improve manufacturability.
Tighter Tolerances Do Not Always Mean Better Parts
One common misconception is that the tightest possible tolerance always produces the best component.
In reality, every tolerance should have a functional reason.
Unnecessarily tight tolerances can increase:
- Tooling complexity
- Inspection requirements
- Production costs
- Scrap risk
- Manufacturing difficulty
- Lead times
If a dimension does not affect fit, function, or performance, a tighter tolerance may provide little practical benefit.
The objective should be to establish the right tolerance for the application, not simply the smallest possible tolerance.
Designing for Manufacturability
The best time to address tolerance requirements is during the design stage.
Early collaboration with a metal stamping manufacturer can help identify potential problems with:
- Material selection
- Hole placement
- Bend locations
- Formed features
- Deep-draw requirements
- Tooling clearances
- Critical dimensions
- Tolerance stack-up
Acro provides die design and re-engineering support and maintains an in-house toolroom for tooling development and modifications.
Acro also supports quality-control processes including Statistical Process Control (SPC) and Production Part Approval Process (PPAP) requirements.
Deep Drawing and Tolerance Control
Deep drawing presents unique tolerance challenges because flat sheet metal is progressively formed into three-dimensional components.
During deep drawing, material can stretch and change thickness as it moves through the die. The geometry, material properties, tooling, number of drawing operations, and forming conditions can all affect the final component. Acro identifies deep drawing as a core capability for producing components such as cups, housings, sleeves, enclosures, collars, and covers.
For deep-drawn components, engineers should consider not only overall dimensions but also wall thickness, flatness, parallelism, concentricity, and other application-specific requirements.
Choosing the Right Metal Stamping Partner
Tolerance requirements should be evaluated alongside production volume, material, part geometry, tooling, quality requirements, and total manufacturing cost.
A capable stamping manufacturer can review an engineering drawing and help determine whether the specified tolerances are appropriate for the intended process.
Acro Metal Stamping has been producing precision production stampings since 1942 and specializes in tight-tolerance and complex metal components. Its capabilities include progressive and compound dies, deep drawing, in-house tooling, servo press technology, and quality-control processes designed for demanding production applications.
Get the Right Tolerances for Your Stamped Parts
Metal stamping tolerances are an important part of designing reliable, manufacturable components. The right specifications can help ensure proper fit and function while avoiding unnecessary manufacturing costs.
Whether your project involves a simple stamped component, a precision electrical terminal, a deep-drawn enclosure, or a complex progressive-die part, tolerance requirements should be evaluated early in the design and tooling process.
Need help determining the right tolerances for your stamped metal component? Contact Acro Metal Stamping to discuss your part requirements, material, production volume, and engineering specifications.