Deep drawing limits and parameters
Deep drawing is a sheet metal forming process in which a flat blank is radially transformed into a die by the mechanical action of a punch, obtaining hollow parts with depths greater than the dimensions of their opening.
Definition and fundamentals of the process
Section titled “Definition and fundamentals of the process”Deep drawing is defined as a forming process with material retention, where the sheet metal blank is clamped at the edges while the central section is forced by a punch into a die. The process is considered “deep” when the depth of the drawn part exceeds its diameter, reaching typical depth/diameter ratios of 1.0 or higher. During the operation, the flange region experiences radial tensile stress and tangential compressive stress; these circumferential compressive stresses can cause wrinkles, which are prevented by a blank holder that controls the flow of material toward the die radius.
The working cycle is characterized by fast process times, with typical press speeds ranging from 100 to 500 mm/s depending on the material and geometric complexity. Contact between the punch, blank, and die must be kept controlled throughout the stroke to ensure dimensional integrity.
| Process parameter | Typical range |
|---|---|
| Drawing speed | 100 – 500 mm/s / 3.9 – 19.7 in/s |
| Blank holder force | 1 – 3 % of maximum drawing force |
| Punch-die clearance | 1.1 – 1.4 × sheet thickness |
| Working temperature (cold) | 20 – 25 °C / 68 – 77 °F |
| Lubrication | Mineral oil, emulsions, or dry film |
Parameters and limits of the process
Section titled “Parameters and limits of the process”The limit drawing ratio (LDR) is the main indicator of material formability, defined as the ratio of the maximum blank diameter that can be drawn without failure to the punch diameter. LDR values for deep drawing steels are typically around 2.0, reaching up to 2.2 with optimal tool and lubrication conditions. The maximum reduction per pass must not exceed 50 % of the initial diameter to prevent failure due to excessive wall thinning.
The depth/diameter ratio for deep drawing starts at 1.0 and can exceed 5.0 in multi-stage drawing applications with intermediate annealing. For square and rectangular shapes, inside corner radii must be at least 6 times the material thickness to avoid stress concentrations leading to fracture; the recommended optimum radius is between 6 and 10 times the thickness. Perpendicularity can be maintained at ±1° and flatness at 0.3 % of part height, values improvable through secondary calibration operations.
| Limit parameter | Typical value |
|---|---|
| Limit drawing ratio (LDR) | 2.0 – 2.2 |
| Maximum reduction per pass | ≤ 50 % of initial diameter |
| Minimum depth/diameter ratio | ≥ 1.0 |
| Minimum inside corner radius | 6 × sheet thickness |
| Recommended inside corner radius | 6 – 10 × sheet thickness |
| Perpendicularity tolerance | ±1° |
| Flatness tolerance | 0.3 % of height |
| Wall thinning limit | ≤ 20 % of original thickness |
Applicable materials
Section titled “Applicable materials”Deep drawing accepts a wide range of both ferrous and non-ferrous materials, provided they have sufficient ductility and work-hardening capacity. Low-carbon steels with controlled inclusion content offer the best performance, while aluminum alloys from the 5000 and 6000 series are preferred for weight-reduced applications. Material quality is critical for obtaining compliant parts, since variations in thickness, anisotropy, or purity can cause wrinkling defects or premature fracture.
| Material | Typical LDR | Minimum punch radius | Recommended maximum thickness | Observations |
|---|---|---|---|---|
| Mild steel (DC04) | 2.0 – 2.2 | 4 – 6 mm / 0.16 – 0.24 in | 4 mm / 0.16 in | Excellent formability, low cost |
| Stainless steel AISI 304 | 1.8 – 2.0 | 5 – 8 mm / 0.20 – 0.31 in | 3 mm / 0.12 in | Requires special lubrication; work-hardens quickly |
| Aluminum 5052-O | 1.8 – 2.0 | 4 – 6 mm / 0.16 – 0.24 in | 4 mm / 0.16 in | Lightweight; requires generous radii |
| Aluminum 6061-O | 1.6 – 1.8 | 5 – 8 mm / 0.20 – 0.31 in | 3 mm / 0.12 in | Precipitation-hardenable, lower LDR |
| Brass (CuZn37) | 1.9 – 2.1 | 3 – 5 mm / 0.12 – 0.20 in | 3 mm / 0.12 in | High ductility, good surface finish |
| Copper | 1.8 – 2.0 | 3 – 5 mm / 0.12 – 0.20 in | 3 mm / 0.12 in | High conductivity, electrical applications |
| Titanium Ti-6Al-4V | 1.4 – 1.6 | 8 – 12 mm / 0.31 – 0.47 in | 2 mm / 0.08 in | Difficult formability, requires partial heating |
Tool operational parameters
Section titled “Tool operational parameters”Punch-die clearances are set based on blank thickness, ranging from 1.1 to 1.4 times that thickness to allow controlled material flow without causing wrinkles or excessive thinning. The die radius must be 4 to 10 times the material thickness to facilitate progressive bending of the flange; radii less than 4 times the thickness significantly increase the required force and the risk of fracture. The blank holder force represents between 1 % and 3 % of the maximum drawing force and must be uniformly distributed over the flange surface.
During severe drawing processes, the material work-hardens and intermediate annealing in controlled atmosphere furnaces may be necessary to restore original ductility. The number of drawing stations or passes depends on the required final depth; each pass reduces the diameter and increases the height, maintaining volumetric constancy of the material.
| Tool parameter | Recommendation |
|---|---|
| Punch-die clearance | 1.1 – 1.4 × sheet thickness |
| Die radius | 4 – 10 × sheet thickness |
| Punch radius | 4 – 12 × sheet thickness (depending on material) |
| Die entry angle | 5° – 10° |
| Blank holder force | 1 – 3 % of maximum load |
| Surface finish of punch and die | Ra 0.2 – 0.4 µm / 8 – 16 µin |
Advantages and limitations
Section titled “Advantages and limitations”Advantages
Section titled “Advantages”Deep drawing produces seamless parts with complex axisymmetric geometries, combining wall and bottom formation in a single operation. Cycle times are very fast, with automated mass production requiring minimal direct labor. The process work-hardens the product during deformation, increasing its mechanical strength compared to the starting material. It accommodates both ferrous and non-ferrous materials, offering application flexibility across multiple industries.
Limitations
Section titled “Limitations”The process is not effective for small production series due to the high cost of tooling and the required setup time. It demands a considerable level of expertise for parameter calibration and resolution of defects such as wrinkles, uneven stretching, or fracture. The quality of the starting material is critical, as variations in composition or thickness cause rejects that are difficult to compensate during the process. Drawing dies represent a high investment, with costs that can exceed several tens of thousands of dollars per complete set.
Associated processes
Section titled “Associated processes”Deep drawing is often combined with other forming techniques on the same press to complete the final geometry of the part in a continuous production line. Among the most common associated processes are ironing (reducing wall thickness up to 30 % of original), flanging (creating material rings to house O-rings), knurling (forming internal or external ribs), curling (rolling the edge under a curling die), stamping/marking (identifying parts with part numbers or logos), threading (forming threads using a wheel and spindle on the press itself), trimming (removing excess material necessary for the drawing process), and hole extrusion (expanding a pilot hole to increase material length).
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What distinguishes deep drawing from shallow drawing?
Section titled “What distinguishes deep drawing from shallow drawing?”Deep drawing is characterized by a depth/diameter ratio greater than or equal to 1.0, whereas shallow drawing has a draw depth less than the smallest dimension of the opening. This limit marks the transition from simple bending with stretching to a process involving significant radial material flow from the flange.
What is the limit drawing ratio (LDR) for low-carbon steels?
Section titled “What is the limit drawing ratio (LDR) for low-carbon steels?”The limit drawing ratio for low-carbon steels ranges from 2.0 to 2.2, meaning the maximum blank diameter can be up to 2.2 times the punch diameter. This is the highest value among commonly used industrial materials, achieved only with optimal lubrication and tool design conditions.
Why is a blank holder necessary in deep drawing?
Section titled “Why is a blank holder necessary in deep drawing?”The blank holder applies a clamping force representing between 1 % and 3 % of the maximum drawing force to prevent first-order wrinkles in the flange. These wrinkles originate from the circumferential compressive stresses generated when reducing the blank diameter during radial flow toward the die.
What is the most common defect in drawn parts and how is it avoided?
Section titled “What is the most common defect in drawn parts and how is it avoided?”The most frequent defect is wrinkling in the flange area, which occurs when the blank holder force is insufficient to contain the tangential compressive stresses. Control is maintained between 1 % and 3 % of the drawing load applied as clamping force, combined with a die radius of at least 4 times the material thickness.
How many passes are required to achieve a depth/diameter ratio of 5.0?
Section titled “How many passes are required to achieve a depth/diameter ratio of 5.0?”To achieve a depth/diameter ratio of 5.0, typically 4 to 6 successive drawing passes with intermediate annealing of the material are required. Each pass reduces the diameter and increases the height, always respecting the maximum reduction limit of 50 % relative to the diameter of the previous pass.
What effect does deep drawing have on the mechanical properties of the material?
Section titled “What effect does deep drawing have on the mechanical properties of the material?”Deep drawing increases the mechanical strength of the material through work hardening, potentially increasing the yield strength by 30 % to 70 % compared to the starting material in the annealed condition. The part wall experiences controlled thinning of up to 20 % of the original thickness in the punch radius area, which is the most critical section of the formed part.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/paper-drawing-sizes-d_140.html
- efunda.com: https://www.efunda.com/processes/metal_processing/stamping_drawing.cfm
- manufacturingguide.com: https://www.manufacturingguide.com/en/deep-drawing