What is Deep Drawing?

1. Calculate the blank size and optimize

One of the most common hidden costs associated with deep drawing is the scrap generated from producing blanks. When parts are produced in large batches in the thousands, or ten thousands annually, custom coil sizes can be sourced to reduce waste. If not, at TMS, blanks are laser-cut from sheet metal in-house. By optimizing the blank diameter and shape, excessive engineered scrap or unnecessary drops can be reduced or eliminated, significantly impacting the overall cost of the part. It is key to take into account extra material, sufficient enough for trimming and work holding in the blank size.

2. Design to minimize the material needed for trimming & work holding

It is normal for the finished part to be a different size than the initial blank size used to form the part. This is because of the necessary method to hold and process the part from start to finish. It is important to keep in mind that the final part may require additional material to accommodate secondary processes. At Toledo Metal Spinning, examples of secondary services offered are adding interior and/or exterior finishes or welding inlets or fittings.

3. During the design phase, plan for thinning 

Throughout the drawing or deep drawing process, material the material may endure significant surface tension and stretching. This typically causes thinning near the closed end or first contact surface on the punch. It also results in thickening near the flange or open end. Accounting for this variation during the design process will ensure proper fit, reduce scrap, and improve part performance.

4. Design to allow for a taper

Because the punch and die require adequate clearance to accommodate mill tolerance on material thicknesses, there is a taper in their side walls. The taper is influenced by the material type, thickness, part depth, and punch-to-die clearance, typically ranging from 0.005 to 0.010 inches per inch of depth.

To minimize taper:

• Minimize the part depth
• Use tooling designed specifically for the application
• Select materials with better formability that thin less
• Accommodate material flow with larger draw radius

If the taper is not acceptable, secondary forming processes can reduce and sometimes eliminate the taper. However, this oftentimes results in an increased cost per part.

5. Select material that is formable 

Selecting the most formable material and/or temper for the deep draw metal stamping process is crucial. Material selection can significantly reduce or eliminate scrap during the draw process. While some applications require higher stiffness or strength, optimizing for formability often lowers the overall cost.

6. Use existing tooling when able 

As many manufacturers do, at Toledo Metal Spinning, we maintain a large library of existing tooling that can be of use. Like TMS, a company that chooses to invest heavily in their own tooling can produce shapes very close to designed dimensions. Sometimes, minor design modifications can eliminate the need for new tooling or engineering charges. For a re-cut charge, repurposing inactive tooling is another cost-saving option when dimensions align closely with a new part design.

7. Hydro-mechanical drawing (hydroforming) requires less tooling 

Hydro-mechanical deep drawing, also known as hydroforming, is a process that uses hydraulic fluid as either a punch that pushes the material into the cavity or a die to push the metal over a punch. Though it is similar to deep drawing, it differs because a rubber bladder acts as the die with thousands of PSI behind it. When comparing hydroforming with deep drawing, the rubber blader pushes the blank around the plug, instead of stretching the material. This results in less stress on the metal, and allows for greater reduction ratios and more elaborate or complex geometries.

8. Uniform metal thickness is achieved by hydro-mechanical deep drawing (hydroforming).

Hydro-mechanical forming applies lower forces on the material, allowing more uniform wall thickness throughout the part. This is especially helpful for difficult to draw, irregular or asymmetrical shapes, where a metal die wouldn’t allow the metal to flow or change to be forgiving of the metal’s needs.

9. Optimize for a minimum number of draws.

Each time a part is deep drawn, its diameter or length/width are reduced. The number of draws required for the final shape is dependent on the material’s elongation capacity. For example, 14-gauge stainless steel can typically be reduced:

• 45% in the first draw
• 30% in the second draw
• 15% in subsequent draws after annealing (this additional process would most-likely be required to further form the drawn part)

With this in mind, a 10-inch blank could be drawn to approximately 3.27” in diameter after three reductions. Minimizing the number of draws helps to reduce cost and processing time.

10. Add features that leverage the benefit of in-house secondary operations.

Forming is often followed by cutting, finishing, secondary forming, or joining, processes that are necessary to complete the part. A deep drawing facility typically offers these services in-house, such as TMS, and can streamline production and reduce total cost, depending on the part design.

During the prototyping phase, reputable manufacturers like TMS, will conduct a design for manufacturing and assembly, or DFMA, to review and identify opportunities for cost-savings, and features that may assist in overcoming design or cost barriers.

Take into account the variety of processes the manufacturer is offering.

At Toledo Metal Spinning Company, we offer deep draw metal stamping and hydroforming. These processes are used for different purposes, and having an understanding of when and why they are used, could lead to significant cost savings, depending on the shape and use of the final part. Hydro-mechanical drawing, or hydroforming, utilizes hydraulic fluid, rather than a punch to push the material into the cavity or die to push the metal over a punch. The difference between hydroforming forming and deep drawing is that a rubber bladder is used, rather than a die, with thousands of PSI behind it. The bladder pushes the material to shape it, instead of stretching, resulting in less stress on the metal and allowing for greater reduction ratios or complex shapes.

Is a polish or any other secondary processing needed?

It is important to keep in mind that the final part may require additional material to accommodate secondary processes. At Toledo Metal Spinning, examples of secondary services offered are adding interior and/or exterior finishes or welding inlets or fittings. If a sanitary polish is needed, a fitting or inlet needs to be added, make sure to account for a few extra steps in the fabrication process.

If possible, plan to use existing tooling.

Many manufacturers like Toledo Metal Spinning Company maintains a large library of tooling in-house that can product shapes very close to the designed dimensions. Sometimes, when minor design modifications are needed, re-cutting an inactive tool when dimensions align close enough with a new part design. This can lead to significant cost savings, rather than making a brand new tool.

Key Variables in the Deep Drawing Process

Successful deep drawing depends on controlling several process variables that influence material flow, dimensional accuracy, and final part quality. Understanding these factors helps ensure consistent, repeatable production of high-quality deep drawn components.

Blank Size, Material Thickness, and Part Geometry

Selecting the correct blank size is one of the first, and most important steps in the deep drawing process. The blank must contain enough material to form the finished component while accounting for changes in wall thickness that occur as the metal flows into the die.

For components requiring multiple draw operations, calculating the proper starting blank becomes even more critical. An undersized blank may not fully form the part, while an oversized blank can create wrinkles or excess material that complicates production.

Draw Radius

The entry radius of the forming die plays a major role in how smoothly the material flows during drawing.

If the die radius is too small, excessive resistance can cause the material to stretch beyond its limits, increasing the risk of tearing or fracture. An overly large radius reduces material control and may allow wrinkles to develop as the blank enters the die cavity. Proper die radius design balances material flow while minimizing defects.

Draw Ratio

The draw ratio is one of the primary design considerations in successful deep drawing. It compares the diameter of the starting blank to the diameter of the punch (or draw post) and helps determine whether a part can be produced in a single draw, or requires multiple drawing operations.

During forming, the blank experiences compressive forces around its circumference while being pulled into the die. If material flow is overly restricted, the metal may crack. If insufficient material is available, excessive stretching can lead to thinning and failure.

A commonly accepted guideline for conventional deep drawing is:

D / d ≤ 2

Where:

• D = Blank diameter
• d = Punch (draw post) diameter

When the draw ratio exceeds this value, additional redraw operations are generally required. The allowable ratio varies by material. For example, aluminum alloys often have a practical draw ratio closer to 1.8:1.

Lubrication and Die Surface Finish

Proper lubrication is essential for reducing friction between the blank and tooling during sheet metal forming. Lubricants help prevent galling, a form of adhesive wear that occurs when metal surfaces slide against one another under pressure.

A polished die surface combined with the correct lubricant allows the blank to flow more freely into the die, improving part quality while extending tooling life.

Die Temperature

Tool temperature has a direct impact on lubricant performance throughout the forming cycle.

As temperature increases, lubricant viscosity typically decreases, allowing it to flow more easily. Lower temperatures generally increase viscosity, which can change how effectively the lubricant reduces friction.

Selecting the appropriate lubricant requires considering several factors, including:

• Tool operating temperature
• Blank material
• Draw severity
• Production speed

Some lubricants perform best only after reaching a specific operating temperature, while others are designed for room-temperature or cold-forming applications.

Blank Holder (Binder) Pressure

Blank holder pressure, sometimes called binder pressure, controls how tightly the blank is held as it enters the forming die. This is one of the most important machine settings in the deep drawing process because it directly affects material flow.

Too little pressure can allow the material to wrinkle, while excessive pressure restricts metal flow and increases the likelihood of tearing.

At Toledo Metal Spinning, binder pressure is carefully adjusted to create the proper balance between restraint and material movement, producing consistent, high-quality drawn parts.

Material N-Value (Strain Hardening Exponent)

The N-value, or strain hardening exponent, describes a material's ability to strengthen as it is plastically deformed.

Materials with higher N-values distribute strain more evenly during forming, allowing them to stretch further before localized necking or failure occurs. In general, higher N-values improve formability and increase the likelihood of a successful deep draw.

Material R-Value (Plastic Strain Ratio)

The R-value, also known as the Lankford coefficient, measures a material's resistance to thinning during deformation.

Materials with higher R-values tend to draw more easily because they resist wall thinning while allowing material to flow into the die cavity. This property is especially important when manufacturing deep, thin-walled components where maintaining consistent wall thickness is critical.

When evaluating materials for deep drawing, engineers often consider both the N-value and R-value together, as they provide valuable insight into how the metal will behave throughout the forming process.

Deep drawing can be performed using a wide range of materials, with Stainless Steel, Copper, Aluminum and Cold Rolled Steel among the most commonly specified for precision metal components.

Stamping is a manufacturing process when coils or flat sheets of material are formed into specific shapes. The Stamping process is used to make small changes to parts, such as bends, tabs, or embossments. These features tend to be much shallower in depth than a deep drawn part. Stamped parts start flat and go through a sequence of stamps from a press, where new features such as small tabs, are folded in, or holes are punched out. These features are very sharp, detailed, and precise. Stamping is a broad term that includes many specific forming techniques such as embossing, blanking, punching, bending, flanging, and the list goes on. Each of these methods involve short, quick, and abrupt hits or press movements.

At Toledo Metal Spinning, our stamping capabilities lie with our Komatsu Mechanical Press, where we intertwine our deep drawing abilities with stamping and are able to pierce holes, or form small tabs or flanges. Before the integration of our laser cutting technology, we used to cut blanks with this press.  

Deep Drawing is used to make larger features such as as cups, pans, or domes. We draw parts from our two hydraulic AP&T presses. Drawing a cup requires exerting a significant amount of pressure on a flat sheet, and gradually drawing it over a die to sculpt it into the cup shape. Forming these shapes requires much more pressure over a longer period of time than a quick stamp. If the pressure is not controlled properly or is performed too fast, the metal will fracture or break, and will not be usable.  

The shape of the part is the main difference between a stamped or deep drawn product. Drawn parts will have more pronounced curves in the shapes, and will be larger than a stamped part. Below is an example of one of our deep drawn cups. Take note of the defined edges and curves, while its strength and durability is present. 

Hydroforming, also referred to as sheet hydroforming, is an advanced metal forming process that uses high-pressure fluid to shape sheet metal into complex, seamless components. While it shares many similarities with deep drawing, hydroforming offers greater flexibility for producing parts with asymmetrical or irregular geometries that are difficult to manufacture using conventional deep drawing methods.

Unlike traditional deep drawn parts, which are typically rotationally symmetrical, hydroformed components can incorporate more intricate contours and non-uniform shapes. However, hydroforming is generally limited in the depth of parts it can produce and is not well suited for components requiring sharp corners or steep vertical walls.

How the Hydroforming Process Works

The hydroforming process begins by placing a laser-cut metal blank over a forming die. High-pressure hydraulic fluid then forces the material into the die cavity, allowing the sheet metal to conform to the desired shape. Because the material is formed from a single piece of metal, hydroforming produces seamless components without the need for welding, helping improve strength, appearance, and dimensional consistency.

Hydroforming vs. Deep Drawing

Both hydroforming and deep drawing are highly effective sheet metal forming processes, but each offers distinct advantages depending on the application.

Deep drawing is typically the preferred solution for high-volume production of deep, symmetrical parts with excellent repeatability and cost efficiency. Hydroforming, on the other hand, is often selected for lower-volume production or components that require more complex, irregular geometries that cannot be achieved through conventional deep drawing alone.

Combining Hydroforming, Deep Drawing, and Metal Spinning

At Toledo Metal Spinning, we leverage deep drawing, hydroforming, stamping, and metal spinning to provide the most efficient manufacturing solution for each application.

One common approach is using our press equipment to create a preform before the metal spinning operation. This allows material to be strategically redistributed toward the flange of the part before spinning begins, reducing wall thinning during the spinning process and improving the overall strength, dimensional accuracy, and quality of the finished component.

304/L Stainless Steel

Good – Lowest cost of high quality deep drawing stainless steel material. The high nickel content allows for good deep draw working. Elong = 60%, Yield 34/30 KSI, Tensile 85/75 KSI

316/L Stainless Steel

Good – More corrosion resistant than 304 grade due to the addition of molybdenum with the same higher levels of nickel, thus allowing for it to be an excellent deep drawing stainless steel. Elong = 60%, Yield 30 KSI, Tensile 75 KSI

410 Stainless Steel

Low – 400 series, generally lower cost stainless steel than 300 series since there is typically very little or no nickel, is not ideal for extremely deep parts since the lack of nickel reduces stainless steels deep draw ability. Elong = 30%, Yield 65 KSI, Tensile 95 KSI

430 Stainless Steel

Low – 430 is similar to 410 with little less strength. Like 410, material is readily available and is less expensive than 300 series stainless steel. Elong = 30%, Yield 45 KSI, Tensile 75 KSI

444 Stainless Steel

Low – 444 stainless steel is similar in its ability to form compared to 400 series stainless grades. Uncommon to 400 series, this specialty stainless grade has Molybdenum added with Titanium and Niobium added to stabilize the microstructure. This allows the material to be similarly corrosion resistant to 316, without the cost of 316 due to the lack of Nickel. The low Nickel also allows for excellent resistance due to corrosion cracking to chloride induced stress, which is why SS 444 is frequently used for parts in contact with tap water. Elong = 20%, Yield 40 KSI, Tensile 60 KSI