Determining the blank size is a very crucial step for a successful draw. The amount of material needed for the final product must be included within the blank. When there are multiple draws for a single product, it can be tricky to determine how much material is needed. Since the draw process causes thinning and thickening of the metals, this is an important first step to a successful draw.
It is important to note the size, accuracy, and finish of the die entry radius. If the die radius is too small, the material will not easily flow. This results in stretching and fracturing of the drawn product. If the die radius is too large, the material will wrinkle after leaving the pinch point between the draw ring surface and binder. If the wrinkling is extreme, the material flow may be restricted when pulled through the die entry.
The draw ratio is one of the most important elements of maintaining successful deep draws. The draw ratio is the relationship between the size of the draw post and size of the blank. During the forming process, the blank is pressed into a circumferential compression which creates a resistance of metal flow. If there is too much resistance, the metal will fracture. If the draw post is not big enough, the metal will stretch, becoming thinner until it cannot be formed. If the draw post is the appropriate distance from the edge of the blank, the metal will be able to flow, while becoming thicker as it enters into the die cavity.
The formula for the draw ratio is: D/d ≤ 2 for a successful draw.
If this ratio is greater than 2, re-draws (or break downs) are required. In our industry, this is a general rule of thumb. Certain materials may have more accurate, material-specific rule of thumb ratios. For example, Aluminum is 1.8.
Adding lubricants and a polish to the die surface helps with friction and reduces the chance of galling. Galling is when two metallic surfaces slide against each other, creating friction. This can harm the product and the tooling. Applying lubricant to the blank is a very important step in the deep drawing process, to create the highest quality product, while protecting the draw post tooling. Avoiding galling enables the blank to slide easier, allowing for free flowing of the metal.
The die temperature can cause the lubricant to thicken or thin, depending on how hot the die is. When lubricants heat up, their viscosity drops and they thin out. As they get cold, their viscosity increases. Understanding this relationship is key to creating the best quality drawn part, while maintaining the quality of the die.
It is critical to select the correct lubricant for each deep drawing process. Each lubrication brand, type, and formulation performs differently at different temperatures, depending on their intended use. Certain lubrications need to increase to a certain “working temperature” before they will exhibit any friction-fighting properties at all. In contrast, other lubricants only work in a cold or room-temperature environment. When determining the correct lubrication, the tool temperature, (mid-run and at rest) blank material, and draw severity are all taken into account.
At Toledo Metal Spinning, we use pinch and pressure to control the material flow. Binder Pressure is a machine setting that controls the upwards force and/or pressure in the press that will be applied through the draw ring/binder, which sits on top of the cushion pins. The draw ring pressure rises, while the die pressure and slide force is in a downward motion, this is how the blank is “pinched.”
The N value is known as the Work Hardening Exponent, or the Strain Hardening Exponent. This describes steel’s ability to stretch. The larger the material’s N Value is, the more the material is able to elongate without necking, or deforming.
The R Value, also known as the Lankford Coefficient or Plastic Strain Ratio, describes the ability of a material to flow or draw. The blank size affects the ability of metal to flow because the press’ speed need to allow for time for the material to flow through. For a more technical explanation, it is a measure of how resistant a metal alloy is to thinning. Mathematically, it is the ratio of the true width strain to the true thickness strain at a specific value of longitudinal strain, up to the point of uniform elongation.
Deep Draw Metal Stamping for Strength and Efficiency The deep drawing sheet metal forming process is a cold-forming metal fabrication process that is conducted in a room-temperature environment. A metal blank is stretched around a die cavity, eventually conforming to the shape of the plug, shape of the die, and the depth of the draw.
Benefits of Forming Deep Drawn Metal Stamped Parts The deep drawing sheet metal forming process is a cold-forming process performed in an environment at or near room temperature, where the metal is permanently deformed into the desired geometry. In this process, the flat metal blank is formed and stretched around a die cavity with a
What is the Trimming Process and How is it Performed? Trimming is a process used to remove excess material to achieve a desired shape, size, and finish, while removing burrs and smooths out sharp edges. To trim a part, it is put on a lathe and processed by a highly skilled metal spinner, or a
The Metal Finishing and Polishing Process The polishing process is a secondary metal fabrication process that is done to create a smooth and shiny surface by utilizing abrasives or chemical treatment, and can be done by hand or robotic automation. The purpose of adding a finish or polish is to improve the appearance by creating
The Benefits of One-piece Constructions At Toledo Metal Spnning Company, we have been forming metals since 1929. With nearly a century of experience, we have mastered a wide range of processes including laser cutting, metal spinning, deep drawing, machining, rolling and seam welding, to build strong and durable high-performance parts. But what truly sets us
The History of Deep Draw Metal Stamping What is Deep Drawing? Deep Draw forming with conventional tool and die technology is the conforming of sheet metal, commonly referred to as a blank, around a plug in either a hydraulic or mechanical press. The edges of the blank are restrained yet allowed to slide by a precise
What is Hydroforming? Hydroforming, or utilizing the hydro-mechanical-press is a metal forming process where complex and structurally sound parts with tight tolerances that can be made from various metals. A water-based fluid force, oil, gas, or a flexible elastic polymer membrane, is highly pressurized up to 10,000 PSi is applied onto a piece of metal,
Clarifying Elements to the Deep Draw Design Process – The Draw Ratio When it comes to tool design, the most important formula is The Draw Ratio, also known as Limiting Draw Ratio (LDR). The formula is: LDR = D / d D = blank diameter d = cup ID or punch diameter This ratio shows
What are the differences of Deep Drawing and Hydroforming? Hydroforming is a specialized Deep Drawing process also known as Sheet Hydroforming. Sheet hydroforming allows various materials to become complex and structurally sound parts. It allows for asymmetrical or irregular shaped geometries, while conventional Deep Drawn parts are symmetrical and uniform throughout the entire shape. Another
