What Is Deep Drawing?
Deep drawing is a method of processing by applying a die to a single sheet of sheet metal.
It can be used to form deep shapes, such as containers, which are deeper than the diameter of the finished product. It is distinguished from shallow drawing, in which the shape is shallower than the diameter of the finished product.
Available materials can be selected based on four mechanical properties (tensile strength, yield point, elongation, and hardness). When considering whether deep drawing is possible, the critical drawing ratio is calculated. When a disk of diameter D is drawn with a punch of diameter d, the critical drawing ratio is expressed as D/d. As a rough guide to the critical drawing ratio for each material, pure titanium 1 is 2.7, while aluminum and copper are 2.0.
Uses of Deep Drawing
Deep drawing is a process that uses a die to process a single sheet of sheet metal, so it is possible to produce seamless products in a shorter time than welded or riveted products. It is used for engine covers, aluminum cans, bath containers, caps, etc.
It can produce good-looking products at a low cost, but since tooling costs are incurred when introducing production, it is not suitable for small-lot, high-variety production and is better suited for mass production. When considering deep drawing, choose a supplier that has the jigs and tools needed to perform the process in advance to reduce initial costs.
Principle of Deep Drawing
Deep drawing is a simple method of forming by applying pressure with a die. A lower die with a concave shape and an upper die that sinks into the lower die are combined as a set to apply pressure to a plate. The lower die is called a die and the upper die is called a punch.
The mechanism is simple, requiring fewer working hours for processing and ensuring consistent quality, but the design of the die requires precise calculations. If a poor quality die is used, defective products with wrinkles and cracks may be produced.
Thin metal sheets can be processed for bottomed containers in a wide variety of shapes, such as cylinders, cones, and rectangular cylinders. It is suitable for mass production, but the design cost to improve accuracy and quality is high.
Types of Deep Drawing
Deep drawing methods differ depending on the shape of the product to be manufactured. It is important to understand which of the following six processing methods is applicable to the shape of the sheet metal product to be manufactured.
1. Cylindrical Drawing
Cylindrical drawing is a processing method in which a die with a hollow center is inserted between the die and a punch is punched into the sheet metal from the hollow to form it by metal plasticity. It is used for processing pots and pans.
2. Square Tube Drawing
This process is used for products with a square bottom container, such as kitchen sinks.
3. Deformed Drawing
This process is necessary to form complex shapes and is applicable to press working for automobiles. Since the stress value applied to sheet metal differs depending on the shape, strength design is required to confirm the validity of the shape.
4. Conical Drawing Process
This is a method of processing tumbler-like shapes whose diameters vary depending on the depth. The circular sheet metal is rotated and pressed against a bar called a spatula.
5. Pyramidal Drawing
Like conical drawing, this method is used to produce vessels with different shapes in the depth direction, but the depth and shape is characterized by the presence of a flat section. It is used for processing pyramidal shapes.
6. Spherical-Head Drawing
This process is used for products that form a spherical surface, such as bowls used for cooking.
How to Select a Deep Drawing
In deep drawing, the blank shape and dimensions are first determined. The design must also take into consideration the re-drawing that follows after the initial drawing. Next, the number of drawing processes is considered. The number of drawing processes is determined by calculating the squeezing diameter per drawing based on the drawing ratio.
Deep drawing also requires the design of die and punch dies. The diameter of the die is calculated based on the gap when the punch enters the die, and the width of the holding stand is set according to the width of the flange. If the hold-down table is not designed properly, wrinkles will occur during flange forming.
The press machine to be used is selected to meet the torque output based on the calculated drawing force, and the drawing material to be processed is selected. Two types of lubricants exist: water-based type and oil-based type.