Deep drawing is a manufacturing method that is widely used as structures to form sheet metal into a cup or box. Cooking pots and pans, containers, sinks, automotive parts, such as panels and gas tanks, are among some of the sheet metal deep drawing products. This method is sometimes referred to as drawing and should not be confused with the large phase of deformation.
Deep drawing process
Deep sheet metal drawing is done with a punch and die. The punch is the part’s required base shape, once drawn. The die cavity matches the punch and is a bit wider as well as clearance to allow for its passage. This configuration is comparable to activities of sheet metal cutting. The lateral distance between the die top and the punch surface is clearance, as in cutting. The sheet metal job piece is put on top of the die opening, called a blank. A blank holder surrounding the punch puts pressure on the entire surface of the blank (with the exception of the region under the microscope), holding the sheet metal job flat against the die. The punch is traveling to the blank. The punch forces the sheet metal into the die cavity after contacting the job, forming its shape.
Deep drawing detailed video:https://www.youtube.com/watch?v=iY1ZbjUCpUM
Equipment would require a double action for sheet metal profound drawing procedures, one for the blank holder and one for the punch. In the production sector, both mechanical and hydraulic presses are used. Typically, the blank holder and punch actions can be controlled independently by the hydraulic press, but the mechanical press is fast. Punch and die materials are generally tool steels and iron for profound sheet drawing. The variety of punch and die products, however, can vary from plastics to carbides. Parts are normally drawn at speeds between 4 and 12 inches per second.
Deep Drawing Practice
Deep drawing is a process of sheet metal forming involving complex distributions of material flow and force. The punch and die configuration, as stated above, is somewhat comparable to a sheet metal cutting procedure, like punching or blanking. The punch in deep drawing will result in two primary variables drawing the metal into the die cavity instead of shearing it.
The die corner radius and the punch corner radius are a significant factor in deep drawing. There is no radius for the punch and die corners when cutting sheet metal. On the punch, sharp edges and dying cause it to cut. A radius on an edge changes the distribution of force and causes the metal to flow through the radius into the die cavity. The other significant factor that causes the punch to draw and not cut the sheet metal is the clearance quantity. Clearance is comparatively low in cutting activities, generally 3% to 8% of sheet metal thickness. In the production of profound drawing, the sheet may be sliced or penetrated (not well) despite the radius if the clearance is too low. Deep drawing clearance is higher than sheet thickness, normally clearance values are 107% to 115% sheet thickness.
The sheet metal thickness is supposed to stay continuous for many calculations. Due to the forces concerned, however, there are changes in density in some fields. To shape the side walls of the portion, material must flow through the die corner radius from the peripheral of the blank, then directly into the punch direction. The material forming the straight wall is subjected to tensile stress, which naturally thinens it. To mitigate thinning, deep drawing process variables are regulated, but some sheet metal thinning is inevitable. Most probably, maximum thinning will happen on the side wall, near the part’s base. In some fields, a properly drawn portion may have a decrease in thickness of up to 25%.
Deep Drawing Ratio
It is possible to quantify the quantity of drawing carried on a sheet metal blank. The drawing proportion can do this. The greater the drawing ratio, the greater the deep drawing quantity. There is a limit to the amount of deep drawing that can be performed on a sheet metal blank in a single operation due to the geometry, forces, metal flow and material properties of the work. Drawing ratios can assist in determining the highest possible quantity of deep drawing. The drawing ratio is calculated approximately as DR= Db / Dp.
Db is the blank diameter and Dp is the punch diameter. The maximum diameter is sometimes used for non-circular forms, or the drawing ratio is occasionally calculated using surface regions. For an operation, the drawing ratio limit is generally 2 or less. It also depends on the depth of the drawing, the punch radius, the die radius, the sheet anisotropy and the material of the blank..
Deep drawing Reduction
The decrease (r) is another way of expressing the drawing percentage. Reduction is evaluated with the same factors as the proportion of drawing. R= (Db-Dp)/(Db) can be used to calculate reduction.
Db and Dp are blank diameters and punch diameters. There should be a reduction of.5 or less. The percentage decrease r= (Db-Dp)/(Db) X is often displayed as 100%. The decrease should be 50 percent or less in this situation.
Redrawing Sheet Metal
If sheet metal decrease is more than 50 percent needed, the component must be created in various activities. Redrawing is the subsequent deep drawing of a job which has already undergone a process of deep drawing. A higher extent of profound drawing can be achieved by using more than one procedure.
Multi deep drawing operation processes
Intermediate shape design is essential and for each intermediate step distinctive tooling and configuration will be needed. Each procedure will influence the next one and each stage has to be analyzed. The sheet metal reduction should be considered when designing intermediate shapes, and in most cases the surface area of the blank, any intermediate shapes, and the part can be assumed to be the same.
Occasionally reverse sheet redrawing, or inverse drawing, is used to redraw components. Before being placed on the die for the next operation, the intermediate part is flipped over in reverse redrawing. This will result in the sheet metal being drawn as the first draw in the reverse direction.
Deep Drawing Sheet Metal forces
Force used to perform a sheet metal profound drawing procedure must be sufficient to ensure deformation of the sheet, proper metal flow and overcome friction during the process. The force magnitude must not be too elevated or wrongly applied, or sheet metal tearing may happen. The punch and the blank holder will exert separate forces and force analysis should be done for both.
Understanding the material flow during the production phase is crucial in order to understand the forces that act on the job. Imagine putting on a round cup a piece of paper flat. This is like a piece of sheet metal on a cavity of a round die. Now, by imitating the punch action, the paper is compelled into the cup to take the cup’s cylindrical shape. The paper folds or wrinkles in the process are what happens. In a deep drawing procedure, this is not how a sheet metal work piece should behave. One reason is that, unlike the paper, metal material may flow. Place a piece of aluminum foil on the cup instead of the paper. Aluminum foil is metal, but when forced into the cup it still wrinkles. When forced into the cup, the reason aluminum foil wrinkles is due to the foil’s insufficient density.
Imagine now that a blank sheet of metal is drawn deep into a round cylindrical portion. The material under the punch is compelled into the cavity to form the walls of the portion, pulling material with it. A quantity of sheet metal material is sometimes not drawn into the die in deep drawing and forms a flange around the finished part. However, all the material not yet drawn over the die radius and in the die cavity is often referred to as the flange during a deep drawing procedure. Material from the flange is continually compelled into the die during the continuing process. The die cavity diameter is lower than the sheet metal blank and metal flows inwards from the outer peripheral
Metal flow in Deep drawing
It can be shown that more material is compelled into larger spaces as the same peripheral material moves into a larger diameter circle.
Material forced into regions of smaller diameter(exaggeration)
In the figure bellow, metal flow can be noted. As metal from area A is forced into area B as the profound drawing progresses, metal from area B is forced into area C and metal from area C is compelled into the die chamber. This continues until finally, even the material in area A is compelled into the cavity (giving no flange in the final product). Space constriction will cause the material to behave with compressive forces. Due to the drawing of metal into the die, tensile forces will also be present in the flange.
Forces action on material element in Flange during deep drawing
Compressive forces on material elements in the flange may be related to the compression analogy of a metal beam, such as the one shown in the figure below.
Now imagine the beam’s width decreasing. If the width is small enough, the beam will tend to buckle under stress relative to the length.
Buckling in a metal bean under stress
This is similar during a sheet metal deep drawing procedure to the scenario in the flange. The force exerted on the beam, as stated above, is comparable to the compressive forces acting on the fabric of the blank. Reducing the beam width is tantamount to lowering sheet metal thickness. The beam’s buckling is expressed in sheet metal’s wrinkling. The thicker beam has sufficient width to allow the correct flow of metal. A larger metal beam is the equivalent of a thicker sheet of blank metal. It is now obvious that the reduced the thickness of the sheet metal, the more likely it is to wrinkle during deep drawing. Wrinkles in the flange beginning. It will continue to propagate once wrinkling begins. Wrinkles starting in the flange are drawn into the die and ending in the walls of the part.
Wrinkling during Deep drawing
A blank holder is used to fix the sheet metal wrinkling issue. The blank holder can stop wrinkling for many components by applying pressure on the surface of the blank. The blank holder would be the equivalent of force applied over the thinner beam’s side, causing it to compress correctly instead of buckling. Remember, though, that’s just an analogy to assist you know the mechanics that happen. The real scenario is distinct as forces and material flow also occur in other directions concurrently.
Pressure on Metal beam prevents buckling
The thickness of the sheet metal is significant element of the deep drawing process design. The proportion of thickness to diameter is a major variable used to quantify a blank’s geometry and can be calculated using t / Db. Thickness is t, and Db is the blank’s diameter. The maximum diameter is sometimes used for non-circular sheet steel components. It is usually expressed as a 100% t / Db X. Blank holder usually efficient at 1 percent and above thickness ratios. Ratios of.5 percent to 1 percent are marginal, and even a blank holder may not stop wrinkling for thickness proportions below.5 percent.
During the sheet metal profound drawing method, the corner radius and the punch corner radius are essential in the distribution of power and material flow.
Corner Radius in Deep drawing
Corner radius should be adequate to enable smooth metal flow for profound drawing production. The sheet metal can split if a radius is too tiny. This often happens when the material travels across the corner. Corner radius optimization should be accomplished because it can cause wrinkling if the radius is too big. While small corner radius can be a cause of stress, tearing can be initiated at another part place. Sometimes, however, the place of the tear event will be an indication of the cause in the sheet metal
Sheet metal teraing caused by a low corner Radius
It is also essential to have forces engaged in the creation of the part wall – Wall formation in deep drawing
It brings material from the flange into the die cavity as the punch advances, increasing the length of the part wall. The metal that forms the walls of the part is in tension. Despite constantly drawing material from the flange region to supply the increasing part walls, the tension forces will tend to produce a thinning impact. Thinning is generally the biggest close to the base of the part. The reduction in density that occurs in a deep drawn part’s walls is mitigated by process parameter control. Usually a certain degree of thinning is inevitable. The ironing production method is often used to complete deeply drawn components by the thickness of the wall at night.
When developing a specific sheet metal deep drawing procedure, punch force and blank holder force should be determined. During the entire procedure, the punch force will differ. The punch force will usually achieve its peak at approximately 1/3 of the stroke. Both the strength of punch and the force of the blank holder depend on the geometry of punch and die, punch and die radius, blank geometry, blank size, blank material and friction. Although it will vary, about 30 percent to 40 percent of the maximum punch force is a common value for the blank holder force. References are available to calculate these forces, based on these variables.