# Fundamentals of sheet metal design technology of t

2022-10-03
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SolidWorks' sheet metal design technology foundation

I. Introduction to the calculation method of sheet metal

engineers of sheet metal parts and dealers of sheet metal materials will use various algorithms to calculate the actual length of material preparation in the unfolded state in order to ensure the desired size of parts after final bending. The most commonly used method is the simple "finger pinching rule", that is, the algorithm based on their own experience. Generally, these rules should take into account the type and thickness of materials, the radius and angle of bending, the type of machine tool and step speed, etc

on the other hand, with the emergence and popularization of computer technology, in order to make better use of the super strong analysis and calculation ability of computer, people increasingly use the means of computer-aided design, but when computer programs simulate the bending or unfolding of sheet metal, a calculation method is also needed to accurately simulate the process. Although each store can customize a specific program implementation according to its original finger pinching rules only to complete a certain calculation, most commercial CAD and 3D solid modeling systems today have provided more general and powerful solutions. In most cases, these applications can also be compatible with the original experience based and pinch rule methods, and provide a way to customize the specific input content into its calculation process. SolidWorks has naturally become a leader in providing this sheet metal design capability

to sum up, there are two popular sheet metal bending algorithms that are widely adopted today, one is based on bending compensation, and the other is based on bending deduction. SolidWorks software only supports bending compensation algorithm before 2003 version, but since 2003 version, both algorithms have been supported

in order to make readers better understand some basic concepts in the calculation process of sheet metal design in a general sense, and also introduce the specific implementation methods in SolidWorks, this paper will summarize and elaborate in the following aspects:

1, the definitions of bending compensation and bending deduction, their respective corresponding relationship with the actual sheet metal geometry

2, how bending deduction corresponds to bending compensation, How can users using the bending deduction algorithm easily convert their data to the bending compensation algorithm

3. The definition of K factor, and how to use K factor in practice, including the application range of K factor value for different material types

II. Bending compensation method

for a better understanding of bending compensation, please refer to figure 1, which shows a single bend in a sheet metal part. Figure 2 shows the expanded state of the part

figure 1

the bending compensation algorithm describes the unfolded length (LT) of the part as the sum of each length of the part after flattening plus the length of the flattened bending area. The length of the flattened bend area is expressed as the bend compensation value (BA). Therefore, the length of the whole part is expressed as equation (1):

LT = D1 + D2 + BA (1)

Figure 2

the bending area (shown as the light yellow area in the figure) is the area that deforms in the bending process theoretically. In short, in order to determine the geometric dimensions of the unfolded parts, let's think as follows:

1. Cut the bending area from the bent parts

2. Lay the remaining two flat parts on a table

3. Calculate the length of the bending area after flattening

4. Bond the flattened bending area between the two flat parts, The result is that the slightly difficult part of the unfolded part is how to determine the length of the flattened bending area, that is, the value represented by Ba in the figure. Obviously, the value of Ba will vary with different situations, such as material type, material thickness, bending radius and angle. Other factors that may affect Ba value include machining process, machine tool type, machine tool speed, etc

Where does the

ba value come from? In fact, there are usually the following sources: sheet metal material suppliers, experimental data, experience, and some engineering manuals. In SolidWorks, we can directly input Ba values and provide one or more tables with BA values, or we can use other methods such as K factor (which will be discussed in depth later) to calculate Ba values. For all these methods, we can enter the same information for all bends in the part, or we can enter different information for each bend separately

for different thicknesses, bending radii and bending angles, the bending table method is the most accurate method. Let's specify different bending compensation values. Generally speaking, there will be a table for each material or combination of materials/processes. The formation of the initial table may take some time, but once it is formed, we can constantly reuse some parts of it in the future

III. bend deduction

bend deduction usually refers to the amount of fallback, which is also a different simple algorithm to describe the process of sheet metal bending. Referring to figure 1 and Figure 2, the bending deduction method refers to that the flattening length lt of the part is equal to the sum of the length of the two flat parts extending to the "cusp" (the virtual intersection of the two flat parts) minus the bending deduction (BD). Therefore, the total length of parts can be expressed as equation (2):

LT = L1 + L2 - BD (2)

bending deduction is also determined or provided through the following ways: sheet metal material suppliers, test data, experience, manuals for different materials with equations or tables, etc

IV. relationship between bending compensation and bending deduction

because SolidWorks usually adopts bending compensation method, it is very important for users who are familiar with bending deduction method to understand the relationship between the two algorithms. In fact, it is easy to derive the relationship equation between the two values by using the two geometric shapes of bending and unfolding of parts. In retrospect, we have two equations:

LT = D1 + D2 + BA (1)

LT = L1 + L2 - BD (2)

the right side of the above two equations is equal and can be changed into equation (3):

D1 + D2 + Ba = L1 + L2 - BD (3)

make several auxiliary lines in the geometric part of Figure 1 to form two right angled triangles, as shown in Figure 3

angle a represents the bending angle, or the angle swept by the part during bending. This angle also describes the angle of the arc formed by the bending area, which is shown in Figure 3 as two halves. If the inner bending radius is represented by R, the thickness of the sheet metal part is represented by T. Use a right triangle to help clearly express various geometric relationships, such as the green right triangle in Figure 3. According to the dimensions of the right triangle and the trigonometric function principle shown in the figure, we can easily get the following equation:

Tan (a/2) = (l1-d1)/(r+t)

after transformation, the expression of D1 can be obtained as:

D1 = L1 – (r+t) Tan (a/2) (4)

using the same method and using the relationship of the other half of the right triangle, the expression of D2 can be obtained as:

.4) (5) Substituting into equation (3), we can get the following equation:

L1 + L (r+t) Tan (a/2) + Ba = L1 + L2 BD

after simplification, we can get the relationship between Ba and BD:

Ba = 2 (r+t) Tan (a/2) -bd (main machine maintenance: 6)

when the bending angle is 90 degrees, because Tan (90/2) =1, This equation can be further simplified:

Ba = 2 (r+t) -bd (7)

equation (6) and equation (7) provide users who are only familiar with one algorithm with a very convenient calculation formula to convert from one algorithm to another, and the required parameters are only the thickness of the material, bending angle/bending radius, etc. Especially for SolidWorks users, equations (6) and (7) simultaneously provide a direct calculation method for converting bend deduction to bend compensation. The value of bending compensation can be used for the whole part/independent bending, or it can form a bending data table

v. K-factor method

k-factor is an independent value that describes how sheet metal bending bends/unfolds under a wide range of geometric parameters. It is also an independent value used to calculate bending compensation (BA) in a wide range of cases such as various material thicknesses, bending radii/bending angles, etc. Figures 4 and 5 will be used to help us understand the detailed definition of K-factor

Figure 5

we can be sure that there is a neutral layer or axis in the material thickness of the sheet metal part. The sheet metal material in the neutral layer in the bending area of the sheet metal part is neither stretched nor compressed, that is, the only place in the bending area that does not deform. In Figures 4 and 5, it is shown as the junction of pink area and blue area. During bending, the pink area is compressed and the blue area is extended. If the neutral sheet metal layer is not deformed, the length of the neutral layer arc in the bending area is the same in its bending and flattening states. Therefore, BA (bending compensation) should be equal to the length of the arc of the neutral layer in the bending area of the sheet metal part. The arc is shown in green in Figure 4. The position of the neutral layer of the sheet metal depends on the properties of the specific material, such as ductility. Assume that the distance between the neutral sheet metal layer and the surface is "t", that is, the depth of entering the sheet metal material from the sheet metal part surface to the thickness direction is t. Therefore, the radius of the arc of the neutral sheet metal layer can be expressed as (r+t) Using this expression and bending angle, the length (BA) of the arc of the neutral layer can be expressed as:

Ba = pi (r+t) a/180

in order to simplify the definition of representing the neutral layer of sheet metal, and considering that it is applicable to all material thicknesses, the concept of K-factor is introduced. The specific definition is: K-factor is the ratio of the thickness of the neutral layer of the sheet metal to the overall thickness of the sheet metal part material, that is:

k = t/T

therefore, the value of K will always be between 0 and 1. If a k-factor is 0.25, it means that the neutral layer is located at 25% of the thickness of the part sheet metal material. Similarly, if it is 0.5, it means that the neutral layer is located at 50% of the whole thickness, and so on. Combining the above two equations, we can get the following equation (8):

Ba = pi (r+k*t) a/180 (8)

this equation is the calculation formula that can be found in SolidWorks manuals and help. Several of these values, such as a, R, and T, are determined by the actual geometry. So back to the original question, where does the K-factor come from? Similarly, the answer is the old sources, namely, sheet metal material suppliers, test data, experience, manuals, etc. However, in some cases, the given value may not be obvious K, or it may not be fully expressed in the form of equation (8), but in any case, even if the expression is not exactly the same, we can always find the connection between them

for example, if the neutral axis (layer) is described in some manuals or literatures as "located at the place 0.445x material thickness away from the surface of the sheet metal", it is obvious that its carbon fiber content is about 10% to 40%, which can be understood as that the K factor is 0.445, that is, k=0.445. In this way, if the value of K is substituted into equation (8), the following formula can be obtained:

Ba = a (0.01745r + 0.00778t)

If equation (8) is modified in another way, the constant in it is calculated, and all variables are retained, then:

Ba = a (0.01745r + 0.01745 k*t)

comparing the above two equations, we can easily get: 0.01745xk=0.00778, In fact, it is easy to calculate k=0.445

after careful study, according to the disclosure of the prospectus, the following types of features are also provided in the SolidWorks system

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