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Sheet Metal Fabrication Handbook – Forming

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Looking to learn more about sheet metal fabrication and forming? Look no further than this comprehensive guide, which covers everything from partial shearing to hole extrusion and embossing.

Whether you’re a seasoned pro or just starting out, this article has everything you need to know to take your sheet metal fabrication skills to the next level.

So why wait? Dive in and discover the world of sheet metal fabrication today!

Section 1: Partial shearing

1. Definition:

Applying a certain pressure in a direction perpendicular to the surface of the material to cause the material to flow in the direction of the force, resulting in a forming effect.

2. Functions:

Positioning, such as for welding with half-cutting.

Riveting, such as for riveting electrostatic conductive rails.

3. Processing methods:

NCT: using regular tool combinations (downward half-cutting) or specially developed tools for processing.

Pre-processing: special half-cutting can be used to achieve plate pressing and easy die realization (when the batch size is not large).

4. Precautions:

The height of half-cutting is best not to exceed 0.6T.

Section 2: Bridge drawing

1. Function:

Used for positioning by the top surface, sometimes with a punch mark on it.

Used for limiting by the side edge.

Used for passing binding wire through the hole.

2. Processing methods:

Machining with NCT-specific tools.

Easy mold forming by pre-processing.

Easy mold forming by folding machine.

Mold forming.

Section 3: Louvers

1. Function:

Counterbore hole for use with countersunk screws.

Countersink hole for use with flat head screws.

Rivet nut hole for use with expanding rivet nuts.

2. Processing methods:

Machining with NCT-specific tools.

Machining with a drilling machine.

Section 4: Hole extrusion & embossing

1. Structure description:

Hole extrusion & embossing is a process of vertically punching a hole with a certain inner diameter, outer diameter, and height on a metal sheet. It is mainly used for riveting, passing through holes, tapping, and other purposes.

There are two types of punching: general punching and special-shaped punching.

The forming diagram is shown below:

2. Processing methods:

General punching uses a shared mold for processing, while special-shaped punching requires the design of a specific die.

3. Mold processing methods:

(1) Shared molds for general punching are shown in the following table:

Shared molds for general punching.

Upper Die for Punching Hole.(1)Die numberShared mold 001 Description:

Clamping outer diameter is Φ12.00.
“A” value1.0~7.9
Inter-grade Size0.1
Quantity (Grade X pieces/grade).70X4=280
Upper Die for Punching Hole.(2)Die numberShared mold 004 Description:

Clamping outer diameter is Φ12.00.
“D” value8.0~12.0
Inter-grade Size0.2
Quantity (Grade X pieces/grade).21X3=63
Upper Die for Punching Hole.(3)Die numberShared mold 005 Description:

Clamping outer diameter is Φ12.00.

One end at R position is chamfered, the other end is not chamfered.
“E” value12.5~20.0
Inter-grade Size0.5
Quantity (Grade X pieces/grade).16X2=32
Lower Die for Punching Hole(1)Die numberShared mold 010 Description:

Used together with the punch holder (1).

The maximum outer diameter is Φ8.00.
“F” valve1.0~6.0
Inter-grade Size0.5
Quantity (Grade X pieces/grade).10X2=20
Lower Die for Punching Hole(2)Die numberShared mold 011 Description:

Used together with the punch holder (1).

The maximum outer diameter is Φ8.00.
“F” value1.0~6.0
Inter-grade Size1.0
Quantity (Grade X pieces/grade).6X1=6
Lower Die for Punching Hole(3)Die numberShared mold 012  Description:

Used together with the punch holder (2) when G value is 8.0 and 10.0.

The maximum outer diameter is Φ12.00.        
“G” value8.0~12.0
Inter-grade Size2.0
Quantity (Grade X pieces/grade).9+5+3=17
Lower Die for Punching Hole(4) Die numberShared mold 013 Description:

Used together with the punch holder (2) when G value is 8.0 and 10.0.

The maximum outer diameter is Φ12.00.
“G” value8.0~12.0
Inter-grade Size2.0
Quantity (Grade X pieces/grade).3X1=3
Punch Holder(1)Die numberShared mold 002  Description:

Used together with the lower die for punching holes.

Clamping outer diameter is Φ12.00.
“B” value3.0~6.0
Inter-grade Size1.0
Quantity (Grade X pieces/grade).4X5=20
Punch Holder(2)Die numberShared mold 003       Description:

Used together with the lower die for punching holes.

Clamping outer diameter is Φ12.00.                     
“C” value8.0~10.0
Inter-grade Size2.0
Quantity (Grade X pieces/grade).2X1=2

4. Parameters Table for Punching Marking Holes

Metric System:

Tapping Marking Hole ModelThread DiameterPunching Hole Inner DiameterRequirements for Punching Hole Inner Diameter
MINMAX
M1*0.250.750.780.7290.785
M1.1*0.250.850.880.8290.885
M1.2*0.250.950.980.9290.985
M1.4*0.31.11.141.0751.142
M1.6*0.351.251.321.2211.321
M1.7*0.351.351.421.3211.421
M1.8*0.351.451.521.4211.521
M2*0.41.61.651.5671.679
M2.2*0.451.751.831.7131.838
M2.3*0.41.91.971.8671.979
M2.5*0.452.12.132.0132.138
M2.6*0.452.22.232.1132.238
M3*0.52.52.592.4592.599
M3.5*0.62.93.012.853.01
M4*0.73.33.393.2423.422
M4.5*0.753.83.853.6883.878
M5*0.84.24.314.1344.334
M6*155.134.9175.153
M7*166.135.9176.153
M8*1.256.86.856.6476.912
M9*1.257.87.857.6477.912
M10*1.58.58.628.3768.676
M11*1.59.59.629.3769.676
M12*1.7510.310.4010.10610.441

Imperial System:

Tapping Marking Hole ModelThread DiameterPunching Hole Inner DiameterRequirements for Punching Hole Inner Diameter
MINMAX
1-641.551.571.4251.582
2-561.81.861.6951.871
3-482.12.141.9412.146
4-402.32.362.1572.385
5-402.62.692.4872.697
6-322.82.862.6422.895
8-323.43.523.3023.530
10-243.93.913.6833.962
12-244.54.574.3444.597
1/4-205.15.254.9795.257
5/16-186.66.726.4016.731
3/8-1688.157.7988.153
7/16-149.49.59.1449.550
1/2-1310.811.010.59211.023
9/16-1212.212.311.98912.446
5/8-1113.613.813.38613.868
3/4-1016.516.816.30716.840
7/8-919.519.619.17719.761
1-822.222.521.97122.606
1 1/8-72525.224.63825.349

Note:

1. Use cutting tap.

2. The punching hole height should not be less than 3 times the pitch.

3. When the material thickness is less than 0.5mm, the wall thickness of the punching hole is the same as the material thickness. When the material thickness is between 0.5mm and 0.8mm, the wall thickness of the punching hole is 0.7 times the material thickness. When the material thickness is greater than or equal to 0.8mm, the wall thickness of the punching hole is 0.65 times the material thickness.

Section 5: Shim

Shim is a common forming method with fixed shape and function. The size of the shape has little effect on its function, and its forming method mainly relies on shared molds.

Now we will introduce the function and forming method of shim:

I. Shim structure and function:

Basic types:

There are generally two basic types of shims (Figure 1) (Figure 2), and the structure of the shim is shown in Figure 3. There are also several shapes with protrusions in a hemispherical form.

Function analysis:

It is a circular punching shape, and its main function is to use its punching shape to support the chassis or fix the motherboard, to avoid the bottom contacting the ground completely, so their height is consistent.

If it is a chassis shim, the shape is generally like Figure 4; if it is a motherboard shim, the shape is like Figure 5.

It generally has punching marks on top because the chassis shim mainly serves as a support function and generally has a rubber pad attached underneath, and Figure 5 generally only has four.

However, the motherboard shim not only serves as a support function but also a fixing function, so it has punching marks on top.

Note that the punching mark height is less than the shim height, and the number corresponds to the motherboard.

II. Forming methods for shims

Due to the fixed shape of shims, their size has little effect on their function as long as the height and center position are ensured. Therefore, several specifications of shared molds have been designed.

In the case of similar sizes (±1mm), a similar specification of shared mold can be used instead. For shapes with greater differences and no similar specifications of shared molds, the method of designing a pressure plate mold can be used for forming.

The shim molds for sample production are generally divided into pressure plate molds and shared molds.

Pressure plate molds have a fast forming speed and can form multiple shims at once, but they are not flexible and can only be used for forming a specific workpiece.

Shared molds use the common characteristics of shims and can be repeatedly used to form shims with the same specifications, reducing production costs.

Pressure plate mold (pre-processing)

Below is an example of a shim (NKB83001A), and note that the material for a circular block can be obtained directly from the waste material of the previous ring block.

The module stacking diagram is shown in Figure 9.

Shared mold (folding machine)

The design method of using a folding machine mold increases the forming height by 0.2 to account for rebound, and a positioning hole is added to the center of the upper mold.

A positioning punch is designed to be placed in the positioning hole, and a center point is marked for positioning the shim, which matches the positioning punch.

The schematic diagram of the mold is shown below (Figure 11).

Fig.11

Currently, there are four types of shared mold specifications for shims (see Table 1).

There are four sets of molds, with the first three types forming the shape shown in Figure 2 and the fourth set forming the shape shown in Figure 1, as shown in Table 2.

The upper and lower mold punches are fixed to the upper and lower mold fixtures, and the fixtures are fixed to the upper and lower slots.

NCT tool processing

See NCT tool table.

III. Appendix.

Table 1: Common shared mold specifications

Serial numberUnit of useCorresponding valueRemarks
Outer diameter (D1).Inner diameter (D).Height (H)
1Folding machine28202.0 
232251.8 
326.512.52.8 
412.56.51.0 
1  NCT26.7213.282.5   T=1.0

Table 2: Forms and specifications of shared molds

           Upper mold            Lower mold
     First set     
      Second set  
        Third set  
      Fourth set   

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