# Example of processing pressed parts –Metal clip

## Explanation of parts analysis

### 1. Part shape and general requirements

As shown in Figure 1-1, the material must be stainless steel, the material thickness must be 0.5 mm, and the dimensional accuracy of the workpiece must meet the drawing requirements. Unmarked accuracy according to IT12 level, the production program has an annual production of 100,000 pieces.

**Part process analysis**

The shape of the workpiece is simple, the size and thickness are modest, and it is generally mass-produced. Although it belongs to normal press parts, please note the following points when designing cold press dies.

### 2. The outline and structure of the part is simple, but some hole machining needs to be considered.

- A, two two-hole position requirements,
- B, by assembly
- C, the two holes must have the same
- D, shaft requirements
- E, its value is 0.15 mm.

The difficulty in processing this portion is mainly the positioning of the center distance of the hole 2.

Since some holes have a small diameter and a particular batch size, the design of the mold material and structure should be emphasized to guarantee a particular mold life.

## Process planning decisions

According to the analysis of the process of the workpiece, the basic process includes punching, punching and bending. There are several types of processing methods and their rational processing methods in the following order.

- 1, blanking-punch-bending, single process stamping.
- 2, blanking-bending-punch, single process stamping.
- 3, blanking punching-bending ribs, compound stamping.

### Scheme 1) It is a single step stamping die.

It is not suitable to adopt this method because this part has some production batch, too many steps, reduces the accuracy of the product, and the production efficiency of this method is not suitable for mass production.

### Scheme 2) It is also a one-step stamping die.

In addition to the drawbacks of Method 1, it is difficult to secure the position accuracy of the holes, and it is difficult to secure the lack of positioning accuracy in bending, so it is not appropriate to adopt this method.

### Scheme 3) Composite stamping die.

Due to the structure of the parts, the thickness of the material is thin, and punching and punching are completed once. Therefore, it is best to adopt this scheme.

The specific plan is as follows.

## Process parameter determination

### 1. Calculation of blank size

Calculation of external dimension length

The relative bend radii of the part are:

R / t = 2 / 0.5 = 4> 0.5

Where X is the experimentally determined strain-neutral layer displacement coefficient.

T material thickness

Apparently, for parts belonging to large bend radius members, the radius of curvature ρ of the neutral bend deformation zone should be determined.

Textbook p145 Neutral position calculation formula

Where X is the experimentally determined strain-neutral layer displacement coefficient.

Table 4-5 from p145 of the textbook takes X 0.42

Such:

- ρ = R + Xt
- = 2 + 0.42 × 0.5
- = 2.21mm
- Calculation formula for blank length of curved surface parts with large fillet radius (R> 0.5t)
- L = ∑L straight + ∑L bend
- L bend = [(180-a) / 180] * πρ

Therefore, the length of the part is shown in Figure 2-2.

- L = LAB + LBC + LCD + LDE + LEF + LFG + LGH + LHI + LIJ + LJK + LKL
- L = 3 + 3.0342 + 8.54 + 14 + 1 + 1 + 1.8028 + 13 + 1.8028 + 1 + 2
- L = 50.1798

The DE segment belongs to the process settings. The purpose is to reduce bending springback. The length of the DE segment is calculated as a straight line because it has a large radius and can be considered a straight line.

#### 1. The width of the contour is calculated.

Considering the use of sheet materials and the convenience of layout, the process size of the work created by CAD is as follows. Outline width is L = 53.74 mm

#### 2.Layout size calculation

Determining edge value

From Table 3-14 on page 46 of the textbook, we can see that the value of a1 between workpieces L> 50 is 2.2 * 0.8 = 1.76.

The value of side a is 2.5 * 0.8 = 2.

#### 3. Calculate the width of the material

For convenience of mold design, the strip width calculation formula using the non-side pressure device feed method is as follows.

- B = (D + 2a + Z) 0 −δ
- formula
- B-Basic size of strip width.
- D-Maximum size of part profile in strip width direction
- a –Side edge
- Z—Gap between the guide plate and the widest strip
- Δ—Negative deviation of strip width
- Margin a is as above
- Gap δ, shear tolerance Z Check textbook p47 Table 3-17 Measured value δ = 0.5mm, Z = 0.5mm
- It is calculated by the above formula. B = (53.74 + 2 * 2 + 0.5> 0 –0.5 = 56.240 –0.5 mm)

#### Calculation step distance

Development view of parts (see Figure 2-3 on the right)

Generated effective horizontal dimension Ls = 53.74mm

The formula for calculating the step interval is as follows:

- L = Ls + a1
- Where L is the step interval
- Ls-horizontal effective size
- A1-margin
- L = 53.74 + 2 = 55.74mm

The nesting from which you can get the mold is:

According to the requirements, the material board specifications are 1500 x 800 x 0.5. Each board can cut 14 1500 x 56 strips with a material utilization of over 80%.

## Calculate material utilization rate

- Textbook p43 Style 3-19
- η = nA / BL × 100%
- η –About material use
- A-The actual area of the blanking area within one step.
- B-Strip width
- L-Strip length
- n –Total number of blanks on the sheet
- η = 28 × 1932.765 / (56 × 1500) = 65%

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