Stamping forming technology for threaded bottom ho

2022-06-22
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Stamping forming technology for threaded bottom hole of sheet metal stamping parts

Abstract: according to the thickness of sheet metal stamping parts, the process methods of fine punching small hole, thinning flanging and cold extrusion are used to form threaded bottom hole. This paper discusses the stamping process, die structure, design and manufacturing technology of the above thread

subject words: cold punching and extrusion forming technology for thinning and flanging of the bottom hole of the punched part thread

thread connection structure, especially the tight thread connection structure, is the most important connection structure type of parts and components in various electromechanical and household appliance products. For tight thread connection of sheet metal stamping parts, it is necessary to have a connection thread length greater than the material thickness to ensure its connection reliability and enhance its load capacity, so as to achieve the purpose of reliable connection and small weight of sheet metal stamping parts, so as to make them become solid, lightweight and compact ideal structural parts

m2-m10 small thread tight connection structure is often used for sheet metal stamping parts of instruments, electronic appliances, various household appliances, household appliances, toys and other products. In order to improve efficiency and meet the needs of mass production, the process methods of fine punching small holes, thinning flanging, cold extrusion and so on are adopted to punch these small threaded bottom holes, which can not only greatly improve production efficiency by replacing drilling with punching holes, but also obtain bottom holes with accurate size and good consistency, and make the threaded connection have enough length, so as to ensure its connection reliability and the bearing capacity required by the design. Therefore, processing small threaded bottom hole with stamping forming technology has the effect of high quality and high yield, and it is also a mature and worth popularizing technology

1 calculation of threaded bottom hole

the appropriate size of threaded bottom hole depends not only on the thread diameter, but also has a close relationship with its pitch. Generally, it can be calculated by the following formula:

when TL ≤ 1, take: dz=d-tl

when tl>1, take: dz=d- (1.04 ~ 1.06) Tl (2)

where tl- pitch, mm

dz- diameter of threaded bottom hole, mm

d- thread diameter, Mm Table 1 reasonable value of thread bottom hole diameter (mm)

thread diameter D pitch TL bottom hole diameter dzm1m2

m3

m4

m5

m6

m8

m10

m12

m14

m16

m18

m20

m22

m24

m27

m300.250.4

0.5

0.7

0.8

1

1.25

1.5

1.75

2

2.5

2.5

2.5

3

3.5

0.751.6

2.5

3.3

4.2

5

6.7

8.5

10.2

11.9

13.9

15.4

17.4

19.4

20.9

23.9

26.3

2 basic process methods for punching threaded bottom holes in sheet metal stamping parts

(1) punching small holes with thick material and fine punching

when the punching part thickness t can meet the required length of threaded connection, it can be solved by punching hole making process. In this case, it is usually thick material punching holes, that is, the diameter of the punched thread bottom hole DZ ≤ t or slightly greater than t, as shown in Table 2. The minimum effective length of threaded connection depends on the diameter and pitch of the thread and is closely related to the material type of the connection. Table 2 parameters of small thread bottom hole punched by thick plate (medium carbon steel punch)

punch material thickness

t (mm) screw diameter D pitch TL (mm) bottom hole diameter DZ (mm) minimum length of threaded connection required

lmm (mm) 3M2

M3

M40.4

0.5

0.71.6

2.5

3.31.7

2.2

2.64M3

M4

M50.5

0.7

0.82.5

3.3

4.22.2

2.6

3.25M4

M5

M60.7

0.8

13.3

4.2

52.6

3.2

3.36M5

M6

M8

M100.8

1

1.25

1.54.2

5

6.7

8.53.2

3.3

4.6

5.78M8

M10

M12

M141.25

1.5

1.75

26.7

8.5

10.2

11.94.6

5.7

6.8

7.810M10

M12

M14

M161.5

1.75

2

28.5

10.2

11.9

13.95.7

6.8

7.8

8.512M10

M12

M14

M16

M18

M201.5

1.75

2

2

2.5

2.58.5

10.2

11.9

13.9

15.4

17.45.7

6.8

7.8

8.5

9.6

10.5

it can be seen from table 2 that the material thickness of some medium and thick plate punches with t ≥ 3 ~ 12mm can meet the thread connection length required for tight thread connection with moderate thread diameter. Therefore, the thread bottom hole can be punched by punching, precision punching and small hole punching

not only the size requirements of threaded bottom hole are strict, but also the hole wall should be vertical and flat. Otherwise, when tapping the thread, the tap is thin and long, and the punching hole wall is hard due to cold work hardening, so it is easy to wear and break. Therefore, punching with standard clearance or large clearance can not meet the tapping requirements unless additional reaming or reaming procedures are added. This is obviously uneconomical. Here, it is recommended to use the fine punching or small gap thick material punching process to punch the small thread bottom hole listed in Table 2. These punching and hole making processes have been popularized and applied in production and are relatively mature. Even if the common domestic standard press is used for fine punching or thick material punching, it is widely used in China, especially in the instrument and switch circuit industries

(2) thinning flanging

it is a widely used process in China to punch small threaded bottom holes with thinning flanging for thin material punching parts. By thinning and flanging the thin material, the axial length of the thread bottom hole is increased, so that the thread connection length is increased, and the thread connection structure is more firm and reliable. At the same time, it can effectively reduce the weight of the product. The use of thinning flanging to punch threaded bottom holes is mostly used for sheet metal stamping with material thickness t ≥ 3mm. The flanging geometric dimension parameters are listed in Table 3 for reference. Table 3 recommended parameters for thinning flanging stamping forming threaded bottom hole

punching part material thickness

t (mm) thread diameter

d flanging pre punching bottom hole diameter

d0 flanging pre thread hole diameter

dz flanging flange outer diameter

dz flanging flange height

m3

m4 φ 1

φ 1.1

φ 1.15

φ one point two φ 1.6

φ 2.1

φ 2.5

φ three point three φ 2.4

φ 3.1

φ 3.6

φ 4.41.7

2.0

2.2

2.61.5M3

M4

M5

M6 φ 1.5

φ 1.6

φ 1.7

φ two point two φ 2.5

φ 3.3

φ 4.2

φ five φ 3.2

φ 4.2

φ 5.6

φ 6.42.2

2.6

3.2

3.32M4

M5

M6

M8 φ 2

φ 2.1

φ 2.2

φ three φ 3.3

φ 4.2

φ 5

φ six point seven φ 4.3

φ 5.4

φ 6.6

φ 8.33

3.4

3.8

4.62.5M5

M6

M8

M10 φ 2.5

φ 2.6

φ 3

φ three point six φ 4.2

φ 5

φ 6.7

φ eight point five φ 5.6

φ 7

φ 8.4

φ 10.73.9

4.2

4.9

5.43M6

M8

M10

M12 φ 3.2

φ 3.4

φ 3.8

φ four point three φ 5

φ 6.7

φ 8.5

φ ten point two φ 7.1

φ 8.5

φ 11

φ 12.44.6

5.3

5.7

6.2

(3) cold extrusion

for sheet metal stamping with material thickness t ≤ 2mm, the cold extrusion method is used to punch and extrude threaded bottom holes similar to flanging on the sheet metal. This process does not require pre punching, but punching and extruding with a closed cold extrusion die. After the punch is pressed into the sheet metal, the material is redistributed into a ring flange around the punch in the concave die, so as to obtain a threaded bottom hole with accurate hole diameter and sufficient height. The end of the hole is provided with a thin connecting skin, which is punched by a tap when the thread is reformed. This process has been applied abroad as early as the middle of 60 years. The utility model has the advantages that the wall thickness of the cold extruded hole flange is thicker and more uniform than that of the flanging, and the cold work hardening in the cold extrusion is more severe than that of the flanging, so that the threaded connection has a higher load capacity. However, the process has not been popularized and applied in China

3 technology of punching small threaded bottom hole

punching small holes D ≤ t on medium and thick plates with t>3 ~ 12mm as threaded bottom hole DZ not only has high production efficiency, but also has good quality and strong interchangeability. At the same time, the cold work hardening effect can also improve the thread strength. Therefore, when the material thickness can ensure the length of the thread connection, in order to ensure the hole shape, hole wall perpendicularity and smooth surface of the threaded bottom hole, even if dz>t, the small hole punching or fine punching technology is still used for processing, which can eliminate the common punching and increase the reaming and reaming process, and obtain good economic benefits

the main difference in process technology between thick material punching small hole and fine punching and ordinary punching large hole is:

(1) the punching clearance Z value of ordinary punching large hole, taking medium carbon steel as an example, z= (5% ~ 10%) t (unilateral, the same below). Therefore, the punching hole diameter is small at the top and large at the bottom with obvious taper. Only about one-third of the material thickness at the upper part is a bright band, and about two-thirds of the material thickness at the lower part of the hole is a rough tearing section. However, the punching clearance between small hole punching and fine punching z= (0.5% ~ 1%) t is only about one tenth of that of ordinary large hole punching, so the punching hole size is accurate, the hole wall is vertical, and the surface roughness of the hole wall can reach Ra0.8 ~ Ra0.4

(2) punching large holes in medium and heavy plates usually adopts hard discharge plates, and the plates are punched in free state; Strong pressing plate shall be used for small hole punching and fine punching in cleaning the work site. During punching, 0.3 ~ 0.5 pressure shall be applied within (5 ~ 8) d around the punching diameter of the plate σ Pressing force of S( σ S is the yield limit of the punching material), which is about 3 ~ 5 times of the pressing force of the ordinary elastic unloading plate, as shown in figure 2 A ~ m drawings

(3) different from the well-known separation deformation process of common punching large holes, thick punching small holes and fine punching both make the material in the state of three-dimensional compressive stress, and carry out the separation deformation process of plastic pure shear or near plastic pure shear with micro gap. The punching waste is forced into the die hole by the same punch. When higher punching dimensional accuracy and hole wall surface quality are required, the punching clearance must be properly reduced and the pressing force must be increased to produce a better punching and extrusion process, as shown in Figure 1

(4) the hole wall of fine punching and small hole punching is parallel to the center line of the punch, there is no taper like the common large hole punching, and the size of the hole is relatively stable. Generally, the diameter of the punched hole is slightly larger than that of the punch, the hole wall is 100% bright band, and the surface roughness Ra value is 0.4 ~ 0.8 μ m。

(5) due to hole cleaning and punching, the separation and deformation process of punching holes is quite different from that of ordinary punching large holes, as shown in Figure 1. If the common standard mechanical press is used for fine punching, the punching work shall be calculated in addition to the maximum punching force when punching small holes, so as to accurately select the equipment tonnage. When calculating the maximum punching force, the well-known traditional calculation formula is not in line with the actual situation of small hole punching and fine punching. It is recommended to use timmerbeil formula:

pmax=loto (1-t'/t) σ B (n) (1)

where Pmax -- Maximum punching force, (n)

l -- punching line length, i.e. punching perimeter, (mm)

t -- punching part material thickness, (mm)

t'-- punching initial stage, punch extrusion depth, (mm)

p> σ B -- tensile strength of punching part material, (MPA)

(tensile machine manufacturer prepares experimental software 1-t'/t) -- depends on the yield strength ratio of punching part material, i.e σ s/σ B ratio. For 05 ~ 20 steel, the value of (1-t'/t) is about 0.6 ~ 0.7

it is not enough to select the tonnage of the press only according to the maximum punching force (punching force). Because the output pressure of the press depends on the bending strength of its crankshaft and the shear strength of the gear tooth profile; The stamping (effective) work output by the press depends on its flywheel reserve energy and its motor output power and the allowable厌食症如何治疗
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