2.2.2 Cold heading (pressing) process for nuts
(1) Classification of Common Nut Cold Heading Processes
Hexagonal nuts are also a widely used fastener with various production methods. Nuts with specifications below M24 are generally produced by cold forging (pressing). The commonly used cold heading processes for nuts include the following:
a. Using smaller diameter wire for cold heading to produce nuts
This is the most commonly used production method for cold heading nuts. Use wire diameter do=0.60s~0.70s, s - the size of the nut on the opposite side. Using cutting, shaping, upsetting, hexagonal pressing, and punching workstations (processes), as shown in Figure 36-23. Production can be carried out on automatic cold heading machines at three or four workstations, or in sequence on a press. Production on a three station cold heading machine can eliminate the need for shaping, but nuts larger than M12 and above do not undergo shaping, making it difficult to control the quality of the end face and the uniformity of the bald angle.
Figure 36-23 Schematic diagram of multi-station cold pressing and sequential cold pressing deformation of nuts
b. Using larger diameter wire for cold heading to produce nuts
This process uses a wire diameter of do ≈ 0.9s, which is cut, shaped, initially upset, preformed, precision formed, and punched. It is generally produced on a five station automatic cold heading machine, with a clamp and flipping mechanism, as shown in Figure 36-24.
c. Hexagonal steel forming process
This process method is less commonly used and is generally used for the production of large-sized nuts above M20. It is completed by sequential cold pressing on a press. The production process follows cutting, initial pressing, precision pressing, and punching.
(2) Analysis of Nut Cold Heading (Pressing) Process and Process Parameters
a. Cut off
In automatic cold heading machine with multiple workstations or sequential production on a press, cutting is the first and most critical process. Because the flatness of the cutting fracture and the size of the horseshoe mark formed by the cutting blade pressing (see Figure 36-25) have a direct impact on the shaping and upsetting of the next sequence. The cutting length can be calculated from formulas 36-22.
Figure 36-25 Schematic diagram of horseshoe print on nut material column
(Formulas 36-22)
In the formula, Lo - cutting length mm, V-shaped - volume of blank before nut punching (mm3)
Fo - cross-sectional area of wire mm2
This is only a calculated value, and in actual production, the cutting length needs to be corrected by adjusting the material blocking column. Sometimes the weighing method is also used to measure the accuracy of cutting, that is, the weight of the billet is equivalent to the weight of the cut material column. The aperture of the cutting die should be 0.05-0.1mm larger than the maximum diameter of the material, and the gap between the blade and the cutting die should be about 0.1mm.
b. Plastic surgery
As shown in Figures 36-26, shaping involves flattening the end face of the material column and pressing 1-2 out at the lower end × A 45 ° chamfer is used to repair the defects in the cut material and ensure the quality of the next pressing process.
Plastic size d=do+(0.1-0.25) (mm)
In the formula, do - wire diameter in mm.
Figure 36-26 Nut Material Column Shaping
c. Upset ball
Upsetting ball is the process of upsetting (pressing) the shaped material column into a drum shaped ball shape, as shown in Figure 36-27. Its quality affects the clarity and quality of the nut's end face, bare corners, and edges. When determining the geometric dimensions of the drum shaped ball, based on experience, with a chamfer of 40 °, the dimensions dM and h should be as small as possible. In this way, when pressing the hexagonal, the friction force in the corresponding area should be small. Under the action of the molding force, the metal has good fluidity and is easy to fill the hexagonal. If dM and h are too large, it is not easy to fill the hexagon when pressing it. If the compression force is increased to fill the hexagonal shape, the nut end face will produce burrs.
The size of the drum shaped ball is based on empirical data as follows:
DM=(0.7~0.8) d-diameter
Dmax ≤ Smin
In the formula, diameter d - nominal diameter of the nut mm
Dmax - Maximum diameter of drum shaped ball mm
Smin - minimum size of nut s square mm
Based on the dimensions of dM and D and the volume of the nut blank, the other dimensions of the drum shaped ball can be calculated:
Figure 36-27 Nut drum shaped ball failure
(Formulas 36-23)
H=h+(D - dM) tg40 ° (Formula 36-24)
d. Compression molding
Pressing, that is, forging the hexagonal shape of a nut to meet the requirements of the external dimensions of the hexagonal nut. Whether the deformation size is reasonable directly affects the quality of the product and the lifespan of the mold.
The main factors to consider for the size of the hexagonal blank include the demolding of the hexagonal blank in the hexagonal concave mold and the expansion of the subsequent punching. Therefore, it is required that the side of the nut have an inclination angle γ (See Figure 36-28), its size tends to increase with the increase of specifications, such as nuts above M10, γ Generally taken as 0 °. 30 ′ -1 °, such as γ If the angle is too large, there will be a significant difference in the size of the upper and lower ports of the hexagonal concave die, which will cause the positioning of the hexagonal punch (also known as the pressing die) in the sleeve die to be unstable, which can easily cause eccentricity of the upset nut blank and affect the verticality of the nut( β) Out of tolerance, and at the same time, the size of s after punching and expanding does not meet the standard requirements. γ The actual range of 0 °. 30 ′ to 1 ° is determined by practical production experience.
In addition to this dimension, there are many other dimensions that are directly related to the external dimensions of the nut and the appearance of the product (see Figure 36-29), indicating the dimensions of the nut pressing blank. Among them, the geometric shape and size of the concave holes at both ends are very important. D1 is a critical dimension that is too small and prone to burrs during punching; Too large, punching can easily produce a trumpet mouth, which affects the integrity of the internal thread. The empirical data is:
＜ M8: d1=d small max+(0.02-0.04) mm
M8~M14: d1=d small max+(0.05~0.10) mm
M14~M18: d1=d small max+(010~0.15) mm
M18~M24: d1=d small max+(0.15~0.30) mm
Figure 36-28 Nut Side Tilt Angle Y
In the formula: d small max - maximum size of the minor diameter of the internal thread of the nut (mm)
D=(1.05-1.1) d-diameter
In the formula, diameter d - nominal diameter of the nut (mm)
D size is too small, which is not conducive to nut upsetting and forming, and is not conducive to metal flow, with unclear hexagonal corners; D size is too large, resulting in a reduction in the nut support surface, which affects the appearance and fastening strength.
After determining the dimensions of d1 and d, the internal chamfer of the standard nut should be approximately 120 °, usually taken as 106 °. The reason is that the internal chamfer should be slightly smaller, and according to the formula, the size h can be larger. This not only saves steel, but also benefits the deformation of the nut during pressing, and reduces the thickness of the punching skin (i.e. the iron beans punched out), which is beneficial for punching.
H=(d-d1) tg37 ° (Formula 36-25)
Another important dimension in the concave cavity is h1 and α Angles have an impact on the hexagonal punch that is pushed out from the hexagonal die after the nut is upset formed. H1 should not be too high. If it is too high, it will affect the timely detachment of the hexagonal billet from the hexagonal lower mold, and then the next billet will enter the concave mold, causing heavy caps and resulting in faults. The empirical data is:
M8~M10: h1=(0.4~0.5) mm
M10~M16: h1=(0.6~1.0) mm
M18-M24: h1=(1.2-1.6) mm
For nuts above M20, the h1 of the upper die can be (0.30-0.50) mm higher than that of the lower die, which is more conducive to cold heading deformation.
α Generally, 10 ° to 15 ° is taken. H1 α After confirmation, the size of d2 can be calculated using the following formula:
D2=d1-2h1tan α (Formulas 36-26)
The top of the concave cavity is a cone, with a cone angle of 150 °. The angle of the cone is tg15 °, and the height of the entire concave cavity is:
H2=h+h1+tg15 ° (Formula 36-27)
The size of the cavity is generally not used as a basis for inspection, but is ensured by the size of the mold. The above data is based on GB/T 6170-2000 standard nuts. Not fully applicable to other types of nuts.
e. Punching
The size and quality of the punching hole are all to meet the requirements of the next sequence of threading. The diameter of the inner hole of the nut is generally determined by the maximum size of the minor diameter. Considering that the hardness of steel affects the quality of punching, the aperture can be set between the minimum and maximum dimensions of the nut diameter, which can be flexibly controlled by the operator within its tolerance range. In fact, considering the factor of tapping, the tolerance of punching size should be smaller than the tolerance of small diameter.
2024 January 4th Week WBM Product Recommendation:
Heading dies,Punch:
WBM produces taper roller dies with high efficiency and automation. Rollers are formed on a single automatic cold heading press and are fed, cut, and punched into the die for five steps.
We can produce different types and sizes taper roller dies with quality assurance,include:Combination Punch,Outside Sleeve,Blade,Combination Punch,Feed Cylinder,Combination Dies,Double Layer Sleeve,Insert.
https://www.w-bm.com/products/Taper-roller-cold-heading-dies/Heading-dies,Punch/400.html
