Cold extrusion core technology
As a screw person, we must first fully understand each cold extrusion product, what kind of cold extrusion equipment is bred and produced, and then step by step to find the core key points of each link, cold extrusion deformation process In the division of labor steps, there is a core of each step, and there is also one of the most critical cores. The problem is that we must have a "nail spirit", unyielding and persevering to find the core key points.
The core technology of cold extrusion is as follows:
Open cold extrusion forming standard and design
The technical requirements of the cavity: the cavity must be smooth and there is no trace of processing tools; D, d and d1 coaxiality requirements are extremely strict: ≤ 0.015.
Cold extruded wire must be pickled, phosphatized or oxalic acid treated, ie coating and lubrication required, HRB 70~90. If it is too soft, the adhesive mold can't get into the "H" ligament. If it is too hard, it will easily damage the "H" ligament.
Closed cold extrusion forming standard and design
The technical requirements of the cavity are the same as those of the open cold extrusion forming technology.
The requirements for cold extrusion materials are basically the same as for open cold extrusion molding, and only the wire hardness lower limit HRB70 can be appropriately relaxed.
Upsetting process
The process of increasing the cross-sectional area of ​​the original blank and reducing the height is called upsetting. (See Figure 2.1-3), the degree of deformation ε is expressed as the ratio of the difference between the fractured area F2 after the upset and the fractured area F1 before the upset, and the fractured area F2 after the upset, namely:
Extension process
The process of reducing the cross-sectional area of ​​the original blank and increasing the length is called extension (see Figure 2.1-4). Drawing, reducing diameter, etc. belong to this category, the degree of deformation of the extension:
As shown in Figure 2.1-5, Figure (1) is a reduction mode, which is a part of the material exposed outside the cavity for shrinkage, and the elongation ε can reach 28%; Figures (2) and (3) are all materials entering the cavity. The inner diameter is reduced, and the elongation ε can reach 75%. This mold is also called an extrusion mold, and the graph (3) with the R reduction diameter is specifically referred to as an R reduction mold.
Figure 2.1-5
The cold extrusion deformation process is nothing more than a small deformation of large material, a small deformation of large material or a deformation of the intermediate material to the two ends. In the cold extrusion forming application of fasteners or few cutting products, the rotating metal wire is mostly For blanks, first selecting the blank diameter becomes a crucial issue. Although there is a saying that “all roads lead to Romeâ€, there is only one best diameter. How to choose the blank diameter? Whether it is upsetting or extending (Reducing the diameter), anti-extrusion, etc. should consider the degree of deformation of the metal plastic deformation, so we have summarized the calculation formula of the core technology of cold extrusion deformation into one:
Where ε and d are known conditions and D is solved. ε : Different materials have different degrees of allowable deformation; the authors introduced in the process of extending (reducing the diameter) are based on years of practical experience, defining ε = 30% as watershed, and ε ≤ 30% by open cold extrusion (opening) Reduced diameter), ε >30% is formed by closed cold extrusion (closed diameter reduction or strong shrinkage mold, also known as strong beam mold). The upper limit of ε value of closed cold extrusion forming is generally based on the allowable deformation of the material. To determine the degree, stainless steel ε ≤ 50%, the general control of ferrous metals is ε ≤ 60%, and some medium and low carbon steel can reach ε = 80%.
The guide angle α of the reduced diameter die: open cold extrusion α=22~24°, closed cold extrusion α=90°. d We call the sizing belt, width H = 0.8 ~ 2. D1 is called guarantee hole, when d≤6: d1 is larger than d by 0.03~0.06; when d>6: d1 is larger than d by 0.07~0.12. The transition angle of d1 to d is uniformly set to 15°.
For the reverse extrusion of the perforated cylindrical member, the selection of D is determined according to d. Whether it is upset or reduced diameter will cause cold work hardening, which is not conducive to the formation of the reverse extrusion hole, so D is close to d . The female mold does not move, the male mold punches the movement, and the reverse extrusion hole depth can generally reach 2 to 3 times the aperture. The coaxiality of the outer diameter and the aperture of the cylindrical member is generally within 0.10, and the high precision can reach 0.03~0.05.
The male die punch adopts a rectangular spring floating motion through the compression female die, and the reverse extrusion punch punch is not moved in the female die, and adopts a six-needle structure, a three-pin rectangular spring float, and a three-needle discharge sleeve unloading, and then The extrusion hole depth can be more than 3 times of the aperture, and the low carbon class can even reach 9 times of the near aperture. At this time, the coaxiality of the outer diameter and the aperture of the cylindrical member is generally within 0.15, and the high precision can reach 0.05 to 0.10.
Cold extrusion nut: large material small deformation with a circular section diameter D generally takes the nut S to the opposite side of 0.9~0.92; small material large deformation with a circular section diameter D generally takes the nut S to the opposite side of 0.7~0.72; The wire is taken from 0.9 to 0.95 on the opposite side of S.
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