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Home > Haisen Blog > Analysis of deformed shape of working procedure and working position in cold heading process

  • The cold heading (pressing) of the fastener products is completed by a press and an automatic cold heading machine. In the cold-pressing, single-station, and multi-station cold forging, the shape of the semi-finished product of the upper sequence or upper station upsetting (pressing) directly affects the forming of the lower sequence or the next station.

    Therefore, how to determine the correct deformation shape on the basis of a reasonable distribution of the deformation ratio has a direct relationship with the future deformation and product quality.

    Cold heading (pressing) process of rod-shaped fasteners
    In order to change the stability of the blank during the initial punching deformation, especially for steel grades with poor cutting properties such as low carbon steel, and to increase the stability of the blank during deformation, in addition to the working cavity of the small end of the initial punching In addition to the cone, there is also a cylindrical cavity with a height of 1.5-2mm.

    Determination of the initial upsetting shape of the head of the hexagon head bolt
    The shape of the initial upsetting is reasonably determined, which will facilitate the flow of metal in the cavity, make the flow of metal fibers not turbulent, and facilitate the deformation of the next station.

    The shape of the initial upsetting is tapered. The initial upsetting cone-shaped cavity has two forms, one is without spring ejector pin (needle), the other is with spring ejector pin (needle).

    The tapered die without spring ejector rod is used for the upsetting of long rod workpieces; the punch die with spring ejector rod is used for workpieces with shorter rods. The cone angle of the tapered cavity without the spring mandrel initial punching is appropriately larger, so that the workpiece is easily separated from the initial upsetting die, generally α is taken

    N8°~16°, the cavity shape of the initial upsetting punch.

    In the three-stroke upsetting, it is necessary to upset the taper twice. The first taper has a very small taper angle, α is 2°~3°, which basically plays a role in shaping, making it deformed in the second initial upsetting. There is a good neutrality and stability. The size of the working cavity of the tapered die can be calculated according to the volume of the head to be forged, the diameter of the wire, and the distance between the die and the die.

    The volume of the entire cone head is composed of two parts: the volume V1 and V2, namely V cone=V1+V2, and the V cone is equal to the volume of the product head after fine upsetting, namely V. V can be calculated from the product size, then V1=V-V2.

    Determination of the initial upsetting shape of machine screws
    There are many types of machine screws, which are mainly different from the geometry of the head. Generally speaking, the upsetting ratio (S=Lo/do and D/h) of machine screw head forming is relatively small, and it is easier to upset.

    For machine screws with simple head shapes, one-click cold heading can be used to produce workpieces, which can be upset at one time. However, many types of machine screws have complicated head grooves. For cross groove type, etc., head forming requires two or more upsettings. To upset products that meet the requirements of the groove shape according to the standard, the shape of the initial punch plays a decisive role.

    Determination of the initial upsetting shape of hexagon socket head screw
    Cold heading hexagon socket head screws (head upsetting ratio is less than 1.5), because the head has a deep inner hexagonal hole, the geometric shape is complicated, and the product performance requirements are high. The grades are 8.8, 10.9, and 12.9. The steel used is medium Carbon steel, alloy steel, and cold forming performance are poor, and the deformation of the head is complicated, including upsetting, forward extrusion and reverse extrusion. Therefore, the initial forming of such products should generally undergo the initial upsetting and the second pre-upsetting.
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