Thursday, May 20, 2010

Honing Process

Honing is a process of machining with bonded abrasive grains. It serves to improve the shape, size, accuracy and surface quality of the work piece. So this often time use if car cylinder head uneven.

One distinguishes between long stroke honing and short stroke honing (superfinishing). In terms of the movement cycles. Both processes can’t be used for internal surface (holes) as well as for outer surfaces (shaft).

Long stroke honing (honing).

The honing foot has four or more honing sticks mounted in it. The foot rotates and goes through an axial stroke motion at the same time. The stroke length is set so that the tool moves upward and downward beyond the workpiece by about ¼ of the own length. These motions combine to form a helical grinding track. This not only improves the surface quality, but also the cylindrical shape of the honed workpiece. This process does not significantly affect the roundness of holes. The honing sticks are pressed and fed against the generated surface by two cones inside the tool.

On the honing machine, the workpiece (engine block, brush, etc.) travel under the honing tool on a table which moves and endwise and crosswise. The honing tool is suspended in the honing spindle with a ball and socket joint so that it can move and adjust to the position of the hole. The rotary motion of the spindle is imparted to it by an electric motor over a steplessly variable belt or chain drive. The stroke motion is generated hydraulically, and can be regulated in length, position and speed.

Because it must adjust precisely to the axial position of the hole being honed, the honing tool cannot be rigidly fixed to the spindle. A ball and socket joint is therefore interposed between the spindle and the tool (cardanic suspension).

Superfinishing




This process is characterised by a third movement. In addition to the rotation of the workpiece and the stroke movement of the tool (honing block), the tool also reciprocates through a distance of 1 to 5 mm at 700 to 1500 cycles per minutes. The grinding track is a continuous wavy spiral. The curvature of the honing block is matched to the workpiece diameter, so that the threshold movement improves the circularity as well as cylindrical shape or the workpiece.

In both processe, longer and broader honing blocks (i.e. of greater surface area), improve the shape of the workpiece. The infeed pressure is however, reduced when the tool is of greater area, which increases production time.



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