Broach
A broach is an elongated, slightly conical broach for interior broaching , a machining process in which a broach is pulled through an existing hole on a broaching machine .
It is used on a broaching machine in an adjustable guide and mostly moved by a hydraulic cylinder.
The cross-section of the broach corresponds to the contour of the shape to be broached. These contours can be round (for example to broach an inner diameter), or rectangular (for example for broaching grooves), or have other free shapes. Internal gears are often also produced by broaching. The cross-section of the broach is always reflected in the workpiece .
After a cutting path of 70–80 m, a broach should be sharpened (re-ground). By grinding the rake faces of the teeth, the outside diameter of the needle also decreases somewhat. A broach therefore has replacement teeth at the end so that tool wear can be compensated for. If the target profile can no longer be generated with the broach, it is worn out and must be replaced.
Between the teeth of the broach there are gaps (so-called chip spaces ) in which the chips can collect until the broach is pulled through the workpiece.
The size of the chip spaces also limits the maximum length of the inner profile (maximum broach length). The chips cannot leave the chip chambers within the workpiece bore because the chip chambers are completely enclosed. The broach therefore gets stuck in the workpiece when the chip chambers are completely filled with chips. This usually leads to the destruction of the tool and workpiece.
Components of a broach
- Shank with driving notch, standardized according to DIN 1415
- Guide area for centering the needle in the bore of the workpiece
- many ascending rows of teeth that cut deeper into the workpiece from row to row
- as the last row of teeth, several rows of calibration teeth that bring the profile to its final dimensions
- Rear shaft to support longer broaches on machines in a horizontal arrangement
The largest row of cutting teeth (row of calibration teeth) is present several times in order to achieve the desired final dimension even after repeated regrinding .
The production of broaches is quite complex. A broach z. B. for a splined shaft connection (internal toothing) according to DIN 5480 with a diameter of 40 mm costs approx. € 2000 (as of 2008) and the delivery times are usually 12 weeks. Broaching tools with spiral thread, helical teeth , protuberances or other profiling properties can, depending on the diameter, reach the value of single-family houses, whereby their production can take several months.
history
Krünitz encyclopedia from 1812 already describes the space needle as "a strong needle, or long pointed wire to clear out the shooting and ignition holes with it". There are four types mentioned:
- "The first one is triangular, and is so pointed at the bottom, with which one grants to the ignition hole, both before, before loading, and afterwards, before pouring igniter."
- "The second has a neat nail drill at one end, so that if something has got stuck in the ignition hole, it can be pierced."
- "The third is designed like a spoon or a marrow puller to remove what has been drilled out of the ignition hole."
- "The fourth has a small barb, and is only used to research the thickness of the metal on the ignition hole."
