What is a Broach?

During broaching, the broach makes constant linear motion and is the main motion. Because the latter tooth (or group) of the broach is higher than the former tooth (or group), it is possible to cut the metal layer from the workpiece to obtain the desired surface. During broaching, the feed movement is replaced by the tooth lift of the cutter teeth, so there is no feed movement during broaching. There are many types of broaches, generally divided into two major categories of internal broaches and external broaches.

1. What are the classification of broach?

   • Different processing surfaces:
     

     The internal broach is used to process the inner surface of various shapes. The name of the broach is generally determined by the shape of the hole being processed, such as a round hole broach, a square/hexagonal broach, a key slot broach, and a spline broach. . The internal broach can also process spiral internal splines and internal gears. The bore diameter that can be processed by the internal broach is usually 10-120mm, in special cases it can be processed to 5-400mm, the slot width of broaching is generally 3-100mm, the length of the hole is generally not more than 3 times the diameter, in special cases Reach 2m. Commonly used are round hole broaches, spline broaches, square hole broaches and keyway broaches.

     External broaches are used to process various shapes of external surfaces, such as flat surfaces, forming surfaces, flutes, complex grooves and tenon grooves and tenons in steam turbines, to replace these parts for milling, planing, grinding and other processing, especially suitable for automotive , Motorcycles, tractors and other parts of the mass production surface. In production, internal broaches are more commonly used than external broaches.

   • Different directions of force
     

     Can be divided into broach and push knife. The former is under tension and the latter is under compression. Considering the stability of the compression bar, the length-diameter ratio of the pusher should be less than 12.

   • Different broach structure
     

     Can be divided into combined type and integral type and assembly type.

     Combined broach The combined broach not only saves tool material, but also simplifies the manufacture of broaches, and can be easily adjusted or replaced when the teeth of the broach are worn or damaged.

     Integral broaches Integral broaches are mainly small and medium-sized high-speed steel broaches.

     Assembled broaches Assembled broaches are mostly used for size and carbide combination broaches.

     Broaches can be used to process through holes of various cross-sectional shapes, straight or curved outer surfaces. The following shows the cross-sectional shape of the classic workpiece for broaching.

2. Features of broach

   The broaching process is carried out with a broach. It is based on the latter (or a group) of teeth of the broach is higher than the previous (or a group) of teeth, and the margin is cut off layer by layer to obtain the required processing. surface. During broaching, the broach moves at a constant speed. Because the latter tooth (or group) of the broach is higher than the previous tooth (or group), it can cut off excess metal from the workpiece layer by layer.

   Because the broaching speed is low and the cutting thickness is small, higher accuracy and better surface quality can be obtained. Compared with other processing methods, broaching has the following characteristics:

   • The broaching machine has a simple structure. Broaching usually has only one main motion (straight motion of the broach), and the feed motion is completed by the tooth lift of the broach teeth. Therefore, the broaching machine has a simple structure and is easy to operate.
   • Processing precision and surface quality are high. Generally, the broaching machine adopts a hydraulic system, and the transmission is stable; the broaching speed is low, generally 0.04-0.2m/s (2.5-12m/min), it is not easy to produce built-up edge, the cutting thickness is very small, and the cutting thickness of fine cutting teeth is 0.005-0.015mm, because the processing accuracy can reach IT7, and the surface roughness value Ra0.8-2.5μm.
   • High production efficiency. Because the broach is a multi-tooth tool, it has many teeth participating in the work at the same time, the total length of the cutting edge is large, and rough, semi-finish and fine machining can be completed in one stroke, so the production efficiency is very high.
   • Long service life. Because the cutting speed is low and the broaching wear is slow, the broach has a high durability. At the same time, after the broach teeth are ground, they can be reground several times and have a longer service life.

   Because the structure of the broach is more complicated than that of a general tool and the manufacturing cost is high, it is generally used for mass or batch production. However, except for certain high precision requirements and special shapes.

3. Structure of broach

   • Head-connects with the machine tool to transfer movement and pulling force.
   • The neck-head and over-cone connection are also marked.
   • Transition cone part-plays a guiding role, making the broach easy to enter the prefabricated hole of the workpiece.
   • Leading part-the guide broach transitions smoothly to the cutting part without skew.
   • Cutting part-Responsible for the removal of the entire machining allowance. It consists of primary teeth, transition teeth and fine teeth.
   • Calibration part-The last few teeth without tooth lift and chip grooves are used for polishing and calibration to improve the machining accuracy and surface quality of the hole, and can be used as the back teeth of the fine cutting teeth.
   • Rear guide part-used to maintain the correct position of the last few teeth of the broach to prevent the broach from damaging the processed surface quality and teeth due to the sagging of the workpiece when it is about to leave the workpiece.
   • Tail-When the broach is long and heavy, you can use the bracket to support the tail of the knife to prevent the broach from sagging due to its weight. Generally, a lighter broach does not need a tail.

4. Broach case

   Internal hole broach: The internal broach can effectively and accurately form a specific shape of the inner surface of the workpiece. Usually, the internal broach is inserted into the guide hole formed in the workpiece before machining. By selecting the best cutting edge shape and cutting method (such as round holes, square holes, polygonal holes, and various spline holes and tapered holes), various types of holes can be formed.

   Surface broach: The surface broach can efficiently and accurately form a specific shape of the outer surface of the workpiece. Roughing and finishing can be performed at the same time, which means that the productivity is significantly higher than milling, finishing and grinding. It can process a variety of shapes (such as flat surfaces, contour surfaces, various concave and convex surfaces, gears, turbine blade roots, turbine disk grooves), and its outline can be either a simple shape of a key groove or a complex shape of a Chinese fir shape.