Broaching

Internal broaching can be used to machine through holes of various shapes, such as round holes, square holes, polygonal holes, spline holes and internal gears. It is also possible to machine grooves of various shapes, such as keyways, T-slots, dovetail slots, and gutters on turbine disks. External broaching can be used to machine flats, forming surfaces, external gears and blade boring heads.
Introduction Broaching is a type of machining operation that uses a broaching machine (broaching) to machine a variety of internal and external forming surfaces.

The broaching tool is a very complex component made from a single piece. The material is mainly high-speed steel, and the hard alloy is used as a tool material only for the machining of gray cast iron. Unlike many other cutting operations, the main consideration is tool wear or tool life.

In the case of broaching, several teeth are engaged at the same time, and the chip width is often large. Removing the chips can be very problematic and therefore generally requires a low viscosity oil.

From the perspective of the supply of cutting fluid, internal broaching is more problematic than external broaching. Horizontal broaching is more difficult than vertical broaching.
Classification broaching

A broach is used as the cutting tool for the tool. When the broach moves linearly with respect to the workpiece, the machining allowance of the workpiece is sequentially cut by the teeth of the broach that are incrementally increased in size. Usually, it can be formed in one working stroke, which is a highly efficient finishing method. However, due to the complicated structure of the broach, high manufacturing cost, and certain specificity, broaching is mainly used for mass production in batches. According to the different surface characteristics, the broaching is divided into internal broaching and external broaching.

1 Internal broaching: used to machine through-holes in various cross-section shapes and through-holes in holes, such as round holes, square holes, polygonal holes, spline holes, keyways, internal gears, etc. There must be a machined hole before broaching so that the broach can be inserted from it. The broaching aperture ranges from 8 to 125 mm and the hole depth does not exceed 5 times the aperture. In special cases, the aperture range can be as small as 3 mm, as large as 400 mm and with a hole depth of up to 10 m.

2 External broaching: used to machine non-closed surfaces, such as planes, forming surfaces, grooves, gutters, blade boring heads and external gears, etc. It is especially suitable for processing relatively large flat and composite profiles in mass production, such as Cylinder blocks, housings and connecting rods for automobiles and tractors. The dimensional accuracy of the broached surface can reach IT8~5, the surface roughness is Ra2.5~0.04μm, and the precision of broaching gear can reach 6~8 grade (JB179-83).

In the case of broaching, the order and manner of cutting the machining allowance from the workpiece are in the form of a form, a progressive form, a wheel cut type and a comprehensive wheel cut type. 1% form. High processing precision, small surface roughness, but low efficiency; long broach length, mainly used for processing small and medium-sized round holes and forming surfaces with high precision. 2 The progressive form is suitable for rough broaching of complex machining surfaces, such as square holes, polygonal holes and spline holes. The broach used in this method is easy to manufacture, but the surface quality is poor. The 3-wheel cutting type cutting efficiency is high, which can reduce the length of the broach, but the surface quality is poor. It is mainly used for processing round holes with large size, large machining allowance and low precision requirements. 4The comprehensive wheel cutting type is a rough broaching by the wheel cutting method and a fine broaching by the forming method, which has the advantages of both, and is widely used for round hole broaching.
Features

Broaching can be considered as a further development of planing. As shown in the figure, it uses a multi-tooth broach to cut a very thin metal layer from the workpiece one by one in order to achieve a higher precision and a smaller roughness value. When machining, if the force received by the tool is not the pulling force but the thrust, it is called the pushing. The tool used is called the pushing knife. The machine used for broaching is called a broaching machine. The boring is mostly carried out on the press.

Compared with other processing, broaching mainly has the following characteristics:

(1) High productivity

Although the cutting speed of the broaching process is generally not high, since the broach is a multi-toothed tool, the number of teeth participating in the work is large at the same time, and the cutting edge participating in the cutting is long, and can be completed in one working stroke of the broach Rough – semi-fine – finishing, greatly reducing the basic process time and auxiliary time. Under normal circumstances, the production capacity can reach 100-800 pieces, and the automatic production can reach 3,000 pieces.

(2) High processing precision and small surface roughness

The broach has a calibrated section that functions to calibrate the dimensions, smooth the surface, and act as a backup tooth for the precision teeth. The amount of cutting of the calibrated teeth is small, and only the amount of elastic recovery of the workpiece material is cut. In addition, the cutting speed of broaching is low (currently
(3) The structure and operation of the broaching machine are relatively simple

The broaching has only one main motion, that is, the linear motion of the broach. The feed motion is achieved by the latter tooth of the broach being higher than the previous one. The high amount of the adjacent tooth is called the tooth lift amount f.

(4) The broach is expensive

Due to the complicated structure and shape of the broach, high precision and surface quality requirements, the manufacturing cost is high. However, the cutting speed is lower during broaching, the tool wear is slower, and the grinding can process thousands of workpieces once, and one of the broaches can be reground many times, so the broach has a long service life. When the batch size of the machined parts is large, the cost of the tool allocated to each part is not high.

(5) Wide processing range

Internal broaching can be used to machine through holes of various shapes, such as round holes, square holes, polygonal holes, spline holes and internal gears. It is also possible to machine grooves of various shapes, such as keyways, T-slots, dovetail slots, and gutters on turbine disks. External broaching can be used to machine flats, forming surfaces, external gears and blade boring heads.

Since the broaching process has the above characteristics, it is mainly suitable for batch and mass production, and is particularly suitable for processing relatively large composite profiles in mass production, such as the cylinder block of an engine. In single-piece and small-batch production, for some forming surfaces with high precision and special shape, it is difficult to process by other methods, and broaching is also used. However, for blind holes, deep holes, stepped holes and obstacled outer surfaces, broaching cannot be used.

In the case of push-cutting, the length is relatively short in order to avoid the bending of the pusher (L/D Note: When broaching ordinary structural steel and cast iron, the general drawing speed is 3 to 7 m/min, and the fine drawing speed is less than 3 m/min. For hard-to-machine metal materials such as high-temperature alloys or titanium alloys, only hard alloys or new high-speed steel broaches can be used for broaching at a speed of 16 to 30 m/min or higher on a high-speed ram. Satisfactory results. The spiral broaching device is used to make the helical tooth broach and the workpiece move in a straight line and rotate, and the internal thread, the spiral spline hole and the spiral internal gear can be broached.

Broaching generally uses cutting fluids with good lubrication properties, such as cutting oils and extreme pressure emulsions. In high-speed broaching, the cutting temperature is high, and the chemical cutting fluid and emulsion with good cooling performance are often used. If an internal cooling broach is used to inject high-pressure cutting fluid into each chip pocket of the broach, it has a good effect on improving surface quality, reducing tool wear and improving production efficiency.
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