There are many machining processes in CNC operation. Broaching is one of them. CNC broaching is a type of machining operation. It is a cutting process that uses a broach (broach) to process various internal and external formed surfaces. .
One, the characteristics of broaching knife
Broaching tools are very complex components, manufactured from a single piece. The material is mainly high-speed steel, and cemented carbide is only used for the machining of gray cast iron as a tool material.
Unlike many other cutting operations, the main consideration is tool wear or tool life.
In the case of broaching, several teeth mesh at the same time, and the chip width is often very large. Removal of swarf can be very problematic, so low-viscosity oil is usually also required.
From the perspective of cutting fluid supply, internal broaching is more problematic than external broaching, and horizontal broaching is more difficult than vertical broaching.
- Classification of broaching:
Use broach as a cutting tool. When the broach moves linearly relative to the workpiece, the machining allowance of the workpiece is sequentially cut off by the teeth of the broach with increasing sizes (Figure 1). Usually, it can be processed in one working stroke, which is a highly efficient finishing method. However, due to the complex structure of the broach, the high manufacturing cost, and a certain degree of specificity, broaching is mainly used for mass production. According to the characteristics of the machined surface, broaching is divided into internal broaching and external broaching.
- Internal broaching:
Used to process through-holes and through-holes with various cross-sectional shapes (Figure 2), such as round holes, square holes, polygonal holes, spline holes, keyway holes, internal gears, etc. There must be a machined hole before broaching so that the broach can be inserted through it. The broaching hole diameter ranges from 8 to 125 mm, and the hole depth does not exceed 5 times the hole diameter. Under special circumstances, the aperture range can be as small as 3 mm, as large as 400 mm, and the hole depth can be up to 10 meters.
- Outer broaching:
Used to process non-closed surfaces (Figure 3), such as planes, forming surfaces, grooves, tongue and grooves, blade tenons and external gears, etc., especially suitable for processing relatively large planes and composite profiles in mass production, such as automobiles And the cylinder block, bearing seat and connecting rod of the tractor. The dimensional accuracy of broaching profile can reach IT8～5, the surface roughness is Ra2.5～0.04 microns, and the precision of broaching gear can reach 6～8 grade (JB179-83).
When broaching, the order and methods of cutting the machining allowance from the workpiece include the final form, the progressive form, the wheel cutting type and the comprehensive wheel cutting type. Let’s take a look at these four forms in detail.
- Into the form. The processing accuracy is high, the surface roughness is small, but the efficiency is low; the broach is longer, and it is mainly used to process small and medium-sized round holes and high-precision forming surfaces.
- The progressive type is suitable for rough broaching of complex processing surfaces, such as square holes, polygon holes and spline holes. The broach used in this method is easier to manufacture, but the quality of the processed surface is poor.
- Wheel-cutting has high cutting efficiency and can reduce the length of the broach, but the quality of the processed surface is poor. It is mainly used to process round holes with larger dimensions, more machining allowances, and lower precision requirements.
- The comprehensive wheel-cutting method uses the wheel-cut method for rough broaching and the forming method for fine broaching, which has the advantages of both, and is widely used for round hole broaching.