Broaching is a type of machining operations, is the use of broaching machine (broach) processing a variety of internal and external forming surface of the cutting process.
1. brief introduction.
Broaching tools are very complex components made from a single piece.The main material is high speed steel, hard alloy as tool material is only used for the machining of gray cast iron.
Unlike many other cutting operations, the main concern is tool wear or tool life.
In broaching, several teeth mesh at the same time, and chip width is often large.Removing chips can be very problematic, and low viscosity oils are often required as well.
From the supply of cutting fluid, internal broaching is more problematic than external broaching, horizontal broaching is more difficult than vertical broaching.
2. Classification
To cut with a broach as a tool.When the broach moves linearly with respect to the workpiece, the machining allowance of the workpiece is cut off successively by the cutter teeth of increasing size on the broach (figure 1).Usually, a working stroke can be formed, is a high-efficiency finishing method.However, broach is mainly used for mass production due to its complex structure, high manufacturing cost and certain specificity.According to the characteristics of the processed surface, broaching is divided into internal broaching and external broaching.
(1) internal broaching: used for processing all kinds of cross section shape through hole and hole through groove (figure 2), such as round hole, square hole, polygonal hole, spline hole, keyway hole, internal gear, etc..There should be machined holes before broaching so that broach can be inserted.The aperture range of broaching is 8 ~ 125 mm, and the hole depth is not more than 5 times of the aperture.In special cases, the aperture range can be as small as 3 mm, as large as 400 mm, hole depth up to 10 meters.
(2) external broach: used for processing non-closed surface (figure 3), such as plane, forming surface, groove, tenon groove, blade mortise and external gear, especially suitable for processing in large quantities of plane and compound surface, such as automobile and tractor cylinder, bearing and connecting rod.The size accuracy of broaching profile can reach IT8 ~ 5, the surface roughness is Ra2.5 ~ 0.04 micron, the accuracy of broaching gear can reach 6 ~ 8 .
In broaching, the sequence and mode of cutting the machining allowance from the workpiece have form, form, wheel cutting and comprehensive wheel cutting.
(1) High machining accuracy, small surface roughness, but low efficiency;Broach length is long, mainly used for machining small and medium size hole and high precision forming surface.
(2) the gradual form is suitable for rough broaching complex machining surface, such as square hole, polygonal hole and spline hole, the broach used in this way is easier to manufacture, but the quality of the processing surface is poor.
(3) high efficiency of wheel cutting cutting, can reduce the length of broach, but the quality of the processing surface is poor, mainly used for machining larger size, more machining allowance, low precision requirements of the round hole.
(4) comprehensive round cutting type is to use the round cutting method for rough broaching, with the forming method for fine broaching, both advantages, widely used for round hole broaching.