4.honing holes
1) Honing principle and honing head
Honing is a method of finishing a hole by using a honing head with a grindstone (oil stone). When honing, the workpiece is fixed, and the honing head is rotated by the machine tool spindle and reciprocating linear motion. In the honing process, the bar acts on the surface of the workpiece with a certain pressure, and a very thin material is cut off from the surface of the workpiece, and the cutting path is a cross-web. In order to make the movement track of the sand abrasive grains not repeat, the number of revolutions per minute of the rotary motion of the honing head and the number of reciprocating strokes per minute of the honing head should be mutually prime.
The crossing angle of the honing trajectory is related to the reciprocating speed and the peripheral speed of the honing head. The size of the horn affects the processing quality and efficiency of the honing. Generally, the 珩 is taken when it is rough, and it is taken when it is fine. In order to facilitate the discharge of broken abrasive grains and chips, reduce the cutting temperature and improve the processing quality, sufficient cutting fluid should be used for honing.
In order to achieve uniform processing of the wall of the machined hole, the stroke of the sand bar exceeds a certain amount of overrun at both ends of the hole. In order to ensure uniform honing allowance and reduce the influence of machine tool spindle rotation error on machining accuracy, most of the honing head and machine tool spindle use floating connection.
The radial expansion adjustment of the honing head grinding bar has various structural forms such as manual, pneumatic and hydraulic.
2) The process characteristics and application range of honing
a. Honing can obtain high dimensional accuracy and shape accuracy. The machining accuracy is IT7~IT6. The roundness and cylindricity error of the hole can be controlled within the range, but the honing can not improve the position accuracy of the hole to be machined.
b. The honing can obtain a high surface quality, the surface roughness Ra is, and the depth of the deterioration layer of the surface metal is extremely small ().
c. Compared with the grinding speed, the circumferential speed of the honing head is not high (vc=16~60m/min), but the reciprocating speed is relatively high due to the large contact area between the sanding rod and the workpiece (va=8~20m/ Min), so there is still a high productivity in honing.
Honing is widely used in the mass production of engines for the machining of precision holes in engine cylinder bores and various hydraulic devices. The bore diameter range is generally larger or larger, and deep holes with a length to diameter ratio greater than 10 can be processed. However, honing is not suitable for processing holes in non-ferrous metal workpieces with large plasticity, and cannot process holes with keyways, spline holes, and the like.
5. pull holes
1.Broaching and broaching
The pull hole is a high-productivity finishing method that is carried out on a broaching machine using a special broach. There are two types of broaching machines: horizontal broaching machines and vertical broaching machines. Horizontal broaching machines are the most common.
The broach is only used for low speed linear motion (main motion) during broaching. The number of teeth of the broach at the same time should generally be no less than three, otherwise the broach will not work smoothly and it will easily produce annular ripple on the surface of the workpiece. In order to avoid excessive broaching force and break the broach, when the broach is working, the number of working knives should not exceed 6~8.
There are three different ways of broaching in the hole, which are described as follows:
1) Layered broaching This broaching method is characterized in that the broach cuts the workpiece machining allowance layer by layer. In order to facilitate chip breaking, the teeth are ground with interdigitated chip flutes. The broach designed in a layered broaching method is called a normal broach.
2) Block broaching This broaching method is characterized in that each layer of metal on the machined surface is composed of a set of teeth of substantially the same size but intertwined with each other (usually consisting of 2-3 teeth per group) ) removed. Each tooth cuts only a portion of a layer of metal. The broach designed according to the block broaching method is called a wheel broach.
3) Integrated broaching This method concentrates on the advantages of delamination and block broaching. The rough cutting part adopts block broaching and the fine cutting part adopts layered broaching. This can shorten the length of the broach, increase productivity, and achieve better surface quality. The broach designed according to the comprehensive broaching method is called a comprehensive broach.
2. Process characteristics and application range of the hole
1) The broach is a multi-blade tool that can finish the roughing, finishing and finishing of the hole in sequence in one broaching stroke, and the production efficiency is high.
2) The precision of the hole is mainly determined by the precision of the broach. Under normal conditions, the precision of the hole can reach IT9~IT7, and the surface roughness Ra can reach 6.3~1.6 μm.
3) When the hole is pulled, the workpiece is positioned by the hole to be machined (the leading part of the broach is the positioning component of the workpiece), and the hole is not easy to ensure the mutual positional accuracy of the hole and other surfaces; for those inner and outer circular surfaces having the coaxiality requirement For the machining of body parts, it is often first to pull the holes, and then the other surfaces are processed with the holes as the positioning reference.
4) The broach can not only process the circular hole, but also can process the forming hole and the spline hole.
5) The broach is a fixed-size tool with a complicated shape and high price, which is not suitable for processing large holes.
The through hole is usually used to process through holes in small and medium-sized parts with a hole diameter of 10~80mm and a hole depth not exceeding 5 times in a large number of mass production.
