As the most common and commonly used feature of mechanical parts, holes in Guangdong machining plant play different roles and uses, such as positioning holes, datum holes, assembly holes, process holes, etc. the accuracy and requirements of holes are also very different. With the application of advanced numerical control equipment, the traditional processing technology of holes is bound to be greatly impacted, such as the way of hole processing, the process of hole processing, the quality of hole processing, the quality of hole processing and the quality of hole processing Cutting tools and so on also changed, and milling instead of drilling, milling instead of reaming, and milling instead of boring also came into being,
In order to improve the quality and efficiency of product processing, Guangdong mechanical processing plant should constantly explore the hole processing technology, find new processing methods, and constantly improve the manufacturing level. Based on the author's own experience in hole processing, this paper attempts to take this as an example to analyze and discover the general rules of hole processing. Starting from the process of drilling, reaming, boring and milling, this paper analyzes the advantages and disadvantages of each process, aiming to explore the process of high-quality and high-precision processing, and find out the simple and feasible technical analysis method. Hole is a very common feature of mechanical parts, and there are holes in many kinds of parts. However, with the continuous application of the three-axis CNC milling machine and machining center, the hole processing technology has also undergone significant changes. The hole processing is no longer based on drilling, but replaced by the composite processing technology with centralized technology, even so, It can not be said that the processing technology of a hole with high precision requirements is fixed. Jin Fuji, deputy chief technologist of Beijing Machine Tool Research Institute, pointed out to the point: "the quality of hole processing technology in China is not too much behind that of developed countries for 30 years. The reason lies in the backward hole processing technology." In fact, the machining of the hole is carried out by the tool inside the workpiece, so it is difficult to remove the chip, heat dissipation and observe. The size of the hole limits the size of the tool, and the accuracy of the hole also limits the accuracy level of the tool, so it is not convenient to measure the size of the inner hole. It can be seen that on the basis of traditional hole processing technology, new hole processing technology is urgently needed, which requires the processing personnel to pay attention to the hole processing technology and various characteristics. Guangdong Machinery processing factory is really good and deserves attention.
1、 Drilling processing
1. Tools used: common twist drill, indexable shallow hole drill, flat drill, etc. In the machining center drilling, most of the ordinary twist drill. There are two kinds of twist drills: high speed steel and cemented carbide. The twist drill is mainly composed of working part and handle. The working part includes cutting part and guiding part. The cutting part of twist drill has two main cutting edges, two auxiliary cutting edges and one transverse cutting edge. The two spiral grooves are the surfaces through which the cutting passes and are the rake faces; The two end surfaces opposite to the transition surface (i.e. hole bottom) of the workpiece are the main flank; The two edge strips opposite to the machined surface (i.e. hole wall) of the workpiece are the secondary flanks. The intersection of rake face and main flank is the main cutting edge, the intersection of rake face and auxiliary flank is the auxiliary cutting edge, and the intersection of two main flanks is the transverse cutting edge. The angle between the projection of the cross cutting edge and the main cutting edge on the cross section is called the cross cutting edge angle Ψ= 50°—55°; The rake angle and rake angle of each point on the main cutting edge are variable. The rake angle at the outer edge is about 30 ° and the rake angle at the drilling center is close to 0 ° or even negative; The angle between the projections of the two main cutting edges in the plane parallel to them is the vertex angle, and the vertex angle of the standard twist drill is 2 ψ= 118°。 The guiding part of twist drill has the functions of guiding, polishing, chip removing and cutting fluid conveying, which is also the backup of cutting part. There are two kinds of twist drills: Morse taper shank and cylindrical shank. Twist drills with a diameter of 8-80mm are mostly Morse taper shank, which can be directly installed in the shank with Morse taper hole, and the tool length cannot be adjusted. Most twist drills with a diameter of 0.1-20 mm are cylindrical shank, which can be installed on the shank of drill chuck. Medium size twist drill can be used in two forms.
2. Process characteristics
Drilling is an essential rough machining stage in hole machining in Guangdong Machinery processing plant. In this stage, the main consideration is the removal of materials. This process mainly depends on the axial stress of the machine tool spindle for cutting. Therefore, the chips are extruded. Therefore, the rough machining mainly based on drilling will result in the chip entanglement and large deformation at the inner wall of the hole, In this process, the key consideration is to solve the cooling of the drill tip and the chip entanglement, that is to say, the efficiency is considered in the drilling based processing, but for the hole, the processing quality of the hole can not be guaranteed, even if the drill is used to enlarge the hole from small to large, the deformation caused by extrusion can not be solved. It can be said that the drill is mainly used for drilling, and it is only used for rough machining and semi finish machining. This process is not allowed to complete the finish machining of a hole. At this stage, the selection of bit is generally smaller than the size of the hole. Once the same size bit is selected, the processing of the hole will be scrapped.
2、 Reaming
1. Tool used: machine reamer. Reamer for universal standard machine. The working part of reamer includes cutting part and calibration part. The cutting part is conical, which is responsible for the main cutting work. The main deflection angle of the cutting part is 5-15 degrees, the front angle is generally 0 degrees, and the back angle is generally 5-8 degrees. The function of the calibration part is to correct the aperture, smooth the hole wall and guide. For this reason, this part has a very narrow blade belt（ γ o=0°， α o=0°)。 The calibration part includes cylinder part and inverted cone part. The cylindrical part ensures the reamer diameter and is easy to measure, and the inverted cone part can reduce the friction between the reamer and the hole wall and reduce the enlargement of the hole diameter. The standard reamer has 4-12 teeth. In addition to the reamer diameter, the number of teeth of reamer is mainly selected according to the requirements of machining accuracy. The number of teeth has little effect on the surface rough reading. If the number of teeth is too many, the tool manufacturing and regrinding are more troublesome, and the chip groove between teeth will be reduced, which will cause the chip to block and scratch the hole wall, so as to break the reamer. If the number of teeth is too small, the stability of reaming is poor, the cutting load of cutter teeth increases, and the geometric error is easy to occur. The number of reamer teeth can be selected according to the table below. Reamer tooth number selection table
2. Process characteristics:
In order to improve the surface quality of the hole and obtain a lower roughness value, reaming is essential in Guangdong machining plant. Affected by the characteristics of the cutter, in this process, the reaming allowance must be small, otherwise, the reamer will be damaged, not to mention, or even the final size and shape of the hole will be affected. Reaming plays a role in polishing the inner wall of the hole, and the dimensional accuracy all depends on the accuracy of the reamer. The reamer H7 must be used to ream the hole H7, and the reamer H6 must be used to ream the hole H6. However, reaming has a major defect, that is, the process can not correct the perpendicularity of the hole; The bottom hole is inclined, and the reamer is inclined. " Obviously, the accuracy of the tool can only ensure the dimensional accuracy of the hole, but can not guarantee the position accuracy of the hole. Therefore, if this process is used for finishing, the perpendicularity of the hole must be solved in advance.