Drilling knowledge for design and precision machining Ⅰ
2020-09-05 11:30:36
二、drilling
1、Consult the advantages of using carbide drill bits often heard that the original use of high-speed steel lead, now use carbide drill bits. The company is also considering switching to carbide drill bits. To this end, I would like to ask what are the specific advantages of introducing carbide drill bits.
Performance comparison of carbide bits and high speed steel bits Drill performance evaluation index Machining effect (advantages) Carbide or high speed steel which is better?(1)High temperature hardness characteristics · High speed cutting · Extended tool life cemented carbide(2)The tool stiffness can inhibit the skew and expansion of the hole, and achieve high precision machining of cemented carbide(3)Resistance to fusion, can inhibit the production of chip nodules, processing surface excellent cemented carbide(4)Toughness [high] resistance to collapse, defects and other abnormal damage performance Strong high-speed steel [low] can inhibit the skew and expansion of the hole, to achieve high precision processing of cemented carbideDue to the different materials of carbide and high-speed steel, the performance of drill bits is also different. |
Advantages of carbide drill bit （1）High-speed machining reduces processing costs. High-speed machining can reduce processing time and thus greatly reduce processing costs. ■ Comparison of processing costs (mechanical cost = 6.6RMB/ min.396RMB /h) When the cutting length is 5m (for example), the processing time of cutting tool carbide bit (TAC-ESDRA) high-speed steel bit (G-ESDRA) is about 12 minutes. The mechanical cost is 79.6RMB219RMB （2）The tool life is significantly longer than that of high-speed steel, and the tool cost per unit of cutting length is greatly reduced. ■ Tool cost comparison (when using φ5mm drill bits) When the cutting length is 5m (example) The cutting length of the cutting tool carbide drill bit (TAC-ESDRA) high-speed steel drill bit (G-ESDRA) reaches the service life of about 50m about 10m tool unit price 109.6RMB119.2RMB The tool cost of this example (Cutting length =5m)10.9RMB59.6RMB（3）Due to the large rigidity of the tool, the drill bit will not be skewed during processing, and the hole processing with high cylindricity and high roundness can be realized. |
2、The hole processed by the drill will be skew, really troublesome drilling process after processing the bottom hole and then use the reamer to finish the hole, the bottom hole of the drill processing will sometimes be skew, and it can not be corrected when finishing. Because it will lead to the positioning pin can not be inserted normally and other faults, so want to process a non-skew hole, how can you suppress the skew of the hole in the drilling process?
The reason for the skew of the hole when drilling
(1) | Skew when the drill enters |
When the bit rotates, the cutting speed of its center is zero, and there is no cutting function. Therefore, when the drill enters the plane of the workpiece, the front part sometimes fails to enter the surface of the workpiece vertically, or vibration occurs, which will lead to the skew of the hole.
（2）Cutting edge height difference
When the height difference between the two shoulders of the bit (the height difference of the cutting edge) is large, the hole will be skewed during the processing.
A way to avoid crooked holes | ||||
(1) | Machining the center hole first | |||
Machining the center hole before drilling improves the accuracy of the drill, thereby preventing skew when entering the workpiece. | ||||
(2) | Choose the tool material with high stiffness | |||
Choose a drill with large stiffness material to prevent the skew of the hole. Specifically, the use of carbide drill bits is a typical measure. Center drill (or positioning drill) is the same, the use of rigid carbide material can effectively prevent skew, improve accuracy. | ||||
Hole defect without center hole
（1）The hole is easy to skew, and the position accuracy is low
（2）Tool life reduction
By pressing the front part without cutting function into the workpiece for drilling, the transverse edge part is badly worn, which will significantly shorten the service life of the tool.
3、Ask for the best way to drill holes on inclined planes.What is the most efficient way to drill a hole on a slope rather than a plane?
General method of drilling holes on inclined surfaces | |
When drilling on the inclined surface, the bit is subjected to lateral resistance, which will cause the bit to skew, and it is difficult to achieve stable processing. At this time, before drilling the drill, you can use the end mill for plane processing, or use the center drill to process the positioning center hole, which can inhibit the bit's beating and skew, and achieve stable processing. | |
End mill for surface machining | Center drill for positioning hole machining |
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4、Stainless steel drilling processing, how to avoid damage?
The processing efficiency is lower when using high-speed steel bits, so consider using carbide bits. When the carbide drill bit is used in the hole processing of stainless steel, is there any effective measure to worry about the loss?
Stainless steel processing points
The thermal conductivity of stainless steel is low, and the cutting heat generated during cutting is concentrated in the tip part of the tool, so it aggravates the wear of the tool. (Refer to: characteristics of stainless steel)
There is a limit to mitigating this phenomenon by changing the cutting conditions, and it is necessary to use a bit type and cutting method that can cope with the phenomenon of heat during cutting.
A circular Angle bit with a large tip Angle (around 135 to 140°) and a cutting edge shape with a cross edge grinding is effective, while helping to reduce shoulder wear.
In addition, by changing the Angle of the helix Angle in the middle of the double lead carbide drill bit, it can simultaneously improve the chip discharge performance and the stiffness of the tool, which is also very effective.
It is recommended to use the minimum number of gradation or stepless machining processing conditions to reduce the phenomenon of cutting edge and cutting surface collision. There is no need to specially reduce the processing speed and feed speed. (See: stepless processing)
5、At the bottom of the deep cavity and other deep positions such as hole machining is difficult if the use of extended drill bit at the bottom of the deep cavity or worried about the workpiece and the tool interference in the hole machining, it will cause the tool bending or broken, etc., very troublesome.How to ensure stable drilling in such difficult areas?
The use of extended drill bit for ordinary machining methods and their existing problems When hole machining is carried out in the part where the tool interference is concerned or hole machining is carried out in the depth of the workpiece, the extended bit is generally used for hole machining and the extended reamer is used for hole finishing. However, compared with the end mill, the drill bit with thinner core thickness has lower tool rigidity when the cavity is deeper, and there are defects of machining instability. |
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Deep hole machining using a long neck drill bit To solve the rigidity problem of this kind of tool, it is more effective to use an end mill drill with a long neck structure. The neck design ensures that it is kept close to the machining site while remaining rigid, thus avoiding problems such as lack of rigidity, flutter, etc., as shown in Figure 1. |
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6、It is hoped to improve the efficiency of gate processing, etc., which is unique to plastic molds. It is relatively time-consuming to use EDM for mold gates, and it is hoped to save processing time and avoid the use of complex processing procedures.
Point gate guide bush processing After the bottom hole is machined with a drill, the workpiece is mounted on a lathe and then machined with a special tool. (Processing steps) ①Step machining with bits of different specifications. ②The SR part of the gate and the tip part of the gate are finished by special cutting tools. |
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Submerged gate processing After the bottom hole is stepped with a drill, it is finished with a special tool. (Processing steps) ①Place the workpiece in the vise. Step machining with bits of different specifications (machining allowance accurate to percentile). ②Using a cutting fluid with high lubrication performance, the finishing is carried out by special tools. |
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7、It is hoped that a drill can realize all processing, including hole finishing, in order to improve the roughness of the hole wall after drilling, reaming processing. However, for holes that are not pursuing high aperture accuracy, if there is a drill bit that can make the inner surface of the hole smooth and beautiful when machining the bottom hole, it will help shorten the processing time.
Structure and hole machining of common drill bit
As shown in the figure above, the outer part of the drill has a guiding part for the purpose of ensuring straight travel, but the finishing function of the inner surface of the hole is not strong. Therefore, even if it is a high-quality drill bit, the effect is not optimistic when relying on it to finish the hole with high surface roughness. Moreover, even in improving the aperture accuracy, machining surface roughness on the basis of suppressing the runout accuracy, there are certain limits。 |
Hole machining using a roller smooth edge drill bit
The drill with roller finishing edge has the function of finishing the inner surface of the hole (= roller finishing edge), which is a typical example of the above composite tools.
The edge belt design with roller finishing edge can improve the precision of the aperture and the machining surface, and realize the finishing of the bottom hole and the inner surface of the hole at the same time, so as to shorten the machining process and reduce the cost.
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