1. CNC Milling Machine Selection of Reaming Amount
(1) CNC Milling Machine Reaming allowance
Reaming allowance is the size of the depth of cut reserved for reaming. Usually, the reaming allowance is smaller than the reaming or boring allowance. Too much reaming allowance will increase the cutting pressure and damage the reamer, resulting in the roughness of the machined surface. When the allowance is too large, the coarse hinge and the fine hinge can be separated to ensure the technical requirements.
On the other hand, if the blank allowance is too small, the reamer will wear prematurely, it will not cut properly, and the surface roughness will be poor. Generally, the reaming allowance is 0.1~0.25mm. For larger diameter holes, the allowance cannot be greater than 0.3mm.
There is an experience that recommends setting a thickness of 1~3% of the diameter of the reamer as the reaming allowance (diameter value). For example, a reamer of Φ20 and a hole diameter of about Φ19.6 are more suitable: 20-(20*2/ 100)=19.6 For hard materials and some aerospace materials, the reaming allowance is usually made smaller.
(2) CNC Milling Machine Reaming feed rate
The feed rate of reaming is larger than that of drilling, usually 2~3 times. The purpose of taking a higher feed rate is to make the reamer cut material rather than friction material. However, the roughness Ra value of the reaming hole increases with the increase of the feed rate. If the feed rate is too small, the radial friction will increase, and the reamer will wear quickly, causing the reamer to vibrate and roughen the surface of the hole.
For standard steel reamers to process steel parts, to obtain surface roughness Ra0.63, the feed rate cannot exceed 0.5mm/r, and for cast iron parts, it can be increased to 0.85mm/r.
(3) CNC Milling Machine Spindle speed for reaming
Each element of reaming amount has an effect on the surface roughness of the reaming hole, among which the reaming speed has the greatest influence. For example, reaming with a steel reamer should have a better roughness Ra0. It is said that the reaming speed should not exceed 5m/min, because it is not easy to generate built-up edge at this time, and the speed is not high; and when reaming cast iron, because the chips are broken into granular, no built-up edge will be formed, so the speed can be increased. to 8~10m/min. Usually the spindle speed of reaming can be selected as 2/3 of the spindle speed of drilling on the same material.
For example, if the speed of the drilling spindle is 500r/min, it is reasonable to set the speed of the reaming spindle to 2/3 of it: 500*0.660=330r/min
The so-called reamer is actually boring. The fine boring usually has a unilateral allowance of 0.03-0.1, and the speed is 300-1000. The feed rate of 30-100 is suitable.