Introduction of the hottest CNC machining technolo

2022-08-11
  • Detail

Introduction to CNC machining technology

1 Process analysis of digital control CNC machining

(1) structural characteristics of the part. The material of the part is duralumin LY12, which has good cutting performance. It belongs to a typical thin-walled disk structure, with large overall dimensions, the thickness of the surrounding and internal ribs is only 2mm, and the depth of the cavity is 27mm. If the process plan or processing parameters of the part are set improperly in the processing process, it is very easy to deform, resulting in out of tolerance of size.

(2) process analysis the blank of the part selects bar materials, and adopts the process plan of rough machining and finish machining. The specific process flow is as follows: blank → rough turning → rough milling → aging → finish turning → finish milling. Rough turning: Reserve 1.5mm finishing allowance on the excircle and end face respectively, and pre drill the center hole. Rough milling: reserve an allowance of 1.5mm on the side and bottom of the cavity respectively, and φ Pre drill the process hole at 12mm hole position. Aging: remove material and processing stress. Finish turning: finish turning the end face and excircle and boring the process hole φ 6mm, which requires one-time clamping to ensure coaxiality and lay a foundation for subsequent processing. Finish milling: ensuring the final requirements of parts is the focus of this paper

① rough milling cavity rough machining is mainly to remove large surplus and lay a good foundation for subsequent precision machining, so when machining cavity, choose low-cost ordinary digital control CNC machining milling machine. This process requires that the inner contour be machined according to the part structure drawing shown, the arc corner is r5mm, and the finishing allowance is even, which is 1.5mm. And this process also needs to φ The positioning holes required for finish machining are pre machined at the 12mm hole position

② precision milling cavity high-speed machining technology is a manufacturing technology applied in recent years. In high-speed machining, due to the small cutting force, the machining deformation of parts can be reduced, which is more suitable for thin-walled parts, and the chips are removed in a short time, most of the cutting heat is taken away by the chips, and the thermal deformation of the workpiece is small, which is conducive to ensuring the size and shape accuracy of parts; High speed machining can obtain high surface quality and greatly shorten the machining cycle. Therefore, combined with the characteristics of this kind of thin-walled disk parts, high-speed machining is selected for finishing the cavity

③ machining of positioning hole the central hole is selected for the finishing of the part φ 6mm and φ 12mm hole is used as positioning hole, so it must be machined in place before finishing the cavity. Central hole φ 6mm fine turning excircle φ When 301.5mm, boring it to φ 6H8; φ 12mm holes are drilled and reamed by CNC milling machine with digital control to φ 12H8。

(3) positioning and clamping of parts during precision machining of cavity in order to make the workpiece can be clamped quickly and correctly on the machine tool, and it is not necessary to align one by one when machining a batch of workpieces, so the positioning method of one side and two pins is adopted for this machining. Based on the existing φ 6mm and φ The 12mm hole is used as the positioning hole to make a simple tooling, which uses a cylindrical pin and a flat pin as the positioning element. As this part is a thin-walled part, it is easy to deform. When clamping the workpiece, the pressing plate should be pressed on the part with good rigidity of the workpiece, and the distribution should be as uniform as possible to ensure the reliability of clamping, and the clamping force should be appropriate to prevent damaging the positioning of the workpiece or causing unacceptable deformation of the workpiece. Its specific positioning and clamping. Weili said that the clamping method fully conforms to the characteristics of the machining center. One clamping can complete the processing of the cavity and all holes

2. General scheme of CNC machining program for machining cavity

(1) programming software the CNC machining program for digital control of the part is generated based on the software MasterCAM. The software does not need to draw entities, but only needs to correctly draw the contour line to be processed according to 1:1, and select the appropriate graphics and parameters to generate the program for processing

(2) selection of equipment. Machining center equipment is selected for finishing cavity: German HERMLE (Hummer) c1200u. The operating system of this equipment is heidenhin (heidenhan). Its performance indicators are: maximum speed of spindle 18000r/mm, rapid movement 30000mm/min, stroke 1200mm × 1000mm × 800mm, sensitive response, suitable for high-speed machining. This part has been processed by other machining center equipment before, but because the wall is thin, the thickness of the rib is only 2mm, and the depth of the cavity is 27mm, in order to prevent the deformation of the part, only small-size cutters can be selected, the processing speed is small, and multiple aging is carried out, and the processing cycle is very long, so the digital control CNC processing equipment suitable for high-speed processing is selected for this processing

(3) the choice of cutting tools is based on the part materials, and the domestic inlaid cemented carbide end milling cutter is selected. It has double edges, large spiral angle, large space in front of the edge, wear resistance and low cost. Through practice, it is found that the tool is very suitable for high-speed machining of aluminum. For the specific parameter selection, we need to explore in the actual cutting and find the appropriate speed. Of course, we should also refer to the manufacturer's information

3. During the fine milling process of the machining center, the milling of the cavity is carried out in two steps

respectively for the bottom and side processing, first the bottom and then the side. The center of the numerical control CNC machining program is set at the center of the outer circle of the workpiece, and the safety height is 50mm above the surface of the part

(1) specification of bottom processing tool: selection φ 14mm end milling cutter. Cutting method: using spiral cutting can improve the cutting state during cutting, maintain a high cutting speed and low cutting load, and the price of recycled waste plastic is far cheaper than the rising price of plastic raw materials in recent years. Tool feeding mode: Pocket parallel, spiral, clean cor ners (parallel surround and angle clearing) mode is selected, and the three cavities are processed from inside to outside, which can reduce tool lifting and improve milling efficiency. During machining, the machining allowance of 1.5mm on the bottom surface is completed in two times according to the forward milling method. The first tool back has a cutting amount of 1.4mm, the tool path overlaps 50%, the rotating speed is 8000r/min, and the feed speed is 1400mm/min; During finish machining, the back feed is 0.1mm, the rotation speed rises to 12000r/min, the feed remains unchanged, and the surface quality of the bottom surface is very good, so they understand immediately. The tool path is gradually expanded from the inside to the outside, which is similar to the shape. The tool path is smooth and soft, and drastic changes are minimized to avoid machine tool vibration. Note: when finishing the bottom surface, 3mm allowance is reserved for the side to avoid the increase of the cutting amount when milling to the side

(2) side processing tool specification: in order to prevent the sudden change of the tool path at the corner from causing too much impact, the tool consistent with the corner radius should be avoided as much as possible during high-speed processing. This time φ 8mm end mill (corner r5mm). When installing the cutter, the extension length of the cutter shall be shortened as far as possible to ensure the strength of the cutter during high-speed machining. Tool advance and withdrawal mode: approach and leave the workpiece in an arc way, which can avoid the tool contact mark when suddenly contacting the workpiece and ensure the surface quality of the parts. Cutting mode: contour (contour milling) mode is selected. During processing, it is layered according to the Z-axis and carried out in the way of forward milling. The rotating speed is 10000r/min and the feed speed is 1000mm/min. The three cavities are milled down layer by layer at the same time, and the back cutting amount of each time is 2mm. Note: it is not allowed to mill the next cavity after milling one cavity. Because when the first cavity is processed, the wall thickness of the internal reinforcement is only 3.5mm, while when the next cavity is processed, the cutting amount of 80 mm of the internal reinforcement will be 1.5mm, which will reduce the local support force, and the workpiece is easy to deform under the influence of the cutting force; If the three cavities are milled down layer by layer at the same time, the wall thickness of the rib is 5mm, and the supporting force is much larger relatively. After the machining operation of the tool path path is completed, select heidenhin post-processing, generate NC program, and transmit it to the machine tool by line

Copyright © 2011 JIN SHI