1. Analysis of the structural characteristics of the parts
A company needs to process a batch of parts, the material is 35CrMo, and the material hardness is 290-320HBW. The part has a small volume, length, width and height are 50mm, 60mm and 6mm, respectively, similar to the size of an adult palm; the surface has a groove, the gap between the groove and the groove is 2 mm, and the surface roughness value Ra = 3.2 μm.
The part is machined because the hardness of the material is high and the gap between the groove and the groove is small. When selecting a tool, the diameter must be
<2mm, the cutter bar is too thin and the strength is insufficient. It is easy to break the milling cutter due to excessive torque during machining, and the surface roughness is strict. Therefore, the difficulty in machining is how to determine the appropriate cutting parameters. The quality, but also to improve processing efficiency. Based on the above factors, select the model number as
The vertical machining center of the VTC 200-CN is machined.
2. Process route design
(1) Design of the processing technology. The machining process of the parts will directly affect the machining accuracy and machining efficiency. It is the key to the machining of parts to develop reasonable machining processes and process measures. By analyzing the structural characteristics and machining difficulties of the parts, the machining process of the milling process is divided into rough milling, semi-finishing milling, finishing milling and rooting, taking into account the processing efficiency and processing quality, specifically: rough milling Upper surface → semi-finishing milling groove, groove width and groove depth are respectively 0.2mm → finishing each groove, groove width and groove depth processing to finished product size → clearing root, eliminating arc between groove and groove bottom.
(2) Selection of machining tools. When roughing the upper surface, due to the large area to be milled, the common φ63mm flat disc milling cutter is used to improve the machining efficiency. When semi-finishing, according to the groove width, the Sandvik model is selected as R216.24. -06050BCC10P 1640 φ6mm end mill (see Figure 1); In the case of finishing and root cleaning, in order to further improve the surface quality of the groove and remove the rounded corners, select the φ1.5mm stand of the Sandvik model IP230-0150-XA 1630 Milling cutter (see Figure 2).
Figure 1 Semi-finishing cutter
Figure 2 Precision milling cutter
(3) The solution of the fixture. Due to the small size of the part, the clamping is difficult to achieve when milling the flow cell. Therefore, the following simple and effective methods are adopted: firstly, a round steel with a diameter and a length suitable for the hardness requirement is selected, and then the three-claw self-centering card is used. The discs are placed in parallel, and the end mill is used to mill the swirling grooves on the round steel. After the milling, the wire cutting is performed, and finally the surface grinding is performed. This eliminates the need to design a dedicated fixture, easily solves the clamping problem and reduces costs.
(4) Design of the NC program. The programming is based on the UG NX version 6.0, which is milled in a pocket. When programming, it is necessary to pay special attention to: 1 cutting mode needs to select the layered cutting mode of the following components, and adopts down-cut milling, and selects the depth-first principle. 2 The feed mode adopts the method of feeding the knife from the edge of the workpiece to the inner arc. 3 Retracting method adopts the method of direct retracting to improve processing efficiency.
When planning the machining path, the three principles must be observed: 1 Safe machining path to ensure the normal cutting of the tool. 2 Plan the appropriate processing path to meet the dimensional accuracy and surface quality requirements of the machined parts. 3 Plan the shortest machining path and reduce the cutting time to improve the processing efficiency.
Based on the above, the processing paths as shown in FIGS. 3 and 4 are determined.
Figure 3 Semi-finishing path
Figure 4 finishing milling path
(5) The amount of cutting is preferred. The selection principle of cutting amount is to ensure the cutting performance of the tool and the performance of the machine tool under the premise of ensuring the processing quality of the part (such as precision and surface roughness), thereby maximizing production efficiency and reducing production cost.
According to the internal characteristics of the swirling groove, the cutting amount is determined by the method of “small step and fast walking”, that is, the method of high speed, snack knife and fast feed is used to improve the stress state of the tool, machine tool and workpiece. Reduce tool breakage and improve surface finish quality.
Through a series of tests and demonstrations, test data as shown in Tables 1 and 2 were obtained, and the amount of cutting as shown in Table 3 was finally determined.
3. Conclusion
It can be known from the process test that the use of a numerically controlled milling machine to machine the swirl groove of the shape can well ensure the accuracy, dimensional requirements and technical conditions of the part. The processing method and the cutting parameters used can provide reference for the processing of similar parts.
references:
[1] Liu Huimin,Tian Haiwen,Zhang Ying.Study on NC Machining Technology of Multi-head Swirl Groove[J].中国科技浏览,2013(28):282.
[2] Chen Yanchun.Study on Determination of Cutting Parameters in CNC Milling[J].Mechanical & Electrical Engineering Technology,2006(12):21-24.
