Application of the hottest UG in the machining of

The application of UG in taper stub shaft machining

Abstract: This paper describes the process of using UGII software of EDS company of the United States to subcontract cad/cam for the production of important taper stub shaft by snacma company of France, involving CAD modeling, part process analysis, cam machining

Keywords: cad/cam; NC machining; Conical stub shaft

0 preface

conical stub shaft is an important part of the low pressure turbine of cfm-56 engine produced by SNECMA company of France. The main characteristics of this part are: the geometry of the part is relatively complex, the material processing performance is poor (deformed superalloy), and the processing accuracy requirements are high (the surface profile of the curved surface is ± 0.075). The minimum wall thickness of the whole part is only 2.33mm, and the height of the whole part is 550mm

parts have great difficulties in the whole process arrangement and machining. The contour of the whole part is complex (see Figure 1), so it is difficult to use manual calculation of control points for NC programming. In order to successfully complete the subcontracting production task of France, we introduced UGII cad/cam software of EDS company of the United States, used modern cad/cam technology to compile the NC program of the part, and carried out the NC trial processing of the part, and successfully completed the trial production task

Figure 1 overall effect drawing of parts

based on the following reasons, we choose UG v13.0 software as the software platform for this trial production:

*cad/cam has powerful functions and can carry out 5-axis and turning processing

*cad/cam can be seamlessly integrated

* good versatility

* the processing algorithm is stable

1 part process analysis

the part material is nc19fenb deformed superalloy. The cutting performance of the material is poor, which is specifically manifested as: when cutting, the material has high hardness, large cutting deformation, large work hardening tendency, large cutting force, high cutting temperature, easy tool wear, and difficult to ensure surface quality and accuracy. The processed surface hardness of the material can reach 200 ~ 500 times that of the matrix; The cutting force is about 2 ~ 3 times higher than that of ordinary steel. If the machinability of 45 steel is 1, the cutting performance of superalloy is only between 0.5 ~ 0.2. Due to the thin wall of the part, the deformation of the part due to the characteristics of large cutting force and large cutting deformation should be considered when arranging the tool path, and the tool path and cutting parameters should be reasonably arranged to ensure the dimensional accuracy and surface quality requirements of the part

in terms of process arrangement, grinding is not allowed due to the design requirements of the part itself, so turning is only allowed. 40 outer circles, 24 lace in the inner cavity, 0.7 chamfer on all lace and all holes are completed by the machining center. All turning is divided into two parts: rough turning and fine turning. During the programming of rough turning, the non-uniformity of raw material allowance should be taken into account. In the parts with serious non-uniformity of raw material allowance, manual idling should be carried out to save processing time. At the same time, due to the release of residual stress on the part surface during cutting and the easy deformation of the part material itself, natural aging should be carried out for a period of time after the rough machining is completed to release the residual stress on the part surface, so as to avoid serious deformation and scrapping of the part caused by the release of surface stress after finishing

due to the severe work hardening and high hardness of part materials, we mainly use ceramic tools and cemented carbide tools as tool materials. The tools are mainly santavik tools

2 establishing mathematical model

key points and difficulties: Taking the processed qualified parts as the ultimate goal, the former key consulting project of Chinese Academy of Engineering "China's primary plastic product waste treatment and biodegradable plastic utilization and development status" which meets the requirements of part design was launched in Nanjing, and a reasonable CAD mathematical model was established according to the requirements of cam

in the process arrangement of this part, four turning processes should be carried out first, and then the outer ring and inner diameter should be introduced to help enterprises seize the customized high point of the standard system and milling lace process. If the modeling is directly carried out according to the design drawing, the lace and hole system on the outer ring and inner diameter will interfere with the normal work of the turning module, resulting in the failure to select the required processing boundary. Therefore, in line with the purpose of modeling for processing, the part model cannot be modeled directly according to the dimensions given in the design drawing. After the turning process is completed, there should be a margin of two millimeters on the total height to facilitate the processing of the lace milling process. At the same time, because the turning process on the NC lathe does not involve geometric features such as hole system, the hole system should be excluded in modeling, and only the boundary required for turning should be modeled. On the design drawing provided by SNECMA, France, only some discrete points are given for the curve part. First, select the curve menu under the toolbox in modeling, then select the spline icon, and select the points from file item under through points to establish a non-uniform rational B-spline curve. When establishing the mathematical model, smooth the B-spline curve constructed according to the discrete points to meet the design requirements. After excluding geometric features such as lace and hole system, the part can be regarded as a rotating part, but its shape is more complex. Because this part is a revolving part, it only needs to make a bus and rotate 360 ° to make the shape of the part, so it is more advantageous to use the sketch function of UG to process the whole part. Define all the dimensions and geometric constraints in sketch, and then select the body of revolution icon in modeling to rotate the sketch curve of the part just constructed 360 ° to form a solid. (see Figure 2)

Figure 2 modeling entity figure

3 cam machining

according to the conclusion of process analysis, start the preparation of machining and turning program. In the rough turning of 10 and 15 processes, due to the uneven raw material, the parts with thick raw material should be treated first to make the raw material allowance basically consistent. Otherwise, it is either empty cutting that wastes most of the processing time, or the cutting depth is too deep, which leads to the cutting of the tool. In the specific operation, we deal with it like this:

first of all, do the tool path of other parts without considering this problem. When making the tool path, it should be noted that due to the poor cutting performance of the part material, the tool path cannot be cut from the beginning to the end, otherwise the tool wear is serious and cannot be processed at all. At the same time, the part boundary should be appropriately extended in the sharp corner to cut off the flash generated by cutting. Only 1mm allowance is left for all geometric dimensions. When 1mm stock is left, the minimum curvature radius of the part surface will change. The selection of tool diameter should pay attention to the existence of this change, and the tool diameter should be reasonably selected to avoid the negative impact on subsequent processing caused by the large local allowance caused by the larger tool diameter than the minimum curvature radius. At the same time, it should be noted that the default value of engage/retract in UG is auto CIRC. In general, it is reasonable to use this value, which can make the points of advance and retreat coincide, eliminate the tool receiving table, and avoid tool pricking. However, the method of tool advance and withdrawal should be selected according to the actual situation. If the default value is blindly used in this part, the tool will hit. (see Figure 3)

then, rename the corresponding processing track and copy it. For this track, set the stock value in stock as a value that can eat the knife on the selected boundary during cutting. Then, given the number of pass, it should be ensured that the first tool is cut and the cutting depth is reasonable. Then select the edit item under the edit item in part geometry to stretch or crop the start point and end point of the boundary proportionally or by length. In order to limit the processing scope to the parts with thick wool. After the front rough turning is completed, carry out the reverse rough turning. After rough machining, due to the thin wall of the part, the easy deformation of the part material and the surface stress caused by rough turning, the deformation of the part is more serious. Therefore, it is necessary to conduct natural aging for about two weeks before finishing, so as to release the surface stress as much as possible and avoid large deformation of parts in subsequent processing. After natural aging, semi finishing and finishing of parts can be carried out. Since the minimum wall thickness of the part is only 2.33mm, semi finishing shall be carried out at important parts, leaving a margin of 0.2mm for finishing (that is, enter 0.2 in stock)

during finish machining, it should be noted that according to the requirements of the part design drawing, the tool joint mark of the part is not allowed to exist on the surface, but only on the part where R is transferred at the root of the surface. Therefore, when designing the tool path, it is not the same as the rough turning process, and it doesn't matter where the tool mark is

in the finish turning process, the knife joint mark must be left at the R adapter. In other words, if the upper and lower surfaces are not machined by one knife, the boundary between the upper and lower surfaces should be at the R transition at the root of the surface. After all tool paths are completed, the tool position source file * CLS (actually an ASCII apt language source program), then select CLSF in the toolbox, specify the tool position source file, select the select all menu, then select the postprocess menu, enter the name of the finished machine tool post-processing file under MDF name, and select the postprocess menu to get the required G code file (the file suffix in UG is *.ptp)

4 milling lace

after the four turning processes of the part are completed, Carry out lace milling process. According to the requirements of the design drawing, the three-dimensional modeling required by cam is constructed. Select the planar mill module of UG. If it is seamless copper pipe, it should be connected to the main machine for processing. When selecting a tool, you should pay attention to: first use the minimun radius in info to determine the minimum radius of curvature of the part, and then select the tool to ensure that the tool diameter is less than the minimum radius of curvature. Otherwise, UG will automatically let the knife in order to avoid overcutting, which will leave uncut areas after the parts are processed. At the same time, in order to ensure that there is no knife mark, automatic arc knife advance and retreat should be selected as far as possible. In order to ensure the accuracy requirements, this process can be carried out on a two-and-a-half axis or three-axis machine tool with high accuracy. See Figure 4 for cutting effect

Figure 4 effect drawing of lace milling

5 conclusion

through the trial machining of conical stub shaft, we have preliminarily mastered the operation of UG lathe module and have some experience. First of all, the mathematical model required by cam does not necessarily have to carry out CAD modeling exactly according to the design drawing, but should be convenient for cam processing as much as possible on the premise of meeting the design requirements. For example, there is no need to stretch the defined boundary into a solid for cam machining. In fact, as long as there is a boundary line, it is enough. CAD modeling should be carried out according to actual needs, not rigid work. The processing conditions of each process introduced above have fully explained this point. Secondly, the default value in UG is generally better. However, whether to adopt it or not should be decided according to the actual situation. The processing of this part has fully reflected this point. Third, being able to compile part processing procedures does not mean that qualified products can be processed. How to arrange the cutting path should be closely related to the actual situation. Determine the reasonable process route and cutting parameters according to the cutting performance of machine tools, cutting tools, fixtures, part materials, part structure and other factors. As we are engaged in cad/cam, European automotive emission standards are further driving the automotive industry to reduce carbon emissions for a short time, and our experience is not rich enough. Mistakes are inevitable. Please criticize and advise. (e