Research on accurate modeling of threaded parts

There are two important features: the effective thread and the thread finish (also known as thread tail). Precise modeling of the thread, the usual practice is to simulate turning machining for spiral material removal. Taking the modeling of ordinary thread as an example, the basic tooth shape is drawn on the normal surface of the screw axis according to the provisions of GB/T193 and then swept and cut along the specified tool path. For the basic tooth type drawing method and sweeping method, it is not the scope of this article. This paper will focus on the modeling method of thread finishing.

1. The basic modeling of effective thread can be divided into two methods: material removal method and material addition method. In terms of thread modeling, whether it is internal thread or external thread, the material removal method is more scientific and better than the material feeding method. . Because the modeling method is not seen in this article, we can use a redundant cutting method to obtain a reasonable thread finish for the full thread. But for non-full threads, the situation is different. As shown and shown, the stop of the thread is visible. It is very abrupt and does not conform to the actual processing situation. In the following, several modeling methods for the thread finishing (software environment Siemens NX6.0) will be highlighted. Since the drawing of the internal thread and the external thread are the same, in order to save space, only the finishing of the external thread will be described below as an example.

3 Threading Finishing Modeling Method 1: Difference Algorithm This method can be regarded as the simulation of the boring thread. (!) Establishing the shape of the fangs In the actual external thread boring, the lance needs to be rotated. Walking through the full length of the thread, cutting off the excess material to form the thread, and in 3D software, if this method is also used, the data to be calculated will be quite large, so we can build the "fangs" into parts. The thread characteristic part is longer, generally 3 thread larger than the thread feature to be formed. The effective length of the thread thread is consistent with the thread cut-off position of the part, and it is not necessary to care about the true shape of the "fang", only to get correct The result is as shown.

(3) The external thread formed by the differential operation is as shown.

The thread finishing made by this method has the advantage of moving the retracting knife outward along the radial direction of the workpiece (for example, retracting the knife at a constant radial speed) to form a finishing end of the thread. Through analysis, we can know that when cutting the effective thread, the cutting rail is a fixed spiral with a lifting path and a pitch. In the process of retracting, the pitch of the spiral formed by the cutting rail is still the cutting process of the front. Consistent, but the radius is gradually increasing. It is conceivable that the tool path should be flared. Therefore, in NX modeling, we want to simulate this retracting motion, the main point is to draw this tool trajectory.

NX6 does not directly provide us with the command to create such a spiral. However, we can use other methods to obtain such a curve. At present, several methods are commonly used to obtain: the intercept line method and the projection method. The expression control method and the regular curve control method will be introduced separately.

U) Intersection line method This method establishes a large helicoidal surface and a racquet-like surface, and the two sides intersect to form a Rab-eight-shaped spiral.

Create a spiral (see), the radius of this spiral must be large, generally take /=> (r is the radius of the spiral, D is the nominal diameter of the thread).

Individual, the outline of the shape of this body is the outer contour formed by the path of the tool path we want. It can be built according to the actual situation, and one of them has a rounded corner.

The forming surface of the threaded finishing helix is ​​clearer, and the formed external thread feature is also relatively simple. The disadvantage is that the calculation amount is large, and the part with too long dry thread is too long, and the difference operation may fail. .

4 Threading Finishing Modeling Method 2: Reduced Thread Sweeping Method This method can be considered as the process of simulating the threading of the thread. In the same step as the thread is generated, the sweep and the difference are formed to form the required thread characteristics (see figure ).

Figure u Threaded feature model with threaded finish (2) The principle of projection is to cast the shadow of the thread onto the desired wheel porch. The first two steps of the projection method are the same as the intercept line method. When proceeding, it is necessary to draw a straight line, which needs the axis of the bow thread feature to be combined, which will make the state of the projection direction, otherwise the spiral will be discontinuous (see).

In the Projection Line dialog box, select “Point to Line” in the direction column and R to select the line created in the previous step (see Figure I3).

Press OK to generate the desired rail path to create a threaded finish with threaded features.

Expression functions, application expressions, we can create a variety of expression curves. Of course, the variable diameter spiral is no exception. The following is an example of the M1OXI external thread.

Click the "Tools" expression in the NX modeling interface, or directly press the CTKL + E key combination to open the expression input interface, and press 4 to enter the parameters.

In the graph expression interface ,, the radius increase coefficient, the larger the value, the faster the tool track ends; the total number of turns of the spiral, the number of effective spiral turns, that is, the number of turns of the straight spiral; / is the pitch; 〃 is the radius of the effective helix; f is the NX system changes M, changes from 0-1; Q is the reciprocal of the f value before the effective number of turns reaches n, that is, before the start of the closing; after the input is completed, press OK, then M is inserted into the formula The curve has a shape as shown in 5.

The shape can be adjusted by straightening 5 lines, and the final finished thread is finished as shown in 6.

Other parameters of the pattern, straight 1 in the expression interface to modify its corresponding value is ". (4) regular curve control method This method is to directly use two lines to twist the radius of the thread, so that it is as desired To make changes, create two sketches separately, as shown in 7. Note that the two lines should not be built on the same sketch. Moreover, the ruler of the regular curve in the direction of the thread should preferably be the same as the total length of the thread.

Insert the helix and select “Use Regular Curve” in the Radius Method item of the dialog box (see 8>. In the dialog box that opens, select it as prompted. Finally click OK to generate the required curve. Thread finishing (see 9) 2013 羌琴期卷卷冷加工 SolidWorks surface scanning function application Shanxi Jingwei Heli Machinery Manufacturing Co., Ltd. No. 3 Factory (Jinzhong 030601) Zhang Guanghui SolidWorks surface modeling function is often used in various product designs, in In the modeling process of solid features, surface modeling and feature modeling can be complementarily applied. This can intersperse surface modeling in product design with complex shapes, and can smoothly and quickly meet the SolidWorks product design requirements we need. After the product is completed, various attributes and interference checks can be performed to optimize the design. Now the following two examples are applied to the most common scanning functions of SolidWorks surfaces.

In order to complete the scanning of the middle upper edge hemming, a scanning contour needs to be established. In this example, the contour of the line segment is selected as a scanning open loop contour with a length of 12 mm. This line segment should first create the sketch datum (perpendicular to plane 1, see) before drawing the line segment, and then constrain the constraints by adding a geometric relationship.

Next, you need to create the surface scan path. Now you can use the surface feature: insert the curve combination curve, and finally you can scan with the surface scan function, and the hemming feature is created (see). The creation of the scan path is the most critical factor in the success of the scan. This method of creation subtly avoids the discontinuity of the edge. (5) Comparison of the four modeling methods. As can be seen from the above, the key to establishing the thread finish model is that the key is good. The required tool path line. The several methods described above have the characteristics of simple modeling, easy operation, and good feasibility. The dependence on the NX version is not too strong.

In terms of comprehensive comparison, the last method is the simplest. Expression modeling can be a bit difficult to understand, but it is a way of doing things. Through the control of several parameters, full-parameter modeling can be realized, which should be the first choice for modeling. The first and second methods can also be seen as a favorable complement. It may not be practical from the perspective of modeling, but it is of great benefit to help us understand the use of NX in depth and explore a variety of modeling approaches.

Comparison of the impact of the accurate model on the analytical data In the course of the study, the comparison between the tensile data of the physical specimen and the analytical data of the three-dimensional model shows that the CAE data obtained by the accurately modeled model is closer to the corresponding physical stress and strain change. Happening.

This paper takes Siemens NX6 as the modeling environment, taking ordinary thread as an example, combining the forming principle of thread and closing, simulating the two processing methods of threaded thread and turning thread, systematically studied several precise modeling methods of thread finishing, among which Some techniques have certain reference value for the establishment of other special models. MMf

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