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Parametric design of NC tools

1 introduction

tools for NC machine tools and machining centers (hereinafter referred to as NC tools) have developed rapidly abroad, and their varieties and specifications have formed a series. The research and development of numerical control tools in China started late. The development and production of numerical control tools has become a weak link in China's tool industry. The backwardness of numerical control tools has become one of the main obstacles affecting the full play of domestic and imported numerical control machine tools

at present, the way of designing NC tools abroad is basically to form new varieties or specifications by directly invoking the existing design results or local modifications. However, most domestic enterprises (including China's first automobile manufacturer) use commercial CAD (mostly AutoCAD) software platform for interactive drawing by designers in NC tool design. Because interactive drawing is difficult to use the existing design results, it is labor-intensive and inefficient to meet the actual production needs. Therefore, research open 1 If the display is abnormal in the test process or the middle beam does not move, it is necessary to develop advanced cad/cam technology for NC tools to improve the quality and efficiency of NC tool design and manufacturing

in the development of CAD technology, the emergence of parameterization technology is an important revolution. This technology takes constraint modeling as the core, and allows engineering designers to modify the design results in a size driven way. It is very suitable for the design of serialized products with similar structures

taking the numerical control boring cutter as an example, this paper studies the realization ways and methods of parametric design. The design method of other NC tools is similar to it

2 product model of NC boring cutter

in order to realize the parametric design of NC boring cutter on computer, it is very important to establish an appropriate product model. The product model of NC boring cutter should include blade, cutter bar, blade clamping device, etc. For more complex parts such as tool bar, in order to facilitate the realization and management of the model, it can be further decomposed into two geometries: head and rod. In the design, the tool parts are described in the form of geometry. Figure 1 is the product model block diagram of NC boring cutter

it can be seen from Figure 1 that the geometry of each part of the boring cutter is composed of structural constraints, graph element sets and parameter sets. The set of pixels is the basic geometric elements that make up the geometry, such as points, line segments, arcs, polygons, etc. In order to improve the efficiency of software, closed polygons are often used to define geometry, so as to reduce the number of pixels. Structural constraints are used to define the structure of geometry, such as the opposite edges of a rectangle are parallel to each other, and the adjacent edges are perpendicular to each other; Parameter sets are used to determine the size of geometry, such as the side length of a rectangle, the radius of a circle (ARC), etc. Because adjacent pixels or pixels with common position constraints or direction constraints in space should have a common parameter set, in order to reduce data redundancy and avoid unreasonable splicing between pixels, a total parameter set is constructed to determine that the parameter sets of each geometry are subsets of the total parameter set. If the intersection between subsets is not empty, it means that there is an adjacency relationship or position direction relationship between them

Figure 1 block diagram of NC boring tool product model

3 parametric modeling of geometry

it can be seen from Figure 1 that realizing parametric modeling of geometry and determining parameter set are the key steps of design. Once these two steps are completed, the design of the whole boring cutter is basically completed. Next, we first discuss the parametric modeling of geometry. In order to illustrate the whole modeling process, the geometric figure shown in Figure 2 is taken as an example for discussion. Figure 2a is the top view of the boring tool bar with square blade installed by pressing plate clamping, figure 2b is the shape of the tool bar head, and figure 2C is the shape of the tool bar

Fig. 2 Schematic diagram of boring tool bar

for the geometric shape of the tool bar head shown in Fig. 2B, its graphic element set includes blade groove graphic element II, screw hole graphic element, pressing plate groove graphic element I and head outer contour graphic element. The process of parametric design is to determine the location of feature points under certain constraints. For the head contour elements in Figure 2B, the structural constraints P0 point, horizontal lines p0p3, p0p1 ⊥ p0p3 are fixed in the design, and Kr α、β As the parameters driving its structural change, l, m and B are the parameters driving its size change (width B is limited by the width of the tool bar, belonging to the splicing constraint). After the outer contour element of the head is determined, the blade groove element II can be determined according to the blade size and its assembly position with the head, and then the screw hole element and the plate groove element I can be determined according to the size of the pressing plate and its relative position with the blade groove element II. The key to determine the feature points in Figure 2b is to determine P2 point. If the coordinates of P2 point relative to P0 point (i.e. the L and m values in the figure) are determined, on the one hand, the blade groove element Ⅱ, screw hole element and pressing plate groove element Ⅰ are determined, on the other hand, P3, P4, P5 and P1 are also determined. Point P6 is the center of the milling cutter arc designed considering the processing technology, and its position is determined with the determination of the blade groove graphic element II

Figure 3 is the schematic diagram of boring bar head used to calculate the coordinates of P2 point top view. It can be seen from the figure that P2 point is related to tool tip point P. The position of point P is determined by the cutting requirements, and the blade thickness h is a known value. Therefore, when the installation position of the blade is determined, the D value in the figure has been determined. According to the known D value, H value and the main deflection angle Kr, the spatial coordinates of P2 point can be determined

Figure 3 Schematic diagram of boring tool bar head

the algorithm for determining P2 point coordinates is discussed in detail below. In order to calculate the coordinates of P2 point, establish two local coordinate systems whose coordinate origin coincides (Note: for the convenience of calculation, the selection of coordinate axis direction is inconsistent with the coordinate axis direction of the coordinate system used for tool calculation). O-xyz and o-xqyqzq, where o-xyz is the projection coordinate system of boring tool graphics, and o-xqyqzq is established on the rake face, and its coordinate axis is parallel to the coordinate axis of the coordinate system used for machining the rake face (see Figure 3). Therefore, there is the following relationship between the two coordinate systems, even if they cannot work normally: rotate the o-xyz coordinate system around the X axis by the angle GP (the front angle in the cutting direction), so that the Y axis coincides with the YQ axis, and then rotate the angle y around the YQ axis to obtain the coordinate system o-xqyqzq. The relationship between Y angle and GF (feed direction front angle) and cutting depth front angle GP is

tgy=tggf cosgp

to simplify the calculation process, make the X and Y coordinates of point P0 zero, that is, located directly below point O (for convenience of observation, the position of the coordinate system is translated in Figure 3), and make the Z coordinate of point P zero at the same time. In the coordinate system o-xqyqzq, the relationship between P2 (x2q, y2q, z2q) and P (XQ, YQ, ZQ) is (let P2 point be located on the diagonal of the blade, otherwise, the included angle between D and the bottom edge of the blade can be obtained by calculation)

x2q = XQ DSIn (kt-p/4)

y2q = YQ DSIn (kt-p/4)

z2q =zq-h2

get P2 point in the coordinate system o- after the coordinates in xqyqzq, the coordinates (x, y, z) of its projection in the top view can be calculated, where the X and Y coordinate values are equal to m in Figure 2B L value

according to the relationship between the coordinate systems o-xyz and o-xqyqzq and the coordinate rotation formula, the relationship between (x, y, z) and (x2q, y2q, z2q) can be obtained as

x=x2qcosy+ (y2qsingp+z2qcosgp) siny

y=y2qcosgp-z2qsingp

z= (y2qsingp+z2qcosgp) cosy-x2qsiny3

the coordinates (x, y, z) of point P2 can be calculated from equations (1) to (3). The X and Y coordinates are used to determine the top view, and the Z coordinates are used to draw the main view. After P2 points are determined, other feature points are determined according to the above method, and the basic contour modeling of the boring bar head shown in Figure 2B can be completed

similarly, the top view, main view, side view and other auxiliary views of the whole boring tool bar can be designed according to the design process similar to the above tool bar head. In order to reduce the amount of calculation in the actual design, the algorithm program is compiled. Users only need to input relevant parameters to realize the parametric design of NC tools

4 management of parameter set

there are many kinds of NC tools and a large number of parameters. For the convenience of users, we use open database interconnection (ODBC) technology to store common parameters in the way of external database

in traditional database field, database application program usually refers to the program developed with specific embedded query language under the support of specific database management system. This kind of database program often needs the support of a huge database management system, and has high requirements for users' software and hardware. ODBC technology provides a new way to realize database applications. It establishes a set of specifications, provides a set of high-level application call interfaces and a set of running support based on dynamic link library. The application program developed with such a group of interfaces can operate the database by using standard functions and structured query language, regardless of the database management system from which the data source comes. All the underlying operations of the database can be completed by the corresponding ODBC driver

in ODBC technology, ODBC driver manager is the bridge and link between ODBC applications and data sources. The relationship between ODBC driver manager, ODBC driver, data source and ODBC application is shown in Figure 4 with the recovery of the global economy. Using ODBC technology, different kinds of boring cutter parameters are stored as records in the database. Users can search the database according to the type of boring cutter designed, obtain the corresponding parameter set, or directly carry out dimension driven drawing or local modification to realize the design of new products. Because there is no need to input parameters one by one, the design process is very convenient and fast

Figure 4 ODBC technology application block diagram

5 boring tool coding system

in order to facilitate retrieval, the data record adopts the standard coding system. The first digit of the code represents the clamping mode of the blade, the second digit represents the shape of the blade, the third digit represents the main deflection angle, the fourth digit represents the rear angle of the blade, the fifth digit represents the cutting direction, the sixth and seventh digits represent the tip height, the eighth digit represents the boring tool code, the ninth digit represents the boring tool installation mode, and the eleventh and twelfth digits represent the blade size code. For example, csfnr25ca-12 represents a boring cutter with clamping plate, square blade, main deflection angle of 90 °, back angle of blade of 0 °, right cutting, blade tip height of 25mm, standard installation method, and blade side length of 12.70mm. For new products designed by users after modification on the basis of the original design, the coding has been adjusted accordingly on the basis of following the above provisions. For example, if the user changes the main deflection angle to 93 ° and the blade side length to 9.525mm on the boring tool design template coded as csfnr25ca-12, the code of the new boring tool is csunr20ca-09

6 program running framework

the newly developed NC tool parametric design platform allows users to carry out standard design and derivative design based on standard design. In order to facilitate data management, two databases are established: the standard database is used to store the existing finalized design data; Non standard database is used to store users' new design data. Accordingly, two layers of design interfaces are provided, namely standard design interface and non-standard design interface

the specific design steps are as follows:

1) determine the design code

three methods can be used to determine the design code: ① direct input method: the user directly enters the code of the designed tool on the design interface; ② Item by item determination method: after the user selects items such as blade clamping mode, blade shape, cutting direction, blade back angle, etc., the system automatically determines the boring tool code; ③ List browsing method: users can browse through the code table provided on the interface to find the required code. In order to make users clearly know the basic form of boring cutter represented by each code, each code is provided in the form of preview on the interface

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