数控类外文文献翻译--模具型腔数控加工计算机辅助刀具选择和研究

Mould type of numerical control process computer assist the cutter choose and study

Foreword

Numerical control include cutter production and cutter of orbit choose two key problems process ,. The first problem has been got and studied extensivly and deeply over the past 20 years, a lot of algorithms developed have already got application in commercial CAD/ CAM system. Most CAM systems can produce the cutter orbit automatically after users input relevant parameters at present. Comparatively speaking , it is still not ripe to regard quality , efficiency as the research of choosing the problem of cutter of optimizing the goal correctly, do not have commercial CAM system that can offer the preferred decision support tool of cutter at present, therefore it is difficult to realize the integrating automatically and organically of CAD/ CAM.. The cutter is chosen to usually include cutter type and cutter size. Generally speaking , suitable for one processing cutter of target for much kind , one cutter can finish different processing tasks, so it is easier to only consider meeting the cutter that basically processes the requirement and choose, especially to geometirc characteristics of model such as the hole , trough ,etc.. But in fact, it is common for cutter to choose and sure optimization goal interrelate, for instance most heavy to cut efficiency , process time , minimum process cost , longest service life ,etc. at least, so the cutter is chosen it is a complicated optimization question. Such as mould type one of parts, because the geometirc form is complicated (usually include curved surface of freedom and island), influence geometry that cutter choose it restrains from to be can explicit to say among CAD model, need to design the corresponding algorithm to draw, therefore choose the cutter specification suitable and cutter association , it is not easy things by improving efficiency and quality processed in numerical control.

Mould type generally with preparation method that numerical control mill, usually including rough machining, half finish machining , precise process of processing etc.. The principle of rough machining is to spare no effort to remove the surplus metal with high efficiency, therefore hope to choose the larger cutter, but the cutter is oversized, may cause

the increase of the crude volume ; Half finish machining of tasks to remove rough machining leave over step that get off mainly; Finish machining mainly guarantees size of the part and surface quality. Consider , go on , select exist , sure by computer difficult automatically totally up till now, therefore assist the cutter to choose in the computer that we developed (Computer Aided Tool Selection , CATS) among the system, base on , provide one aid decision tool for user, rough machining , half finish machining , precise to process etc., the real policy-making power is still left to users, in order to give full play to the advantages of computer and people.

1 Basic structure of the system

CATS system is CAD model, output for cutter type , cutter specification , mill depth of sharpening , enter the giving amount , rotational speed of main shaft (cut the pace ) and process six parameters such as time (such as Fig. 1), including choosing the aid decision tool in cutter type, rough machining cutter choose aid decision tool, half finish machining cutter choose aid decision tool and finish machining cutter choose aid decision tool ,etc.

Given the rough machining in Xingqiang processing of the important position (usually rely time 5~10 times), rough machining, the system automatically optimize portfolio with cutlery functions to enhance overall processing efficiency. In addition to the decision-making tools, the system also has a detailed look cutlery norms, based on the type and size cutlery recommended processing parameters and assess the function of processing time, the last generation of the overall results of choice cutlery statements (figure 2). All the data and knowledge systems cutlery done by the background database support.

2Key technologies and algorithms

2.1C utlery type choice

According to Assistant Xingqiang digital processing practice, Xingqiang Xi state general processing cutlery into milling cutter, milling cutter radius milling cutter and the first three balls. D based cutlery diameter, radius radius r when r=0 for milling cutter, 0

material steel, stainless steel, cast iron, nonferrous metals, materials and hard to cut materials six groups. Machine tool jig stability into good, better and less than three levels. Cutlery investigation into the short and long cantilever structures two, the system automatically reasoning on the basis of the specific circumstances of razor blades materials, decision-making knowledge from Walter cutlery manual system by the users first choice cutlery type in the world. To embed film style cutlery, a rules-based automated reasoning suitable razor blades materials. For example, if the final processing of materials for the "steel", machine tool jig for good stability, cutlery cantilever structures for short, razor blades materials for WAP25.

Rough machining cutlery portfolio optimization

Xingqiang rough machining the aim is to maximize the removal of excess metal normally used milling cutter, take-cutting approach. Thus, 3D mould Xingqiang the rough machining process, is actually a series of 2.5D components Xingqiang processing. Cutlery optimization is to find a group of cutlery portfolio, allowing for maximum efficiency removal of most metals. Cutlery portfolio optimized basic methods as follows :

A.To do some long step into knife in the direction of a group of vertical and horizontal search Xingqiang another entity to form a search layer.

B.Derive closed to the contours.

C.Calculated between Central and outside the island or islands and the distance between the key that affect cutlery choice geometric constraints algorithm flow As shown in figure 3

D.According to the principle of the merger (adjacent to the critical distance will be smaller than the difference between the threshold) to search layer merger, graphic processing and identifying viable cutlery sets, a processing layer.

E.Determine the use of each processing layer cutlery, cutlery Xingqiang processing portfolio.

F.According cutlery recommended processing parameters (cutting speed, depth and into Xianxiao to speed), the calculation of material removal.

G.According to the actual removal of the volume processing layer, the processing time for each processing layer.

H.Xingqiang calculating the total processing time and residual volume.

I.The overall portfolio of the Group cutlery processing efficiency assessment.

J . Repeat a~i until derive optimal mix of cutlery. If time is the goal, called for the entire processing time t Xingqiang shortest portfolio to optimize cutlery.

2.2Semi-finished cutlery choice

The main purpose is to remove semi-finished rough machining residual contours of the new warrants. To completely remove height, depth must be greater than Xianxiao parts of each level to the surface distance x. Its algorithm steps are as follows :

Step 1:entity models from parts of two adjacent to the cross section of the surface contours and the corresponding length;

Step 2: The average length of contours;

Step 3:calculate its width;

Step 4 : calculating height floor to the surface of parts to the law distance x;

Step 5 : steps 1~ repeat steps 4, each level of decision Xianxiao depth;

Step 6 : calculate cutlery diameter D, by or under cutlery experience D=x/0.6 manual recommended;

steps7 : choose Xianxiao x depth than the smallest cutlery.

2.3fine cutlery choice

Fine cutlery choice is the basic principle : cutlery parts surface radius smaller than the smallest size R curve radius r, the general admission R= (0.8~0.9) r. Its algorithm steps are as follows :

Step 1 : from the smallest curve radius calculation model parts entities;

Step 2 : From cutlery database search radius of less than a cutlery calculated radius of the curve all cutlery;

Step 3 : select the best cutlery meet the above requirements;

Step 4 : If all cutlery than the smallest curve radius, the smallest chosen as a recommended cutlery.

3 summary and discussion

Mould type of craft of processing plan , need high technology and experience very usually, prepare NC time of data nearly and process time to be large. So person who

produce of craft of processing plan and NC process demand of the order right away seem further more urgent automatically.

This text system research mould type of craft cutter plan , choose problem, put forward mould of rough machining , half finish machining , finish machining principle and method that cutter chooses, the realization algorithm with corresponding structure , and has carried on the realization of preliminary programming under the environment of UG/OPEN API, have developed CATS prototype system. In cutter type and on the foundation that the specification is fixed, system also can recommend parameter of processing according to cutter manual (cut pace , mill , sharpen depth , enter person who give ,etc.), evaluate corresponding processing time. Final purpose its to realize integration of CAD/CAM really , produce through aftertreatment numerical control process the order.

Need to point out , should improve the mould type totality of and process efficiency, need it from the rough machining , half finish machining , consideration on the whole of finish machining , make up and optimize many targets, this will be work that we want to carry on next .

模具型腔数控加工计算机辅助刀具选择和研究

引言

数控加工中包括刀具轨迹的产生和刀具选择两个关键问题。前一问题在过去的20 年里得到了广泛而深入地研究，发展的许多算法已在商用CAD/ CAM 系统中得到应用。目前大多数CAM 系统能够在用户输入相关参数后自动产生刀具轨迹。比较而言，对以质量、效率为优化目标的刀具选择问题的研究还远未成熟，当前还没有商用CAM 系统能够提供刀具优选的决策支持工具，因而难以实现CAD/ CAM 的自动有机集成。刀具选择通常包括刀具类型和刀具尺寸。一般来说，适合一个加工对象的刀具通常有多种，一种刀具又可完成不同的加工任务，所以仅考虑满足基本加工要求的刀具选择是较容易的，尤其对孔、槽等典型几何特征。但实际上，刀具选择通常和一定的优化目标相联系，如最大切削效率、最少加工时间、最低加工成本、最长使用寿命等，因此刀具选择又是一个复杂的优化问题。比如模具型腔类零件，由于几何形状复杂(通常包含自由曲面及岛) ，影响刀具选择的几何约束在CAD 模型中不能显式表示，需要设计相应的算法进行提取，因而选择合适的刀具规格及其刀具组合，以提高数控加工的效率与质量并非易事。

模具型腔一般用数控铣的加工方法，通常包括粗加工、半精加工、精加工等工序。粗加工的原则就是尽最大可能高效率地去除多余的金属，因而希望选择大尺寸的刀具，但刀具尺寸过大，可能导致未加工体积的增多;半精加工的任务主要是去除粗加工遗留下来的台阶;精加工则主要保证零件的尺寸及表面质量。考虑到目前完全由计算机进行自动选刀还存在一定困难，因而在我们开发的计算机辅助刀具选择(Computer Aided Tool Selection ，CATS)系统中，立足于给用户提供一个辅助决策工具，即粗加工、半精加工、精加工等，真正的决策权仍留给用户，以充分发挥计算机和人的优势。

1 系统基本结构

CATS系统的输入为CAD模型，输出为刀具类型、刀具规格、铣削深度、进给量、主轴转速(切削速度) 和加工时间等六个参数(如图1) ，包括刀具类型选择辅助决策工具、粗加工刀具选择辅助决策工具、半精加工刀具选择辅助决策工具及精加工刀具选择辅助决策工具等

鉴于粗加工在型腔加工中的重要地位(通常为精加工时间的5～10 倍) ，粗加工时系统具有刀具自动优化组合的功能，以提高整体加工的效率。除了上述决策工具外，

系统还具有查看刀具详细规范、根据刀具类型和尺寸推荐加工参数及评估加工时间等功能，最后生成总的刀具选择结果报表。系统所有的刀具数据及知识均由后台数据库做支持。

2 关键技术及算法

2.1 刀具类型选择

根据模具型腔数控加工实践，型腔铣加工的刀具一般分为平头铣刀、圆角铣刀及球头铣刀三种。设刀具直径为D，圆角半径为r ，当r=0 时为平头铣刀，0

WALTER刀具手册，系统由用户首先交互选择刀具类型。对镶片式刀具，基于规则自动推理出合适的刀片材质。例如，如果被加工工件的材料为“钢”，机床夹具的稳定性为很好，刀具悬臂为短悬臂，则刀片材质应为WAP25 。

粗加工刀具组合优化

型腔粗加工的目的就是最大化地去除多余的金属，通常使用平头铣刀，采取层切的方法。因此，3D模具型腔的粗加工过程，实际上就是对一系列2.5D模具型腔的加工。刀具优化的目的就是要寻找一组刀具组合，使其能够以最高的效率切除最多的金属。刀具组合优化的基本方法如下：

A. 以一定的步长做一组垂直于进刀方向的搜索平面与型腔实体相交，形成若干搜索层。

B. 求出截交轮廓。

C. 计算内外环之间或岛与岛之间的关键距离，即影响刀具选择的几何约束.

D. 根据合并原则(相邻关键距离相差小于给定阈值) 对搜索层进行合并，确定加工平面和可行刀具集，形成加工层。

E. 确定每一加工层使用的刀具，即型腔加工的刀具组合。

F. 根据刀具推荐的加工参数(切削速度、铣削深度和进给速度) ，计算材料去除率。

G. 根据加工层实际切除的体积，计算每一加工层的加工时间。

H. 计算型腔总的加工时间和残余体积。

I. 对该组刀具组合的总体加工效率进行评估。

J. 重复a～i，直至求出最优的刀具组合。如以时间为目标，即要求以整个型腔的加工时间t 最短来优化刀具组合。

2.2半精加工刀具选择

半精加工的主要目的是去除粗加工残留下的台阶状轮廓。为完全去除台阶，铣削深度必须大于每一台阶到零件表面的距离x。其算法步骤如下：

步骤1 由零件实体模型获得两个相邻截面的表面积以及相应的轮廓长度;

步骤2 计算平均轮廓长度;

步骤3 计算台阶宽度;

步骤4 计算台阶拐角到零件表面的法向距离x ;

步骤5 重复步骤1～步骤4 ，决定每一台阶的铣削深度;

步骤6 计算刀具直径D，按经验D=x/0.6或根据刀具手册推荐;

步骤7 选择铣削深度大于x 的最小刀具。

2.3 精加工刀具选择

精加工刀具选择的基本原则是：刀具半径尺寸R 小于零件表面最小的曲率半径r，一般取R=(0.8～0.9)r。其算法步骤如下：

步骤1: 从零件实体模型计算最小曲率半径;

步骤2: 从刀具库中检索出刀具半径小于计算所得的曲率半径的所有刀具;

步骤3: 选出满足上述要求的最大刀具;

步骤4: 如果所有刀具大于最小的曲率半径，选择最小的作为推荐刀具。

3 小结与讨论

模具型腔加工的工艺规划通常需要很高的技术与经验，准备NC 数据的时间几乎和加工时间一样多。因此，自动产生型腔加工的工艺计划及NC加工指令的需求就显得愈加迫切。

本文系统研究了模具型腔工艺规划中的刀具选择问题，提出了模具型腔粗加工、半精加工、精加工刀具选择的原则和方法，构造了相应的实现算法，并在UG/OPEN API 环境下进行了初步编程实现，开发了CATS原型系统。在刀具类型和规格确定的基础上，系统还可根据刀具手册推荐加工参数(切削速度、铣削深度、进给量等) ，对相应的加工时间进行评估。其最终目的是真正实现CAD/CAM的集成，继而通过后处理产生数控加工指令。目前CATS系统的界面还是独立于UG的CAM界面，CATS的决策结果还需要用户重新输入到CAM。

需要指出的是，要提高模具型腔的总体加工效率，需要从粗加工、半精加工、精

加工的整体上考虑，进行多目标组合优化，这将是我们下一步要进行的工作。