A级曲面范文（精选3篇）

A级曲面 第1篇

在现代汽车工业中,车身作为汽车四大总成之一和新车的象征,它的研制与生产技术水平是汽车工业水平的重要标志。一个总体设计优良的汽车品牌在市场竞争中的成败,除了其功能上的体现,还取决于其外形能否吸引顾客。如何利用现代设计方法,加快车身总体和外观设计, 缩短车身的设计周期,提高车身的制造精度和经济效益, 实现产品不断的推陈出新是汽车品牌在市场竞争中立于不败之地的重要因素之一。

文中探讨了自由曲线、曲面在NX中的描述方式,总结了一些有创意的曲线、曲面编辑特性,并以某汽车前保险杠盖板曲面实现为例,通过曲面几何特征划分,主、辅曲面构建以及曲面品质检测等设计过程,探讨了在NX中实现汽车A级曲面[1]建模和曲面品质检测的关键技术和方法。

1车身A级曲面设计流程

图1为车身A级曲面开发流程图,在车身总体布置方案完成后进入车身外形设计阶段。首先通过绘制草图, 进行概念草模的构建、渲染、评审、修改,设计草图主要突出设计创意,是设计师快速捕捉创意灵感的最好方法。接着进入精细效果图绘制阶段,即产品数据模型建构阶段, 通过添加局部细节细化模型,添加前大灯,前格栅等细节部分,确定具体样式,内部评审、修改数字模型,将最后确定的数字模型反馈到1∶ 5小比例油泥模型即数模验证模型上。经过反复评审,修改、检测、完善,直到确定符合要求的1∶ 1全尺寸油泥模型,并将最终确定的全尺寸油泥模型,通过逆向工程反馈成计算机数据模型。该数据模型是用于后期工程输入的数据,因此对数据模型曲面质量要求很高,即A级曲面标准。A级曲面完成后即可对该车进行数字模型发布,该车的外形设计阶段也到此结束。从图1可以清楚地看到如何由扫描油泥模型得到的点云数据快速实现精确曲面的构建,成为车身A级曲面设计最关键的一环。

2曲线、曲面编辑操作特性

贝塞尔 - Bézier曲线( 曲面) 和非均匀有理b样条NURBS曲线( 曲面) 是CAD软件中常见的两种自由曲线 ( 曲面) 表达方法[2],图2为3次Bézier曲线图,图3为4段3次NURBS曲线图。

贝塞尔 - Bézier曲线 ( 曲面) 是由单一的表达式控制的单段( 片) 曲线( 面) ,其形状由控制顶点和插值方式决定。Bézier曲线( 曲面) 内部光滑,其形状调节有很强的整体性,移动一个控制点对整个曲线( 曲面) 都有影响,可通过增加次数来实现形状调节的灵活性。但随着其次数的增加,调控性变 差。与Bézier曲线 ( 曲面) 曲面相同, NURBS曲线( 曲面) 形状同样是由控制顶点和插值方式决定。NURBS样条曲面表达式更复杂,但更灵活,通过调整插值方式改变曲面形状,复杂的形状可通过低阶的次数获得,并可准确表达二次曲面( 线)[3]。NURBS曲线( 曲面) 可以认为是多段( 片) Bézier曲线( 曲面) 首尾相接而成 ( 见图4) ,每一段( 片) 有自己的控制表达式[3]。图5为4段3次NURBS极点控制区域示意图。Bézier曲线( 曲面) 可看作是只有一段( 片) 的特殊NURB曲线( 曲面) 。通过增加NURBS曲线( 曲面) 次数或内部的段( 片) 数来改善样条局部属性,提升其形状控制灵活性。曲线( 曲面) 内部参数连续性[3]由插入的节点数量来决定( 见图6) 。

3车身A级曲面分类、建构和检测

NX工业设计模块提供了强大的高级曲面构建和分析工具,能快速实现汽车A级曲面建模以及曲面品质评估。汽车保险杠外板是汽车外形的重要装饰部件,是整车造型风格 的重要体 现,具有极高 的外表面 品质要求[1]。以某汽车前保险杠盖板A级曲面的建模实现为例,从曲面几何结构分类、曲面构建方法以及对构建曲面品质检测3个方面探讨汽车车身A级曲面在NX中实现的过程。

3.1车身A级曲面几何结构特征类型

汽车外表面是由多张大面、过渡面、圆角面等通过一定的几何拓扑关系组合的几何体。根据汽车外表面几何特征,将汽车外表面几何特征结构划分为图7所示的几种类型:

主曲面: 相对独立的,大面积,小曲率且无曲率反转片体,根据能否由扫掠特征构建,又分为均匀和非均匀主平面,能由单一的扫掠特征构建的为均匀主平面,反之为非均匀主平面。

艺术圆角: 两主曲面之间过渡桥接的面片,通常表现为窄、长特征,截面呈现艺术圆弧形。

倒角面: 通常出现在三个面相接的位置,呈现空间倒角结构。

桥接过渡曲面: 连接主曲面,不表现为艺术圆角表现的窄、长圆角特征的桥接面。

消失面: 外观上的局部特征从突出逐渐变化到和其他外观融合并消失的曲面。

翻边面: 平面部分或曲面部分的边缘,沿一定曲线翻起竖立的曲面。

汽车外表面几何特征划分将有助于确定正确的造型思路,明确每个曲面的类型和生成方法,即通过先主后辅的建模思想,选定合理的造型方法。先构建各主曲面,再细化辅助区域,如桥接过渡面、圆角面、消失面等,来达到方便建模的目的,同时有规律的构面比较容易获得较高的面片品质和配合精度,也有利于建模经验积累。

经过对油泥模型相应部位扫描点云数据处理( 去噪点、拼接、稀疏、光顺等)[4]得到如图8示点云数据,并通过对点云与油泥实物模型对照分析,将保险杠盖表面结构特征划分为: 主片体,艺术圆角,桥接过度曲面,消失面,翻边面等细化结构。

3.2车身曲面构建

曲面构建是车身A级曲面设计的关键环节,通过所划分的几何特征结构,选定合理的造型方法,先构建各主曲面再构建辅助区域: 桥接过渡面、圆角面、消失面等,来实现曲面建模。

主曲面构建方法一般遵循1) 由点→线→面; 2) 由点 →面的原则进行。

a) 基于曲线的构件方法

根据能否由扫掠特征构建汽车内、外饰面中相对独立、大面积、小曲率且无曲率反转的片体,基于曲线的构建方法可分为下面两类:

1) 过网格曲线

直接由扫描数据点拟合网格曲线,再通过这些网格曲线构建主片体。曲面品质主要有输入拟合曲线决定。 网格线要求: 与输入点数据贴合度高( 可由deviation gauge - 偏置误差检测保证) ,分布均匀,走势合理、一致、渐变 ( 由curve analysis - 曲率梳检测保证) ,光顺度高达G2以上连续( curve continuity - 曲线间连续性检测保证) 。通常是根据输入点云轮廓走势,截取特征轮廓线,轮廓线采样, 再由艺术样条( studio spline) 、圆弧、直线、二次、三次曲线等拟合采样点构建,且NX提供了强大的拟合曲线功能 ( fit curve) 来拟合曲线。接着应用过网格( through curve mesh) ,过曲线网格( through curve mesh) 等命令构建曲面。 图9为一过网格曲线构面示例。

2) 扫掠

通过对输入的数据点的几何拓扑结构进行分析,确定扫掠区域: 相对独立的、大面积、小曲率且无曲率反转片体,构建扫掠截面线和轨道线,生成扫掠主片体。该方法的难点在于抽取合理造型特征主轮廓和引导曲线,相较过网格线法有较少的拟合曲线过程。通过扫掠由输入点数据得到的高品质拟合曲线构建相应的曲面特征。图10为一扫掠构面示例。

b) 基于曲面的构件方法

该方法不需要提前构建任何输入曲线,是由输入数据点直接拟合特征曲面。一般是先构建4点面( four point surface) 或拟合面( fit surface) 覆盖输入的点云( 覆盖范围比点云片略大) ,然后应用NX高级曲面编辑功能X成型 ( xform) 拖拽调节控制极点逐步达到所需面体形状,并结合实时的面品质分析工具来保证所构建面的品质。该方法对设计人员的要求比较高。图11为一由拖拽控制点构建曲面示例。

各主曲面构造完成后,应用NX提供的曲线拟合( fit curve) 、桥接曲线( bridge curve) 、艺术圆角( styled blend) , 艺术倒角( syled corner) ,法兰构建( silhouette flange) 等命令完成辅助特征曲面的构建。注意在构建桥接过渡面片所需网格曲线时,为保证桥接片体与主体面间的光顺性, 一般要求连接主片体的过渡线连续性满足G2以上[5]。 在曲面建构过程中,如果零件对称,只需对一半进行建模后镜像,最后再填充两者之间的间隙,这样可以减少建模工作量。图12为某汽车前保险杠盖板曲面数据模型。

造型时所采用的方法、步骤、技巧往往因设计师的经验和技术特点而有所差异。在设计中一般混合使用上述方法。过网格曲线是一种传统方法; 而对表面几何特征明显,分布均一的大曲面可以通过扫掠快速获取; 对表面形状几何不宜描述清楚的面片,则通过拖拽控制点的基于曲面的构建方法的实现。同时对一些特征比较明显的规整部位,可由NX提供的造型功能直接实现,如连接大片体间过渡曲面通常可考虑由二次曲面组功能,艺术圆角功能,艺术倒角功能等。

3.3A级曲面品质检测方法

汽车A级曲面检测包括曲面特征检测和曲面品质检测,曲面特征检测指造型人员根据汽车造型要求评价所做的曲面是否符合造型意图( 即构建好的曲面与原始输入数据间的贴合程度) ,曲面品质检测指对组成它的每张曲面片的品质及面片之间连续性进行检测。NX提供了一组丰富的、功能强大的曲线、曲面检测工具,如偏置公差检测,高斯曲率检测,曲率梳检测,高亮检测,斑马条纹,曲线间连续性检查,曲面间连续性检查等。在设计过程中可以实时对造型结果进行评估,能有效及时修正设计缺陷, 保证设计意图和设计品质。为满足A级曲面要求,如对高光面检测方法要求高光走势一致,条文均匀,过渡光顺, 无扭曲; 对曲率梳检测方法则要求曲率梳均匀或渐变、走势有规律、无跳动、扭曲、突变、反曲等都是结果品质的判定标准[5,6]。图13为保险杠盖A级曲面斑马条纹检测分析结果。

4结语

大学英语3级考试A级答案 第2篇

Directions: This part is to test your ability to construct grammatically correct sentences.It consists of 2 sections.Section A

Directions: In this section, there are 10 incomplete sentences.You are required to complete each one by deciding on the most appropriate word or words from the 4 choices marked A), B), C)and D).Then you should mark the corresponding letter on the Answer Sheet with a single line through the center.16.We must find a way to cut prices _______ reducing our profits too much.A)without

B)despite

C)with

D)for

17.She didn’t know ________ to express her ideas in English clearly in public.A)which

B)why

C)what

D)how

18.________ the weather improves, we will suffer a huge loss in the tourist industry.A)As

B)Since

C)While

D)Unless

19.We are happy at the good news ________ Mr.Black has been awarded the Best Manager.A)that

B)which

C)what

D)whether

20.It is important that we ________ the task ahead of time.A)will fish

B)finished

C)finish

D)shall finish

21.Would you please pass me the book ________ cover is black?

A)which

B)whose

C)that

D)its

22.________ in the company for three years, Mark has become experienced in business negotiations.A)Having worked

B)Have been working

C)Have worked

D)Worked

23.Not until she arrived at the meeting room ________ she had forgotten to bring the document.A)she realized

B)did she realize

C)she did realize

D)does she realize

24.John had never been abroad before, ________ he found the business trip very exciting.A)because

B)though

C)so

D)while

25.________ some students are able to find employment after graduation, others will have to return to school and earn an advanced degree.A)Since

B)While

C)Because

D)If Section B

Directions: There are 10 incomplete statements here.You should fill in each blank with the proper form of the word given in brackets.Write the word or words in the corresponding space on the Answer Sheet.26.Employees are not allowed(make)________ personal phone calls in the office.27.The shop assistant priced the goods before(put)________ them on the shelf.28.The purpose of new technology is to make life(easy)________, not to make it more difficult.29.The proposal about the annual sales(discuss)________ at the next board meeting.30.Since we work in different sections of the company, we see each other only(occasional)________.31.Some domestic manufacturers are busy increasing production, losing the chance to develop more(advance)________ technology.32.I shall appreciate your effort in(correct)________ this error in my bank account as soon as possible.33.If your neighbors are too noisy, then you have a good reason to make your(complain)________.34.30 percent of the students who(interview)________ yesterday believe they should continue with their education until they have a university degree.35.Measures should be taken to avoid the negative effect(bring)________ about by unfair competition.Part III Reading Comprehension(40 minutes)

Directions: This part is to test your reading ability.There are 5 tasks for you to fulfill.You should read the reading materials carefully and do the tasks as you are instructed.Task 1

Directions: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 to 40.For each question or statement there are 4 choices marked A), B), C)and D).You should make the correct choice and mark the corresponding letter on the Answer Sheet with a single line through the center.Google, the Internet search-engine company, has announced it will give more than twenty-five million dollars in money and investments to help the poor.The company says the effort involves using the power of information and technology to help people improve their lives.Aleem Walji works for Google.org--the part of the company that gives money to good causes.He said the company’s first project will help identify where

infectious(传染性的)diseases are developing.In Southeast Asia and Africa, for example, Google.org will work with partners to strengthen early-warning systems and take action against growing health threats.Google.org’s second project will invest in ways to help small and medium-sized businesses grow.Walji says microfinance(小额信贷)is generally small, short-term loans that create few jobs.Instead, he says Google.org wants to develop ways to bring investors and business owners together to create jobs and improve economic growth.Google.org will also give money to help two climate-change programs announced earlier this year.One of these programs studies ways to make renewable(再生的)energy less costly than coal-based energy.The other is examining the efforts being made to increase the use of electric cars.The creators of Google have promised to give Google.org about one percent of company profits and one percent of its total stock value every year.Aleem Walji says this amount may increase in the future.36.The purpose of Google’s investments is to ________.A)help poor people

B)develop new technology

C)expand its own business

D)increase the power of information

37.According to Aleem Walji, the company’s first project is to ________.A)set up a new system to warn people of infectious diseases

B)find out where infectious diseases develop

C)identify the causes of infectious diseases

D)cure patients of infectious diseases

38.What kind of businesses will benefit from Google.org’s second project?

A)large enterprises

B)cross-national companies

C)foreign-funded corporations

D)small and medium-sized businesses

39.From the fourth paragraph, we learn that Google’s money is also invested to help ________.A)start more research programs

B)make more advanced electric cars

C)develop renewable and coal-based energy

D)conduct studies related to climate changes

40.From the last paragraph we learn that the investments by Google.org come from ________.A)Google’s profits and stock value

B)some international IT companies

C)the company’s own interests

D)local commercial banks

Task 2

Directions: This task is the same as Task 1.The 5 questions or unfinished statements are numbered 41 to 45.Your boss holds your future prospects in his hands.Some bosses are hard to get along with.Some have excellent qualifications but no idea when it comes to dealing with people.Of course, not all bosses are like that.The relationship you have with your boss can be a major factor in determining your rise up the career ladder.Your boss is not only your leader, he is also the person best equipped to help you do the job you are paid to do.He can inform you of company direction that may affect your professional development.Your boss also needs you to perform at your best in order to accomplish his objectives.He needs your feedback in order to provide realistic and useful reports to upper management.But how does this help you establish a meaningful working relationship with your boss?

The key is communication.Learn and understand his goals and priorities(优先的事).Observe and understand your boss’s work style.If he has not been clear with his expectations, ask!Likewise, ask for feedback and accept criticism gracefully.And if he understands that you do not view your job as just something to fill the hours between 9 and 5, he may be more likely to help you.In short, getting along with your boss requires getting to know his likes and dislikes and learning to work with his personality and management style.41.The main idea of the first paragraph is that ________.A)bosses are hard to deal with

B)bosses have good character

C)bosses determine your career future

D)bosses must have similar personality

42.In the second paragraph, “rise up the career ladder”(Line 2)means ________.A)going to work abroad

B)changing jobs frequently

C)being promoted in position

D)pursuing an advanced degree

43.In order to achieve his objectives, your boss expects that you will ________.A)do your best in your work

B)show your management skills

C)get along with your colleagues

D)write reports to upper management

44.The most important factor for establishing a good working relationship with the boss is ________.A)high expectations

B)quick feedback

C)frequent criticism

D)effective communication

45.The best title for the passage might be ________.A)How to Take Care Of Your Boss.B)How to Get Along with Your Boss

C)How to Accept Your Boss’s Criticism

D)How to Accomplish Your Boss’s Objective Task 3

Directions: The following is an announcement.After reading it, you are required to complete the outline below it(No.46 to No.50).You should write your answers briefly(in no more than three words)on the Answer Sheet correspondingly.We welcome you aboard the Eastern Flight and will do our best to make your trip comfortable and enjoyable.For your safety and convenience

To begin the trip, we would like to draw your attention to some safety-related details.These are also explained on the instruction card in the seat pocket in front of you.Seat belts must remain fastened while the “Fasten seatbelts” sign is on.It is advisable to keep them fastened at all times while seated.All flights are non-smoking.The use of mobile telephones is now allowed when the airplane is on the ground.During the flight the use of CD and DVD players is not allowed.For your entertainment

To help you enjoy your trip, we provide a range of newspapers.On our MD-11 and Boeing aircraft, we provide music and video programs.On Airbus A 321/320/319, short videos are shown.Meals and drinks

During most flights we serve you a tasty meal and drinks.Beer, wine and other drinks are served free of charge.Coffee, tea and juice are served free of charge on all domestic(国内的)flights.On domestic flights leaving before nine and on all flights to Northern China, a snack is served.Eastern Flight Service

Safety and convenience

1)Seat belts: remain-46-while the “Fasten seatbelts” sign is on

2)Smoking: not allowed on board

3)Mobile phones: used only when the airplane is-47-

4)CD and DVD: not allowed to play-48-

Entertainment provided

1)newspapers

2)music and-49-on MD-11 and Boeing aircraft

Meals and drinks on board

1)meals served on most flights

2)coffee, tea and juice served free of charge

3)a snack served on all flights to-50-

Task 4

Directions: The following is a list of terms related to Security.After reading it, you are required to find the items equivalent to(与„等同)those given in Chinese in the table below.Then you should put the corresponding letters in the brackets on the Answer Sheet, numbered 51 through 55.A-----------------air traffic control system

B-----------------armed police

C-----------------crime prevention

D-----------------entry requirement

E-----------------international criminal police organization

F-----------------level of security

G-----------------picket line

H-----------------police station

I-----------------patrolling vehicle

J-----------------safety precaution measure

K-----------------safety control device

L-----------------security command center

M-----------------security service

N-----------------security control center

O-----------------security personnel

P-----------------valid documents

Q-----------------security monitoring and control

Examples:(M)保安服务(G)警戒线

51.()空中交通管制系统()安全预防措施

52.()巡逻车()武装警察

53.()国际刑警组织()有效证件

54.()入境要求()安保人员

55.()安全保障级别()安全监控

Task 5

Directions: The following is a business letter.After reading it, you should give brief answers to the 5 questions(No.56 to No.60)that follow.The answers(in no more than 3 words)should be written after the corresponding numbers on the Answer Sheet.Dear Mr.Smith，I am pleased to offer you the position of after-sales manager at our company starting on 16 June, 2009.I propose that the terms of employment will be those in the attached draft individual employment agreement.Please note that you are entitled to discuss this offer and to seek advice on the attached proposed agreement with your family, a union, a lawyer, or someone else you trust.If you want some information on your employment rights, you can also contact the Employment Service Office or visit our website.Also, if you disagree with, or do not understand or wish to clarify anything in this offer, please ring me to discuss any issue you wish to raise.If you are happy with the proposed terms and wish to accept this offer of employment, please sign the duplicate copy of this letter and return it to me by 1 June, 2009.In the event I have not heard from you by that date, this offer will be automatically withdrawn on that date.I look forward to working with you.Yours sincerely，John Brown

56.What job position is offered to Mr.Smith in the letter?

___________________________________________________________.57.From whom may Mr.Smith seek advice about the proposed agreement?

His family, a union, _____________________, or someone else he trusts.58.How can Mr.Smith get information about employment rights?

By contacting the ___________________________ or visiting its website.59.When should Mr.Smith return the signed duplicate copy of this letter?

By _______________________________________________________.60.What will happen if the duplicate copy of the letter is not returned by the deadline?

This offer will be ___________________________________ on that date.Part IV Translation--English into Chinese(25 minutes)

Directions: This part, numbered 61 through 65, is to test your ability to translate English into Chinese.After each of the sentences numbered 61 to 64, you will read four choices of suggested translation.You should choose the best translation and mark the corresponding letter on your Answer Sheet.And for the paragraph numbered 65, write your translation in the corresponding space on the Translation/ Composition Sheet.61.If either party wants to renew the contract, it should submit a written notice to the other party three months prior to the expiration of the contract.A)如果任何一方希望撤销合约，必须将撤销的理由在三个月内通知对方。

B)如果合同一方希望重签合同，必须在合同到期三个月内写信通知对方。

C)如果任何一方希望更改合同，必须提前三个月向对方书面提交其理由。

D)如果合同一方希望续签合同，必须在合同期满前三个月书面通知对方。

62.There is no sign that the world economic crisis will lessen in the next few months, although a certain degree of recovery is in sight.A)尽管没有人认为未来几个月内世界经济危机会消失，但是在一定程度上的复苏是肯定的。

B)尽管世界经济复苏的迹象是肯定的，但是未来几个月内经济危机缓和的现象还不很明显。

C)尽管已经显现出一定程度的经济复苏，但没有迹象表明世界经济危机在未来几个月会减缓。

D)尽管没有人承认未来几个月内世界经济危机会触底，但我们肯定会看到世界经济的复苏。

63.Most of the issues concerning personnel managementhave been solved satisfactorily;only a few of secondary importance remain to be discussed.A)多数有关人员管理的问题顺利地解决了, 仅剩下几个问题还需要进行第二次讨论。

B)大多数有关人事管理问题已经得到圆满解决，只剩下几个次要的问题还有待于讨论。

C)很多有关人员配备问题基本上都得到了答复，只有第二个重要问题还未经过讨论。

D)第二个重要问题是有关人员调动的问题，这次已经得到妥善解决，不必再次讨论。

64.Only in this way can Chinese enterprises improve their competitiveness and avoid being defeated by their foreign rivals after China’s entry into the WTO.A)只有这个方法才能帮助中国企业去参加竞争，避免在加入世贸组织后被其外国对手所击败。

B)只有这样中国企业才能提高竞争力，并且在中国加入世贸组织后不会败给它们的外国对手。

C)如果中国企业要想在世贸组织中参加竞争，必须通过这种办法才能击败它们的外国对手。

D)中国企业只有通过这种途径来击败外国的对手，才能表明它们在世贸组织中具备竞争力。

65.Thank you, Mr.Black.It’s a great honor to be appointed as Overseas Sales Manager.To be honest, this promotion came as quite a surprise to me.I’d like to think it’s mainly the contribution of the whole team.I’d like to thank all my colleagues in the company for their support and hard work.Due to their efforts, we’ve started some overseas projects successfully.Looking to the future, I’d still like to maintain contact with everyone, even though I’ll be working at the management level.Part V Writing(25 minutes)

Directions: This part is to test your ability to do practical writing.You are required to write a business letter according to the following information given in Chinese.Remember to do the task on the Translation/Composition Sheet.说明：根据下面中文信息写一封询问信。

发信人：Mark Zhang

收信人：Mr.Smith

发信日期：2009年12月22日

内容：

1.Mark在最近的广交会上认识了Smith先生；

2.Mark对Smith先生所在公司展出的新款手机很感兴趣；

3.询问产品的详细信息，包括产品的规格、颜色、价格和功能等；

4.说明该款手机市场销售前景看好；

5.希望和对方建立长远的上午关系。

Words for references:

广交会 Guangzhou Trade Fair

3+A可变轮廓铣曲面加工 第3篇

关键词：可变轮廓铣,曲面加工,多轴加工

0 引言

3+A轴数控机床具有3个直线坐标轴和1个旋转坐标A轴 (数控分度头) , 且这4个坐标轴可以在NC或CNC系统控制下协调运动。通常3+A轴数控机床是在3轴数控系统支持情况下, 通过设备改造或扩展的方式, 配备部件A轴或B轴, 实现多轴联动的功能。相对资金投入量小, 机床功能拓展显著:能在一次装夹定位条件下完成多面加工, 提高零件加工精度和效率, A轴或B轴的增加, 使零件的姿态角随A轴或B轴转动而调整, 在一定程度避免了刀具干涉、欠切和过切现象的发生, 与普通3轴机床相比, 可以获得更高的切削速度, 更优质的表面质量, 降低刀具采购成本, 使进给速度、切削速度得到显著提升。3+A轴数控机床可以广泛应用于各种曲面, 如螺旋类零件和平面内斜孔的异形件加工, 特别适合于零部件圆柱面、球面等结构部位半精、精加工, 能提升设备利用率, 降低加工成本。

1可变轮廓铣投影矢量与刀轴组合方式

内、外圆柱面在3+A轴下的数控编程中较有代表性, 可以达到一通全通的效果。UG软件可变轮廓铣操作, 能实现圆柱面x、y、z、A联动且刀路轨迹流畅、加工质量高的效果。驱动方法选曲面, 投影矢量与刀轴组合方式如表1所示。

内圆柱面组合方式仅需将刀轴更改为“朝向直线”, 其中刀轴控制中“远离直线”、“朝向直线”是指刀轴远离或朝向某条直线产生刀具轨迹 (图1) 。当零件表面较复杂时, 无法选取加工驱动表面, 可手动做辅助面, 驱动方法中的驱动曲面可以不是零件表面。

2 可变轮廓铣操作设置

打开可变轮廓铣界面, “指定部件”一般情况下建议不选取, 或是在选取部件后产生异常刀轨时, 取消“指定部件”选择项。按图2依次设置“驱动方法”、“投影矢量”、“刀轴”控制。“驱动方法”选为“曲面”时, 要求连续曲面或辅助曲面具有以下关系:曲面拐角与拐角匹配, 并且按特定顺序选择, 相邻曲面共享一条公共边, U、V栅格线对等。连续曲面是否可选取的判别方法有:UG主菜单下, “编辑”→“对象显示”, 在对话框“线框显示”分别设置“U”“V”栏中输入“10”, 部件模型以“静态线框”显示, 侧壁两相连面分别出现均等U、V栅格线, 若相邻边等分栅格线无对等性 (图3) , 则连续曲面不能作为驱动几何体。也可直接在可变轮廓铣操作“驱动方法”—“曲面”对话框中, 选取连续曲面, 当弹出“不能构建栅格线”提示框说明曲面U、V不对等, 不能作为驱动几何体。

2.1 解决曲面U、V不对等性方案

1) 合并曲面。选取曲面选项中的缝合命令, 点击目标栏中选取片体按钮, 选择主曲面, 点击刀具栏中的选择片体按钮, 选取需要和主曲面合并的曲面完成曲面缝合。

2) 重新做面。根据连续曲面的边线可利用扫掠等构面方式重新获取单一曲面。

2.2 曲面驱动区域方法中切削区域控制

曲面驱动区域方法中, 切削区域控制主要分为曲面百分比和对角点控制。曲面百分比中第一起点、最后一个起点、起始步长系统默认为零, 输入负的百分比可延伸切削区域至曲面边缘外, 与边沿相切线性延伸, 反之减小。当指定多个驱动曲面, 切削区域控制中的最后一个起点、终点不可用。对角点控制, 是通过曲面区域的对角点缩放切削区域, 其相对使用率较低。切削方向对话框激活状态下, 会在曲面出现几组成对箭头, 每组交于一点背向指出。选择其中一个箭头后, UG系统会在箭头柄部生成一个小圆圈, 代表该方向为切削方向, 剩余方向为步距方向。材料反侧调整时, 箭头方向为刀轨生产方向, 即需要剔除材料方向, 相当于箭头所指材料侧为毛坯。偏置和驱动设置根据具体情况设置。

3 案例分析

为进一步阐明可变轮廓铣曲面加工的数控编程方法, 选用飞机起落架某一定载释放接头为案例进行讲解。零件近似哑铃结构, 材料牌号为A100, 槽宽为A±0.1mm, 中部转接R11, 侧壁根部R2, C型槽为热处理后需精加工表面, 粗糙度Ra1.6μm。编程具体步骤如下。

如图4所示, 在UG“加工”模块下, 选择可变轮廓铣, 设置按以下方法依次进行:

1) “驱动方法”→“曲面”, 选取侧壁曲面;“切削区域”仅调整最后一起点2%和最后一终点96%, 即最后一条刀轨起刀点与抬刀点相对缩小, 避免切伤C型槽两端平面区域;“刀具位置”默认“相切”;“切削方向”选择沿圆弧方向;“材料方向”选箭头朝基体外的方向;

2) “切削模式”→选择“往复”, 其余参数选取见表2, 在机床主轴转速S=3000, F=300, 刀具为D20R2整体合金刀时, 精加工后零件表面粗糙度达Ra1.6μm;

3) 刀轴指向:远离直线, 直接选择圆柱面的轴线。

4) 投影矢量:默认“刀轴”。部件, 检查体不选、加工区域选侧壁曲面或不选。

C型圆弧面及侧壁数控编程操作方法基本相同, 仅是曲面选取略有差异。按案例分析步骤依次完成可变轮廓铣曲面加工编程, 生产的刀轨及在Vericut中模拟仿真如图5。

4 结论

可变轮廓铣曲面加工, 采用“远离直线”和“朝向直线”刀轴控制方法, 可以充分发挥3+A轴功能, 且生产的刀路整洁, 加工的零件表面质量高, 是端面凸轮、扭簧类零件加工的首选方案[4,5], 同时, 可变轮廓铣曲面加工作为一种有效的半精、精加工策略, 也是解决倒扣类问题的一种有效方法。文中详细介绍了可变轮廓铣曲面加工的参数设置、案例分析等。经多年编程经验知, 可变轮廓铣曲面加工, 是4轴机床编程的不二之选, 对5轴数控编程有其重要的指导意义。

参考文献

[1]詹才浩.CATIA V5数控加工教程[M].北京:清华大学出版社, 2009.

[2]刘江涛, 陈仁越, 谢龙汉.UG NX6中文版数控加工视屏精讲[M].北京:人民邮电出版社, 2009.

[3]陈海舟.数控铣削加工宏程序及应用实例[M].北京:机械工业出版社, 2007.

[4]王伟, 田辉, 郭辉, 等.超高强度低合金钢扭簧机械加工[J].机械工程师, 2015 (10) :114-115.