问题 问答题 简答题

试简述定位与夹紧之间的关系。

答案

参考答案:定位是指工件在机床或夹具里占据一正确位置,是为了保证加工表面与定位面之间的位置精度。选择基准与夹具一起来限制工件的自由度;夹紧是在工件定位后把工件固定在机床上或夹具里,给工件施加足够的压力,防止工件运动,破坏已确定了的定位,并承担切削力。定位与夹紧是工件安装不可缺少的两个部分。

阅读理解

阅读理解。

     Jack went to a barber's shop and had his hair cut, but when he came out, he was not happy

with the result(结果). When his friend Bob saw him, he laughed and said, "What has happened to

your hair, Jack?" 

     Jack said, "I tried a new barber's shop today, because I wasn't quite satisfied with my

old one, but this one seems even worse."

      Bob agreed (同意). "Yes, I think you're right, Jack. Now I'll tell you what to do when

you go into a barber's shop next time: look at all the barbers' hair, find out whose hair

looks worst, and then go straight to him."

      "Why shall I go to him?" Jack asked. "But that would be foolish!"

      "Oh, no, it wouldn't," answered Bob. "Who cut that man's hair? Just think it. He couldn't

cut it himself, could he? Another of the barbers cut it. So you know he can't be the worst

barber."

1. When Jack went out of the barber's shop, he was not happy because _____. [ ]

A. nobody had cut his hair

B. the barber hadn't cut his hair well

C. the barber had cut his hair carefully

D. he was not satisfied with his old barber

2. "I tried a new barber's shop today." means _____. [ ]

A. this barber's shop was a new one

B. this was the only barber's shop in this town

C. Jack often went to this barber's shop

D. it was Jack's first time to go to this barber's shop

3. After Jack had his hair cut, he thought _____. [ ]

A. the new barber's shop was the best one

B. the old barber's shop wasn't so good as the new one

C. the new barber's shop was worse than the old one

D. the old barber's shop was the worst one

4. Bob told Jack to find out which barber's hair looked the worst and then go straight to him. Why? [ ]

A. Because he was certainly the best barber.

B. Because he was free all the time.

C. Because he was the worst barber.

D. Because he wasn't the worst barber.

5. From the story we know that _____. [ ]

A. it's foolish to have one's hair cut at a barber's shop

B. barbers cut each other's hair

C. barbers never have their hair cut 

D. a barber always cuts his hair by himself

名词解释