影响加工精度的基本因素--中英文翻译

3.0 闻远设计 2023-08-11 35 4 32.5KB 5 页 20光币

侵权投诉

Fundamentals of Manufacturing Accuracy

Manufacturing can be defined as the transformation of raw materials

into useful products through the use of the easiest and least-expensive

methods. It is not enough, therefore, to process some raw materials and

obtain the desired product.

It is, in fact, of major importance to achieve that goal through

employing the easiest, fastest, and most efficient methods. If less efficient

techniques are used, the production cost of the manufactured part will be

high, and the part will not be as competitive as similar parts produced by

other manufacturers. Also, the production time should be as short as

possible to enable capturing a larger market share.

Modern industries can be classified in different ways. There include

classification by process, classification by product, and classification

based on the production volume and the diversity of products. The

classification by process is exemplified by casting industries, stamping

industries, and the like. When classifying by product, industries may

belong to the automotive, aerospace, and electronics groups. The third

method, i.e., classification based on production volume, identifies three

main distinct types of production, mass, job shop, and moderate. Let us

briefly discuss the features and characteristics of each type.

Mass production is characterized by the high production volume of

the same (or very similar) parts for a prolonged period of time. An annual

production volume of less than 50 000 pieces cannot certainly be

considered as mass production. As you may expect, the production

volume is based upon an established or anticipated sales volume and is

not directly affected by the daily or monthly orders. The typical example

of mass-produced goods is automobiles.

Job-shop production is based on sales orders for a variety of small

lots. Each lot may consist of 20 up to 200 or more similar parts,

depending upon the customers` needs. It is obvious that this type of

production is most suitable for subcontractors who produce varying

components to supply various industries. The machines employed must

be flexible to handle variations in the configuration of the ordered

components ,which are usually frequent. Also, the employed personnel

must be highly skilled in order to handle a variety of tasks, which differ

for the different parts that are manufactured.

Moderate production is an intermediate phase between the job-shop

and the mass-production types. The production volume ranges between

10 000 to 20 000 parts, and the machines employed are flexible and

multipurpose. This type of production is gaining popularity in industry

because of an increasing market demand for customized products.

A very important fact of the manufacturing science is that it is almost

impossible to obtain the desired nominal dimension when processing a

workpiece. This is actually caused by the inevitable, though very slight,

inaccuracies inherent in the machine tool as well as by various

complicated factors like the elastic deformation and recovery of the

workpiece and/or the fixture, temperature effects during processing, and

sometimes the skill of the operator. Since it is very difficult to analyze

and completely eliminate the effects of these factors, it is more feasible to

establish a permissible degree of inaccuracy or a permissible deviation

from the nominal dimension that would not affect the proper functioning

of the manufactured part in a detrimental way. According to the ISO

(International Standardization Organization) system, the nominal

dimension is referred to as the basic size of the part. The deviations from

the basic size to each side (i.e. , positive or negative ) determine the high

and the low limits, respectively, and the difference between those two

limits of size is called the tolerance. The tolerance is an absolute value

without a sign. As you may expect, the magnitude of the tolerance is

dependent upon the basic size and is designated by an alphanumeric

symbol called the grade. There are eighteen standard grades of tolerance

in the ISO system, and the tolerances can be obtained from the formulas

or the tables published by the ISO. It is obvious that smaller tolerances

require the use of high-precision machine tools in manufacturing the parts

and therefore increase production costs.

Before two components are assembled together, the relationship

between the dimensions of the mating surfaces must be specified. In other

words, the location of the zero line to which deviations are referred must

be established for each of the two mating surfaces. This actually

determines the degree of tightness or freedom for relative motion between

the mating surfaces. There are basically three types of fits, namely,

clearance fit, transition fit, and interference fit. In all cases of clearance

fit, the upper limit of the shaft is always smaller than the lower limit of

the mating hole. This is not the case in interference fit, where the lower

limit of the shaft is always larger than the upper limit of the hole. The

transition fit, as the name suggests, is an intermediate fit. According to

ISO, the internal enveloped part is always referred to as the shaft,

whereas the surrounding surface is referred to as the hole. Accordingly,

from the fits point of view, a key is referred to as the shaft and the

keyway as the hole.

There are two ways for specifying and expressing the various types of

fits, the shaft basis and the hole basis systems. The location of the

tolerance zone with respect to the zero line is indicated by a letter, which

is always capital for holes and lowercase for shafts, whereas the tolerance

grade is indicated by a number, as previously explained. Therefore, a fit

designation can be H7/h6, F6/g5, or any other similar form.

When the service life of an electric bulb is over, all you do is buy

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

20 光币 4人已下载

立即下载

摘要：

FundamentalsofManufacturingAccuracyManufacturingcanbedefinedasthetransformationofrawmaterialsintousefulproductsthroughtheuseoftheeasiestandleast-expensivemethods.Itisnotenough,therefore,toprocesssomerawmaterialsandobtainthedesiredproduct.Itis,infact,ofmajorimportancetoachievethatgoalthroughemploying...

展开>> 收起<<

影响加工精度的基本因素--中英文翻译.doc

共5页,预览2页

还剩页未读，继续阅读

影响加工精度的基本因素--中英文翻译

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

推荐作者

热门标签

举报选择: