Process foundation of mechanical processing

一、生产过程和工艺过程

1. Production process and process

生产过程是指从原材料（或半成品）制成产品的全部过程。对机器生产而言包括原材料的运输和保存，生产的准备，毛坯的制造，零件的加工和热处理，产品的装配、及调试，油漆和包装等内容。生产过程的内容十分广泛，现代企业用系统工程学的原理和方法组织生产和指导生产，将生产过程看成是一个具有输入和输出的生产系统。能使企业的管理科学化，使企业更具应变力和竞争力。

The production process refers to the whole process of making products from raw materials (or semi-finished products). For machine production, it includes transportation and preservation of raw materials, preparation of production, manufacture of blanks, processing and heat treatment of parts, assembly and commissioning of products, paint and packaging, etc. The content of the production process is very wide. Modern enterprises organize production and guide production with the principles and methods of system engineering. The production process is regarded as a production system with input and output. It can make the management of enterprises scientific and make enterprises more responsive and competitive.

在生产过程中，直接改变原材料（或毛坯）形状、尺寸和性能，使之变为成品的过程，称为工艺过程。它是生产过程的主要部分。例如毛坯的铸造、锻造和焊接；改变材料性能的热处理；零件的机械加工等，都属于工艺过程。工艺过程又是由一个或若干个顺序排列的工序组成的。

In the production process, the process of directly changing the shape, size and properties of the raw material (or blank) and turning it into finished product is called the technological process. It is the main part of the production process. For example, casting, forging and welding of blanks, heat treatment to change material properties, machining parts and so on, all belong to the technological process. The process is made up of one or more sequential processes.

工序是工艺过程的基本组成单位。所谓工序是指在一个工作地点，对一个或一组工件所连续完成的那部分工艺过程。构成一个工序的主要特点是不改变加工对象、设备和操作者，而且工序的内容是连续完成的。例如图32-1中[cc1] 的零件，其工艺过程可以分为以下两个工序：

The process is the basic unit of the process. So called process is a part of the process that is completed continuously at one working place for one or a set of workpieces. The main characteristic of a process is not to change the object, equipment and operator, but also to complete the process. For example, the parts of [cc1] in Fig. 32-1 can be divided into the following two processes:

工序1：在车床上车外圆、车端面、镗孔和内孔倒角；

Process 1: turning the outer circle, end face, boring hole and inner hole chamfer on lathe.

工序2：在钻床上钻6个小孔。

Process 2: drill 6 small holes on the drill machine.

在同一道工序中，工件可能要经过几次安装。工件在一次装夹中所完成的那部分工序，称为安装。在工序1中，有两次安装。第一次安装：用三爪卡盘夹住 外圆，车端面C，镗内孔 ，内孔倒角，车 外圆。第二次安装：调头用三爪盘夹住 外圆，车端面A和B，内孔倒角。

In the same process, the workpiece may have to be installed several times. The part of the workpiece completed in one clamping is called installation. In process 1, there are two installment. First installation: use three jaw chuck to clamp the outer circle, end face C, boring hole, inner hole chamfer, vehicle circle. The second installment: turn around and clamp the outer circle with three claw plates, A and B of the car end, chamfer of inner hole.

二、生产类型

Two, production type

生产类型通常分为三类。

The type of production is usually divided into three categories.

1．单件生产  单个地生产某个零件，很少重复地生产。

1. single piece production produces a single part and seldom produces repeatedly.

2．成批生产  成批地制造相同的零件的生产。

2. batch production to produce the same parts in batches.

3．大量生产  当产品的制造数量很大，大多数工作地点经常是重复进行一种零件的某一工序的生产。

3. mass production. When a large number of products are manufactured, most workplaces often repeat the production of a certain part of a part.

拟定零件的工艺过程时，由于零件的生产类型不同，所采用的加方法、机床设备、工夹量具、毛坯及对工人的技术要求等，都有很大的不同。

When the process of parts is drawn up, the method of adding, machine tool, tool, blank and technical requirements for workers are very different because of the different production types.

三、加工余量

Three, processing allowance

为了加工出合格的零件，必须从毛坯上切去的那层金属的厚度，称为加工余量。加工余量又可分为工序余量和总余量。某工序中需要切除的那层金属厚度，称为该工序的加工余量。从毛坯到成品总共需要切除的余量，称为总余量，等于相应表面各工序余量之和。

In order to process qualified parts, the thickness of the metal that must be cut from the blank is called machining allowance. Machining allowance can also be divided into working allowance and total allowance. The thickness of the metal that needs to be removed in a process is called the machining allowance. The total allowance from blank to finished product is the total allowance, which is equal to the sum of the remaining parts of the corresponding surface.

在工件上留加工余量的目的是为了切除上一道工序所留下来的加工误差和表面缺陷，如铸件表面冷硬层、气孔、夹砂层，锻件表面的氧化皮、脱碳层、表面裂纹，切削加工后的内应力层和表面粗糙度等。从而提高工件的精度和表面粗糙度。

The purpose of leaving the machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as the cold hard layer of the casting surface, the hole, the sand layer, the oxide skin, the decarburization layer, the surface crack on the surface of the forging, the inner stress layer after the cutting and the roughness of the surface and so on. Thus the precision of the workpiece and the surface roughness are improved.

加工余量的大小对加工质量和生产效率均有较大影响。加工余量过大，不仅增加了机械加工的劳动量，降低了生产率，而且增加了材料、工具和电力消耗，提高了加工成本。若加工余量过小，则既不能消除上道工序的各种缺陷和误差，又不能补偿本工序加工时的装夹误差，造成废品。其选取原则是在保证质量的前提下，使余量尽可能小。一般说来，越是精加工，工序余量越小。

The machining allowance has a great influence on the machining quality and production efficiency. The excessive processing allowance not only increases the amount of labor in machining, reduces the productivity, but also increases the consumption of materials, tools and electricity, and improves the processing cost. If the machining allowance is too small, it can not eliminate all kinds of defects and errors in the preceding process, nor can it compensate for the clamping error during the process, resulting in waste products. The principle of selection is to make the allowance as small as possible under the premise of guaranteeing quality. Generally speaking, the more machining is, the smaller the working allowance.

四、基准

Four. Datum

机械零件是由若干个表面组成的，研究零件表面的相对关系，必须确定一个基准，基准是零件上用来确定其它点、线、面的位置所依据的点、线、面。根据基准的不同功能，基准可分为设计基准和工艺基准两类。

A mechanical part is made up of several surfaces. To study the relative relation of the surface of a part, a datum must be determined. The datum is the point, line and surface used to determine the position of other points, lines and surfaces. According to the different functions of datum, the benchmark can be divided into two categories: design basis and process reference.

1．设计基准

1. design benchmarks

在零件图上用以确定其它点、线、面位置的基准，称为设计基准。如图32-2所[cc2] 示的轴套零件，各外圆和内孔的设计基准是零件的轴心线，端面A是端面B、C的设计基准，内孔的轴线是外圆径向跳动的基准。

The datum used to determine the position of other points, lines and planes on the part drawing is called the design datum. For the shaft sleeve parts shown in figure 32-2 [cc2], the design datum of the outer and inner holes are the axis of the parts, and the end A is the design datum of the end B and C. The axis of the inner hole is the base of the radial runout of the outer circle.

2．工艺基准

2. process datum

零件在加工和装配过程中所使用的基准，称为工艺基准。工艺基准按用途不同又分为装配基准、测量基准及定位基准。

The datum used in parts processing and assembly is called process datum. Process benchmarks are divided into assembly datum, measuring datum and positioning datum according to their different uses.

（1）装配基准  装配时用以确定零件在部件或产品中的位置的基准，称为装配基准。

(1) the basis for assembling a reference assembly to determine the location of parts in parts or products is called assembly datum.

（2）测量基准  用以检验已加工表面的尺寸及位置的基准，称为测量基准。如图32-2中的零件，内孔轴线是检验外圆径向跳动的测量基准；表面A是检验长度L尺寸l和的测量基准。

(2) the datum used to measure the size and location of the machined surface is called the datum datum. As part of figure 32-2, the inner hole axis is the measuring datum for checking the radial runout of the outer circle, and the surface A is the measuring datum of the length L dimension L sum.

（3）定位基准  加工时工件定位所用的基准，称为定位基准。作为定位基准的表面（或线、点），在第一道工序中只能选择未加工的毛坯表面，这种定位表面称粗基准.在以后的各个工序中

(3) the datum used for locating the workpiece in the positioning datum processing is called the positioning datum. As the surface (or line, point) of the positioning datum, the surface of the unprocessed blank can only be selected in the first process. This positioning surface is called the coarse reference.