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1、Chapter 3 Basic concepts and knowledge in machining process,3.1 The task and content of parts machining3.2 Basic concepts 3.3 The location principle of workpiece3.4 Choice of location datum and calculation of location error3.5 Workpiece clamping,3.6 Relationship between clamping and machining accura
2、cy3.7 The motion analysis of machine tool3.8 The principle and procedures of process planning3.9 metal removal, process dimensional chain and economical machining accuracy,Questions preview,Questions related with “process ”Have you ever heard about the word “process(工艺）” before? Can you give some ex
3、amples?What words will occur in your mind when people talk about “process”? Give the key words.Do you think a process is unique or variational? Why?According to your understanding, what will be involved in a machining process?,Card of process routine,Operation card,forming of the roughcast or partca
4、sting、forging、punching,welding、pressing、agglomeration（烧结）、infusing(注塑)、moulding Machiningcutting、grinding, special machining(non-conventional machining) Materials properties adaptation and treatmentheat treatment,electroplate、coating, filming Machine assembleconnect the parts according to the defini
5、te relationship and specification, including part fixing, connection, adjustment, balance, inspection and test,Question: Can you tell the functions and specifications（技术条件） for these parts?,A screw to be machined,3.1 The task and content of parts machining,Manufacturing is to utilize and manage mate
6、rials, people, equipment, and money to produce products. To achieve a successful and economical manufacturing, the planning must be made from the beginning of the design stage and go through the selection of materials, processes, equipment, and the scheduling of production.,The essential of manufact
7、uring is to turn raw material (or semi-product) into finished product which satisfies the requirement.,The task of machining is to turn the raw material (roughcast) into the finished parts which satisfied the requirement of product.,Machining involves the method (means) and process.,3.2.1 manufactur
8、ing process (生产过程） The process of a product involves： Product design and prepare、transport of the raw and processed materials、roughcast forming、machining 、heat treatment 、assembly、 deburring、test 、painting and packing. These related processes constitute the so-called “production process”. It is usua
9、lly completed by the coordinated work of different factories or workshops.,3.2 The basic concepts in machining,3.2.2 Process of a part （工艺过程）,Process of a part: The process by which the shape, dimensions and performance of raw material or rough casting are changed and turned into the desired parts d
10、irectly by machining is called the process of a part, or part processing route. When parts are assembled into a product, it is called the assembly process.,4.1.2.1 What constitutes a part process?,Part process consists of one or several operations in sequence. A rough casting can be turned into a fi
11、nished or semi-finished product by the operations. (1) Operations or jobs（工序） The job finished by one operator (or a group of operators) who works in a fixed work position(one machine tool or clipping table) to achieve the continuous manufacturing for one or several parts is called the operation. An
12、 operation is the basic element of a part process, and as well as the element for the production schedule cost assessment.,If the number of the parts in a batch is small, the manufacturing process can be completed through 5 operations, which are shown in table 4-1.,Fig 4-1 is the engineering drawing
13、 of a shaft movie,Table 4-1 the process of shaft manufacturing,To produce the same part as Fig 4-1, if the number of parts is large, the operation 1 in table 4-1 can be divided into the following 2 operations: a） facing and centering one end in an engine lathe by one operator b） transferring the par
14、t to another engine lathe for facing and centering another end by another operator,（2）Operation Step or sub-jobs（工步）,An operation step is the basic element of an operation. An operation step is defined as an operation that is completed under the condition when the surface to be machined, the cutting
15、 parameters (including cutting speed, feed and back engagement) and cutting tool remain the same. If any of the condition is changed, it will become another operation step. When several surfaces of a part are machined simultaneously, it is called a composite operation step. The purpose of classifyin
16、g an operation into steps is to make a complex operation more convenient and easier to analyze and describe, to make the manufacturing more efficient to organize, and to make the operation time easier to calculate.Question: Can you make the operation steps for the shaft process ?,（3）cutting pass （走刀
17、）,When the amount of metal removal is large, several cutting passes may need. A cutting pass is a kind of operation step that is completed by the same cutting tool to cut the same surface under the same cutting parameters.,（4） Setup （安装）,Before it can be machined, the part must have a proper positio
18、n relative to the cutting tool, and be clamped by a fixture in the machine tool. This procedure is called the clamping. The job finished by one clamping is called the setup. Each operation may have either single setup or several setups In the same operation, the number of setups should be arranged t
19、o be as few as possible. It can not only raise the production efficiency, but also reduce the errors caused by setups.,（5）operation position（工位）,In order to reduce the number of setups, a rotational worktable or fixture is usually used to make a sequential machining in different positions possible b
20、y a single setup. The job performed in one position is called one operation position.,Demonstration of operation, operation step，position and cutting pass,3.2.3 Production expectation and production type (生产纲领与生产类型）,(1) Production expectation,The expected number of parts can be calculated according
21、to the following formula, Np=Nn(1+) (1+)Where, Npthe expected number of parts in one year； N the expected number of products in one year； n the number of parts in one product ； percent of spare parts； percent of scrap parts；,3.2.3 Production expectation and production type (生产纲领与生产类型）,（2）production
22、type,Usually, the production is classified into 3 types, single, batch and large quantity production according to the workpiece size, the production expectation, the production batch and the characteristic of production continuity.,Process planning are highly affected by the production type. When th
23、e production type changes, the production organization and management, the layout of the workshops and machine tools, the forming method of the raw material, the machining equipments(including the machine tools,cutting tools, fixtures and inspection tools) and the technical skill of the operators wi
24、ll also change accordingly. Therefore, before planning a process, a concise explanation of the effect of production batch size will be given.,3.2.3 Production expectation and production type (生产纲领与生产类型）,（1）Single production,Production type refers to the specialized degree of the production classific
25、ation within an enterprise ( for example in a workshop, a workshop section, a group or a work place). Generally, it can be classified into 3 types, which are,The number of workpieces with different structure or different dimensions is only one produced at a time, or only in small quantity, rarely re
26、peated. For example, the manufacturing of heavy-duty machines, specialized machines and new products are all done in small quantity.,3.2.3 Production expectation and production type (生产纲领与生产类型）,（2） Batch production,Within a year, the same products are manufactured repeatedly in batches. For example,
27、 the manufacturing of machine tools is characterized by batch production. The number of the same products in one batch is called the batch size. According to the batch size , it can be further classified into : small batch -the characteristic is similar to that of single production； large batch - th
28、e characteristic is similar to large quantity production ； medium batch - the characteristic is between the single and large quantity production.,（3）Large quantity production,The quantity of each part being produced is large, and many work places often carry out the same operation of the same part. For example, the manufacturing of vehicles, trucks and bearings are all characterized by large quantity production,Table 3-2 the main characteristics of different production types,