Chapter Three Metal Cutting Machine

Understanding the use, classification and scope of the lathe; Instructional objectives Understanding the use, classification and scope of the lathe; Master the machine drive transmission and transmission schematic; Master the main drive and feed motion system of CA6140; Master the transmission system analysis and formulation of the rotational speed diagram; Master the meaning of structural formula.

3.1 Types and Parameters of Machine Tool Machine operation is a kind of process to change the size or performance of workpiece using processing machinery. Machine tool: is a form of cutting method of metal parts processing machine, is a machine that can manufacture machines, so called "machine tool" .

Lathe

Milling Machine

Grinding Machine

Drill Press

3.1.1 Classification of Machine Tools It can be divided into 11 types: Lathe, drill press, boring machine, grinding machine, gear machine, screw machine, milling machine, plane machine, broaching machines, saw machine and other machine Degree of versatility: versatile machine, specialized machine, special purpose machine Degree of accuracy: engine lathe, accurate machine, high accurate machine

(1) Type code, represented with the first letter in its Chinese

(2) The characteristic code, represented with the first letter in Chinese

(3) Group types and sequence code Represented with Arab number the preceding one is for group, and the later one is for sequence. There are 10 groups for each type of machine tools, represented with number from 0-9, each group can be farther divided into several sequences.

(4) The primary parameter, degine sequence and econdary parameter The primary parameter stands for the standard size of the machine tools, represented with a discount value in Arab form(1/10 or 1/100).The secondary parameter has different meanings, such as the spindle number, the maximum span or workpiece length etc, represented with the same way as that of the primary parameter. (5) The sequential number of important improvement of machine tools. Choose a letter according to the sequential order of A, B,C……

For example: CA6140

For example: MG1432A

3.1.2 The main technical Parameters of machine tools 3. 1.2.1 Dimensions Dimensions of machines usually refer to the chief stucture of the machines.The principal parameters of most machines are dimensions. But the term of dimentions may include other dimensions besides the principal parameters, such as the maximam rotating diameter or maximum stock diameter allowable, the maximun workable stroke and etc.

3.1.2.2 Motions Characteristics of the main motion ①Spindle Speed, it is the main motion for rotational machin tools Spindle speed n(r/min): Cutting speed v (m/min); Workpiece or tool diameter d(mm). For the machine that moves in straight line, such as planers and shapers, the parameter of the main motion is the return times in one minute.

② Definition of nmin and nmax of the spindle The range of the spindle speed

③ The speed sequence of the spindle A certain speed of the spindle under step variation is as bellow: Under stepless speed changes, the speed can be any desired value within the range. But under step speed change, after the speed range is determined, the speed grade must be determined further so as to decide a definite speed. ④ Standard in design Usually, the standard of 1.06 is recommended, from which the following standard can be derived 1.06, 1.12, 1.26, 1.41, 1.58, 1.78, 2

3.2 The Shape Generation and the Motion Analysis of Machine Tools 3.2.1 The shape of the workpiece and its shaping method (1) Track Machining—Tools travel in a certain track while machining (2) Form Machining—The edge of the tool is completely coincidental with the expected generated line on the the surface of the workpiece. (3)Tangential Machining—The edge moves along a certain track while rotating. (4)Generating Process—The motions of the tool and the workpiece have a constant relationship to generate the desired shape.

The processes of shaping 1-generatrix, 2-lead

Tracking method and forming method

3.2.2.2 The Transmission System of the Machine Tool Transmission chain can be divided into external chain and internal chain. External chain: link the power and the implement element. Internal: link the individual parts with a reciprocated movement, it decides the path of the reciprocated movement.

Principle transmission system

3.3 Lathe and Lathe Cutting Tools Lathe is mainly used to produce parts in round shape. It removes material by rotating the workpiece against a single-point cutter, while the latter feeds linearly. Operations that can be performed on a lathe: a). Straight turning b). Taper turning c). Profiling d). Facing e). Turning and external grooving f). Face grooving g) Form cutting h). Boring O). Drilling j). Cutting off k).Threading i). Knurling Let's take CA6140 lathe as the example. It is very typical among the common lathes.

Typical operations by lathe

3.3.2 The transmission system diagram

The transmission way

i2≈i3 The transmission ratio from axis 3 to axis 5 is:

When M1 left： Low Speed：2 ×3 ×（2 × 2－1）＝18 High Speed：2 ×3 ＝6 When M1 right： Low Speed：3 ×（2 × 2－1）＝9 High Speed：3

3.4 Design of Stage Variable Speed Main Drive 3.4.1 Rotational speed diagram The rotational speed diagram can intuitively express the changing law of the rotational speed of each shaft in the transmission system and the speed ratio relationship of the transmission pair. It can intuitively express the change rule of the speed of each shaft, the speed series of the shaft, the transmission route of each speed, the transmission ratio of each transmission pair, the number of transmission pairs and the transmission sequence of the transmission system.

Rotational speed diagram is an important tool for analyzing and designing the transmission system of machine tools. It can be used not only to formulate new transmission systems, but also to analyze and compare the transmission systems of existing machine tools.

(1) Vertical straight lines with equal distances represent the axes of the transmission system. Mark from left to right. (2) The intersection point of the horizontal and vertical straight lines with equal distances represents all the rotational speed. (3) The coordinates are logarithmic coordinates, and the rotational speed is written directly at the intersection point. (4) The corresponding speed between adjacent axles represents the transmission ratio of the corresponding transmission pair. Inclination from left to upward is a speed-up transmission, and from left to downward is a speed-down transmission.

Motor—I： I—Ⅱ： Ⅱ—Ⅲ： Ⅲ—Ⅳ： The figure shows the spindle system of a medium-sized lathe. The spindle speed ranges from 31.5 to 1400r/min, and the common ratio is 1.41, speed grade number is 12. Motor—I： I—Ⅱ： Ⅱ—Ⅲ： Ⅲ—Ⅳ：

Vertical line-axes; horizontal line-all the speed; vertical and horizontal intersection point-speed at all axes; speed connection between axes-transmission ratio between axes (transmission line), downward inclination-reducing speed, upward inclination-increasing speed; parallel line-the same transmission ratio.

(1) Transmission route of spindle rotational speed at each grade (1) Transmission route of spindle rotational speed at each grade. (2) The number of transmission groups and the number of transmission pairsare obtained under the condition that the spindle has an equal ratio sequence. (3) Ratio index of transmission group At the same point on the driving axis, two adjacent lines to the driven axie represent two adjacent transmission ratios. Lattice number between intersection points of driven axis，is called Ratio Index.

3.4.2 Structural formula Structural formula description: (1) Composition of transmission chain and transmission sequence. (2) Ratio index of each transmission group. (3) The enlargement sequence can be seen from the ratio index.

SUMMARY 1. The machine drive transmission and transmission schematic. 2. The main drive and feed motion system of CA6140. 3. The transmission system analysis and formulation of the rotational speed diagram. 4. The meaning of structural formula.