Chapter2 Manufacture processing Equipment

Section1 Basic knowledge in the metal cutting process

Section1 Basic knowledge in the metal cutting process

• 2.1.1 Basic definition• 1 、 Cutting motion and cutting regime• 2 、 Essential definition for the working parts of cutting tools• 3 、 Conversion of tool angles• 4 、 Working angles for cutting tool• 5 、 Parameters of the cutting layer and cutting mode

2.1.1 Basic definition• The process in which the excess metal ona blank is cut off by a cutting tool, and formedinto a required part, is called metal cutting.

1 、 Cutting motion and cutting regime（ 1 ） Cutting motion1 ） Main motion2 ） Feeding motion3 ） Combination of cutting motions and combined speed

Figure2-1 Cutting motion in turning

Figure2-2 Cutting motions in planning, drilling, milling

Figure2-3 Combination of cutting motions

（ 2 ） Three elements of cutting regime1 ） Cutting speed2 ） Feeding speed, feed and feed per tooth3 ） Back engagement of the cutting edge

2 、 Essential definition for the working parts of cutting tools

（ 1 ） Structure elements for the working part of cutting tools

1 ） Rake face2 ） Flank3 ） Cutting edge4 ） Tool nose

Figure2-4 Working part of typical turning tool

（ 2 ） Reference system for the marked angles of cutting tools

1 ） Tool reference plane2 ） Tool cutting edge plane3 ） Predetermine condition for motion4 ） Predetermine condition for setup5 ） Main section and main section reference system6 ） Normal section and normal section reference system7 ） Transverse section, longitudinal section,transverse section or longitudinal section system

Figure2-5 Main section and normal section reference system

Figure2-6 Transverse section and longitudinal section reference system

（ 3 ） Reference system for the working angles of cutting tools

Figure2-7 Working angles of cutting tool

（ 4 ） Marked angles of the cutting tool

1 ） Rake angle2 ） Clearance angle3 ） Cutting edge angle4 ） Minor cutting edge angle5 ） Tool cutting edge inclination angle

Figure2-8 Nominal angles of cutting tool in main section reference system

3 、 Conversion of tool angles

Figure2-9 Conversion of tool angles between in main section and in normal section

4 、 Working angles for cutting tool（ 1 ） Influence of feeding motion on working angle1 ） Transverse turning2 ） Longitudinal turning（ 2 ） Influence of setup for cutting tool on working angle1 ） Influence of locating position for tool nose on working angl

e 2 ） Influence of the direction for the center line of the tool bar on working angles

Figure2-10 Influence of transverse feeding motion

Figure2-11 Working angles in turning Figure2-12 Influence of locating position for tool nose on working angles

5 、 Parameters of the cutting layer

（ 1 ） Cutting layer1 ） Undeformed chip thickness 2 ） Width of uncut chip3 ） Cross-sectional area of uncut chip

（ 2 ） Cutting mode

Figure2-13 Parameters of the cutting layer in longitudinal turning

Section1 Basic knowledge in the metal cutting process

2.1.2 cutting tool materials• 1 、 Performance for cutting tool materials • 2 、 Frequently-used cutting tool materials• 3 、 Other tool materials

1 、 Performance for cutting tool materials

（ 1 ） High hardness and wear –resistance（ 2 ） Sufficient strength and toughness（ 3 ） High heat resistance（ 4 ） Good technological properties （ 5 ） Good economy conditions

2 、 Frequently-used cutting tool materials

At present, the most commonly used of cutting materials are high-speed steels and carbide alloys. Carbon tool steels such as T10A, T20A, alloy tool steels such as 9SiCr, CrWMn, are only used in some hand tools or cutting tools working at low cutting speed, due to their poor heat resistance.

（ 1 ） High-speed steels • There are high alloy tool steels having more tungsten,

molybdenum, chromium, vanadium etc elements so that these possess higher heat resistance and strength, toughness as well wear resistance, can work from 500~650 . Due to their good technological properties ℃these are the main material of complex tools, such as drills, formed cutters, broaches, gear cutting tools etc .According to applications, high-speed steels can be divided into plain high-speed steels and high property high-speed steels, and melting high-speed steels and powder metallurgic high-speed steels according to its manufacture technology.

（ 2 ） Carbide alloys The carbide alloys are made of metallic car

bide powder (WC, TiC, etc.) and bonding mediums (Co, Mo, Ni) through powder metallurgy. It is usually referred to as sintered carbide and sometimes it is called cemented carbide.

The performances of carbide alloys are decided by the varieties, properties, content and grain size of the carbides, and the content of bonding medium. The higher the carbide content in carbide alloys, the higher the hardness of carbide alloys but the lower the bending strength of carbide alloys. When the content of the bonding medium is higher, the status reverses. In general, carbide alloys posses high hardness, wear-resistance and heat –resistance because they mainly consist of metallic carbides with high melting point and hardness, good chemical stability and heat stability. The cutting temperature for carbide alloys reaches up to 800~1000 , therefore, the chief ℃advantages of carbide are its ability to remove metal much faster (higher cutting speeds) and it required less frequent sharpening. The disadvantages of carbide alloys are mainly their poor bending strength and impact toughness so thy are not suitable for heavy cutting or for intermittent cutting.

3 、 other tool materials （ 1 ） Coated tools （ 2 ） Ceramics （ 3 ） Diamond （ 4 ） Cubic boron nitride (CBN)

Section4 Machine tools and machining operations

2.4.1 Generating Motion of Machine Tools

2.4.2 Engine Lathes

2.4.3 Turret lathes

2.4.4 CNC turning centers

2.4.1 generating motion of machine tools Machining is the most versatile and accurate of

all manufacturing processes in its capability to produce a diversity of part geometries and geometric features (e. g., screw threads, gear teeth, flat surfaces). Casting can also produce a variety of shapes, but it lacks the precision and accuracy of machining. The principle used in all machine tools is one of generating the surface required by providing suitable relative motions between the cutting tool and the workpiece.

Fig2-14 Generating shapes in machining

(a) Straight turning; (b) Taper turning; (c) Contour turning; (d) Plain milling; (e) Profile milling

Fig2-15 Forming to create shape in machining

(a) Form turning; (b) Drilling; (c) Broaching

Fig2-16 Combination of forming and generatingto create shape

(a) Thread cutting on lathe; (b) Slot milling

2.4.2 Engine Lathes• The oldest and most common machine tool is

the lathe, which removes material by rotating the workpiece against a single-point cutter. Lathes used in manufacturing can be classified as speed lathes, engine lathe, toolroom lathes, turret lathes, automatic lathes, tracer lathes, and numerical control turning centers.

• Turning processes are very versatile. The following processes are capable of producing a wide variety of shapes illustrated in Fig.4-7:

• (a) Facing － The tool is fed radially into the rotating work on one end to produce a flat surface on the other end.

• (b) Taper turning － Instead of feeding the tool parallel to the axis of rotation of the work, the tool is fed at an angle, thus creating a tapered cylinder or conical shape.

• (c) Contour turning － Instead of feeding the tool along a straight line parallel to the axis of rotation as in turning, the tool follows a contour that is other than straight, thus creating a contoured from in turned part.

• (d) Form turning － In this operation, sometimes called forming, the tool has a shape that is imparted to the work by plunging the tool radially into the work.

• (e) Chamfering － The cutting edge of the tool is used to cut an angle on the corner of the cylinder, forming what is called a “chamfer”.

• (f) Cutoff － The tool is fed radially into the rotating work at some location along its length to cut off the end of the part. This operation is sometimes referred to as parting.

• (g) Threading － A pointed tool is fed linearly across the outside surface of the rotating work part in a direction parallel to the axis of rotation at a large effective feed rate, thus creating threads in the cylinder.

• (h) Boring － A single-point tool is fed linearly, parallel to the axis of rotation, on the inside diameter of an existing hole in the part.

• (i) Drilling － Drilling can be performed on a lathe by feeding the drill into the rotating work along its axis. Reaming can be performed in a similar way.

• (j) Knurling － This is not a machining operation because it does not involve cutting of material. Instead, it is a metal forming operation used to produce a regular cross-hatched pattern in the work surface.

Fig2-17 Engine lathe

Fig2-18 Friction clutch

Fig2-19 Manipulation Mechanism

Fig2-20 Spindle Assembly

2.4.3 Turret lathes• Turret lathes are a major departure from engine or basic lathes.

These machines possess special features that adapt them to production. The “skill of worker” is built into these machines, making it possible for inexperienced operators to reproduce identical parts. In contrast, the engine lathe requires a skilled operator and requires more time to produce parts that are dimensionally the same. The principal characteristic of turret lathes is that the tools for consecutive operations are set up for use in the proper sequence. Although skill is required to set and adjust the tools properly, once they are correct, less skill is required to operate the turret lathe. Many parts can be produced before adjustments are necessary.

• Horizontal turret lathes, shown in Fig. 3-10, is used for chucking work, and the turret is mounted directly on a saddle that moves toward the headstock by hand or power to feed the tools to the workpiece, and withdraws to index the turret.

2.4.4 CNC turning centers• Turret lathes have evolved into computer numerical controlled

(CNC) turning centers. These machines contain X, Y, Z, and C axis control, so turning and milling can be done on the same machine. The turret can hold 8 to 10 tools, with many of them powered (having individual motors), as shown in Fig. 4-8 (a). Some machines have automatic tool change (ATC) capability with additional tools in a magazine. The C axis control provides 360°location on the spindle, so the spindle can be held in any orientation while the power tools operate. More complex versions of these machines have two turrets and two spindles, and parts can be automatically transferred from the main spindle to the subspindle as shown in Fig. 4-8 (b).

Fig2-21 CNC turning center