Common turning tools are mainly used for rough and fine turning of internal and external surfaces and end faces of various parts, and meet the dimensional, geometric tolerance accuracy and surface quality required by the drawings.
Ordinary turning tools are divided into D-type pressing, lever pressing, screw pressing, pressing plate pressing, composite pressing and other forms according to pressing methods.
Type D pressing is shown in fig. 3-11a, and the double-sided blade with negative front angle can be used.
Fig. 3-11 pressing mode of common turning tool
- a) Type D compression
- b) Lever pressing
- c) Screw compression
- d) Pressing plate (alloy blade)
- e) Pressing plate (ceramic blade)
- f) Composite compaction
In turning, stability and safety are the key factors.
The reliable clamping of the blade will have a great impact on the surface quality of the parts.
Class D pressing system combines the downward clamping force with the positioning of the blade seat.
It not only effectively ensures the rigid clamping of the blade, but also has high repetition accuracy when the blade is rotated.
The lever pressing is shown in fig. 3-11b, and the ISO standard single-sided or double-sided blade with negative front angle is used.
The lever pressing structure can obtain the most ideal three-way clamping force (down and to both sides of the blade), and also has the advantages of convenient and fast blade disassembly and smooth chip removal.
The disadvantages are poor rigidity, short clamping stroke, lever damage and difficult chip removal of screw wrench hole.
It is mainly used for cutting medium and small machine tools.
Now it is the most commonly used structure of indexable turning tools in turning at home and abroad.
Screw pressing is shown in fig. 3-11c.
Compared with class D pressing system, it has the advantages of simple structure, convenient operation, more stable and smooth chip flow, and various blade shapes.
The disadvantage is that the impact resistance is poor.
The screw pressing system is the first choice for cutting excircles and inner holes on small and medium-sized machine tools.
As shown in Fig. 3-11d and Fig. 3-11e, the pressing plate has the advantages of large clamping force and simple structure;
The disadvantage is that it affects the chip flow and is mainly used for medium, heavy and intermittent cutting conditions.
Composite pressing is shown in Fig. 3-11f. Its advantages are reliable clamping and can withstand large cutting load and impact force.
Its disadvantages are that the pressing plate will affect chip flow and is mainly used for heavy cutting conditions.
(1) Cylindrical turning
Common cylindrical turning is to process the cylindrical surface of parts to obtain the required dimensional, geometric and surface quality.
Ordinary cylindrical turning tools are divided into 95 °, 90 °, 75 °, 60 ° and 45 ° according to the main deflection angle of the tool.
The 90 ° and 95 ° main deflection angle tools have large axial force and small radial force during cutting, which are suitable for turning slender shaft parts.
The 75 °, 60 ° and 45 ° main deflection angle tools are suitable for turning the outer circle of short and coarse parts.
The 45 ° main deflection angle tools can also carry out 45 ° chamfer turning.
The negative angle blade turning tool is more economical than the positive angle blade turning tool, while the positive angle blade turning tool has sharp edge and light cutting.
However, the positive angle blade is generally small in size and is only suitable for processing with small back feed and small feed, while the negative angle blade can be made larger in size and can be used for processing with large back feed and large feed, and the tip strength is also better than the positive angle blade (the blade with the same shape, size and tip arc).
The strength of the cutting edge of different shape blades is different, the effective cutting edge length is different, and the number of available tips is also different.
(2) End turning
End turning refers to the main cutting edge cutting the end face of the workpiece.
1. Precautions for turning the end face
(1) The tool tip of the turning tool shall be aligned with the center of the workpiece to avoid a boss left in the center of the end face turned out.
(2) The end face of the partial cutter turning machine is easy to cut when the back cutting amount is large.
Selection of back cutting amount a: a=0.5 ~ 3mm for rough turning and ap = 0.05 ~ 0.2mm for fine turning.
(3) The diameter of the end face changes from the outside to the center, and the cutting speed also changes.
The cutting speed must be calculated according to the maximum diameter of the end face.
(4) In case of concave center or convex belly on the end face with large diameter, check whether the turning tool, square tool rest and large sliding plate are locked.
In order to make the turning tool feed accurately, the middle sliding plate should be fastened on the bed, and the back feed should be adjusted with a small tool rest.
(5) When the end face quality is required to be high, the last tool shall be cut outward from the center.
2. Quality analysis of turning end face
(1) The end face is uneven, resulting in convex concave phenomenon or “small head” left in the center of the end face;
The reason is that the lathe tool is not installed correctly, the tool tip is not aligned with the center of the workpiece, the back feed is too large, and the lathe has clearance sliding plate movement.
(2) Poor surface roughness.
The reason is that the turning tool is not sharp, the shaking of manual tool walking is uneven or too fast, and the automatic feed rate is improperly selected.
(3) Inner hole turning
The characteristics of inner hole turning are: in the semi closed state, it is not easy to observe the chip removal, which affects the machining quality.
Deep hole cutting often causes the vibration of the tool bar, making the cutting edge wear quickly. Carbide tool bars are used for small diameter hole cutting, and vibration reducing tool bars are used for medium and above diameters.
During cylindrical turning, the workpiece length and the selected tool bar size will not affect the tool overhang, so it can withstand the cutting force generated during machining.
When boring and turning inner holes, because the hole depth determines the overhang, the hole diameter and length of parts have great restrictions on the selection of tools.