1. External turning
Ordinary external turning is to process the outer surface of the part to obtain the required dimensional accuracy and surface quality. Ordinary external 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 larger axial force and smaller 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 thick parts. Among them, the 45° main deflection angle tool can also perform 45° chamfering.
Negative angle blade turning tools are more economical than positive angle blade turning tools. Positive angle blade turning tools have sharp cutting edges and light cutting, while positive angle blades are generally smaller in size and are only suitable for small back cutting and small feed processing. Negative angle blades are larger in size and can be used for large back cutting and large feed processing. The tip strength is also better than that of positive angle blades (blades of the same shape, size and tip arc). Different shapes of blades have different edge strengths, different effective cutting edge lengths, and different numbers of available tool tips.
2. Face turning
Face turning refers to the main cutting edge cutting the end face of the workpiece.
1. Precautions when turning the end face
1) The tip of the turning tool should be aligned with the center of the workpiece to avoid leaving a boss in the center of the turned end face.
2) When turning the end face with an offset tool, it is easy to get stuck when the back cutting amount is large. Selection of back cutting amount ap: ap=0.5~3mm for rough turning, 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. When calculating the cutting speed, it must be calculated according to the maximum diameter of the end face.
4) When turning an end face with a larger diameter, if there is a concave center or a convex belly, check whether the turning tool and the square tool holder, as well as the large slide plate, are locked. In order to accurately feed the turning tool horizontally, the middle slide plate should be fastened to the bed, and the back cutting amount should be adjusted with a small tool holder.
5) When the end face quality requirements are high, the last cut should be cut from the center to the outside.
2. Quality analysis of the turning surface
1) The end face is uneven, with convex and concave phenomena or a "small head" left in the center of the end face; the reason is that the turning tool is not installed correctly, the tool tip is not aligned with the center of the workpiece, the back cutting amount is too large, and the lathe has a gap and the slide moves.
2) Poor surface roughness. The reason is that the turning tool is not sharp, the manual tool movement is uneven or too fast, and the automatic feed rate is improperly selected.
3. Internal hole turning
The characteristics of internal hole turning are: in a semi-closed state, it is not easy to observe the chip removal situation, which affects the processing quality. Deep hole cutting often causes vibration of the tool bar, causing the cutting edge to wear quickly. Carbide tool bars are used for small diameter hole cutting, and vibration-damping tool bars are used for medium and above diameters. When turning an external circle, the workpiece length and the selected tool bar size will not affect the tool overhang, so it can withstand the cutting force generated during processing. When boring and internal turning, the hole depth determines the overhang, so the hole diameter and length of the part greatly restrict the choice of tool.
