Turning

Turn is a machined manufacturing production processes for metals and plastics. Turning is manually on a lathe or automatically on a lathe. In contrast to the spindles and milling here the workpiece or semi-finished turns; it performs the main cutting motion with his rotation. The firmly clamped tool ( turning tool ) is the rotating workpiece along with the help of the tool carriage moves to lift a chip; it performs the delivery and feed movement. Only in special cases (for example, thread whirling ) also carries the tool for cutting movement at.

In the classification of the manufacturing method according to DIN 8580 turning counts as separation processes.

In the classical turning rotationally symmetrical (round ) parts are mainly processed. The modern technology of a CNC lathe makes it possible also to produce workpieces that used to produce only on a milling machine.

Are the rotating parts on the microscopic level (so-called micro turned parts ), for example, in medicine, as well as watches or microtechnology, one speaks of décolletage.

In woodworking, a similar process is called turning or rotating. During the turner, the tool performs manually in the hand turning method, there are similar shelf technologies such as in metal processing. So come in Drechsler craft cross supports for use and there are half -, full-and CNC-controlled machines use.

• 3.1 Location of the processing site
• 3.2 movement direction
• 3.3 Geometric shape of the machined surface
• 3.4 Roughing & Finishing
• 3.5 Turning - Grooving - Parting
• 3.6 Threading - Thread chasing

Axes when rotating

The reference axis during rotation is the axis of rotation of the main spindle, to which the workpiece and the chuck rotates. This is normally referred to as the Z- axis and shows the feed towards the tailstock. Vertically it is the X -axis. When pure rotation, there is no Y- axis, the height of the tool on the XZ plane is fixed during set-up, usually the cutting edge lies exactly in the XZ plane. In turn-mill centers there may be other axes. In some cases there is also the Y-axis.

The scale marks, and any position encoders in the X-axis to double the actual movement. A movement of the tool about a millimeter is shown with two millimeters, as the movement will affect the workpiece radius, and so that the workpiece diameter is varied by two millimeters.

With computer-controlled lathes usually the angle of the spindle is displayed as a third coordinate and also determined at appropriate skills of the hardware and software.

Choice of cutting data

The sectional data can be adjusted while rotating the cutting speed, feed and depth of cut. By optimizing these parameters, the following conditions occur:

• Optimum tool life
• Improved chip formation
• Required surface quality
• Largest possible removal rate
• Small cutting force

Average speed and speed

The choice of cutting speed depends on material, tools and turning process. Standard values ​​for cutting speed are shown in tables. The speed is dependent on cutting speed, diameter and the rotating tool.

Feed

The feed f is expressed in millimeters per revolution. It should be set as large as possible at pre-turning for economic reasons. It is limited by the performance of the rotary machine, of the possible load on the cutting edge and the stability of the workpiece (risk of deflection ). The finish-machining is often worked with lower feed rate, in order to achieve a higher surface quality.

Depth of cut

The cutting depth is dependent on the cylindrical turning of the delivery of the rotary tool, the grooving of the width of the cutting edge. The depth of cut should be chosen as large as possible to the pre-turning. When you finish turning the cutting depth corresponds to the allowance.

Rotation method

• The machined surface is color-coded

Cross - Plan- turning

Cross - holly - turning

Longitudinal tech- turning

The turning process can be classified according to various criteria:

Position of the working point

Depending on how the machining point on the workpiece is located, it is called external rotation or from the internal turning. When external turning the exterior surfaces are machined, the inner turning surfaces lying in a hole.

Direction of movement

Depending on the feed direction between longitudinal and transverse turning turning ( facing ) is distinguished. When longitudinal turning, the tool moves along the rotation axis (Z- axis), the transverse rotating vertical / transverse thereto, ie, along the X -axis. These are the basic movements when turning. More complex shapes to be generated by the superposition of the two motions. When the tool moves on a straight path at an angle to the Z axis, arise conical surfaces. In the form of rotating the tool can also move to any curved paths and thus produce a variety of rotationally symmetric shapes.

Geometric shape of the machined surface

• Turning round, there arises the surface of a cylinder
• Facing, it creates the base of a cylinder, ie a level
• Taper turning, there arises the lateral surface of a cone
• Schraubdrehen, there arise areas along a helical line
• Profiling, the shape of the tool is transferred to the workpiece, for example for rounding corners of a quarter of a circular cutting edge
• Form turning, any surface of revolution generated by the matching tool path. Form rotation can be further divided into: Freeform turning, in this case, the tool is either performed by hand and placed on a support or the two cranks ( Z- and X -axis) are simultaneously operated manually. For this, a certain amount of practice is necessary, dimensionally stable parts can not be made so.
• Nachformdrehen, in this case the form of a pattern is electronically or mechanically scanned and transmitted to the tool and thus to the workpiece.
• NC form turning, the tool path is controlled by a program from a computer.

Roughing & Finishing

Arbitrate

Grooving in aluminum

As with many other machining processes you can also when turning between a roughing and a finishing operation differ. When roughing significantly more volume than when finishing the component is removed. The workpiece is in this case placed close to measure. The finishing on the other hand is intended to serve the achievement of high surface quality.

Turning - Grooving - Parting

When rotating the tool is moved along the surface, parting is cut directly into the semifinished product to be processed so that it detaches itself from the rest, so it will be stabbed in the workpiece. Many profile tools are used in the grooving process, for example for making grooves for retaining rings. Continuing to use the plunge turning to the center of the workpiece, the workpiece can be separated from the clamped semi-finished products. This is called then parting.

Threading - Thread chasing

In both processes, a tool used in longitudinal turning process. The feed rate equal to the thread pitch, so leaves the tool has a track on the desired helix. When threading a profile tool is being used. The profile of which corresponds to the shape of the desired thread, for example a 60 ° angle on a metric, and a 55 ° angle for a pipe thread. Since the cutting forces are too big, especially for coarse threads in a single pass, this tool each time a piece is moved several times by the same track, deeper. In contrast, a tool for thread chasing has several cutting one after the other. Each of which has the profile of the thread, the pitch of the blades corresponds to the slope. The blades are staggered so that each runs a bit deeper in search of her predecessor.

The threading is more flexible than the thread chasing, as threads of different pitch can be manufactured with the same tool. For this you need the thread chasing only a single pass, the processing time is therefore significantly shorter.

With threading also keglige thread to be made. So that the thread cutting tool exactly moved by the pitch per revolution, its feed movement is either mechanically linked to the drive spindle or the feed movement is electronically synchronized with the rotation of the spindle.

Tools

Indexable inserts for finishing

Holders for grooving inserts

Grooving inserts

Holders for indexable inserts profile

Turn profile indexable insert for thread

Whether one insert is designed to roughing a workpiece or to arbitrate, decide the radius of the cutting edge. This may vary from 0.2 mm to 2.4 mm. Inserts having a radius smaller than 0.8 mm are generally used to arbitrate a workpiece. All about serving the roughing operation. The insert to be used is also dependent on the material used. In gray cast iron ( brittle material) ceramic inserts recommended with a smooth surface. For steel, aluminum, brass (large chip formation ) is prescribed the use of inserts with chip breaking edge. These allow a better lifting the processing chip.

As with other machining processes, the cutting tool is subject to wear, which varies depending on the material, feed rate, cutting speed and quality of the insert also used in turning.

Special Problems

By the regenerative effect of the work may oscillate in such a way that a wave-shaped cut is produced.