Turning for high accuracy and best surfaces
Working area of a SPRINT 32|5
Turning is one of the metal-cutting processes which, according to DIN 8580, are assigned to the main group "cutting". Accordingly, the change in shape takes place with local elimination of the material cohesion, more concretely through the separation of material particles in the form of chips. The high flexibility of the cutting processes with regard to geometry generation and the possible manufacturing accuracies (dimensional, form and positional precision) as well as the achievable surface qualities result in a wide range of possible applications, especially in the field of finish machining.
It all depends on the cutting edge
Basically, machining processes are differentiated into those with geometrically defined cutting edges and those with geometrically undefined cutting edges. For cutting with geometrically defined cutting edges, a tool is used whose number of cutting edges, geometry of the cutting parts and position of the cutting edges relative to the workpiece are defined, as is the case with turning or milling. Cutting with geometrically undefined cutting edges, on the other hand, is a cutting process in which a tool is used whose number of cutting edges, geometry of the cutting parts and position of the cutting edges relative to the workpiece are undefined, as is the case with grinding). In terms of industrial use, the group "cutting with geometrically determined cutting edges" is the most significant.
Turning according to DIN
DIN (Deutsche Industrie Norm) defines turning as "machining with a closed, usually circular cutting motion and any feed motion transverse to the cutting direction". The axis of rotation of the cutting motion is workpiece-bound, i.e. it retains its position relative to the workpiece regardless of the feed motion. The objective in turning is to produce the workpiece with a precise geometric shape and dimensions in accordance with the technical drawings. The shape of the workpiece is determined by the geometry of the tool and the relative movements between the workpiece and the tool, which is called the working couple.
Differentiation of turning in detail
The relative movements during machining generally consist of a cutting movement and one or more feed movements. In turning, the workpiece usually performs the rotary cutting motion and the tool performs the required feed and infeed motions. The resulting movement from the cutting and feed movements is called the effective movement. In turning, the main cutting motion is thus performed by the workpiece to be machined. The chip removal itself takes place by means of a rotating workpiece against which a tool is guided that executes the feed and infeed movements. Consequently, the cutting speed, the feed rate and the depth of cut at which the tool engages the material are the cutting data that require particular attention.
Not all turning is the same
But not all turning is the same. Technically, the turning process is also differentiated according to the characteristics and shape of the surface into facing, round turning, screw turning (including thread turning), hobbing, profile turning and form turning. A further differentiation is made according to the position of the surface into external and internal turning and subdivided according to the surface quality into rough turning, finishing and fine turning.
Form turning from manual to CNC
The bridge between tradition and the future of machining is built in particular by form turning - even if the term hardly plays a role in the general linguistic usage of the practice. The meaning becomes obvious with the reference that the shape of the workpiece is generated during form turning by the control of the feed or cutting movement. The cited bridge function is documented in the type of control of the movements according to which form turning is classified. In so-called "free-form turning", for example, the feed movement is controlled by hand, which requires specific knowledge and, from today's point of view, almost extraordinary skills in order to be able to produce the shape of the workpiece in accordance with the drawing. By contrast, in postform turning or copy turning, the feed motion is controlled by a two-dimensional reference die. In so-called "kinematic form turning", the feed motion is then controlled (kinematically) with the aid of a mechanical gear.
Finally, "NC form turning" represents the current state of modern turning technology in the broadest sense and also offers the greatest potential from DMG MORI's perspective. Here, the workpiece shape is generated by controlling the feed motion by means of entered data and using numerical control.