Expertise

Bar Turning

Micro-turning: machining micro workpieces by automatic turning

Bar turning is a process enabling the production of parts through automatic turning and machining with the removal of metal. The material, in the form of bars or coiled metal wire, is machined on "Escomatic" cam-type turning machines or CNC sliding headstock automatic turning machines. At Polydec SA, our bar turning department is formed of two sections: Bar turning and Additional operations performed on the turning machine.

Micro-turning

"Tornos" Swiss type CNC automatic turning machines with sliding headstock for complex workpieces from small to large runs

Numerical control (CNC) automatic turning machines are reserved for bar turning of very small workpieces with complex shapes that cannot be produced on "Escomatic" bar turning machines. They all contain an additional feeder which automatically loads the material in bars. Unlike the "Escomatic" process, in this case it is the material that turns and the tools are fixed.

Other technical operations can be performed during the same operating cycle, often as secondary operations: polygon operation, hobbing, milling, drilling,thread-whirling/tapping or threading.

Examples of the most commonly used materials

  • mild steels for automatic machines
  • hardenable steels for automatic machines
  • construction steels
  • martensitic stainless steels
  • austenitic stainless steels
  • copper alloys (CuBe, brass, nickel silver, bronze)
  • precious metals (palladium alloy, gold)
  • titanium

Usual dimensions
Diameters between 0.05 mm and 6 mm
Max. length 80 mm

Activity sectors

  • watchmaking
  • automotive
  • electronics
  • medical

Tolerances
Possibility of achieving tolerances of +/- 0.002 mm depending on the material and shape of the part

"Escomatic" type turning machines for simple workpieces in large volumes

"Escomatic", cam-type or CNC turning machines are mainly used to machine workpieces with a simple design such as pins, shafts, knurled shafts or bent shafts. With this type of machine, the material is fed in as a wire on a reel and the tools rotate around the material.

Due to its short cycle times, this method has the advantage of improving productivity, allowing the company to achieve long production runs at competitive prices compared to parts produced with turning machines with a sliding headstock!

Other operations can be performed simultaneously on the turning machine: milling, knurling, frosting or bending.


Examples of the most commonly used materials

  • mild steels for automatic machines
  • hardenable steels for automatic machines
  • construction steels
  • martensitic stainless steels
  • austenitic stainless steels
  • copper alloys (CuBe, brass, nickel silver, bronze)
  • precious metals (palladium alloy, gold)
  • titaniu

Usual dimensions
Diameters between 0.30 mm and 3 mm
Max. length 50 mm


Activity sectors

  • watchmaking
  • automotive
  • electronics
  • medical

Tolerances
Possibility of achieving tolerances of +/- 0.005 mm depending on the material and shape of the part

Additional operations performed on the turning machine

Polygon operation

As it can be executed in the same cycle as conventional turning, polygonal turning is a milling and/or cutting operation which allows non-circular forms to be machined without interrupting the rotation of the raw material.

Polygonal turned parts therefore have several points or teeth at the ends. At Polydec SA, we often use this procedure to manufacture test probes for the electronics industry.

This technique requires perfect synchronisation of the movement of the polygonal turning mill and the part being treated. To design the tools, the manufacturing engineers must have specialist knowledge and an accurate representation of movements in space.

Polygon operation allows rapid production and clean machining, thereby offering more beneficial solutions than conventional milling.

Knurling

Knurling is an operation which deforms the material, using toothed knurling wheels to create grooves on a cylindrical surface to improve adherence. This operation requires a pressure of several tonnes, applied hydraulically.

Depending on the profile of the knurling wheels used, the grooves produced on the knurled part may be straight, helical or hatched.

For subsequent use by customers, the knurled part offers resistance and adherence during overmoulding (e.g. plastic) or countersinking of end pieces, gears, magnets or any other component.

Knurling and turning operations are carried out simultaneously on the turning machine.

Hobbing

Hobbing is an operation for milling and/or machining wheels, gears and pinions. These teeth can be produced using different methods. At Polydec SA, we perform gear hobbing during the same operating cycle as turning.

In gear hobbing, the teeth on the workpiece are produced by removing material with a cutting (hobbing) tool. This process requires perfect coordination of movement between the workpiece being machined and the milling tool, which resembles a worm.

This process has the advantage of saving time and increasing precision compared to conventional secondary hobbing operations.

Thread-whirling/tapping

Thread-whirling is a process used to machine a screw pitch inside a drill hole. This machining process is performed directly on the automatic turning machine and requires a spindle with teeth at the end rotating at high speed.

Located on the axis of the workpiece being machined, this hard metal tool must have a profile similar to that of the thread to be produced. It is first inserted into the pre-drilled workpiece, and rotates around its own axis to machine a spiral in the workpiece, which is also rotating. The internal thread is machined in a single pass.

Tapping also enables a screw pitch to be machined inside a drill hole, by screwing in a machine tap or thread former. In the first case, the thread is produced by removing metal, and in the second case by shaping the material. This method is very rarely employed by us since it is less precise and less clean than thread-whirling.

Threading

Threading is a machining process used to produce an external screw thread or pitch along the axis of a cylindrical workpiece, such as a screw. Three machining techniques are used:

  • The threaded workpiece is machined in a single pass using a milling tool with a thread profile, whose movements are synchronised with the workpiece rotation.
  • A chasing tool is used to produce the workpiece diameter in several passes until the desired profile is obtained. The movements must be synchronised.
  • Threading is performed by screwing a helical cutting tool, known as a die, onto the workpiece axis. This process has the advantage of being faster, but is less precise and clean than older techniques.
Quickfinder Glossary Manufacturing process

Quickfinder

Products

Topics

Interlocutors