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You are here  PRODUCTS Plastics Processing
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Turning Plastics |
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Machines
All types of turning machines can be used when turning plastic parts. There are no major demands to the rigidity and driving power of the machines as the cutting force is small compared to turning steel. On the other hand it should be possible to set a high speed and the machine must be stable and must have minimal slack in order to get a good result. Therefore, the new, controlled turning machines have advantages in preference to conventional machines.
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Tools
For plastics processing high-speed steel (HSS) or tool-bits are suitable tools. It can be sharpened and tolerates the heat that is generated during the processing. However, better qualities of hard metal and ceramic tips as well as hard metal tips coated with industrial diamonds, which all deliver good results, are continuously being developed. It is not the tips' high heat resistance that is used, but the good wearability and by that you obtain a high tool life. When processing fiber reinforced materials, both glass and carbon, which are very abrasive, it is most suitable to use hard metal tips coated with diamonds. If it concerns other than single unit productions it is in fact necessary. The below figure shows the combination of wearability and toughness for various tips. |
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Geometry of the Edge
Correct shape and right angles of the cutting tools are of decisive importance for a good tooling result and for minimising the tooling tensions in the material. The geometry of the edge is illustrated in the below figure by using a free steel that is used for turning, planing or milling with a bit. In the figure you will the denomination for the angles. |
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Chip Angle g (Gamma)
Large positive chip angle gives an easy cutting steel that reduces power and power demand when chipping. Furthermore, you reduce the potential risk of deformation of soft materials as well as the deflection of the item is being reduced. Negative g is rarely used when processing plastics.
Cutting Edge Angle b (Beta)
As a, b og g adds up to 90°, a large g (chip angel), means that b (cutting edge angle) will become more sharp. Therefore, the cutting edge power is smaller.
Clearance Angle a(Alfa)
Usually soft materials require a large a, and by that a smalles warming-up and compressive load on the material is secured. At the same time a large a gives high wearing on the steel. Therefore, a should normally be around 5-15° when processing most materials.
Cutting Edge Inclination l (Lambda)
The most critical and vulnerable part of the tool is the cutting point. At continued chip, e.g. when milling, it is in danger in particular. When processing plastics an cutting edge inclination from 0-4° is the fittest. |
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Pointing Angle e (Epsilon)
The total of f, e and k is 180°. The largest possible e gives the best heat conduction through the tool, which is an advantage when roughworking.
Tool Cutting Edge Angle k (Kappa)
The tool cutting edge angle is very important fo the thickness of the chip as well as for the size and direction of the cutting power. It influence the chip's slide direction. When k is less than 90°, the chip will become thinner (h) and longer (l) for the same cutting depth (a), where the heat dissipation will increase (please also see the below figure).
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Chip Section
The energy, that is being added during processing, will more or less be transformed into heat. When processing plastics this is unfortunate, as most plastic types do not tolerate that high temperatures and at the same time they have a low heat conductivity. Therefore, the aim must be to drain if from the work place. Dependts on the processing method, the geometry of the item and the material it can be necessary to cool it, either by using a cooling agent or air.
The heat development in the item is reduced by a long and narrow chip section, which can be obtain at a smaller tool cutting edge angle (k) and less tension. |
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Therefore, the conditions for a rational turning are:
- high cutting speed
- small chip cross cut
- sharp tool
- effecient colling
- reasonable set-up
- long and thin chip
Also aviod:
- vibrations
- growing flashes
- sharp crossings
At long chip materials: |
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