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2D Cutting
1. Types of sheet metal cutting
2D Cutting operations which makes it easy to develop NC programs for sheet material cutting equipment such as :
- OXY-FUEL cutting
- Plasma cutting
- WaterJet cutting
- Laser cutting
OXY-FUEL cutting
OXY-FUEL cutting is based on a long and narrow high temperature flame generated by burning a mixture of presurised oxygen and gas such as acetylene, propane, or natural gas. The flame is used to create sufficient local heat to melt the metal being cut, and at the same time remove the molten metal to leave a gap. The resulting edge is quite rough and has a burnt appearance.
Plasma cutting
Plasma cutters work by sending an electric arc through a gas (air, nitrogen, oxygen etc.) that is passing a constricted opening (nozzle) and so the temperature of the gas is raised so much that a plasma (4th state of matter) is created. At the same time the the nozzle increases the speed of the gas so that it cuts through the molten metal. The arc is established between an electrode inside the nozzle and the metal being cut, and the distance of the nozzle from the metal surface must be controlled.
WaterJet cutting
The water-jet cutting process consists of a nozzle with a very small orifice (0.08 to 0.5mm) out of which comes a very high speed jet of water (1000 m/s or more) which is achieved by the use of extremely high pressure (exceeding 400MPa). The nozzle moves above the material to be cut just a few millimeters away from the surface and the jet of water erodes material by an abrasive action.
SprutCAM support both types of water-jet cutting processes:
- cutting by water, or hydrocutting - waterjet cutting;
- hydroabrasive-cutting (water plus abrasive) or abrasive waterjet cutting.
The presence of an abrasive in the water stream extends its technological possibilities by increasing the cutting rate and making it possible to cut hard and intractable material of substantial thickness.
Laser cutting
The mechanical forces that are applied to the material being cut by other techniques are absent in laser cutting. The focused laser radiation allows cutting and engraving of practically any material regardless of its thermalphysic characteristics. The use of laser makes cutting of deformable and non-rigid parts a possibility. The laser ray has a diameter of around 0.2 mm, this allows the creation of holes from as small as 1 mm diameter.
Using laser cutting it is possible to cut out complex profiles in practically any sheet material.
2. The equipment
Some manufacturers of cutting equipment are: Flow International Corporation; Water Jet Sweden AB; Bystronic; Trumpf; Sato Schneidsysteme (Germany); Aliko (Finland), Trenntec (Germany), Eurolaser GmbH (Germany), ESAB Welding & Cutting Productions (Sweden), Digital Control (France). Russia: "Lazer complexes", JSC., "Tulamashzavod", JSC, "ENIMS", JSC, "SPOZHITOK", Inc.
3. Technological features
From the standpoint of developing NC programs for profiling equipment, the cutting method used is of no real importance. For example, the command for enabling the plasma torch (M53) and the command for enabling the generator (M73) in laser cutting from the standpoint of the CAM system – are one and the same. So, the development of NC programs for laser, oxy-fuel, plasma and water-abrasion cutting can be successfully combined in one CAM module, the differences in the equipment are accommodated by their respective postprocessors.
4. CAD requirements
For the generation of the details of the patterns to be cut and their layout on a sheet of material an appropriate CAD system is used depending on the number and complexity of the pattern, repeatability, difficulties of the profile etc. For example, if the plasma machine is used for the production of a large amount of a variety of patterns, then it is necessary to optimize the placement of the patterns over the sheet of material so that the maximum utilization of the material is obtained as shown below.
On the other hand, when the quantity of profiles does not require filling a sheet entirely, then the geometry could also be imported from an external design system e.g. Corel Draw or Rhinoceros etc.
5. 2D geometry in SprutCAM
The advanced SprutCAM geometry editor has the construction tools to enable the production of profiles of any complexity.
Moving, rotating, mirroring, copying
Using the cursor, it is very easy to interactively manipulate contours to find their best fit in the ‘working zone’ of a sheet of material.
6. Generating the Cutter toolpath in SprutCAM
The system automatically generates the cutting cycle, including nested parts and arrays and cutting sequence to optimise material use and reduce scrap generation
The most efficient cutter toolpath is calculated to reduce the total manufacturing process time. Cutter movement is optimised both within each pattern as well as for moving within the sequence of patterns, making sure that the part is never undercut. The lead-in and lead-out points are determined on the basis of speed, of minimising the number of piercings, and on assuring that the part is not cut-off prematurely before all the details within it are cut. At all points in the process the user has the ability to edit the algorithm.
Automatic calculation of the optimum points of approach to a contour with the simultaneous control of waste products on cutting of the next profile
The system automatically calculates the start positions for cutting based on the chosen method of approach, also avoiding any over-cutting of adjacent profiles.
Automatic corner smoothing schemes
In order to prevent distortion of sharp corners of the patterns, the system has several ways of smoothing the toolpath around corners. These can be fixed either automatically or manually, based on type of corner being handled and chosen preference as shown below.
Photorealistic simulation of the cutting process
The whole cutting process can be seen within the simulation mode. The simulation is a true photorealistic reproduction of the cutting cycle and allows the user to verify the validity of the algorithm generated and if nessecary modify the path according to the user’s exigences.
NC programme
Having verified and accepted the toolpath, the user can generate the NC programme, automatically, using one of the several postprocessors supplied with SprutCAM.
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