Optimal cutting of critical materials
In practice, materials and material combinations that cannot easily be cut or machined with standard circular saw blades keep appearing again and again. Several factors are important here. One is the workpiece, with its dimensions and material properties.
Furthermore, the tool with its dimensions, its geometry, such as diameter, root blade thickness, number of teeth, cutting width, rake angle, clearance angle, special tooth forms with protective chamfer, chip breaker, hollow tooth or group tooth forms. Finally, the situation on the machine side, which machine with which mode of operation is available to me in order to master the given task. This results in the application parameters, which can be favourable or very unfavourable from a machining point of view. The aim is always to achieve the optimum solution, with regard to cutting quality on the one hand and tool life on the other (economic efficiency). We want to take a closer look at some "more special materials":
- PP solid material in sheet form, thickness 40 mm.
- Fibre cement board (Eternit), 8 mm aluminium composite board
- Melamine resin impregnated paper, as plate with decorative overlay (Trespa) 6mm
- PMMA plate (Plexiglas)20 mm
- Aluminium solid material in sheet form, thickness: from 40 mm HPL layer covered with stainless steel foil, glued on both sides on chipboard (Homapal)
- Paper-covered foam plate (Kapa) 12 mm
- Mitre cuts KFP latte, HPL coated plate etc.10-60 mm
Polypropylene is a very thermoplastic material, which means that PP melts very quickly when exposed to heat. For this reason, it is necessary to create operating conditions during machining that generate as little temperature as possible.
This can be achieved when selecting the tool by using a saw blade with very few teeth, such as the type GUHDO 2005LF. This saw blade is particularly characterized by a large rake angle, an arc tooth shape with a huge chip space and expansion slots with a very large end bore.
It is preferable to work on horizontal panel sawing machines or sliding table sawing machines. In order to minimize friction as much as possible, the tooth projection should be as large as possible so that the tooth's contact arc in the material is as small as possible. The generation of heat can also be reduced by reducing the speed. If, however, the feed speed is increased until the cutting quality deteriorates and is then lowered again slightly until a satisfactory result is achieved, then the maximum service life of the tool used is obtained.
By using a minimum quantity lubrication, the operation can be further improved, speed and feed rate can be further increased.
Fibre cement board (Eternit)
Fibre cement boards are very hard and abrasive, so a tool wears out relatively quickly. In order to achieve the longest possible tool life, some adjustment parameters should be taken into account, provided that the technical possibilities are available.
A saw blade with a particularly wear-resistant, fine-grained carbide grade should be used. The tooth geometry should be very compact (tooth shape: trapezoidal flat), a positive rake angle should also be used, such as type GUHDO 2139TF, in order to minimize the feed forces required.
Machines with manual feed, e.g. manual circular saws or vertical panel saws, are not well suited, as the feed speed is a very important prerequisite for long tool life. Horizontal panel saws with infinitely adjustable feed speed and speed are excellently suited for sizing fibre cement panels. Feed speeds of 70-100m/min are easily possible and extend the tool life extremely. If a feed speed of 1.5m/min is achieved with a hand-held circular saw and the feed speed of a horizontal panel saw is 100m/min. in relation to this, then the circular saw blade of the horizontal panel saw can be used ~ 67 times longer.
than with the same saw blade used on the circular hand saw. This means, if one assumes that a saw blade can be resharpened ~ 20 times, then the owner of the hand circular saw must buy 4 circular saw blades and pay 64 resharpenings, and has cut just as many running meters again owner of the horizontal panel saw with a service life of a saw blade.
However, the service life of the saw blade is not only dependent on the feed speed. Thus, the service life can be further improved by selecting the greatest possible tooth projection of the saw blade. This shortens the path of the tooth through the material.
Aluminium composite panel (Alucobond/Dibond)
Aluminium coated plastic sheets tend to form a burr on the tooth exit side, this phenomenon varies from manufacturer to manufacturer and from coating to coating.
By using saw blades with hollow-ground tooth face, which have an axis angle due to the hollow tooth shape, almost burr-free cuts can be produced here. For brittle external coatings, the tooth form trapezoidal tooth is by far the best choice in combination with the hollow tooth form, such as the type GUHDO 2141KTH.
There are no special requirements placed on the machine here, but from a tool life point of view the same operating conditions apply which apply to all materials (as high a feed rate and tooth projection as possible, with acceptable cutting edge quality).
Melamine resin impregnated paper, pressed as a plate with decorative overlay (Trespa) 6mm
This material is very hard, brittle and abrasive and the decorative top layer tends to crack on the tooth exit side.
If you do not have the possibility to work with a scoring saw blade, an axis angle is absolutely necessary if you also want to maintain a clean tooth exit side. The tooth form trapezoidal hollow is particularly suitable as with the type GUHDO 2141KTH. As this is a very brittle coating, no sharp-edged cutting edge corner should be used here, but a prism-shaped cutting edge corner. In this case, the tooth is pulled so that microcracking of the surface is prevented.
If a scoring unit is available, we recommend the use of a saw blade combination: main saw blade tooth form trapezoid, GUHDO type 2053TPV, scoring saw blade one-piece and the cutting width matched to the main saw blade, tooth form flat, GUHDO type 2055RS. In combination, as set: Type GUHDO 2101VPS for vertical panel saws.
Here, as already described above, the generally valid rules for cutting from the point of view of the optimum tool life apply; a machine should be selected which permits the greatest possible feed rate and which is variable in speed as far as possible. Panel sawing machines are best suited for this purpose.
The material has two negative properties for processing, on the one hand the material is brittle, so it tends to break out quickly. On the other hand, it is also thermoplastic, i.e. it starts to melt, resulting in a partially white cutting edge.
In order to minimise scoring in the narrow surface, a tooth shape should be selected that has a chamfer on the flank like type GUHDO 2030KFD, so basically a prism works with a pulling cut and this leads to a homogeneous cutting pattern. In order to counteract breakouts, a large saw blade diameter should be selected if possible, because the tooth projection should not be too small so that breakouts do not occur on the tooth entry side. Due to the large saw blade diameter, the exit angle of the tooth is still favourable with relatively large tooth protrusions. Cooling is required to prevent melting. By using a minimum quantity lubricator, the cutting edge is cooled down by compressed air and by evaporation of e.g. a slightly volatile lubricant to such an extent that white formation is prevented.
A machine should be used which is equipped with a minimum quantity of lubrication device, be it a sliding table saw or a horizontal panel saw with pressure beam. An even feed improves the cutting result.
Aluminium solid material as panel material from 40 mm thickness
Aluminium is very homogeneous and can be cut relatively easily.
Since we are dealing here with relatively thick material, the number of teeth of the saw blade must be drastically reduced. A large rake angle, a large chip space and an arc tooth shape are advantageous here, such as type GUHDO 2005LF. In addition, however, chip breaker grooves should be ground in so that the chip folds up in the kerf and does not rub against the workpiece over its entire width. In order to prevent the build-up of aluminium on the saw tooth and the narrow surfaces, a minimum amount of lubrication should also be used here.
This is only a panel processing which should be carried out on sliding table saws or horizontal panel saws, a minimum amount of lubrication is very desirable.
HPL layer covered with stainless steel foil, glued on both sides on chipboard (Homapal)
This is a very critical application, where compromises have to be made in any case.
For cutting stainless steel, cutting speeds of 95m/min (1.58m/sec) should not be exceeded. For cutting the chipboard as carrier material, however, cutting speeds of 60-100m/sec. are used.
Since the coating on the underside of the panel would be flaring if only one main saw blade were used, a scoring saw blade should be used. However, a one-piece scoring saw blade such as type GUHDO 2155.120.22 should be used instead of a two-piece or conical scoring saw blade. Here it is important that the saw blade is also set very far out so that the stainless steel is cut as steeply as possible.
Tooth projection approx. 12 - 15 mm, if possible. It may be necessary to change the basic setting of the scoring saw blade for this purpose.
The main saw blade should be an alternating tooth saw blade such as the type GUHDO 2123.350.31 (sharp cutting edge corner in order to be able to shear the tough stainless steel cleanly) with a quite large diameter, so that the cutting edge projection can be selected extremely large, i.e. set the maximum cutting edge projection.
The tool life of the scoring saw blade is approx. 60 m and the tool life of the main saw blade is approx. 30 m. The saw blade has a maximum cutting edge projection of 60 m. A set with two main saw blades and one scoring saw blade is therefore useful.
Machine: Sliding table saw with scoring saw or horizontal panel saw
Paper-covered foam plate (Kapa) 12 mm
The material is used for posters, displays, model making and presentations and has a tough paper coating and a thermoplastic middle layer.
Due to the tough top coating, the tool must be cut with extremely sharp edges (large corner angle) so that the paper can be separated cleanly. The best choice is the GUHDO 2195HC saw blade and the GUHDO 2196HCL for package cuts or thicker materials. However, this material is usually also cut with a ruler using razor blades or cutter knives.
The material can be cut well with many different machines, hand circular saw, vertical panel saw, format circular saw and horizontal panel saw.
Mitre cuts in plastic-coated panels
For mitre cuts on board materials with a brittle coating, such as KFP laths or HPL coated boards, the entry angle and exit angle play a very important role in achieving perfect cut quality.
The GUHDO Excalibur Saw Blade 2138HDFFN fulfills all requirements for the saw blade, in addition this saw blade has a 30% higher number of teeth due to the cutting edge geometry, compared to normal hollow tooth saw blades, which also significantly improve the cutting quality.