KommerlingUSA in Spanish

Fabrication: Machining

KOMADURWhen working with KOMADUR PVC sheets, there are a number of special guidelines and directions that must be complied with. The following data and values are provided for orientation purposes. Although they have been obtained by conducting a great variety of trials and tests, they cannot be assumed to be binding for every type of application.

Almost all tools and machine tools used to work metal and wood can also be used to work KOMADUR PVC sheets. The cutting speeds are high, the feed rate low and the cutting depth also low. In most cases, there is no need to cool either the cutting tools or the cuts themselves, provided that the cutting edges of the tools are kept sharp and the heat that arises through the cutting process is dissipated by quickly removing the chips. If the depth of the cut is deeper, the cut will have to be cooled in order to prevent the material from “smearing”: this can be done using compressed air or water (cooling medium).

Furthermore, the existing safety instructions also require that chips and dust be properly extracted.

Please note that whichever method is chosen to work KOMADUR, deep grooves and sharp edges must be avoided as they would lead to early breakage of the material due to the known notching effect when put under strain. Smooth surfaces at the edges can be obtained by finishing them with buffing wheels made of felt, unbleached calico or sisal weave, or with felt tapes. Grinding or polishing pastes can also be used. Uneven edges that arise during sawing, drilling or milling can be given a clean finish using flat scrapers (grinding angle 15°).

Guideline values regarding the cutting conditions and shapes of cuts and sections in connection with the working processes described below can be found in the table on page 15; for further details, see VDI Specification 2003.

High-speed band saws and circular saws with a cutting speed of up to 3,000 m/min are recommended. Depending on the thickness of the sheets, saw blades with a tooth pitch of between 5 and 10 mm are used. For circular saws, it is normally recommended to use blades with a tooth geometry that alternates between flat teeth, trapezoidal teeth and carbide-tipped teeth.

The saw blade diameter (Ø) and the number of teeth (t) must be coordinated to match the material to be machined, the machine type and the machine speed.

In order to obtain clean edges to cuts and to avoid cracking, always clamp the sheet material in the work-holding fixture in such a way that it does not vibrate. This is especially important for thin sheets with a thickness of 1-3 mm, not only when machining them singly, but also in a stack. Use guillotine shears to cut a thickness of 1 mm.

In the case of jigsaws, use only sharpened, unset saw blades (plastics, PVC). The feed (manual) must be at a slow, constant speed. In particular cases, it may be advisable to make use of the consulting service offered by the saw-blade manufacturer.

Information about the cutting geometry of the machining processes can be found in the Working process/Cutting geometry table. The information and instructions given by the respective machine manufacturer must of course be observed.

All PVC sheets in question can be drilled using the sort of twist drills familiar from drilling metals (DIN 1412 twist drills) whose angle of twist is approx. 30°. The point (or nose) angle can be up to approx. 110°, while the lip relief angle should be no smaller than 12-16°.

The cutting and feed speeds depend on the depth of the hole to be drilled: the thicker the sheet, the slower the speed.

For holes larger than 20 mm in diameter, two-flute cutters with pilots are used. Holes larger than 40 mm in diameter are cut using circular cutters (e.g. quick- helix drills).

When rough turning, it is advisable to combine a slow feed rate with a greater cutting depth and to use a cutting tip with a radius of at least 0.5 mm in order to obtain a groove-free surface.

The cutting depth should be maximum 2 mm for fine turning. If a faster feed rate is selected, cracking of the material can be avoided by setting a slower cutting speed.

The milling tools have to be ground so that they are suitable for working the plastic material. They must also provide enough space for an adequate volume of chips. Working with a fast forward feed rate along with moderate cutting speed and deep cuts will lead to good results. 3-D milling can also be performed without any problem with KOMADUR. For this purpose, the plotter system is equipped with a special ball nose end mill and linked with suitable computer software.

Cutting, punching, perforating
KOMADUR sheets up to 3 mm thick can be cut with guillotine (sheet) shears. The cut must be made swiftly and without interruption. The sheets should have room temperature, i.e. at least 20 °C. Thicker sheets (> 3 mm) should be cut using a saw.

KOMADUR sheets up to 3 mm thick can be punched and perforated with profiling knives or two-piece tools. Also recommended are punching tools (made of strip steel) with facet cut (beveled edge) on both sides. Heating the PVC material to 30 to 40 °C is useful and aids the working process.

Laser Cutting
Due to the heat that is transferred to the material during laser cutting, this process is unsuitable for rigid foam sheets.

Water-jet cutting
An alternative cutting technology (cold-cutting process) is water-jet cutting.
This cutting method is especially suitable for KOMADUR when complex contours are to be cut out.

Up to a sheet thickness of 3 mm, cutting can be performed using a pure water jet. For thicknesses of 4 mm and more, however, an abrasive agent (e.g. silica sand) should be added to the cutting water.

Different cutting speeds can be used depending on the type and thickness of the sheet and the type and quality of the cutting unit. The cutting speed depends mainly on the quality of the cutting surface wanted and should perhaps be discussed and agreed upon with the customer.

At the beginning of every series, therefore, we advise you to first of all determine the correct cutting speed with respect to the quality of the cutting surface.

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