Standard beginning of hole pattern
This means the full hole patterns are not formed at the beginning of the hole pattern until after the second of third hub.
Equally, the completed hole pattern ends after the second last or third last hub.
The terms for this standard configuration customary to the trade are:
“Large beginning and end”
“double offset beginning and end” “not pushed out”
Start 1. Hub
With Figure 1, the operating process for such a configuration is diagrammed from the first to the last row of holes.
Theoretically, the missing rows of holes can be added during the punching process with almost all configurations, yet it must be agreed upon separately.
Unperforated borders, bases and zones
The key advantage when using perforated plates is that they can be manufactured with unperforated borders and zones. This way considerable costs can be saved in part if, for example, the manufacture of a frame can be left out.
A distinction is made between the front border and the side border. It is customary for the types produced to usually be sheets with small unperforated front and side borders.
If an unperforated border is not needed, costs can frequently be saved by cutting through the perforation.
However, it is possible to manufacture practically any desired border size. By switching off and on individual stamps during the perforation process, even sheets with unperforated zones or any other hole pattern contour can be manufactured.
Which design is more economical needs to be determined on a case to case basis.
It is thus important to lay down all requirements during the construction and enquiry phase of the perforated product.
If an unperforated border is required, it must be noted that this depends on the division of the holes. If the division is given, this shall have an influence on the theoretical size of the border.
In addition, the hole pattern can also stretch from the perforating process; it is not until after that when the actual pattern size is shown.
When nibbling, unevenness can develop on the cutting edge from the offset of the punching die.
Finishing work by sanding the nibble contour can be agreed upon separately. Usually, no finishing work is necessary when the contours are laser-cut.
However, the kind of finishing work to be done has to be announced so that the right cutting gas can be chosen.
Position of the holes in relation to the outer dimensions
Thanks to the correctly chosen sieve direction, the sieving cannot move along the unperforated bases, thus guaranteeing an optimal performance of the plant.
To help recognise this, the so-called machine direction, which is at a right angle to the direction of sieve, can be looked at.
The machine direction is the direction in which the arrangement of holes is recognisable in straight rows.
With elongated holes, no clear allocation is possible frequently due to the sole statement of the sieving direction, as it depends on the intended use. For this reason, when there is no drawing, the direction of the hole axis to the sheet outer measurement should always be stated with elongated or crossed holes. Clearly defined is the specification: Length of hole// to length of sheet [e.g. 20mm // 2000mm]
Sabre shape, hole pattern asymmetries
the different stress distribution for sabre formation. The more of the aforementioned criteria are fulfilled, the stronger this happens. Particularly in the case of perforated plates with a high proportion of holes, which are extremely stretched during punching, asymmetrical perforated fields or wide edges on one side can promote uneven stretching and cause sabre shapes, trapezoidal formations or bulges.
During subsequent straightening, it must be ensured that the less stretched areas, such as unperforated edges, undergo the same change in length as the perforated area due to the punching process. If this is not sufficiently successful, unevenness or a curvature of the outer edges and the perforated field will remain. The outer edges can be straightened by subsequent trimming, but the asymmetries present in the perforated field remain. Deviations in the unperforated edge are therefore unavoidable.
For the reasons mentioned above, an evenness of the hole patterns and edges should be ensured as early as at the construction phase.
The purpose of straightening is that the less stretched areas such as the unperforated borders experience the same change in length as the hole pattern from the punching process.
Extremely wide unperforated borders, unperforated zones or strips can impede the full rolling out of these tensions and partially even make them impossible and need to be avoided during construction where possible. erschweren und teilweise sogar unmöglich machen und sind möglichst bereits bei der Konstruktion zu vermeiden.
Conicity of the lunched holes
The width of the hole (w) is measured in the cutting zone. The length of the cutting zone is about 30% of the thickness of the sheet, depending on the firmness of the material and the mould design. As approximate value, it can be assumed that the punched hole on the stamp exit side is 0.15-0.2 mm larger per mm sheet thickness than on the stamp entry side.
Punching burr and raw edge
The raw edge and the tension developing during perforation correlate with each other so that a minor formation of a raw edge is often associated with great tension.
In order to achieve better evenness, a somewhat stronger raw edge formation is accepted in most cases. With drafts and drawings, if no deviating specifications are known or have been noted down, the stamp entry side is in the top view, i.e. the punch burr is on the bottom of the drawn part.
This regulation applies to pre-treated plates (sanded, brush-finished, coated) in equal measure. If the parts to be produced are not symmetrical or of they are bent or rounded off afterwards, the specification of the raw edge is absolutely necessary.
Hole width (w) and division (t) in the event of marginal holes
During the punching process, with so-called marginal holes, stamps can break fully or in part. This can entail the risk that, in the event of a stamp breaking, the area of the material affected is not hole-punched – DIN 24041 2002-12 allows for a lacking percentage of holes of 2%. Where necessary, it is possible to rebore and remove the missing spots in return for payment for the effort. The boreholes inserted this way do, however, differ optically from the punched holes; for this reason, we advise against this type of rework in visible parts.
If holes in the border area are a must-have for you, then enquire about our possibilities. We will submit a solution to you where it is possible production-wise.
Materials, material qualities, surfaces
Tolerances standard dimensions
The nominal dimensions of the standard sheets 1000×2000 (small format); 1250×2500 (medium-sized format); 1500×3000 (large format) as well as coils of 1000; 1250 and 1500mm in width and their sections are usually not given special processing treatment after the hole-punching and straightening.
Depending on the hole punched, tensions develop during processing that stretch the punched field and the outer contour. Above all in the longitudinal direction, greater tolerances need to be anticipated than the standards for unperforated sheets permit.
With fixed dimension lengths with a small tolerance zone, it is necessary to cut the sheets after punching and straightening to the desired finished dimension.
The changes in length in the hole pattern caused by stretching can no longer be rectified by this cutting process, so that possible deviations in the unperforated front borders occur.
With larger production lots, the stretching can be determined by trials and thus be taken into consideration from the offset by appropriate measures such as reducing the number of hole rows.
Standards and terms/supplementary information
Delivery condition of the surface
In order to ensure constant quality of the punching during processing, lubricants have to be applied in most cases.
This results in the following delivery conditions:
- Not degreased (all materials)
Delivery condition for parts made from steel, aluminium, stainless steel, copper and titan. With non-alloy steel, this grease coating also serves as corrosion protection.
- Pressure cleaned (materials resistant to corrosion)
Pressure cleaned parts are degreased, yet 100% degreasing cannot be guaranteed. This type of cleaning is not recommended for materials susceptible to corrosion because there is no subsequent passivation.
- Cleaned (all materials)
Parts are degreased and passivated in a special cleaning plant. This process is suitable for all metals as well as materials resistant to temperature, chemicals and liquids.
- Powder-coated (all materials)
By way of electrostatic or electro-kinetic application, coating powder is applied in the desired colour, structure, quality and thickness. After that, the polymerisation process is conducted by feeding heat.
The colours are named in line with the RAL colour register (other names are: NCS, Sikkens, British Standard or DB).
Using powder-coating, metallic effects can also be manufactured, with special processing even imitations of natural and artificial surfaces such as wood grain, granite or as per a graphic file provided.
Powder-coated parts are fat-free.
- Use of evaporating lubricants (non-alloy materials)
After evaporation, only a light film remains of the material surface that has no negative impact on possible further processing (coating, anodising).
- Blued/electro-polished (alloy steel)
Contaminations such as welding scales, oxide coatings, discolouration, extraneous rust, greases, oils and metallic components incorporated into the surface from mechanical processing can be removed by bluing.
The metallic pure surface achieved from bluing can form the passive layer which protects the stainless steel from corrosion. The surface achieved in this way is not, however, suitable for decorative use.
- Afterwards, with stainless steel, a smooth shiny surface can be achieved by an electrochemical removal of the tips of roughness.
- Anodised (aluminium)
The anode oxidation after processing is of great significance for high quality aluminium parts. Due to the electrochemical change in the edge layers, a surface more resistant to corrosion and wear than with untreated aluminium is achieved.
There is a wide range of colours available for decorative areas of application.
Anodised parts are fat-free.
- Pre-treated/coated basic material (all materials)
Material pre-treated on one side is used for material coated, sanded or brush-finished prior to processing unless other specifications are made.
In order to avoid damage to the surface during machine processing as much as possible, the material is often given protective foils. Due to the reduced adhesive area and the use of punching oil, the protective foil may peel off during processing. In order to prevent damage to the surface of wrong hole-punching caused by the peeling off protective foil, it has to be removed completely. The standard condition on delivery here is also without further processing “not degreased”.