Sheet metal production processes – a small brief into the stages of fabrication and process – part 1

Sheet metal parts after bending stocked on the exhibition

A lot of time we are talking about technologies we are selling – mainly about our bending tools and about press brake machines because the process of sheet metal bending is the core business. But for sure bending is not only one process and in this article we will try to explain the complete fabrication process for sheet metal. By the way usually the term “sheet metal” we use for all types of flat metal. But you should note that on the market are also differences, mainly they are all “sheet metal” up to 8-9 mm, all other is called “plate metal”.

From material storage

If you think that the first stage is the material cutting – you are wrong. The first part is the material storaging and based on the typology of the production there could be a lot of different solutions – from simple racks to automatic storages. Automatic storage mainly in the modern factory means that it will be not computer-based storage to have the notes of quantity and types of your sheets but also the system to transfer the sheet metal directly to the cutting operation. Or it could be the separate storage for the main input of sheet metal and also separate automatic storage for the cutting operations.

The technologies today are quite different and we encountered also the installation of more than 10 big towers to store sheet metal and to transfer it between the machines. And when we are talking about modern technologies for sure we take note of digital production management to identify the flow, available metal at storage, types, and any other important and necessary information.

But we also need to note that the storage automatic solutions are not only to keep the raw parts and metal but to feed it to the working zone next. The other transfer task is also (if we are talking about automatic storage systems connected with the machines) the removal of the prepared parts from the working zone and the next storage as the final products.

Sheet metal cutting

Next, is the cutting process. There are different technologies and they are completely based on applications, factory type, product type, productivity and quantity of pieces, and many other parameters. For sheet metal, the cutting could be made by:

  • guillotine shears to make necessary transversal cuts
  • notching machines (but mainly used not just for complete cutting but to notch the angles for future operations)
  • plasma-cutting machine or any other plasma-cutting technology, for example even a robot
  • laser cutting machine or any other laser-cutting technology, for example even a robot
  • waterjet cutting machine
  • punching press
  • combination system as a shearing and punching machine
  • combination system as a punching and laser-cutting machine
  • manual devices (but in this way about manual tools we can talk only about small quantities and limited production with thin sheet metal, for example for HVAC industry and air ventilation.

Depending on the technology it could be only piece cutting (like with shears), complete part cutting (like on a punching machine or laser cutting machine), or even complete part fabrication (if the part is flat and doesn’t request the other production operations to be done). Also, the cutting operations could be one or several machine combinations like shears and notching machine or shears and after laser cutting or laser cutting and punching, etc.

What are the advantages of combination machines? Speed and precision everywhere. Every machine has limits so for example punching + cutting can provide the best speed and cut complicated contours of parts if necessary and there is no tooling for it to be punched. Or sharing in one stroke can achieve the maximum speed against the punching if the question is to cut for example for 1 meter. Also, combination machines offer precision because any part reinstallation means the loosing of the previous positioning.

Material from coil

It is also reasonable to speak a little about the coil. From one side it is not connected with sheet metal, from the other side, it is very close. First, the factory can have slitting lines which means that it receives the metal coils and then decoils and cuts them to metal sheets for future operations. For example, there are a lot of real installations with slitting lines and then the classical laser cutting machine. The lines could be more complicated with included forming units, punching units, etc. to make complete part or partial operations for the part. There are also presented complete laser cutting lines with production from metal coil with the recoiling of metal and then cutting of it “fly”. Generally, this is not very popular technology but anyway, it is presented on the market and there are users of it.

The coils from the supplier could be also not as raw material but as pre-fabricated products as well such as metal already perforated with holes for future use, for example, bending for architectural panels.

Deburring and surface preparation

Then there could be deburring and cleaning operations to remove the burrs from sheet metal after cutting, punching, or even de-slagging after plasma cutting. Burrs are presented everywhere but they could be really small and not important for the production but could be requested to remove before any other actions. There are a lot of different types of deburring from manual machinery and tools, vibration barrels, sheet metal deburring machines, chemical or explosion deburring, etc. For sure it also depends on the production, parts requirements from the design office and future operations, speed, and application. But it could be not only the deburring but also other actions for surface preparation such as polishing, grinding, satination, etc. Estetic parameters are important for different architectural components and mass-market parts production.

Additionally, we should discuss some words about surface preparation itself. It is used for architectural applications as we told already but could be also for the automobile industry, food and kitchen furniture, terminal cabinets, ATMs, kitchen hoods and equipment, and a lot more. When this article was written I was sitting and looking at the coffee machine with a case of sheet metal with polished surface. There are different ways to sheet metal with a prepared surface such as purchasement outside and receiving the prepared sheets (mainly covered also with polyethylene film to protect the surface) or to prepare the surface necessary inside of the factory. In both ways as you can imagine the operations should be made with flat metal i.e. before any operations of bending and forming because then it will be impossible. Also most modern machines, for example laser cutting allow to work with wrapped sheet metal. 

If we talk about the complete polish process for sheet metal it is usually made with special machines with different texture brushes, abrasive belts, and textile flap wheels in the final with the addition of the polishing paste. Depending on the necessities it could be one or several machines in one line and additional devices and units to cover the polished surface with the film. 

Spinning technology

One more note about spinning lathes and spinning technology for deformation itself. Because it is completely different the raw parts to be used there are round so usually the main sheet metal material cutting is made with special shears to cut in the round shape. Usually, such types of machines are made directly by the manufacturers of spinning machinery. Spinning technology provides the deformation of blank parts into the necessary shape by the positioned die or tooling and based on the force or pressure of rollers on the other side to deform the part into the shape of tooling. Probably in some applications like bottle-type parts tooling is not used and the position of rollers is controlled numerically. The technology of spinning metal is completely stand-off technology of other sheet metal processes but we are trying to make our articles more informant and to describe all possible.

Levelling of sheet metal

More operations that are not widely used but somewhere could be very important and necessary. It is sheet metal leveling or straightening to flatten the sheet metal before production (for example sheets before laser cutting) or after production. The reasons could be quite different. We know that for precision parts the normal supply of sheet metal could be not enough and tolerances are not good so they proceed with flattening operations with special leveling machines before the cutting. These machines have pressure rollers to pressurize the sheet and remove the waviness to prepare it perfectly for other operations. Even with precise machine tools for cutting the problems of non-flattness of sheet metal can rush completely the main process to perform the precise cutting.

Leveling is also an absolutely necessary operation and is used 100% of the time in any installation of any coil proceeding line. Decoiling of metal in coil requests flattening before any future operations so the special leveling machine is installed inside the line. The purpose is to provide the flat metal but also to perform the role of the automatic feeder and pulling of the metal off the decoiler device.

The next request for flattening could be after the parts cutting, for example, perforation punching with a punching press which affects the flatness of the parts and makes the curling which is impossible to eliminate by punching machine. In this case, could be recommended also to make the flattening of the part after the cutting operation, moreover work with pre-fabricated parts and not sheet metal complete sizes can decrease in several times the investments for the leveling machine and necessities for forces and pressure to be done.