After its article analysing the costs of manufacturing with sheet or coil punching machine, “Lamiera” is continuing with the same calculation procedure to decide whether to roll form or press form a metal profile/section.
Whoever machines sheet metal knows how important it is to choose the right process for making the product. This decision often has a profound effect on production results in economic terms. When making a metal profile/section it is also important to choose the most suitable technology.
The processes being considered in this article are roll forming (fig. 1) and press forming (fig. 2). Certain profiles/sections can only be made by roll forming (fig. 3), while others are easier to make by press forming.
If the profile/section can be made in either way then the best process will be the one that completes production at the lowest total cost. Press forming is more flexible than roll forming and requires no investment in tools, making it a suitable choice for small production runs. Roll forming, on the other hand, offers the possibility of a much higher output (fig. 4) and is therefore the natural choice for mass production. The decision of which is the best technology to use should be taken on the basis of these criteria combined with experience. When only medium quantities of a profile/section have to be made, however, it is helpful to have a method of calculation which offers some guidance. The purpose of this article is to give the reader a simple but strict procedure to follow. Firstly the production cost must be broken down into its basic factors (raw material, hourly cost, production time, equipment). Then a chart showing the meaning of the formula in the case of a single lot will be given for each factor (the set-up cost being included in the cost of the equipment/tooling).