1. What do I need to start?
For trouble-free flow punch forming the former must run centrally. It should be clamped using a collet in a centerdrillcollet chuck with cooling ring. The cooling ring prevents overheating by deflecting the heat away from the machine spindle. Parting lubricant is also needed for flow punch forming.
2. What mechanical equipment do I need for flow punch forming?
Any machine with a rotating unit that can achieve the required speed and with a motor that has the necessary kilowatt output can be used. Normally, this means a column drilling machine or NC or CNC machines. To produce a through-hole for an M8 thread in 2 mm thick sheet steel, you will need a machine with a minimum speed of approx. 2100 rpm and an output of 1.5 KW.
3. Can I also use a manual drill?
Usually no. As mentioned above, a minimum speed and kilowatt output is required that most manual drills cannot achieve. In addition, very large axial forces are required to bring the metal into the formable phase.
4. Can I also use a drill chuck?
No, because of the danger that the flow punch former will break and the spindle in the drill unit will overheat. The use of a drill chuck will invalidate the warranty.
5. Do I have to lubricate?
A parting paste must be used. The centerdrill parting paste prevents metal from building up on the flow punch former or from baking onto it. Depending on the type and thickness of the material, it should be applied in small quantities every 5 to 50 drillings. Too much paste can cool the former down too much and thus adversely affect the quality of the formed hole and the collar.
6. What metals can I process with flow punch forming?
Virtually all thin-walled metals (except tin and zinc); in other words, all:
- Welding steels
- Stainless steels
- Magnetic materials
- Special alloys
8.What process sequence do you recommend to produce a flow-punch formed hole and a thread in zinc-plated material?
For the reasons explained above, it is generally better to zinc-plate the material after flow punch forming. If this is not possible the zinc layer, if it is too thick and uneven, should be removed before flow punch forming. If the workpiece is zinc-plated after the thread forming, the threads must be cut subsequently if it wasn’t closed with a plug beforehand.
9. What is the maximum thickness that can be flow-punch formed?
There are known applications with a wall thickness of 12 mm in which flow punch forming was used. In our experience most applications involve a material thickness from 1 – 3 mm. Thinner material can also be processed, but an underlayment beneath the workpart is required because of the risk of deflection. Flow punch forming in solid material is not possible.
10.Should I use a short or a long flow punch former?
Every former tip consists of a cylindrical and a conical part. The cylindrical part is responsible for forming the core hole. If a thread is formed afterward, we recommend leaving the core hole slightly tapered at the end so that the thread is well formed. However, if the core hole is fully formed because it functions as a through-hole, the cylindrical part must have a corresponding length. The length of the flow punch former depends on the thickness of the sheet steel, the desired core hole, the type of metal, and the desired surface (with or without collar). Refer to the table “Maximum Material Thickness” on page 15. For pipe profiles the working length of the flow punch former must not exceed the inner width of the profile.
11.Examples of a former selection:
» A core hole for an M8 is to be flow-punch formed in 2 mm thick sheet metal made of S235JR/ST37: required is a machine with a speed of 2100 rpm and an output of at least 1.5 KW. Recommended is a short flow punch former ø 7.3 mm; alternatively, if the surface should be smooth, a short/flat flow punch former ø 7,3 mm.
» The same core hole as above in 4 mm thick sheet metal. In this case the long or long/flat version ø 7.3 mm should be used. If problems occur during thread forming that result in the thread former “squeaking” and wearing excessively, the cylindrical part should be extended. That means that a special flow punch former must be fabricated.
» The same core hole as above in 2 mm thick sheet metal made of stainless steel: in this case we recommend the above mentioned flow punch former, but with a 0.1 mm larger diameter, i.e., ø 7.4 mm.
12. The collar formed by material that is displaced upward, is a problem. How can I achieve a smooth surface?
For this we recommend the flat version centerdrill. With this model the collar is removed in the last part of the operation. Of course, this results in a smooth surface only for flat sheet metal. With round pipes leftover metal remains on two sides and must be removed mechanically.
13. Is the thread formed in the same operating step?
No, if the thread was produced in the same operating step it would be destroyed again when the larger-diameter flow punch former is extracted.
14. The flow punch former gets dark red during forming? Is that dangerous?
No. Usually, the flow punch former develops a temperature of up to 600° C and begins to glow dark red. If the color changes to bright red or yellow, that means that the flow punch former is too hot. This redu- ces the tool life and adversely affects the quality of the core hole.
15. How can I reduce the material that runs inward?
The best way to achieve this is predrill a hole before beginning the standard flow punch forming process. With the predrilled hole a reduction of the bushing toward the inside and smoother edges of the bushing can be achieved. However, this also reduces the number of possible thread turns.
16. The bushing that emerges toward the inside is too long or torn.
Predrilling of an appropriate hole will reduce the length of the bushing and prevent tearing on the edges of the bushing.
In case that you do not find the answers to your questions on these pages or wish to test centerdrill in practice our specialists are ready to assist you.
Tel: 021-3132 6508
Fax: 021-5168 5302