Manufacturing Technology

In the first quarter of 2019, WAFIOS Umformtechnik successfully delivered two type ND 91 tandem double-blow forming cold formers to a well known German customer, having restarted the mature technology when it took over responsibility for the ND machines from WAFIOS Group.

The high performance ND tandem double-blow cold former can be used for the production of long blanks up to 300mm and for drywall screws, wood screws, sheet metal screws (DIN 7970) and similar parts in wire from 2.2mm up to 5.2mm diameter (0.087 inches – 0.205 inches).

Technology
This very well proven technology has been used on the world market for many years, but when it comes to the above wire range, WAFIOS Umformtechnik states that its ND type of machine is the fastest on the market.

Common double-blow machines are generally limited to the production of short screws, ranging from 25mm to 50mm (0.985 inches – 1.97 inches) and outputs between 400 – 600 pieces/min. However, the tandem principle allows output numbers up to 1,400 pcs/min for 70mm (2.758 inches) blanks and 700pcs/min for lengths up to 170mm (6.698 inches).

Performance and driving system
The wire is fed from a driven pay-off into a roller straightening unit. As an option, a rotary straightening spinner is available. A steplessly adjustable sliding infeed guides the wire into the cut-off bushing.

The wire pins are positioned in the transport system. Two gripper belts lead the pins to the tandem punching stations for separate preform and finish punching. At the preform punching station the first blow forms the pin end. The finish punching station forms the final size and the head of the screw. In the last operation, the double-headed blank is separated into two single blanks.

The cam shafts for the punching and pressing tools are located on either side of the transport system. An additional cam drives the cutting system for the separation of the blanks.

Short punch stroke – long tool life
The pictures to the right show the reduced punch stroke of the ND machines in comparison to the common production principle with closed dies. Independent of the screw length, the punch stroke of the ND series is always as long as the necessary volume to form the head. With conventional cold formers the punch stroke is at least as long as the length of the pin, resulting in large size punch slides, higher wear and problems when centering the tools.

The short stroke principle of the ND series allows more time for the forming process itself and tool life is increased.

Quality control
An integrated process monitoring system for the ND machines allows ‘operator-free’ production. The quality control processes include the length measurement of the wire pin in the cutting station, sensor monitoring of the cutting and forming processes, and control of the cut in the last work station. WAFIOS can also prepare the machine for adaption to a common monitoring system for the product, the production, the machine, as well as SPC and PC interfaces.

Quick changeover
WAFIOS points out that the ND line of machines are easy to set-up and almost maintenance free. For changeover to another length of blank, with the same diameter, only minutes are required. Punching tool change cassettes also reduce the amount of time for a changeover from one diameter to another.

Environmental aspects
The ND machines work with clean bright wire, which is cheaper than phosphated material and does not pollute the environment. In addition, for the forming process only the ends of the wire pins are mist lubricated – the reduction of oil consumption this creates is significant.

www.wafios-umformtechnik.com