Multiple-Axis Forming Applications
Changing the economics of segmented dies used in cold forming can dramatically increase the size, quality and dimensional control potential of today’s forming machines.
Cold forming parts from wire has evolved around a multitude of products made on a single axis. Naturally, the machines created to fabricate these parts have been designed to be fast and efficient while functionally handling the typical single-axis geometry. In progressive forming machinery, each sheared cylindrical blank is transported to a stationary die and the reciprocating tools push the blank into the die and deform it along a single axis. The simplest parts will have asymmetrical upset section on the end of the blank in contact with the heading slide tooling. Upset features can be located at other positions along the length of the blank when the heading slide tooling is used to contain a portion of the blank.
When the machine possesses multiple dies and the blank is indexed to each successive die, many different external diameters are possible by upsetting and/or forward extrusion, thereby increasing the variety of parts that can be produced. Still more part shapes are possible if extruded or pierced holes are added to the forming sequence. However, these features remain on the common axis and the different external diameters must be arranged in successively decreasing sizes so they can be removed from the solid tool or die.
A few parts are formed with some of the shape on one axis and another portion of the shape on an offset axis (Figure). Still others involve forming or piercing holes on different axes. But with both of these variations, the secondary axis is parallel to the primary axis, so standard machine motion and handling are possible (Figure 2).
In today’s competitive climate, end users are looking for lower cost and higher quality solutions to their design problems. When captive and undercut features can be formed on a part, many costly secondary operations can be eliminated to produce a multifunctional component. This may very well provide the design solution for a simpler and better product. However, new processes and tool designs are needed to achieve these shapes.
Segmented-Die Cold Forming Economics
Segmented die forming is one answer to achieving more complex and higher-value formed parts. Notches, grooves, trepanned features and multiple upsets can be theoretically forged into the finished part. Offsets and non-symmetrical features can also be produced using segmented tool designs. The addition of just one special feature may provide a high quality and low-cost component design for the end user.
Up until now, the biasing springs used in most segmented die assemblies were located within the confines of the die bore of the machine. This space limitation dramatically limited the preload that could be used to hold the segments in position during the forming blow. Of course, when segments are not held in position, flash lines, mismatched features and tapered dimensions show up in the final formed part.
To counteract the lack of spring biasing attainable, the tool designer has been forced to resort to shallow segment angles. This in turn limited the amount of radial clearance that could be attained for any die size. And the net effect was that a given machine could only produce a fraction of the part sizes available within its capability range. And when a 16 mm machine is utilized to produce a 6 mm part, economics can fly out the window and users resort to alternative designs.
National’s latest invention has the potential to change the economics of segmented-die cold forming. The modular removable die block of a FORMAX machine, can be equipped with an underslung, gas-spring lever mechanism that dramatically increases the biasing force on a sliding segmented die assembly (Figure 3). This additional biasing force has the potential to dramatically increase the size, quality and dimensional control attainable on a machine today. And the modular die block assembly can be exchanged quickly for a standard die block assembly without further machine alterations.
Multiple-Axis Parts Forming
Applications Using Segmented Tooling
Some examples of parts produced using segmented tooling are shown in Figure 4.
• Part 1 is normally made at 75 ppm on a 25 mm machine. By using the a high-force biasing spring design, this part could potentially be produced at 150 ppm using a 16 mm machine with the correct feed, PKO and DKO specifications.
• Part 2 was produced on a 14 mm machine and could have been produced 30% faster on a smaller machine.
• Part 3 would probably not be attempted because of the tapered flange, knurls and feature relationships, but is feasible today.
• Part 4 has been successfully produced as a solid using segmented tools, but conceivably could be produced in a hollow configuration with more spring force available to support extrusion operations.
The whole concept of precision multiple-axis forging is now open on cold forming equipment with both the high force biasing mechanism for segmented or sliding tools and the blank rotation to a new plane. At IFFI 2003 last June, National introduced and featured modular precision multi-axis forming technology. When the blank is worked along one axis and then reoriented to a new axis in front of the heading slide in the machine, completely new forged shapes can be produced that always required secondary forming before. See the following examples, also in Figure 4.
• Part 5 is a common 6 mm rod end produced in a five-die machine using simple blank rotation after two initial traditional forming steps were used to prepare the blank.
• Part 6 was originally trimmed to form the flat sides of the finish part, but could easily be rotated, trapped in a high force sliding tool station and formed to controlled dimensions without scrap.
• Part 7 was formed from an expensive drawn shape cutoff and fed into a cold former. Today with high force segmented tooling and blank rotation, this part could easily be made from inexpensive wire.
The objective is to utilize the high production speed and efficiency of a progressive die cold forming machine to eliminate secondary machining operations or re-feeding to slower single-purpose forming or rolling machines. National chooses to go a step further and confine the necessary special mechanisms to the die area of the machine so the machine is easily convertible to standard production.
For receive additional information on equipment for economical multiple-axis forming operations, contact the author or Circle 220.
More than 125 years old, National Machinery LLC designs, develops and manufactures high-speed metal parts forming machines. The company offers the FORMAXfamily of headers and threaders; bearing headers including ball, roller and Combi; customized formers and forming systems; the MicroFormer; and QUIKCALC PLUS software. In addition to advanced forming machines, the company provides parts analysis, machine selection and tool design assistance as well as training, machinery service, repair and rebuilding.