Wepuko Pahnke Engineering - The Fast Forging Press

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Developed by Wepuko Pahnke Engineering as a competitor to the forging hammer and 4-hammer forging mill.

Introduction

Today many forge shops still use forging hammers, particularly to forge smaller pieces that are susceptible to rapid cooling and hence require short part-die contact times and relatively high stroke rates. The forging hammer has historically had the advantage for these pieces compared with a conventional forging press.

However, the disadvantages of hammer forging are becoming more and more apparent:

Precise position control for forging hammers is almost impossible hence automation is difficult. Thus most hammers are manually controlled and forging quality depends on the operator. Variable quality is thus inevitable.

Efficiency of forging hammers is very low at 5% to 30% compared with a oil hydraulic press which can achieve an efficiency of 80%.

There is a large environmental impact due to the inevitable high noise levels caused by the high impact velocities of hammer forging. This can reduce drastically production capabilities.

Forging hammers typically have about 30% higher maintenance costs than an equivalent hydraulic forging press.



	These typical disadvantages were the main reasons for WPE to develop a hydraulic Fast Forging Press (FFP) that could on one hand combine the advantages of a hammer and a hydraulic press and on the other hand avoid the disadvantages of both concepts. If a new machine could be based upon a simple concept then investment costs could also be minimized. Concept of the FFP Pahnke Engineering of Germany had good experience of the drive system for their hydraulic four hammer forging mill and this was adapted for single axis application. A variable speed motor drives a pump which has a flywheel mounted on the shaft. This flywheel recovers the compression energy generated within the press frame and hydraulic fluid during the pressing stroke. The single pump cylinder is connected directly with the press-cylinder by a short connecting pipe so that the moving crosshead of the press performs a high frequency, shock free sinusoidal motion. There are no operating valves in the main circuit which makes this a simple and highly reliable system.


	Because of the pump crank drive, the stroke rate is almost constant regardless of the momentary press force. However the resulting stroke decreases with increasing load due to compressibility of the hydraulic oil. To compensate for this and perform a precise position-control, a servo-valve is mounted between the main line and an additional pump. Thus the oil volume in the main line can be adjusted utilizing this valve to compensate for forging dimension deviations.


				There is a stop valve in the circuit allowing the press movement to be started or stopped within one stroke. As mentioned above, the moving crosshead of the press moves in a sinusoidal manner. By adding a second pump with a suitable volume and rotation speed, the stroke-diagram of the FFP can be varied in many ways. If, for example, the second pump has half the volume of the first but double the rotation speed, a stroke pattern will result with a larger stroke and a shorter contact time between tool and forging.

	Fast Forging Press Schematic


	Features of the FFP

The lower impact velocity, compared with a hammer, causes much less noise emission and the closed frame of a press eliminates ground vibrations. Thus operation of the new FFP is not as strictly limited by official restrictions. This means that the FFP can work around the clock so that one FFP could substitute more than one hammer. Nevertheless the stroke rate of an FFP can compete with a hammer.

The valve free oil hydraulic drive system minimizes shocks and vibrations and the resulting decrease in system wear considerably decreases maintenance costs.

A further feature of the FFP is the excellent efficiency achieved by the use of the fly-wheel and also by the automation of the process. The variety of stroke diagrams available by modifying the drive system makes this system very interesting for many applications.

The cost of the FFP is below the cost of a conventional forging press. The price of an FFP is about 35% of a four-hammer forging mill but offers about 65% of the mills productivity.

The flexibility of the FFP on a variety of products is comparable with Open Die Forging Presses

Remotely controlled die changing devices are available for the FFP but are not with a Forging Mill. This adds to the universal application possibilities for the FFP.

The remotely or automatically variable penetrating speed of the FFP makes it very efficient for isothermal forging operations.

Results with a FFP prototype:

To test the new FFP machine concept under realistic conditions a cooperation project was undertaken with a medium sized German forge shop. An old C-type press frame was used with the new drive system to realize the first FFP-prototype. The following table shows the technical data of the machine:


	Technical Data of the FFP Prototype Machine :

Max Press Force	250 Tons
Mechanical Stroke Range	12 inches
Working Stroke	1.8 inches
Stroke frequency per minute	235 / 137
Tool speed inch/sec. :
Average	13 / 9
Peak	21 / 14

The press is suitable for forging blocks with a weight of up to 450 lbs and an input dimension of up to 6 inches.

A PC based electronic control system for one man operation is installed and features the following modes:

Manual forging
Manual forging with finished-size-control
Automatic forging
Programmed forging

During the process, the system continuously displays on a diagnostic screen important process data like hydraulic pressures, temperatures, positions etc.

The initial production tests were undertaken using an existing floor bound manipulator with manual control. This caused some process limitations and a better but more costly option would have been to use an integrated rail-bound manipulator.

The maximum stroking rate using this second operator was thus limited to 157spm (strokes per minute) in manual mode.

In a series of experiments the following blocks were forged in a single heat (without the grip end):

INGOING BLOCK	FORGING
6 ins Weight=310 lb	3.2 ins square 3.0 ins square 2.75 ins square 5.5 x 2.4 ins flat 6.5 x 1.3 ins flat
6 ins square Weight=350 lb	4.3 ins square
6.1 ins square Weight=730 lb	5 ins octagon
3.5 ins square Weight=150 lb	4 x 1 ins flat

Due to manual control being used, the manipulator steps were changing from bite to bite, but nevertheless the forging accuracy was still within +/- 0.02 ins

The machine described above is now operating at a small forging company in California under production conditions. However it’s best manipulating system would be a twin track rail-bound fast operating manipulator system. The current owner uses a relatively slow mobile manipulator. Even though the machine is not equipped with integrated manipulators, the FFP has demonstrated that it is a very interesting and economic alternative to a conventional forging hammer. The prototype has shown that it is an easy task to convert an existing hydraulic press of suitable size to a modern Fast Forging Press and thus keep investment costs to a minimum.

Synopsis

Production rate of the FFP is about 65% of a 4-hammer forging mill unit, but investment cost is only about 35%. It is as flexible on forged products as a conventional Open Die Forging Press. The forged products not only include bars and shaped pieces but the FFP can also operate on disc and hollow forging as well as upsetting operations. See Case Study.


	Technical Comparison :

	Hammer	Hydraulic Press	FFP
Average penetration speed - inches per sec.	8 - 40	2 - 8	5 - 14
Starting penetration speed - inches per sec.	40 - 200	2 - 8	7 - 20
Stroke frequency per min.	up to 150	10 - 120	80- 240
Material contact time in milliseconds.	500 - 10	3000 - 250	150 - 50
Efficiency	30% - 50%	60% - 80%	90%
Noise emission	high	medium	medium
Service intervals	medium	high	high
Investment cost (based on productivity)	medium to high	medium	low
Environmental compatibility	poor	good	good
Available for automation	poor	good	good
Product Flexibility	high	high	high


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