January 2005

MFC offers right size at right time for parts makers

A new pressing concept is available that meets the demands of modern PM manufacture and offers sizing for complex sintered components. The multi-function sizing centre has other potential advantages too, says Albert Rundel...

Over the past few years considerable progress has been made in the field of pressing complex, multi-level sintered components. New developments in press, adapter and control technology increased efficiency, precision and process safety in forming technology. But due to growing demands for accuracy and capacity in sizing technology led by the automotive industry, new concepts were needed to fulfil future requirements. Until recently these requirements could not be met since only simple presses or adapters with few possibilities to influence sizing were available. Parts manufacturers were forced to develop quite complex and cost-intensive tool construction for multilevel parts.

Faced with immense cost pressures, some PM suppliers contemplated avoiding sizing parts. As they considered that route however, customer requirements with regard to complexity and tolerances of sintered parts became even more stringent, making further post-sintering operations almost inevitable.

There was an obvious need for a new approach to sizing multi-level sintered components.

"Our philosophy was to establish a standardised system that allows the sizing of complex sintered parts with different geometries without the necessity of using special designs," says press builder Lauffer's marketing manager Albert Rundel.

In co-operation with PM technology company Alvier AG, Lauffer has developed an overall centre whose individual components are in optimum tune with one another. The process offered by the multi-function sizing centre (MFC) is the most favourable alternative to further operations. Its increased output and ability to integrate further working steps offers a big step in the direction of increased efficiency and competitiveness.

The centre is modular in design so that additional functions can be easily integrated. Basically, the centre consists of a hydraulic press, a multi-platen adapter and a three-axes rail transfer plus optical orientation (vision) system. Additional modules that may be integrated are, for example, adapter change-over systems, parts lubrication systems and chamfering systems, as well as measuring and sorting units.

These individual features were optimised in such a way that new standards could be achieved with regard to output, adapter standstill times during tool changes as well as delicate parts handling.

Heart of the system - a 400-ton press.

Another important driver has been the increasing demands of the automotive industry with regard to process safety and process documentation, which have been taken care of by the integration of respective data recording and monitoring systems.

The press is a hydraulic sizing press in-frame design with a stiff shield-type press frame, massive press bolster and press ram. Parts transport is effected across the press for which the unit is provided with openings at the sides.

As a standard, the upper piston is equipped with an adjustable mechanical stop - advantageous in achieving highest possible speeds.

Alternatively, the press can be operated with a servo-valve closed-loop controlled upper piston. In both cases tool and process parameters are stored in the control and can be called-up again immediately after re-commissioning. Fundamental functions such as ejection, spring-back and withdrawal are already backed up in the control and just need to be selected when running in a pressed part.

A schematic diagram of the award-winning multi-function sizing centre

Special attention was paid in development to establishing a standardised system that allows the sizing of complex sintered parts with many different geometries not needing special designs.

An important point is that the adapter concept is based on the ejection principle; eg the part will be ejected from the matrix before the individual lower punches are released so that even delicate, complex sintered parts such as aluminium components or pre-sintered PM parts can be processed.

A first for aluminium

The adapter concept allows for the most different parts geometries, a fast tool design and a considerably simplified tool stack-up. Due to the fact that the tool levels are hydraulically activated any necessary movements (eg ejection, punch displacement, punch spring-back compensation) can be programmed. Because height adjustments can be made easily by hand-wheel, these tool levels can be quickly adjusted when running in a new part or when adapting to part variations in continuous-run production.

PM parts are transported to individual stations by a proven rail transfer system, the design of which is aimed at satisfying requirements in various key sectors. The individual axes are driven by electronic servo-motors and can be freely programmed, making a quick and flexible set-up for most different part geometries possible. Safe and damage-free transport of even the most delicate parts is guaranteed by gripping and lifting from below. In this way clamping the parts can be avoided so that neither the parts´ roundness nor their surfaces get damaged. In summary, the transport system features:

• Design with two rails and three axes (transport, clamping and lifting strokes);
• Rail separation on the inlet and outlet side with electronic synchronisation of the axes;
• Programming of the speeds of the axes and their respective acceleration;
• Programming of clamping stroke and lifting stroke; and
• Quick change-over of gripper rails during tool change with quick coupling.

Apart from sizing PM parts, further process steps can be built in. These are handled in individual stations that are integrated in the press to maximise productivity and process safety. The individual stations are modular in design and include the following operations as standard:

• Optical part orientation by marking or geometry via the camera system;
• Part deburring and corner rounding in the chamfering station before and/or after the sizing process;
• Precise part and/or die lubrication via a micro dosing unit;
• Tempering of tooling via a heating/cooling unit; and
• Measuring and logging of process parameters.

Current applications include complex, multi-level parts such as synchroniser hubs, belt pulleys, timing gears and variable camshaft timing systems, as well as pump components and helical gear components.

One of the presses recently delivered is being used for complex parts made out of aluminium for the first time. This application constitutes a big potential for the PM industry as a whole with the multi-function sizing centre as one major process step to guarantee the quality and function of complex aluminium components.

Seeking perfect PM pressing in a tough world

Customer specifications for pressed components have reached a level that until recently seemed unthinkable. To be competitive as a component supplier in a cut throat industrial landscape companies must achieve optimum powder compaction...

There have been significant improvements in pressing technology over the past 20 years. Much important progress has been made by focusing on machine precision and process control and documentation, with the sole objective of obtaining higher production efficiency.

Today, highly intricate parts are pressed within the closest tolerances and at stroke rates which nobody could have imagined at the end of the 1990s.

Reliability and the ability to reproduce machine settings are a critical issue. What matters is maximum flexibility in production. So how does a comparatively small machine-building company cope with ever-increasing requirements?

Hydraulic presses with closed-loop controlled movements have been used for many years, but so far as powder presses are concerned real progress has been made only recently. Thanks to the introduction of latest state-of-the-art hydraulic systems using pressure accumulator technology and highly sensitive servo valves, Dorst hydraulic presses are capable of producing parts within a tolerance range of only a few hundredths of a millimetre over a production lot of some tens of thousands of compacts. The new generation of the company's hydraulic automatic presses range from 1200 kN to 20 000 kN pressing force. All Dorst machines are based on the same hydraulic circuits and have identical electronic control systems.

But close limits can only be realised by using additional highly sophisticated controls. They must be able not only to actuate the various functions of a press during each cycle, but also verify the position of individual movements to recalculate the hydraulic power, pressure and oil flow in real time. The speed and precision of the control system are of vital importance.

Dorst programming combines advantages inherent in the latest hydraulic and electronic systems. The software has been developed by the company and is linked to updates. Specialists with wide-ranging experience in both powder compacting and electronic systems have enabled the development of special software for the latest generation of hydraulic presses, providing for almost every feature of the pressing process.

A touch-screen is used for bringing the man/machine interface to life. Operation is user-friendly and easy as all data are entered directly on-screen. The software incorporates a statistical database providing various options for numerical evaluation of the process data from the system, enabling the user to memorise and check the quality of compacts.

To facilitate the set-up of "high-end" powder presses, Dorst developed a software system called the Intelligent Program Generator (IPG). Using IPG it is only necessary to enter the geometry of the part to be pressed and add some characteristics of the tooling and the powder to be processed. Based on the calculation of these values and long-standing experience of the makers, IPG is capable of generating a programme that can be run to produce a prototype. By measuring the density within the different segments of the prototype in the IPG's optimisation mode, the machine cycle is recalculated to generate a new programme. After only a few steps of pressing and measuring, the compact produced will show the customer's desired characteristics. The system assists set-up by programming the withdrawal movement to prevent cracking. It calculates the punch spring-back and displays correction values for individual movements of each punch.

Dorst won the prestigious EPMA Award for progress in pressing technology in 2001 for introducing the system.

The company has a long history of automating machine functions, among them changing die sets on big multi-platen presses. The weight and the size of the sets (adaptors) for big presses have to be considered because they are by no means easy to handle. A die set (adaptor) for a 5000 kN press weighs about nine tonnes, including an upper part of some 3.5 tonnes. A special rail system is needed to change it. To change to a second die set the transport trolley must be capable of carrying both - ending up with a total load of some 18 tonnes. This has to be moved and adjusted within 0.1mm to ensure faultless operation. Dorst has developed a modular system that can combine different die sets on one trolley servicing several machines. To economise on expensive machine time in tool set-up, parts are assembled away from the press.

In continuous operation it is important to have compacts quickly and gently removed from the die. A pneumatic proportional axis with a gripper has been designed to do this, programmable to meet the individual specifications for new parts.

This is only the first step from the press to the furnace. Compacts are weighed, and the press adjusted automatically, before the parts are sent to the furnace by conveyor belt.

Sizing feeder systems are also available that feed pre-sintered parts to the press, and from the press to the next step in the production cycle. The control of these sizing feeders is integrated into the computer system.

Double dose of skill makes a market leader

Manufacturing carbide hardmetal indexable inserts for cutting tools is highly specialised. Among the leaders in the field is Fette, based in Schwarzenbek not far from Hamburg. It can boast nearly a century’s experience of building tools for the metalworking industry…

For more than 90 years, Fette has been one of the best known manufacturers of cutting tools in metal working. Since the introduction of numerically controlled technology and the emergence of machining centres, the company has worked to achieve a strong position in precision tool manufacture.

Carbide indexable inserts need to be manufactured identically in long production runs. They, and the tools that carry them, represent the company's largest and most interesting product group. Fette is part of the Leitz Metalworking Technology (LMT) Group, which has been among the world's leading companies in this sector for the past two years.

But the real reason that the company holds such a unique position in the field of pressing carbide powder is that there is a second technological string to its bow.

There is more to industrial powders than metal powders alone, and the development and production of tableting presses, primarily for the pharmaceutical industry but also for chemicals and foodstuffs, is a sector where Fette has had a large and active division for more than 50 years.

It builds very precise presses for highly sensitive products, meeting extreme demands for cleanliness, dimensional control and properties. In most cases they are used for medium-sized to large batches of tablets with small dimensions and precisely defined shapes and surfaces. These are exactly the properties that apply to the carbide indexable inserts used on cutting tools.

No other company in the world combines the know-how from these two fields. Working against this background, Fette has designed and developed a powder metal press from the ground up, offered in three different versions: the MP 120/250/500, for maximum pressing forces of 120 kN, 250 kN and 500 kN.

The crucial factors that give these presses such outstanding market presence are their precision, flexibility and accurate reproduction of all working steps. When combined with the robot press-to-sinter tray transport system Roboworker RAG 2000, the MP 120/250/500 creates an automated pressing cell for insert presinter production.

It is critical to the economic viability of index production that the level of production precision achieved either eliminates the need to rework the pressed blanks or reduces it to such a low level that it is no longer economically significant.

While high-quality pressed blanks are one contemporary production requirement, cast-iron documentation of the quality status of every blank is the other. Both of these requirements are met by the MP 120/250/500. This begins with the provision and supply of the metal powder.

Fette’s MP120/250/500 metal press, with Roboworker RAG 2000

The pressing procedure is typical of the PM industry. A die with the exact shape of what will become the indexable insert, but with a volume some 40 per cent greater than the final product is filled with the metal powder by a filling shoe. The die has extremely good surface quality and is machined to within a few µm, allows for the shrinkage of the pressed blank during sintering. It is closed from beneath by a lower punch. A pin keeps the hole for the indexable insert's fastening bolt clear. Accurately defined filling quantities determine dimension and shape. They also prevent loss of material, and reduce the dust pollution in the press to a minimum.

The punch movements can be finely programmed, allowing accurately repeatable compression and ensuring that planned density distribution within the pressed blank is achieved. In addition to dimensional accuracy and a clean surface, this is the most important criterion for the quality of the blank.

Adapter unit with upper punch above the die

The compression compartment with direct compression force measurement for the upper and lower punches

The best possible stress figures in the machining process are achieved through the defined density of the unsintered indexable insert. This carefully adjusted density raises the insert's edge strength, and minimises the risk of premature wear at the cutting edge. The result is even wear during the machining process. This is of considerable significance to the service life of the tools fitted with these inserts.

The vertical precision with which the punch is positioned relative to the die is 3 µm and the repeatability of the punch positioning is better than +/- 1.5 µm. This means the critical location on the indexable insert, the cutting edge, is produced with extreme precision.

Position measurement that is free from expansion effects contributes to this. It is based on a parallel arrangement of the measuring system to the die being reduced to a very short distance, only that between the tool holder and the die. The incremental measurement is passed to the controller every millisecond. The resolution of the measuring system is 0.08 µm.

Adaptable to changing conditions

The upper and lower punches move synchronously over the entire travel range. These movements allow the user to check the maintenance of extremely tight tolerances by comparing the pre-programmed curve with the curve actually followed, as recorded every millisecond.

In parallel with the pressing process, accurate measurements are made of the force (with a Lorenz load cell) positioned within the force transmission path - exactly where the force acts in the immediate neighborhood of the punch.

The force figures from the two punches, above and below, are documented in the log and are continuously available for analysis and control. This more accurate method of measurement makes it possible to adjust the filling depth more frequently and omit the otherwise usual but time-consuming weight-checking procedure.

The software is set up so that any irregularities that go beyond the programmed warning or switch-off limits will cause it to issue warnings or to switch off the press. All the accumulated measurements, including the adjustment procedures, are comprehensively logged, and are statistically analysed in real time. Production data is displayed online on a monitor.

All production data is saved and can be recalled for comprehensive procedure tracing if necessary. The recall function can be used to optimise production runs.

The flexibility and adaptability of the system should assure the future of the MP 120/250/500. The rapidly changing trends in the market for cutting tools fitted with carbide indexable inserts call for high levels of freedom. Geometries of indexable inserts are becoming more and more complex, and in some cases this means that reworking through peripheral grinding is no longer possible. An example is the incorporation of geometries transverse to the pressing direction. Modular construction is fundamental to this success, making it easy to fit supplementary devices. The hydraulic system has plenty of redundancy - an important feature in preparing it for highly varied pressing tasks and compression characteristics.

The press is capable of comprehensive and entirely flexible integration into existing computer networks. Linking into the user's management information systems and operating data acquisition environments is also possible. The software is based on systems commonly available on the market, and is widely compatible.

For new jobs the control software is the provided with a complete range of specified values for all its parameters, so that basic programs can be created merely through modifying a small number of special parameters. Repeat orders only require the granulate properties to be modified. All other parameters are stored.

The high productivity of the press is shown by extremely short cycle time of 30 strokes per minute.

This advantage is leveraged in combination with the Roboworker to construct a pressing cell that produces 23 parts per minute including 100 per cent weight checking. Other additional functions available include deburring the blanks and cleaning the pressing punches.

The presses can be fitted with a variety of fast tool change systems. This ensures the possibility of low-price, economically viable production.

It's an argument that carries weight in the highly competitive market conditions in the tooling sector.