Turn Key Press Plant
PCA 1

Powder compaction

A powder metallurgical production route is almost exclusively applied when manufacturing magnets from Rare Earth - transition metals alloys. The manufacturing process for anisotropic magnets, based on the intermetallic phases Nd₂Fe₁₄B, SmCo₅ and Sm₂Co₁₇ and their modifications, requires monocrystalline powder with grains between 2.5 and 4.5 microns, which are aligned in a magnetic field and sintered to yield a dense and uniform microstructure with a high degree of uniaxial orientation. Powder compaction is the most critical step with respect to the economics of the powder metallurgical route, as well as the quality of the finished product.

The compaction of Rare Earth based permanent magnetic powders is impeded by some characteristic features of these materials as there are:

- high reactivity regarding oxygen and moisture
- poor rheological properties of the milled powders, due to the fine grain sizes and magnetic properties of these powders
- cold welding tendencies of the powders in conventional, economic tungsten carbide dies
- the relatively strong magnetic fields required for alignment

 

Press plants supplied by NKE have been developed with special consideration given to the above mentioned factors. These press plants are designed for automatic operation.

The plants are manufactured with all the peripheral equipment necessary to optimize compaction with respect to the difficult powder

The main components are:

Uniaxial press: either mechanical or hydraulic presses may be used as the base of a plant

- mechanical eccentric presses: we use presses of type Dorst TPA 6 - 70 and Dorst Dacs 30
- hydraulic presses: type NKE PCA 1, covering maximum press forces between 100 and 1400 kN

Tool adaptor: the presses are equipped with tool adaptors, which are clamped between upper and lower ram. The adaptor is easily removed from the press for tool change and setting, such reducing tool change time to a minimum.The design of the adaptor is done under special considerations of the magnetic circuit.

Magnetic aligning system: There are two different basic adaptor designs for the compaction of Rare Earth magnet powders.
Adaptor design with the aligning field orientated parallel to the pressing direction: the aligning coil surrounds closely the tool.
The adaptor provides the path for the magnetic flux.
Adaptor design with the aligning field orientated transverse to press direction. Two coils create the aligning field. A magnetic yoke conducts the flux. The adaptor base plate forms part of the magnetic circuit.

 All other tooling pieces and adaptor components have to be non magnetic.

Powder supply: A two stage powder feed system is applied to obtain consistent cavity filling . The powder flows from a hopper via a feeder into the feed shoe. A constant powder level within the feed shoe is critical for consistent cavity filling. Therefore the design compensates for the poor flow characteristics of the magnetic powder. Die filling may be done just by gravity filling or by means of a magnetic sucking field. In case of gravity filling shaking mechanisms within the feed shoe yield homogeneous filling.

Tool lubrication system: Automatic tool lubrication can be achieved by means of wetting the die cavity walls with an organic liquid. The advantages of the liquid technique are:

- an extra production operation for blending in the lubricant is not required,
- the lubricant is removed completely before sintering with ease,
- lubrication dosage is fully controlled and adjustable during press operation.

The liquid technique is standard on Dorst/NKE press plants designed for R.E. permanent magnets.

part removal and cleaning unit

press controller

NKE´s hydraulic presses of type PCA 1 are available with maximum press forces between 100 and 1400 kN.

A four column design offers maximum flexibilty regarding the day light dimensions of the press and allows adaptations to special customers wishes.
As standard four hydraulic cylinders are installed: upper (A-) and lower (B-) main cylinders, core rod cylinder integrated in the B cylinedr and feed shoe drive cylinder. Press forces and speeds of the cylinders are optimally controlled by servo solenoid valves with integrated amplifiers. Each cylinder is energized by its own hydraulic circuit.

DOWNLOAD here
Standard technical data of PCA 1 presses (as Word - Document)

PCA 1 presses may be equipped with parallel magnetic aligning systems as well as with transverse magnetic aligning systems.
Optimization of the magnetic circuits by means of Finite Element calculationsand the application of latest contemporary techniques in designing the power supply for the aligning coils yields highest aligning fields in very short times.

DOWNLOAD here
Two examples (as Word - Document)

Press Control System

When operating the press plant in automatic mode, constant press density and press height are critical for near net shape pressing, in order to optimize the yield and costs on the sintered magnets. An accurate control system is the base for consistent quality and economic conditions.

High accuracy and process reliability is achieved by means of a high sophisticated press controlling system. NKE press plants are equipped with electronic press controller corresponding to latest contemporary technologies.

The controller monitors and controls the function of the press plant. Encoders are used for monitoring the position of the cylinders and the feed shoe, and transducers monitor the pressing forces. Programming is done menu guided by means of a screen. A luminous diagramm indicates the actual state of the peripheral equipment.

The main features of the controller are:

- adjustment and controlling of all parameters related to the movements of the press,
- controlling and monitoring the functions of the magnetic aligning system, powder feed system, tool lubrication, part removal unit, and handling units for the green parts,
- automatic filling height correction and adjustment,
speed variation of main drive motor by frequency controller,
- 3 operation modes: manual, single stroke, and continuous operating mode,
- safety control,
- visual error indication,
evaluation of press data using  statistical process control techniques,
interface for integration into manufacturing and controlling system of the production line.

Press plants, supplied by NKE offer all the potential for economic, high accuracy compaction of Rare Earth permanent magnetic powders, meeting all the criteria as dicussed in this report. The variety regarding type and maximum force of the press, and the flexibility in designing the peripheral equipment allows the optimum choice with respect to the specific spectrum of magnets to be produced. The press plants are a key tool in achieving technically and economically competitive advantages in the open market place.

A very important factor is the pre- and after sales service offered by NKE. Personnel training at their works or on the customers site is available, whilst technical assistance is for the disposal of the clients to optimize their press plants.