FAQ - Frequently Asked Questions
1. What is the difference between FAST and SPS?
There is no difference. These are just synonyms for the same technology. The term SPS (Spark Plasma Sintering) is often used in academic literature, even though it is technically not correct. No spark nor a plasma has ever been observed. Therefore, more and more manufacturers and also end users are using the term FAST (Field Assisted Sintering Technique).
2. Why are there so many names for the same technology?
This is marketing. Back in 1953, Dr. Fritsch was the first industrial producer of this technology. It has been introduced to the market under the name “Direct Hot Pressing”. Still today, this term is widely used by industrial end users. There are even customers who use verb “to fritsch” as a synonym for quick sintering. In the 1970ies the term SPS (Spark Plasma Sintering) came up which – even though it is technically not correct – became a standard term especially in the academic world. Other common names are for example Rapid Hot Pressing (RHP), Electric Resistance Heating, DC Current Sintering and Direct Current Sintering.
3. What is the difference between sintering with pulsed and unpulsed DC current?
There is no difference. The pulsed current is a marketing-gimmick. In the 1970ies an other company started to build FAST/SPS sinter presses. In order to create a unique selling proposition they pulsed the current and claimed that this creates a spark between the powder particles and a plasma. That`s why they called it Spark Plasma Sintering (SPS). Both phenomenons have never been observed but due to the pulse generator the machines became much more expensive.
Many academic papers and experts in the field of FAST/SPS sintering have shown that the sintering result is only depending on the steep heating rate, the application of pressure and the sintering time. The pulsing has no measurable effect on the sintering result (please refer to the publications of the Fraunhofer IFAM Institute Dresden and Prof. Guillon of the Research Center Juelich).
4. Why is Dr. Fritsch not manufacturing sinter presses with pulsed current?
The disadvantage of pulsing the current is that it has no measurable effect on the sintering result, but makes the machines much more expensive due to the pulse generator. This makes this great FAST/SPS technology unattractive for many industrial users because the sinter costs per piece become too high. The pulsing can even be a source of error because the sintering activity is influenced negatively if the break between the pulses is too long. Since 1953 Dr. Fritsch has put a focus on industrial applications and we will not use a technology which does not deliver any advantage – and sometimes even strong disadvantages - for our customers.
5. Is FAST/SPS sintering only an R&D technology for universites or can I really do production with it?
Up to now, Dr. Fritsch has sold more than 1000 FAST/SPS sinter presses. 95% to industrial companies from many different sectors. The machines are often used 24hrs per day on 5 -7 days per week, often partly or even fully automated.
So, yes, it is a reality proven mass production technology which can also be used for production of small series or even single parts.
6. FAST/SPS is expensive, isn`t it?
Most competitors of Dr. Fritsch produce only small numbers of FAST/SPS machines per year. And they equip the machines with a pulse generator which has no measurable effect on the sintering result. These are the reasons why their machines are often very expensive.
Dr. Fritsch produces more FAST/SPS sinter presses per year than all other manufacturers combined. And we only build in technology which is really useful. Therefore, the Dr. Fritsch FAST/SPS machines are much more affordable. That`s how this innovative sintering technique becomes so interesting for all customers who put a focus on the cost / performance ratio.
7. Which mold material is used?
Usually, graphite is used for the molds and also for the plates and electrodes. Graphite is a low cost material and has got good thermal and electrical properties. We recommend some special graphite grades, pelase contact us anytime if you have any questions regarding this.
At temperatures below 950°C also steel molds can be used. We can also give recommendations regarding this.
Sometimes thermoactive molds are used which can be heated independently from the machine. The Dr. Fritsch FAST/SPS sinter presses can be equipped with a socket on the vacuum chamber which allows to connect such molds (option).
8. Which geometries can be sintered?
Due to the uniaxial pressing system flat geometries are preferred. Very complex shapes are not suitable. For some geometries, for example very thick parts, it is preferable to produce a cold-pressed green part beforehand. Depending on the machine size and sinter material, parts from a few millimeters up to diameters of 350mm or more can be produced, often even in multiple layers. Similar is true for square parts. Please refer to the technical specifications of the machines for details regarding the electrode size and clear distance between the electrodes.
9. Can FAST/SPS also be used for materials which are bad or no electrical conductors?
Basically yes. Restrictions may apply regarding the maximum part size because materials with bad thermal or electrical conductivity tend to have an inhomogeneous heat distribution.
10. Is my intellectual property safe at Dr. Fritsch?
In contrary to other manufacturers of FAST/SPS sinter presses, we have never developed own ceramic materials, nor have we ever sold any sintered products. We will never send your data to third parties without your consent. Therefore please be ensured that your know how and intellectual property is in safe at Dr. Fritsch. Of course we can sign a Non-Disclosure Agreement (NDA) before any sensitive data is exchanged.
11. Can I test the Dr. Fritsch machines somewhere?
We have a technical application center in Fellbach near Stuttgart / Germany. There you can test three FAST/SPS sinter presses of different sizes with up to 2.400°C (4.350°F), three mixers, two granulation machines, the dosing machine and several cold presses using your materials.
Some external partners have Dr. Fritsch FAST/SPS sinter presses with fine vacuum (5x10-2 mbar). Furthermore, tests can be done at research institutes and universities in Germany, Slovakia, Great Britain, Russia, China and USA. Please contact us if you are interested in this, we will be pleased to establish the direct contact.