Thermomechanical Treatment Simulator (TMTS) is a specialist machine that Servotest has created for metallurgical research. Between 1995 and 2005 Servotest has built around 7 of these complex machines. I don’t know if we compete against anyone else with these machines.
The production of steel (and other metals) usually involves a mechanical process (rolling, etc.) and the temperature of the metal during this process is extremely important. In fact, choosing the correct temperature can improve the qualities of the metal.
A TMTS machine facilitates research into metal production by using a servohydraulic actuator to simulate the mechanical process and a Fast Thermal Treatment Unit (FTTU) to heat and cool the metal sample.
A TMTS machine has several important components:
Servohydraulic actuator
High forces and high velocities are required to replicate the mechanical processes and hence the actuator will use a large (1200 l/min) valve (or valves) and accumulators (2 valves gives 3 m/s at forces upto 500 kN). The test stroke is relatively short, less than 50 mm (100 mm stroke actuators). A second actuator, called the wedge actuator, is used to stop the main actuator at the end of the test stroke. A third servohydraulic device, usually referred to as the robot, is used to place the test samples in the correct position under the main actuator.
FTTU
Heat and cool the sample in a control manner between room temperature and 1200 °C.
TMTS Software
Specialist UI interface to facilitate the very specialised tests. The software and control system configuration also include a number of features to improve machine performance and data analysis.
It should be noted that, as with everything Servotest does, each TMTS machine is slightly different to the one before because each customer has a different budget and slightly different requirements.
This article is this first phase of an attempt to address a number of issues Servotest has with TMTS machines:
Frank
Traditionally Frank has done (or directed) a great amount of the work that goes into TMTS machines. Frank understands the principles behind the TMTS machines, the mechanics and the software. It is important that this knowledge is dispersed around other Servotest engineers so that it is possible support existing customers and sell more machines.
DCS
The TMTS software is only available on DCS hardware. As DCS becomes older, and used less, it is going to become more and more difficult to support it (there won’t be any software engineers who can work with it). If Servotest wants to sell more TMTS machines we will have to use Pulsar hardware and create some new TMTS software.
The TMTS software uses a number of folders for storing the tests specs and results.
c:\servotst\testspec
c:\servotst\testdata
c:\servotst\tempdata
There will also be a DCS database folder (whose name is different on every job) and c:\servotst\servotst.ini.
The TMTS application comprises/requires the following files:
TMTS program file (.exe). Each job has its own program file, usually named after the original customer name. For example, The Arcelor program file is called IRSID.exe because Arcelor was originally called IRSID. Just to be difficult IBF has 2 program files IBF2.exe and IBF2NR.exe. (c:\servotst)
In some cases there is a French translation file with the same names as the program file, for example CRV.frn. In SourceSafe? there is a CRV.frn and an IRSID.frn. (c:\servotst)
HOOGOVEN.DLL (c:\servotst)
CURVEFIT.DLL (c:\servotst)
SVUFILE.DLL (c:\servotst)
DOORCLOS.BMP (c:\servotst)
DOOROPEN.BMP (c:\servotst)
HOOG.BIN (c:\servotst\DSPCode?)
HOOG.PCI (c:\servotst\DSPCode?)
CSCOMBO.VBX (c:\winnt\system)
CSSPIN.VBX (c:\winnt\system)
CSVLST16.OCA (c:\winnt\system)
CSVLST16.OCX (c:\winnt\system)
SSBC.VBX (c:\winnt\system)
VTSS.VBX (c:\winnt\system)
VTSSDLL.DLL (c:\winnt\system)
To reconstruct a TMTS computer the following things are required:
database
servotst.ini
generic install disks
TMTS install disks (unfortunately the maintenance of these disks is a bit patchy so what's on servodem is not always the latest)
TMTS folders as above
Backing Up
Customers should be encouraged to:
keep the generic install disks
back up the database and servotst.ini
back up the TMTS folders
back up the application files or check they have an install disk with the correct files (these files don't change so this only has to be done once)
servotst.ini contains a test counter which increments every time a test is run and should match the results available in testdata hence these 2 things should be backed up at the same time.
Swapping Computers
When the customer buys a replacement computer the initial installation can be done at Servotest but the customer will have to do the following (unless they send us all their data files and don’t do any testing until the new computer arrives):
Make copies the database and c:\servotst\servotst.ini on the network
Make copies of existing TMTS data folders (on the network):
c:\servotst\testspec
c:\servotst\testdata
c:\servotst\tempdata
Switch off the old computer and replace it with the new computer
Replace database and c:\servotst\servotst.ini on the new computer with the ones from the old computer
In servotst.ini: * Ensure DisplayWarningIfProblem?=1
Set WaitStates?=6
Add Chassis=2 to [DSP Parameters]?
Add VffMin?=-300 and VffMax?=300 to [Generic Operate]?
Remove Password entries
Remove BlockProgrammer? entries
Add FilteredVelocity?=Vitesse (x20 Filt) just below Velocity20=Vitesse (x20)
Add LargeServoDrive1?=3 Stage Pilot Drive just below SmlServoDrive?=SV 38 Servo Drive
Run TMTS
Complete Install
To do a complete install on a new computer (this is normally done by Servotest):
Install Windows2000 and latest updates
Create c:\servotst
Copy the servotst.ini to c:\servotst
Copy the database folder to c:\servotst
Run the generic installation
Restart the computer
Install the TMTS application by copying the files from the install disk
Compliance
The inverse of stiffness i.e. the amount a body deflects when a force is applied. Usually m/N or mm/kN.
Deformation - Elastic and Plastic
Deformation is a change in shape due to an applied force. TMTS test are all about deformation!
There are 2 types of deformation, elastic and plastic. Elastic deformation is reversible and plastic deformation is not.
The research done with TMTS machines is usually focussed on the plastic deformation of the material.
http://en.wikipedia.org/wiki/Deformation
Plane Strain
Type of test where the material deformation occurs in a single dimension (or plane) i.e. a rectangular block is squashed and it only gets wider.
Take some pictures!!
Stiffness
Stiffness is the resistance of an elastic body to deflection by an applied force.
http://en.wikipedia.org/wiki/Stiffness
Strain
Strain is the geometrical expression of deformation caused by the action of stress on a physical body, strain expresses itself as a change of size or shape. Strain is fundamental to all the experiments done with TMTS machines.
Strain is given by “change in length / length” or “delta l / l”. The TMTS software tends to refer to height rather than length so you may hear the phrase “delta h / h”.
http://en.wikipedia.org/wiki/Strain_(materials_science)
Strain Rate
Strain Rate aka rate of change of strain. This is an important parameter in the TMTS tests.
TMTS
Thermomechanical Treatment Simulator
Upsetting or Uni-axial
Type of test where the material deformation occurs in all horizontal directions i.e. a cylinder is squashed and as it gets shorter it remains a cylinder but the diameter gets bigger.
Take some pictures!!
Most customers require the test data in a MUS file which can be used with their own data analysis software.
I don’t know what a MUS file is and I think that the mus extension is used by some music software.
The TMTS software takes various Servotest files created during the test and produces a single MUS file for the customer.
The TMTS software keeps a record of all tests performed. I’m not sure what’s in the record or how much it is actually used.
The deformation is actually an impact test that can be considered in 2 parts, the approach and the actual deformation.
The Approach
The main actuator starts above the sample so that it strikes the sample at a given velocity. The test starts with actuator moving towards the sample at the test velocity or 20 mm/s which ever is largest (when the test is slow we approach at 20 mm/s and slow down just before impact, this helps to reduce the test time).
The Deformation
Perform a velocity profile to produce the reqired strain rate.
A massive disturbance occurs as the actuator strikes the sample (we go from approach to deformation) i.e. the load rises extremely rapidly which makes it extremely difficult to control the actuator. Consequences of the load rising:
The machine frame deforms. The increasing load means the machine frame bends so that the actuator body is moving relative to the piston rod i.e. we see a velocity but it is not the piston rod that is moving. The machine frame is actually pretty stiff and in most Servotest applications machine frame deflection is not a big problem. Unfortunately TMTS tests are performed over very short distances, a typical test could squash a 10 mm sample down to 3 mm, so if the machine frame deflects by 1 mm it is significant.
The oil gets compresed. As the load increases the oil in the cycliner compresses more so oil is being supplied to the cyclinder but it is not making the piston rod move forward.
Luckily the region of the test just after the impact is not too important because the sample is in the elastic deformation region, the important part of the test is during the plastic deformation.
TMTS deformations are done using replay and files created by the TMTS software. The test is primarily driven using a velocity command and the velocity feedforward input of the servocontroller. The velocity command is created from the desired strain rate (and other test parameters). TMTS tries to compensate the velocity command for the machine frame compliance and oil compressibility, it can do this because the test parameters include an estimate of the initial load i.e. if you know the load you can estimate the machine frame deflection and the oil compression and increase the drive accordingly. The velocity command is integrated to create a displacement command, this displacement command should equal the actual displacement and give zero error thus allowing the velocity feedforward to provide all the control output.
For the fastest tests it is necessary to do data acquisition at rates higher than normally available on DCS i.e. upto 20.48 kHz. These high rates are achieved by logging the unlinearised transducer values, only real transducers, and not debug signals, can be logged like this. These high speed files are only created during short, high speed parts of the tests.
The normal logger is used for large parts of the test. Some parts of the test take a long time so the logging rate is sometimes varied within a single data file i.e. the sbf file is non-standard!
Several files are created by a TMTS test, fast logger file, slow logger file and sec file.
The database provides a displacement corrected for the machine frame deflection using the load and an estimate of the machine frame compliance.
The natural frequency of the LVDT is such that the measurements made at high frequencies are affected by it. When DAP opens a TMTS data file it removes the oscillations caused by the LVDT natural frequency.
The natural frequency of the load cell is such that the measurements made at high frequencies are affected by it. When DAP opens a TMTS data file it removes the oscillations caused by the load cell natural frequency.
A wide range of velocities from 0.1 mm/s to 1500 mm/s is required. Velocity is important so a velocity transducer is always used. 2 velocity ranges are created by using a +/-10 V input for full range and a +/-0.5 V input for the low range.
On the low velocity range transducer and electronic drift becomes significant so the TMTS software always tares the low velocity input before a test.
The natural frequency of the velocity transducer is such that the measurements made at high frequencies are affected by it. When DAP opens a TMTS data file it removes the oscillations caused by the transducer natural frequency.
In essensce the TMTS test is about hitting a bit of metal, sometimes it is hit once, sometimes it is hit several times (with precise short delays) and sometimes it is hit several times with changes in temperature between.
A common process in metal manufacture is rolling a large, hot ingot through several (upto 10) stands where each stand rolls it thinner. As the metal moves between stands it cools. This process is simulated on the TMTS machine by heating the sample, hitting it, cooling it, hitting it again, etc.
In the TMTS software tests are built up from segments where each segment defines some function which could be temperature related, time related or a deformation. Putting these segments altogether makes it possible to simulate processes as described above. All TMTS tests must contain at least one deformation.
There are a number of types of deformation or ways of doing the deformation:
Constant strain rate
Constant stress
User defined profile
Zener-Holomon
There are also some options for what happens at the end of the deformation:
Nothing, the test stops
The actuator holds its final displacement. In this case the load drops as the sample relaxes.
The actuator switches to load control and maintains a constant load (or more precisely a constant stress).
It would be great to sell hardware updates but a hardware update is likely to be extremely costly and therefore difficult to justify!
I believe Servotest has to continue supporting DCS hardware in the foreseeable future. We are shipping new TMTS systems in 2005 (TMTS has to be DCS) and the customers are going to expect support for these for a number of years.
The Pulsar hardware is unlikely to provide any measurable improvement in accuracy because the electronics is not normally the limiting factor.
Pulsar hardware has the following advantages but I don’t see why any of them would justify the replacement of a perfectly servicable DCS system (although I suppose this it’s up to the customer):
supports Windows XP
possible use with a laptop or any spare PC with USB2
Demo Unit is available, can be used for offline preparation or simulation
PC maintainence and updating will be easier
module TEDS means replacing modules is simpler than replacing DCS cards
transducer TEDS means replacing transducers is simpler
Pulsar cables are easier to route and easier to replace if damaged
No signal degradation from optical cables with lengths up to 300m
increased DSP processing power with upgrade path from OEM supplier
extended servicability because it is built using modern components that are easily obtainable
Analogue I/O can be positioned where it is required
Potential upgrade to greater than 16 bit accuracy using new mdoules when available
A hardware update would require that all the project engineering done with the DCS hardware be repeated hence the likelyhood of high costs.
Hopefully we will meet situations where the customer is doing a complete lab update, including actuator refurbishment, in which case the cost of changing DCS hardware to Pulsar hardware will not be so significant with respect to the entire project cost.