NX MCD Virtual Commissioning: The Short Version
NX MCD virtual commissioning runs the real PLC program against a physics-based 3D model of the machine inside Siemens NX (Designcenter). A virtual PLC alone tests logic. MCD tests logic against mechanics, collisions and material flow. inteliScience prepares NX models so MCD can use them. The question is which level your machine needs, not which Siemens tool wins.
| PLCSIM Advanced alone | SIMIT + PLCSIM Advanced | NX MCD + virtual or real PLC | |
|---|---|---|---|
| Tests | Logic, sequences, HMI | Logic plus drive and process behaviour | Logic plus 3D mechanics and collisions |
| Plant model | Hand-written or none | Behaviour blocks, no geometry | Physics on the NX assembly |
| Owner | Automation | Automation | Mechanical + automation |
| Fits | Module and sequence tests | Drives, timing, fault scenarios | Handling, transport, multi-axis, rigs |
The Problem: “Virtual Commissioning” Means Four Different Things
Ask three engineering managers what virtual commissioning is and you get a virtual PLC, a SIMIT behaviour model, and a moving 3D machine. All three are correct, and all three are Siemens. The purchase question is not whether to do it. It is how much of the machine you want in the loop before the steel arrives.
The German search term is “virtuelle Inbetriebnahme NX MCD”, and it usually comes from someone who already owns TIA Portal, already owns NX for the mechanical side, and has been quoted an MCD seat. The quote is easy to read. What the seat needs from the CAD department is not on the quote.
Our position up front: the levels stack. Nobody skips a virtual PLC because they bought MCD. MCD is the level you add when the failure you are afraid of is mechanical, not logical.
What Does a Virtual PLC Test Without a 3D Model?
S7-PLCSIM Advanced tests the STEP 7 program on a simulated S7-1500 instance, with or without a plant model. Siemens describes it as software-in-the-loop simulation for machine tools, production machines, cells and lines, and the S7-PLCSIM Advanced V7 Upd1 function manual (June 2025) lists an API for C++ and C# programs, OPC UA over TCP/IP, virtual time, and up to 16 parallel instances per computer. One licence covers two instances.
What it does not contain is the machine. Inputs are whatever you write to them: a test table, a small IO block in TIA Portal, or a simulation partner on the API. Fine for interlocks, mode logic, alarms and HMI screens. It says nothing about whether the gripper clears the fixture.
SIMIT adds the behaviour layer. In the Siemens getting-started example for virtual commissioning, SIMIT “maps the behavior of active components (e.g. of drives or valves)”, receives the process image from the PLC, sends setpoints on, and lets you inject error scenarios. SIMIT supports hardware-in-the-loop with real automation hardware and software-in-the-loop with PLCSIM Advanced. Still no geometry: a PROFIdrive drive block reports a position, it does not know what that position hits.
This is the level most machine builders we work with need first. We advise starting here even when MCD is already on the purchase order. If the automation team cannot keep a PLCSIM Advanced setup alive across TIA Portal versions, a 3D physics model on top will not survive either.
What Does NX MCD Add on Top of PLCSIM Advanced and SIMIT?
Mechatronics Concept Designer turns the NX assembly into a physics model: rigid bodies with mass and inertia, collision bodies, joints that define the degrees of freedom, transport surfaces, sensors and actuators, and signals that map to PLC tags. Siemens’ own wording is that MCD “brings CAD data together with a physical engine: The CAD data is made kinematic.” The Mechatronics Concept Designer product page calls it physics-based, interactive simulation to verify machine operation.
Three things matter for the decision.
First, the model is the design model. MCD is an NX application, so the assembly the mechanical team releases is the assembly MCD kinematizes, in the same file, without an export. Change the fixture in NX and the simulation follows.
Second, the signal circuit is documented, not improvised. In the Siemens example the PLC writes its outputs, SIMIT converts them into drive setpoints, MCD moves the mechanics and returns actual positions and sensor states, and the PLC reads them back as inputs. MCD can also be coupled directly to PLCSIM Advanced. For hardware in the loop, Siemens’ example 109758739 puts a real controller on PROFINET against a SIMIT Unit, with MCD supplying the kinematic model through SIMIT. OPC UA connections exist in MCD’s external signal configuration as well.
Third, the versions are paired publicly. The getting-started guide (06/2024) runs NX MCD 2406 with S7-PLCSIM Advanced V6.0 Upd1, SIMIT V11.2 and TIA Portal V19; the kinematics toolbox example (07/2025) runs NX MCD 2506 with PLCSIM Advanced V7.0 Upd1, SIMIT V11.3 and TIA Portal V20. With the June 2026 release NX became Designcenter 2606 (released June 23, 2026), with faster and smoother animations for Mechatronics Concept Designer among the listed updates, and Siemens ran the Early Access Program for Designcenter 2612 in September 2026. If your NX and TIA teams are two releases apart, that is the first project risk.
Comparison: NX MCD vs PLCSIM Advanced vs SIMIT vs Hardware in the Loop
| Criterion | PLCSIM Advanced alone | SIMIT + PLCSIM Advanced | NX MCD + PLCSIM Advanced (optionally SIMIT) | HiL: real PLC + virtual plant |
|---|---|---|---|---|
| What is simulated | S7-1500 CPU, program, communication, web server | Drives, valves, sensors as behaviour blocks, fault injection | 3D mechanics, collisions, material flow, sensors on geometry | Real CPU and fieldbus timing, plant from MCD or SIMIT |
| Mechanical validation | None | None (positions without geometry) | Yes, on the released NX assembly | Yes, if MCD is the plant |
| Timing fidelity | Virtual time, no fieldbus | Cycle-coupled, PROFIdrive telegrams modelled | Physics step coupled by time slice | Real cycle and bus |
| Setup effort | Hours (project has to be simulation-enabled) | Days (behaviour model per drive and device) | Days to weeks (rigid bodies, collision bodies, joints, signals) | Hardware bench plus one of the above |
| Who owns the model | Automation | Automation | Mechanical design and automation together | Automation and commissioning |
| Licences involved | PLCSIM Advanced (two instances per licence) | SIMIT plus PLCSIM Advanced | NX with MCD, PLCSIM Advanced; MCD Player for run-only seats | Controller hardware plus one of the above |
| Reuse of the model | Test tables, usually thrown away | Behaviour library reused across variants | Model lives with the CAD, follows design changes | Same as source model |
| Best for | Module logic, sequences, HMI, regression | Motion axes, process equipment, error handling | Handling, robots, conveyors, multi-axis rigs, anything that can collide | Acceptance, safety, bus timing |
Two footnotes. An MCD Player licence can run and connect an existing model but cannot configure it; Siemens states that a model read with a Player licence exposes only signals, not physics objects, in the SIMIT coupling. And hardware in the loop is not a fourth tool but a fourth arrangement: the real PLC replaces PLCSIM Advanced, everything else stays.
Which Level of Virtual Commissioning Fits Which Machine?
Our clear recommendation is to pick the level by the failure you cannot afford on site, not by the tool you already licence. Logic failures are cheap to fix on site. Collisions and cycle-time misses are not.
Stay at PLCSIM Advanced when the machine is mostly digital IO and sequences: modular stations, packaging modules with pneumatic cylinders, test benches with valves and relays. Write a small IO simulation block, run regression on every TIA Portal change, and stop there.
Add SIMIT when drives set the schedule: PROFIdrive axes, S7-1500T kinematics, process equipment where drive and valve behaviour under fault conditions is the risk. The behaviour library pays back on the second machine of the same family.
Add NX MCD when geometry is the risk: handling systems, robot cells, conveyors with product flow, multi-axis positioning, and test rigs for energy equipment where a moving fixture, a heavy part and a clamping sequence share one workspace. If “we will see whether it fits when it is built” appears in the design review, MCD is your level.
Go to hardware in the loop for acceptance: safety functions, fieldbus timing, and everything the customer signs off. The virtual plant stays; the CPU is real.
Not sure which level your next machine needs? We map NX model readiness and the PLC test setup in one session; see Siemens NX consulting for how we run that.
One more opinion. In our projects the MCD seat is rarely the constraint. The constraint is a mechanical department that has never modelled for simulation and an automation department that has never named signals before the panel was wired. Buy the seat after those two have agreed on a signal list, not before.
What NX MCD Needs From the CAD Model
MCD will simulate whatever the assembly gives it, which is the problem. A model built for drawings and BOM is not yet a model built for physics. Siemens says it in one line: “The machine needs to have physical properties in order to be simulated. To equip the machine with physical properties, you need to kinematize it.” Kinematizing is CAD discipline, and it starts before MCD is opened.
What we ask of the NX assembly before the first rigid body:
- One moving unit, one component. A gripper that moves as one body is one subassembly, not forty loose parts. MCD assigns mass and joints per rigid body.
- Reference sets that hide detail. Fasteners, fillets, engraving, cable clips: out of the simulation reference set. Collision bodies of type Box or Mesh belong on simplified faces, not on the full production solid.
- Joints from the design DOF, not from constraints. Assembly constraints are for placement. MCD joints (hinge, sliding, fixed) come from the axis list the automation team already has.
- Sensors and actuators where the wiring says they are. Position control, speed control, transport surface, collision sensor: each maps to a real device named in the electrical design. That name is the signal name.
- Signals and signal adapters named like PLC tags. They map through the external signal configuration to PLCSIM Advanced, SIMIT, OPC UA or the real controller. Renaming later is where signal maps rot.
- Variants handled by the variant mechanism, not by copies. If the machine family comes from part families, WAVE links or code, the physics objects must follow the same mechanism; we wrote up that choice in part family vs WAVE vs NXOpen.
The MCD objects are also scriptable. The NXOpen.Mechatronics namespace (licence key nx_mcd_core) exposes builders for rigid bodies, collision bodies, signals and signal adapters, which is how we generate a hundred signals from a spreadsheet instead of clicking them. That is NX Open work for machine builders, a separate article. The point here is simpler: a modelling standard for simulation fits on one page, and most NX departments do not have one yet.
How NX MCD Virtual Commissioning Projects Fail in Practice
Not on physics. On ownership, versions and scope.
| Symptom | Usually means |
|---|---|
| The model moves in MCD but the PLC sees nothing | Signal names diverged after a rename, or the TIA project was never set to support simulation during block compilation |
| Hours spent tuning friction and mass | Fidelity chase. MCD validates sequence, clearance and cycle time. It is not a FEM or drive sizing tool |
| Simulation runs at a fraction of real time | Collision meshes on full production geometry, static parts defined as rigid bodies, or a time slice nobody set on purpose |
| Works on one PC, fails on the next | MCD Player licence on a seat that needs full MCD, or NX, SIMIT and PLCSIM Advanced from different release pairs |
| Mechanical team refuses to maintain it | Physics built by automation on a copy of the assembly. Copies die at the next design change |
We’d advise against letting the first MCD project be the biggest machine in the portfolio. Take one station, one axis group, one product flow. Get the signal list, the reference sets and the release pairing right on that. The second machine is where the tooling pays.
And keep the virtual PLC regression running in the build pipeline whether MCD is in the loop or not. The 3D model is the visible part. The test that runs on every commit is the part that keeps working.
Frequently Asked Questions
What is NX MCD virtual commissioning in one sentence?
It is running the real STEP 7 program (on S7-PLCSIM Advanced or a real S7-1500) against a physics-based 3D model that Mechatronics Concept Designer builds on the NX assembly, so mechanics, sensors and sequences are validated before the machine exists.
NX MCD vs PLCSIM Advanced: do I need both?
Yes, if you want geometry in the loop. PLCSIM Advanced is the controller; MCD is the plant. MCD without a controller is an animation, PLCSIM Advanced without a plant is a logic test. SIMIT sits between them when drive behaviour needs modelling.
How much does NX MCD virtual commissioning cost?
We do not quote list prices; Siemens sells MCD as an NX add-on, PLCSIM Advanced per licence for two instances, and SIMIT separately. The licences are the smaller number. The larger one is the engineering time to kinematize the assembly and agree the signal list, which is why we scope model preparation first.
Can MCD connect to a real PLC for hardware in the loop?
Yes. Siemens’ hardware-in-the-loop example runs the real controller on PROFINET against a SIMIT Unit, with MCD providing the kinematic model through SIMIT. The usual sequence is PLCSIM Advanced during development and hardware in the loop for acceptance.
Do we need a special CAD model, or can we use our existing NX assembly?
The existing assembly, prepared. MCD works on the released NX model in the same file, but it needs reference sets that hide detail, components that match moving units, and joints from the real axis list. That preparation is CAD work, and most quotes leave it out.
Next Step
Want a 60-minute map of which virtual commissioning level your machines need and what your NX models are missing for it? Book a free strategy call. Talk to our engineers about NX MCD virtual commissioning