## LS Dyna

#### Tool Design

• Fernando Torres
Subscriber

Hy! I recently got a mechanical manufacturing project. BROACH manufacturing to cut splines in a hollow cylinder. Required part should carry the following dimensions after being broached (given in drawing). Problem here is how to calculate the stress on the teeth of broach while material removal, heat generation by the process and can we simulate all this "broaching environment" in ansys. Thanks

• peteroznewman
Subscriber

Hi Fernando,

Welcome to the Student Community.

Explicit Dynamics is one of the available solvers in the Toolbox that has the ability to simulate metal cutting.

• pgl
Ansys Employee
• Fernando Torres
Subscriber

I'm new here so sorry for re pasting my question. How can I check the validity of my ANSYS results whether they are true or I'm missing out some important parameters? In other words, how can I cross check my ansys results ???

• peteroznewman
Subscriber

First you have to define the specific goal of an analysis model. What are you trying to predict? That will help define what you will need for validation.

Example 1 Goal: Predict the pull force of the broach tool. Validation: Use an instrumented fixture to measure the pull force of the broach. It will also need to have a way to measure the advance speed of the tool.

Example 2 Goal: Predict if a tool tip will fracture in use. Simulate a family of tool tips of different designs and predict which ones fracture. You will have to make sure that some designs fracture. Validation: Make those tool tips and observe which tips fractured and which did not.

Example 3 Goal: Predict the temperature of the workpiece. Simulate the temperature rise for steady state cutting. Validation: Use a calibrated infrared camera to capture the full temperature field of the chip and workpiece.

Models that simulate chip formation will involve plastic deformation and failure, so you will need a plasticity material model. The workpiece is Steel 18Cr2Ni4WA, but if you choose the Johnson-Cook (JC) Strength material model, you will need to obtain the JC parameters for that material.  Where are you going to get those?

A broach is a series of single point tools that make orthogonal cuts. Perhaps you could start out more simply and build a model of a single point tool to cut a chip off a workpiece. You can even start with a 2D plane strain model to make it even simpler.

Good luck Fernando!

Regards,

Peter

• Fernando Torres
Subscriber

Thanks Sir , i tried material removal in workbench but I think I'm missing out some important parameters and I'm not getting the results right. Sometimes it says "ENERGY BALANCE TOO..... ERROR" sometimes step time too short Can you please send me some kind of ansys file in which material removal is being done. So that I can clarify my mistakes. Thanks

mhaseebomar@gmail.com

• peteroznewman
Subscriber

Here is a coarse simulation that takes 26 minutes to solve on 16 cores. Note that velocity =constant*time which means at t=0, v=0 so there is no impact that sets the workpiece oscillating and causes the maximum energy error to exceed the threshold. But I also increased the threshold, just in case : )

I made the vertical elements half size to get better resolution, but it took 47 minutes to solve.

It only takes 47 minutes to solve because I made the block 1.1 m thick and I am cutting a 100 mm deep chip.
If I wanted to cut a 1 mm deep chip, that would take 100 times longer to solve so the time would be 4700 minutes or 78 hours.  I didn't want to wait that long to show you a video.

• Fernando Torres
Subscriber

Thanks Sir! You informed me that a 2D plane strain model will be easy and simple approach to solve my broach model. I want to mention here that the dia of the broach along its length is not constant rather its increasing along its length and there are three sections of teeth on it i.e. roughing teeth, semi finishing and finishing teeth. As shown in figure. So now can I use the 2D plane strain approach or some other approach will be feasible to solve (i.e. to calculate stress on teeth) ? Thanks

• peteroznewman
Subscriber

I suggested you could study a single point milling tool using 2D plane strain, but if you download the file attached to my post and open it, you will see I created a 3D model. I just made the video from a side view because I thought that best showed the simulation. The issue with 2D models in the AUTODYN solver is that it doesn't distribute the solution to multiple cores like it does for 3D models.

Except for the Chip Breakers, the teeth on the broach are axisymmetric, so you could do an axisymmetric model but you would still have the single core limitation. I recommend you study a single tooth for your first model. You will need a hole the size made by the previous tooth and the tool with one tooth to cut the next step.

• ozkantekin90
Subscriber

I suggested you could study a single point milling tool using 2D plane strain, but if you download the file attached to my post and open it, you will see I created a 3D model. I just made the video from a side view because I thought that best showed the simulation. The issue with 2D models in the AUTODYN solver is that it doesn't distribute the solution to multiple cores like it does for 3D models.

Except for the Chip Breakers, the teeth on the broach are axisymmetric, so you could do an axisymmetric model but you would still have the single core limitation. I recommend you study a single tooth for your first model. You will need a hole the size made by the previous tooth and the tool with one tooth to cut the next step.

• peteroznewman
Subscriber

• Fernando Torres
Subscriber

Trying to do an explicit dynamic analysis but here are some problems. It gives following error before I "solve".

1."Only axis-symmetric and 2d plane strain are available for 2d explicit analysis."

Then when I shift the problem to axis symmetric it says "Parallel analysis is only supported for 3d explicit dynamic analyses"  and sometimes it says "Bounded contact is not supported for 2d explicit dynamic analyses ?

2. It gives the "bounded contact is not supported for 2d explicit dynamic analyses" when I change the problem to 2d plane strain too.

3.In 3d, while solving it generates the error "energy error too large" ?

Kindly explain the above errors and how to do a 2d explicit dynamic analyses on ansys 18.2. Will be very thankful.

• peteroznewman
Subscriber

1. Explicit Dynamics will only use 1 core when solving a 2D problem.  When it solves a 3D problem, it has parallelized code that runs on multiple cores.

2. You can't use bonded contact in 2D.  Spend time in Geometry and eliminate the need for bonded contact.

3. Get a model working in 2D first before you worry about 3D.

• peteroznewman
Subscriber

Please copy your post to a New Discussion in the Static Structural category and insert an image of the current element sizes relative to 1 mm.