Using special form tools in your CAM system

September 27, 2011 By cjordan Leave a Comment

For machining some applications, the easiest way to produce a shape is to use a special form tool. To use this effectively in your CAM system you need to be able to define the cutting portion of the tool, the non-cutting part and the control point.

Using special tools in your CAM system

By specifying the control point, the CAM system should be able to accurately drive the tool along the geometry you have defined for it. With the information about the cutting edge it should also be able to machine the special form and avoid a collision with the holder, the non-cutting part of the tool and the job. If your CAM system has rest modeling, the system will know what is left after you have used the special tool. It will then be able to use that rest model for subsequent operations so that tool loads are kept low and the part is completely and accurately machined without any sudden dig-ins or shock loading.

With this technology, you can combine standard tools with special tools to reduce machining time and get exactly the results you want for the finished part.

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CADCAM Stock Models – Part 4

May 19, 2011 By jjaje Leave a Comment

Since starting this corporate blog back in September of 2010, this current series on Dynamic Stock Models has not only been rewarding to write, but has generated some commentary among Twitter and certain CADCAM forums.

There still seems to be many people that think a Dynamic Stock Model simply is used to constrain cutterpaths from one cutterpath to the next. While this is in part true for a Static Stock Model, it is far from explaining all the benefits of using a Dynamic Stock Model. For a description of some of the differences between the two, read Part 2 of this series.

This post is going to highlight some other benefits of stock models, especially Dynamic Stock Models.

Dynamic Stock Model: Knows stock condition during calculation

As previously mentioned, the Dynamic Stock Model knows the stock condition during calculations (as necessary). So besides the reliability, efficiency and safety this provides for toolpath calculations it can also benefit certain other cutterpaths.

Trochoidal Cutterpaths

Trochoidadl Cutterpath

Trochoidal Cutterpath

Many CAM systems have a form of Trochoidal movements in roughing applications. Recall that the reason for making the Trochoidal movement is to not allow the tool to exceed a particular width of cut. In an extreme case, instead of cutting with 100% of the cutter width, Trochoidal cutterpaths can allow for cleaning out and entire area with a non full, 100% width,  cut.

The real question to ask is, how is the CAM system determining the actual cut width on the cutter? Most systems are doing this by examining the individual cutterpath offsets and corners and finding the theoretical width. The better way, of course, is to base it on the actual stock remaining at that point in time, which is exactly how the Dynamic Stock Model works. Actual measured cut width versus calculated theoretical width logically makes sense.

Plunge Roughing

Plunge Roughing

Plunge Roughing

Plunge Rough

Plunge Rough

Many people have tried Plunge Roughing with mixed results. Part of the problem is the retract movement of the cutter after the plunge cut. As the picture at the right shows, it is best if after the vertical cut, that the tool move up and away from the wall it just cut against, then retract for the next cut. This movement keeps the inserts from rubbing on the way back up, extending tool life and increasing safety. Again, if you are not updating the Stock Model in a Dynamic fashion, as it is calculating, then you can not know where there is and is not material and you can not perform the step away prior to the retract the safest way.

RestMachining

WorkNC was the first CAM system to introduce automatic remachining. Where a smaller tool is used to mill residual material leftover from larger tools, all in a completely automatic fashion.

Typically in RestMilling, one can input a reference cutter or less commonly use a stock model. With the reference cutter, the CAM algorithm finds all the theoretical areas of additional material by analyzing the CAD model and looking at the corners and valleys in the part. Quality of the areas found to remachine are only as good as the algorithm used to find it.

Utilizing the stock model, the remachining areas will be based on the actual remaining stock, and not theoretical corners. This method can also be more efficient, especially in the instance of using different cutter shapes when finishing. In the pictures below, the part was finished with three different sized and shaped cutters, a flat, a ball and a bullnose cutter. Utilizing a reference cutter for calculations means you have to go with the ball cutter. Notice the difference in the remachining cutterpaths between using a reference cutter, and the actual stock model, making a huge difference in mill time and efficiency.

Remachine to Stock Model

Stock Model Remachining

Remachine

Remachine to Reference Cutter

Conclusions

From the previous blogs, and this one, hopefully you understand the differences in Stock Models a little better, and also what some of the advantages of using a Dynamic Stock Model over a Static one are, such as:

  • Utilizing Shorter Tools for more of your milling
  • Extending Tool Life
  • Increasing Efficiency and Productivity by optimizing cutterpaths
  • Increasing Safety for unattended machining
  • Automating routines such as Rough and Finish Remachining
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CADCAM Stock Models Part 2

May 9, 2011 By jjaje 10 Comments

In part 2 of this installment, I wanted to talk about what stock models are typically used for and also explain the difference between a Static and Dynamic stock model.

What Stock Models are used For:

If you ask people what stock models are used for, you may get an answer like re-roughing or remachining or possibly something else. This may be technically true from a feature standpoint, but from a business perspective, stock models help with two big things:

  • Stock Models Improve Efficiency
  • Stock Models Improve Safety

Stock Model Re-roughing:

Stock models, as mentioned before, show the state of the stock at some point in time. Their first use in CAM software, was for automatic re-roughing of parts. Basically one would rough a part with a particular sized tool, update the condition of the stock, then automatically re-rough the remaining material. Depending on the size of the part, it is not uncommon to use several different sized tools to complete the roughing operations. Anytime you can use the power of computers to automatically find leftover areas to mill, that increases the efficiency of the CAM programmer, and saves him from certain tedious tasks of trying to do that work manually.

This is basically shown in the colllection of pictures below. Where you may start with a solid rectangular block, eventually it is roughed with smaller and smaller tools, until the programmer/machinist is ready to move on to other operations, such as semi-finishing.

Stock Model CAM software

Stock Models after each operation

Dynamic vs Static Stock Models

Static stock models are where the CAM software knows the condition of the stock material at the beginning and end of the cutterpath calculation, but it does not update it internally during the calculation.

Dynamic Stock models update the condition of the stock during calculations. To use an analogy, for those readers that mow their lawns, as you mow, you can see the grass that has been removed, and what remains to be milled. You use your intelligence to make optimized cuts to reduce the amount of effort you have to spend to mow the lawn. Dynamic stock models do the same thing.

For example, in a Dynamic Stock Model, the software algorithm would know the condition of the stock not just at the beginning and end, but also during, as illustrated in the picture below.

Dynamic Stock Model

Dynamic Stock Model

So the Static Stock model can make you more efficient when programming the model. Dynamic stock models can actually make the cutterpath more efficient, because it has a better internal understanding of where the tool has been and not been. For example, look at the picture below, you may want to click on it to blow it up larger. This is a simple example, but note the areas marked with the red arrow. Many CAM software packages connect all of the offset sections (shown with the straight red line), however that is not really necessary as the stock had already been removed.

Dynamic Stock Model

Move to next pass without closing loop

Just like when mowing your lawn, you can move into the next pass as soon as the material is cut, without needing to completely close the loop. Depending on your feeedrates, this may save one to a few seconds. Multiply a few seconds saved, times each loop, then multiply that by the number of depths and all of those seconds saved start to add up to a real savings of mill time. Customers often ask why our parts come off the mill faster than similar parts from other CAM software. The answer is that it’s never one big thing, it’s the sum of a whole bunch of little things, like the efficient cuts utilizing a Dynamic Stock Model.

A secondary benefit to not closing the loop gets to the safety aspect of dynamic stock models. It is safer for tools to stay engaged in material, and not have unnecessary exits and entries into material. By utilizing a strategy as outlined above, the tool stays engaged in the material without those superfluous exits from and entries into material. This actually extends insert life. So something that makes things more efficient, actually makes it a little safer.

In the next blog, we will look while the Dynamic Stock Model makes some things safer, it will actually make those things more efficient.

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CADCAM Stock Models part1

May 4, 2011 By jjaje 2 Comments

We are going to dedicate a couple of blog entries on the concept of a stock model and how it is used by CAM software and its importance to the milling process.

CAM Stock Model

Remember that milling is a process where you get the desired shape via a material removal process, versus some form of additive process. You start with some amount of material, which we will refer to as the stock. You then remove, via milling machine, cutters and usually CAM software, what you don’t need, leaving the finished part of what you do need.

So the stock model is simply what the material that you are milling looks like.

Using CAM software and milling is a process. That is you may do multiple milling operations to get to the final product. For example, you may rough and finish one side of a part, then refixture it (or use 5-Axis machining) and rough and finish other sides. So the state of the stock is changing from one operation or process to the next.

Thus, it’s important to keep track of the stock as you go through the milling process. That is where Stock Model Management for CADCAM software comes into play. What this does is give the user, and smart CAM software packages, the ability to know the condition of the stock.

Knowing the condition of the stock allows, among other things, for more automated milling routines, greater safety as the toolpath is created, greater reliability and also greater productivity.

Different types of Stock Models

For the initial condition of the stock, there are of course many possibilities. CAM software that allow for a wide range of initial stock models allow for more manufacturing flexibility. Some examples of different initial stock models are:

  • Simple prismatic shapes such as a Rectangular Block or Cylinder. These are often the most common stock models used today.
  • Castings, where there is a near constant amount of material over the whole part. Common in the automotive and aerospace industries. Note, one trend today for maximum efficiency, especially with inconsistent castings, is to use a laser or other scanner on the actual casting, and use the resultant point cloud as the stock model.
  • CAD models, when the initial stock condition can not be defined as a simple prismatic shape, or a casting, then it can still be quickly designed within a CAD system and utilized. This is fairly common with some military and medical parts.
  • Previous Parts, Sometimes you may mill or partially mill something, and the project changes or gets canceled. You can always use the condition of the stock from one part and apply it to another part down the road. Basically, the stock is being defined from an as milled state of some other part.

Utilizing stock models allows for better machining. Today’s blog was to provide an introduction to our readers that are unfamiliar with CAM software processes about one aspect of programming. In part two, we will discuss the advantage of a dynamic over a static stock model.

Until then, leave a comment below. What do you think of stock models? Does your CAM software use them as well as you would like? What are other benefits to stock model management?

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