Autodesk Inventor comes with a standard set of built-in materials, but unfortunately they are for the most part unsuitable for the woodworking trades. What you will find are a set of generic materials loosely aimed at metal and plastic trades. You will need some of them such as brass, steel, and rubber when you need to create you own content —which at this point is almost always as there is very little content out there for the wood trades. We will try our best to remedy that by offering up free content which will be located on the Parts Tab, but as for the materials, we will need to build the library. When complete, it will be made available here. There are a few barriers though which I will outline below, along with how Inventor handles materials in general..
The image above and to the right shows a quarter sawn white oak material that I have made. As you are limited to one image per material, what you need to do is make numerous ‘colors’ that will give you more representations of the given species –otherwise it will look like plastic laminate with the same image used over and over. This is perfectly fine in most instances, but if you are preparing a presentation, have a client looking over your shoulder, or just want a more realistic view on screen, you will need to create numerous versions of each species and apply them manually as you go. I’ll create a tutorial on how to manipulate images shortly, but in the long term, the program needs to be updated as to how it handles the images. There needs to be the ability to specify multiple images for a given material, whether the images should tile or not, a setting to allow random (numerous images) or default (single image) placement, and the ability to mirror or flip the images once placed. You can get a good look the way it is, but the process is convoluted and time consuming. The best that can be done at this point is to supply the needed images and describe their use.
How Colors are Applied
As stated earlier, Inventor materials are limited to one color or image per material. The grain pattern will follow the extrusion of the part as is shown in the part to the left which was extruded upwards (if the base image is oriented correctly, which is a horizontally). Some CAM programs use this schema as well to determine grain direction regardless of whether you have a bitmap that shows it. If the image to the right had a blue color, the ‘grain’ would still be in the same direction.
There are problems with this schema in that extrusions must always start with what would be the profile of the end grain, which is not a natural way to design wood products unless you are starting with pre extruded boards. A good example would be an instance where you are projecting the geometry of a complexly cut rafter tail to a new part. The easy thing to do would be to just extrude in thickness and specify the grain direction, but as-is, you would now need to create a new plane tangential to the plane that your projected geometry is on, create a sketch that represents the board, extrude this profile in length, then go back to the projected geometry sketch, enclose it in a rectangle, and extrude-cut away the negative profile. You can clearly see that the ability to easily describe grain direction is imperative if Inventor is to be adopted by any industry where grain direction is critical to design.
The only property that would generally be used by most people working with Inventor in the wood trades is mass. The mass property along with the volume will give you weight, albeit it would be a rough weight as wood weighs more with a higher moisture content.
I’m not sure if a Finite Element Analysis (FEA) tool such as Algor Simulation (image to the right) would work reliably on an orthotropic material such as wood, and inventor parts currently have no means for adding these properties to begin with. What would be needed is to have the ability to describe material properties for each of the three axes, and have all three vary according to a specified moisture content. From the Mechanical Properties of Wood:
“Wood may be described as an orthotropic material; that is, it has unique and independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal, radial, and tangential. The longitudinal axis L is parallel to the fiber (grain); the radial axis R is normal to the growth rings (perpendicular to the grain in the radial direction); and the tangential axis T is perpendicular to the grain but tangent to the growth rings.”
The most important feature would be the ability to describe moisture content as wood and wood products are hygroscopic in nature, and this fact must be accounted for in the design. There is readily available data that can be used to describe the expansion/contraction characteristics of nearly every lumber species there is, and the ability to do so would lead to a lot less product failures. In non construction industries, a very large part of callbacks are due to designs that did not properly account for these factors. Broken joints, splitting, etc., can be avoided in most cases by using the material’s expansion ratio set to shop conditions, which could then be tested against expected end-use conditions. You can do so now using contact solver and simply changing the parameter, but it is a less than elegant solution. It is also possible to add a moisture content factor using iLogic, and I will give it a shot, but it would be better to have this spelled out at the material level.
And lastly, there are the sheet goods. Most have veneered faces that need to be described, and there are tons of variables. All of which should be pretty easy to define in an iLogic ‘sheet goods’ part. When I get enough images to call a library, I will post the file here for download. Until then, progress will be posted in the forum and in the blog. I will be adding multiple materials to the iCabinet, so keep an eye on that for progress as well. For now, we just need people to donate images of the woods described in the Mechanical Properties of Wood, or, if you have reliable properties for other species, that would be nice as well. Numerous images of every species are needed, including end grain shots. Thanks in advance for any help.
Forest Products Laboratory
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