Designing your product
Now that you have developed your grand idea, the challenge becomes transferring the conceptual design from your mind into a three dimensional design complete with dimensions, materials, tolerances and working parts. There are several ways to do this. You can, for instance, begin cutting paper or working with clay. Physically building a model of your product using available materials is a perfectly legitimate way to refine the design. Alternatively you can sketch various aspects of your design with pad and pencil. In the end, however, you are forces to assemble engineering drawings before moving to the next phase of your design.
The next design phase is 3D CAD. For those unfamiliar with the term, 3D CAD is three-dimensional computer-aided drafting. Within the CAD design package, you virtually build up a model of your design. Need a block? Start with a rectangle in two of the geometric planes and extrude that rectangle in the third plane. Want a hole in the block you just built? Draw a circle and extrude that circle through the block. But this time, you remove volume from the extruded cylinder to make the hole. You get the idea. There are hundreds of commands available within the CAD program build the conceptual idea.
There are many 3D CAD software packages available. You get what you pay for. Not only is a robust 3D CAD expensive, it has a very steep learning curve. SolidWorks(C) is one of the main software packages used within the product design industry. Solidworks also evaluates the strength of the part you’re building, can put together assemblies of many parts. Assemblies can be evaluated for part interference, clearances, and a variety of engineering tools to help design your product. You can size motors for the moving parts, and can eventually output the files necessary to have these parts built by a machine shop. Solidworks currently sells for about $10,000 and requires a pretty good computer and about a year of time to learn the basics to use this program. Being an engineer also helps.
OK, what if you, the person with the idea, don’t have the ability to transfer the idea into the computer. This is where you are going to have to hire some work out. To convey your design to the engineer or designer you will need to list the design criteria on paper and describe your design intent. Everything is about design intent. What do you want your product to do? Does it need to be strong? Pretty? Will there be moving parts? If so, what do they do? How does your design fit together? The list, even for small assemblies, can be large. While it seems to you that everything about your design is obvious, it is only obvious to you.
While there are other CAD programs out there, I am somewhat familiar with the SolidWorks platform. This program, made by Dassault Systemes from France, has been used for building design drawings for 20-30 years. This program is extensive. I’ll try to describe the scope of SolidWorks (SW) in design and manufacturing to give you an idea of it’s capabilities.
Like other CAD programs, this program lets you build your design in the computer. The basic design element of SW is the PART. Everything begins with a part. You build your part by extruding shapes, sweeping shapes, and lofting shapes. You can place holes in the solid volumes you create to simulate bolt holes or cuts. You can cut square holes in your shapes, add or subtract volumes together to make a single solid shape, and slice and dice these solid volumes together to ultimately get the shape you want.
Once you design the parts you need to build your design, it’s time to go the the next step: the ASSEMBLY. Here, you bring in the files for the various parts you just built. Once the parts are imported to your file, you can begin to orient the various parts together. These are done by creating MATES. You tell the program how two parts fit together and the imported part orients itself to another part. Mates follow the rules you establish. For example, faces of the two parts can be in the same plane. Or they can be concentric for cylindrical surfaces such as a bolt and a hole. If two parts are constrained properly, they can rotate. Or they can be fixed in space. You would certainly expect an engine cylinder head to be bolted into place and not move. The shaft, however, needs to rotate and the piston needs to move up and down.
Once the assembly is put together, you will need to check for interference. SW has no problem with one part moving through the volume of another part. However, that can be problematic and expensive if you try to build the part. SW comes with a variety of tools to make sure that part do not interfere with other part and can save the designer great sums of money and consternation to evaluate the fit of an assembly. If a part needs to be modified to prevent it hitting another part, it’s easy to do in SW. Just edit the part dimensions and put it back in the assembly again to check fit tolerances.
Now it the time to evaluate the strength of the assembly. First, choose the materials that the parts are made from. Are you building it from steel or aluminum? There are hundreds of materials built into the SW program, and more can be added should you need it. After choosing the materials, pick which part of the assembly doesn’t move and which part is loaded. How much and what direction. Then run the simulation to see if any part fails. This is an iterative process where you run the simulation, check the results, and beef up the failing parts if you need to. The goal is to get realistic evaluation on what is called the safety factor. The safety factor is the ratio of two numbers: how much stress the weakest part in your assembly will experience compared to the breaking point (ultimate stress before failure). You want to see a safety factor greater than 1.0 as a number less than 1.0 means the part fails. Usually, safety factors should be in the 2.0 range and can depend on how well the expected loads are characterized. Remember, there are all kinds of loads your part will see, not just the expected working load. If motors are involved, consider the stresses involved during start up and shut down. Or when the motor binds. Will the part be dropped? How?
A robust system such as SolidWorks can also include a flow simulation. If you are building parts with fluids, you can perform a flow simulation to make sure that the fluid flows correctly and without cavitation that can damage the part. You can also size motors to transfer fluids at the designed flow rates.
In addition to flow analysis, you can also perform a heat transfer analysis. Here you would check the flow of heat through the part to evaluate the stresses involved with expansion and contraction of metal parts. Will the part buckle if it gets too hot? How much will a certain section of the part move if another portion of the part gets hot?
Thousands of parts and assemblies can be put together in a Solidworks model. When you think of the complexity of an automobile, where thousands of components must fit together correctly, you begin to grasp the magnitude of the capability of the Solidworks model.
In summary, Solidworks is much more than a drafting tool. Design, simulation, form and fit are all possible within the realms of the computer. The next installment of this article will look at bringing the design into the real world by discussing the role to 3D CAD and part manufacturing. Stay tuned at the techniques and tools as we explore the next frontier of manufacturing.