The Reverse engineering process has been used for many centuries. The Romans were probably the first to use this method as described by Polybius, the greatest Greek historian of his time. Polybius reported in his works how the Roman army replicated methods developed by the Carthaginians, using an existing model of Phoenician bireme ship.
So, Why reverse engineer something?
There are many reasons to use reverse engineering of physical objects. For example, the reverse engineering process can be used if the original design is not supported by adequate documentation or if the original CAD model is not appropriate to support modifications and/or standard production methods. In some cases, the original manufacturer no longer exists nor manufactures a product but there still may be a need for that product. In other cases, with CAD software becoming more affordable, reverse engineering of current market products allows engineering companies to speed up time to market and offer a reduced cost on current products.
That being said let’s look at our project for reverse engineering.
This is a Dry Clutch for a high-end racing motorcycle. The need to reverse engineer this part is due to the manufacture discontinuing the production of this product, but there is still a high demand for it.
The scanner of choice for this project is the HandyScan 700 by CREAFORM. This particular scan has an accuracy of 0.030mm and a resolution of 0.050mm so I know that I will be able to capture all my features within the tolerance required for this part .
The workflow to reverse engineer this part goes like this:
SCAN PART > GENERATE MESH > ALIGNMENT > ENTITY SELECTION > CAD
AQUIRING THE SCAN
Let’s take a look at our Scan:
WHAT ENTITES TO OBTAIN
Let’s first talk about Design Intent, one of the first questions in reverse engineering applications is always, “do you want the data to reflect the as-built part that is being scanned, or to create a perfect CAD model reflecting the original design intent?” This question involves a little planning. You need to ask yourself what manufacturing processes will be used; CAM, casting, laser cutting, etc. and what imperfections need to be idealized. Unfortunately, reverse engineering is a process and real parts as manufactured never exactly match the unambiguous design; there are always some variations which can be shown in an inspection report. That’s why it’s important to identify ahead of time the important features that you wish to capture and how you want to relay that information for manufacturing.
From here we start by collecting the important features to use for reverse engineering. One thing to keep in mind is that this part is not perfect and for this project the design intent is to re-create the manufactural CAD model. Therefore, we idealize the model by excreting simple geometry such as cylinders, cones, planes, cross-sections and hole locations.
For example, we need to know the location of a hole and the diameter so we tell the software to extract that information from a hole on the scan. The software will assume that the hole is perfectly circular and it will only extract the hole location and diameter based on a specified tolerance that way when the entity is transferred to CAD it will be parametric.
So let’s see what this information would look like in SOLIDWORKS.
As you can see there is some parametric solids and some cross-sections which are all in their relative location to each entity. From here, we need to use our simple modeling tools such as: extrudes, revolves, lofts, etc. Since this part is symmetrical we could have created a revolve pattern around the center axis but thinking down the road this would not provide adequate information for manufacturable drawings.
Here is the breakdown of the build:
At this point we have our simple CAD model in a parametric state the only things left would be the finishing features such as: chamfers and fillets. Also, we have a cut along each fin that changes in 3 dimensions. This will be a little hard to describe and most likely will be done on a CNC therefore, we can use the surface profile from the scan to create a cut out of the solid model.
Since this cut will be symmetrical across each fin, we can use a revolve feature to cut the other fins.
Finally, we will add the chamfer and fillets.
BEHOLD we have a complete reverse engineered part.
The last step in this process is to validate your CAD model if you have access to validation software such as VxInspect. VxInspect is a dimensional inspection software for quality control and allows direct measurement comparison with CAD models to better understand scan/CAD deviations.
For more information on VxInspect or other 3D scanning solution, check back into CATI’s Tech notes for future blogs.
Thanks for reading and remember:
The engineer’s first problem in any design situation is to discover what the problem really is.
Computer Aided Technology, LLC