Pro/ENGINEER Professionals: Test Your Expertise

by John Driscoll  

You’ve bought all the high-priced Introduction to Pro/ENGINEER books you could find. You’ve surfed the Internet for Pro/E websites until you thought your arm would fall off. You’ve taken every Pro/E course you could afford. Finally, you feel you’ve mastered Pro/ENGINEER (or are at least pretty good at it) because you can create a complex variable section sweep surface in any direction with TRAJPAR.

To see how expert at design you really are, try this little test. By selecting the correct bracket, you should be able to save your company quite a bit of money….and maybe offset the cost of some of that expensive Pro/ENGINEER training.

Challenge #1: Order the following six brackets from the lowest to the highest cost.

Assume that all options are made from the same common steel, have adequate structural strength, and have similar dimensions based on a 50mm (2-inch) square opening and .090 thick material. While you can ignore any costs of finishing or painting, note that some versions do require welding. The initial quantity is 50,000 pieces per year.

Design Specification

Option A is made up of two pieces—a “hat” section and a flat base. The parts are staked, glued or tack-welded together to keep them from separating before they are assembled to the next assembly.

Option A

Option B is a single-formed part made from a 80mm-wide strip, with two legs bent in opposite directions.

Option B

Option C is made from 2-inch square tubing sliced at 45 degrees. The holes can be drilled before the pieces are cut, and a single cut separates 2 pieces.                             

Option C

Option D is a formed part, welded at the joint for structural integrity.

Option D

Option E is similar to Option D except the holes are to the side rather than at the ends. This part is also welded at the seam.

Option E

Option F is similar to Option E except both ends are folded over. There is no weld requirement here.

Option F

Challenge #2.  Estimate the ratio between the lowest- and highest-cost brackets and provide the design reasoning behind it.

This is the pro level. A good score here puts you in the elite category.

Designers frequently argue about the “correctness” of each solution, and results often depend on how each designer interprets the design requirements. In addition, prices from individual vendors depend upon their available manufacturing equipment, the business climate, and their willingness to do business with you. For instance, are we talking about the best source economically? Are delivery times of the parts sensitive? Would it be better to deal with a local vendor to avoid shipping and communications problems? The changing cost of steel in your market and countless other factors can be important to your decisions.

Answers to the Quiz

Here is the correct order for the bracket options, along with the current cost ratios for a quantity of 50,000/year.

1. Option A uses the most material, but because it is the simplest, most flexible design, it is the cheapest to manufacture. Cost ratio = 1.0  

2. Option F is a simple roll if the vendor has the equipment. Cost ratio = 1.1

3. Option E, while similar to Option F, entails an added cost for the seam weld. Cost ratio = 1.2

4. Option D involves slightly more metal cutting and trimming on ends than Option E, as well as the separate weld operation. Cost ratio = 1.3

5. Option C is made from structural tubing, which is more expensive than sheet and usually harder to procure. The higher raw material cost is somewhat offset by the fact that this part is the simplest to machine. Cost ratio = 1.6

 6. Option B is the most expensive to fabricate and inspect because of the complexity of the bends. Cost ratio = 2.0

John Driscoll is a contract engineer. He can be reached by email at jjd_contractor@yahoo.com or (617) 922-6423.