Design for manufacturability to break through "The Wall"

When designing a stamping die or set of dies, engineers can avoid manufacturability problems by keeping the end results in mind and by involving the tool- and diemaker.

The conflict between the engineering and the tool- and diemaking departments responsible for manufacturability has been called “The Wall” for at least 60 years. This wall is hard to pass through, because engineers and tool- and diemakers come from different educational backgrounds and disciplines. An academic degree is needed for engineering, while a diemaker training curriculum, yearslong apprenticeship, and hands-on experience are what it takes to be a Class A tool- and diemaker.

When designing a stamping die or set of dies, engineers and die designers can avoid manufacturability problems by keeping the end results in mind. Everyone needs to know not only what is to be stamped, but also what is to be made. To manufacture almost any mechanical project, all departments, such as engineering, die design, machining, and tool and die, are needed for the best end results.

When components are designed and engineered without consulting with people from the other departments and without considering the end product, problems can occur.

Problem Case Example: Weldment

Here is an example of a problem that can occur when the end product is not taken into consideration and departments don’t confer regarding weldments.

Many stampings are just one part of a weldment. Some stampings get tinged, or discolored, when they are spot welded. Whenever welding is involved, stampings can change, even with one weld.

Let’s say you have a perfectly formed tube with a straight seam that must be joined with round stampings at each end. The stampings are end pieces the same diameter as the tube’s inside diameter that are designed to guide a rod down the center of the tube. The stamped end pieces are supposed to be spot welded at the ends of the tube off a center guide ring.

When the stamped end pieces are spot welded to the tube, the spot weld appears to work great. You take the 10 welded tubes to the quality assurance department. The QA engineer on the job inspects the parts. Well, the spot welds on the tubes and ring at the tube ends are good, but in the course of spot welding them, a wide gap has occurred in the middle of the tube seam. This is unacceptable. You now have 10 pieces of scrap.

You didn’t meet with the spot welding department so they could offer the proper welding tips. You go to the tool- and diemaker, who suggests that you use a rigid fixture to hold the inner rings. In addition, the tool- and diemaker notices that the spot weld on the outside tube is being pushed inward and creating the gap in the tube. The welder suggests positioning the inner ring with the breakaway to the outside so the spot weld pulls the outer tube to the end and closes the gap.

The engineering department has not had experience on why this made such a difference. The diemakers are familiar with the breakaway on stemmed parts. It is very important in many ways. The spot welder knew of the difference it can make in weldments.

Once these changes are made in spot welding the stamped end pieces on 10 new tubes, the tubular weldments are made correctly and pass the QA inspection.

Computer design software is great for engineers in the design of tooling, jigs, and fixtures, but the human experience factors cannot be duplicated by CAD or other design software unless the user is experienced in the application of tool and die stampings.

Consider Consequences in Designing Tolerances

Another example of the need for other perspectives on the function of the end product applies to designing tolerances.

In some types of manufacturing, tolerances are large and open. Tool and die building requires much tighter tolerances, because if you are making a progressive stamping die, you could run into stacked tolerance deficit.

This can happen because a slight miscalculation is compounded as the material travels through the die. If you have 0.001-inch tolerance, by the time you get a finished part out of the last station, your tolerance may be off by 0.003 to 0.004 in. because the 0.001 tolerance adds up during the progression.

No manufacturing industy has as tight a tolerance as tool and die because tolerances must be so precise. Usually the bigger the part, the larger the tolerances required.

Many times, pilot holes are punched in the first station of a progressive die. Piloting these holes throughout the die can ensure that tolerances are maintained. These holes also can be used to locate the finished piece to join other parts, jigs, or fixtures to aid the manufacturability of the finished product.

Accept Advice from the Experienced

The engineer who takes the advice and knowledge of the tool- and diemaker will progress in their field much faster and be more successful than their peers for doing so. A very experienced tool- and diemaker can make a stamping die from a handmade sketch and a file and mill.

It’s best if a briefing of the entire project is given to the tooling department before the design is engineered so the tool- and diemaker can offer all their experience and training to avoid errors.

Ron Hayes is a tool- and diemaker consultant, P.O. Box 517, Glen Rose, TX 76043, 580-382-1021.