As OEMs and aftermarket equipment companies tighten tolerances, manufacturers face the challenge of producing stamped parts that meet and exceed their customers’ requirements. Poor die design along with scrapped or reworked parts cost everyone involved time and money. It’s critical to get it right the first time and every time.
The best way to save money on a customer’s stamping project is in the part design phase. Working closely with a customer’s engineering staff on part design allows for collaboration and adjustments before final prints are frozen and issued.
A major goal in developing parts is design for manufacturability (DFM), which includes both theoretical design drawings and an appreciation for the physical limitations of machines and raw materials in the real world. The trick is to design a part that is technically optimal, while still being able to be mass-produced. In addition to manufacturability, there are other important considerations about getting finished parts to their final destination intact and ready to use.
Solid modeling in three dimensions allows designers to develop and manipulate dies and parts quickly at the click of a mouse. Software tools, like Logopress3, include powerful features for determining the sizes of holes and tabs, locating bend-relief notching, virtually “unbending” finished parts to predict blank size, adding and removing features, and even modeling strip layout to determine the optimal sequence for progressive stamping. Special functions also show potential flaws, stress points, and areas that are too thick or thin before a part even goes to prototyping. It’s easier and less expensive to fix problems in a computer model than to discover problems on the production line.
Raw Material Selection
Using the correct raw material for the part application is critical. If a high-performance application does not utilize a high-performance raw material, the component will fail. If a high-performance raw material is not needed for the component application, part cost will unnecessarily increase. There is a balance between performance and application. Once formed into a finished part and in use, materials are subject to stresses and loads that impact their durability and performance. When considering raw material for part components what keep the following in mind:
- Electrical Conductivity
- Thermal Conductivity
- Modulus of Elasticity
- Coefficient of Thermal Expansion
- Tensile Strength
- Yield Strength
- % Elongation
- Superficial Hardness
Secondary and Post-Manufacturing Considerations
Some parts require additional operations before or after stamping. These can include:
- Plating – pre-plating may be less expensive than post-plating or coating completed parts; however, cut edges expose base metals to corrosive agents.
- Cleaning – dirt, dust, and other contaminants, along with corrosion, contribute to contact resistance, which can lead to overheating, contact erosion, and poor contact performance.
- Packaging – not only does thoughtful packaging keep finished parts safe from damage, packing inserts can be engineered to maximize capacity for easier transportation and storage.
Die Design, Manufacturing, and Maintenance
Tooling Component Material Selection
Some finished parts need to be made of high-strength or other specialized materials that are notoriously tough on dies, and may call for premium (and expensive) tool steel. Extremely large runs can also cause significant wear and tear over the life of a die. By analyzing part geometry and determining which features will result in the most wear and tear on the die, it may be possible to use premium tool steel in certain die components and less expensive tooling components in other sections of the die. This reduces the price to make a custom die without sacrificing durability.
In addition to saving money on making the entire die from premium steel, “using small inserts not only reduces tool steel cost, but also makes for easy replacement. In addition, if the insert needs to be coated, it is far less expensive to coat a small section than a larger tool steel section,” notes an article in The Fabricator.
Precise dies stamp precise parts, which saves production costs in the long run. An excellent tool for creating precision dies is wire electrical discharge machining, or wire EDM. This technology cuts hard metals, leaving a smooth surface, which requires minimal extra finishing. Die details can then be perfected with secondary grinding.
Bear in mind that while nice-looking dies are aesthetically pleasing, it is possible to over-finish them. Whenever possible, balance form with function. Surface finish and secondary grinding can achieve exact shapes and smoothness required to meet specs, but it’s also possible to do more finishing work than is absolutely necessary, which doesn’t contribute to the performance of the die.
Depending on the design of the die and the part being produced, build up of air or fluid under pressure can cause problems. Unless vented properly, air and fluids can cause die breakage and part deformations like thin spots, lumps, or buckles, all of which result in more time and money to repair or recreate a die and rework parts.
Vent holes must be sized and placed to release enough air quickly so it doesn’t have a chance to build up. For example, holes located in the die cavity reduce pressure on the downstroke, and those in the in drawing punch avoid a vacuum effect on the return stroke.
Trapped fluids, such as lubricants, also cause problems. “Within the boundaries of a die [fluids] can cause surface defects and can hydroform the metal, resulting in nonconforming part geometries and additional thinning and stretching. Excessive trapped fluid being displaced very quickly can cause the die to explode,” explains this article on venting from The Fabricator’s die science series.
Sensors and Machine Vision
According to Stamping Journal, “compact in-die and in-press vision cameras and systems can be deployed into tight spaces and hard-to-reach areas in presses and material handling robots. They can be deployed almost anywhere on the production line for guidance, inspection, gauging, and identification.”
“Consider slug marks, which often only appear for only a few parts, or even just one, and then disappear after the slug embeds itself into another part and gets carried away,” says The Robot Report. Machine vision, using cameras with appropriate resolution, speed, and lighting, can inspect parts as soon as they’re completed instead of when the whole run is finished. Identifying problems and defects as soon as they happen minimizes downtime and scrap.
Routine maintenance should include visual inspection of the punch, die, and the last few finished parts for signs of damage or defects like burrs, chips, dirt, slugs, cracks, and built up lubricant or other contaminants. Checking for proper lubrication and blocked vent holes also ensures dies are in good working order. Mechanical parts of the die, like fasteners, springs and cams, also need to be inspected. A proactive approach to maintenance means that time spent now will save time later as well as reduce scrap rates and increase first pass yield.
Even with excellent regular maintenance, all dies wear over time. Common signs of wear include burrs on parts, feeding problems in progressive dies, and even auditory clues. “Sound is another indicator of wear: New stamping presses with tonnage monitors that automatically increase tonnage as the tooling gets more and more worn will get noticeably louder as the tonnage goes up,” notes Fabricating and Metalworking.
With everything there is to consider about die and part design and implementation, it helps to have an experienced partner who can discuss your needs, explain your options, and even suggest alternatives. If you’re planning your next micro stamping project, CEP Technologies can help – please contact us today.