To manufacturing companies that depend on stamping, the question is: how many more uses can this die have? It may not make a million dollars question (not literally, of course!), but it certainly makes a difference. Until now, unfortunately, there is no singular, simple answer. The service life of a metal stamping die is unpredictable unlike a lightbulb which has a reasonably predictable life. It is not realistic to expect one number, but having knowledge on which variables is important.
Why There's No Magic Number:
Consider a die as being not a frozen instrument but a sports star on steroids and working under the greatest physical pressures thousands of times a min. The life expectancy of this is conditioned by:
1.Die Design & Construction:
Complexity: Blank chips at simple blanking dies generally have much longer life compared to progressive die forms of many complex features per strike. The more complex, the more places it may wear out and places in which there may be stress concentrations.
Material: Basic is the quality and hardness of the tool steel (e.g. D2, A2, Carbide inserts). High grades hardened to a specific tolerance are able to withstand wear and impact much better than softer/ lower hardened grade steels.
Robustness: The application of sufficient support, clearances, judicious selection of wear plates and coatings (such as TiN, TiCN, CrN) and effective guiding mechanisms are a major contribution to both stresses and wear on important parts.
2.Operational Factors:
Press Conditions: Misalignment, over deflection, wrong shut height or unstable press contributes extreme damaging energy to the die that contribute heavily to wear and breakage.
Stokes Per Minute (SPM): Fast speed creates further heat and impact cycles within a lesser amount of time, which increases wearing processes such as abrasion and fatigue.
Lubrication: This is the lifeblood of the die where applicable and proper lubrication must be used and there should be a regular flow of lubricant to the die. It also lowers friction, cools off, eliminates galling and flushes out debris. Poor or wrong lubrication is a serious problem of early die discovery.
Tonnage: Producing at a rate close to or above the rated maximum wears out a die quite soon since it is overloaded.
3.Material Being Stamped:
Strength & Hardness: Stamping of high-strength steels (HSS), advanced high-strength steels (AHSS) or hardened material results in substantially greater die wear on the surfaces of the die (compared with stamping of lighter soft metals, such as aluminum or mild steel).
Abrasiveness: materials that have an abrasive scale (e.g. hot-rolled steel) or which contain harder particles tend to blunt cutting edges and forming surfaces quickly.
Thickness: Materials that are thicker demand greater tonnage putting more strains on the die structure.
4.Maintenance & Handling:
Preventative Maintenance (PM): Preventative Maintenance involves proper cleaning, inspection, sharpening of cutting and cutting-off sections, replacing wear parts (pads, springs, guide pins) and doing general maintenance lubrication to achieve maximum die life. Lack of PM results in the small problems turning into major disasters.
Storage & Handling: Storage of the items must be handled in order to avoid rust and handling, to avoid nicks, dents or even dropping. The process of changeover or transportation can be very expensive when the products are damaged.
Failure Modes Dictate "End of Life":
Die life never ends when it ceases to work completely; it is many times economically obsolete when the maintenance cost is prohibitively expensive, or when the quality of the parts is worn out. The typical modes of failures are:
Wear: Visible abrasion of cutting edges and forming surfaces and resulting to burrs, dimensional inaccuracies or bad part surface finish.
Fatigue Cracking: The fatigue is built up by stress cycles and causes cracking which, over time, causes pieces to break off.
Plastic Deformation: The deformation of the die steel is permanent by soft spots or overloads.
Brittle Chipping: The brittle mode of failure, usually on sharp edges or sharp corners.
Galling: This is the transfer and adhesion of materials between the die and the workpiece, and results in serious surface damage.
Realistic Expectations and the ROI Perspective:
⦁ What then are normal ranges? Although it is largely subject to the influences of the above factors:
⦁ Simple high-volume blanking dies under favorable conditions may achieve 1 mil.+ before a drastic refurbishment.
⦁ Complex progressive dies that stamp materials that are difficult (stamping harder materials) may last 100,000 to 500,000 cycles between major work programs.
⦁ Dies that create very abrasive or ultra-high-strength materials may last only 50,000 cycles or less before attention is necessary.
Maximizing Your Investment:
Rather than concentrate in an impossible-to-obtain quantity of years, program in getting as much out of the life you do get:
1.Invest in Quality: Invest in quality; i.e. invest in quality design and quality materials/construction.
2.Streamline the Process: Maintain press health, proper settings and ideal lubrication.
3.Rigorous PM: Preventative maintenance should be preached and practiced.
4. Train Personnel: Handling of dies, setting and operation is very important.
5.Monitor Part Quality: Monitor wear indicators such as burr size or dimension drift to predict maintenance.
Conclusion:
The life of a metal stamping die cannot be decided beforehand. The latter is a direct consequence of the decisions that were taken in its layout, construction, use and maintenance. By learning and effectively addressing the wear and failure determining factors, dies makers can greatly increase product life and die life can be continued, quality parts will be produced at their lowest cost and the ROI of this critical capital investment. It is not so much immortality that is aimed at, and it is not a thing of chance and optimal longevity that is being aimed at, but a predictable longevity that has been optimized using hard work in process regulation and maintenance.