The concept and principle of mold life
Die life refers to the number of production cycles (stamping times, forming times) that a die can achieve while ensuring product quality. It includes repeated grinding and replacement of wearing parts, until the total number of qualified products formed before the main parts of the die are replaced.
Die Service Life: The number of times a die has been used in production. Die failure can be categorized as abnormal failure and normal failure. Abnormal failure (early failure) refers to dies that cease to function before reaching the generally accepted lifespan under a certain industrial standard. Forms of early failure include plastic deformation, fracture, and severe local wear. Normal failure refers to dies that can no longer work after mass production due to slow plastic deformation, relatively uniform wear, or fatigue fracture.
1. Normal Die Life
The number of qualified products produced before a die experiences normal failure is called the normal die life, or simply die life. The number of qualified products produced before the first die repair is called first-time life; the number of qualified products produced after one repair until the next repair is called repair life. Die life is the sum of first-time life and all repair life cycles.
2. Die Failure Forms and Principles
Although die types are diverse with greatly varying working conditions and damage locations, failure forms can be roughly categorized into three types: wear, fracture, and plastic deformation.
① Wear Failure
When a die works, it contacts the forming blank and produces relative motion. The phenomenon of gradual material loss on contact surfaces due to relative surface movement is called wear. Wear failure can be divided into the following types:
a. Fatigue Wear
When two contact surfaces move relatively under cyclic stress (mechanical stress and thermal stress), the phenomenon of surface metal falling off due to fatigue is called fatigue wear.
b. Cavitation Wear and Erosion Wear
The phenomenon where bubbles burst on a metal surface, producing instantaneous impact and high temperature, forming small pits and depressions on the die surface is called cavitation wear.
The phenomenon where liquid and solid microparticles repeatedly impact the die surface at high speed, causing local material loss on the die surface and forming pits and depressions is called erosion wear.
c. Corrosive Wear
During the friction process, the die surface undergoes chemical or electrochemical reactions with the surrounding medium, combined with the mechanical action of friction forces, causing surface material to fall off, which is called corrosive wear.
In the relative motion between die and workpiece (or blank), wear often exists in multiple forms simultaneously, influencing each other.
② Fracture Failure
When a die develops large cracks or separates into two or more parts losing its working capacity, it is called fracture failure.
Fractures can be divided into plastic fracture and brittle fracture. Die materials are mostly medium and high-strength steels, and the form of fracture is predominantly brittle fracture. Brittle fracture can be further divided into one-time fracture and fatigue fracture.
③ Plastic Deformation Failure
Dies bear large and uneven stresses during operation. When the stress at a certain part of the die exceeds the yield limit of the die material at the current temperature, plastic deformation occurs through mechanisms such as lattice slip, twinning, grain boundary slip, etc., changing the geometric shape or dimension. When these changes cannot be repaired for further work, it is called plastic deformation failure. Forms of plastic deformation failure include upsetting, bending, cavity expansion, collapse, etc.
The plastic deformation of a die is the yielding process of the die's metal material. Whether plastic deformation occurs is primarily determined by the mechanical load and the room temperature strength of the die. For dies working at high temperatures, whether plastic deformation occurs mainly depends on the working temperature and the high-temperature strength of the die material.
