Impression die forging is a highly cost-effective manufacturing process for producing high volumes of strong, near-net components. However, because the dies (tooling) used in the process are a significant cost and time investment, it’s a priority to extend their lifecycles for as long as possible.
Although tooling is designed to last over many cycles, it will eventually wear and deform from extended use. If the same tooling is used, despite obvious wear, this will result in poor detail formation and surface defects in the parts being produced. Eventually, the tooling must be withdrawn from service and either reconditioned (known as resinking) or replaced.
Lifecycle Influences
Generally speaking, smaller dies last longer than larger ones because the loads are lower. As an example, a small-to-medium die might produce up to 10,000 parts before needing resinking, whereas a large die might produce only 2,500 parts.
Still, the total lifecycle of forging dies is influenced by multiple factors, including:
Forging Temperature
Forging is usually done hot, so the metal flows more readily and requires less force. However, this means a hot billet is placed into the die on every cycle, then contacted by the upper die as it closes.
Additionally, dies are sprayed with a lubricant on each cycle to further improve material flow. This lubricant is at ambient temperature because the carrier (water or solvent) evaporates rapidly. This repeated heating and cooling of the metal surface can result in microcracks that eventually grow and could lead to failure if not addressed.
This potential issue can be addressed by carefully selecting die material (discussed below) and by precisely monitoring temperature throughout the forging process. Dies should also be pre-heated before use to lessen thermal shock.
Tooling Material
Forging dies are subjected to high loads at elevated temperatures, which can lead to plastic deformation. They also experience significant abrasive wear as metal flows through the die cavity and into the flash gutters. To handle these conditions, the materials used to create the tooling must have exceptional strength at both ambient and high temperatures, as well as good wear/galling resistance.
The steels most often used to create forging tooling are the chromium-molybdenum-vanadium H11 and H13 grades. Both are excellent for hot work; H11 has very good impact toughness, while H13 has excellent shock-absorbing properties, making it suitable for press forging. Of course, this doesn’t mean that these specific grades will be used to create the tooling for your specific project. At Trenton Forging, our die engineers work closely with metallurgists to determine the best tool steel grade to use for your project.
Die Design
Close attention to die features can have a significant impact on life. Particular aspects to look at are:
- Flash Land & Gutter: Flash design is especially important because narrow restrictions raise loads inside the cavity. The challenge is to provide enough space for the metal to flow out while still completely filling the cavity.
- Radii: Maximizing radii reduces forging forces and stress loads, helping avoid thermal cracking.
- Adequate Draft Angles on Vertical Surfaces: Draft angles help reduce friction and wear that occur during part ejection.
- Minimizing Cavity Height/Depth: This helps reduce the loads needed to ensure a complete fill.
- Surface Finish: Smoother surfaces offer less friction to the flowing metal, which in turn, reduces the loads needed.
Process Parameters
While minimizing time and maximizing output rate are key goals in setting up the forging operation, conditions during forging also affect die life. Two factors in particular are time spent in contact with the hot billet and compression speed. The former determines the amount of heat transferred to the upper die, and the latter affects metal flow rate, abrasion, and forging loads. Process engineers optimize both to hit output and die life goals.
In multi-impression progressive dies, it becomes even more difficult to dial in the ideal temperature management and compression rate. This is where experience and specialist expertise are essential.
Production Volume
Forging tool life is directly related to the number of cycles performed and the number of parts forged. Higher volume means higher wear, more deformation, and increased thermal surface cracking.
Longer production runs do have some benefits, though. Tooling can achieve a level of thermal stability, and an even flow of billets from pre-heating can reduce piece-to-piece temperature variation.
Additionally, automated lubrication spraying systems can be integrated into high-volume forging operations to improve application consistency and reduce force variation between press cycles. Together, these factors mean dies suffer less wear and other damage per cycle on longer production runs.
Maintenance & Resinking
Beyond process control, the lifecycle of tooling can be extended through effective maintenance (cleaning, smoothing, regular inspections) and resinking, or the process of removing the die’s surface layer to remove thermal cracks. For shallow impression dies, as many as eight resinks are possible.
Localized deformation and wear can sometimes be corrected by welding on additional material and machining to the required form. However, extensive wear is best addressed through resinking, and the same is true for any thermal cracking. Die replacement may be required for extensive damage that goes beyond the die’s surface.
How Trenton Forging Improves Tooling Life
Trenton Forging has been committed to quality and customer support since our founding in 1967. As part of our mission to provide the best service possible, we design, produce, and maintain tooling for all customers and perform over 450 resinks annually. Plus, we only source high-quality tool steel from trusted mills. To further ensure quality tooling, we use 3D models to prototype tooling and support rapid design reiteration, and we’ve integrated induction heating technology to ensure precise temperature control during forging.
Visit our website to learn more about our many capabilities, or contact us today to request a quote or first article sample.
