Evaluating Conformal Cooling Circuit Hydraulics to Reduce Machine Cycle Time
Turbulent flow inside conformal cooling circuits requires managing additive channel roughness and diameter to prevent pump choking and inflated cycle times.
Stress Corrosion Cracking
Meaning
Environmental degradation involving the combined action of tensile stress and a corrosive medium leads to the premature failure of metal components. In the production of polymers, stress corrosion cracking often targets the cooling channels and fasteners of a mould when the water chemistry is not properly managed. This phenomenon progresses through the initiation and growth of microscopic pits that eventually evolve into structural fractures.
It is a particularly dangerous failure mode because it can occur at stress levels far below the yield strength of the material.
Chemical Environment
Specific combinations of alloys and chemicals create the conditions necessary for the rapid propagation of cracks. For tool steels used in injection moulding, the presence of chlorides or high oxygen levels in the cooling water triggers stress corrosion cracking. The cooling lines are often the first to fail because they are exposed to both the thermal stresses of the process and the corrosive agents in the fluid.
Protecting these surfaces with specialized coatings or inhibitors is a standard preventive measure. Monitoring the pH levels and mineral content of the process water provides an early warning system for corrosive conditions.
Stress Source
Internal tensions resulting from the hardening process or the mechanical loads of the clamping unit provide the energy needed for crack growth. When a tool is subjected to stress corrosion cracking, the failure often appears as a sudden brittle fracture without any prior deformation. This makes the detection of the problem difficult before a catastrophic leak or tool breakage occurs.
Stress relieving the tool after machining helps to reduce the underlying susceptibility of the metal.
Economic Impact
Unplanned downtime resulting from tool failure significantly increases the total cost of ownership for a high-volume production line. Replacing a mould damaged by stress corrosion cracking requires both the capital for a new tool and the loss of revenue during the lead time for fabrication. Proactive monitoring of water quality and regular non-destructive testing of the tool can identify early signs of degradation.
These investments are small compared to the risk of a complete production stoppage.