Coherence Scanning Calibration Procedures for High Aspect Ratio Tool Steel Sidewalls
Calibrating optical coherence scanners on tool steel sidewalls requires specular tilt mapping, transfer function correction, and noise floor subtractive adjustment.
Sinker EDM Sidewall
Meaning
Electrical discharge machining of deep mold cavities creates unique surface textures and dimensional tolerances on the vertical boundaries of the cavity. The sinker EDM sidewall suffers from a specific discharge distribution because of the parallel alignment between the electrode and the cavity wall. This geometry affects the flushing of debris and the uniform delivery of electrical pulses.
Discharge Mechanics
Machining the sinker EDM sidewall involves a series of controlled electrical sparks generated between a graphite or copper electrode and the tool steel workpiece in a dielectric bath. Because of the vertical orientation of these surfaces, dielectric fluid flushing is less efficient in this narrow gap than at the bottom of the cavity. Trapped metal particles and carbon debris can cause secondary sparking, which alters the spark gap distance, increases tool wear, and degrades the dimensional accuracy of the mold cavity.
Surface Texture
The lack of uniform spark distribution produces a rougher surface finish along the sidewalls than on flat horizontal faces. This rough texture consists of overlapping craters, melted zones, and a brittle recast layer that is highly prone to micro-cracking. Mold makers must use a sequence of orbital finishing cycles with lower discharge energy to reduce this roughness and prepare the steel for final polishing.
Molding Consequence
A poorly finished sidewall hinders the injection molding process by increasing the friction during part ejection. Rough textures create draft angle issues and can cause drag marks or scuffing on the molded plastic housing. Ensuring a smooth finish on the cavity sidewalls is necessary for maintaining low cycle times and high part quality.