Standard Operating Points to Prevent Deformation During Mold Deep Cooling Channel Drilling
Deep hole cooling channel drilling is a key machining process for mold temperature control systems. Deep cooling holes feature slender apertures and long drilling depths, and mold steel retains residual stress from forging and rough milling. Without standardized operation control, deformation defects such as bent hole passages, out-of-round holes and warped mold plates will occur, resulting in water leakage, uneven mold temperature and unstable product dimensional accuracy in later molding. Combined with automotive precision mold processing standards, this paper sorts out full-process control points including pre-machining preparation, in-process cutting parameter management and post-processing stress relief, to control deep hole deformation from the source.
1. Pre-Machining Workpiece & Tooling Control to Eliminate Fundamental Deformation Stress
Residual stress inside mold steel is the primary cause of deep hole deformation, and improper clamping will aggravate distortion caused by stress release. All mold plates after six-sided rough milling must undergo low-temperature stress relief tempering to eliminate surface cutting stress generated by milling; workpieces can only be sent to the deep hole drilling station after fully cooling to room temperature, and hot workpieces are strictly prohibited from being put on the machine directly.
Large-area equal-height support pads are adopted for the deep hole drilling workbench, with pad positions distributed according to the workpiece stress area to avoid single-point support causing suspended compression deformation. The pressing position of the pressure plate avoids the drilling area, and the clamping force is kept uniform to prevent local extrusion deformation of the template. Check the flatness and parallelism of the template with a dial indicator before processing; workpieces with excessive flatness error shall be returned to the milling process for re-grinding. Clean all iron filings and oil stains in the screw holes and cavities to avoid inclined placement caused by foreign matter padding.
2. Cutting Parameter & Tool Control to Suppress Dynamic Deformation During Drilling
Cutting impact, poor chip removal and tool wear will continuously squeeze the hole wall and template, so dynamic control during processing is the core to avoid deformation. Select lengthened solid carbide internal cooling drill bits and anti-vibration tool holders according to the hole diameter to reduce cutting vibration. The drill cutting edge must be symmetrical without chipping, and severely worn tools shall be replaced immediately to avoid increased cutting resistance and bent hole passages.
For ultra-long deep holes, adopt segmented progressive drilling instead of one-time through drilling; retract the drill bit to remove chips after drilling a fixed depth. Reduce the rotating speed and feed rate for deep hole sections to lower cutting resistance. Sufficient high-pressure cooling liquid shall be continuously supplied to the cutting area to take away cutting heat and smoothly discharge iron filings, avoiding iron filings stuck in the hole to scratch the hole wall and deflect the drill bit. Adopt symmetrical drilling sequence for multiple cooling holes on the same template, alternately drill holes on the left and right to prevent unilateral concentrated stress release leading to template warpage.
3. Post-Processing Stress Relief & Inspection to Avoid Secondary Deformation
A large amount of cutting residual stress remains inside the workpiece after deep hole drilling; if it flows to the next process without treatment, secondary deformation will occur when stress is released during grinding and polishing. After drilling, lay the template flat on a smooth backing plate for natural aging standing, and prohibit stacking heavy objects or vertical placement to avoid irreversible bending caused by self-weight.
For templates with cooling channels longer than 300mm, low-temperature stress relief tempering is carried out again after standing to eliminate concentrated cutting stress. Use depth gauges, dial indicators and inner diameter gauges to detect the hole straightness, aperture and template flatness one by one; isolate unqualified workpieces and carry out reaming and grinding correction. During turnover, keep the template flat and avoid collision and extrusion deformation caused by improper handling.
Summary
The deformation of deep cooling holes is superimposed by raw material residual stress, clamping force, cutting dynamic resistance and post-processing residual stress. The prevention logic follows three steps: eliminate hidden deformation risks in advance through aging treatment and reasonable clamping, reduce dynamic extrusion and vibration deformation by matching anti-vibration tools, segmented cutting and symmetrical drilling during processing, and avoid secondary deformation through aging tempering, full inspection and standardized turnover after processing. This set of operating specifications is applicable to precision automotive mold processing, which can stably control the straightness of cooling holes and template flatness, fundamentally solve mold water leakage and uneven cooling problems caused by hole deformation, reduce mold repair costs and extend mold service life.
