The tool holder is the key interface between the cutting tool and the machine tool spindle, and the failure of the tool holder will cause the tool holder to fail to function, resulting in shortened tool life and unreliable cutting process.
1. Analysis of the cause of tool holder failure
a. The chip is wrapped around the tool holder, and the tool holder is worn due to the friction between the tool holder, workpiece and chips.
b. Intermittent cutting forces lead to surface fatigue of the holder.
c. Tool holder deformation caused by cutting force.
d. Cutting heat and cutting temperature cause a phase change in the structure of the tool holder material.
e. Oxidation and corrosion of the handle.
f. Wear of spare parts, fittings and connecting surfaces.
2. How to judge when to replace the handle
The main point: check machine tool spindle wear and automatic tool changer alignment.
Worn spindles can cause runout problems, affect toolholder accuracy, and reduce achievable workpiece quality and machining efficiency. The quality of the machine tool spindle can be evaluated, such as checking its T.I.R. (radial runout). Maintaining ATC (automatic tool changer) alignment is critical. If the ATC does not grip the tool holder properly, damage to the spindle and tool holder will result, and tool performance and tool life will be significantly reduced.
Assessment of tool holder wear: A worn tool holder will not provide good accuracy and will wear out the tool rapidly, will also result in poor machined surface roughness, and may even damage the machine tool spindle.
Cone wear (fretting wear): Check whether the positioning cone is worn or damaged. Any problem with the taper will directly affect the machining accuracy, if there is any defect in the taper, the tool holder should be replaced.
If there are obvious marks on the taper surface, fretting wear may have occurred. When two rigid parts (tool holder and spindle) rub against each other, fretting wear will occur. Fretting wear is due to the fit between the taper surface of the tool holder and the spindle. Bad cause, wear creates vibration and heat.
If small copper-colored pits or marks are visible on the taper, this indicates that the handle is wearing. Fretting wear is often easily mistaken for oxidation, and once significant fretting wear occurs, the holder should be replaced. If the new shank experiences rapid fretting wear, or if the shank sticks in the spindle, it is a sign that the spindle needs regrinding. Fretting wear marks on the holder taper: When the holder is inserted into the spindle, the worn taper will cause eccentric positioning, which is called "runout".
Runout during processing will cause premature wear and failure of the tool, and it will also cause excessive vibration resulting in poor surface roughness, which requires additional processing to correct it. Vibration can also lead to fatigue heating of the spindle and damage to the spindle bearings. T.I.R. (radial runout) is used to measure the axial deformation of the tool in the tool holder assembly. Every 0.02mm of runout will reduce the life of the tool by 10%.
Bushings and collets: Bushings have special grooves and patterns that hold the tool securely, so they will wear out faster than collets. Worn bushings will cause the tool to fail earlier, when bushing wear is noticeable They should be replaced when necessary to maintain the accuracy and performance of the tool-holder assembly. Graining on the bushing due to insufficient clamping force, the bushing should be replaced if there is any damage to the OD or ID. The rotation of the tool in the inner diameter of the bushing will cause damage to it, so check the traces in the inner diameter. Once damaged, the bushing will not be able to effectively clamp the tool holder, which will result in a reduction in clamping force and accuracy.