- Tips on machining 2018/10/09 UP
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Tips on machining vol.24
How to keep machining accuracy with better workpiece clamping (machine vise)
- Tag
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- Fixture/chuck
In general, machining centers clamp workpieces with machine vises and turning centers with chucks. However, a workpiece can strain when clamped too tightly. Without knowing well about machine vises and chucks, you might fail to utilize their full potential and lose clamping accuracy. Therefore, this volume presents the nature of machine vises.
To understand machine vises, we measured distortion of a vise against clamping forces.
We applied a load cell to a machine vise and measured clamping force, inclination of a stationary jaw (displacement in Z-axis) and parallelism of a sliding jaw against a base, as shown in Figure 1.
*Machine vise: “LOCK TIGHT CV VISE 125,” produced by NABEYA CO., LTD.
As a result, the stationary jaw showed almost no inclination up to the clamping force of 3kN, but it was inclined by 0.005 mm with 3-6kN and 0.01 mm with 9kN (Figure 2). The parallelism of the sliding surface was merely 0.0015 mm with 10kN (Figure 3).
Figure 1
①‐⑤ : measurement points of parallelism (upper)
①‐② : measurement points of inclination (lower)
Figure 2: Correlation between clamping force and inclination
Figure 3: Correlation between clamping force and parallelism
Although this data is just an example, the correlation between clamping force and inclination of a stationary jaw, as well as that of clamping force and parallelism of a sliding jaw, matters in your daily operation. The inclination and distortion volume vary with the vise’s size and structure. Therefore, an operator should constantly pay attention to the clamping forces and the resulting displacement to maintain high machining accuracy.
When you loosely tighten a vise with the handle, the clamping force is around 5kN. When a vise is tightened a little harder, the force goes up to 10kN. A vise maker generally recommends 10kN for conventional machining and 15kN for heavy cutting. The clamping force should ideally be measured with a load cell, but otherwise you should know how strong your normal clamping force is and adjust it to meet the machining requirements.
This is how to optimize “vise distortion against clamping forces” by understanding the nature of machine vises.
With support of various partner companies, DMG MORI has accumulated knowhow to pursue higher machining accuracy with better clamping. Please contact us if you have concerns over clamping; we will provide customized solutions to any requirement.
