Performance and Design Criteria of Tool Holders in Machining

Abstract:

In this study, theoretical models and experimental data are presented to investigate the dynamic and static performances of tool holders in machining, their effects on surface quality and their roles on energy consumption.

1. Introduction

In machining, tool holders ensure that the tool operates in a stable, precise and vibration-free manner during machining. The design of these components depends on factors such as moment (T), cutting force (F), rigidity (K) and vibration frequency (ω).

For example, the rigidity of the tool holder can be expressed as follows:

K=FδK = \frac{F}{\delta}K=δF​

Where:

• FFF: Cutting force (N),

• δ\deltaδ: Deformation (mm).

2. Tool Holder Types and Calculation of Cutting Forces

Cutting force is one of the main parameters in the metal cutting process and can be calculated with the following formula:

Fc=kc⋅AF_c = k_c \cdot AFc​=kc​⋅A

Where:

• FcF_cFc​: Cutting force (N),

• kck_ckc​: Cutting strength coefficient (N/mm²),

• AAA: Cross-sectional area (b⋅hb \cdot hb⋅h).

For example, for steel material, when kc=2000 N/mm2k_c = 2000 \, \text{N/mm}^2kc​=2000N/mm2, chip width b=2 mmb = 2 \, \text{mm}b=2mm, chip depth h=0.1 mmh = 0.1 \, \text{mm}h=0.1mm:

Fc=2000⋅(2⋅0.1)=400 N.F_c = 2000 \cdot (2 \cdot 0.1) = 400 \, \text{N}.Fc​=2000⋅(2⋅0.1)=400N.

3. Dynamic Behavior: Vibration and Stability

The vibration behavior of tool holders directly affects the surface quality and tool life in machining. The vibration behavior of the tool holder is analyzed as follows:

ωn=Km\omega_n = \sqrt{\frac{K}{m}}ωn​=mK​​

Where:

• ωn\omega_nωn​: Natural frequency (rad/s),

• KKK: Rigidity (N/m),

• mmm: Mass (kg).

Hydraulic holders and heat shrink holders increase the rigidity, increase ωn\omega_nωn​ and reduce vibration.

4. Effect on Surface Quality

The eccentricity (eee) of the tool holder can increase the surface roughness. Theoretical roughness is calculated as follows:

Rt=f28r+eR_t = \frac{f^2}{8r} + eRt​=8rf2​+e

Where:

• RtR_tRt​: Surface roughness (µm),

• fff: Feed rate (mm/rev),

• rrr: Tool tip radius (mm),

• eee: Off-axis runout (mm).

Example:

When the axial runout e=0.01 mme = 0.01 \, \text{mm}e=0.01mm, feed f=0.2 mm/rev = 0.2 \, \text{mm/rev}f=0.2mm/rev, tool nose radius r=1 mmr = 1 \, \text{mm}r=1mm:

Rt=0.228⋅1+0.01=0.015 mm.R_t = \frac{0.2^2}{8 \cdot 1} + 0.01 = 0.015 \, \text{mm}.Rt​=8⋅10.22​+0.01=0.015mm.

5. Energy Consumption and Efficiency

In high-speed operations, the weight and balance of the tool holder affect energy consumption. The energy consumption is expressed as follows:

P=T⋅ωP = T \cdot \omegaP=T⋅ω

Where:

• PPP: Power (W),

• TTT: Torque (Nm),

• ω\omegaω: Angular velocity (rad/s).

For example, if torque T=2 NmT = 2 \, \text{Nm}T=2Nm, angular velocity ω=100 rad/s\omega = 100 \, \text{rad/s}ω=100rad/s:

P=2⋅100=200 W.P = 2 \cdot 100 = 200 \, \text{W}.P=2⋅100=200W.

6. Experimental Results

A study investigated the cutting forces and surface quality using different types of holders:

Tool Holder TypeCutting Force (N)Surface Roughness (µm)Collet Holder4200.02Hydraulic Holder4000.015Heat Shrink Holder3800.01

7. Conclusion and Recommendations

The selection and design of tool holders are of critical importance in machining processes. Dynamic balance and rigidity provide higher surface quality and lower energy consumption. It is expected that smart holder technologies will be adopted more in the future.