Specific cutting force

The specific cutting force is the cutting force related to the cutting cross section . The following applies: ${\displaystyle k}$ ${\displaystyle A}$ ${\displaystyle F}$

${\displaystyle k={\frac {F}{A}}}$

It is determined in experiments and recorded in tables that are used to calculate the cutting force. She then surrenders to

${\displaystyle F=k\cdot A}$.

Often one limits oneself to the calculation of the most important component, the cutting force (from English: c ut for cut). It results from the specific cutting force . The specific feed force and the specific passive force also exist analogously . ${\displaystyle F_{c}}$ ${\displaystyle k_{c}}$ ${\displaystyle k_{f}}$ ${\displaystyle k_{p}}$

However, the specific cutting force and its components are not constants, but depend on a large number of influences. The most important are the material and the chip thickness . The value is the specific cutting force that applies to a chip thickness of 1 mm and a chip width of 1 mm. If only the chip thickness is considered as an influence, the following relationship applies: ${\displaystyle h}$ ${\displaystyle k_{c1.1}}$ ${\displaystyle b}$

${\displaystyle k_{c}=k_{c1.1}\cdot h^{-m_{c}}}$.

With:

${\displaystyle m_{c}}$ Material constant

The cutting force then results in ${\displaystyle F_{c}=k_{c}\cdot A=k_{c1.1}\cdot h^{-m_{c}}\cdot h\cdot b=k_{c1.1}\cdot b\cdot h^{1-m_{c}}}$

Determination of the specific cutting force

The specific cutting force depends on a variety of influences. The value that applies to certain standard conditions is used as the constant . These include, above all, a chip width and thickness of 1 mm. The other influences are taken into account using so-called correction factors. In general: ${\displaystyle k_{c}}$ ${\displaystyle k_{c1.1}}$

${\displaystyle k_{c}=k_{c1.1}\cdot h^{-m_{c}}\cdot K_{c\gamma }\cdot K_{V}\cdot K_{st}\cdot K_{ver}\cdot K_{css}\cdot K_{ckss}}$

With

${\displaystyle K_{c\gamma }}$Correction factor for the rake angle .

${\displaystyle K_{v}}$Correction factor for the cutting speed

${\displaystyle K_{st}}$Correction factor for the chip compression

${\displaystyle K_{ver}}$Correction factor for the wear occurring during machining

${\displaystyle K_{css}}$Correction factor for the cutting material

${\displaystyle K_{ckss}}$Correction factor for the cooling lubricant

material	${\displaystyle k_{c1.1}}$ [N / mm²]	${\displaystyle m_{c}}$	Specific cutting force for [N / mm²] ${\displaystyle k_{c}}$ ${\displaystyle h=0,1mm}$	Specific cutting force for [N / mm²] ${\displaystyle k_{c}}$ ${\displaystyle h=0,63mm}$
Brass	780	0.18	1180	850
S 275 JR (St 44)	1780	0.17	2630	1930
E 335 (St 60)	2110	0.17	3120	2280
16 MnCr5	2100	0.26	3820	2370
42 CrMo4	2500	0.26	4550	2820
GG 30	1130	0.3	2255	1298

Rake angle

${\displaystyle K_{c\gamma }}$records the influence of the rake angle. If it is small, the chip can slide over the rake face more easily. It applies . This is the reference rake angle and the actual rake angle. The reference rake angle is + 6 ° for steel and + 2 ° for machining cast iron . ${\displaystyle K_{c\gamma }=1-{\frac {\gamma _{tat}-\gamma _{0}}{100}}}$ ${\displaystyle \gamma _{0}}$ ${\displaystyle \gamma _{tat}}$

Cutting speed

${\displaystyle K_{v}}$indicates the influence of the cutting speed, which is only slight and is rarely taken into account. The cutting force decreases with increasing cutting speed. In addition, the influence usually only occurs in the range of low cutting speeds (v <80 m / min). In the range between 80 and 250 m / min, the influence can be estimated with . It can also be added for the range between 30 and 50 m / min . The influence of the cutting speed can be traced back to two causes: on the one hand, the temperature of the material increases with increasing cutting speed, which reduces its strength, on the other hand it has an influence on the formation of built-up edges . Generally applies . At a cutting speed of 200 m / min it is 0.93. ${\displaystyle K_{v}=1{,}03-{\frac {3\cdot v_{c}}{10^{4}}}}$ ${\displaystyle K_{v}=1{,}15}$ ${\displaystyle K_{v}=\left({\frac {100}{v_{c}}}\right)^{0,1}}$

Chip upsetting

During machining, the material is compressed before it is sheared off. The influence of this chip compression is taken into account with the factor . It is 1 for external turning and 1.2 for internal turning, drilling and milling. It is 1.3 for grooving and parting and 1.1 for planing, slotting and broaching. ${\displaystyle \lambda }$

wear

See also : wear (cutting)

The wear that occurs on the tool can have different effects, depending on where the wear occurs. Flank wear leads to increased friction between workpiece and tool and thus to increasing forces. Crater wear, on the other hand, increases the actual rake angle and thus reduces the forces. Since the wear and tear during machining is rarely known, the correction factor is usually set with an empirical value of 1.5. ${\displaystyle K_{ver}}$

Cutting material

The value reflects the influence of the cutting material . It is largely based on the different coefficients of friction between the rake face of the tool and the chip. For high-speed steel it is 1.2, for carbide 1.0 and for cutting ceramics 0.9. ${\displaystyle K_{css}}$

Cooling lubricant

The factor takes into account the influence of the cooling lubricant . It is also based on the influence on friction. Therefore, oil-containing cooling lubricants have a lower cutting force than cooling emulsions. In the dry processing of the value is 1, with the use of coolants and 0.9 for oil 0.85. ${\displaystyle K_{ckss}}$

literature

• Heinz Tschätsch: Practice of machining technology. Process, tools, calculation . 7th edition. Vieweg, Wiesbaden 2005, ISBN 3-528-44986-1 , pp. 16-21 (former title: Praxiswissen Zerspantechnik ).
• Herbert Schönherr: Machining production . Oldenbourg-Verlag, Munich 2002, ISBN 3-486-25045-0 , pp. 16-22.

Individual evidence

1. ↑ ^{a b} Tschätsch, H .: Practice of machining technology. Process, tools, calculation. 10th revised and updated edition, Vieweg-Teubner Verlag, 2011. ISBN 978-3-8348-1502-6 , p. 18.
2. ↑ ^{a b} Schönherr p. 18.
3. ↑ Schönherr, p. 18f.
4. ↑ Tschätsch, p. 18f.
5. ↑ Tschätsch, p. 19, Schönherr, p. 19.
6. ↑ Schönherr, p. 20.