Machinability of metals in watches
Machinability is a concept that describes the ease with which a material is machined. A material of this kind has the advantage of breaking with low shear force, with a good finishing surface without using many tools. Good machinability breaks the material easily.
There are two sets of parameters that define the machinability of a material:
1 Working conditions of a material including 8 factors
– Microstructure affects physical properties such as strength, ductility, toughness, corrosion resistance, performance of high / low temperature, wear resistance etc.
– Grain size also affects various properties such as ductility, the tensile strength or surface finish.
– Heat treatment
– Chemical composition, as it is very important to know the components and quantity of each to provide different properties.
– Manufacture, manufacture by casting, extrusion forming, pressing, etc. It will affect the hardness, fracture toughness, ductility
–Hardness, relates to the yield strength.
– Elastic limit. Materials with high resistance to traction need much initial torque to be machined and removing the original chip. High level of strength is more difficult to machine
– Tensile strength. Materials with high tensile need much initial torque to breaks and remove the chip. High level of strength is more difficult to machine
2 Individual physical properties of materials
– Modulus of elasticity. A high modulus is better because the cut is more stable and accurate.
– Thermal conductivity. Low heat conductivity increases and hardens the piece
– Thermal expansion. High thermal expansion enables dimensional changes in alloys
– Work hardening. Low-speed machining hardens alloys
A table machinability of metals uses for us,
Aluminum 7750: 320
Stainless steel 316 L: 42
B 14 Bronze: 20
Magnesium Elektron: 480
Titanium 6 AL 4 V: 21
Machinability data are important for a company with large production of watches. Possibly unprofitable machining large series, because many tools with low life are used. Hence, these processes are based on the pressing mold boxes, annealing and minimal turning.
For small businesses, the most important data are hardness, tensile strength and yield strength, to know the torque required for the chip load or cutting speeds. Other properties may be very interesting but for the end customer.