Question

AT mechanics of material,
Can you explain why the contact point between chip( or work) and cutting tool is larger when the cutting speed is slow? I'm very pleased if you explain this to me by using picture or drawing.

Answer 1

Cutting speed is defined as the speed at which the work moves with respect to the tool (usually measured in meters per minute (m/min) or in feet per minute(fpm) ). Feed rate is defined as the distance the tool travels during one revolution of the part. Cutting speed and feed determines the surface finish, power requirements, and material removal rate. The primary factor in choosing feed and speed is the material to be cut. cutting speeds must be used for the type of material being cut. If a cutting speed is too high, the cutting tool edge breaks down rapidly, resulting in time lost recondition the tool. At too slow a cutting speed, the machining operation time is large or more loss of time, resulting in low production rates. However, one should also consider material of the tool, rigidity of the workpiece, size and condition of the lathe, and depth of cut. For most Aluminum alloys, on a roughing cut (.005 to .020 inches depth of cut) run at 600 fpm. On a finishing cut (.002 to .004 depth of cut) run at 1000 fpm.

the heat generated during cutting operation going into the tool,workpiece and chip, as a function of cutting speed. Most of the heat is carried away by Chips.

A low cutting speed will cause a long tool life and a high feed velocity will make the cutting time per workpiece short. Therefore, the number of workpieces machined per tool life will be maximized.
Cutting speed, depth of cut, feed, cutting fluids influences forces, pwer, temperature rise, tool life, type of chip, surface finish.

The cutting speed and feed greatly dependent on the type of metal which is being cut or machined. in metals such as aluminium,copper,iron and nickel, cutting forces are high as the area of contact between the rake face and the material is high at slow speed.pure metals are traditionally difficult to machine. High ductility results in high contact area.
Contact area will decrease with certain types of metals Like when cutting magnesium, hardened steel, titanium and hard plate, chips will be much smaller and thinner. In fact, forces will decrease as the cutting speed is raised, because there is less contact area.

Feed Rates for Turning:
For general machining purpose, suggested feed rate of 0.005 – 0.020 IPR (inches per revolution) for roughing surface and 0.002 – 0.004 IPR for finishing surface.
Feeds for Various Metals (with HSS cutting tool)

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