Equipment, tools, materials

Screw-cutting lathe 1

Single-spindle automatic lathe 1

Set of cutting tools 2

Dimension gage 6

Timer 6

Bar of low-carbon steel

20 mm in diameter, 500 mm in length 4

 

The work should be executed as follow:. Study the design and action principle of the screw-cutting laths; make acquaintance with tools, lathe accessories and main technological operations employed.

Study the design, action principle and setups of the semi-automatic lathe. Study the draught of the part (Fig. 6.5) and determine the sequence in which machining operations should be performed to manufacture the part in screw-cutting lathe and semi-automatic machine. Gage the workpiece diameter D_w and determine machining allowance (stock):

Z₀ = 0.5(D_W – D),

where D is external diameter of the finished part.

 

Fig. 6.5. Draught of the part

 

It is for an instructor to specify the cutting regime giving the V, S_L, S_C values for all the operations performed in screw-cutting lathe. The depth of cut should be adopted as (0.7…0.8) Z₀ in rough and (0.2…0.3) Z₀ in finish machining while turning, 0.2…0.3 mm while facing or tapering.

The formula for spindle revolutions per minute in determination is following:

.

Enter the cutting regime parameters in the setup table (table 6.1).

 

6.1. Screw-cutting lathe setup table

Operation	Tool	Cutting speed m/min	Spindle revolutions per minute	Feed mm/r	Depth of cut, mm

 

Mount and lock the workplace and proper tools for machining in screw-cutting lathe. Make setups according to the table 6.1 and machine the workpiece in a given sequence. Manufacture 5…6 parts. The same parts should be manufactured in semi-automatic lathe. Note machining time in these two cases.

Turn the workpiece with roughing tool, then with finishing one. Investigate the influence of cutting tool geometry on surface quality, comparing the surface roughness R_Z, obtained in mentioned cases (use surface roughness standards).

Study the cutting speed effect on surface quality after turning with speeds slower (by 30…50%) and higher (by 60…70%) than the recommended one. Determine the R_Z value of finished surface and plot the dependence between cutting speed and R_Z.

Turn the workipece with feeds slower (by 30…40%) and higher (by 30…50%,) than the recommended one and determine R_Z value. Plot the dependence between feeds S and roughness R_Z

Gage the parts manufactured on screw-cutting and semi-automatic lathes and determine accuracy in the two cases.

Determine the average time for manufacture in the two types of lathes.

Make inferences.

Contents of the report. Present the draught of the part. Depict the machining operations in screw-cutting and semi-automatic lathes.

Present the setup table with necessary explanations and calculations. Plot and explain the dependences between surface roughness R_Z on the one hand and cutting speeds as well as feeds on the other hand (2 graphs).

Present the turning productivity data (for two lathe types employed).

Explain the tool geometry effect on surface roughness.

Present the inferences.