Mumbai University > Mechanical Engineering > Sem 4 > Production Process II

Marks: 10M

Year: May 2014, Dec 2014

Design Procedure of an Internal broach tool:

a) Details on a internal broach tool:

A typical internal broach is shown in the figure;

b) Determination of maximum and minimum hole sizes;

Assume desired hole 45H7

D=geometric mean diameter whose ranges are 1-3, 3-6, 6-10, 10-18, 18-30, 30-50, 50-80, 80-20.

45 fall in the range of 30-50; $D= \sqrt{30 x 50}$ =38.73mm

i=0.001D + 0.45 $\sqrt[3]{D}=1.56$ microns

tolerance=IT7 (as hole size has 7)

IT7=16i=24.98micron=0.025mm

Now calculate the maximum and minimum size of the hole as basic size of 45 mm is given.

c) Maximum broaching allowance;

It is defined as the total thickness of the metal to be removed by broaching. It is given by:

Ab=0.005Db +(0.1-0.2) √L ; L=length of the hole to be broached.

$\hspace{4.2cm}$ Db= basic diameter of the hole.

d) Rise per teeth;

It is selected from the following table

Let rise per tooth for roughing and semi-finish teeth be 0.03 and 0.015 mm respectively. (Assume)

e) Number of semi finish teeth;

$= \frac{0.1 × A_b}{2 x 0.015}$

round this value to the next integer value if in point form.

f) No of roughing teeth;

=(A_b-4[2 × 0.015])/(2×0.03)

Always round this value to the next higher value.

g) Pitch;

i) for roughing teeth and semi finishing teeth=1.3√L =pr

ii) for finishing teeth=0.6 x 1.3√L = pf

h) No of teeth simultaneously in action;

$Z_{max} = \frac{L}{p_r} +1$

this value should be greater than 3 for proper action of broach.

i) Chip space ratio;

$kc= {\text{Gullet area}}{\text{Area of longitudinal section of chip}}$ kc=6 (Assume)

Area of longitudinal section of chip=L x Max rise per tooth

therefore we get gullet area which is given by the formula

$A_g=0.5 x p_r x h_c$

and hence hc (depth of chip space)can be found out.

j) Land width (W);

i) For roughing an semi finishing teeth=0.3 x pr

ii) for finishing teeth=0.3 x pf

k)Rake angle;

Assume rake angle 15 degree and 5 degree for roughing and semi finish teeth respectively.

i) Primary and secondary clearance angle;

l) Chip Breakers;

Dimensions are 2mm wide and 1.5 mm deep usually.

They are used to break wide chips to several narrow chips.

m) Fillet radius;

i) For roughing an semi finishing teeth=0.3 x pr

ii) ) for finishing teeth=0.3 x pf

n) Force;

$F=e_c x D_b x Z_{max} x K x \text{max rise per tooth} x π \hspace{1cm} ; ec=4250 N/mm^2$ $\hspace{9cm}$ k=1.4

o) Power for Broaching = $\frac{F ×V}{4500}$ ; V for broaching is 8 m/min

$\hspace{9cm}$ F in kgf

p) length of broach;

=length of the toothed portion + length of shank + length of rear pilot length of toothed portion= length of roughing and semi finish teeth + length of finishing teeth = pr x total number of teeth + pf x 5

length of shank = 250mm assume

length of rear pilot= length of hole