Support for broached workpieces

The device allows the broaching of thin-walled workpieces with high precision and an excellent surface condition. It comprises mainly a fixed support defining a radial abutment surface, a sleeve defining ramps, wedge-shaped members bearing against said ramps and against the outer surface of the workpiece. These wedge-shaped members are carried by a plate which is capable of being brought to a wedging position under the effect of springs or to a disengaged position by means of ramps.

The present invention relates to the broaching of tubular workpieces, 
especially workpieces having a thin wall, and more particularly to support 
devices for such workpieces which must undergo a broaching or like 
operation. 
It is known that the broaching of thin-wall workpieces is often impossible 
owing to the radial deformation of the wall due to the component 
perpendicular to the cutting edge and to the direction of displacement of 
the cutting tool. This deformation results in chatter or considerable 
irregularity of the cut which gives an unsatisfactory surface condition 
and lack of precision. It has been contemplated to surround certain 
workpieces, such as tubes having a thin wall, so as to be able to effect 
localized broachings, such as the cutting of keyways or splines, but this 
operation requires a high precision of the outside dimension of the tube 
so as to achieve a good bearing throughout the inner surface of the 
gripping means while allowing the introduction and the disengagement of 
the workpiece after broaching. Now, when the workpiece has been obtained 
by a forming or drawing operation or some other conventional operation, 
its sides are not sufficiently precise and vary excessively from one 
workpiece to the other so that this improvement is hardly effective. 
Indeed, if the blank has an outside dimension exceeding the theoretical 
dimension, the introduction of the workpiece in the gripping means is 
difficult and results in a radial elastic contraction which, after 
disengagement from the gripping means and release, results in a lack of 
metal relative to the desired dimensions. On the other hand, if the blank 
has an outside dimension less than the theoretical dimension, the 
workpiece is freely introduced in the gripping means and, during the 
broaching operation, the workpiece elastically expands under the effect of 
the thrust of the cutting edges so that, after the passage of the broach, 
there is a contraction of the workpiece due to an elastic return to its 
initial shape and there is an excessive amount of metal with respect to 
the desired dimensions. The risk of chatter is moreover greater in this 
case. 
An object of the invention is to permit a broaching operation which gives 
precise dimensions and a good surface condition on workpieces having thin 
walls, even if the thickness of the blanks is not maintained within very 
precise tolerances. The invention may in particular permit the broaching 
of sectional tubes obtained by drawing, rolling, welding, forging, 
forming, hot or cold wire drawing. 
According to the invention, there is provided a device for supporting 
tubular workpieces for the broaching thereof, said device comprising a 
rigid sleeve carried by a support and defining at least one bearing 
surface which extends roughly in the longitudinal direction of the 
workpiece, at least one wedge-shaped means mounted to be longitudinally 
movable relative to the sleeve and in contact by a first face with the 
bearing surface of the sleeve, said means being shaped on a second face 
opposed to the first face in such manner as to fit throughout the length 
thereof a sector of the outer surface of the workpiece which is located in 
the region of a sector of said means and which must be broached, a fixed 
abutment surface roughly perpendicular to the longitudinal direction of 
the workpiece, said abutment surface having a centre opening and being 
adapted to cooperate with an end face of the workpiece, means for urging 
the or each wedge shaped means in a direction corresponding to the wedging 
thereof, and means for displacing the or each wedge-shaped means in the 
direction opposed to the wedging direction. 
According to other advantageous features: 
the or each bearing surface of the sleeve and the adjacent surface of the 
wedge-shaped means are inclined relative to the longitudinal direction of 
the workpiece at an angle of the order of about 2.degree. to 10.degree.; 
another plate is provided between the support and the withdrawing and 
thrusting plate.

Reference will first be made to FIGS. 1 to 3 for describing a device for 
supporting workpieces according to the invention which is adapted to 
maintain thin-walled tubular workpieces intended to be subjected to a 
broaching operation by a broach B. In the illustrated embodiment, it is 
assumed that the workpiece concerned P is a member of a tripod homokinetic 
joint defining three pairs of raceways C of part-circular cross-sectional 
shape. However, it will be understood that the sectional shape of the 
workpiece to be broached could be different, the device according to the 
invention being then modified in shape, if not in its operation, and 
adapted to each particular shape. 
The device comprises a fixed support formed by an annular plate 1 for 
example fixed by screws 2 to a cylindrical ring 3. Disposed inside the 
ring is a rigid and massive sleeve 4 which, in the illustrated embodiment, 
comprises three identical parts each of which subtends an angle of 
120.degree. at the centre. Each of these three parts defines a cavity 
having a generally U-shaped section and comprising a flat bottom 5 and two 
lateral walls 6 generally oriented in the longitudinal direction of the 
workpiece, but inclined relative to the axis X--X of the workpiece and of 
the device at an angle which may be between about 2.degree. and 10.degree. 
(FIGS. 2 and 3). The walls 6 converge in the direction of the plate 1. The 
latter has a centre opening 7 the shape and dimension of which are such 
that radial abutment surfaces 8 are defined in the vicinity of the bottom 
5 of the cavities of the sleeve. 
Fixed on the fixed support, and more precisely on the ring 3, is a 
sub-assembly which comprises three guide rods 10 comprising a 
screwthreaded end portion 11 which is screwed in the front wall 3a of the 
ring 3 and a head 12 which acts as an abutment for a washer 13 against 
which a spring 14 bears. The sub-assembly is completed by a first plate 15 
applied against the front face of the ring and carrying three ramps 16 
having an inclined portion 16a and terminated in a roughly horizontal 
portion 16b (FIG. 2). Provided moreover in this plate 15 are three curved 
openings 17 which are centered on the axis X--X and through which the rods 
10 extend. The plate 15 is rigid with a handle 18 whereby it is possible 
to rotate the plate. A second plate or holder 20 is mounted to be slidable 
along the guide rods 10 and is biased by yieldable means such as springs 
14 toward the first plate 15. This second plate has three openings 21 into 
which the ramps 16 normally extend. The second plate carries six 
wedge-shaped members 22 which are pivoted by one end 23 to this plate to 
pivot about fixing members 24. These wedge-shaped members have an inclined 
face 25 adapted to cooperate with the adjacent lateral wall 6 of the 
sleeve and inclined at roughly the same angle. They also have a second 
face 26 which is opposed to the sliding face 25 and fits or conforms to 
the outer shape of the workpiece P which is to be broached, the 
wedge-shaped members bearing against this workpiece in zones located in 
the region of the zones to be machined. 
Such a device is employed in the following manner. The blank of the 
workpiece to be machined is placed in position while the withdrawing and 
thrust plate 20 is brought to a withdrawn position by rotation of the 
handle 18 and the plate 15 and action of the ramps 16. The wedge-shaped 
members 22 are then moved away toward the left and allow the blank to be 
placed in position. 
The latter bears by its right end (as viewed in the drawing) against the 
abutment surfaces 8 of the fixed plate 1. The thrust plate 20 is then 
released so as to bring it to the position shown in FIGS. 1 to 3 under the 
action of the springs 14. The planes 25 of the wedge-shaped members then 
slide along corresponding planes 6 of the sleeve and the blank is blocked 
in position. The slope of the wedge-shaped members is chosen to be small 
enough to ensure that the friction produced renders the system 
irreversible. These wedge-shaped members consequently maintain their 
initial position obtained under the action of the springs 14 during the 
broaching operation. During the passage of the broach B, the inner 
surfaces to be machined, which are formed by the surfaces of the raceways 
C in the presently-described embodiment, cannot bend under the effect of 
the component of the cutting force which is perpendicular to these 
surfaces since the wedge-shaped members firmly maintain the corresponding 
outer zone of the blank since they are themselves supported on the 
inclined planes of the rigid sleeve. In this way, there is achieved a 
broaching of a thin-walled and flexible workpiece with the same precision 
as if it were thick and radially rigid. 
When the broaching operation has finished, the workpiece is disengaged by 
turning the intermediate plate 15 so as to shift the plate 20 and the 
wedge-shaped members 22 toward the left. 
It will be understood that the means employed for disengaging or bringing 
into engagement the wedging device may be modified without departing from 
the scope of the invention. Thus, the camming mechanism may be replaced by 
hydraulic jacks which urge the plate 20 in the direction of axis X--X, or 
by any other more or less complicated like arrangement. 
FIGS. 4 and 5 show a modification of the device according to the invention 
which has on the whole the same structure, but differs from the embodiment 
shown in FIGS. 1 to 3 by the following points. First, the two plates 30, 
31 which correspond to the plates 15 and 20 of the first embodiment are 
assumed to be slidably mounted on rods such as the rods 10 (not shown in 
FIGS. 4 and 5). Springs, such as the springs 14, are also provided. It is 
assumed that each of these plates may be moved manually away from the 
adjacent face of the sleeve and of the ring and maintained in a withdrawn 
position by means of spacer blocks 32, 33 shown in FIG. 5. 
Further, each block 35 is here formed by a plurality of sections 36, 37, 
38, 39, an end section 36 of which is fixed to a rod 40 which is pivoted 
to the withdrawing and thrust plate 31. The other sections are mounted to 
be slidable on this rod and spaced apart from each other by springs 41. A 
spring 42 is also provided between the section 39 and the plate 30. 
After the sectional blank to be broached has been placed in position, which 
abuts as before against the end plate 1, the plates 30, 31 and the 
wedge-shaped members 35 are released so that the elementary wedge-sections 
bear against the inclined planes 6 of the sleeve 4 and the outer faces of 
the wall of the workpiece to be broached. This wall is thus firmly 
maintained throughout its length and any possible variations in thickness 
or shape between the two ends of the blank are compensated for, since each 
one of the elementary wedges moves until it reaches a wedging position in 
accordance with the available space. 
The fact of providing two blocks 32, 33 respectively between the front wall 
of the fixed support and the plate 30, and between the two plates 30 and 
31, enables the wedge withdrawal travel to be increased and facilitates 
the disengagement and the placing in position of the workpieces. It will 
be understood that if this is sufficient, only the plate 31, could be 
axially displaced, as in the embodiment shown in FIGS. 1 to 3.