FIELD OF INVENTION :

This invention relates to a method and apparatus for piercing a part such as a component for use in the automotive industry.

PRIOR ART :

In various engineering industries, parts such as pipes or tubes are frequently used for various purposes. For example, in the automotive industry - particularly the motorcycle manufacturing industry - pipes are used in fabricating the frame structure of motorcycles, Pipes forming a frame member of a motorcycle frame are typically required to be provided with openings or apertures which are used in mounting or connection of other parts to the frame member.

One conventional process of forming apertures in a part is achieved by a drilling operation. Drill bits are cutting tools used to create cylindrical holes. Bits are held in a drill tool, which rotates them and provides torque and axial force to create the hole. Specialized bits are used for forming non-cylindrical-shaped holes.

The spiral, or rate of twist in the drill, controls the rate of chip removal in a drill. A fast spiral drill is used in high feed rate applications under low spindle speeds, where removal of a large volume of swart is required. Low spiral drills are used in cutting applications where high cutting speeds are traditionally used, and where the material has a tendency to gall on the drill or otherwise clog the hole, such as aluminum or copper.

The drilling process, or complete operation, involves selecting the proper twist drill or cutter for the job, properly installing the drill into the machine spindle, setting the speed and feed, starting the hole on center, and drilling the hole to specifications. The drilling process must have some provisions for tolerance because of the oversizing that naturally occurs in drilling. Drilled holes are always slightly oversized, or slightly larger than the diameter of the drill's original designation.

Oversizing is due to several factors that affect the drilling process: the actual size of the twist drill, the accuracy of the drill point, the accuracy of the machine chuck and sleeve, the accuracy and rigidity of the drilling machine spindle, the rigidity of the entire drilling machine, and the rigidity of the workpiece and setup.

Selecting the proper twist drill means getting the right tool for the job (see Table 4-2). The material to be drilled, the size of that material, and the size of the drilled hole must all be considered when selecting the drill. Also, the drill must have the proper lip angles and lip clearances for the job. The drill must be clean and free of any burrs or chips. The shank of the drill must also be clean and free of burrs to fit into the chuck.

Where drilling is used, a deburring step is required to remove burrs formed during the drilling operation. In addition, chips formed during the drilling process need to be removed from the part and this calls for still further equipment and/or processing.
As such drilling is an expensive and cumbersome process. The other practice is 'punching'. A punch is used in a machining operation for the cold working of metal. A typical punch has a punching head that engages the workpiece. The head is forced, in an axial direction, through the workpiece, thereby removing the metal in its path. Punching is useful for quickly forming a rough hole in a material, and can be a preliminary to a boring operation and/or a tapping operation.

Several problems are encountered in a typical known punching operations. A punch typically creates a rough hole in non supported pipes and curved surfaces Due to deformation of the metal that occurs during the punch operation, the hole may not be suitably large enough. This can result in extra boring time and wear on the boring tool during the subsequent operation. Further, the punched hole may be irregular in shape, or may have metal burrs that remain along the edges. These problems lead to scrap parts, or at best, they necessitate reworking of the parts.

An alternative process involves forming apertures in a part by a piercing process involving the use of a mandrel. A mandrel supports the part from the back, protecting it from excessive deformation during the piercing process. At the same time, the mandrel enables a shearing action between the mandrel and the piercing head so as to produce a clean hole or aperture without excessive deformation of the material of the part to cause a dimple. Use of a mandrel is not always possible, particularly where the part is a tube or pipe of curved shape. In these cases, piercing will result in noticeable deformation causing the formation of a dimple or deformation in the vicinity of the aperture and inaccurate hole size.
Moreover, the above described piercing processes as known in prior art all call for loading and unloading of parts into some fixture such as a clamp to enable formation of apertures at the desired location. Accordingly, conventionally used piercing methods have reduced productivity while being sub-optimal from a cost reduction perspective. Error in accuracy and positioning of apertures is an additional problem.

OBJECTS OF THE INVENTION :

The present invention is made in view of the above known problems in drilling and piercing process , and it is an object of the present invention to provide a manufacturing method of piercing a part having an un supported non-planar surface , in which a burr-like unnecessary portion on the inner periphery of the through hole can be removed by a pressing process as a hole is formed. However, the method can be used for supported non planar and planar surfaces also.

It is an object of the present invention to provide a method and apparatus for piercing a part which avoids one or more of the disadvantages noted above. When the aperture forming method or the aperture forming apparatus/tool of the present invention is employed, a hole/aperture can be formed in part which may even possess a non-planar surface at once by pressing. As a result the manufacturing efficiency can be largely improved.

In order to achieve the above object, according to the first solution employed by the present invention there is a provided a first tool characterized by to firstly reduce the thickness of the part at the intended location where the aperture is to be formed which facilitates entry of the second tool. The geometry of the second tool prevents burr from being formed on the peripheral edge of the intended hole.

DESCRIPTION OF INVENTION

This invention provides a forming method capable of forming through holes at once with a single pressing operation. A hole is formed in a part with a piercing punch after reducing the thickness of work at the intended location and the piercing punch having a guiding portion which is a tapering portion and a deburring portion which includes a geometric shaped portion also formed on the piercing punch.

With this object in view, the present invention provides a method for piercing a part to form an aperture comprising the steps of:

a) reducing the thickness of the part at an intended location of an aperture; and

b) subsequently working the part at said intended location of the aperture with a piercing tool of predefined geometry to form the aperture.

Piercing or punching is a press working process and it is distinct from drilling.
In the present invention, atleast the first prepared thickness reduction step, intermediary prepared pilot hole step and the novel punching step are perfomed in order to improve the method of punching a hole with clean and improved accuracy of the inner diameter. In this case the portion of the part wherein the desired aperture is to made is prepared and processed to reduce thickness and thereby the step of punching can be performed more efficiently. Moreover due to the geometry of the second tool used in punching step not only the step of cutting and deburring is performed at a time more stably but at reduced manufactured cost.

The part may have a non-planar surface at the intended location of the aperture and, furthermore, across the extent of the part. So, where the part is a pipe - for example to be used as a frame member of a vehicle such as a motorcycle - the method enables formation of apertures even where the pipe has a non-planar surface. That is, the pipe may be curved or of circular or other rounded cross section at the intended location(s) for aperture(s) - making a conventional mandrel based piercing method unsuitable - yet the above described piercing method may be used to good effect. The method may be used with benefit where the part has a closed section though the method could be applied to parts without closed section also.

The thickness of the part may be reduced, or thinned, using a first tool, through a variety of techniques at an intended location for the aperture. Thinning may involve forming a pilot aperture in the part. The pilot aperture, formed in step (a), is likely to possess neither the desired dimension(s) nor geometry for the final aperture to be formed. The pilot aperture may take the form of a small slit or like opening. Thinning may also be achieved by a notching operation, a grinding operation and/or a milling operation. Advantageously, the thinning step results in at least a 50% reduction of the thickness, or wall thickness, of the part at the intended location of the aperture.

The thickness of the part may be reduced, or thinned, in a mid or other determined portion of the intended location for the aperture. The thinning step is advantageously accomplished, at least in part, by a first tool suitable for achieving whichever thinning operation is preferred, whether that be notching, milling, grinding or a combination of these.

In a punch process as the punch size increases the chisel edge of the punch will not have a sharp cutting action due to the large width and this creates a considerable strain on the machine. To eliminate this strain as per the invention a pilot hole is punched first and then followed with the larger punch. This pilot hole should be punched accurately and selectively as the larger punch will follow the small pilot hole punch. A pilot punch is also useful when average-sized holes are to be punched on small punch machines. The small punch machine may not have enough power to drive the larger punch through the metal. Generally the pilot punched hole is much smaller than the larger punch hole.
As such the invention introduces a intermediate step. An intermediate processing step may be performed between steps (a) and (b), the intermediate step comprising a step in which a tool is inserted into the part to form a pilot aperture; or expand any pilot aperture formed in a portion of the part during step (a). The tool may advantageously be of tapered shape, as such shape is readily applied to expansion of a pilot aperture, though other shapes are not precluded. This intermediate tool may be inserted from any direction relative to the part. That is the intermediate tool may be inserted from the top, bottom or side of the part. This intermediate processing step does not necessarily remove any substantial material from the part but is useful in preparing the part for the final step of forming the aperture to desired geometry with a second tool.

The first and/or intermediate tool(s) may be separate from, or combined with, a second tool such as a profile cutter tool of predefined geometry. The first or intermediate tool causes slitting or thinning of walls for entry of the profile cutter. The insertion of this profile cutter tool forms the aperture in step (b) of the above method. The intermediate and second tools may be tapered with at least one cutting edge formed along the taper. The first tool is also provided with cutting edge(s) though the first tool need not be of tapered geometry. Preferably, however, the profile cutter tool comprises two cutting edges diametrically disposed either side of the tool. Although the cutting edge along the tapered portion is required on only one side of the tool, to provide a better force balance during the piercing process, a cutting edge is advantageously provided on both sides of the tapered piercing tool. More cutting edges could be incorporated, if desired, and not prevented by design constraints.

Cutting edge(s) of the first tool form(s) a notch/opening in the material of the part during insertion of the piercing tool into the part. This weakens the wall material in preparation for the second working step (b) of the piercing method. The notch/opening may extend towards an outer edge of the aperture which may be substantially equal to or less than final size of the aperture/opening required.

During step (b), one cutting edge, for example a bottom edge (assuming that the piercing tool is inserted from above), of the tapered portion of the profile cutter tool enters into the thinned area or aperture formed in the pipe and the this cutting edge of the tapered portion forms a slit, or pilot aperture, substantially equal to the total dimension of the aperture to be formed in the pipe. This is followed by profile cutting to form an aperture of the desired size and geometry. Cutting forces during the cutting operation should be less than the force (bending force) required to deform the part. The desired geometry may pertain to the cross-sectional shape of the aperture and may also pertain to the geometry of the walls of the aperture which may, for example, require to be threaded. If necessary, a still further tool may be employed in accordance with the method to achieve the threading or other required forming of the aperture walls.

The invention achieves the object of providing a piercing tool, which forms an aperture in a non-planar surface which is so configured and shaped that there is no need to conduct the additional step of removing the burr caused by the cutting. According to the invention, this object is attained in that the second tool is so constructed in shape that it can smoothen the end face and also to round off the end face around the hole so that burr caused by cutting in the hole will not axially project beyond other parts of end face of the hole.

The geometric shape of the second tool may be constructed as described above differently but always provided with a tapering tip. As such if the removal of the material in the end face of the aperture surrounding the aperture must be avoided the piercing tool as per the invention can be used, of which the leading portion is tapered tip and second portion has a desired geometry.

Where the part is a pipe or other hollow member, the method may be employed to form a through opening in which an aligned set of apertures is formed in the wall of the pipe or hollow member. If the pipe or hollow member is used as a frame member of a motorcycle, for example, the aligned set of apertures allows for fitting of one or more other frame members or components to the frame member using fastener(s) fitted through the respective apertures. To this end, the second tool (and the first/intermediate tool if combined with the second tool) may be progressed through the wall of the part to form the first aperture of the set and then a second and any further walls of the part to form the aligned set of apertures. Alternatively, the method may be controlled such that a single aperture is formed in the wall of the pipe or hollow member at the intended location.
The aperture may be of any desired geometry or shape. The desired geometry or shape of the aperture is dictated primarily by the predefined geometry of the piercing tool, for working the part to form aperture which is predefined or selected as required. Predefined geometries may include spiral or corkscrew (forming, for example, circular apertures) and possibly circular, oval, elliptical, quadrilateral, triangular and other geometries. Any taper of the tool also comprises part of the predefined geometry and may be designed with required slope and so on to achieve the required predefined geometry.
In a further embodiment, the present invention provides an apparatus for piercing a part to form an aperture, the apparatus comprising:

a) a first tool for reducing the thickness of the part at an intended location of an aperture; and

b) a second tool for working the part at said intended location of the aperture with a piercing tool of predefined geometry to form the aperture.

More specifically, a burr-like unnecessary portion protruding radially inward of the prepared hole is formed after the prepared-hole punching step, the first step (a) and the intermediate step. As described above, in the second step (b), the second portion is formed by driving the second punch having the generally geometric shape in the trailing pressing portion extending from the center of the leading tapered tip.

The second tool is generally spaced from the fist tool to form the apparatus.

The first and second tools may be combined or integrated into a single piercing tool. The apparatus may be configured to carry out any of the steps and various processes of the method as above described. For example, if a pilot opening is formed by the first tool, an intermediate tool as above described may be employed to work the thinned material and expand that opening prior to use of the second tool to form the aperture of desired geometry, advantageously through profile cutting.

The second or piercing tool may be of predefined geometry for use in forming an aperture in a part, the piercing tool having a first portion and a second portion, the first portion comprising a tapered section intended for penetrating the wall of the part and the second portion comprising a profile cutter intended to cut and remove material from the part so as to form in aperture in the part.

The shape of the second tool is consisting of geometry such as screw thereby when the tool is advanced it scoops up a volume of the debris and perform simultaneously the essential step of deburring the edge formed during the punching operation.

The piercing tool is characterised in the second tool, wherein the second tool has a tapering leading end portion as a tip and a defined geometric second portion adjoining the leading end portion coaxially.

The tapered tip is the leading edge of second tool head with surfaces that extend perpendicular to the tool axis. The taper along tip allows the second head to "get a bite" on the part, so as to result in a hole having the desired shape and size.

The invention is further described and illustrated with the aid of the following
drawings.

The method and apparatus of the invention may be more fully understood from
the following description of a preferred embodiment thereof made with reference
to the accompanying drawings in which:

Figure 1 schematically indicates a prior art method for forming an aperture in a part;

Figure 2a schematically indicates a method for piercing a part to form an aperture in accordance with one embodiment of the present invention;

Figure 2b illustrates a cross sectional view of a pipe after reduction of part thickness or thinning by a method in accordance with one embodiment of the present invention;

Figure 3 schematically illustrates a piercing tool that may be used in accordance with one embodiment of the present invention;

Figure 4a is a side view of the piercing tool shown in Figure 3;

Figure 4b is a detail perspective view of the piercing tool of Figure 4a;

Figures 5a to 5f show steps in a flowsheet schematically illustrating the progress of a pipe through the method of one embodiment of the present invention.

Referring now to Figure 1, there is shown a part being a pipe 1, of circular cross section and having a curved portion along its length, in which an aperture is to be formed by a drilling process marked as 2. Drilling, as previously explained, has disadvantages in terms of requirement for a deburring process and requirement for chips produced due to drilling to be removed.

Referring to Figures 2a and 2b, the pipe 10, forming a part or member of a motorcycle frame and required to be provided with an aperture or hole, is subjected to a two step method for forming the aperture. In the first step (a), the pipe 10 has its wall thickness reduced, or thinned, by a first tool at the intended location of the aperture which is to be a circular through aperture extending through two segments of the wall of pipe 10, the correspondent aligned circular apertures enabling a frame fastener or connector to be inserted through the pipe wall which is to act as a motorcycle frame member. In the subsequent second step (b), the pipe 10 is worked at the intended location of the aperture with a second piercing tool 13 of predefined geometry to form the desired circular apertures.

The first step (a) is conducted by passing pipe 10 through a thinning process by way of forming notches 12 by the first tool at portions including points diametrically opposed across the bore of pipe 10. The first tool is a notching tool 11 is used for this purpose, one for each of the notches 12. Prior to this thinning or notching process, the pipe 10 is clamped in a suitable fixture. The notching process itself is performed by progressing the notching tool 11 through the wall of the pipe 10, at the intended location of the aperture, and in a direction perpendicular to the longitudinal axis of the pipe at the location where the aperture is to be formed. Such a notching process could be replaced with a milling, grinding or any like thinning process. It may be understood that such thinning processes may be used in combination. For example, notching could be used with milling; milling could be used with grinding.

During the thinning step (a), material is removed from both sides of the pipe wall at the intended location of the aperture. For example, where it is desired to form a circular aperture of 16mm diameter in a pipe having an inner diameter of 30mm and wall thickness 1.6mm, a thinning process may be used to thin the pipe wall thickness to 0.2mm at the intended location of the aperture (normally at the centre point of the aperture to be formed though this point could be varied for example with reference to the geometry of the aperture to be formed). A small or pilot aperture may be formed during this thinning step depending on the thickness of the wall of pipe 10. This pilot aperture is not of the desired diameter or other required dimension for the aperture, hole or opening to be formed. Formation of a small or pilot aperture may also be conducted as a deliberate step of the method of piercing the pipe. In either event, a further step is required to form the desired aperture.

Figure 2b shows a cross-sectional view of pipe 10 after thinning step (a). The thinned portions or notches are marked "12". In an alternative and second embodiment, small pilot aperture 12a, as shown in Figure 5b, is formed in the thinned portions 12.
The next step (b) of the method is indicated by Figure 3. The pipe 10, having been subjected to thinning step (a), is clamped on a suitable clamping arrangement (not shown). A second or piercing tool 13 of predefined geometry, with a suitable holding and sliding arrangement (not shown) is allowed to progress towards the thinned area or notch 12 of pipe 10. For example, the tool may be mounted on a press ram using a mounting plate. The press ram provides the sliding required for the tools. A leading or front portion of the tool 13, which dependent on the orientation of the tool and part may be a lower portion, is provided with tapered profile 14. As the tool 13 progresses towards pipe 10, tapered portion 14 gradually enters into the thinned portion or notch formed during thinning step (a).

As may be better seen in Figures 4a and 4b, the dimension of trailing or rear end 14b of tapered portion 14 of tool 13 has a dimension so defined that, on insertion of the tapered portion 14, into the notch 12, a pilot aperture is formed having substantially equal dimension to the diameter of the desired circular aperture to be formed in the pipe. 10 The dimension of tapered portion 14 of tool 13 may, alternatively be slightly less than (but not exceeding) the desired diameter of the circular aperture to be formed in the pipe 10 depending upon the pipe dimensions and the shape of pipe and size of aperture to be formed in pipe 10. As may be seen in Figure 4b, the tapered portion 14 may comprise two cutting edges 20 which taper from end 14a of the piercing tool 13 to the end 14b of the tapered portion of piercing tool 13. Further along piercing tool 13 is a profile cutter portion to be described below. The cutting edges 20, at end 14b, have dimension equal to or just slightly less than the intended diameter of the aperture to be formed in the pipe 10.
As the piercing tool 13 is inserted further into the notch 12 of pipe 10, the profile cutter portion 15 of the piercing tool 13, cuts and removes material from the pipe to form the desired final aperture. To that end, profile cutter portion 15 of piercing tool 13 has a predefined geometry correspondent with the desired geometry of the circular aperture to be formed. Here, the profile cutter portion 15 has a cutting edge 16 in the form of a spiral or corkscrew shape which is suitable for forming the desired circular aperture. It may be noted that, during linear movement of the cutter portion 15 through the pipe 10 wall, there is no rotation of the piercing tool 13 and a distinction may be made, in this respect, from a drilling operation which requires such rotation, sometimes at appreciable speed with a motor being required to achieve rotation.

The piercing tool 13 is then progressed on and through the pipe wall to the opposed side of the pipe 10 and the process is repeated to form the second aperture which is aligned with the first so, for example, fasteners may be inserted through the pipe 10 to connect other parts during assembly of a motorcycle. These other parts could include other frame members.

Figures 5(a) to (f) show the state of the pipe 10 at the beginning and end of the piercing method as well as after each of the steps of the method of piercing described as the second embodiment, in which a pilot aperture is formed in the thinning step (a).

So, Figure 5(a) shows the pipe 10 in its initial condition. Figure 5b shows the pipe 10 after notches, or thinned portions, 12 are formed in the wall of pipe 10 in accordance with step (a) of the method. A pilot aperture 12a is formed during this step as shown in Figure 5(b).

At Figure 5(c), is indicated the result of the intermediate step of inserting the tapered portion 14 of piercing tool 13 such that the cutting edges 20 expand the pilot aperture 12a to a larger aperture 12b (in this case without removing any additional material from the intended location of the aperture). Aperture 12b has a span equal to, or slightly less than, the intended final diameter of the desired aperture.

At Figures 5(d) to (f) is indicated the progressive working of the pipe 10 by the piercing tool to form circular apertures through operation of the profile cutter portion 15 of piercing tool 13, rather than the tapered portion 14, the profile cutter portion 15 having a cutting edge 16 of spiral or corkscrew shape. Operation of the profile cutter portion 15 involves forcing the profile cutter portion 15 through pipe 10 walls. Removal of material during this stage of the method may be achieved, for example, by gentle tapping of pipe 10 on a softer material.

Following the method, as above described, the Applicant has - during trials -achieved reduction in cycle time for forming an aperture from 30 seconds to 10 seconds as compared with a drilling method. Also, better tolerance and positional accuracy has been achieved. Appreciable marginal cost benefits in using the method of piercing of the invention, as described here, may be expected.

The difficulties and drawbacks of previous punch press tools are overcome by the tool of the present invention, for use with a punching press for punching holes in parts. More particularly, the present invention provides a tool with improved useful application. A punch body is with a unique geometry shape and as will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative and not restrictive.

By providing a double-portion second tool punch with a uniform linearly tapered tip, it has been discovered that a cleaner, more efficient punch operation can be obtained. Metal is inherently somewhat elastic, and during a punch operation, the metal part expands around the punch. In operation with the present punch, the intermediary tool penetrates the metal. The part expands around the intermediary tool head and contracts around the tapered tip of the second tool. The part subsequently encounters the second tool head, which performs a second punching operation. In this way, the intermediary tool head cuts the part, and the second punch tool cleans the punched hole, thereby producing a clean hole that requires little or no subsequent machining, superior to the results obtained with a typical punch. The second punch tool also helps to ensure that proper tolerances are maintained on the hole that is being formed as intermediary tool punch head wears. The tapered tip of the second tool serves to provide a location so as not distort the dimensions of the hole being formed in the part.

Modifications and variations to the method and apparatus for piercing a part in accordance with the present invention may be apparent to those skilled in the art. Such modifications and variations are deemed within the scope of the present invention. Therefore the scope of the invention is defined not by the detailed description but by various changes in form and details that may be made therein without departing from the spirit and scope of the invention.

WE CLAIM :

1. A method of piercing an aperture having a desired geometry in a part at an
intended location from one side of the part towards the other side of the
part, which part may have a non-planar surface at the intended location of
the intended aperture comprising the steps of:

a. reducing the thickness of the part at the intended location of the aperture,

b. punching the said part with a piercing tool to create a pilot aperture
having a diameter substantially equal to or less than the intended

aperture diameter at the intended location of the desired aperture,

c. inserting further the piercing tool with a predefined geometry including a tapered tip with a predefined slope corresponding to the desired geometry of the intended aperture linearly without any rotation of the piercing tool through the pilot aperture wall of the part for piercing through the pilot aperture and removing the material
from the part so as to form the intended aperture having the desired
geometry in the part at the intended location.

2. An apparatus for piercing a part to form an aperture extending from one side of the part towards and through to the other side of the part having a desired geometry in the part at an intended location and which part may have a non-planar surface at the intended location of the intended aperture, the said apparatus comprising of the following portions :

a. a first tool with atleast one cutting edge adapted to progress through the part in a direction perpendicular to the part and adapted to form a notch in the material of the part thereby reducing the thickness of the part at the intended location of the intended aperture,

b. a tapered intermediate tool having atleast one cutting edge and adapted to enter from one side or both sides of the part at the intended location now with reduced thickness after step (a) to form a pilot aperture in the part, and

c. a second tool which is a piercing tool having a predefined geometry including a tapered tip with atleast one cutting edge and adapted to pierce through the pilot aperture and removing the material from the part so as to form the intended aperture having the desired geometry in the part.

3. Reducing the thickness as claimed in claim 1 or 2, means removal of portion of the part by notching, grinding, milling or any other operations or combination thereof.

4. Removal of the part as claimed in claim 3, means removal of material from one side of the part.

5. Removal of the part as claimed in claim 3, means removal of material from more than one side of the part.

6. Predefined geometry of piercing tool as claimed in claim 1 or 2, means a tapered tip and including spiral, cork screw, circular, oval, elliptical, quadrilateral, triangle and other geometries.

7. Predefined geometry of the piercing tool as claimed in claim 6 is based on the desired cross sectional shape of the intended aperture and also on the desired geometry of the walls of the intended aperture.

8. The part claimed in claim 1 is a component for use in the automotive industry.