Claims:We claim:

1. A triple-margin drilling tool for making accurate tappet holes, the drill comprising:

(i) a first margin configured as drilling margin provided for centering and drilling,

(ii) a second margin configured as hole-milling margin for milling the drilled hole, and

(iii) a third margin configured as reaming margin for reaming the milled hole to obtain the targeted hole-size accurately,

wherein the first margin has the maximum drilling diameter, the second margin has the medium drilling diameter and the third margin has the maximum drilling diameter, which is exactly equal to the targeted hole-size to be drilled.

2. Triple-margin drilling tool as claimed in claim 1, wherein the drilling margin diameter is between 0.6 and 0.10 mm, preferably 0.08 mm less than the targeted hole-size to be drilled.

3. Triple-margin drilling tool as claimed in claim 1, wherein the hole-milling margin diameter is between 0.5 and 0.08 mm, preferably 0.05 mm less than the targeted hole-size to be drilled.

4. Triple-margin drilling tool as claimed in claim 1, wherein the reaming margin diameter is exactly equal to the targeted hole-size to be drilled.

5. Triple-margin drilling tool as claimed in claim 1, wherein the web width at the point of the drill is between 0.15 and 0.30 mm, preferably between 0.18 and 0.25 mm.

6. Triple-margin drilling tool as claimed in claim 1, wherein the point angle is between 1200 and 1500, preferably 1400.

7. Triple-margin drilling tool as claimed in claim 1, wherein the flute length is between 40 to 50 mm, preferably 45 mm.

8. Triple-margin drilling tool as claimed in claim 1, wherein the primary cutting angle is between 60 and 100, preferably 80.

9. Triple-margin drilling tool as claimed in claim 1, wherein the relief angle is between 250 and 300, preferably 280.

10. Triple-margin drilling tool as claimed in claim 1, wherein the cycle-time required for making the tappet hole is between 2 to 3 minutes, preferably 2.4 minutes.

Dated: this 28th day of September, 2015. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT , Description:FIELD OF INVENTION

The present invention relates to the drilling tool for making accurate holes on machined components. In particular, the invention relates to a single drilling tool for making accurate tappet holes. More particularly, the present invention relates to the triple-margin drilling tool for making accurate tappet holes.

BACKGROUND OF THE INVENTION

Web thinning of the drills is used for making holes in components, e.g. automotive components is very important factor, because a 2 degree change in angle of entry and exit angle changing, substantially changes the dimensions of the holes drilled. It is a common practice worldwide to use four different cutting tools for obtaining holes of desired accuracy. These tools are:

(i) Centering tool for precise positioning of the hole to be made,

(ii) Rough drilling tool for making the hole,

(iii) Hole milling tool for correcting the hole-axis, and

(iv) Reaming tool for sizing to obtain desired hole accuracy and finish.

The International Standards Organization (ISO) has prescribed a coordinated system of limits and fits for hole and shaft tolerances used for engineering and manufacturing practices, to be for cutting tools, material stock, gauges etc. All cutting tools, material stocks and gauges are generally available within these tolerances throughout the world. In particular, the hole-basis fits have four preferred hole tolerances, i.e. H11, H9, H8 and H7 and the shaft basis fits have four preferred shaft tolerances, i.e. h11, h9, h7 and h6.

DEFINITIONS

The most important terms relating to limits and fits are defined as under:

Basic size is the size to which limits and deviations are assigned. The basic size is the same for both members of a fit. For example, it is designated by the number 40 in 40H7.

Clearance: The space provided to eliminate undesirable contact between the drill and the workpiece.

Clearance Diameter: The diameter over the cut away portion of the drill lands.

Clearance fit indicates the relationship between assembled parts, when clearance occurs under all tolerance conditions.

Double Margin Drill: A drill whose body diameter clearance is produced to leave more than one margin on each land and is normally made with margins on the leading edge and on the heel of the land.

Drill Diameter: The diameter over the margins of the drill measured at the point.

Deviation is the algebraic difference between an actual size and the corresponding basic size.

Fundamental Deviation is one of the two deviations closest to the basic size. It is designated, e.g. by the letter H in 40H7 above.

Hole-basis system is a system of fits, where the minimum hole-size is basic. The fundamental deviation for a hole-basis system is ‘H’.

International Tolerance Grade (IT) is a group of tolerances which vary depending on the basic size, but which provide the same relative level of accuracy within a given grade. It is designated, e.g. by number 7 in 40H7.

Interference fit indicates the relationship between the assembled parts, when interference occurs under all tolerance conditions.

Land: The peripheral portion of the body between adjacent flutes. Therefore, land is the remainder of the outside of the drill body after the flutes are cut and thus land is cut-back a little from the outer drill diameter to provide clearance.

Land Width: The distance between the leading edge and the heel of the land measured at a right angle to the leading edge.

Lower Deviation is the algebraic difference between the minimum size-limit and the corresponding basic size.

Margin: The cylindrical portion of the land which is not cut away to provide clearance, therefore preserves the full drill diameter.

Multiple-Margin Drill: A drill whose body diameter clearance is produced to leave more than one margin in each land.

Shaft-basis system is a system of fits, where the maximum shaft-size is basic. The fundamental deviation for a hole-basis system is ‘h’.

Tolerance is the difference of maximum and minimum size limits on a part.

Tolerance zone is a zone representing the tolerance and its position in relation to the basic size.

Transition is the relationship between the assembled parts, when either a clearance or interference fit results depending on the tolerance conditions of the mating parts.

Triple-Margin Drill: A drill whose body diameter clearance is produced to leave three margins in each land, e.g. drilling margin, hole-milling margin and reaming margin, as in the drill of the present invention.

Upper Deviation is the algebraic difference between the maximum limits of size and the corresponding basic size.

Web is the central portion of the body that joins the lands; the extreme end of the web forms the chisel edge on a two-flute drill.

Web Thinning is the operation of reducing the web thickness at the point to reduce drilling thrust.

Web-width is the minimum dimension of the web measured at the point of the drill.

By combining the International Tolerance Grade (IT) number and the tolerance position letter, the tolerance symbol is established which identifies the actual maximum and minimum limits of the part. The tolerance sizes are therefore defined by the basic size of the part followed by a symbol composed of a letter and a number, e.g. 40H8 (Figure 10).

DISADVANTAGES WITH THE PRIOR ART

It was observed while adopting the conventional methods for making tappet holes with H8 tolerance that it involves four (4) steps, as mentioned above, i.e. centering of the hole, rough drilling of the hole, hole milling for axis correction and finishing of the hole by reamer for arriving at the required dimension and surface finish. Therefore, the total process takes very long cycle time to complete. This high cycle time is the main constrain for completing this hole making operation on any component.

Generally, a burnishing drill with at least two lands is currently available in the market. However, the major disadvantage of this drill is the inconsistency of the hole size and hole axis made thereby, because these two lands are provided for drilling and burnishing of the surface finish of the hole. The main disadvantages of the existing technology are as under:

• The cycle time for Conventional method of hole-making was very high.

• The occurrence of drill breakage due to less or more stock available for finishing operation is also very high.

• The drills available in market were not consistent for providing the desired hole-accuracy.

Normally the any machining of finished tappet hole via the conventional machining process consumes a significantly higher cycle time. The centering of the hole over the casting surface, rough drilling and reaming for finishing operation also consumes a large part of this high cycle time. This a conventional process usually adopted by everywhere.

Therefore, there is an existing need for providing a single drilling tool for tappet holes, which has an additional cutting land for the reamer between the drilling and burnishing operations to obtain accurate tappet holes in internal combustion engines.

DESCRIPTION OF THE PRESENT INVENTION

In accordance with the present invention, a triple margin drill is developed, which assures the size (reamer margin), surface finish (burnishing land) and the hole-axis (hole-mill margin). After the primary angle of 8 degrees, the relief angle removes the material radially up to the end of the lip. This lip profile has a unique feature giving the last margin in up position with respect to the middle margin. This profile is only adjusted by changing the gashing angle and by controlling the angles of entry and exit. The lip profile governing the total drill life and size is designed and produced in-house for own use. In order to reduce the cycle time and thus the cost of the tool and also to obtain the required quality of the hole, the following measures were adopted:

• Developing a drill with triple margin with centering, drilling, hole-milling and reaming operations simultaneously.

• The lip profile is obtained such that after the drilling operation, the extreme lip comes in contact with the surface and then only the middle reamer land comes in contact. The lip profile shown in Figure 7.

Therefore, providing a triple margin simultaneously for centering, drilling, hole milling and reaming in the geometry of one single cutting lip) becomes the very special feature of the present invention. Each and every margin land (3 margin lands) has special features, such as margin width, radius and angles, which determine the size, axis and the surface finish of the hole. At present, the invention is successfully being used, its testing is also over and the results are very positive. Even the relevant TPM consultants have witnessed the improvements brought about by the present invention.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a single tool for machining accurate holes in internal combustion engines.

Another object of the present invention is to provide a single tool for drilling holes with a reduced cycle time.

Still another object of the present invention is to provide a single tool for making holes of consistent size and surface finish.

Yet another object of the present invention is to provide a single tool for machining holes which reduces the cost of machining.

A yet further object of the present invention is to provide simplified method for making accurate holes using a single tool, which reduces the overall cycle time of machining such holes.

These and other objects and advantages of the present invention will become more apparent from the following description when read with the accompanying figures of drawing, which are, however, not intended to limit the scope of the present invention in any way.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a triple-margin drilling tool for making accurate tappet holes, the drill comprising:

(i) a first margin configured as drilling margin provided for centering and drilling,

(ii) a second margin configured as hole-milling margin for milling the drilled hole, and

(iii) a third margin configured as reaming margin for reaming the milled hole to obtain the targeted hole-size accurately,

wherein the first margin has the maximum drilling diameter, the second margin has the medium drilling diameter and the third margin has the maximum drilling diameter, which is exactly equal to the targeted hole-size to be drilled.

Typically, the drilling margin diameter is between 0.6 and 0.10 mm, preferably 0.08 mm less than the targeted hole-size to be drilled.

Typically, the hole-milling margin diameter is between 0.5 and 0.08 mm, preferably 0.05 mm less than the targeted hole-size to be drilled.

Typically, the reaming margin diameter is exactly equal to the targeted hole-size to be drilled.

Typically, the web width at the point of the drill is between 0.15 and 0.30 mm, preferably between 0.18 and 0.25 mm.

Typically, the point angle is between 1200 and 1500, preferably 1400.

Typically, the flute length is between 40 to 50 mm, preferably 45 mm.

Typically, the primary cutting angle is between 60 and 100, preferably 80.

Typically, the relief angle is between 250 and 300, preferably 280.

Typically, the cycle-time required for making the tappet hole is between 2 to 3 minutes, preferably 2.4 minutes.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with reference to the accompanying drawings, which include:

Figure 1 shows an example of the combination of IT number and the tolerance position letter.

Figure 2 shows an exemplary fit indicated by the basic size common to both the components (hole, shaft).

Figure 3 shows a perspective view of the conventional tool for making tappet holes by using a central drill for centering the hole position over the surface of any casting required to be drilled.

Figure 4 shows a perspective view of the step drill for making a tappet hole and chamfer on entering the surface to be drilled.

Figure 5 shows a perspective view of the tappet hole milling tool for correcting the hole-axis.

Figure 6 shows a perspective view of the of the standard reamer for finishing of the tappet hole-size and surface fining as per the requirement.

Figure 7 shows a perspective view of the tool for making accurate tappet holes in accordance with the present invention.

Figure 8 shows a detailed view of the tip of the tool of Figure 7.

Figure 9 shows the lip profile of the tool of Figure 8.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, different embodiments of the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

Figure 1 shows an example of the combination of International Tolerance Grade (IT) number and the tolerance position letter (H or h). The tolerance zone symbol is established which identifies the actual maximum Mx and minimum Mn limits of the part. The tolerance sizes are therefore defined by the basic size BS of the part followed by a symbol composed of a letter expressed in terms of the fundamental deviations (H for holes with internal dimensions or f for shaft with external dimensions) in the basic size BS. These are upper deviation UD and lower deviation LD respectively.

Figure 2 shows an exemplary fit indicated by the basic size (40 mm here) common to both the components (hole and shaft) followed by a symbol corresponding to each component (H or f). The symbol of the part with internal dimensions (H8 here) precedes the symbol of the part with external dimensions (f7 here). The tolerance zone symbol (H8) is established which identifies the actual maximum and minimum limits of the part. Therefore, the tolerance sizes are defined by the basic size (40 mm here) of the part followed by a symbol composed of a letter (H or f) and a number (8 or 7).

Figure 3 shows a detailed front view of the conventional tool 10 for making tappet holes by using a central drill for position of the centering hole over any casting surface. It includes a cutting tool length L1 and cutting tool diameter D. Tool lips make a point angle A1 and the web-width at the point of the drill is WW. Normally, drill length is L1 and transition zone between the cutting tool and tool shank face makes an angle A2, preferably of 900.

Figure 4 shows a detailed front view of the conventional step drill 20 for making a tappet hole and forming a chamfer on entering the surface to be drilled. Normally, drill length is L3 and it includes a cutting tool length L4 and cutting tool diameter D. Tool lips make a point angle A3, which is slightly higher than point angle A1 for centering tool and the web-width WW at the point of the drill is the same as for centering tool (Figure 3). The transition zone between the cutting tool and tool shank face makes an angle A4, preferably of 900.

Figure 5 shows a detailed front view of the conventional milling tool 30 for correcting the tappet hole-axis by milling of the hole already drilled (Figure 4). Normally, milling tool length is L5 and it includes a cutting tool length L6 as per the requirement. Normally reamer tool diameter D1 is about 0.3 mm less than the final hole-size to be obtained by subsequent final reaming operation.

Figure 6 shows a detailed front view of the conventional standard reamer 40 for finishing of the tappet hole-size and surface fining. Normally, reamer length is L7 and it includes a cutting tool length L8 as per the requirement. Tool tip is flat and the edges thereof make an angle A5 with the tool sides for safeguarding tool edges from chipping off. Normally, the tool diameter D2 is as per the final hole-size to be obtained.

Figure 7 shows a perspective view of the tool 100 for making accurate tappet holes by a single drilling tool in accordance with the present invention. Here, the single drilling tool includes triple land margins, i.e. for centering, drilling, hole milling and reaming. This drilling tool includes a cutting tool length 9 and the tool lips make a point angle A6, e.g. of 1400, the transition zone between the cutting tool and tool shank makes an included angle A7, preferably of 900. The detail tool profile is given with reference to Figure 8 described further below.

Figure 8 shows a detailed view of the tip 150 (encircled) of the tool tip of Figure 7. According to the specific embodiment illustrated in this figure, the drill land margin DM includes a size of about 0.08 mm less diameter than the required final / finish drilled hole-size. This extra material is provided as stock for hole-milling operation by the subsequent hole-milling land margin HM, which in turn has a size of about 0.05 mm less diameter than the required final / finish drilled-hole size. This extra material also is provided as stock for final finishing during reaming operation by the subsequent reaming land margin RM. After this final reaming operation, the final / finished hole of the required diameter / specified size is obtained. At the point of the drill, the web-width WW1 is, e.g. in a range of 0.18 to 0.25 mm.

Figure 9 shows the lip profile of the tool tip of Figure 8. It illustrates the cutting land 152, reaming land 154 and burnishing land 156. The front cutting edge makes a point angle A1 with the face of the cutting land 152. Similarly, the burnishing edge 156 makes an angle A2 with the rear edge of the tool tip. In addition, the face of the cutting edge makes a point angle A3 with the tool face to provide a relief for removal of chips produced during tool cutting.

WORKING OF THE INVENTION

The drilling tool in accordance with the present invention is configured as a triple margin drill for making tappet holes, which assures the accurate hole-size by the reamer margin, surface finish by the burnishing land and the hole-axis by the hole-mill margin. After the primary angle of 8 degrees, the relief angle removes the material radially up to the end of the lip. This lip profile has a unique feature giving the last margin in up position with respect to the middle margin. This profile is only adjusted by changing the gashing angle and by controlling the angles of entry and exit. Therefore, this triple margin drill consists of different land margins having specific profiles for centering, drilling, hole-milling and reaming operations in this very chronology. The point of the drill has a web width WW1 having a value of 0.18 to 0.25 mm. This drill point web touches the work piece first and thereby helps in center positioning the tool on the work piece. Further, once tool tip is centered, the drilling land margin DM comes into play for making a rough hole, which consists of the largest diameter having a drilling size of about 0.08 mm less diameter than the final hole-size to be drilled with a lower cycle time. Next, the hole-milling margin HM comes into play, which consists of a medium diameter having a drilling size of about 0.05 mm less than the required final / finish drilled-hole size. Finally, the reamer margin RM comes into play, which has the exact drilling size equal to the targeted accurate hole size to be drilled by this triple-margin drilling tool. This unique drill is designed in such a way that its triple-margin lip profile facilitates in that after drilling, the extreme lip comes in contact with the surface and only then the middle reamer land comes in contact therewith.

Thus, the triple margin at the same time (i.e. for centering, drilling, hole-milling and reaming in this single cutting lip geometry) is a very special feature of the present invention. Each and every margin (3 margins) has special features, such as margin width, radius and angle, which govern the size, axis and the surface finish of the holes obtained thereby. This triple-margin drill also improves productivity by lowering the drilling cycle time and also makes this drill useful for obtaining holes of consistent accuracy.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

The triple-margin drilling tool for making tappet holes in accordance with the present invention has the following advantages:

1) Low cycle-time, thus increased productivity.

2) Tool breakage is eliminated / reduced, thus reduces tool cost.

3) Holes of consistent size and surface finish are obtained.

4) Also reduces drill cost by combining four tools, i.e. centering, drilling, hole-milling and reaming in a single tool.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.

The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention.

Although, only the preferred embodiments have been described herein, the skilled person in the art would readily recognize to apply these embodiments with any modification possible within the spirit and scope of the present invention as described in this specification.

Therefore, innumerable changes, variations, modifications, alterations may be made and/or integrations in terms of materials and method used may be devised to configure, manufacture and assemble various constituents, components, subassemblies and assemblies according to their size, shapes, orientations and interrelationships.

The description provided herein is purely by way of example and illustration. The various features and advantageous details are explained with reference to this non-limiting embodiment in the above description in accordance with the present invention. The descriptions of well-known components and manufacturing and processing techniques are consciously omitted in this specification, so as not to unnecessarily obscure the specification.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.