GB2122931A

GB2122931A - Forming workpiece location holes on centreless grinding machines

Info

Publication number: GB2122931A
Application number: GB08317892A
Authority: GB
Inventors: Leonardus Andries Pieters
Original assignee: Cincinnati Milacron Inc
Current assignee: Milacron Inc
Priority date: 1982-07-02
Filing date: 1983-07-01
Publication date: 1984-01-25
Also published as: FR2529496A1; JPS597508A; GB8317892D0; NL8301118A; DE3323451A1; GB2122931B

Abstract

To enable the formation of location holes in the ends of a workpiece while undergoing or subsequent to a centreless grinding operation, such grinding machine including location hole cutters (38) movable into engagement with the end faces of a workpiece (14), the cutters (38) being mounted on slides to enable movement into engagement with the workpiece (14). Adjustment means (31, 34) may be provided to move the axis of rotation of the cutting tools (38) in a plane substantially at right angles to the axis of the ground workpiece. Each cutter (38) may be in the form of a grinding wheel or a drill. <IMAGE>

Description

SPECIFICATION Apparatus and method for forming workpiece location holes during or subsequent to a centreless grinding operation The invention applies to a method of and apparatus for grinding workpieces and has prime but not exclusive application to the grinding of shaft like workpieces having a plurality of operations to be performed on the shaft.

In the manufacture of shaft like workpieces such as transmission shafts, a shaft is fitted with machined or punched location holes at its extreme opposite ends, whereby lathing operations can be performed while the workpiece is turned about an axis extending between said centres. During subsequent centreless grinding operations, certain ground diameters are generated concentric with one another, but the concentricity of those diameters with the centre holes and central axis of the shaft is destroyed. If a gear cutting operation, for example, is performed subsequent to the outside diameter centreless grinding operation, the location holes must be re-established in the workpiece so that the gear cutting operation can be performed.

Applicant has considered the difficulty in the above described processing steps, and has determined that it would be most desirable to have a workpiece which, at the end of the centreless grinding operation, would have centre holes concentric with the ground outer diameters.

It is an object of the present invention to provide an improved apparatus for grinding workpieces that overcomes or reduces the above mentioned problems.

According to one aspect of the present invention, we provide a centreless grinding machine comprising a base part, a workpiece grinding wheel capable of grinding a workpiece at a work station, said grinding wheel mounted for rotation relative to said base wherein said machine further comprises a pair of cutting tools or cutting tool holders capable of forming location holes in said workpiece substantially axial with a surface ground by said grinding machine on said workpiece, said cutting tools or cutting tool holders being mounted relative to said base adjacent either end of said workpiece and capable of movement towards and away from the workpiece so as to enable formation of said location holes during a grinding operation or subsequent thereto.

Preferably said machine base is provided with slideways and said cutting tools or cutting tool holders are supported in slides movable relative to said slideways to enable movement of said cutting tools towards and away from said workpiece, and conveniently means are provided to move said cutting tools into contact with said workpiece during or subsequent to said grinding operation.

Preferably said cutting tools or said cutting tool holders are mounted relative to the machine base and adjustment means are provided to enable adjustment of said cutting tools or cutting tool holders in a plane substantially at right angles to the axis of rotation of said grinding wheel Preferably the machine further comprises a regulating wheel supported on said base movable relative to said grinding wheel, said machine further comprising end location means for axially locating a workpiece, a workpiece support for said grinding wheel, said regulating wheel and said workpiece support together defining a predetermined work station for said workpiece.

According to another aspect of the invention, we provide a centreless grinding machine comprising a machine base, rotatably driven outside diameter grinding and regulating wheels supported on said base and relatively movable with respect to one another to a predetermined workpiece cylinder position, an end stop for axially positioning a workpiece, a workrest blade supported by said base and located between said outside diameter grinding and regulating wheels, defining with said wheels at said position an axis of a circumscribed predetermined workpiece cylinder, an apparatus for machining workpiece location holes while performing an outside diameter grinding operation, characterised by:: (a) first and second relatively fixed slideways located on said base proximal to first and second opposite faces of said outside diameter grinding wheel, respectively; (b) first and second relatively movable slides supported on said slideways respectively, each slide having a rotatable location hole cutting spindle mounted with its axis of rotation disposed coextensive with the other and parallel to the axis of rotation of said outside diameter grinding wheel and radially shifted from said axis of said predetermined workpiece cylinder; (c) first and second location hole cutting tools oppositely disposed to one another and respectively mounted to said centre cutting spindles; and (d) means for relatively moving said slides in accordance with a predetermined operating cycle while said outside diameter grinding and regulating wheels are relatively moving.

Alternatively the machine may be modified in that the axis of rotation of said rotatable centre cutting spindle is coextensive with said axis of said predetermined workpiece cylinder and parallel to the axis of rotation of said grinding wheel.

It is a second object of the present invention to provide a method of forming location holes in a workpiece during or subsequent to a grinding operation.

According to a second aspect of the invention we provide a method of forming location holes in a workpiece, said method comprising the steps of: (a) establishing a desired location axis on a workpiece positioned in a work station on a centreless grinding machine; (b) grinding a surface of revolution on said workpiece by a grinding wheel and causing relative movement between said workpiece and location hole cutting means to cause formation of said locating holes in said workpiece at a predetermined time during or subsequent to said grinding operation.

In one form of the invention, the axes of the centre cutting spindles are radially shifted from the axis of the predetermined work cylinder, so that the centre holes may be generated or cleaned up while the outside diameter is ground in a centreless manner.

In an alternative form of the invention, the axes of the centre spindles are located co-extensive with the axis of the predetermined work cylinder, so that the centre holes may be drilled or otherwise machined subsequent to the centreless operation. In this alternative form of machining, a pressure roll assembly is employed to apply radial force to the workpieces, thus holding it between the regulating wheel and work rest blade.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, wherein:~ FIGURE 1 is a plan view of a centreless grinding machine comprising apparatus for machining centre holes in a workpiece during the centreless grinding operation; FIGURE 2 is an elevational view of the centre cutting apparatus for cutting one end of a shaft, taken in the direction of arrow 2 of Figure 1; FIGURE 3 is an enlarged sectional view taken through the centre hole cutting spindle along the line 3-3 of Figure 2; and FIGURE 4 is a section through a centre hole cutting tool and generated centre hole taken along the line 4-4 of Figure 3.

Referring to the drawings, Figure 1 illustrates a plan view of a centreless grinding machine 10 having a machine base 11, and rotatably driven outside diameter grinding and regulating wheels 12. 13 supported on the base 11.

The grinding and regulating wheels 12, 13 are relatively movable with respect to one another to a predetermined workpiece cylinder position, e.g.

where an exemplary cylinder 14 is established by the wheels 12, 13 and a work rest blade 15 carried on the machine base 11 between the outside diameter grinding and regulating wheels 12, 13, in a manner well known in the art.

A workpiece shoulder 14b is held against a stop 15a formed on the work rest blade 15 by the axial thrust of a slightly canted regulating wheel assembly in a well known manner. At the position shown, the wheels 12, 1 3 and work rest blade 15 are said to "frame" a workpiece cylinder 14, thereby establishing an axis 1 6 of the circumscribed predetermined workpiece cylinder 14.

At opposite side faces 1 7, 1 8 of the grinding wheel 12, the machine base 11 is extended to provide support for a pair of identical centre hole cutting fixtures 19, each comprising in general, a fixed slideway 20, axially movable with respect to the workpiece 14a.

The slideway 20 described herein has a fabricated support carrying parallel slide bars 23 between end blocks 24, 25 and the movable slide 21 consists of a generally plate like member 26, having a pair of bearing blocks 27, 28 affixed thereto, wherein the bearing blocks 27, 28 are complementarily adapted to the slide bar 23.

The centre hole cutting fixture 19 has an adjustable cutting head portion 29, wherein a first head block 30 is adjustable in a vertical direction by means of a vertical adjusting screw 31 and block 32 carried in the slide 21, and a second head block 33 is adjustable by means of a similar horizontal screw 34 and block 35, wherein the adjusting block 35 is affixed to the first head block 30.

The cutting head portion 29 has a rotatably mounted cutting tool spindle 36, having a quill 37 adapted to receive a stem-mounted centre hole cutting tool 38, which, in this case, is depicted as a conical grinding wheel.

A prime mover 39 is mounted to the second head block 33 and coupled to drive the cutting tool spindle 36. The prime mover 39 shown is an air motor of commercial design, but other motors may be substituted. At the opposite end of the workpiece 14a, an identical cutting fixture 19 is employed, so that further description of the second fixture will be omitted.

Figure 2 illustrates an elevational view of the centre hole cutting fixture 19 of Figure 1 , wherein the extended base 11 is shown, having the fabricated slideway support 22 affixed thereto.

The slide bars 23 are securely mounted in the support end blocks 24, 25 and bearing blocks 27, 28 are shown in the advanced position on the slide bars.

The bearing blocks 27, 28 are secured to the movable slide member 26 (depicted in phantom), and the slide has the cutting head portion 29 shown so that the horizontal and vertical head blocks 30, 33 are correctly adjusted for positioning the centre hole cutting tool 38.

The slideway support 22 has a fluid powered cylinder 40 mounted thereto between the bars 23, having a piston rod 41 axially movable with respect to the cylinder 40. The rod 41 is attached to the front bearing block 27 by a yoke portion 42, so that linear movement of the piston rod 41 due to fluid propulsion will likewise cause the slide 21 to move in a linear direction.

Figure 3 illustrates a workpiece cylinder 14 which is of predetermined finished size, supported or "framed" by the regulating wheel 13; grinding wheel 12; and work rest blade 15. The predetermined cylinder 14 establishes a reference axis 16. Tangent lines to the work rest blade and regulating wheel A, B, intersect at a point C which forms a crotch for an oversize workpiece 14a as it rounds up and diminishes in size.

During machining, the axis of the workpiece will therefore generally move along a substantially constant line D which bisects the included crotch angle (the large radius surface of the regulating wheel considered substantially flat).

The axis 43 of the centre hole cutting tool spindle 36 is radially shifted an amount e and is aligned parallel with the cylinder axis 16 and cutting tool axis 44. In the example shown, the workpiece 14a has a rough, or preformed conical opening 45 in its end, which may be either punched or centre drilled. The opening 45 allows the entry of an axially moving centre hole cutting tool 38, which engages the workpiece 14a and generates a conical finished hole as the rough opening 45 gyrates around the conical tool 38.

By a timed cycle, the final axial position of the centre hole cutting tool 38 is attained simultaneously with or immediately following the final size of the ground outer diameter, so that final machining of the centre hole is accomplished as the workpiece 14a is undergoing pure rotation with no radial translation (translation occurring during the rounding up cycle).

The section of Figure 4 illustrates the conical grinding wheel 38 during its approach, illustrating the eccentricity or radial shift, e of the axis 43 of the centre cutting spindle, relative to the predetermined reference axis.

It is preferable to use a cutter which will hold its form over a range of parts. Therefore, when using a grinding wheel as a tool, a hard wheel is preferred to avoid the necessity of continually re-shaping the wheel.

During actual cutting tests, it was found that CBN (cubic boron nitride) grinding wheels, commercially available under the Trade Mark "Borazon", are not very suitable for soft steel applications, but they work well on hardened steel parts.

Diamond impregnated type wheels have been successfully applied and, in general, tend to last longer than other grinding wheels.

Multi-tool tapered cutting tools (either high speed steel or carbide tipped) have been employed to mill the centre holes to the correct size and concentric with the finished diameters.

It is also possible to employ a conventional centre drill on the cutting tool spindle when used in an alternative form of the invention which will be discussed further.

Figure 5 depicts an electro-hydraulic circuit diagram which is of simplified form for applying the apparatus. Pressure is received from a fluid pressure source in the machine (not shown) and is directed to a pressure port 46 of a solenoid operated four-way valve 47 which is spring centred to a position where pressure is routed through an exhaust port 48 back to the hydraulic tank 49, and the cylinder lines 50, 51 are blocked to flow.

When it is desired to feed the centre hole tool 38 to the workpiece, the feed forward solenoid 52 is actuated on the four-way valve 47, thereby directing pressure along cylinder line 50 to one end of the respective feed cylinders 40 to cause the slides 21 to advance. The slides 21 will advance at a controlled rate, since the exhausting fluid is routed along cylinder lines 51 which pass through a pressure compensated flow control valve 53 on their return to the tank 49.

The control valve 53 has a check valve 54 mounted in parallel with it, and the check valve 54 is blocked when this line 51 is exhausted to the tank 49. The slides 21 will advance until a trip dog 55 (affixed to the slide) contacts a limit switch 56 (affixed to the slideway), at which time the feed solenoid 52 is de-energised and the rapid return solenoid 57 is energised.

When the rapid return solenoid 57 is energised, the four-way valve 47 is shifted to the extreme left position depicted, wherein pressure is directed through the four-way valve 47 along line 51 and freely through the check valve 54, by-passing the flow control valve 53 and returning the piston rod 41 to its former retracted position.

The cylinder line 50 at the exhausting end of the cylinder 40 is directed without obstruction to the hydraulic tank 49. In its reverse travel, the slide 21 will return until a second trip dog 58 contacts a second limit switch 59. When the second limit switch 59 is contacted, the rapid solenoid 57 is de-energised and the four-way valve 47 is spring centred to the mid position shown on the diagram.

It is noted that various fluids may be utilised, such as hydraulic oil, requiring a reservoir, or air, which may be exhausted to the atmosphere.

It will also be appreciated that various hydraulic valves may be utilised in combination to accomplish varying feed rates on the advance movement of the slides, including a rapid approach movement in the cycle. The flow control valve is set to closely match the end of feed position with the final outside diameter grind position.

In an alternative form of the invention depicted in Figure 6, a pressure roller 60 is carried on a lever 61, which is pivoted at its mid-point 62 by a clevis mounted piston rod 63 affixed to the outboard end 64 of the lever 61. The piston rod 63 is slidable in a cylinder 65 which is clevis mounted to a fixed base such as the work rest blade 15. At selected times, the roller 60 is moved against and away from the workpiece 14.

Figure 7 depicts the roller 60 located against the workpiece 14, and the cutting tool 38 is shown co-axial with the workpiece 14.

At the option of the user, the workpiece 14 may be held by the roller 60 against a non-rotating regulating wheel 13, and a co-axial cutter 38 such as a centre drill may be used to machine the workpiece 14, either before or after outside diameter grinding, or both before and after grinding.

Similarly, at the option of the user, a centre hole operation might be performed subsequent to an outside diameter grinding operation, but with an eccentric cutter 38, such as a grinding wheel.

In such case the roller 60 would be impressed against the workpiece 14 but the workpiece 14 would be turned by a rotating regulating wheel 13.

It will be appreciated, therefore, that various combinations of cutters; pressure rollers; regulating wheel rotations and cutter eccentricities can be utilised with respect to an outside diameter grinding operation to perform pre-process; in-process and post-process centre hole machining operations.

It will be appreciated that while certain embodiments have been shown and described, the invention is not limited to such embodiments, but rather the invention extends to all such designs and modifications as come within the scope of the appended claims.

Claims

1. A centreless grinding machine comprising a base part, a workpiece grinding wheel capable of grinding a workpiece at a work station, said grinding wheel mounted for rotation relative to said base wherein said machine further comprises a pair of cutting tools or cutting tool holders capable of forming location holes in said workpiece substantially axial with a surface ground by said grinding machine on said workpiece, said cutting tools or cutting tool holders being mounted relative to said base adjacent either end of said workpiece and capable of movement towards and away from the workpiece so as to enable formation of said location holes during a grinding operation or subsequent thereto.

2. A grinding machine according to Claim 1 wherein said machine base is provided with slideways and said cutting tools or cutting tool holders are supported in slides movable relative to said slideways to enable movement of said cutting tools towards and away from said workpiece.

3. A grinding machine according to Claim 1 or Claim 2 wherein means are provided to move said cutting tools into contact with said workpiece during or subsequent to said grinding operation.

4. A machine according to any one of the preceding claims wherein said cutting tools or said cutting tool holders are mounted relative to the machine base and adjustment means are provided to enable adjustment of said cutting tools or cutting tool holders in a plane substantially at right angles to the axis of rotation of said grinding wheel.

5. A machine according to any one of the preceding claims further comprising a regulating wheel supported on said base movable relative to said grinding wheel, said machine further comprising end location means for axially locating a workpiece, a workpiece support for said grinding wheel, said regulating wheel and said workpiece support together defining a predetermined work station for said workpiece.

6. A centreless grinding machine comprising a machine base, rotatably driven outside diameter grinding and regulating wheels supported on said base and relatively movable with respect to one another to a predetermined workpiece cylinder position, an end stop for axially positioning a workpiece, a workrest blade supported by said base and located between said outside diameter grinding and regulating wheels, defining with said wheels at said position an axis of a circumscribed predetermined workpiece cylinder, an apparatus for machining workpiece location holes while performing an outside diameter grinding operation, characterised by:: (a) first and second relatively fixed slideways located on said base proximal to first and second opposite faces of said outside diameter grinding wheel, respectively; (b) first and second relatively movable slides supported on said slideways respectively, each slide having a rotatable location hole cutting spindle mounted with its axis of rotation disposed coextensive with the other and parallel to the axis of rotation of said outside diameter grinding wheel and radially shifted from said axis of said predetermined workpiece cylinder; (c) first and second location hole cutting tools oppositely disposed to one another and respectively mounted to said centre cutting spindles; and (d) means for relatively moving said slides in accordance with a predetermined operating cycle while said outside diameter grinding and regulating wheels are relatively moving.

7. A machine according to Claim 6 modified in that the axis of rotation of said rotatable centre cutting spindle is coextensive with said axis of said predetermined workpiece cylinder and parallel to the axis of rotation of said grinding wheel.

8. A machine according to any one of the preceding claims wherein each cutting tool comprises a plurality of cutting faces.

9. A machine according to any one of Claims 1 to 7 wherein each cutting tool comprises a grinding wheel.

10. A machine according to any one of Claims 1 to 7 wherein each cutting tool comprises a drill.

11. A machine according to any one of the preceding claims wherein said grinding wheel is a diamond impregnated wheel.

12. A machine according to any one Claims 1 to 10 wherein said grinding wheel is a CBN grinding wheel.

13. A machine according to any one of the preceding claims wherein said machine comprises a regulating wheel and a pressure roller, said pressure roller applying radial force to a workpiece to clamp said workpiece against said regulating wheel subsequent to a grinding operation.

14. A method of forming location holes in a workpiece, said method comprising the steps of: (a) establishing a desired location axis on a workpiece positioned in a work station on a centreless grinding machine; (b) grinding a surface of revolution on said workpiece by a grinding wheel and causing relative movement between said workpiece and location hole cutting means to cause formation of said locating holes in said workpiece at a predetermined time during or subsequent to said grinding operation.

15. A method for machining location holes in a workpiece as claimed in Claim 14, said method comprising the steps of: (a) establishing an axis of a predetermined workpiece cylinder circumscribed between a regulating wheel, a grinding wheel and a workrest blade on a centreless grinder; (b) locating a pair of rotary machining cutters with axes coextensive with one another and parallel with the rotary axis of said grinding wheel but radially shifted from said axis of said predetermined work cylinder; (c) grinding an outside diameter of a workpiece on said grinder; and (d) advancing said cutters into machining contact with said workpiece at a predetermined point in the outside diameter grinding cycle.

16. A method for machining location holes in a workpiece as claimed in Claim 14, said method comprising the steps of: (a) establishing an axis of a predetermined workpiece cylinder circumscribed between a regulating wheel, a grinding wheel and a workrest blade on a centreless grinder; (b) locating a pair of rotary centre machining cutters with axes coextensive with one another and with said axis of said predetermined work cylinder; (c) grinding an outside diameter of a workpiece on said grinder; and (d) advancing said cutters into machining contact with said workpiece at a predetermined point in the outside diameter grinding cycle.

17. A method of machining location holes in a workpiece as claimed in Claim 14, said method comprising the steps of: (a) establishing an axis of a predetermined workpiece cylinder circumscribed between a regulating wheel, a grinding wheel and a workrest blade on a centreless grinder; (b) locating a pair of rotary centre machining cutters with axes coextensive with one another and said axis of a predetermined workpiece cylinder; (c) grinding an outside diameter of a workpiece on said grinder; (d) separating contact of said workpiece and said grinding wheel; (e) stopping rotation of said regulating wheel and said workpiece; (f) impressing pressure roller means against said workpiece while work rotation is stopped; (g) advancing said cutters into machining contact with said workpiece.

18. A method of machining locating holes in a workpiece substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

19. A centreless grinding machine substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 of the accompanying drawings.

20. A centreless grinding machine substantially as hereinbefore described including pressure roller means as illustrated in Figure 6 of the accompanying drawings.

21. A method of forming location holes in a workpiece during or subsequent to a centreless grinding operation including any novel feature or novel combination of features disclosed herein and/or illustrated in the accompanying drawings.

22. A centreless grinding machine including any novel feature or novel combination of features disclosed herein and/or illustrated in the accompanying drawings.