US2255094A - Gear cutting machine - Google Patents

Description

Sept. 9, 1941. A. AEPPLI GEAR CUTTING #MACHINE Filed Nov. 7. 1938 a Sheets-Sheet 1 I'll/111111111111.

In venfor Sept. 9, 1941.

' A. AEPPLI GEAR CUTTING MACHINE Filed Nov. 7, 1938 3 Sheets-Sheet 2 Sept. 9, 1941. M A. AEPPLI 2,255,094

GEAR CUTTING MACHINE Filed Nov. 7, 1938 3 Sheets-Sheet 3 Niamey Patented Sept. 9, 1941 GEAR CUTTING MACHINE Albert Aeppli, Zurich, Switzerland, assignor to Maag-Zahnriider und-Maschinen A. G.,

Zurich, Switzerland Application November 7, 1938, Serial No. 239,198

6 Claims.

My invention relates to a gear cutting machine and to an improved method of operating the same. More particularly, my invention is concerned with a gear shaping machine having a tool of rack form and operating on the rolling principle.

In machines of this type, the accuracy or operation and of the product obtained is liable to be adversely afiected by heat expansion of the tool. This applies particularly to machines where the Germany November 9, 1937 ting all of the teeth on the blank in the course of a single uninterrupted rolling cycle of the blank. In this regard the machine differs from machines using a rack-shaped tool of a shorter length in which the tool must be withdrawn and the blank must be indexed whenever one or sevtool has a length not less than the circumference of the blank thus cutting all of the teeth of the blank in a single rolling cycle without requiring any intervening indexing motion.

The object of my invention is to provide a method of operating gear cutting machines in which improved accuracy of operation is secured by eliminating the influence of heat expansions of the tool.

Another object is to provide an improved machine in which the difference between the temperatures of the tool and of the rolling elements producing the rolling motion is kept substantially constant.

I attain these and other objects of my invention by measuring the thermal conditions of the tool and of the rolling mechanism and by so controlling the temperature of the latter as to keep the heat expansions of the tool and the rolling mechanism substantially equal.

My improved method and a machine capable of carrying out the same will be described hereinafter by reference to the drawings in which a preferred embodiment of the machine is illustrated.

In the drawings,

Fig'. 1 is a side view of the machine partly in section;

Fig." 2 shows cross-sections through the tool and through one of the rolling elements and the coordinated circuit arrangement;

Fig. 3 is a portion of Fig. 1 showing elements not illustrated therein;

Fig. 4 is a partial cross-section through the tool holder and. the tool inserted therein taken along line 4-4 of Fig. 5; and

Fig. 5 is the section taken along line 5-5 of Fig. 4;

Fig. 6 is a cross-section through a modified form of the rack; and

Fig. 7 a plan view of this rack partly shown in section.

eral teeth have been completely cut.

The rolling motion is preferably produced by a rack of a length equal to the length of the tool. A master gear coaxially connected to and rotatable with the blank roll along this rack thus producing the required relative rolling motion between the blank and the tool.

The accuracy of the teeth to be cut depends largely on the exact agreement in length between the tool and the rack. This exact agreement is required in order that the entire circumference of the work piece will have been properly operated upon when the master gear has completed one revolution in rolling along the rack. The tool, however, is liable to expand in operation owing to the heat produced in the cutting operation and to become longer than the rack. If this happens, the spacing of the first tooth flank cut into the blank from the last tooth flank will be too small; thus, the tooth pitch will become inaccurate. It is the object of my invention to avoid such inaccuracy, and I attain this object by expanding the rack in accordance with the expansion of the tool.

While I wish it to be understood that my invention is applicable to any gear cutting machine of the type in which the tool and the blank perform a relative rolling motion, I shall describe it hereinafter as applied to the machine shown in Fig. 1.

The bed I of this machine is provided with an upright having a swivel member I0 rotatable about a horizontal axis and provided with a guide extending in a verticalplane. On this guide there is slidingly mounted a ram 2 carrying a In the machine shown in Fig. l, a tool is used the length of which corresponds to the pitch circle circumference of the blank, the tool cuttool 5| of the rack-shaped type. The ram is reciprocated by means of a connection rod 3 and a crank 4 of the shaft 5. The shaft 5 is driven through gears I, 8, 9, III which are fixed on the crank shaft 5 and two parallel gear shafts 6, II respectively. Moreover, on the shaft ii there is fastened a bevel gear I! meshing with bevel gear l3 fixed on a drive shaft. A second drive serving to produce the rolling motion is derived from shaft 6 and is operative to impart a reciprocating motion to a slide 36 carrying the blank. This slide 36 is movable on longitudinal guides II which are provided on the support 42 and extend horizontally at right angles to the crank shaft 5.

The slide 36 is provided with a vertical bearing lihaving a comparatively large diameter for a purpose to be explained hereinafter. In this hearing, there is'qournalled a circular bearing member-3l constituting a rotary work table or work spindle. This member has a conical bore accommodating a mandrel 33 fixed therein. The downwardly projecting cylindrical end of this mandrel is joumalled in 9. depending portion 33 of the slide 36. On the mandrelthere is fixed a master spur gear 40 engaging a rack tool 4I. This rack and the rack BI are located within a common plane indicated by the dotted line 11 which extends parallel to the axis of the work spindle 31 and is preferably vertically disposed. This is the plane in which the tool 5| performs its reciprocating cutting. motion relative to the work spindle 31, while the slide 33 moves in a direction parallel to the tool II causing the master gear 40 to roll along the rack 4 I, whereby the blank ill is revolved.

For a more detailed description of the machine reference may be had to the application of Georg Fischer Ser. No. 226,415 filed on August 24, 1938.

Let us assume that 2' represents the number of teeth of the master gear 4% connected to and rotatable with the blank 50; t' the pitch of the master gear 40 and of the coordinated rack 4|; 2 the number of teeth of the gear to be cut; in the proper pitch of the gear to be cut and iv the pitch of the tool 5|. equations result:

(2) tw=-: '-t' Since the ratio is constant, I obtain the following equation:

(3) tw=k-t' When the heat produced in the cutting operation raises the temperature of the tool 5| so that the latter expands and becomes longer than the rack 4 I, this equation (3) is no longer complied with and the pitch of the work piece produced will become inaccurate. I avoid this disadvantage by expanding, by application of heat, the rack H to cause the rack to expand to the same extent as the tool 5|. As a matter of principle, it is immaterial if the temperatures of the two racks are the same or are different provided that the equation (3) is complied with.

In order to carry out my improved process I provide the tool 5| (Figures 3, 4 and 5) with a recess II3 extending. the entire length of the tool. This recess I I3 accommodates a thermometric element I I 4 which is preferably formed by a heatconductive ribbon of a material the electrical resistance of which varies considerably when the temperature changes. Similarly, the rack 4| (Figs. 2 and 6) is provided with a recess 3' accommodating a .thermometric element 4'. The terminals of the two elements are connected Then the following by suitable conductors I I5 and I III with a source I each of the two elements H4, H4 amounts to T=To(1+at) and thus is proportional to the temperature t, the currents amount to 1' 1+al Therefore, the currents depend on the temperature of the elements.

A second recess I2I provided in the rack 4I accommodates an electrical heating element I22. This heating element is connected to the output terminals of a transformer IIS, the input terminals of which are connected with a source of al-temating current. Within the circuit of the heating element I22 there is included an interrupter III which is normally opened but may be closed by engagement of a stop III therewith attached to the indicating hand I" of the instrument IIIi. Preferably, an adjustable resistance I20 is included in the heating circuit.

The operation is as follows: When the temperature of the tool II rises owing to the generation of heat by the cutting process, the resistance of the element H4 is increased, whereby the current flowing through the conductors II5 tends to decrease. At the same time, the current flowing through the conductors IIS tends to remain constant. Therefore, the hand I I1 will move towards the right thus closing the circuit of the heating element I22 through the contact III. The current thereby supplied to the heating element I22 raises the temperature of the rack 4I until the resistance of the element 4' increases to the same extent as the resistance I I4 with the result that the current flowing through the conductor 5' decreases until the hand III moves to the left disengaging and permitting the contact II8 to move to circuit opening position and thus interrupting the circuit of the heating element I22.

The contact H3 is adjustable towards and away from the stop III'.

Owing to the control of the heating circuit by the thermometric elements H4 and 4', so much heat is applied to the rack H as is required to effect expansion of the rack equal to the expansion of the tool 5|. The function is entirely automatic and maintains the rack H and the tool 5| substantially at the same temperature.

As shown in Fig. 5, the recess II 3 of the tool 5| is preferably provided with an insulating lining I30 in which the resistance II 4 is embedded.

In Figs. 6 and 7, I have illustrated a preferred form of the rack 4I. This rack isprovided with a longitudinal bore I3I extending through the entire length thereof. This bore is provided with an insulating lining I32 within which a heating coil I33 is embedded. This design has the advantage of a more uniform distribution of the heat through the entire rack.

As the rack 4| is stationary in operation, the supply of current thereto does not offer any difficulties. Special means are required, however, to supply current to the thermometric element associated with the tool 5| as this is mounted on the reciprocating ram 2.

In Fig. 3 the current supplying means used for this purpose are illustrated. One terminal of the thermometric element I I4 is connected by a conductor I34 to a hook I23 which is adjustably mounted in a bracket I24 attached to the ram 2. This hook is connected by a metallic helical spring I23 with a member I26 which is adjustably mounted in a bracket I35 attached to the swivel member III. The other terminal of the thermometric element H4 and one terminal of the source of current are preferably grounded in the material of the machine which completes the electric circuits. The brackets I24 and I35 are made of insulating material. When the ram reciprocates up and down, the spring I23 is expanded and contracted accordingly. The member I26 may be adjusted in accordance with the stroke of the ram.

As shown in Fig. 2, I may shunt an adjustable resistance I20 across the resistance I20 and the interrupter H8. This resistance I20 permits a constant amount of current to be supplied to the heating element I22 so that the surplus of heat only need be regulated by the instrument II6.

If for some reason or the other, the tool should have at normal temperature a length less than that required for accurate operation or, in other words, if the rack 4| should be too long, the

contact H8 is so adjusted as to be opened only be normally closed and not opened until the rack ll has attained a temperature above normal. In this event, the resistance I20 may be so adjusted as to keep the rack 4| substantially at the required temperature.

The lengths of the tool 5| and the rack 4| are preferably measured by measuring the pitch of a work piece cut by the machine. 0n the basis of measurement the interrupter H8 and the resistances I20 and I20 may be adjusted to. meet the requirements.

In the process above described, the rack 4i only is heated while the master gear 40 remains a little cooler. This will cause a definite even though very small difference between the tooth pitches of the master gear and the rack. This difference, however, has no influence on the accuracy of the gear to be out since the master gear always performs one complete revolution after all of its teeth will have been brought to engagement with the rack succesively, the length of the rolling path z'-t' equalling the length e-tw of the tool.

Preferably, the adjustment of the rack 4| towards and away from the master gear 40 by suitable means (not described) may be accomplished after the gear has been warmed up into its average operating temperature by a suitable adjustment of the resistance I20.

My invention is not restricted to the embodiment thereof described hereinabove. Other rolling elements may be used instead of the rack BI and the master gear 40. Also, other heating and measuring means may be used than electrical resistances. Instead of determining the temperatures of the tool 5| and the rack 4|, I may measure the conditions thereof by determining their relative lengths by suitable measuring instruments and may control the application of heat to the rack 4| in dependence on any difference in lengths.

Also, the tool 5I could be maintained at a predetermined operating temperature above that of the rack H by controlled application of heat. In this event, the tool 5| would be made so much shorter than the rack 4| as to expand to the same length upon being heated to its operating temperature.

, Further possible modifications will be readily apparent to anyone skilled in the art. Therefore, my invention is not limited to the details thereof hereinabove described but is to be broadly interpreted in accordance with the appended claims.

What I claim is:

1. A gear cutting machine which comprises a blank holder, a cutting tool, means including an element rotatable with the blank adapted to have rolling movement relativeto a member coextensive with said tool and cause said blank to have rolling motion relative to said tool, thermometric elements coordinated to said tool and said element, a heating element associated with said rotatable element, and means governed by said thermometric elements and controlling said heating element, whereby inaccuracies owing to heat expansion of said tool are compensated by expansion of the rotatable element.

2. A gear shaping machine operating ,on' the rolling principle which comprises a blank holder, a gear connected thereto, a rack meshing with said gear, a rack-shaped tool, means causing said gear and blank to have rolling movement relative to said rack and tool, thermometric elements coordinated to said tool and said rack, a heating element associated with said rack and means controlled by said thermometric elements and regulating said heating elements so as to maintain a constant differential between the temperatures of said tool and said rack.

3. A gear shaping machine operating on the rolling principle which comprises a blank holder, a gear connected thereto, a rack engaging said gear and having a longitudinal bore, a rackshaped tool, means causing said gear and said rack to perform a relative rolling motion, thermometric elements associated with said tool and said rack, an electrical heating element provided within the bore of said rack, and means governed by said thermometric elements and controlling said heating element so as to maintain the difference between the temperatures of said tool and said rack constant.

4. In a machine for shaping spur gears, the combination comprising a tool of the rack-type, a rack located in a common plane with said tool and coextensive therewith, a slide adapted to move parallel to said rack, a work spindle journalled in said slide and extending parallel to said plane, a spur gear attached to said work spindle and meshing with said rack, said tool having a length not less than the circumference of said spur gear, means for producing a relative reciprocatory cutting motion between said tool and said work spindle within said plane, thermometric measuring elements associated with said tool and said rack, and a heating element coordinated to said rack and controlled by said thermometric elements so as to maintain the difference between the temperatures of said tool and said rack constant.

5. In a machine for shaping spur gears, the combination comprising a support provided with a guide, a rack mounted on said support extending parallel to said guide, a longitudinal slide movably mounted on said guide, a .work spindle journalled in said slide and extending transversely to said rack, a spur gear mounted on said work spindle in engagement with said rack, whereby said work spindle will be rotated upon movement of said slide, a shaping tool of the rack-type extending within a plane parallel to said rack and said work spindle and having a length not less than the circumference of said spur gear, a second guide extending parallel to said plane, a reciprocatory ram mounted on said uide and carrying said tool, a thermometric" electrical measuring element associated with said tool, means conducting current through said measuring element including a helical spring extending between a point of said ram and said support, a thermometric measuring element and an electrical heating element both associated 'with said rack, an interrupter controlling said heating element, and means governed by said thermometric elements and controlling said heating element so as to maintain the diflerence between the temperatures of said tool and said rack constant.

6. A gear cutting machine which comprises a blank holder, a cutting tool, means including a

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