GB2099193A

GB2099193A - Method of making hands for a timepiece

Info

Publication number: GB2099193A
Application number: GB8212940A
Authority: GB
Original assignee: AGEO SEIMITSU Manufacturing CO Ltd; Citizen Watch Co Ltd
Current assignee: AGEO SEIMITSU Manufacturing CO Ltd; Citizen Watch Co Ltd
Priority date: 1981-05-26
Filing date: 1982-05-05
Publication date: 1982-12-01
Also published as: DE3215399A1; CH643100GA3; HK66885A; JPS57193247A; DE3215399C2; CH643100B; JPH0138573B2; GB2099193B

Abstract

A method of making aluminium hands for timepieces comprises annealing an aluminium hand member 2 at 160-200 DEG C for 20-60 minutes, forcing the flange 3a of a (brass) bush 3 into the lower surface of a seat portion of the hand member, forming a protrusion 6 on the upper surface of the seat portion of the hand member, shaping the upper surface of the hand member by pressing, and finishing the the protrusion on the upper surface of the seat portion by machining using a diamond cutting tool. As illustrated the bush 3 is staked in the band member 2 by tools 4, 5 prior to annealing. A pressing step using dies 8, 9 forces the flange 3a into the member 2 and simultaneously forms the protrusion 6. After machining the hand is coated with gold. <IMAGE>

Description

SPECIFICATION Method of making hands for a timepiece The present invention relates to a method of making a hand for a timepiece from aluminium strip.

It is the modern trend to produce quartz wrist watches in smaller and smaller sizes and particularly with reduced thickness, and furthermore to minimize the consumption of electric current by the module so that the life of the battery can be extended. To satisfy this requirement for reducing the consumption in an analog timepiece, it is an important factor to reduce the weight of the hands of the timepiece. At present, therefore, hands made of aluminium or an aluminium alloy have been widely employed.

On the other hand, good appearance, high quality and sophisticated design are also required for modern wrist watches, thus presenting another significant factor.

A hand for a timepiece has an enlarged seat portion by which the hand is connected by way of a collar to an operating shaft.

When the upper surface of the seat portion of an aluminium hand was protruded by more than 30 microns in the conventional art, excessive force had to be exerted on this portion, and it was difficult to avoid the development of wrinkles and cracks. That is, to make the upper surface protruded at a seat portion by more than 30 microns in the conventional art, a large pressing force was required. Further, when a large force was exerted, the hand member tended to be deformed and widened, deteriorating the design and appearance. Therefore, it was difficultto make satisfatory hands from aluminium.

An object of the present invention, therefore is to provide a method of making timepiece hands from aluminium which are free from the abovementioned defects.

According to the present invention, in a method of making a hand for a timepiece, a hand-shaped member having an enlarged seat portion and produced from aluminium strip is annealed within the temperature range 160-200 for a period of 20-60 minutes, a flange on a separate collar is forced into the seat portion on a first surface of the member, a protrusion with a tapered outer surface is formed on the seat portion on a second surface of the member, and the surface is finished by a machining action employing a diamond cutting tool.

The method of the present invention employs aluminium material of a thickness equal to that of the hand member. The seat portion of the hand member has sufficient margin for itto be finished by a diamond cutting tool, and other portions are pressed to a desired appearance. A machining margin is required for the upper surface at the seat portion of the hand member so that it can be beautifully finished. Other portions of the hand member are pressed in a pressing die. Here, it is important to form a protrusion on the seat portion of the hand depending upon the requirements. For this purpose, according to the preaent invention, the hand member is annealed at a low temperature before it is pressed, and the flange of the collar is driven into the lower surface of the seat portion of the hand in the pressing step.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure lisa plan view illustrating the operation for obtaining hand shaped members from aluminium strip by a pressing operation; Figure 2 is a sectional view illustrating a step of attaching a collar to the hand member by a caulking process; Figure 3 is a sectional view illustrating a pressing step; and Figures 4 and 5 are a plan view and a sectional view, respectively, of an aluminium hand for a timepiece according to the present invention.

By taking into consideration the strength of the hand and shapeability, aluminium strip (JIS A 5052R H18), having a thickness of 0.10 mm is used for making hands. A mirror-finish rolled material which has been beautifully finished beforehand, is used as the material from which hand-shaped members are obtained. Hand-shaped members 2, each having a hole la in an enlarged seat portion, are obtained by pressing. 1 b denotes the pilot holes for the pressing stage. A brass collar 3 with the hole through it for receiving the shaft of a movement is secured in the hole la ofthe hand member2 by a caulking step, as shown in Figure 2.

The collar is positioned in an opening in a plate with a flange on the collar resting on the top of the plate. The other hand member 2 is arranged so that a part of the collar extends through the hole la in the hand member. A punch 4 engages the open upper end of the collar to enlarge the collar outwards so that it is held in the hand member.

Then, to impart stretchability without losing hardness, the hand member 2 is annealed at a temperature of 180 C for 40 minutes. The hand member exhibits a Vickers' hardness Hv of 105 which is slightly smaller than the initial Vickers' hardness Hv of 123, but which is sufficient forthe hand member for a timepiece. The hand member exhibits a Vickers' hardness of 114 when it is annealed at 1600C for 30 minutes, and a vickers' hardness of 98 when it it annealed at 200"C for 30 minutes. The stretchability after annealing is 8% to 10%, which is considerably greater than the stretchability of 2% to 4% in the initially rolled state of the material. Therefore, good results are obtained when the material is annealed at 160"C to 2000C.Next, to give good appearance to the hands, a protrusion is formed on the seat portion 6 by a pressing step, and the upper surface of the hand member 2 is shaped, for example, to a semicylindrical shape. A tapered surface 6a is formed on the protrusions 6. Since the surfaces of the hands must maintain good quality, the metal upper die 8 for pressing is made of a hard material, and the pressing surface 8a is sufficiently polished until it becomes like a mirror. A flange 3a of the collar is driven into the lower surface of the seat portion 6 by pressing it between the upper die 8 and the lower die 9, so that a sufficient margin is provided on the upper surface of the seat portion 6 that will be machined by a diamond cutting tool. Since the collar and the hand member have been integrally united in the preced ing step, the workability in the pressing step can be facilitated.In this case, the flange 3a having a thick ness of 80 microns is driven into the lower surface of the seat portion 6 by an amount 12 of 20 microns, and the hand member is subjected to pressing.

When the flange 3a is not driven into the lower surface of the seat portion of the hand member, it is difficult to make the upper surface of the seat portion of the hand stably protruded by more than 30 microns. According to the above-mentioned method, however, the upper surface of the seat portion of the hand member is protruded by a distance Ii of more than 30 microns, which makes it possible to stably carry out the next step of machining with the aid of a diamond cutting tool. Therefore, the hands can be easily produced maintaining good quality.

When the annealing temperatures is lower than 160 C, the annealing effect is so weakthat it is not possibe to completely prevent the occurrence of wrinkles or cracks. When the annealing temperature exceeds 200"C, on the other hand, the strength of the hand is decreased and the function and quality deteriorates. According to the present invention, therefore, the annealing time is set from 20 minutes to 60 minutes, by taking the above-mentioned facts and the produceability into consideration.

The protruded portion 7 on the upper surface of the seat portion of the hand member is finished to a very high standard using a diamond cutting tool.

Further, to make the surface more attractive, the hand is washed sufficiently, subjected to sputtering, and is coated with a gold layer to obtain a finished product of gold colour.

The aluminium hand obtained by the present invention is light in weight, has a very attractive surface in which the caulked portion of the collar is also finished by the diamond cuttingtool, and exhibits an excellent appearance consisting of a tapered seat portion and a semicylindrical hand member. Owing to the use of a mirror-finish rolled material and the additional polishing operation, the quality of the surface of the pressing die is comparable to that of the surface of the hand that is beautifully finished by the diamond cutting tool.

Table 1 illustrates the embodiment ofthe present invention in comparison with conventional examples, In the conventional example (a), the flange of the collar is forced into the hand memberwhich is not annealed. In the conventional example (b), the hand member is annealed, but the flange of the collar is not driven into the hand member. In the conventional example (c), the hand is not annealed, and the flange is not driven thereinto.

Table 1

Appearance Amount of of tapered Finish protrusion surface of ing seat portion Embodiment of 30 microns good good the invention or more Aluminium 19 ConJen.ionai | leasthan wrinkieset ~hand ≈ e;;'ampla(a)vith ! 30 microns cracks fair members no annealing l developed of the same shape Conventional 10 - 15 and col- example (b) with microns good poor larks of no flange the same shape are Conventional less than used. example (c), i.e., 10 microns good poor (a)+ (b) In the embodiment of the present invention, the collar is fastened by caulking to the aluminium hand member, followed by annealing at a low tempera ture, and by pressing. However, the same results can also be obtained even when the aluminium hand member is annealed at a low temperature, and then the collar is fastened thereto by caulking, followed by the pressing, or even when the caulking of the collar and the pressing are effected simultaneously.

In addition to the semicircular shape, furthermore, the surface of the hand members can also be formed with a rectangular shape, or a trapezoidal shape, or the like.

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Claims

1. A method of making a hand for a timepiece in which a hand-shaped member having an enlarged seat portion and produced from aluminium strip is annealed within the temperature range 160-200 for a period of 20-60 minutes, a flange on a separate collar is forced into the seat portion on a first surface of the member, a protrusion with a tapered outer surface is formed on the seat portion on a second surface of the member, and the surface is finished by a machining action employing a diamond cutting tool.

2. A method as claimed in claim 1, in which the protrusion is formed and the second surface of the member is shaped by a pressing operation.

3. A method as claimed in claim 1 or 2, in which said enlarged seat portion has a hole therethrough and said collar is fitted into and retained in the hole prior to the flange being forced into the seat portion.

4. A method as claimed in claim 1,2 of 3, in which the second surface of the member is provided with a mirror-finish.

5. A method as claimed in claim 4, in which the second surface of the member is provided with the film of a gold coloured material.

6. A method of making a hand for a timepiece substantially as herein before described with reference to the accompanying drawing.

7. A hand for a timepiece produced by the method of any preceding claim.