JPH0266121A - Detection of melting abnormality in remelting treatment of cam shaft - Google Patents

Abstract

PURPOSE:To discover melting abnormality in an early period by measuring the supply voltage value from a TIG power source and judging the melting abnormality when the value exceeds a prescribed upper limit value or lower limit value. CONSTITUTION:The remelting treatment of a cam 4 is executed by moving a TIG torch 3 having the TIG power source 1 and a tungsten electrode 2 back and forth in an arrow A direction and displacing the torch to follow up at prescribed intervals in an arrow B direction. A cam shaft 5 rotates the cam 4 and a position detector 6 detects the position of the cam 4. An ammeter 7 and a voltmeter 8 are mounted to the TIG power source 1 and the voltmeter 8 can detect the upper limit value and the lower limit value. A melting shear droop 13 is generated on the end face of the cam 4 when the central point of the forward and backward movements of the electrode 2 deviates from a center line 11. The remelting region diminishes when the spacing R between the electrode 2 and the surface 10 of the cam 4 is shorter than the prescribed distance. The voltage of this time is lower than the lower limit value. The defect of the remelting treatment is discovered by measuring the voltage.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention melts the surface of the cam sliding part using a camshaft, more specifically, a TIG (tungsten inert gas) arc, and creates a chill layer by self-cooling. The present invention relates to a method for detecting melting abnormality (melting failure) in manufacturing a remelted chill camshaft.

[Conventional technology]

In camshafts that are incorporated into automobile engines, etc., the surface of the cam sliding part must have excellent wear resistance.The cam sliding part is melted by high-density energy such as TIG arc, and the camshaft is rapidly cooled by self-cooling. A surface hardening treatment is performed to form a chill hardened layer (for example, as disclosed in Japanese Patent Application Laid-open No. 59-23156 and Japanese Patent Application Laid-Open No. 60-234169 by the present applicant, or
20424 and Japanese Patent Application Laid-Open No. 1983-94209). In such surface hardening treatment, if a TIG arc is used, a TXG arc is generated between the cam of the camshaft and the tungsten electrode of the TIG arc torch in an inert gas atmosphere to melt the sliding surface of the cam. At this time, the camshaft is rotated about its central axis and simultaneously oscillated parallel to the central axis (reciprocating motion). The TIG torch is controlled so that the distance between the tungsten electrode and the cam surface is constant. In this way, the arc moves in a meandering manner on the sliding surface of the cam, and a continuous bead of hardened surface layer is formed on the cam surface. Note that instead of the camshaft, the Tic and the torch may be oscillated (reciprocating motion parallel to the camshaft center axis). Then, the cam having the surface hardened layer formed in this way is polished to a predetermined shape.

[Problem to be solved by the invention]

Normally, the TIG arc remelting treatment device operates as set, and a predetermined chill-hardened layer is formed on the cam surface of the camshaft. However, there are problems such as poor centering in the positioning device for matching the TrG arc torch and cam, poor machining of the camshaft, and TIGI.
--Deterioration of the tungsten electrode, poor grounding of the camshaft (workpiece), etc. may cause the cam surface to melt in areas other than those that require remelting. this is,
Melting of the end face of the cam causes sag, making it impossible to secure the cam surface width necessary for design strength. Further, when the gap between the tungsten electrode and the cam surface becomes smaller than a predetermined distance, the remelting range (width) becomes narrower, and the hardening width necessary for design strength cannot be secured.

An object of the present invention is to provide a method for detecting the occurrence of melting defects (abnormalities) such as sag or insufficient chill hardening width.

Another object of the present invention is to prevent defective products due to melting abnormality caused by remelting by TIG arc from being processed in a subsequent process and to reduce the product defect rate.

[Means to solve the problem]

The above purpose is to provide a constant current characteristic to a TIG power supply when forming a remelted chill layer on the camshaft by a TIG arc without reciprocating the TIG torch electrode and the camshaft relative to each other at a predetermined distance with a predetermined mutual gap. A camshaft remelting process characterized by using a DC arc generator, measuring the voltage supplied from the TIG power supply, and detecting melting abnormality when it exceeds a predetermined upper limit or lower limit. This is accomplished by a melt anomaly detection method.

[For production]

Since a DC arc generator with constant current characteristics is used for the TIG power supply, the arc generating current can be kept constant even if the arc length changes, that is, the gap between the tungsten electrode of the TIG torch and the cam surface changes. On the other hand, the supply voltage changes accordingly. Therefore, when melting occurs on the cam end surface, the distance between the tungsten electrode and the cam end surface becomes large (the arc length becomes long), and the voltage supplied from the TIG power source increases.

The upper limit of this supply voltage is set in advance as the voltage value at which melting sag occurs on the end face, which is allowable for the camshaft product, and if the voltage rises beyond this upper limit, a melting abnormality (defect) will clearly occur. That's what I did. On the other hand, as the lower limit of the supply voltage, if the distance between the tungsten scraper and the cam surface becomes narrower (the arc length becomes shorter),
Since the melting width becomes narrower accordingly, the voltage value is set in advance according to the (minimum) melting width required for the product. When the supply voltage is lower than this lower limit value, it is clear that a melting abnormality such as insufficient melting width has occurred. In this way, by appropriately setting the upper and lower limits of the supply voltage from the TIG power supply (
A permissible control range is determined, and any deviation from this range is automatically detected as an abnormality.

〔Example〕

Hereinafter, the present invention will be described in detail by way of preferred embodiments thereof with reference to the accompanying drawings.

FIG. 1 shows a TI equipped with a defective melting detection mechanism according to the present invention.
FIG. 2 is a schematic diagram of a remelting treatment device using a G arc.

The TIG arc remelting treatment device for camshafts includes a TIG power source (DC arc generator power source) 1 whose external characteristics are constant current characteristics, and a TIG torch 3 having a tungsten electrode 2.
, a drive mechanism (not shown) that reciprocates the TIG torch 3 in the direction of arrow A and follows it at predetermined intervals in the direction of arrow B, a drive mechanism (not shown) that rotates the camshaft 5 with the cam 4, and It consists of a cam position detector 6. T
An ammeter 7 and a voltmeter 8 are attached to the IG power supply 1 as shown in Fig. 1, and the voltmeter 8 can be set with an upper limit value and a lower limit value arbitrarily, so that it is possible to set an upper limit value and a lower limit value as desired. When this occurs, an abnormality detection signal is issued. As shown in FIG. 1, the TrGq source 1, the TIG torch 3, and the camshaft 5 are connected, and an arc 9 is generated between the tungsten electrode 2 and the surface 10 of the cam 4. Then, the torch drive mechanism sets the tungsten electrode 2 of the torch to the initial position, which is the center position of the cam width W, in response to a signal from the position detector 6.

Using the TIG arc remelting treatment apparatus described above, the second a
As shown in the figure, a predetermined chilled hardened layer 12 is formed by reciprocating the torch 3 around the center line 11 with the width of the cam 4 while normally generating a TIG arc 9 according to predetermined setting conditions. Can be done.

The current at this time is constant as shown in FIG. 2a, and the supply voltage is between the upper and lower limits and is constant as shown in FIG. 2C. For reference, the voltage oscillogram obtained in the experiment is attached as Fig. 5.

For example, when setting the position of the tungsten electrode 2 of the TIG arc torch 3 based on the position detector 6 of the cam, if for some reason it deviates slightly from the position of the center line 11, the position 1 (with a distance P) of the torch 3 (that is, the position of the tungsten electrode 2)
It becomes the center point of the reciprocating movement of (Fig. 3a), and TI
Due to the G-arc remelting process, melting sag 13 is generated on the cam end face. The current at this time is constant as shown in Figure 3b, but the supply voltage is as shown in Figure 3c.
It fluctuates like a waveform with a part that exceeds the upper limit. This is because the arc length becomes longer at the cam end face where the melt sag 13 occurs in Fig. 3a, and at that time the supply voltage exceeds the upper limit. changes, and the voltage changes accordingly. For reference, a voltage oscillogram obtained in an experiment where there is melting sag (poor melting) on the end face is attached as FIG. 6. Voltage fluctuations with such a clear waveform (exceeding the upper limit value) are determined to be abnormal by the voltmeter and the built-in setting range comparator and become an abnormality (defective) detection signal, causing the camshaft to melt again. Stop the processing equipment.

The defective camshaft and device are examined, and if any defects are found, they are restored to normal condition before the next camshaft is remelted.

Additionally, other fusing failures may occur, as shown in Figure 4a. In this case, the difference from the normal case shown in FIG. 2a is that the gap R between the tungsten electrode 2 of the torch 3 and the surface 10 of the cam 4 is shorter than a predetermined distance. Therefore, the length of the arc 9 is also shortened, and the area to be remelted by the arc is correspondingly smaller, so that the width Q of the chill hardened layer 12 is smaller than a predetermined dimension. The current at this time is constant as shown in Figure 4b, but the supply voltage is
As shown in FIG. 4c, it is constant and lower than the lower limit.

Even in such a case, the voltmeter and the setting range comparator incorporated therein determine that the voltage is abnormal, and an abnormality (defective) detection signal is generated. Then, as in the case of the melt sag defect described above, the processing device is stopped, the defective camshaft and the processing device are examined, and the defect in the device is restored to a normal state.

Therefore, although a melting abnormality (defective) is detected from the measurement of the supply voltage of the TIG power supply and only the camshaft in question becomes a product defect, appropriate countermeasures can be taken and the subsequent camshaft TIG arc remelting process will not be performed. The occurrence of melting defects can be prevented.

〔Effect of the invention〕

Since the camshaft manufacturing process is generally an automatic line, there are a large number of camshafts (approximately 50) being processed from the TIG arc remelting process to the next cam surface polishing process. Furthermore, it takes time to discover melting abnormalities during melting processing, and melting abnormalities (defects) occur.
By the time this is discovered, at worst 50 camshafts will be defective. However, as in the present invention, TIG
By detecting abnormalities in the arc remelting process, stopping the processing equipment, and making appropriate adjustments, the number of defective products can be reduced to 1.
A book will do.

Furthermore, the cam sliding surface (surface) is inspected only visually during the polishing process, and if something is overlooked, it may result in a quality complaint about the camshaft. In the event of such trouble, an abnormality will be detected in the TI'G arc remelting process and the processing equipment will be temporarily stopped.
The outflow of defective products can be prevented.

[Brief explanation of the drawing]

Figure 1 shows a TIG equipped with a defective melting detection mechanism according to the present invention.
FIG. 2b is a schematic diagram of a tungsten electrode of a torch and a cam of a camshaft illustrating a normal TIG arc remelting process; FIG. 2b is a schematic diagram of a cam of a camshaft; FIG. Fig. 2c is a graph of the supply voltage in the case of Fig. 2a, Fig. 3a is a graph of 'I' where cam end face melting blur occurs.
FIG. 3b is a schematic diagram of a tungsten electrode of a torch and a cam of a camshaft for explaining the IG arc remelting process; FIG. 3b is a graph of current in the case of FIG. 3a; FIG. 3C is a graph of the current in the case of FIG. 3a; FIG. 4a is a graph of the supply pressure in the case of FIG. The figure is a graph of the current in the case of figure 4a, figure 4c is a graph of the supply pressure in the case of figure 4a, and figure 5 is the voltage in the experiment corresponding to the case of figure 2a. FIG. 6 is an experimental voltage oscillogram corresponding to the case of FIG. 3a. 1... TIG power supply, 2 3... Torch, 4 5... Camshaft, 8 9... Arc, l... Tungsten electrode, ... Cam, ... Voltmeter, 2...・Chill hardening layer.

Claims (1)

[Claims] 1. When forming a remelted chill layer on the camshaft using a TIG arc while relatively reciprocating the TIG torch electrode and camshaft at a predetermined distance and a predetermined distance, a DC arc with constant current characteristics is generated in the TIG power supply. Using a device, measure the supply voltage value from the TIG power supply,
A method for detecting melting abnormality in remelting processing of a camshaft, characterized in that melting abnormality is detected when a predetermined upper limit value or lower limit value is exceeded.