|Title of Invention||
GRINDING PROCESS FOR GUIDE PINS
|Abstract||This invention enhances the quality of the shank of the guide pins which results in enhanced performance of the Caliper brake. ~ ! Generally the Caliper Brakes are used in Automobiles for smoother and efficient braking unlike drum brakes. The braking pad slides along the guide pins referred earlier. This invention produces a perfect cylindrical shaft of the guide portion and also three flats for r~ease retention. Tpjs invention increases the braking efficiency, reduces the relativ . clearance of the brake pad and the guide rod for a smooth noiseles: operation.|
Before this invention all guide rods had a bend which resulted in friction and noise while operation.
All automobiles have a braking system to brake the vehicle. There are two braking systems namely:
1. Drum Brakes
2. Caliper Brakes
The drum brake works on the principle of a brake pad mounted inside the drum to be circumferentially expanding to brake the drum which is mounted to the wheel.
The load applied to braking is a perpendicular to the direction of the wheel rotation. This braking system produces sudden braking which is not smooth.
Since the drum internal radius and the brake shoe radius will kepp on varying,
the efficiency of braking gets reduced due to lesser contact area after wear resulting in point contact and frequently the drum radius must be re-machined and new brake shoes may be fitted.
Where as in a Caliper brake the braking force is applied in the same direction of the rotating wheel from a side by a braking pad. This braking wheel is connected to the rotating wheel which is made to stop by the side braking shoe which progressively halts the wheel and does not give shock. The braking is very smooth and the efficiency of braking is very high. This means the smoothness by which the vehicle is going to stop is very high and the vehicle will stop within a shorter distance from the braking point. In this system the guide pins play a very important role. These guide pins are normally cold forged, machined and heat treated. The three flats for retaining grease is done in the cold forging stage itself After heat treatment the portion which is sliding is slightly bent. This bend cannot be corrected by any other process like grinding because the grease retaining flats interfere and creates ovality in the diameter. Hence this problem is persistent in the process which has necessitated our invention to get a better product.
In the prior process the Shank diameter is cold forged with a bend max 0.05mm and a shank diameter tolerance of 0.1 mm, and 3 flats are extruded and again creates a further bend in the part.
This invention is in changing the process of making the 3 flat of a guide pin and also making the guide pins Shaft portion without any bend.
The grease retention, flats are cold extruded along with the other portion of the part in a cold heading machine together in one operation.
In this process the present grease retention flat of a separator and in the cold formed part there will be not any flat grooves and this part will be fully grooved. After heat treatment and centreless grind of the diameter is accurate and a true cylinder in formed.. With this cylinder grinding of the 3 flats which will have a perfect geometric location and also have zero bend in done.
In this process, of making the 3 flats, the conventional process of extruding the 3 flats in the cold forging machine itself, has not been followed. Refer our process sequence in following this process, where the Shank diameter is formed in the 2nd die as shown in diagram and the 3 flats are produced by squeezing the shank into a die which has the 3 flat and when the product gets ejected out of the die the product which was originally round will have 3 flat extruded in its shank. In this process the entire shank portion gets a bend up to 0.05 to 0.08mm. further when this component is heat treated finally the shank further bends, without any control.
The bend created by heat treatment of the part cannot be removed by centreless grinding since while grinding the 3 flat will interfere with intermittent cuts and the product shape will totally change and it will not be a cylindrical shaft. This aspect of cylindrical shaft is very much essential in the operation of the pin during braking as the name itself says it is a guide pin and only a cylindrical pin can really guide the brake pad without resistance, and an oral pin cannot guide.
In this process, the 3 flats are not extruded in the cold forging stage. Only a cylindrical shank is produced with grinding allowance. Heat treatment is carried out. Finally the heat treated part will have a bend which is cumulative of the cold forge bend and heat treatment bend.
With the grinding allowance being more than the bend, the centreless grinding of the shank to 0.02mm tolerance makes a true cylinder without any bend. After obtaining a true cylinder. It is loaded in an automatic surface grinding machine built and 3 flats are grinded by indexing each flat grinding on by one and eject the part, automatically.
This part will be exactly the same to look like a cold forging part but, this will have no bend which is the most critical characteristic on this part. This is the new process followed.
The braking pad is suppose to move on two guide pins. The straightness of the guide pins and the grease retention area are the most important critical parameters for smooth movement of brake pads to hit the brake plate and return.
This smooth function is possible only with grinding process without any bend. This process makes the blank over size prior to heat treatment. After heat treatment oversize diameter is centreless ground to the required diameter with a very close tolerance on the diameter, By this operation all most a perfect cylinder is produced for the brake pad to move to and fro. Further then grinding the 3 grease retention flats with a special fixture and a surfce grinder. Hence the total purpose of smooth accurate and cylindrical surfce with grease retention area is available for the brake pads to perform.
By the previous process the bend of the guide pin after heat treatment is not very much controllable and the piece to piece variation and lot to lot variation of the products could give a very high variation in smoothness and high noise, of the brakes assembled in various vehicles. This process has become an absolute necessity to solve this problem.
In this process of manufacture since a perfect cylinder is produced for grinding and also three grease retention flats by surface grinding the reliability of performance is predictable and never a chance. If these pins are used in various occasions the performance will be more or less the same, where as in the previous process it will vary from one vehicle to other vehicle without any comparison. Since this process is capable of getting a very close tolerance of the outside diameter of the guide pins the clearance between the guide pin and brake pad can be a small as possible, so that there would not be any noise at ill due to noise vibration. This noise is normally very irritating to the Driver, which can be totally eliminated by suitably designing the hole size and the shaft size and the shaft size can be manufactured by our process to the accurate dimension of the design which cannot be done by the earlier process as shown in the diagram.
Novel features of this invention are shank diameter is centreless grinded and he bend is zero with a shank tolerance of 0.02mm, 3 flats are surface ground and are straight and has no bend.
1. The guide pin manufacturing process is basically a
cold forging process of a blank, heat treating the
blank and final machining of the blank in the
undercut portion, facing the head portion and
drilling, tapping the threads characterised is that
the improved version of the process is in changing
the making of 3 flats from forging to surface
2. The method of making the 3 flats portion as
claimed in claim 1 is to extrude the 3 flats in
forging state itself where as it has to be surface
ground in a separate machine by indexing 3 times.
|Indian Patent Application Number||883/CHE/2004|
|PG Journal Number||26/2007|
|Date of Filing||01-Sep-2004|
|Name of Patentee||K.R. ANAND|
|Applicant Address||NO.2-B/8,SOUTH PHASE INDUSTRIAL ESTATA, AMBATTUR CHENNAI-600 058|
|PCT International Classification Number||A 61 N 0 01/375|
|PCT International Application Number||N/A|
|PCT International Filing date|