Design and fabrication of an automatic grinding machine

REVIEW OF DESIGN AND FABRICATION OF AUTOMATIC GRINDING MACHINE

Abstract-

Grinding is one of the most important manufacturing process for high precision parts. Grinding characterized by low material removal rate and high surface finish is an abrasive machining process. Geometrically undefined grits of grinding wheel influences part surface finish. Cutting edges worn out during grinding are retained by timely dressing. An operator on shop floor decides on the dressing interval based on end of wheel life such as burns, chatter marks and deterioration in the work piece surface finish. Incorrect dressing of grinding wheel increases unnecessary machining time and wheel wastage. Grinding is an abrasive machining process which is used to improve the surface quality and to achieve dimensional accuracy of a work piece. In grinding, a grinding wheel is used as a cutting tool and material is removed from the work piece. In grinding surface roughness and material removal rate are considered important output responses for quality and quantity of production. In cylindrical grinding out-of-roundness is another important output parameter. It is radial run out of the cylindrical work piece and it is difference between minimum and maximum radius.

Keywords:- grinder, grinding machine, abrasive, pneumatic, rack and pinion, pneumatic indexing actuator etc.

Introduction

Grinding processes are very effective for high precision manufacturing. Grinding is a metal removal process by using abrasive material, which defines the interaction between the grinding wheel surface and the work piece material. By the industries recommendation we use indexing actuator for provide the rotary motion to the work piece. And over which we can placed our grinding wheel.

Aluminium oxide, silicon carbide, diamond, and cubic boron nitride (CBN) are four commonly used abrasive materials for the surface of the grinding wheels. Of these materials, aluminium oxide is the most common. Because of cost, diamond and CBN grinding wheels are generally made with a core of less expensive material surrounded by a layer of diamond or CBN. Diamond and CBN wheels are very hard and are capable of economically grinding materials, such as ceramics and carbides, which cannot be ground by aluminium oxide or silicon carbide wheels.

Objectives

- Reduce the labour cost.
- Increase in mass production of product.
- Reduce the production time.
- Improve safety precautions of worker.
- Increase the accuracy and precision in product.
- Minimizing the rejection of product.
- Increase the overall profit against manufacturing.

Literature Review

Dr. D. Padmanaban described the grinding wheel specification and selection of grinding wheel by using design data book. By using data book we find out grain type, grain size, grade range and bond type.

From Rotomation company catalogue, find the details of pneumatic indexing actuator its size, dimensions and diagram details and its working. In its working of pneumatic Rotary actuator the indexing using clutch bearing(attached to the cam) and rachet(follower), Which the rachet lock the rotation at 90 degree of rotation.

By Ming-Hung Tsai, for selection and designing of pneumatic cylinder played very important role in industry because of low cost, clean of working environment, easy in power transfer, and so on. In recent years, high accuracy high accuracy and high speed system are growing up rapidly.

From grinding wheel catalogue we find out the specification of grinding wheel like finishing of work piece, wheel size and maximum RPM speed.

By Charles chikwendu okpala research paper gave detailed definition of jigs and fixture also identify the numerous advantages that are associated with the uses of jig and fixture: production increase, cost reduction, interchangability and high accuracy parts reduction of the need for inspection and quality control expense.

By V.R. basha and J.J. Salunke they described the cost associated with fixture design and manufacture can account 10 to 20% of the total cost of manufacturing system app. 40% of rejected parts are due to dimensional error that are attributed to poor fixture design. Fixture design work is also tedious and time consuming.

By shailesh s. Pachbhai, the efficiency and the reliability of fixture design has enhace by the system and result as made more reasonable, to reduce cycle time required for loading and unloading parts, this approach is useful. pneumatic fixture reduces operation time and increase productivity, high quality operation, reduced accidents.

By Hoa Nan li, stated that by the number of studies TGW’s are considered to be promising and of great importance field of finishing tools because they cooled provide more superior grinding performance GW’s, such as transportation ability and good heat dissipation of the heat generate in the wheels and workpiece and contact zone, low grinding temp. Force and energy consumption, availability of smooth chip flow and high wheel wear resistance.

By Dhruv H. Patel and V. N. Patni , they analyse and plot the graph. From that graph of S-N ratio it can be observed that optimal value of the surface finish is obtained in first level of tool feed, third level of the spindle speed and second level of the depth of cut. Optimal value of the surface finish with high grade and good accuracy.

By R. Giting and S. Hadiyosa, carried out the work on the implementation 3 axis CNC router for small scale industry. In this paper , discussed about the design and realization of complex axis CNC machine based on microcontroller which combine the spindle drill and this machine is used for cutting , Engraving and marking on wood, acrylic and PCB object. The controller is design such that it works on the principle of PC based control where the serial communication occurs to execute the pattern on object.

CONCEPT AND MECHANISM

For 90 degree of rotation of the shaft, we learned the mechanism of indexing through ratchet and pawl. From that we change some parameter and make the mechanism according to the project requirement. According to that the mechanism works on the principle of one-way clutch through which the shaft rotates at only one direction and stops the anti-rotation of the shaft which either be clockwise or anti clockwise.

The indexer uses the same principle as a standard rotary actuator, where pistons drive a rack back and forth producing a rotary motion of the pinion. But instead of being part of the shaft, the pinion is bored out and has a clutch/bearing pressed in. This clutch/bearing has one set of needles to support the pinion on the shaft, and a separate set of needles that grip the shaft in one direction only.

Notice that the rack and pinion do not reach the end of their stroke in the drive direction, because the cylinder is made longer. This means that as long as air pressure is maintained on the driving piston, the pinion will continue to push the ratchet against the pawl. It also means that the accuracy is not dependent on the stroke of the actuator; it is completely dependent on the ratchet itself.

Once the work is done, the directional control valve can be shifted to drive the rack and pinion back the other way; this is called the reset stroke. Near the end of the reset stroke, a cam attached to the pinion pushes the pawl away from the ratchet so that it is then free to rotate forward. Once the reset stroke is completed, the next drive stroke can begin immediately. For applications where there is no need to maintain the shaft in a locked position, the reset stroke can be initiated immediately following the completion of the drive stroke, so that the indexer is prepared for a drive stroke immediately following a signal that a part is approaching, for example.

Because of the one-way clutch, the pistons cannot exert a reverse torque on the shaft. This means that the speed of an indexer which has an external force or gravity urging the shaft to rotate in the forward direction cannot be controlled and will likely have damaging impact. For small forces, a constant drag may be added to counteract the force, and has the additional benefit of adding a damping effect which will stabilize the system.

Forward acting torques can also cause problems the reset condition, where the shaft is free to rotate in the clockwise direction. In situations like this, a brake can be utilized to hold the load. All indexing actuators are available with a double ended shaft which can be used as a location for a brake, and if the brake is pneumatic, it can be plumbed in parallel with the indexer so that no extra valves or logic are required.

The free-wheeling behavior in the reset mode can also be used to advantage in some cases, for manual “fast forward” to a loading position, or for clearing jams. Since the ratchet is keyed to the shaft, the indexer will always return to its normal pattern of stops.

Selection

For loads that are primarily inertia, the indexer should be sized by its capacity to stop. The inertia and kinetic energy of the load are the important factors; torque is never the limitation.

Controls

Cushions on an indexing actuator will have limited effect, because the pistons drive the load through a one-way clutch. Once the load has been accelerated, slowing the rack and pinion using cushions or shock absorbers will simply reduce or eliminate additional torque from being applied. The inertia of the load will carry it unchecked until the ratchet stops it. But if there is sufficient friction to stop the load within approximately thirty degrees, then the cushion will reduce torque for the last thirty degrees and let the friction slow the load for a softer stop.

During the reset stroke, there is nothing occurring that is visible externally. Since there is no load on the rack and pinion, it can shoot back at extremely high velocity if it is not controlled. The only indication to the user is noise and potentially, breakage of gear teeth or other internal parts. A cushion on the reset stroke can be used to minimize the impact, but must be adjusted essentially “by ear”. A bumper on the reset stroke is less effective, but does not need to be set and cannot come out of adjustment.

Speed control using flow control valves is essential to avoid harmful crashes. A moderate to high pressure gets the load up to speed quickly, and the flow control then limits the maximum velocity. Adjusting system pressure to control speed results in constant acceleration, which for a given stroke time, requires a much higher terminal velocity and resulting impact.

Control System Feedback -

There are two feedback options available for reporting the indexer’s status to the machine’s control system. Magnetic switches are the same used on standard rotary actuators and report the end of the drive stroke and the end of the reset stroke. If the actuator is advanced manually while in the reset mode, then the pistons will not travel their full stroke on the next drive stroke and may not reach the sensor.

Alternatively, the actuator may be ordered with an extended pawl shaft, which projects out the rear of the body. A user-supplied flag can be attached to this shaft and sensed with proximity detector(s) to provide the same signals. The potential for a missed signal following manual motion is eliminated.

If the system requires absolute position feedback, then external sensors must be used. Rotomation can provide a modified rear shaft and other mounting provision for an encoder or other sensor per special order.

Mechanism –

In our mechanism we make the rack and pinion mechanism, where we make the long rack nd set the 6 pinion on the rack. According to that multiple jobs can be mount on the mechanism. Also change the system of pneumatic where only the double acting cylinder which gives the linear movement for the rack. Rack then transfer the movement to the pinion which distributed the movement to the 6 pinion. Then the indexing work according to the concept which gives the rotation to the work-piece with the help of ratchet and pawl which lock the rotation temporary.

Design and calculations for the drive mechanism

For designing the mechanism we first design the rack and pinion mechanism on that basis some parts and parameter are assume. According to that assume parameter can be neglected in actual mechanism working.

For that some parameter such as pneumatic cylinder (Double acting) Which provided by the company. According to that catalogue we design the rack and pinion

From that catalogue we take some parameter that are need to calculate the rack and pinion forces.

That parameter are given below,

m = 60 Kgf

v = 1.08 m/s

tb = 0.7 s

g =9.81 m/s²

KA = 1.2

fu = 1.1

Sb = 1.2

Llhb = 1.2

Accleration of tooths –

Tangential force -

Abbildung in dieser Leseprobe nicht enthalten

Material selection according to the ATALANTA rack and pinion catalogue and calculation

Rack – C45 – Heat treatment – soft and industrial hardened

Pinion – C45 – Heat treatment – soft and industrial hardened

According to that this specifications in ATLANTA catalogue we check the tangential force that can be bear which is 0.8286 kN.

In ATALANTA catalogue(Page No ZB - 37) this tangential force is given in set limits which is from 0.7 to 3 kN

The dimensions of the rack and pinion are given below –

For maximum feed force =Fu tab– 3 kN (considering weaker element pinion)

No. of teeth on pinion – 25

Module – 37.5 mm

For permissible force acting on the pinion

Abbildung in dieser Leseprobe nicht enthalten

Result- According to the given condition the design is safe

From that we can state that the material selection and the size for the rack and pinion is safe for the D40A* Double acting cylinder.

The dimensions Are following for rack and pinion

Conclusion -

According to research papers, concluded that the time consumption, speed of operation and depth of cut for workpiece is more considerable. In that the position control according to NC control mechanism the direction of grinding wheel is control through microcontroller is more accurate and reliable. Also the indexing and rotation of the job is done more accurately and time saving in pneumatic indexing actuator. Clamping and holding the work piece is done efficiently using pneumatic clamps. Also modelling of pneumatic actuator done according to the job dimension and based on those market standards are used.

Reference

1) Ming-Hung Tsai, Chi-Neng Cheng, and Ming-Chang Shih Department of Mechanical Engineering, National Cheng Kung University Tainan, Taiwan, R.O.C(DESIGN AND CONTROL FOR THE PNEUMATIC CYLINDER PRECISION POSITIONING UNDER VERTICAL LOADING )

2) R.Ginting ,S. Hadiyoso and S.Aulia International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 17 (2017) pp. 6553-6558 © Research India Publications

3) Charles Chikwendu Okpala, Ezeanyim Okechukwu C. Department of Industrial/Production Engineering, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria.

4) Shailesh S.Pachbhai, Laukik P.Raut International Journal of Engineering Research and General Science Volume 2. Email- Shai.p@rediffmail.com

5) Prof. V. N. Patni, 1Mr.Dhruv H. Patel S.P.B. Patel Engineering college, Mehsana.

6) Harry Global Engineer (2012), “Grinding Machines and Equipments”, available online at: https://engineerharry.wordpress.com/2012/04/21/grinding-machines-and-equipment/ [accessed on 15/03/2016].

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