effect of machining parameters on geometric form … · effect of machining parameters on geometric...

Effect of Machining Parameters on Geometric Form Control and Orientation Control – A Review

NAVora1, PMGeorge2,SPJoshi3

Mechanical Engineering Department

BVM Engineering College, [email protected]

[email protected]@yahoo.com

Abstract- A major channel of machined components are produced by CNC milling. The milling machine has got specific capability to produce components meeting both the dimensional and geometric requirements. These requirements are to be met with in order to meet the functional requirements by each components as a part of an assembly. This paper exposes the various research work carried out in this direction especially in the content of form and orientation control. The controls considered in this review papers are : Flatness, Straightness and Parallelism. The effect of various cutting parameters on these geometrical parameters are of paramount significance for effective part functioning. Literature surveys indicates that not much work has been carried out in this area.

Keywords – Milling ,GD&T, Flatness, Straightness, Parallelism.

I. MILLING

Milling is process of generating machined surfaces by progressively removing a predetermined amount of material or stock from the workpiece, which is advanced at a relatively slow rate of movement or feed of a milling cutter rotating at comparatively high speed. The characteristics feature of the milling process is that each milling cutter tooth takes its share of the stock in the form of small individual chips. Greater attention is given to the geometry in addition to the dimensional accuracy and surface characteristics of products by industries these days. Milling operations are performed with milling cutters of different types and sizes. Owing to the fact that they give better components leading to faster and economical assembly.[1]

II. LITERATURE SURVEY

In this study, the effects of cutting edge geometry, work-piece hardness, feed rate and cutting speed on surface roughness and resultant forces in the finish hard turning of AISI H13 steel were experimentally investigated.This study shows that the effects of work-piece hardness, cutting edge geometry, feed rate and cutting speed on surface roughness are statistically significant.[2]

In this Paper experimental investigation was conducted to determine the effects of cutting conditions and tool geometry on the surface roughness in the finish hard turning of the bearing steel (AISI 52100). The effect of the effective rake angle on the surface

finish is less, the interaction effects of nose radius and effective rake angle are considerably significant. Mathematical models for the surface roughness were developed by using the response surface methodology. The investigations of this study indicate that the parameters cutting velocity, feed, effective rake angle and nose radius are the primary influencing factors, which affect the surface finish. The results also indicate that feed is the dominant factor affecting the surface roughness, followed by the nose radius, cutting velocity and effective rake angle.[3]

The aim of this work is to analyze the influence of cutting conditions on surface roughness with slot end milling on AL7075-T6.The considered parameters are: cutting speed, feed, depth of cutting and mill radial engage. Surface roughness is influenced by: tool geometry, feed, cutting conditions and other factors such as: tool wear, chatter, tool deflections, cutting fluid, and work-piece properties.[4]

Influence of tool geometry on the quality of surface produced is well known and hence any attempt to assess the performance of end milling should include the tool geometry. In the present work, experimental studies have been conducted to see the effect of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on the machining performance during end milling of medium carbon steel. The first and second order mathematical models, in terms of machining parameters, were developed for surface roughness prediction using response surface methodology (RSM) on the basis of experimental results. The significance of these parameters on surface roughness has been established with analysis of variance. An attempt has also been made to optimize the surface roughness prediction model using genetic algorithms (GA). The GA program gives minimum values of surface roughness and their respective optimal conditions.[5]

III. GEOMETRIC FORM CONTROLS AND ORIENTATION

CONTROLS

A. Form Controls

There are four form characteristics. They are Flatness, straightness, Circularity and Cylindricity. All feature

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India

National Conference on Recent Trends in Engineering & Technology

controlled are individual and are not related to datum. They are assessed by comparison to a perfect geometric counterpart of themselves a feature formed perfectly flat, straight, circular or cylindrical.

B. Flatness

Flatness is a surface form control. A perfectly flat surface is defined as having all its elements in the same plane. Flatness feature control frames create a tolerance zone not related to any datums. The tolerance zone consist of the distance between two parallel planes. All elements of the produced feature under control must lie within the tolerance zone. Thiscontrol is commonly used on planer surface capable of resting on matting planar surfaces without significant rocking. The control is usually limited to a flatness symbol and a geometric tolerance, although if used on a rate basis the control may contain two level of control. The upper level of control contain the usual overall surface control while the lower level of control contain a tighter tolerance to be held over limited portion of the surface. For example if one is concerned about abrupt surface variation within a relatively small area. It may be specified that the out of flatness allowed per 25 x 25 mm2 is smaller than the overall surface flatness tolerance ( fig 1(a) ).

( a) ( b )

Fig.1 Example of flatness

The regular flatness control looks like Fig 1 (b) Which means the entire surface of the control feature must lie within a total wide tolerance zone which is the 0.001 distance between two parallel planes.Flatness is a geometric control in which a part surface is compared to a perfectly flat geometric counterpart of itself. A part surface is real; therefore it has flaws—ridges, grooves, pits, bumps etc.

B1. Flatness Verification Techniques

Use three jackscrews set on top of a surface plate and at the same time underneath the part. The jack could be adjusted until the top surface (Controlled surface) is parallel to the surface plate top Fig 2 & Fig 3. Once the controlled surface is as level ( parallel ) is possible, an indicator on a height gage or surface gage ( Which sits on and runs across the top of the surface plate ) is put in contact with the controlled surface and pulled along registering surface deviation. The deviations

registered must be smaller than or equal to the tolerance in the feature control frame.Another alternative for registering flatness deviation is to set

the controlled surface in contact with a surface plate that is equipped with a plunger type indicator protruding from its surface and move the part over the indicator point, noting the full indicator movement. Since this type of set up is rare an option is put parallels on the surface plate and put the controlled surface on the parallels. Then with the height gage and the indicator, indicate the controlled surface for deviations in flatness.

Fig 2. Flatness verification Techniques.

Fig 3. Alternate Flatness verification Techniques

B2. Tolerance zone

The tolerance zone is to be considered the distance between two parallel planes. Consequently, all elements of the controlled surface must be between two parallel planes which are the distance apart reflected by the tolerance in the feature control frame.

Flatness may be applied on a rate or unit basis. This is done to prevent abrupt variations in the surface within a relatively small area. When using this method a total control



should be used in conjunction with the unit control. The size and shape of the area being controlled should be made clear.

Fig 4. Correct method of Tolerance zone

C. Straightness

Straightness is a form control that may be used as a surface, derived median line or derived median plane control. Fig 5. shows the each of the infinite number of line elements that comprises this surface in the direction shown in controlled by its own tolerance zone. Each tolerance zone consist of two parallel lines 0.003 apart and begins at the optimal location and angle that will allow it to contain the line element that it controls.

Fig 5.Straightness of a surface

This Control does not apply to the line elements running 900 to the view in which the straightness of the surface control is shown. At no time may the surface of the part exceed its size limit requirements.

Fig 6. Correct method of straightness

Straightness is an individual control. Therefore, no datums are allowable in the feature control frame.

D. Orientation controls

There are three orientation or attitude characteristics. They are angularity, Perpendicularity and Parallelism. All Control feature related to datum planes or to datum axes or to a combination of datum planes and datum axes.

D1. Parallelism

Parallelism is a member of orientation family. It can be used to control the orientation of the line elements, surface , axes, and center planes. Parallelism symbol is //.When applies this characteristics, it must also be stated what the controlled feature is parallel to. In other words, a datum feature is necessary and must be included in the feature control frame. If the tolerance zone were defined by two parallel planes within which all elements of the controlled surface must lie and datum was a plane.

Fig 7. Surface to a datum plane

In Fig 7. tolerance zone is the distance between two parallel planes separated by 0.005 and both parallel to the datum plane A Datum plane is formed by the 3 highest points ( minimum ) of the datum feature.[6]

IV SELECTION OF PARAMETERS IN MILLING

A. Speed

The speed of a tool is the speed at which the metal is removed by the tool from the work piece. In a lathe it is the peripheral speed of the work past the cutting tool expressed in RPM.

B. Feed

The feed of a cutting tool in a Milling work is the distance the tool advances for each revolution of the work. Feed is expressed in millimeters per min.



C. Depth of Cut

The depth of cut is the perpendicular distance measured from the machined surface to the uncut surface of the work piece.

V.CONCLUSION.

Milled component represents a wast majority of parts produced in industries. The adherence of the geometrical parameters for attaining the form and orientation controls on the Milled components to meet their functional requirements as part of an assembly is extremely important and the same is planned in this investigation. The influence of cutting parameters on the geometrical features is planned to graduallyby developing empirical models which could be used by process planners for creating components which can functionbetter, can be assembled without any problem as well as can be produced most economically.

REFERENCES[1] A Treatise on milling and milling machine 3rd edition The Cincinnati

milling machine co. [2] Tugrul ¨Ozel • Tsu-Kong Hsu • Erol Zeren (2005) “Effects of

cutting edge geometry, workpiece hardness, feed rate and cutting speed on surface roughness and forces in finish turning of hardened AISI H13 steel” Int J Adv Manuf Technol (2005) Vol 25: 262–269

[3] Dilbag Singh. P. Venkateswara Rao (2007)“A surface roughness prediction model for hard turning process” Int J Adv Manuf Technol DOI 10.1007/00170-006-0429-232: (2007) 1115 –1124

[4] A. Del Prete, A. A. De Vitis, A. Spagnolo (2010) “Experimental Development of RSM Techniques for Surface Quality Prediction in Metal cutting Application” Int J Mater Form (2010) Vol. 3 Suppl 1:471 474

[5] N.SureshKumar Reddy. P. Venkateswara Rao(2005), “Selection of optimum tool geometry and cutting conditions using a surface roughness prediction model for end milling” Adv. Manuf. Technol Vol.26: 1202– 1210

[6] James D meadows “Geometric Dimensioning and Tolerancing” marcel dekker, inc.



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