Manufacturing Management of Aeronautical Surfaces

International Working Conference Total Quality Management Advanced and Intelligent Approaches, 4th 7th June, 2013. year, Belgrade, Serbia.

QUALITY MANAGEMENT AERONAUTICAL SURFACES MANUFACTURING

UDC:

Ph.D. Srdjan ivkovi, Mech.Eng.

Military Technical Institute Belgrade, Experimental Aerodynamic division, Designing and Manufacturing of Wind Tunnel Models Department, Head of section

Belgrade - Serbia; [email protected] Paper received: 08.02.2013.; Paper accepted: dd.mm.yyyy.

Abstract: Production quality management of model's for wind tunnel testing requires the development of specific methods and strict application of prescribed procedures. A model aircraft is a unique high-accuracy requirements and coordinate the optimization of key quality control inspections and the total time of production. Produce wind tunnel model the required quality and within the required total time, defined tasks and objectives of management of the production process: Identification of critical operations and activities, minimize the time of coordinate inspections of model elements between cutting operations, identifying the main parameters of quality (shape, position in space and angular relations), material management for all other machining operations that follow. The paper presents the developed method of production management by providing the required quality of the wind tunnel models.

Key Words: quality management, manufacturing, wind tunnel models, cmm

1. INTRODUCTION Production quality management of aeronautical

surfaces refers to models of aircraft and missiles for wind tunnel testing (Fig.1.). Geometric similarity is the primary requirement that is placed in the project application for model manufacturing. The wind tunnel tests are laboratory tests and the requirements for the accuracy of the model is very high. The model is reduced compared to the aircraft but the tolerances are obtained by simple scaling of tolerances that apply to aircraft that are produced in a factory. Tolerance models are much narrower. Inverse is also true: the geometry tolerances foreign aircraft are not simply the product of the external geometry of the model tolerance. They are much wider. When it comes to similarity geometric model for wind tunnel testing and the original geometry of the aircraft are different aerodynamic and technical tolerances [1]. Aerodynamic tolerances are related only to the

aerodynamic performance of the aircraft model and they include: tolerances on shape and geometrical tolerances of external relations between wing, tail, canard, flaps etc.

Technical tolerances provide functionality and validity of all conections in the model and the actual carrier models and their interchangeability. In contrast to the low-serial, serial and mass-

produced a wide range of material goods, manufacturing a models for wind tunnel testing is a unique prototype production of mechanical assemblies described freeform surfaces with high geometrical accuracy requirements.

Inspection of geometry has its two aspects: one is the final, final inspection prior to model testing in the wind tunnel. CMM report is a key document

supporting the wind tunnel model. This report is final evidence of models quality and geometric similarity with CAD design.

Fig. 1. LASTA-2 (scale 1:5) in Wind Tunnel T-35

Another aspect is a series of geometric inspection during the manufacturing process. Coordinate inspection between cutting operations relates to the production management model to achieve planned quality. Coordinate inspection is key to managing production process model aircraft. Both aspects of the coordinate inspections of aircraft models require the solution of the problems of access to comprehensive.

2. AERONAUTICAL SURFACES MANUFACTURING

Making a wing for wind tunnel models is the best way to explain complexity of production process aerodynamics surfaces. Wing is made of prismatic work piece by first shaped to their top view. Then alternate cutting upper and lower side of the wings to


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get more repeated operations required aerodynamic shapes.

The required form must always be made in a very narrow tolerances of shape. Between each of the cutting operations it is necessary to measure the geometry of the wing.

Milling as a dynamic process of cutting material causes behind the internal stresses in the part being processed. These stresses are higher for larger depths of cut and lead to bending and warping of parts to be processed. Deformation leads to uneven supplements for the next machining operations. Unequal distribution of materials requires moving the machining reference plane in order to maintain maximum material condition.

The flow chart of the technological process wing manufacturing, figure 5, include sequence inspection of geometry coordinate and flattening technological bases. These two sequences are repeated after each machining operations. Directions and the amount of movement of reference plane in the machining process of aerodynamic parts can only be obtained by using the method of CMM coordinate metrology. This is why the technological process cannot be planned and prepared in advance completely.

2.1 Machining errors aeronautical surfaces During manufacturing process of freeform surfaces

that form models of aircraft lifting surfaces may be a few characteristic errors [2]. Error analysis of the shape and position allow making corrections or changes to the technology chosen structure of the model and its lifting surfaces. The quality of the results is evaluated by analyzing the inspection accuracy of the measurement and evaluation of measurement errors.

Translation profiles in the direction perpendicular to the plane of suspension, Figure 2. This error basically has several causes but the most common is the wrong tool length compensation during initial setting by the operator CNC milling machine.

The second important cause of airfoil translation is the thermal deformation of machine tools. Error occurs if the upper side of airfoil made in a thermal balance and the opposite side in the second. A typical situation occurs when the processing is completed in one working day is a whole machine that reached its operating temperature. Machining opposite side begins with the second work day, and cold machine leads to deviations although the machine operator to comply with all the activities required conversion.

Translation profiles in the direction parallel to the plane of the suspension. This error occurs in the incorrect setting of the machining coordinate system of the work piece. It manifests itself as a upper profile

translated in relation to the lower profile. In these cases, the piece usually rejected. Very rarely, only if it occurs in the earliest stages of manufacturing can be improved this error. One of the basic parameters of the airfoil leading edge radius becomes undercut. The most common cause is insufficient experience of the operator on CNC milling machine.

Fig. 3. Manufacturing: Equidistance airfoil

Profiles in sections at a distance equidistant from the theoretical outline, the same variation occurs in the upper and lower surfaces, figure 3. Error occurs in 5-axis milling machine when the cutter is constantly perpendicular to the surface to be processed. It occurs due to the mismatch point of rotation defined by postprocessor (pivot point) and the same settings on the 5-axis milling machine. These errors are easily corrected. It is necessary to repeat previous machining operation (re-manufacturing).

Another cause is the difference between nominal measures of cutter (ball-end) and used during generating the tool path. It occurs due re-sharpening cylindrical cutter with ball end. This avoids the use of cutters with taper cut and spherical end. Sharpening tools leads to the shortening but not nominal changes in measures.

Fig. 4. Manufacturing: Twisted Airfoils

Twisted airfoils (profiles) in successive sections rotated in relation to each other, figure 4. This error is almost always occurs in manufacturing of lifting and control surfaces. Several elements influence the occurrence of these errors: chosen materials, chosen technology process, cutter with low wear resistance and non-sharp cutter. The main cause is the residual stresses in the work piece after machining operations.

By constantly rotating and alternating machining of upper and lower surfaces of the wing, flattening of the technological base leads to work piece without residual stresses. It is necessary during machining process planning to introduce additional technological base mounts to reduce wing deflection. It is necessary to use milling machines with 4&5 axis of simultaneously motion. Preferably it is necessary the cut-off technological base execute on electro discharge machine with wire. Milling cutter hit the work piece introduce additional stresses. After contour

Fig. 2. Manufacturing: Translated Airfoil


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machining operation, there may be only polishing by the hand.

Manufacturing of lift and control surface of models wind tunnel carries all of the previously stated errors. The final surface deviation is always making the combination described above. Their analysis is a very complex task and sometimes it is very difficult to

separate the cases presented. Error detection and separation of production is very important for the final quality and a sure indication of the technology of the process managed to achieve requested quality.

Fig. 5. Flow chart: Manufacturing Wing - wind tunnel models


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3. WIND TUNNEL MODELS ACCURACY Quality management of manufacturing process

models aircraft and missiles for wind tunnel testing requires the development of specific methods and strict application of prescribed procedures. A wind tunnel model is a unique high-accuracy mechanical assembly. Required geometrical similarity and functionality request quality management of complete manufacturing process.

3.1. Foreign and domestic experience Some of respectable world companies give on web

presentation manufacturing tolerances for wind tunnel models.

Tolerances of aerodynamics surfaces for wind tunnel models in Russian CAGI1 are 0,04mm [3].

British ARA2 declares accuracy for wind tunnel models are 0.025 mm where required [4].

Dutch NLR3 declares [5] form accuracy < 0.05 mm and angular accuracy < 0.1 for wind tunnel models.

French ONERA4 and USA [6] NASA5 are not declaring in public manufacturing accuracy of wind tunnel models.

Domestic institute VTI6 is only one company in Serbia that produces, for domestic purposes, models for wind tunnel testing. In recent years VTI provides services of designing, manufacturing and testing wind tunnel models for foreign companies.

Accuracy of wind tunnel models in VTI depends of scale, testing conditions and functional requirements. For example, manufacturing tolerances for Lasta-2 [7], model (scale 1:5, wings span 2m), shown on figure 1, are:

Fuselage tolerances 0.25 mm Airfoil tolerances 0.05 mm Angular tolerances 0.10

Manufacturing tolerances for supersonic missiles models can be narrower.

This brief presentation of manufacturing accuracy shows that domestic technological capabilities are very close to respectable foreign institution.

4. QUALITY MANAGEMENT OF WING MANUFACTURING PROCESS

Inspection of the geometry element model for wind tunnel testing of aircraft and missiles carries many characteristics in relation to other classes of

1 CAGI = - Central Aerohydrodinamics Institute 2 ARA - Aircraft Research Association 3 NLR - Nationaal Lucht- en Ruimtevaartlaboratorium 4 ONERA - Office National d'Etudes et de Recherches Arospatiales 5 NASA National Aeronautics and Space Administration 6 VTI VojnoTehnicki Institut

objects described by the free-form surfaces. It is primarily caused by the shape, configuration and design solutions. Aircraft has a central plane of symmetry and the parts that form the lift and control surfaces are roughly shaped plate. Besides the shape, main interest is their relationships in a space.

The accuracy required in the wings, fin, horizontal and vertical tail, canards, ailerons, flaps and slats is still several times more stringent than required accuracy of the fuselage. Very often tolerances of airfoil leading edge are narrower than the trailing edge zone.

4.1. Critical manufacturing operations Geometry inspection is the key of quality

management of whole manufacturing process. It is most important results of the final geometric inspections of the models assembly and the total time of manufacturing.

Optimization of coordinate inspection activities it is necessary to execute comprehensively. It is necessary to cover the preparations and execution time of metrological task.

Minimizing the time coordinate inspection shall not affect the measurement accuracy and reliability of the results. It is necessary to achieve the projected quality of the completed model aircraft in the shortest possible time interval for the current technical - technological equipment. Total time and final quality are inextricably linked wind tunnel model categories.

Produce the wind tunnel models according the required (designed) quality and within the total time defined mission and goals of management of the manufacturing process wind tunnel models:

Defining the flow chart of manufacturing process. Identifying critical operations and activities.

Minimizing the time coordinate inspections of model elements between machining operations.

Providing management of the additions machining material for all types of machining operations as follow.

Defining methods for identifying quality parameters related to the spatial position and the mutual relations of the elements of the wind tunnel models.

Number of machining operations on most affects the overall execution time. Elements of the wind tunnel models are made by milling on machines with 3-5 axis simultaneous control. Configuration of the aerodynamic surfaces require that the number of machining operations reduced to the least possible number. A number of the machining, with smaller depths of cut, eliminates residual stresses in the part processed but multiplied many times already making great time. A smaller number of operations with greater depths of cut drastically shorten the overall


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production time, but as a result of residual stresses. Residual stresses deform the aerodynamics part and have great influence to the geometric accuracy.

Reducing the time of machining of individual operations is directly linked to the installed power machine tools, the maximum number of spindle speed and wears resistance of cutting tools.

The preliminary-final time related to the activities performed on the machine tool but not a direct machine processing. These activities include preparation of cutting tools and machinery, installation, alignment and clamping of parts.

Measuring geometry of parts between machining operations is the one of the critical operation. It is necessary to have specialized developed measurement method.

4.2. Optimizations of airfoil measuring Optimization coordinate inspection activities

performed for the wind tunnel model and CMM with touch trigger probes in which the coordinates of the measured speed of acquisition low. Less speed acquisitions require more execution time, and this problem is given special attention in the paper.

Presented a method is developed to minimize the number of grid points airfoil inspection. Thus the number of grid points of inspection shall not affect the measurement accuracy and reliability of the information obtained about the state of machining wings.

Fig. 6. Min. number of points for airfoil inspection

Minimum numbers of point for geometric airfiol inspection obtain by following criteria: deviations of applied airfoil mathematical model (cubic spline) to wing surfaces (CAD definition) must be less than uncertainty of CMM. Increasing number of cubic spline points will increase approximation accuracy but will not increase measurement accuracy. In contrary, total time for execution for that metrological operation will be reduced. Reducing total number of airfoil measuring is very important for CMM with touch trigger probe.

4.3. Orientation of Measurement Coordinate System

Any measurement of the CMM starts by the settings of the coordinate system of inspection. Proper

setting of the orientation of the coordinate system of inspection is a basic requirement for all successful coordinate measurement. Spend time is called the preparatory time and it multiplies in all repeated measurements. One of the goals of optimization is to shorten the overall processing time and minimizing the importance of preparation time.

Coordinate systems on the CMM provide procedures simply called "3-2-1. The question of interest is how this method applied to surfaces described by airfoils.

Commercial software programs of coordinate inspection provide a method the settings to free-form surfaces. These methods are referred to as "Best-Fit Alignment". The point is that the program requires the global minimum of the distance measured and theoretical coordinates of the "cloud" of points in roto-translation space. The user is allowed to "steer" the program by selecting only the translation, only rotation or roto-translation in 2D.

Fig. 7. Setting Measuring Coordinate System on Wing Surface

Figure 7. shows the wing cut on the CAD / CAM system with a series of parallel XZ planes. These sections are shown as contour lines wings. Contour is chosen, and its symmetric counterpart, which extends across the wing, and it generates between 20 and 30 points. This number of points is sufficient to reliably set the basic plane of the coordinate system of inspection.

Mathematical method is simplified; total number of points is reduced and executions time is minimized.

4.4. Measuring angular relationships of aerodynamic surfaces

Angle is semi-space between two planes or two lines. The angle between two planes is the angle between the vectors of their normal. Apparently seems impossible to determine the angular relationship between two elements of free-form surfaces is described that on themselves, usually, do not have one part of the plane.

Angular relationships of lift and control surfaces, wings and all the elements needed to determine the model for wind tunnel testing and are essential to the quality of the final assembly. In relation to the measurement of airfoil shape deviation from this determination is complicated and requires complex mathematical models and calculation []. It is necessary to find the plane that represents the wing and calculate


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the required angular relationships such as the wing setting angle and the dihedral angle.

Such a plane exists on the wing and is called the Wing Reference Plane - WRP. This plane is not material and its direct measurement is impossible. Modeling of airplane wings in the CAD/CAM system begins by defining the WRP. Absolute coordinate system is the basis for positioning the wings and the other entire element in model space.

Fig. 8. Calculation of WRP position

Figure 8. represent the characteristic wing section obtained on the CAD/CAM system, and presents the general case. Hamstring airfoil (marked as Chord) and the line represents the reference plane of the wing (WRP). This can be any section of wing LASTA-2 wind tunnel model.

The developed method requires the preparation of measurement and calculation of the CAD/CAM system. It takes information about the relationship between WRP and the upper and lower wing surface transferred to the coordinate inspection program. This information is obtained applying (1) system of equations:

i

LiUM

XXXl

l-

-=

1

i

LiUM

YYYl

l-

-=

1

i

LiUM

ZZZl

l-

-=

1 Where [XM, YM, ZM] represent measured

coordinate of WRP, [XU, YU, ZU] represent measured coordinate of upper side of airfoil, [XL, YL, ZL] represent measured coordinate of lower side of airfoil, and parameter l represent distance between upper and lower theoretical airfoil points and WRP on CAD/CAM system.

4.5. Maximum Material Management Production quality control model aircraft wings

developed method provided the maximum material management. Critical activities in the technological process of making the wing is moving reference plane of machining. These displacements, after each operation, provide a uniform distribution of additives for machining operations that follow. Results coordinate inspection control sections are analyzed according to established criteria and determine the values and directions of moving reference plane machining (Fig.9.). Established criteria in each phase of the airfoil to the measured deviations are within the

scatter of the "six sigma". Such strict criteria decision making is set by the fact that the coordinate inspections performed a minimum number of points of the developed method. Methods presented in this section to minimize the time of preparation and execution of metrological task and ensure achievement of planned quality model aircraft.

Fig. 9. Material distribution after first contour airfoil cutting (Lasta-2 Scale 1:5)

5. CONCLUSION Set goals and objectives are achieved:

Identified the critical activities that can be improved and optimized.

Defined method of determining the minimum points number of airfoil inspection.

Defined a new settings method measuring coordinate system according a wing.

Defined by the original method of measurement used to determine the wing reference plane (WRP). The method is able to identify angles of deflections for control surfaces: flaps, slats, ailerons and rudders.

Defined for a control method for maximum material during machining of lifting and control surfaces of aircraft models the basis on result of the coordinate inspections.

All developed and presented method successfully applied on several different forging and domestic project.

REFERENCES [1] uri Duan, Analysis and contribution design of models for testing in blow-down wind tunnel, M.Sc. thesis, Mechanical Engineering Faculty, Belgrade Serbia, 1986 [2] ivkovi Srdjan, Optimisations of Free Form surfaces measuring using coordinate metrology methods, Ph.D. thesis, Military Academy Belgrade, Technical systems for military purposes department, Belgrade - Serbia, 2011. [3] : . . (on line), http://www.tsagi.ru/rus/base/opi/, (4.12. 2012.) [4] ARA: Inspection. Design & Manufacture. (online) http://www.ara.co.uk/services/introduction/wind-tunnel-models/, (4.12. 2012.) [5] NLR: Manufacturing of wind tunnel models. Products and Services. (online), http://www.nlr.nl/smartsite.dws?l=&id=10295, (8. 1. 2011.) [6] NASA: Wind tunnel models systems criteria, Langley Research Center. (online) LPR 1710.15, 2004, http://lms-r.larc.nasa.gov/admin/documents/LPR1710-15.pdf, (1.10. 2011.) [7] uri Duan, Miladinovic Nebojsa, Design project aircraft model Lasta-2 (scale 1:5) for Wind Tunnel -35, Int: V3-2877-I-, VTI Belgrade - Serbia, 2005

U1U2

U3 U4 U5 U6 U7 U8 U9U10 U11 U12

L1L2 L3 L4 L5 L6

L7 L8L9

L10L11 L12

WRP

ChordW2 W4

W10 W11 W12

W1 W3m5

n5

m6

n6

75 =m5n5

-

(1)

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Manufacturing Management of Aeronautical Surfaces