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SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 1 Issue 6 October 2014

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 36

Design and Optimization of Fixture for Mirror Holder to Get High Surface Finish and Reduce Machining Time

Thati Govindaiah¹ Dr.V.Krishna Reddy²

¹ M.tech student, ²Professor, dept of mechanical engineering, kits, markapur, A.P, INDIA

ABSTRACT The main objective of this paper is to

design and optimize the fixture for mirror holder, which reduces the unit cost of the component and at the same time provides good surface finish. A Mirror Holder is a device that holds a mirror. In optics research, these can be quite sophisticated devices, due to the need to be able to tip and tilt the mirror by controlled amounts, while still holding it in a precise position when it is not being adjusted. Precision mirror mounts can be quite expensive, and a notable amount of engineering goes into their design. Such sophisticated mounts are often required for lasers, interferometers, and optical delay lines.

First, a brief introduction is given on this research area. Secondly, a process plan containing the use of tooling and fixturing is defined to manufacture the mirror holder. From this process plan we would be able to get the tool path and machining time of the component. Thirdly, the strategies based on the defined fixture systems are discussed. Fourthly, the contributions on design methodologies and optimization of the fixtures are examined. Fifthly, optimized process plan containing the optimized fixture is defined to manufacture the mirror holder and verifications are done to reduce the machining time and high surface finish.

Keywords: manufacturing process plan, tool design, NX-CAD, NX-CAM, DMG 5-axis milling machine.

INTRODUCTION

A Mirror Holder is a device that holds a mirror. In optics research, these can be quite sophisticated devices, due to the need to be able to tip and tilt the mirror by controlled amounts, while still holding it in a precise position when it is not being adjusted. Precision mirror mounts can be quite expensive, and a notable amount of engineering goes into their design. Such sophisticated mounts are often required for lasers, interferometers, and optical delay lines.

Laser cavity end mirrors need very precise alignment. Due to their low divergence laser beams need precise steering mirrors. For rapid prototyping on an optical table mirror mounts can be used to hold other elements besides mirrors, for example lenses often need to be aligned for minimal coma. Sometimes prisms only need two axes alignment and can be mounted on a mirror mount rather than a three-axis prism table.

Fixtures accurately locate and secure a part during machining operations such that the part can be manufactured to design specifications. To reduce the design costs associated with fixturing, various computer-aided fixture design methods have been developed through the years to assist the fixture designer. Fixture layout design is a major concern in the development of automated fixture design systems. The task of fixture layout design is to layout a set of locating & clamping points on work piece surfaces such that the work piece is accurately located & completely restrained during manufacturing operations. Fixtures accurately locate and secure a part during machining operations



such that the part can be manufactured to design specifications. To reduce the design costs associated with Fixturing, various computer-aided fixture design (CAFD) methods have been developed through the years to assist the fixture designer. Fixture Design Concepts: (Managing degree of freedom) 3:2:1 (3 At least 3-Point to define a plane) (2 At least 2-Points to define location) (1 At least 1-point for clamping) Fixture layout design has received considerable attention in the recent years. However, little attention has been focused on the optimization of manufacturing fixture layout under dynamic conditions of the work piece.

COMPUTER AIDED DESIGN

2D input of mirror holder

Figure 1: 2D input of mirror holder Final 3D model of mirror holder using Unigraphics NX-7.5

Figure 1: final 3D model

Manufacturing process plan

Identify suitable machine. Selecting suitable tools for

manufacturing mirror holder component.

Designing fixture for mirror holder. Listing down the Sequence of

operations performed on mirror holder

Generating tool path.

Identify suitable machine

DMG 5-axis milling machine is used for manufacturing mirror holder component. In DMG 5-axis milling machine X, Y, Z, B, C are 5 vectors, X & Y are tool movement and Z is for table upwards movement, B for spindle movement, C for table rotation.

Figure 2: DMG 5-axis machine

Selecting suitable tools

FACE_MILLING

Face Milling is the main Face Milling operation subtype. A milling cutter that cuts metal with its face. Face milling creates large flat surfaces.

FACE_MILLING_AREA Face Milling Area is a Face Milling operation subtype that is customized to recognize a cut area and wall selection.


ISSN: 2348 – 8360 www.internationaljournalssrg.org 8

SPOT_DRILLING

This operation subtype allows the tool to pause at the tool tip or shoulder depth of the tool by a specified number of seconds or revolutions.

DRILLING

This operation subtype allows you to do basic point-to-point drilling.

Selection of fixture

An ordinary vise attached to a workbench to hold a material or component in place while it is being worked on. For manufacturing mirror holder Bench vice is the fixtures to fix it on the work table.

Figure 4: Bench Vice

Sequence of operation

Face mill area operation Planar mill Spot drill drilling

Generating tool path

milling operations on mirror holder

Material of mirror holder is alluminium alloy. Aluminium alloys are widely used in automotive engines, particularly in missile

parts and crankcases due to the weight savings that are possible.

Below image shows the face mill area operation of mirror holder maintaining at speed 1500rpm and feed 240mmpm

Figure 5: face mill area operation

Below image shows verification of face mill area operation

Figure 6: face mill area verification

The manufacturing process of mirror holder on CNC machine.

Raw material is placed on the machine, and degree of freedom is arrested using fixtures. Bench vice is used for arresting degree of freedom of the mirror holder.

First step: facing operation is done on the raw material

Second step: planar mill operation will be done on sides of the mirror holder

Third step: angular planar mill operation will be done on mirror holder



Fourth step: drilling operation will be done to create holes

Fifth step: After completing setup_1 operation component is removed from fixture and it is reversely placed in fixture for setup_2 operations.

sixth step: Again facing, planar milling operations will be done on the component. Finally finish operation will be done.

After manufacturing component is rejected due to dimension errors and rough surface finish. this problems taken place due to improper fixturing. While component is manufacturing it should be rigidly fix in fixture because when tool is passing through the component with high cutting speed and feed tool vibrates due to vibration the force will be applied on component and it gets disturbed from its position and leads to dimensional error. To overcome this problem a fixture to be designed to fix the component rigidly in fixture.

Designing Fixture for Mirror Holder

Fixture Design Concepts: (Managing degree of freedom)

3:2:1 (3 At least 3-Point to define a plane) (2 At least 2-Points to define location) (1 At least 1-point for clamping)

2D drawings of the FIXTURE

Figure 7: 2D input of fixture

Final 3D model of fixture using Unigraphics NX-7.5

Figure 8: 3D of fixture

Assembly of fixture and part

Figure 9: Assembly of fixture and part

The manufacturing process of mirror holder on CNC machine using designed fixture.

Raw material is placed on the machine, and degree of freedom is arrested using fixtures. Bench vice is used for arresting degree of freedom of the mirror holder. After setup_1 bench vice cannot fix the component rigidly because of its irregular faces and shape in this case designed fixture is used for arresting degree of freedom of the mirror holder, Other than designed fixture mirror holder cannot be fixed properly and cannot be machined.



First step: facing operation is done on the raw material

Second step: planar mill operation will be done on sides of the mirror holder

Third step: angular planar mill operation will be done on mirror holder

Fourth step: drilling operation will be done to create holes

Fifth step: After completing setup_1 operation component is removed from fixture and it is reversely placed in designed fixture for setup_2 operations.

sixth step: Again facing, planar milling operations will be done on the component. Finally finish operation will be done.

After manufacturing the component obtained is shown below

By Using designed fixture, after manufacturing the component obtained without any damage and cracks.

RESULTS & DISCUSSIONS

Product cost reduction, Reduction of setup

times

Manufacturing component on CNC machine

using Bench vice fixture

The component cannot be fixed rigidly after

setup_1 in bench vice so tool speed will be

reduced in order to reduce vibration created

by tool at high speeds. Manufacturing

component at low speed increases machining

time and cost of the component.

Time and cost calculation for manufacturing

mirror holder as shown below including setup

time and manual modification of NC program

on CNC machine.

Manufacturing time taken by single

component= 5hr 44min

Machining cost per hour for milling

operations = 1200rs

Machining cost per hour for drilling

operations = 800rs

Machining cost per piece for milling

operations (machining cost per min x

machining time in min) = 1200/60*326min=

5020rs

Machining cost per piece for drilling

operations (machining cost per min x

machining time in min) = 800/60*24min=

320rs

Total machining cost per piece=

milling+drilling= 6528+320 = 6848rs

Table 1: Table of machining time& cost using bench vice



Manufacturing component on CNC machine using Designed fixture

Using designed fixture component is rigidly fixed and it can undergo high cutting speeds and feeds to machine the component Manufacturing time taken by single component= 4hrs 3min

Machining cost per hour for milling operations = 1200rs

Machining cost per hour for drilling operations = 800rs

Machining cost per piece for milling operations (machining cost per min x machining time in min) = 1200/60*202min= 4520rs

Machining cost per piece for drilling operations (machining cost per min x machining time in min) = 800/60*24min= 320rs

Total machining cost per piece= milling+drilling= 4520+320 = 4840rs

Table 2: Table of machining time& cost

using designed fixture

Graphical representation of time & cost of fixtures

010002000300040005000600070008000

with Bench vice

with Designed

fixture

time

& c

ost

TIME

COST

Figure 10: Graph of machining time & cost

Optimization of cycle times Cycle time (hrs) with Bench vice = no.of parts x manufacturing time taken by single part in hrs.

Manufacturing time taken by single part in mins = 350mins

Operations Time

Required

In Mins.

Machining

Cost

Per Hour

Machining

Cost/Piece

Milling 326 RS.1200/

HR

RS.6528

Drilling 24 RS.800/H

R

RS.320

Total 350 Rs.6848

operations Time

Required

In Mins.

Machining

Cost

Machining

Cost/Piece

Milling 202 RS.1200/H

R

RS.4520

Drilling 24 RS.800/HR RS.320

TOTAL 226 RS. 4840



Cycle time (hrs) with Designed fixture = no.of parts x manufacturing time taken by single part in hrs.

Manufacturing time taken by single part in mins = 226mins

Cycle time is optimized by using designed fixture. Designed fixture holds the component rigidly and allows high cutting speeds & feeds. This reduces cycle time of the component.

Table 3: Table of cycle time

NO.OF PARTS

cycle time(hrs) with Bench vice

cycle time(hrs) with Designed fixture

50 291 188

100 583 376

150 875 565

200 1167 753

250 1459 941

300 1751 1129

350 2043 1317

400 2335 1505

0

500

1000

1500

2000

2500

50 100

150

200

250

300

350

400

cycl

e tim

e in

hrs

no.of parts

Optimization of cycle times

cycle time(hrs) with Bench vice

cycle time(hrs) with Designed fixture

Figure 11: graph of optimization of cycle time

CONCLUSION:

Modeling of mirror holder is done using unigraphics software. Fixture is designed to arrest the degree of freedom of mirror holder to allow high cutting speeds and to increase production rate. Proper tools are specified which will support for machining typical components like mirror holders. Graphical representation of Product cost reduction, Reduction of setup times & Optimization of cycle times is shown in results. Manufacturing process sequence of mirror holders is shown in the document. Graphical representation of Product cost reduction rate of mirror holders shows reduction of time as well as cost of component when manufactured by using designed fixture which will arrest total degree of freedom and allows high cutting speed and increases production rate and reduces machining time, labour cost.



REFERENCES:

1. Jig and fixture design by Erik Karl Henriksen

2. Jig and fixture handbook by Carr Lane Manufacturing Co.

3. Economics of Tool Engineering by Alexander Peter Gwiazdow

4. Jig and fixture design / Edward G. Hoffman Non-Fiction, c2004. Jig and fixture design / Edward G. Hoffman Non-Fiction, c 2004.

5. Jig and Fixture Design Thomson Learning. Otros clientes que compraron Jig and Fixture Design, también compraron : www.agapea.com/Jig-and-Fixture-Design-n1244984i.htm

6. Colvin, Fred H.; Haas, Lucian L. (1938). Jigs and Fixtures: A Reference Book. New York and London: McGraw-Hill Book Company.

7. Henriksen, Erik K. (1973). Jig and Fixture Design Manual. New York, N.Y.: Industrial Press Inc.

8. 4expertise.com Store Directory: Jig and Fixture Design, 3rd Edition. www.4expertise.com/jigs-fixtures.html

9. Bekijk en vergelijk informatie, beoordelingen, vragen & antwoorden en de beste winkels voor 'Jig And Fixture Design' op BESLIST.nl

10. Boeken Engelsboeken_engels.beslist.nl/boeken_engels/d0000862005/ Jig_And_Fixture_Design.html

11. Taiichi Ohno; foreword by Norman Bodek (1988). Toyota production system: Jig_And_Fixture large-scale production. Portland,

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