Comparison of turning blades produced by a conventional- and additive manufacturing method

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Comparison of turning blades produced by a conventional- and additive manufacturing

method

Rebecca Carlsson

Civilingenjör, Maskinteknik 2018

Luleå tekniska universitet

Institutionen för teknikvetenskap och matematik

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Preface

The master thesis was written at Sandvik Coromant in Sandviken. It has been an enjoyable project with new challenges and learning each day in the past 20 weeks I spent at Sandvik Coromant. The master thesis would not have been possible without the help from coworkers, both at Sandvik Coromant in Sandviken and Gimo, AM center and Västberga. I am thankful for all the help and fun I’ve had with you all but there are some people I want to particularly acknowledge.

One of them is my supervisor at Sandvik Coromant Erik Tyldhed who made this master thesis possible. He has patiently answered all my question and supported me throughout the project. Vaibhav Mane is another supervisor who has helped me tremendous with organizing the different tests and verified the results. My supervisor at LTU helped me with the report and supported me during the project. I want to thank the R&D department in Turning for helping me and making me feel a part of their team.

Also, I would like to thank Elisabeth Bond for her marvelous help with the different tests. Caroline Bäckström, Tommy Gunnarsson and Kjell Åsblom have likewise helped me a lot with the experiments during the project. Gunnar Jansson and Claes Andersson has patiently answered my question and supported me with their expertise.

Finally, I want to thank the people at AM center and Gimo for their tremendous help with information and knowledge. Lina Holmgren, Anders Ohlsson, Per-Olof Jansson, Per Arvidsson and Louise Hansson helped me to gain the knowledge needed to write this master thesis.

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Sammanfattning

Additiv tillverkning har genom åren utvecklats i en radikal hastighet. Sandvik har investerat på området genom att bygga ett additivt tillverkningscenter men på grund av sämre materialegenskaper och för höga kostnader har de inte kunnat implementera detta hos produkterna. Dessa aspekter har förbättrats och därför har detta

examensarbete tagits fram där; syftet med denna rapport är att jämföra två olika producerade blad kring aspekterna material- och produkt egenskaper och

produktionskostnader. Ena bladet produceras genom additiv tillverkning (AM) och det andra bladet produceras idag hos Gimo och tillhör Sandvik Coromant under svarvning, spår och avsticknings divisionen. Om bladet kan produceras genom additiva tillverkning finns det möjlighet att sänka kostnaderna och möjliggöra en designfrihet som inte existerar i dagens produktion. Materialen som kommer jämföras är SS2230 (50CrV4) som används i konventionellt producerade blad samt 1.2709 som används i AM producerade blad.

Undersökningen bestod av fem olika tester med syfte att jämföra de två olika bladens förmåga att leda fram kylvätska, hålla skäret på plats, motstå vibrationer, motstå utmattning och att klara av nötning i nyckelhålet, samt en studie kring

produktionsaspekter där det låg fokus på värdeflödesanalys, investering och

produktionskostnader. Huvudfokusen med resultatet från varje test var att jämföra de två olika bladen, inte att undersöka vilka värden som var optimal. Därför utformades testerna med fokus på kontinuitet där så lite möjlighet till variation kunde existera.

Detta medgav att vissa testvärden som användes inte var optimala för bladen men säkerhetsställde resultatet med att så lite variation mellan testerna förekom.

Kylkanalernas flöde förbättrades med ca 35% hos de AM producerade bladen medan spänntryck, utmattning och nötning inte avvek avsevärt i jämförelse mot

konventionellt tillverkade. Utmattningen gjordes två gånger med två olika skär då resultatet från första testomgången skiljde sig från förväntat resultat på båda bladen.

Produktionskostnaderna kommer bli högre med AM än på konventionellt tillverkade blad men på en längre sikt kan en investering ge större designfrihet och möjlighet för produktionen att producera direkt mot kunden. Detta skulle dock kräva en stor investering med en tidsaspekt på allt upp till 10 år.

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Abstract

Additive manufacturing has developed radical through the years. Sandvik has invested in the area by building a center specific for additive manufacturing. Due to problems with the material- and product properties and high production costs no products have been used with additive manufacturing method. These aspects have improved over the years and therefore the master thesis was made with an objective:

to compare two different produced blades with focus on the aspects of material- and product properties and production costs. One of the blades was produced through additive manufacturing (AM) and the other blade was produced in today’s production at Sandvik Coromant in Gimo. If the blade can be produced through AM there is a possibility to lower the production costs and improve the degree of design freedom.

The material that will be used is SS2230 (50CrV4) which are used in conventionally produced blades and 1.2709 which are used in AM produced blades.

The investigation consisted of five different tests (flow rate, pressure force, vibration, fatigue and keyhole wear) and a study on production aspects with focus on value stream mapping, investments and production costs. The main objective in the result was to compare each test between the two different produced blades, not to

investigate the optimal value. Therefore, was the test designed to have continuity with as small deviation as possible between the tests. This resulted in choosing values which was not optimal for the blades but focused on continuity and deviation.

The coolant channels flow rate improved with 35% on the AM produced blades but pressure force, fatigue and key hole wear resistance did not deviate much from conventionally produced blades. Fatigue tests was made twice with two different inserts because the result from the first test differentiated to much from the expected results on both blades. Production costs will be higher with AM but on a long term may an investment improve the degree of design freedom on a product and a possibility to produce towards costumer (just in time). This will need an expensive investment with a bigger perspective on the timeframe. The value of the product may increase but the production costs will increase too.

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Nomenclature

Symbols Unit

Dm Diameter of workpiece (mm) ap Depth of cut (mm)

n Spindle speed (rpm) vc Cutting speed (m/min) fn Cutting feed (mm/r)

fnx Cutting speed in radial direction (mm/r) ar Depth of groove (mm)

PL Power (W)

vs Scan speed (m/s)

σmin/σmax Stress for minimum and maximum (MPa) σm Mean stress (MPa)

σa Amplitude stress (MPa)

f Frequency (Hz)

k Rigidity

E E-module (GPa)

I Area moment of inertia (M⁴)

m Mass (kg)

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1 Introduction

This rapport is written by a student which studies a master degree in mechanical engineering focus in production at Luleå Technical University. The rapport is a result from a master thesis at Sandvik Coromant during spring 2018.

1.1 Sandvik Machining solutions

Sandvik Machining Solutions is a business area within Sandvik and are world leading in metal cutting tools with 18 000 employees worldwide and a revenue of over 32 000 MSek in 2016. Sandvik has a strategy focusing on operational excellence, technology and customer interactions. The company have seven product areas Coromant, Domer Pramet, Additive manufacturing, powder and blanks technology, Seco tools and Walter which operates in over 100 different markets, may be seen in Figure 1.

Sandvik Coromant produces solutions for cutting processing with focus on inserts, tools and advanced material inserts. Their sales area is worldwide with productions facilities spread over the world [1].

Figure 1. Company branches of Sandvik AB.

Additive manufacturing center within Sandvik machining solutions has been growing and improved the manufacturing of the products but with still some concerns on the production costs and the properties on the material. Sandvik Coromant has an interest in investigating these aspects to see if there are opportunities in the turning division for these techniques. It opens new possibilities for Sandvik Coromant to design components that are not possible in today’s production. The blades produced today has difficulties in the production of coolant channels. The cost of the blades is quite high and the process rather complicated with EDM drilling. Sandvik Coromant sees an opportunity with the design freedom AM process offers but some aspects differ and may not fulfill the criteria of today’s requirements. Therefore, Sandvik Coromant want to test both blades, to see if AM produced blades has a future within the

company.

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8 1.2 Limitations

Sandvik Coromant is interested to test AM blades produced in their center with their equipment, not other methods on other companies, therefore will this master thesis only look on SLM and Binder jetting. Same principles apply for the test where Sandvik wants to use their staff and their equipment at the workshop.

The goal is to compare the blades, not investigate their theoretical capacity, therefore the parameters for the tests will be set by customer’s demand, optimization for tests and recommendations from Sandvik. The time aspect is short due to many tests which will result in help from staff with the tests. The test will be done by staff and the report will focus on collect the correct data, compare it and develop a conclusion.

New data samples from the production in Gimo, a production area within Sandvik AB, will not be done due to time restrictions. The calculations will only be made on present information and data.

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2 Problem description

To understand what tests needs to be executed an understanding on what may deviate in the aspects of production and material- and product properties is required. This information can be assembled from material data, on how the production is today and what AM may offer instead. This section assembles the different material- and

product properties and production aspects. From the information, an objective and problem portrayal is produced.

2.1 Conventionally produced blades

Today the blades (QD-NN2G60C25A) are produced in Gimo. Their facility is practically automatized with high tech robots and machines running the operations.

The material from the blades are bought in from another company and processed in four operations; milling front side, milling and drilling operations at the same time in one machine, EDM drilling and blackened. Under these operations tests are done by the staff to secure the quality of the product. After the processes the blade is sent to a packing station where it is marked and packed to costumer.

The material- and product properties of the blade can be seen in Table 1. The data is assembled from previous tests on the material.

Table 1. Material- and product properties on conventionally produced blade.

Material Yield strength Hardness (HRC)

E-module Elongation at break

SS2230 (50CrV4)

Reference Reference Reference Reference

The coolant channels are an aspect which is expensive and difficult to produced.

Figure 2 shows a CAD model of the blades with the coolant channels visible.

Figure 2. Yellow is the insert and grey is the blade with visible coolant channels of the conventionally produced blades.

2.2 AM produced blades

A batch of AM produced blades were made with aspects of testing. There were no optimizations on the production and was produced as simple as possible. The blade is

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3D-printed in a machine (with the method selective laser melting) and then sent to an oven for hardening. After it is done blades are packaged and sent to Gimo for further operations. AM blades only need two operations; milling front side and milling and drilling operations at the same time in one machine.

The material- and product properties of the blade can be seen in Table 2. The data is assembled from previous test on the materials

Table 2. Material- and product properties on AM produced blades.

Material Yield strength Hardness (HRC)

E-module Elongation at break

1.2709 (AM) Ref + 64% Ref + 4% Ref – 15% Ref – 64%

The coolant channel is redesigned but not optimized. Figure 3 shows a CAD model of the blades with coolant channels visible.

Figure 3.Yellow is the insert and grey is the blade with visible coolant channels of the AM produced blades.

2.3 Objective

The blades are exposed to many different loads when used in operations. Important properties on the blades performance is; fatigue life-span, vibration properties, coolant flow rate, wear resistance in keyhole and stability when a static load is applied. From the information and the comparison with material- and product properties the goal was set to; Compare the two different produced blades and see if AM is good enough to work further with in the aspects of material- and product properties and production costs. To achieve the goal for material- and product properties tests needs to be done in fatigue, wear, vibration and flow rate.

Accomplishing production cost goal, a mapping of the production and corralling information on lead time and tact time needs to be done. The information and results will be calculated and plotted in Excel 2016.

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11 2.4 Conclusion of problem portrayal

Blades produced today has high cost around the coolant channels. Production using AM can improve these aspects but Sandvik is uncertain on the material- and product properties and other costs. To investigate these problems Sandvik wants to get answers to two questions:

• How is the different material- and product properties affecting the product properties for AM compared to conventional made today?

• How much will AM differing in the production in the aspects of:

o Investment/changes o Production cost

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3 Theory

Information research was done through books, articles and web. Google scholar was the main usage to search for articles and the keywords were; Additive manufacturing material- and product properties, additive manufacturing SLM, additive

manufacturing (the different materials). The main reason for using articles to AM is the on growing developments in the area. State-of-art is used for AM when other theories are well acknowledged and are reliable from books.

3.1 Turning

General turning consist of two elements; the workpiece and the tool. The workpiece rotates and the tool moves in the feeds direction. The feed movement of the tool can be both along the axis (longitudinal turning) or on the radius axel (face turning).

Combined movement is called profile turning and will result in tapered or curved surfaces. These operations can be either internal or external and are often controlled by a CNC machine (Computer Numerical Control) [2]. See figure 4.

Figure 4. Turning operation.

There are many aspects which affect the desired result. One of them is the cutting data. The cutting data is presented in Figure 5 where; Dm is the diameter of the workpiece (mm), ap the depth of cut (mm), n is the spindle speed (rpm), vc is the cutting speed (m/min) and fn the cutting feed (mm/r). The spindle speed is the rotation of the spindle, and therefore the workpiece is defined in revolutions per minute.

Different speeds control the tools lifecycle, for example too slow will promote build up edge which deteriorates the lifecycle. The cutting feed is the movement along the axis in relation to the revolving of the workpiece. It is crucial to determine the surface quality [2][3]. The tool holding the insert is important to withstand vibration and forces operating on the insert. Otherwise it can break or influence the surface quality too.

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13 Figure 5. Turning operation with cutting data

3.2 Parting and grooving

Parting and grooving is an operation within turning. The feed of the tool (fnx) is radial against the center of the workpiece. Same principle is applied here as in turning but vc

decreases when the distance to the center decrease and ar is the depth of the groove, as seen in Figure 6. In the process either spindle speed or cutting speed is constant, the machine will compensate for decreasing diameter to minimize the pressure on the cutting edge. [3]

Figure 6. Parting and grooving operation.

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The most common tool consists of a blade and an insert. A coolant is used on the insert when the turning process generates thermal load to enhance the tool life. The coolant flows through cooling channels in the blade. The lifecycle of the blade

influences by different parameters during the turning process, for example: Vibration, fatigue, tangential and radial forces and bending moment.

3.3 Additive manufacturing

Additive manufacturing (AM) is a process which uses computer-aided- design (CAD) to create layer upon layer in 3D-printing. The application of materials is wide and gives big opportunities for the companies to applicate. The process advances in cost reduction, unrivalled design freedom and product process. In manufacturing, there are three categories; powder feed system, wire feed system and power bed system [4]. It means powder or wire is fed and melted by a heat source onto a framework and consolidate until cooled. In detail, it starts with a 3D CAD model which is virtually sliced into 2 micrometer-1 millimetres depending on the AM method. The model is built layer by layer on a structure by either powder or wire which is melted by a heat source (example laser). The most common methods in AM of metals are Electron Beam Melting (EBM), Laser Metal Deposition (LMD), Binder jetting (BJ) and Selective Laser Melting (SLM) where the latter has different names such as Laser Metal Fusion (LMF), Laser Beam Melting (LBM), Powder bed fusion (PBF) and industrial 3D. [5]

3.3.1 Selective Laser Melting (SLM) of metal

A layer of metal powder is distributed over a framework with a layer thickness DS. The feeder of metal powder is a recoater blade levelling the powder fed by a hopper or reservoir. Over the layer a laser beam with a power PL melts the powder with a scan speed vs up to 15 m/s. The pattern scanned by the laser is called scan strategy. A new layer is disposed and the cycle begins again. Not only the exposed material is melted, adjacent areas is affected too, which makes the layers fused. The unmelted powder can be sieved and utilized again in the process. The part may have support structures if needed and the material is fixed onto the framework, results in processing before it can be used once more. Due to the powder, designs with inclusion is not recommended since the powder can’t be removed [5]. The process is seen in Figure 7.

The advantages with SLM is compared to binder jetting; design freedom, high scanning speed, powder is easily removed. The disadvantages are; Often need supports structures, expensive gas, limited material usage and need finishing work.

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15 Figure 7. Description of an SLM operation.

3.3.2 Binder jetting (BJ)

Binder jetting is similar to material jetting and SLM with differences in the dispensed material. In BJ the dispensed material is a liquid bonding agent while in material jetting it is build material. The principles are the same with an inkjet head nozzle disposing the material on a powder bed. The liquid holds the powder together in the desired shape. The similarity with SLM is the mechanics of the powder bed. Instead of a laser it uses a nozzle. BJ needs heat treatment after the process which SLM doesn’t. The advantages with BJ compared to SLM is; models are built easier, no support structure, no limitation at materials and effective usage of the work volume.

The disadvantages are; difficulties with sintering and difficulties with production of prototypes [6][7].

3.3.3 Material- and product properties (powder)

The quality of the product and the efficiency in selective melting is determine by the flow and corresponding layer packing of the powder. There are several properties which influence the flowability; density, cohesive strength, electrostatic forces on the powder, surface tension and wall friction. Particle size or size distribution similarly affect the flowability with space filling or interlocking characteristics. In SLM the smaller the powder particles are, the better for sinter ability and melting. The

conditions are applied when the particles are not distributed in sizes. Explanation for this phenomenon is by the interstitial voids size between the particles, which

promotes pores in the product and lowers the fatigue strength. Sintering minimize the pores and are completed after the AM process [8]. The orientation of the grain

influences the aspect of material- and product properties too. Scanning velocity, scanning strategy and local part geometry is aspects influencing the orientation of the grain and microstructural texture. Because different aspects changes (embrittle) the results of the material- and product properties it is hard to compare with other materials. The advantages of printing the materials is the regulation over

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microstructure. The disadvantages are pores and sometimes deteriorated material- and product properties [9] [10]. This is seen in Tables 3 and Table 4. Information is taken from different articles with different test standards, resulting in uncertain data. Some materials are hardened and has higher values than a newly produced material. The data can only be compared to the same material, not each other [8] [11-18].

Table 3. Material properties when using AM (SLM).

Material Yield

strength

Modules of elasticity

Hardness (HV) Elongation at break

Ti-6Al-4V 967-1075

(MPa)

113-119 (GPa)

4.1-4.9 (GPa) 7-12 (%)

Inconel 718 889-907

(MPa)

201-204 (GPa)

5.4-5.8 (GPa) 19.2-25.9 (%)

Stainless steel 530-555 (MPa)

200 (GPa)

3.8-6.1 (GPa) 32.4-43.6 (%)

Table 4. Material- and product properties when using conventional manufacturing.

Material Yield

strength

Modules of elasticity

Hardness (HV) Elongation at break

Ti-6Al-4V 862

(MPa)

114 (GPa) 3.3 (GPa) 10 (%)

Inconel 718 724

(MPa)

206 (GPa) 3.3 (GPa) 3 (%)

Stainless steel 515-680 (MPa)

200 (GPa) 2.2 (GPa) 45 (%)

3.4 Mechanical properties

3.4.1 Fatigue

Significant amount of all failures occurs from fatigue, implicating that failure on the component happens below the normal ultimate strength when the material is exposed to repeated cycle load. Crack propagation occurs in stress concentrations, defects in micro structures and surface defects. Correct design may increase the life cycle of the material. Three load factors contribute to fatigue; high maximal tensile stress, high variation in stress, high amount of load cycles. Stresses may arise in different forms such as; axial stress, bow stress, shear stress and torsion stress. In real cases,

combined load factors and load cases may occur. Figure 8 shows a stress cycle; the cycles may differ and be more complex depending on the loading pattern.

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17 Figure 8. Fatigue cycle.

Fatigue stress varies between maximum stress (σmax) and minimum stress (σmin) and helps calculate mean stress (σmean) such as

𝜎_𝑚 = ^𝜎^𝑚𝑎𝑥^+𝜎^𝑚𝑖𝑛

2 . (1)

Amplitude stresses has immense influence on fatigue and fatigue test, increasing the amplitude lowers the fatigue life. Amplitude stress are defined such as

𝜎_𝑎 = ^𝜎^𝑚𝑎𝑥^−𝜎^𝑚𝑖𝑛

2 . (2)

Mean stress may differ between positive, negative and zero, depending on the amplitude. If amplitude stress is constant the mean stress has greater influence on fatigue life and fatigue test. Increasing positive mean stress decreases fatigue life [19].

Fatigue stress varies between maximum stress σmax and minimum stress σmin, where the mean stress is calculated as

𝜎_𝑚 = ^𝜎^𝑚𝑎𝑥^+𝜎^𝑚𝑖𝑛

2 . (1)

3.4.2 Vibration

Vibration of a system may be explained such as energy transferring between potential and kinetic forms. The damping properties in vibration is the energy lost for each cycle. To sustain steady vibration, it is necessary to use an external source. In vibration modes are a pattern of motion which occur when a force is applied.

Different direction on the applied force may cause different modes in a material, see Figure 9.

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Figure 9. Different modes with different boundary conditions.

From the information modes gives in how it behaves the properties of damping and the eigenfrequency is obtained. The frequency is calculated as

𝑓 = ¹

2𝜋∗ √^𝑘

𝑚 (3)

The frequency is f, k is the rigidity for a specified shape, m is the mass. Depending on the shape of the specimen different k may be used where the rigidity of a beam is calculated as for the

𝑘 = 𝐶 ∗ ^𝐸𝐼

𝐿³ (4)

and the rigidity for a bar is calculated as 𝑘 =^𝐴𝐸

𝐿 (5)

E is the E-module for the material and I is the area moment of inertia for a beam. The perfect damping properties is called critical damping; no material is at hundred percent of the critical damping. When calculating the damping properties, it is often calculated how much percent of the critical damping a material is [20].

3.4.3 Pipe flow

There are two different cases when speaking about flow of a fluid. Ideal fluid is simplified and presumed to have no viscosity, referring to an idealized situation which does not exist. It is helpful to use when solving engineering problems. The second one is real fluid which introduces the viscosity and gives a result of shear stress between fluid particles traveling in different velocities. This results in velocity adjacent to the wall will be zero and increasing closer to the middle. Different variation in fluids exists i.e., incompressible, compressible, steady or unsteady flow and laminar or turbulent. These are common how flows can be classified. Incompressible fluid defines as fluid with little pressure and temperature variation. Compressible fluid

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defines as fluid with variation in density, caused by variation in temperature and pressure. If the fluid is constant dependent on time the condition is called steady flow and this is found in laminar flow. Unsteady flow is a transient phenomenon which may be described as a periodic motion, for example waves on the beach. Laminar flow is the movement of the fluid, sliding of infinitesimal thickness over layers. The particles move in observable paths. Calculating to solve if the flow is laminar or turbulent the Reynolds figure must be under 2000 or over 2300. Turbulent flow is an irregular flow of the particles in the fluid.

The flow rate can be influenced by many parameters, often referred to as head losses.

Some of these parameters are; pipe roughness, area of the pipe, the curves of the pipes and friction [21].

3.5 Measurement tools

3.5.1 GOM

GOM is a company producing solutions to industrial 3D metrology. This technology predicates from structure light 3D. It refers to surface imaging which acquires true 3D data (measures in x; y; z coordinates on the surface of an object) from structure light.

Authors description of structure light is “active illumination of the scene with

specially designed 2D spatially varying intensity pattern” (Structured-light 3D surface imaging: a tutorial, 2011, 130). The illumination is generated by a light source and the intensity by the pixels on the pattern is represented by digital data. A sensor, for example a camera, sample a 2D image of the object under the light source. See Figure 10. If the object is nonplanar the projected light pattern is distorted for the camera.

This information is computed by different principles and algorithms. The information creates an image of the object in the computer which can be compared to a CAD model. This method is compared to the tolerances acquired for the product. If the object is produced in a correct way [22].

Figure 10. Describes the method of structured light

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20 3.5.2 Strain gage

A strain gage measures the electrical resistance applied in proportion to the strain in the gage. The size of the strain is often very small, eventuates in very small changes in resistances. Due to these small changes the strain gage uses a Wheatstone bridge for calibration. The Wheatstone bridge can be seen in Figure 11. If the bridge is balanced no voltage output will be detected, but if any changes in any arm is detected the voltage output will be nonzero. In the bridge the resistant R4 is replaced with a strain gage which results in any changes in the strain will produce a nonzero output voltage. The voltage symbolizes the strain and can be recalculated to force.

Figure 11. Wheatstone bridge

A gage is made of very fine wire or metallic foil composed in a grid pattern. The grid is on a backing called carrier which can be attached to the test object. Wires are solder on the carrier and metallic grid pattern. See Figure 12. There are three different types of gages, quarter, half and full bridges. Differences between the bridges is the strain sensitivity, what kind of strain is requested, compensation for Poisson’s effect and temperature independence. Temperature affects the resistivity and sensitivity of the gage which may lead to errors. Nominal resistors may be used to reduce heat generated by voltages and may help to reduce signal variation [23].

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21 Figure 12. A strain gage, picture taken from [24].

3.6 Value stream mapping (VSM) in manufacturing

This method is a tool to easier identify wastes in the production cycle of the product.

Wastes can be time consuming, costs, unnecessary work and such. To identify the wastes a collection of all actions is required of the specific product, from the raw material to the costumer. The actions may be all the information and material within the chain of the product. The value stream mapping helps to see everything that affects (value-added and even non-value-added) the product throughout the whole company’s chain. There are three steps in the method, first is to decide what product or product family is the target. The second step is to map the state that is currently being done on the product and the third step is to visualize the future state map, as seen in Figure 13, with other words make the supply chain more efficient and reduce waste. The future state map illustrates what improvements needs to be done and uses the current state map to identify the problems. To help find the problems and what improvements needs to be done questions may be asked and answered. Some

examples for these are; What is the tact time and where can continuous flow be used [25]?

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22 Figure 13. Visualization of a VSM [26].

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4 Method

This chapter includes test preparation and analyze methods for the execution of the master thesis. Five tests (flow rate, pressure force, vibration, fatigue and wear

keyhole) and a production analyze was made with help of staff at Sandvik Coromant.

4.1 Test preparation

Before any test could be initiated some precautions were executed. Certain parameters could influence the result from the tests, for example: Manufacturing flaws in

components, distortion values from measurement instruments and losses or

disturbance between the instrument and the test object. Six AM produced blades and six conventionally produced blades (QD-NN2G60C25A) were sent to the measure lab for GOM testing in the machines; Atos Triple Scan and Atos Capsule sensor. The reason was to see if the blades were in the tolerance range and if the blades had any manufacturing flaws on the geometrics. Each blade needed to be marked with a number and sorted out which test each blade would participate in. Fatigue test and wear keyhole test makes the blades unusable and therefore placed at the end. Table 5 and Table 6 shows the test order and which blade will be tester where.

Table 5. Tests executed on AM produced blades AM Blade GOM Flow rate

test

Pressure force test

Vibration test

Fatigue test

Wear keyhole test

1 X X X X X

2 X X X X X

3 X X X X X

4 X X X X

5 X X X X

6 X X

7 X

8 X

Table 6. Tests executed on conventionally produced blades Conventionally

Blade

GOM Flow rate test

Pressure force test

Vibration test

Fatigue test

Wear keyhole test

10 X X X X X

11 X X X X X

12 X X X X X

13 X X X X

14 X X X X

15 X X

16 X

17 X

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24 4.2 Material- and product analysis methods

To analyze the differences in material- and product properties and production aspects, five tests and information retrieval from Gimo needed to be done. The five tests were chosen from what the company could do in their facilities and what material- and product properties needed to be complemented. The production aspects were collected and analyzed from the existing calculation done at Gimo.

4.2.1 Flow rate test

Due to rougher surface in coolant channels of the AM produced blades a flow rate test needed to be executed. The test was set after customer demands with pressure as the varying parameter. The pressure used was; 10, 20, 40, 70 bar. The requested result is to see if the flow rate in AM produced blades will deviate from the conventionally produced blades. A special built flow testing device (CoroFish) was used to measure the flow and the pressure. A flow rate- and pressure measurement instrument were assembled to the testing rig. See Figure 14. The pressure and flow rate measurement instrument needed to be close to the testing subject, in this case the blade, to secure the measurement and to minimize the losses which may occur in the pipes. The machine was configurated and validated before usage. To validate the test dispersion blade 15 was tested on the different pressures, repeated four times. From the results a standard deviation could be calculated. Five AM produced blades and five

conventionally produced blades were tested in CoroFish with four different pressures.

Since the pressure is not above 70 bar an instrument with max 250 bar was chosen.

Hence to an error range of ±5% and no lower instrument existed. Same principles were set for the flow rate instrument which had max flow on 20 L/min. To get equivalent answers, the hole in the holder (BA-LGC2525-25) delivering the fluid to the blade was parallel with the hole delivering the fluid to the edge. The results were plotted in Microsoft Excel 2016 and standard deviation was calculated on each test and blade.

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25 Figure 14. Test rig in Corofish.

Because the AM blades had a leakage at 40 bar some blades were sent to

measurement lab to see what tolerances the wholes had. The placement of the holes on the blade is not important but the distance between the wholes. The screw is placed over the whole where the fluid goes into and the screw is placed in a drilled hole next to it. If they are placed too far away the screw cannot cover the whole. The test will therefore show the deviations of the holes and if a deviation of the placement is reason for leakage, see Figure 15. The blades sent to the lab were number: AM blades; 1, 2, 3, 4, 6, 7, 8 and conventionally produced blades; 11, 16, 17, 18.

Measurement instrument

Coolant flow Holder

Blade

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Figure 15. Measurement for the deviation of the holes.

4.2.2 Pressure force test

Different material- and product properties affect the forces working on the insert from the clamp. The AM produced blade may affect the forces with deviated material- and product properties. To verify the AM-blade’s capability a strain gage test was used.

The reason for using this kind of test was because Sandvik had the staff and

equipment for only this test. The strain gage selected for the test was a quarter-bridge.

The inserts area underneath is too small to fit any other gages. The strain gage was put on the surface underneath the insert. Due to small forces on the insert a grinding was required on the inserts bottom. This helped to get a little higher deformation on the insert which results in improved results from the strain gage. The strain gage was glued under the insert (with the orientation of the grid pattern parallel with the direction of the insert) and then connected to an adapter with a resistance of 120 Ω.

The adapter was connected to a computer and the program used to sample the data was called Catman. A calibration was needed on the strain gage. The blade (modified to not disturb the calibration) and insert was placed onto a holder under a rig called portable loadcell, which applied a force through a staff and a sphere with diameter 0,2 mm. The force was placed on the top of the insert. The placement of the sphere was decided from a simulation (which is not shown in this report) which showed that the highest force appears in the area close to the edge. A load was applied up to 800 N, high enough to be over the range which the forces will act in, low enough to not affect

the blade. This is shown in Figure 16a.

The calibration was validated in a plot and had a deviation of 50-100 N but the strain gage followed the curves of a variating and known load. All the blades were placed on a cool surface to minimize the temperature difference. The insert was placed in the blade three times before the blade was switched. Seen in Figure 16b. Five blades from each category was used. A calculation of standard deviation on the test and between the blades was required. The strain gage is very fragile and therefore no more test than three tests on each blade was completed. The forces were sampled in Microsoft Excel 2016 and plotted.

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Figure 16. The strain gauge is first calibrated a) followed by test execution b)

4.2.3 Vibration test

When the tool and insert is used in a CNC-machine vibration may occur. This influences the result on the product and on the lifecycle of the tool and insert.

Therefore, it is important to investigate the vibration properties on the blade. There are three aspects which is important in these tests, the damping properties (critical damping), the real value (frequency response function real value) and the

eigenfrequency where the modes occur. They are collected by mode parameters collected from resonance frequencies. There are also many parameters which can influence the results. They are: mass, moment on the screws to the holder, impart location of the force on the blade and the dispatch on the blade from the holder. To minimize the influence from the parameters the test was decided to be measured by a laser (name of the laser). This doesn’t add mass to the test and the lasers data is only integrated once when the accelerometer needs to be integrated twice. The force will be added by a hammer with a voltage sensor in it, translating the voltage to newton.

The data from the laser and the hammer was collected in the program CutPro version 12.0.69.1 and calculated in Matlab. CutPro samples the data, calculates the force per m (N/m) and the frequency. The data collected is a measurement called the frequency response function. The force will be applied in two different directions. One from the side and one from the bottom. Different modes occur when the force is applied in different directions, to calculate the real value, eigenfrequency and damping properties in both modes the different forces is required.

The blade was placed in the holder (BA-LGC2525-25) with a dispatch of 60 mm from the inserts nose. This is the maximum dispatch for the blade. The middle screw was tightened with 15Nm, then the front with the same moment force. The back screw was tightened with the force by hand, just tight enough to keep the screw in place. Then the middle screw was tightened again up to 23 Nm and the same for the front screw. This is because the blade will form a bow if not screwed properly and disturb the results. A reflection tape was put on the front corner of the blade where the laser would be reflected. The force was placed vertical on the blade, on the opposite surface from where the reflection tape was placed. It is important to put the force on

Strain gage is placed under the insert

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the exact same position each time, not too far away and not too close to the holder.

The conventionally made blades has engraved words: “CoroCut” which helped to navigate. After different test the best results came from placing the force from the hammer on the C from “Cut”. The AM blades had nothing engraved on them, to know where to put the force some measurements on the conventionally made blade was done and then marked on AM. The test was repeated five times on the same blade and five different blade was used from each category. To validate the result the test was remade on the standard blade because it had higher distribution than AM. The setup of the test can be seen in Figure 17.

Figure 17. Test set up and direction of the forces.

The test was repeated but the applied force was placed horizontal on the blade, at the bottom, and the reflection tape on the insert. It was important that the hammer hit the surface parallel and not set the blade into a bending motion. That will give the wrong data because the interesting mod is a purely vertical motion. The screw at the back was also removed due to disturbances in the data. Throughout the test data was validated through the program CutPro. The program showed if it was any

disturbances, if it were any variation between the tests and blades. A simulation in NX was also done to validate the test results. The collected data was calculated and

plotted in Matlab. (Write what was calculated and which equations was used).

4.2.4 Fatigue test

Some material- and product properties between the two different produced blades may differ, as seen in Table 1 and Table 2, and influence the results on fatigue. This is

Force from the bottom

Force from the side

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a crucial aspect for the blade because it will be exposed to fatigue load in the machine, both trough the load on the insert and the influences from the holder. The load from the machine will come from a radial force and a tangential force. Due to limitation in time the force will be applied in the resultant from the both forces with a 30º in angle from the tangential force. This is a theoretical angle from the both forces calculated from other tests. Because the test rig can only apply load in a vertical direction the blade need to be angled at 30º, see Figure 18. A special built holder for the blade was constructed and produced for the experiment.

Figure 18. Forces on the blade.

Generally, in a fatigue tests there need to be many tests (around 50) to decide the applied load to get the optimal fatigue strain, in this case the time and the limitation in the number of blades won’t allow that amount of test. The important aspect in these test is not to see where their optimal load is but to compare the both test to each other.

That puts weight in doing the test as equal as possible and get a crack in both blades.

Therefore a test needed to be done on a conventionally made blade with the applied load of 1.9 kN (calculated from the forces) to test if there will be a crack. If not, the load will be raised until the result is reached. The result force from those tests for the applied load was 2.5 kN. The load cycle will alternate between 2.5 kN and

approximately 100 N, with a frequency of 15 Hz. The mean stress will be positive and the amplitude will be the same for every test subject. This is because the machine can’t pull the blade to create negative stress and if the load will be zero measurement fault may occur from the machine. The setup for the test may be seen in Figure 19.

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30 Figure 19. Fatigue test with 30-degree angle.

Five conventionally produced blades and five AM produced blades was tested in the rig and then analyzed in SEM (sweep electrical microscope) to investigate the material surface, crack propagation and material defects. The insert used for the experiment was QD-NG-0440-0002-BG HF10 and was polished to give a horizontal plane for the load. The dispatch on the blade from the holder was 60 mm.

4.2.5 Keyhole wear test

The insert will be replaced many times in a blades lifecycle. Therefore it is important no deformation occur in the hole where the key is operating or plasticization in the clamp. The test needed to be as close as possible to reality with coolant fluid in the keyhole and not too fast rotation from the key. Through a measurement pen the data can be logged in testXpert II V3.71. The interesting result is to see the forces the key needs to turn and how much the clamp will open and close. From that result a

conclusion can be made to see if there are any deformations and if the keyhole has been worn. The blade was set up in a rig with a key plugged to the machine, see Figure 20. A measurement pen was set on a plane surface on the clamp (in this test on the coolant channel). The rotation on the key was set to 4 rpm and the coolant fluid used was HoCut 795B-EU. A coolant fluid is used because the costumer often uses it in the machines and it will help to minimize the thermal load from the key. The speed was decided from a resembled test and the time consumption. When the customer

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changes the insert it doesn’t create any significant heat in the material, because of this it is important to not rotate the key too fast in the test.

Figure 20. Keyhole wear test rig

Three AM produced blades and three conventionally produced blades was tested and the data sampled was compiled in Microsoft Excel 2016.

4.3 Production aspects

Material- and product properties between different produced blades was one objective but another objective in the master thesis is the production cost. To get the

comparison value stream mapping (VSM) on today’s production is required and an investigation on what will make AM possible in the production. The investigation needs to consider; investment, changes in production and staff. To produce a value

Coolant fluid

Rotating key

Measurement pen

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stream mapping there were several ways used to gather the information; visit the production and map the processes, discuss with production staff, collect lead times on the products and investigate exactly what is calculated in today’s costs. A visit to the production site in Gimo was required to get all the needed information for the VSM.

From the gathered information, the VSM was generated. To understand what is needed to produce AM blades a visit to AM centre was executed where the focus was on: what operations needs to be used, what investments is required, how many can be produced in a batch, where will the blades be produced and lead time.

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5 Results

This chapter is the result from the tests; GOM, flow rate, pressure force, vibration, fatigue and wear. The result from the production aspects are as well presented.

5.1 GOM

The result from GOM is summarized in this chapter, see Table 7. Example of GOM is shown in Figure 21a and Figure 21b, further details may be seen in Attachment A.

The data is fitted to the three supports and two sides in the CAD model. The colors indicate a scale of deviation from the CAD model.

Table 7. Summarization of the GOM tests.

Blade Smaller surfaces Keyhole Insert surfaces

1 Some surfaces deviated up to 0.03 mm and -0.07> in smaller areas.

The holes could deviate up to 0.07>.

The deviation in the contact area was small and within limitations.

The deviation in the contact area was little bigger than previous blades around 0.06 to -0.06.

The deviation in the contact area was little larger but within limitations.

The holes did not deviate much

The deviation in the contact area

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was small and within limitations.

Figure 21 The GOM result of blade 1 showing a) surface of the insert and b) on the clamp

5.2 Flow rate test

At 40 bar and over the AM blades started to leak, giving unusable data and therefore only a result up to 40 bar is assembled. If there are a leakage the flow rate will deviate too much and not be sufficient for data usage. In Table 8 is the results from the pretest of blade 15 and in Table 9 and Table 10 is the results from the actual tests, also shown as a graph in Figure 22.

Comparison of turning blades produced by a conventional- and additive manufacturing method