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CNC Milling Process Optimization

Table of Contents

List of Figures:

List of Tables:

1.0 Introduction

1.1 Aims and Objectives

2.0 Literature Review

2.1 CNC Milling Machine

2.1.1 Components and their Functions

2.1.2 Types of Milling Machines

2.2 The Milling Process

2.2.1 Milling Tools and Cutters

2.2.2 Process Cycle

2.2.3 Cutting Parameters

2.2.4 Types of operations

3.0 Methodology

3.1 Types of metal removal strategies

3.1 Setup of part

3.2 Selection of work centre:

3.3 Selection of operation:

3.3.1 Face Milling

3.3.2 Rough Milling

3.3.3 Re-Rough Milling

3.3.4 Finishing

4.0 Result and Discussion

4.1 Surface Roughness Optimization:

4.1 Roughness Grade:

4.2 Surface Roughness Deviation:

4.3 Factors of Surface finish:

4.4 How to measure:

4.4 Comparison of surface roughness in different strategies:

Conclusion

References

List of Figures:

3.1 CREO manufacturing screen…………………………………………………………….24

3.2 Selection of work centre……………………………………………………………. ……25

3.3 Face Milling Parameter……………………………………………………………………26

3.4 Simulation of Face Milling………………………………………………………………..27

3.5 Rough Mill Parameter………………………………………………………………………28

3.6(a) Simulation of Rough Mill…………………………………………………………………..29

3.6(b) Simulation of Rough Mill…………………………………………………………………..29

3.7 Re-Rough Parameter………………………………………………………………………30

3.8(a) Simulation of Re-Rough……………………………………………………………………31

3.8(b) Simulation of Re-Rough……………………………………………………………………31

3.9(a) Finishing Parameter………………………………………………………………………..32

3.9(b) Finishing Parameter…………………………………………………………………………32

3.10(a) Simulation of Finishing…………………………………………………………………..33

3.10(b) Simulation of Finishing……………………………………………………………………34

4.1 Surface Deviation………………………………………………………………………………..37

4.2 Factors of Surface Finish……………………………………………………………………..37

4.3 Variation of Surface…………………………………………………………………………….39

4.4 Face Milling……………………………………………………………………………………….42

4.5 Rough Milling……………………………………………………………………………………..43

4.6 Re-Rough Milling………………………………………………………………………………..44

4.7 Finishing……………………………………………………………………………………………45

List of Tables:

2.1 List of Tools……………………………………………………………………………………….12

4.1 Roughness Grade………………………………………………………………………………36

4.2 Details of Technique…………………………………………………………………………..41

 

1.0 Introduction

Expanding interest of nature of the machined parts are the principle challenges in the worldwide rivalry producing market. Nature of a procedure is estimated as far as qualities. Surface complete is an imperative quality that is a trademark that could impact the execution of machining part and generation cost. Profitability and Quality are vital however clashing norms in machining activities. To guarantee high profitability, degree of quality is to be traded off. Enhancing quality prompts expanding machining time in this way, decreasing efficiency. Machining conditions are determined to CNC machine according to standard handbook, which are a long way from reality. Numerous endeavours have been done to improve machining parameters for machine tasks, however processing activity on composite materials, has increased little consideration. Because of the noteworthy part that milling operations play in the present assembling world, there is a crucial need to upgrade processing machining for this activity, especially when NC machines are utilized. Because of these reasons advancement of machining process parameters is the key part in assembling condition.

Milling is a multi-reason and valuable machining task. End milling process is a standout amongst the most basic and regularly experienced material removal operations in manufacturing industries including the automotive and aviation sector where quality is an imperative factor in the generation of slots, pockets and mould/dies. For the proficient utilization of the machine instrument it is imperative to locate the ideal cutting parameters before a part is put into production. The factors for ideal cutting parameters are tool width and tool length, Number of passes, Depth of cut (radial and axial), Spindle speed or cutting velocity and Feed (per tooth, per revolution or per unit time).

1.1 Aims and Objectives

My aim for this project is to find the optimal manufacturing strategy for material removal using CNC milling for a range of surfaces.  The result would vary with the different parameters such as spindle speed, diameter, length, number of passes, and depth of the cut.  These will affect the surface quality, production time and cost.

To achieve the aim set above the following objectives have been set:

  • Extensive literature review on the CNC milling process and gain a greater understanding of the process
  • Research current manufacturing strategies for material removal using CNC milling
  • Investigate which parameters would have the greatest effect on the surface quality, production time and cost
  • Develop a test piece using CREO to evaluate the approach
  • Evaluate and conclude the results found

2.0 Literature Review

This chapter will provide a fundamental basic knowledge of the CNC milling machine.  This knowledge is important for the understanding of the analysis and evaluating the results in the subsequent chapters of this report.

2.1 CNC Milling Machine

When you’re searching for CNC milling machine parts there are multiple places where you can find them. There are several online websites and the milling machines can come in a range of prices.

Varying on the type of machine you require; the price can be high but there are smaller options that can do the same operations if you need this as part of a small business or a part-time hobby.

You will have the option to purchase a brand-new machine or a used machine. The majority of people do not suggest purchasing a used machine because you aren’t certain what you are getting, however purchasing other types of machines such as CNC routers appear to be a good idea due to the price.

2.1.1 Components and their Functions

All CNC Milling machines contain the following parts:

  • Axis – Dependent on the CNC milling machine it can have anywhere from one to five axes, this also determines the size and what it’s capable of.
  • Column – The column travels along the axis to hold the part that is being cut
  • Control panel – This is the console the holds the computers keyboard, this is where you input the G-codes in the machine.
  • Cutting tool – This is connected to the column and is what cuts the part how the operator programs it.
  • Spindle – This holds the cutting tool in place.
  • Coolant supply tubes – These tubes supply coolant to the cutting tool via a pump to lower temperature and keep tool lubricated
  • Table – The work piece will be attached to this by a clamp or vacuum.  It will sit here while being milled

There is many different types of milling machines that can be found and they are large or small depending on what they can do. Here are a few:

Vertical CNC mills have a vertical spindle axis. This implies the cutters that do the milling are held vertically in the spindle and they turn on the spindle’s axis. In this write, you can broaden the spindle or the table to make drilling or plunge cuts. Bed mills and Turret mills fall into this classification.

Flat CNC mills have an indistinguishable kind of table from vertical CNC mills yet their cutters are mounted on an arbor that sits over the table on a level plane.

Specialists will utilize a box mill which is mounted to a bench and essentially climbs up and down. Knee mills have an x-y table and its climbs up and down the column. It can be balanced with what is known as a vertically adjustable knee. Numerous bigger businesses utilize the C-Frame mill since it is the most helpful for bigger work. They are just vertically moveable and it utilized a settled spindle head for that movement.

2.1.2 Types of Milling Machines

Depending on the type of product being created and type of material being used, there are different CNC milling machines that are preferable for different applications. The amount of axes being used, the amount of control needed for the machine and the size of the product being made will all have an impact on the type of machine being used.

Vertical Mill

The orientation of the mill being utilized greatly affects the item being made. A vertical mill basically implies that the spindle axis on the mill is vertically oriented. Milling cutters are situated on the spindle of the vertical mill, enabling the machine to effortlessly cut into the material as required. The shape, angle, and size of the cutting tool are for the most part reliant on the sort of item being made, with the diverse qualities adding up to various surfaces and coatings.

Turret Mill

Whether the spindle is mobile is dependent upon the type of vertical mill being used. With a turret mill, the spindle is stationary while the table below it moves both perpendicular and parallel to the spindle axis. A quill is usually found in turret mills, which allows the milling cutter to move up and down as needed. The turret mill allows items to be vertically cut either by the milling cutter moving vertically or the table moving vertically. The turret mill is the most versatile vertical mill; however, they are most effective when the machines remain relatively small, so that the tables and the spindle have easier mobility.

Bed Mill

A bed mill is like a turret mill; however, the table of the machine only moves perpendicular to the spindle, opposed to perpendicular and parallel. The spindle is the only part of the machine that moves parallel to the axis, creating a more confined production. Bed mills are also considered to be more rigid than a turret mill.

Horizontal Milling

Horizontal mills function almost the same way as vertical mills, except that the cutters are mounted on a horizontal arbor. Instead of drilling into an object, an arbor shaves unwanted material from a project off, which is why it’s horizontal instead of vertical. Horizontal mills also include a universal table, which allows the product to be cut at various angles and adds to the versatility of the machine.

Generally, horizontal mills are used to cut grooves and slots into a product. However, specialty cutters can also be used to cut bevels and radii, but these specialty cutters tend to be more expensive. Horizontal mills are most commonly used to cut gears.

2.2 The Milling Process

CNC, or Computer Numerical Control, places tools under the immediate direction of an automated working system.

Successful, good quality milling is a mix of three components:

1. A cutter with numerous teeth and perfect sharpness for a material.

2. Rotating a tool at sufficiently high speed to process a material accurately.

3. A fitting feed rate for propelling the picked material through the procedure.

CNC takes into account to a great degree of control of these components. The electronic systems read plan data straightforwardly from a designer’s illustrations or models, taking out conceivable outcomes for error amongst design and production.

The CNC milling process takes bearings in modified programming codes, for example, NC code, G-code, and ISO code, all changed over straight from a projects’ CAM or CAD designs. The codes are then converted into the machine’s controls, which keep running along two axes (X and Y), notwithstanding the tool spindle running in the depth, or Z, axis.

2.2.1 Milling Tools and Cutters

Milling produces 3 dimensional shapes with a rotating multi edge cutting tool. The cutting tool can be programmed to move against a fixed work piece in almost any direction. Milling tools remove material by their movement in the machine and from their shape.

 

 

 

 

 

 Types of Tools:

Sl. No. Description Images
01   

Face Milling Cutter

Face mills are tools with a large diameter that are used to cut a wide shallow path for facing operations. Facing is used for machining a large flat area, typically the top of the part in preparation for other milling operations.

A face mill is a solid body that holds multiple carbide inserts that can be replaced as they wear out. The more inserts, the faster the metal removal rate.

 

Image result for CNC face mill cutter
02   

Index able End Mill cutter

Index able end mills also use replaceable carbide inserts. Index able end mills are convenient for efficient roughing and to save costs on the larger sizes of solid end mills. Index able end mills are typically used to rough the part, which is then finished with a solid end mill.

Image result for CNC end mill inserted type cutter
03   

Solid Carbide End mill

End mills are the most well-known milling cutters. End mills are accessible in a wide assortment of lengths, diameters, and types.  A square end mill is utilized for most broad milling purposes. It creates a sharp edge at the base of slots and pockets.

Image result for CNC end mill inserted type cutter
04   

Solid Carbide Ball mill

Ball end mills produce a radius at the bottom of pockets and slots. Ball end mills are used for contour milling, shallow slotting, contour milling and pocketing applications

 

Image result for CNC end mill inserted type cutter
Selection of Tools, Feeds, and Speeds 

 

Cutting tool selection has a direct impact on the proper programming of feeds and speeds at the machine.

However, many other variables that affect feeds and speeds are:

 Work piece material class and condition

 Work piece diameter

 Cutter material

 Cutter geometry

 Type of cut

 Depth of cut

 Condition of the machine

Cutting tool manufacturers publish the general feeds and speeds and recommended usage for the application. Cutting tool manufacturers are often a good place to start for recommendations on tool selection and feeds/speeds since they rely on customer loyalty. The customer (or potential) should select a cutter and cutter material based on the vendor’s recommendation.

Table – 2.1

2.2.2 Process Cycle

The total time to produce a part of a given quantity includes the initial setup time and cycle time for each part.  This total is divided into 4 segments; these are:

  1. Load/Unload time – The time required to load the work piece into the milling machine and secure it, as well as the time to unload the finished work piece.  This load time can vary depending on size, weight and complexity of the work piece
  2. Cut time – The time for the cutter to cut the work piece according to what it’s programmed.  This can be calculated by dividing the total cut length by the feed rate of that operation, which is the speed of the cutter relative to the work piece
  3. Idle time – This is the time when the cutter is non-productive; it is not engaging any work piece therefore not removing any material.  This idle time also consists of the time of the tool approaching and retracting from the work piece, adjusting machine settings and changing tools
  4. Tool replacement time – The time for a tool to be replaced that has exceeded its lifetime and therefore become too worn to cut effectively and efficiently.  This time is usually not performed every time, only when the tool has reached its lifetime.

2.2.3 Cutting Parameters

The speed and motion of the cutting tools is determined through several parameters, these parameters are selected for every operation based upon the tool material, work piece material and tool size.  These parameters consist of:

  • Cutting speed – Velocity of the work piece surface relative to the edge of the cutting tool during a cut, it is measured in Surface feet per minute (SFM)
  • Cutting feed – This is the length the cutting tool or work piece goes amid one revolution of the spindle and tool, it is read in Inches per revolution (IPR). For a multi-point tool, the cutting feed is ascertained by the feed per tooth, measured in Inches per tooth (IPT), multiplied by the number teeth on the cutting tool
  • Spindle speed – Rotational speed of the spindle and cutting tool in Revolution per minute (RPM). The spindle speed is equivalent to cutting velocity partitioned by the circumference of the tool
  • Feed rate – The speed of the cutting tool’s motion in respect to the work piece as the tool makes a cut. The feed rate is read in Inches per minute (IPM) and is the result of the cutting feed (IPR) and the spindle speed (RPM)
  • Axial depth of cut – This is the depth of the tool along its axis over the work piece, a bigger depth will add a high load to the tool and lessen its tool life, consequently the feed rate must be low. Be that as it may, this component on a work piece is generally cut with several passes until the point when its achieved the required axial depth
  • Radial depth of cut – This is the depth of the tool along its span over the work piece, if the radial profundity of cut is not as much as the tools radius, it isn’t completely engaged and is delivering a peripheral cut. In the event that the radial profundity is equivalent to the tool diameter, at that point it is completely engaged and is influencing an opening to cut. Much the same as ‘Axial depth of cut’, a bigger radial profundity of cut will put a high load on the tool and lower its tool life, subsequently requiring a low feed rate. This element is additionally machined with multiple passes till the desired profundity is achieved

2.2.4 Types of operations

There are different varieties of milling operations that are used to produce the final part from the initial work piece.  The following operations are each defined by the type of cutter and the path the cutter uses to remove material.

  • End milling – An end mill makes fringe or slot cuts, over the work piece to machine a predetermined feature, for example, a slot, pocket, profile or even a perplexing surface form. The profundity of the component will be accomplished with a solitary go with a low feed rate or various goes at a smaller profundity of cut at a higher feed rate
  • Face milling – A face mill takes a shot at the flat surface of the work piece to give a smooth finish. The profundity is ordinarily little so it might be machined in one pass or various goes at a smaller axial depth of cut (In many cases this isn’t essential)
  • Chamfer milling – A chamfer mill is an end mill working along the edge of the work piece or an element to make an angle, regularly at a 45-degree angle. This chamfer can be machined on either the outside or inside of a section and can take after a straight or curved path
  • Drilling – A drill enters the work piece axially, therefore cutting an opening equivalent to the width of the tool. A drilling task delivers a visually impaired hole, which can reach out to some profundity in the work piece or a through hole
  • Boring – A boring tool would enter the work piece axially and cut along the inward surface to shape wanted features. This is a solitary point cutting tool which can be set to cut the wanted diameter by utilizing a movable boring head. This operation is regularly performed subsequent to drilling a hole, to along these lines develop the holes’ diameter or acquire a more exact measurement
  • Counter Boring – A counter bore tool enters the work piece axially and augments the top piece of a current opening to the width of the tool. Counter boring is normally performed subsequent to drilling to permit space for the head of a fastener, for example, a bolt, to sit underneath the surface of the part. The tool has a pilot to manage it into the current opening
  • Counter Sinking – A countersink tool enters the work piece axially and expands the top part of a current gap to frame a cone moulded opening. It is regularly performed in the wake of drilling to permit space for a latch, for example, a screw, to sit easily with the work piece surface. Regular points utilized for a countersink are 60, 82, 90, 100, 118, and 120 degrees
  • Reaming – A reamer enters the work piece axially and broadens the current gap to the width of the tool. Reaming just removes a small measure of material and is utilized to get a more exact measurement and a smoother inner finish
  • Tapping – The tap enters the work piece axially and cuts inside threads into the current opening. The current opening is normally penetrated by the relating tap drill size so it will accommodate the coveted tap when it is prepared for tapping. Threads might be cut to a predetermined depth inside the opening (base tap) or the total profundity of a through hole (through tap)

3.0 Methodology

3.1 Types of metal removal strategies

There are different varieties of metal removal strategies/tool path that are used to produce the final part from the initial work piece in CREO.  The following strategies are explained.

Face Milling —  Face milling is used with a flat or radius end mill. It allows you to put the work piece face down. Process involves selecting a planar surface or one that is coplanar. You can also use a mill window parallel to withdraw plane. The inner lines or ridges in the chosen faces are excluded automatically. The system then selects the most desirable tool path.

Volume Rough —  Volume roughing numerical machining sequence involves removal of matter from the work piece one slice at a time.

The slices are usually in a parallel orientation to the retract plane, axial depth of cut in the work piece is usually defined by step depth and wall scallop dimensions. A slice depth is determined where the first slice is made below the mill volume. The starting dimension must be at the topmost part of the work piece to avoid air milling.

The surfaces that are planar to the volume normal to the normal z axis of the numerical machining sequence coordinate system produce additional slices along the volume of the work piece.

Roughing – These numerical machine sequence types are made particularly for high-speed machining, and particularly to machine imported, non-solid geometry.  Roughing and Re-roughing NC sequences can directly machine models containing facet data in STL format.

Roughing NC sequences generate the tool path that:

  • Removes all material inside a Mill Window limit, with extra depth control in light of the depth of the Mill Window. The thickness of the stock to remain on the reference geometry after machining is specified by the ROUGH_STOCK_ALLOW parameter value.
  • Provides optional scallop height control.
  • Performs automatic debugging against all the surfaces of the reference part.
  • Performs zoning by cavity rather than by slice, which means that in case of multiple cavities the tool will completely machine one cavity before moving to the next.
  • Supports a variety of high-speed roughing scans, with a minimum corner radius control.
  • Permits selection of an alternate high-speed scan for open and shut regions, surveyed on a cut by cut basis.
  • Automatically computes and adjusts the helical diameter when you do not specify any value for the HELCIAL_DIAMETER parameter.
  • Gives diverse entry techniques to open and closed regions. The tool enters open regions from the side. For closed regions, you can determine either helical or slope top entry technique.
  • Does not generate an Automatic material removal feature.

Plunge Milling – Just like the word plunge suggests, it lets roughly machine the work piece by overlapping deep plunges or cuts into the material. The cutting tool makes its first cut along an already drilled axis that is parallel to the z-axis of the numerical machine. The tool then withdraws and retracts to a clear/ safe. The process is repeated for more successive plunges or cuts. Distance between the successive plunges is controlled by the PLUNGE_STEP parameter.

Re-rough – Re-roughing process is used to machine the areas where a previous milling process could not reach due to deep cuts or complex shapes to be milled. Machining depth and shape is usually limited by the size of the tool. Therefore, this process uses a small tool to manoeuvre through the work piece.

Local Milling – Four different types of local milling are available. These are:

  • Prev. NC Seq. – This process removes materials left behind by other milling processes. Usually in areas that are too deep to reach.
  • Corner Edges – This is the edge milling or chamfering.
  • By Prev. Tool – This uses a smaller tool. It calculates materials left by other process and treats it as the new work piece for machining
  • Pencil Tracing – Cleans up edges of surfaces. It makes a single or multiple pass along the corners.

Local milling is constantly performed utilizing a scanning algorithm, subsequently, the ROUGH_OPTION and SCAN_TYPE parameters are inapplicable for this NC sequence type.

Surface Milling – This is milling along level or inclined surfaces. The chosen surfaces must take into account a ceaseless tool path. There are a few techniques for characterizing the cut and producing the tool path:

  • From Surface Isolines – Mill the selected surfaces by following the surface u-v lines.
  • Projected Cuts – With this, the chosen surfaces are anticipated on the withdrawing plane making a “level” tool path in this plane (utilizing the suitable scan type), and afterward anticipating this tool path back on the first surface. This strategy is accessible for 3 Axis Surface milling as it were.

Conventional Milling – During conventional milling, a tool path is generated where:

  • The cutting tool machines the whole of the work piece surface. If the dimensions are not set, the tool straddles by half its diameter boundary by a half diameter.
  • The inner overhangs and outside walls up from the surface, are not machined, automatically. The sides are also not machined
  • If holes are present on the model. The work is set and programmed as though there are no holes.

Profile Milling — Profile milling is the process used to mill slanted faces. The surface must be flat enough to allow continuous pass of the tool. The tool depth is specified using step-depth parameter.

 

Finishing — Use Finishing NC sequences to machine the detail of the reference part after Roughing and Re roughing. Finishing NC sequences can also directly machine models containing facet data in STL format.

The Finishing functionality provides you with an automated procedure for creating optimized tool paths while maintaining certain manufacturing constraints. It allows you to automatically create combinations of vertical and horizontal slicing tool paths to meet your manufacturing objectives within the specified constraints. Vertical slice machining produces straight, curved or circular cuts projected onto the geometry being machined. Horizontal slicing tool paths are in the form of Z profile cuts. You can also specify that only one of these techniques should be used.

An important parameter that controls the tool path for a Finishing NC sequence is SLOPE_ANGLE, which is a threshold angle value dividing all the surfaces being machined into two areas, steep (near vertical) and shallow (near horizontal). You can then use other manufacturing parameters, specific to Finishing NC sequences, to select whether you want to machine just the steep or the shallow area or both, whether to include the flat (horizontal) surfaces into the shallow area, which slicing algorithm to use on either area, and how to perform the connections and entry moves.

Sometimes, when machining the profile portion of the model, the tool may scrape the flat bottom surface or enter an uncut material. To avoid this, you can specify a non-zero LEAD_RADIUS value to create approach and exit moves in a helical fashion on the bottommost slice.

Rest Finishing — Rest Machining processes are used to find or modify the areas of the job where material remains after executing previous tool paths. Use rest finishing passes to machine rest material from corners of the job, not machined by a previous reference tool. The fillets produced by running the reference tool around these corners are re-machined using a smaller, target tool working on the rest area boundaries. Both tools must be of type BALL MILL. The reference tool must be larger than the tool that is used to cut the rest areas.

In shallow areas, the fillets are machined with passes along the fillet. In steep areas, the passes go across the fillet. You can control the step over in shallow areas and step down in steep areas independently. There may not be a constant step over in shallow areas because fillets have the same radius but can have variable widths. The passes, therefore, come closer together as the fillet narrows and get further apart where the fillet widens.

Corner Finishing — Use corner finishing NC sequences to automatically machine corners and valleys that cannot be reached by a previous tool. Corner finishing NC sequences calculate the area left by the previous tool in corners and valleys, perform a slope-based machining operation on this remaining area, and compute the tool path for machining.

You must define the area to be machined using a Mill Window. Within this Mill Window, Creo NC calculates the remaining area in corners and valleys using the following elements:

• Previous tool, which is a ball end mill.

• Excluded Surfaces

• Maximum and minimum cutting depth

• Minimum area to be machined

• maximum corner angle

You can use ball end, radius end (Bull Nose type), and flat end milling tools for corner machining. Creo NC provides automatic gouge checking and avoidance for the tool and the tool holder.

Pocketing — Pocketing can be utilized to finish mill after a rough milling task. The surfaces chosen must take into consideration a consistent tool path. The pocket may incorporate horizontal, vertical, or inclined surfaces. The walls of the pocket will be milled as with Profiling, the base—as the base surfaces in Volume milling.

Swarf Milling —  Swarf milling is a special type of milling in that it allows the user to use the side of the tool to machine a series of surface. The tool path is in form of slices with each slice corresponding to the 5-axis geometry being manufactured. Other shapes can also be machines. The tool is positioned to make an angle of 90 degrees to the surface being milled. Although the default axis positions can be changes

You can also choose between two algorithms for the axis interpolation between the surfaces to be milled by using the AXIS_DEF_CONTROL parameter.

Trajectory — Trajectory milling enables you to sweep a tool along any user characterized direction. It can be utilized for milling horizontal openings: the size of the tool must relate to that of the slot. It can also be utilized for chamfer milling. You can utilize standard milling and drilling tools for a wide range of Trajectory milling, and in addition outline tweaked tools for 2-and 3-axis NC sequences. For the user to define the tool path, a sketch that represents the final trajectory is made. The tool makes one trajectory over the work piece with or without an offset. This pass may be loaded meaning it makes a cut on the work piece or it may be a dummy rum

Engraving — Engraving involves printing imprints on the work piece that involves milling specified shapes and patterns usually logos and letters. The tool follows a curve or a cosmetic pattern. The tool diameter determines the width of the cut.

The depth of cut may be set as desired. A computer numerically controlled milling machine may be programmed to mill different shapes on the same work piece. You can perform Engraving in multiple step increments if you set the parameter STEP_DEPTH to a value that is smaller than the value of GROOVE_DEPTH. You can also select multiple Groove features or curves to be machined within a single Engraving NC sequence.

Engraving can be specified as 3-, 4-, or 5-Axis.

For the 3-Axis Engraving, there are two methods to specify the path followed by the tool:

  • By selecting a reference point or a datum. The tool axis is normal to the surface that the reference Groove feature is projected onto.
  • By selecting different paths or patterns to follow. The set tool axis drives the tool along the curve.

For the 5 Axis Engraving, 3 methods are available to specify tool path:

  • By choosing a reference Groove feature to take after. The tool axis is normal to the surface that the reference Groove feature is put onto.
  • By choosing an arrangement of edges for the tool to follow. For this situation, you should choose a control surface, that is, a surface that the tool axis will be perpendicular to. The control surface must be a surface adjacent to one of the edges chosen for the tool direction. For every other edge, the surface to a same side of the edge is utilized as the control surface.
  • By choosing at least one curve to take after. For this situation, you should choose a typical surface, that is, a part surface that the tool axis is perpendicular to. You can choose the curve independently in the design window, from the Model Tree.

Thread Milling – This is utilized in making cuts on cylindrical and spherical surfaces that would otherwise be difficult to do in an ordinary cnc machine.

When creating a Thread milling NC sequence, you will be required to:

  • a tool type thread mill is used instead of the normal cutting tool
  • specify the thread feed, feed units and the thread diameter in the parameters
  • Select either internal or external thread

You will also be required to define thread sets.

A thread set defines the references that will be threaded; holes for internal threads, bosses for external threads, and axes for either. You can include more than one thread set, which allows threading features with different depth specifications.

There are various methods for selecting references to include in a thread set:

  • Selecting individual axes
  • Including all cylinders on a specified surface
  • Including holes or bosses of a specified diameter
  • Including all features in a pattern
  • Excluding specific axes that are added as a member of a pattern or rule definition

Drilling — Drilling, reaming, boring, tapping.

Auto Drilling – You can characterize groups of hole axes at setup time for later use in Hole making NC sequences. Drill Groups allow you to:

  • Simplify the hole selection. Once a Drill Group is characterized, it can be chosen for any Hole influencing NC sequence by simply choosing its name from a name list menu.
  • Alter Hole making NC sequences by including or barring holes. Changing a Drill Group will consequently update all NC sequences that reference this gathering.

High Speed Milling — Just like the word suggests, High Speed Milling includes high speed machining HSM from Module Works provides four sequences—HSM Rough, HSM Rest Rough, HSM Finish, and HSM Rest Finishing. The following are some of the benefits of HSM Milling:

  • Reduction of cutting forces
  • Good surface finish
  • Accurate parts
  • Fast material removal

You get better results while simulating material removal if you created HSM Milling sequences.

Expert Machinist – A good Expert Machinist process may contain the following basic steps:

  1. Set up the NC Model. Acquire the reference model and make stock.
  2. Set up the database. The database contains things like machine instruments, cutting tools, machining formats and so on. This progression isn’t required however. In the event that you would prefer not to set up all your database at first, you can specifically begin with the machining process and characterize the database items when you require them
  3. Define an operation. An operation setup may contain the following elements:

◦ Operation name

◦ Machine tool

◦ Program Zero (coordinate system for CL output)

◦ Stock material specification

◦ FROM and HOME points

◦ Names used in Cutter Location (CL) data output and PPRINT

◦ Operation comments

Installation setup

You ought to characterize a machine instrument and a Program Zero coordinate system before you can begin making machining features. Other setup components are not required.

  1. Characterize the machining features for the predefined operation. Machining features build up what material should be expelled from the stock to accomplish the reference model geometry. Each closed volume of material to be removed includes a different machining feature. Define the machining features in the order you need them machined. As you define machining features, the system allocates the proper material to be removed, and figures the ensuing feature geometry in light of existing machining highlights.
  1. Create tool paths for each machining feature. Once the features are characterized, you can machine them, that is, make the tool paths, at any time and in any order. You can likewise machine the features by applying predefined machining layouts. These layouts speak to certain oftentimes utilized machining methodologies; every methodology contains an entire arrangement of the machining choices and qualities that you would ordinarily characterize while machining a feature.
  1. After you have defined all the machining features and made the tool paths, output the total operation to a CL document and post process it, or output the tool path information specifically in the MCD format.  The majority of the machining setup components are modular: that is, all resulting machining features will utilize this setting until the point when you unequivocally transform it. Among those are:
  • Operation setup (including the machine tool and Program Zero coordinate system)
  • Tool (provided the tool type is compatible with the machining feature type)
  • Program Zero coordinate system inside the machining feature (for the initial machining feature, the Program Zero coordinate system indicated at the time of setting up the task will be utilized, unless you explicitly specify another)

3.1 Setup of part

  • Open the existing model in manufacturing and set the origin to default.
  • Create automatic work piece or stock for machining.

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT1.png

Fig. 3.1

  • Create a new co-ordinate system at corner and top of the block.

3.2 Selection of work centre

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT4.png

Fig. 3.2

  • Select the work centre – mill

3.3 Selection of operation

3.3.1 Face Milling

Facing down the work piece.

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT9.png

Fig. 3.3

Parameter of Face Milling:

  • Face milling to face the work piece by Ø 50 Face mill cutter.

Step over of 50 % use. DOC – 1 mm.

RPM = 1000; Feed 400 mm/min.

Simulation of face milling operation

 

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT10.png

Fig. 3.4

3.3.2 Rough Milling

High-speed milling sequences used to remove all material inside a Mill Window boundary.

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT18.png

Fig. 3.5

  1. Parameter of Rough Milling

Rough milling by Ø 16 mm Inserted End mill cutter.

Step over of 50 % use. DOC – 0.35 mm.

RPM = 2200; Feed 1200 mm/min.

Simulation of Rough milling operation

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT11.png

Fig. 3.6 (a)

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT12.png

Fig. 3.6 (b)

3.3.3 Re-Rough Milling

. Used to machine only the areas where a previous Roughing or Re-roughing sequence could not reach.

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT19.png

Fig. 3.7

  1. Parameter of Re-Rough Milling

Re-Rough milling by Ø 8 mm Solid carbide End mill cutter.

Step over of 50 % use. DOC – 0.2 mm.

RPM = 3500; Feed 1000 mm/min.

Simulation of Re-Rough milling operation

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT13.png

Fig. 3.8 (a)

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT14.png

Fig. 3.8 (b)

3.3.4 Finishing

Used to machine the detail of the reference part after Roughing and Re-roughing.

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT21.png

Fig. 3.9 (a)

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT22.png

Fig. 3.9 (b)

  1. Parameter of Re-Rough Milling

Finishing by Ø 8 mm Solid carbide Ball mill cutter.

RPM = 4000; Feed 800 mm/min.

Step over = 0.25 mm

Step down = 0.25 mm

Scallop height = 0.012 mm

Overlap angle = 10°

Slope Angle = 30°

Simulation of Re-Rough milling operation

 

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT16.png

Fig. 3.10 (a)

 

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT17.png

Fig. 3.10 (b)

CHAPTER-4:

4.0 Result and Discussion

4.1 Surface Roughness Optimization

Due to increase in engineering demand for closer limits and tighter fits, great surface finish is necessary. Control of surface texture is therefore very important. Furthermore, a great surface finish gives a shiny/glossy appearance to the final product. This discussion locates the various methods to improve and optimize the surface finish. The machining methods need a lot of effort and time. The accuracy attained by such processes is not always according to the desired levels. Computer numerically controlled milling machines achieve a higher accuracy and a better surface finish since measurements can be made to the nearest 10th of a millimeter. From a variety of machining processes, the milling process has the benefit of multi-point cutting tool with high dimensional accuracy. So, it’s key to learn the various parameters that will affect the final surface quality to get the wanted accuracy. Further, it is vital to learn which parameter affects the surface quality significantly and the several optimization methods. This can be achieved after a thorough literature review. An important factor is surface finish for evaluating the products. People are always on the lookout for methods to help improve quality. Surface Roughness Optimization is a technique that has become popular in recent times. Surface finish is a known concept, it is better understood qualitatively. This is clear from the way that numerous enterprises keep on specifying finish as rough, great, smooth, polished, reflect and so forth. None of these terms are adequately exact furthermore, they have a tendency to pass on various implications to various individuals. It is in the basic enthusiasm to embrace a quantitative strategy for assessment with proper investigation strategies which will dispense with the variable subjective factor.

There are endless strategies that can be utilized to measure microscopic asperity. A few examples incorporate finding the level difference between the highest and lowest points within a 1 mm 0.04″ square area or finding the distinction between the normal of 5 high points and the normal of 5 low points on a straight line 2mm 0.08″ long. Be that as it may, if measures are resolved in this kind of discretionary form, irregularities may happen.

4.1 Roughness Grade

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Table – 4.1

4.2 Surface Roughness Deviation

Surface roughness deviation refers to the extent to which the normal surface differs from the machined surface. There are standards set to measure the deviation. There are 2 order deviations. First-and second-order deviations refer to forms, i.e. flatness, circularity, and so forth and to waviness, respectively, and are typically caused by machine apparatus blunders, wrong setups of work piece and lose clamping.  Third and fourth-order deviations allude to occasional notches and to cracks which are associated with the shape and state of the cutting edges, chip development and process kinematics. Fifth and sixth order deviations allude to work piece material structure, which is associated with physical–chemical instruments (slip, dispersion, oxidation, lingering pressure, and so forth.). Different order deviations are superimposed and shape the surface roughness profile, as in Fig.

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word23.png

Fig. 4.1

4.3 Factors of Surface finish

Surface finish is influenced by a number of factors.  Of these, machining parameters cause the greatest difference in surface roughness therefore will be studied in details.

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word24.png

Fig. 4.2

4.4 How to measure

Presently, we examine how surface roughness measurement relies upon various factors and how it can be measured. It relies upon:

  • Instrument to be utilized for measurement.
  • Techniques that can be utilized for measurement.
  • Parameters that significantly affect surface roughness.
  • Noise factors.

Various instruments that can be used for measurement of surface roughness are:

  • Image Processing
  • Microscope
  • Stylus type of instrument
  • Profile tracing instrument

Mathematical techniques can also be used like:

 

Some of the popular parameters of surface finish specification are described as follows:

  • Roughness average (Ra) This parameter is also known as the arithmetic mean roughness value, AA (arithmetic average) or CLA (center line average). Ra is universally recognized and the most used international parameter of roughness. Therefore,

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word25.png

Where,

Ra = the arithmetic average deviation from the mean line

L = the sampling length

y = the ordinate of the profile curve

It is the arithmetic mean of the departure of the roughness profile from the mean line.

  • Root-mean-square (RMS)roughness(Rq)

This is the root-mean-square parameter corresponding to Ra

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word25.png

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word26.png

Fig. 4.3

  • Maximum peak-to-valley roughness heights (R max)

This is the distance between two lines parallel to the mean line that contacts               the extreme upper and lower points on the profile within the roughness               sampling length. Since Ra and Rq are the most widely used surface               parameters in industry, Ra was               selected to express the surface roughness               in this study.

The next step is to determine the various optimization techniques to calculate surface roughness:

A number of optimization techniques can be used:

 

  • Taguchi method
  • PCA(Principle Component Analysis) based Taguchi method
  • RSM (Response Surface Methodology)
  • Artificial Neural Networks
  • Average Roughness Technique
  • ANOVAs Approach
Sl. No. Technique Name Details
1. PCA-based Taguchi method 

 

Taguchi’s Orthogonal Array (OA) gives an arrangement of well-balanced examinations (with less number of test runs), and Taguchi’s signal-to-noise ratios (S/N), which are logarithmic elements of wanted output. Principal Component Analysis (PCA) is a method for distinguishing patterns in the connected data, and communicating the information in such a path to feature their similarities and contrasts. The main advantage of PCA is that once the Patterns in information have been recognized; the information can be compacted, i.e. by decreasing the quantity of dimensions, without much loss of data.
2. Artificial Neural System Artificial Neural system is a versatile system that can learn connections through repeated presentation of information and is equipped for summing up to new, already unseen information. For this study, the system is given an arrangement of sources of info and relating wanted outputs, and the system tries to take in the input-output relationship by adjusting its free parameters. Initially, a reparation input pattern is exhibited to the system input layer. The system at that point engenders the input pattern from layer to layer until the point when the output pattern is Generated by the output layer.
3. Roughness average technique(Ra) Roughness average (Ra): This parameter is also known as the arithmetic mean roughness value, AA (arithmetic average) or CLA (center line average). Ra is universally recognized and the 

most used international parameter of roughness.

4. Taguchi and ANOVA technique ANOVA can be valuable for deciding impact of any given input parameter for arrangement of test. Result by plan of exp. For machining procedure and it can be to decipher test data. While performing ANOVA degrees of freedom ought to be considered together with each sum of square. In ANOVA studies with certain test error, error difference assurance is Important
5. RSM These strategies select orders of polynomial model,  analysis of points and model fitting

Table – 4.2

4.4 Comparison of surface roughness in different strategies

I have prepared this part in CREO manufacturing and simulate all the NC sequences whose screenshots are above mentioned.

In CNC Milling operation surface finish depend on the type of surface like flat, profile, taper wall pocket, waviness surface, etc; types of tools End Mill, Ball Mill, Face Mill etc.

I have used total four strategies to finish this part and they are as follows:

  • Step 1 – Face Milling

In face milling sequence

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT10.png

Fig. 4.4

Face milling machined the flat surface so its surface roughness is standard as parameter.

  • Step 2 – Roughing

In Roughing Sequence

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT12.png

Fig. 4.5

Roughing operation is done by Inserting End Mill and this operation contains a radial surface (concave and convex). Therefore, surface roughness is rough as shown in (figure-).

 

 

 

 

 

 

 

  • Step 3 – Re-Roughing

In Re-Roughing sequence

C:UsersWin7AppDataLocalMicrosoftWindowsTemporary Internet FilesContent.Word14.png

Fig. 4.6

Re-Roughing is done by solid carbide end mill and surface roughness is similar to roughing operation.

We can also achieve the smooth surface by this tool only when it is used in finish NC sequence operation. Its cycle time is 5 times more as compared to the Ball mill finishing.

  • Step 4 – Finishing

In finishing sequence

D:2018FREELANCER_APRILWAMAITHASCREEN SHOT17.png

Fig. 4.7

 

Finishing operation has been done by Ball mill solid carbide and its surface finish is better as per standard of finish component.

Here we can see that both radial surface are smoothly finished by finishing strategies by using Ball mill cutter.

 

Conclusion

Several factors have been seen to affect surface finish roughness for the milled work piece among them the choice of tool to be used. The speed of cutting and the depth of feed.

These parameters have been simulated to obtain the optimum condition for each of them to achieve the best surface finish possible.

It is easily noticeable that machining parameters affect surface finish, process time, tool life and other machining principles.

Simple example to take is feed rate. Increasing feed rates will definitely reduce the process time and this is a desirable advantage.

Another example is step-over. Reducing it will result a better surface finish and this is a desirable advantage too.

Better surface finish, less machining time, longer tool life etc. are always desirable advantages.

So to get good machining results supposed to increase the feed rate and reduce the step-over so we will have a short process time and a good surface finish (as mentioned in the example).

But real life is a bit more complicated than this, because the high feed rate will cause bad surface finish* and low step-over will cause a long time process which are not desirable at all.

There are many techniques to set (choose) the right and suitable parameter to gain the maximum machining efficiency.

Before talking about the techniques let us take a look at the relationships between the machining parameters and the results whether it is a positive or an inverse relationship.

para/result Short process time Tool life Surface finish Low Cost***
Feed rate positive inverse inverse positive
Spin rate positive inverse positive positive
Step down(depth) positive inverse No effect* positive
Step-over positive inverse inverse positive
Tool diameter positive positive positive** positive

down does not affect the surface except at the finishing (final) step.

Increase in tool diameter will make the cutting process less aggressive, because the number of the flutes will increase too. But in the corners and fine details big diameter tool is not useful.

determining the effects on the cost maybe sometimes complicated, but generally the process time is the major factor affecting the cost.

References

PTC CREO 5.0 simulation performed in CREO.

Ab. Rashid M F F, Gan S Y and Muhammad N Y (2009), “Mathematical

Modeling to Predict Surface Roughness in CNC Milling”, World Academy of Science, Engineering and Technology, Vol. 53, pp. 393-396

Cevdut Gologlu, Nazim Sakarya (2008) “The effects of cutter path

strategies on surface roughness of pocket milling of 1.2738 steel based onTaguchi method”, Journal of Material Processing Technology 206, 7-16

H.Oktem, H.Kurtaran, (2005) “Application of response surface methodology in the optimization of cutting conditions for surface roughness”, Journal of Material Processing Technology 170, Pp. 11–16

Choy, H.S.; Chan, K.W. (February 2003). “A corner-looping based tool path for pocket milling”. Computer-Aided Design. 35: 155–166. doi:10.1016/S0010-4485(02)00049-0. Retrieved 11 March 2015

Jeong, J.; Kim, K. “Tool Path Generation for Machining Free-Form Pockets Voronoi Diagrams”. Springer Link. The International Journal of Advanced Manufacturing Technology 1998, Volume 14, Issue 12, pp 876-881. Retrieved 11 March 2015.

Hansen, Allan; Arbab, Farhad (April 1992). “An algorithm for generating NC tool paths for arbitrarily shaped pockets with islands”. ACM Transactions on Graphics. 11 (2): 152–182. doi:10.1145/130826.130832. Retrieved 12 March 2015.

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