Metal Cutting in Detail

Metal cutting is the collection of processes where metal is formed into a desired shape by removing excess material.

This uses various tools and results in two products, the waste or excess material and the finished part.

There are three major categories;  chip producing processes (machining), burning where metal is cut into two parts by oxidizing a kerf, and specialty processes that do not fall into the other two categories.

Examples of these processes are: Drilling a hole for chip producing processes, using a cutting torch to separate a plate of steel is an example of burning, and chemical milling is a specialty process that removes excess material by using etching chemicals and masking chemicals.

Overview of Methods

Every method has limitations in accuracy, cost, and effects on the material.  

Heat, for example, may damage the quality of heat treated alloys, while laser cutting highly reflective materials like aluminium is more difficult.

Cutting fluid or coolant is often used whenever there is significant friction and heat at the cutting interface between a cutter, such as a drill or an end mill, and the workpiece.

It is generally applied as a spray across the face of the tool and workpiece.

Coolant is used to prevent excessive tool wear, and to prevent deformations in the workpiece that may be caused by extreme heat.

Specific Methods

Some methods use basic hand tools like hacksaws, chisels, or shears.

Milling, turning, threading, grinding, filing, and other methods are all used to create cuts in metal.

Milling is a type of machining using rotary cutters to remove material by advancing a cutter into a workpiece.

It requires a milling machine, workpiece, fixture, and cutter.

The workpiece is a pre-formed block of material that the milling process will turn into the finished part.

The workpiece is fitted to a fixture in the milling machine, to lock it in place and allow the cutter to cut cleanly and precisely.

Cutters rotate at high speed while secured to the movable parts of the milling machine.

Moving the workpiece into the cutter shaves small chips of material away and creates the desired part shape.

The finished asymmetrical parts have many features, like slots, holes, shells, pockets, and 3D surface contours.

Parts created completely through milling are often used for limited quantity needs, for example prototypes.

Tooling for other processes is also able to be made, like 3D molds.

Refining or adding features to parts from a different process is also a common milling function.

Milling also offers high tolerance and clean surface finishes.

Turning uses a lathe to cut metal into cylindrical surfaces with single point tools.

Lathes produce objects like candlestick holders, crankshafts, camshafts, and bearing mounts.

They use abrasive, cutting, or deformation tools to produce objects with rotational symmetry on an axis of rotation.

Many Metal Cutting Methods use CNC for Greater Part Accuracy

Threading includes cutting threads with a tap or die, thread milling, single-point thread cutting, thread rolling, cold root rolling and forming, and thread grinding.

Taps cut a female thread on the inside surface of a pre-drilled hole, while a die cuts a male thread on a preformed cylindrical rod.

Grinding is a cutting method that uses an abrasive wheel as the cutting device.

Grinding machines can produce fine finishes, very light cuts, or high precision forms.

The abrasive wheel can be made up of various sizes and types of stones, diamonds and inorganic materials.

Depending on the size and type of material these wheels can vary greatly in their effects, removing large amounts of material or removing tiny amounts of the surface of the workpiece; polishing it.

Modern grinding wheels can even be controlled by CNC, allowing them to have high material removal rates with high precision.

High volume production runs of precision components and aerospace applications are common for computer controlled wheels.

Filing uses a file to combine grinding and saw tooth cutting.

It is rarely used in modern production techniques, usually only to provide a relatively accurate means for the production of small parts.

Files vary in size, shape, coarseness, and whether the teeth single cut or double cut depending on the application the file is used for.

Deburring remains a common use for files in modern machine shops.

Broaching is used to cut keyways into shafts.

EBM or electron beam machining directs high-velocity electrons towards a workpiece heating and vaporizing the material.

Ultrasonic machining uses ultrasonic vibrations to machine very hard or brittle materials.

Technologies for metal cutting include

• Manual technologies: saw, chisel, shear or snips
• Machine technologies: turning, milling, drilling, grinding, sawing
• Welding/burning technologies: burning by laser, oxy-fuel burning, plasma
• Erosion technologies: water jet, electric discharge, abrasive flow machining
• Chemical technologies: photochemical machining.

Article refrences:

https://en.wikipedia.org/wiki/Cutting

https://en.wikipedia.org/wiki/Metalworking#Cutting_processes

https://www.wasatchsteel.com/learning-various-metal-cutting-methods/

Metal Rolling Process

Metal rolling is the metal forming process used to reduce the thickness of metal and make the thickness of the reduced metal uniform.

The process is very similar to the rolling of dough with rolling pins.

There are two types of this process depending on the recrystallization temperature of the metal used, hot rolling and cold rolling.

When the temperature is above the recrystallization temperature of the metal it is hot rolling, and when below it is cold rolling.

Hot Rolling

Hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of all cold working processes.

Roll stands holding pairs of rolls are grouped into rolling mills that quickly process metal into products like I-beams, angle stock, channel stock and other structural steel, bar stock and rails.

Steel mills often have rolling mill divisions that convert the semi-finished casting products into finished products.

Hot rolling allows the devormed grains of the metal to recrystalize equally to keep the microstructure symmetrical and prevent the material from work hardening.

It uses semi-finished casting products like slabs, blooms, and billets.

In continuous casting the products are usually fed directly into the rolling mills at the proper temperature.

Smaller operations heat the material with induction heating, or in the case of larger workpieces a gas or oil fired soaking pit is used.

The temperature of the workpiece must remain above the recrystallization temperature of the metal throughout the process.

Non-uniform cooling adds significant residual stress, usually in non-uniform cross section shapes like I-beams.

Good quality products have their surfaces covered in mill scale, an oxide that forms at high temperatures.

Mill scale is usually removed via pickling or smooth clean surface (SCS) process, revealing a smooth surface.

Hot rolling has a higher carbon tolerance for included carbon, and is therefore more difficult for a blacksmith to use.

Cold Rolling

Cold rolling occurs usually at room temperature, which increases the strength of the metals via strain hardening.

This strengthens the metal up to 20% while improving the surface finish and holds tighter tolerances.

Sheets, strips, bars, and rods in smaller sizes than the ones formed by hot rolling are often produced by cold rolling.

Cold rolling cannot reduce the thickness of a workpiece as much in a single pass as hot rolling can.

Sheets and strips produced by cold rolling come in various conditions, full-hard, half-hard, quarter-hard, and skin-rolled.

Full-hard rolling reduces the thickness of the metal by 50%, half-hard and quarter-hard create smaller reductions in thickness.

Skin-rolling involves the smallest reduction, at 0.5-1%.

It produces a smooth surface, uniform thickness, and reduces the yield point phenomenon. (Where the metal can deform under stress and not return to its original shape.)

Locking dislocations at the surface, and breaking up spangles in galvanized steel are also produced by skin-rolling.

Blacksmiths can more easily process cold rolling, because of its results are smoother, more consistent, and encapsulate low amounts of carbon in the metal.

The process as a whole is more expensive than hot rolling.

Products of cold rolling

• Metal furniture
• Desks
• Filing cabinets
• Tables
• Chairs
• Motorcycle exhaust pipes
• Computer cabinets and hardware
• Home appliances and components
• Shelving
• Lighting fixtures
• Hinges
• Tubing
• Steel drums
• Lawn mowers
• Electronic cabinetry
• Water heaters
• Metal containers
• Fan blades
• Frying pans
• Wall and ceiling mount kits
• Construction related products

Rolling Mill Configurations

The most basic rolling mill configuration is a two-high non-reversing with two rolls that turn in only one direction.

Two-high reversing mills can rotate in both directions, but are at a disadvantage because the rolls must be stopped, reversed, and then brought back up to rolling speed between each pass of the metal.

The three-high mill solves this problem with three rolls that move in one direction, so that the metal can be fed through two of the rolls and then through the other pair.

An elevator is needed to lift and lower the workpiece for a three-high mill.

Small roll diameters result in less power and force required, and four-high or cluster mills use this to their advantage.

Four-high mills use four rolls, two small and two large, the two smaller rolls use contact with the larger rolls to overcome their main problem which is reduction of stiffness.

All four rolls are placed in a vertical line, with the smaller ones placed on the outside.

Cluster mills use the same principal, but place their gradually larger rolls at angles to the small center rolls to maximise contact and use very small rolls to do the work.

Ring rolling increases the diameter of a ring, it is a specialized type of hot rolling.

Two rolls, an inner idler roll and a driven roll which presses the ring from the outside, during rolling the wall thickness decreases as the diameter increases.

This process results in circumferential grain structure, giving better mechanical properties to the finished rings.

Diameters as large as 26 ft and face heights as tall as 79 in can be made.

Ring rolling is used in railway tyers, bearings, gears, rockets, turbines, airplanes, pipes, and pressure vessels.

Roll bending produces a cylindrical product from sheet metals.

Roll forming is a continuous bending operation which uses a long strip of metal (Usually coiled steel) passing it through consecutive sets of rolls, each performing only an incremental part of the bend, until the desired cross-section profile is obtained.

It is ideal for parts with long lengths or large quantities.

Forge rolling is a longitudinal rolling process reduces the cross-sectional area of heated bars or billets, by moving them between two roll segments rotating in opposite directions.

Producing optimized material for die forging.

Forge rolling produces crankshafts, connection rods, steering knuckles and vehicle axles.

Controlled rolling uses controlled deformation and heat treating to control many facets of the worked metals.

Heat treatments can produce fine grain structure, control the nature, size and distribution of transformation products (Like ferrite, austenite, pearlite, bainite, and martensite in steel.) ; including precipitation hardening, and controlling the toughness.

This entire process must be closely monitored and controlled, but result in better mechanical properties and energy savings.

Metal Shaping

Deforming a workpiece through mechanical deformation, and changing the shape of the piece without altering its mass is the process of metal shaping.

It can be done by hand with a form, or an object that has the shape of the finished piece, and a hammer.

The most common form is a tree stump or log that have been carved with bowl shaped tops, with a variety of bowl diameters and depths allowing for more varied final shapes.

Other forms include a leather bag filled with sand or lead shot, or a metal piece already in the shape of the finished piece.

Repeatedly striking the workpiece with the hammer gradually deforms the metal into the desired shape.

This process can also use shop hammers to deform the metal far more quickly.

Planishing is then used to smooth out small irregularities, it uses a smooth, flat, and relatively hard hammerhead and a hard dolly that matches the contour of the part.

Mechanical hammers are especially useful for this process as it requires thousands of small hammer blows.

When a workpiece is finished it is clean and matches the dimensions intended.

Article refrences:

Metal Rolling:

https://en.wikipedia.org/wiki/Rolling_(metalworking)

https://thelibraryofmanufacturing.com/metal_rolling.html

Metal Shaping:

http://www.britishv8.org/Articles/Hammerforming-and-Planishing.htm

https://en.wikipedia.org/wiki/Forming_(metalworking)

Press Brakes in Depth

A press brake is a tool to bend sheet and plate materials.  

Two C-frames form the sides of the press brake along with a table at the bottom and a movable beam at the top.

The tool has two pieces one mounted on the table, and the other tool mounted on the upper beam.

Press Brakes are typically defined by their force, tonnage and maximum length of material.

Other parameters include the stroke length the distance between frame uprights or side housings, distance between side housings and frame uprights, distance to the back gauge, and the working height of the machine.

They can apply force to bend materials with mechanical, pneumatic, hydraulic, and servo-electric means.

Mechanical presses add energy to a flywheel with an electric motor, with a clutch engaging the flywheel to power a crank mechanism that creates vertical ram movement.

This method of powering a press brake leads back to the 1920’s.

In the 1970’s hydro mechanical and hydraulic power became available for press brakes.

These use two synchronized cylinders to move the upper beam.

They can be stopped at any time, unlike a mechanical press brake.

Electric press brakes are commonly used in lighter applications, making smaller parts.

They have a significant advantage in acceleration factor and speed, increasing their efficiency with small parts that have many bends.

Backgauge devices, where a piece of metal is placed with the device to accurately position the bend, allowing for more efficient processes.

They are able to speed up the time-consuming repositioning process, where traditionally the part has to be moved and placed by hand to set up the next bend.

Repositioning can take enough time that only around 20 percent of a shift is spent bending the parts.

Backgauges can also be programmed to move from bend to bend to easily make complex parts.

The die used can allow the press brake to make many kinds of bends and can even allow for multiple bends at once.

Why aren’t they called a metal bender, or metal former?

An old root word in archaic languages from before the year 900, in Old English brecan, in Germain brechen, in Gothic brikan, in Middle English breken, in Dutch broken, and in French brac.

The French term meant a lever, arm, or handle.  

The more general term of brake was “an instrument for crushing or pounding”, and brake eventually became machine.  

This was inherited from machines used to crush grain and plant fibers, so pressing machine and brake essentially mean the same thing.

As Old English brecan changed to break, and shifted meaning to destroy or divide solid objects into fragments the machine name became more confusing.

Middle English comes closer to the meaning of the word brake (as in press brake), with its verb breken.

Breken meant bend, change direction, or deflect.  

This meaning even included breaking light by deflecting it with a mirror, and breaking a bow while drawing back its string to notch an arrow.

Press is simpler to define, as the words presse “to crush or to crowd” essentially kept its meaning and became the modern press.

Essentially meaning a machine that exerts force by squeezing, fabricators often refer to the punches and dies as presses.

Pipe Benders

Creating curves in metal piping is the purpose of a pipe bender.

Some pipe bending processes include:

• Press Bending
• Rotary Draw Bending
• Roll Bending
• Induction Bending
• Packing

Press bending produces an oval cross section as it deforms the pipe as it is bent.

It is commonly used on cold pipes and tubing.

Bending pipe without the tool often results in buckling in the metal, creating crimping and flattening.

These malformed pipes break more frequently under pressure, can crack and generally look horrible.

Pipe benders have a curved piece called a die or former that forces the pipe to take its shape when pressure is exerted by an arm that pushes the pipe into the shoe.

The die must match the size and radius of the tube size, but can produce a variety of shapes.

Rotary draw bending focuses on a constant center line radius, and is programmable to allow for complex bends with differing planes.

It is the most popular for use in manufacturing handrails, frames, vehicle roll cages, lines, and handles.

Their bends are aesthetically pleasing and can be CNC machines for even more precision.

Roll bending uses three or more rollers to gradually apply the bend, decreasing the radius of the pipe in steps.

There is little deformation in the cross section of the pipe.

This method produces good results in coils of pipe and long gentle bends like in truss systems.

Induction coils are placed around a section of pipe for induction bending.

This heats the pipe somewhere between 800 and 2200 degrees fahrenheit.

Then pressure is applied to the heated pipe to bend it.

Afterwards it is quenched with air or water spray, or sometimes with ambient air.

Thick walled or large radius pipe is easier to bend with this method.

Industries that benefit from this process are petrochemical, construction, power generation, and city heating.

Packing fills the pipe with various materials prior to bending.

Water in a solute solution can be frozen into a pipe and then bent while the ice is cold and flexible due to the solute (sometimes soap), trombones, for example, are made this way.

Pitch was used in the past, but the difficult cleanup process made it less and less appealing.

Sand is another method, where the pipe is filled with fine sand capped at the ends and heated in a furnace to 1,600 F or higher.

A slab with pins set into it is then used along with a winch, crane, or mechanical force to bend the pipe.

This minimizes, but does not prevent, distortion in the cross section of the pipe.

Article refrences:

https://en.wikipedia.org/wiki/Press_brake

https://www.thefabricator.com/article/bending/why-is-it-called-a-press-brake-

https://en.wikipedia.org/wiki/Tube_bending

The Engineering Design Process

There is no one accepted model of the engineering design process.

Each model varies in complexity from 3 step loops to very complicated interwoven steps that are made to monitor the overall progress towards a completed and ready for production product.

The three step loop contains the elements ideate, implement, test.

More complete systems have the steps: establishment of objectives and criteria, synthesis, analysis, construction, testing and evaluation.

All of these processes are iterative, almost never reaching completion without repeating steps many times.

Common Steps in the process are:

• Research
• Design requirements
• Feasibility
• Conceptualization
• Preliminary design
• Design for manufacturability
• Production planning

The Steps

Research involves casting a wide net and finding out other solutions or finding out if technology might be transferable from another process.

Factors like problems, existing literature, successes using existing solutions, costs, and marketplace needs all have to be evaluated.

Reverse engineering is also considered part of the research step, and may be an effective choice when there are few other sources of information.

Many sources can be utilized including the internet, libraries, available government documents, personal organizations, trade journals, vendor catalogs, and individual experts.

The next step, design requirements, involves establishing design requirements and conducting requirement analysis.

It is sometimes called problem definition, and is a vital step in the design process.

Defining the functions, attributes, and specifications after finding out user needs is the main task of this step.  

Some of these requirements may be software or hardware related like maintainability, availability, testability.

Problem definition is often performed at the same time as feasibility analysis.

Feasibility studies narrow the scope of the project to find the best scenario.  

Essentially finding out if the project can proceed into the design phase, using two factors the project must be an achievable idea, and within cost constraints.

Engineers with experience and good judgement are necessary for evaluating if these factors can be achieved.

Conceptualization focuses on producing ideas and weighing the pros and cons of implementing those ideas.  

Minimizing the chance of error, managing costs, assessing risks, and estimating the potential success of a project are the goals of this step.

Often called ideation or concept generation there are many common techniques such as:

Further Steps

After ideation is a concept evaluation step, looking for the strengths and weaknesses of the possible alternatives.

Preliminary design bridges the gap between conception and detailed design.

It involves defining the product through schematics, diagrams, and layouts to allow for a framework to build the project.

Detailed design, further describes the project through solid modeling, drawings, and specifications.

It can also involve procurement of materials.

Design for manufacturability creates a method for the project to be easily manufactured.

CAD programs have made this step far more efficient, allowing optimizations like reducing volume without changing the performance of the part.  

These programs can also calculate stress and displacement using the finite element method.

Production planning calculates tool designs and other factors that allow for mass production of the project.  

Determining the sequence of operations, and selection of tools are optimized at this point.

Qualification testing of the project often continues at this point as the finished parts are evaluated in use.

The later steps in the process are often repeated as unplanned and unexpected problems or failures to meet qualifications are found.   

These unwanted factors cause resets back to the step that they most effect, if a part is too heavy then it just needs a material change or redesign.

If there is a failure of the project to address the problem it is made for most of the process would need to be started over.

Many teams split and work on steps of the engineering process in parallel to reduce the time spent iterating.

With good communication the teams can be ideating, testing, and building prototypes at the same time.

The overall goal is reached when the project reaches or exceeds specifications and is mass producible.

Article refrences:

https://curriculum.vexrobotics.com/curriculum/intro-to-engineering/what-is-the-engineering-design-process.html

https://en.wikipedia.org/wiki/Engineering_design_process

Milling Machines and Milling Process

Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece.

It requires a milling machine, workpiece, fixture, and cutter.

The workpiece is a pre-formed block of material that the milling process will turn into the finished part.

The workpiece is fitted to a fixture in the milling machine, to lock it in place and allow the cutter to cut cleanly and precisely.

Cutters rotate at high speed while secured to the movable parts of the milling machine.

Moving the workpiece into the cutter shaves small chips of the material away and creates the desired part shape.

The finished asymmetrical parts that have many features, like slots, holes, shells, pockets, and 3D surface contours.

Parts created completely through milling are often used for limited quantity needs, for example prototypes.

Tooling for other processes is also able to be made, like 3D molds.

Refining or adding features to parts from a different process is also a common milling function.

Milling also offers high tolerance and clean surface finishes.

The milling process

The time to make a quantity of parts includes the initial setup time and the cycle time for each part.

The setup time includes preparing the machine, planning the tool movements, and installing the fixture device into the machine.

This is often greatly shortened by using a CNC machine as the movements are all managed by the computer.

Cycle time depends on these four steps:

Load/Unload time: getting the workpiece into the machine and unloading it after the part is finished.

Cut time: the time it takes for the cutter to run the total length of the multiple cuts as well as the speed of the cutter as it makes each cut.

Idle time: any tasks that do not have the cutter actively removing material, including the tool approaching and retracting from the workpiece, tool movements between features, changing tools, and changing machine settings.

Tool replacement time:  worn or non-effective tools must be replaced, especially on large production runs or with more durable materials.  

After the cycle there is no post processing, scrap material in the form of small chips are thrown away from the surface of the part by the spinning cutter or lubricant spray.  

If the surface of the part needs further improvement additional steps can be required.

The scrap from the process is collected and is discarded after the machine operation.

Cutting parameters

The speed and motion of the cutting tool are defined through several parameters, determined by material, tool material, tool size and additional factors.

Cutting feed: the distance advanced by the cutting tool during one revolution of the spindle and tool, measured in inches per revolution.

Cutting speed: the speed of the workpiece relative to the edge of the cutting tool, measured in surface feet per minute.

Spindle speed: revolutions per minute of the spindle and tool.

Feed rate: the speed of the cutting tool movement relative to the workpiece as the tool makes a cut.

The product of cutting feed (Inches per revolution) and spindle feed (Revolutions per minute) measured in inches per minute.

Axial depth of cut: the depth of the tool along its axis in the workpiece as it makes a cut, can create high load and reduce tool life.

Radial depth of cut: the depth of the tool along its radius in the workpiece as it makes a cut, if the tool is engaged the radial depth will be at least equal to the tool diameter.

Operations of a milling machine:

• End milling
• Chamfer milling
• Face milling
• Drilling
• Boring
• Counterboring
• Countersinking
• Reaming
• Tapping.

Description of Operations

End milling makes peripheral or slot cuts, determined by step-over distance, across the workpiece in order to machine a specific feature.

These may be profiles, slots, pockets, or complex surface contours.

Depth of these features may be machined in a single pass or multiple passes.

Chamfer milling is making a cut along the edge of a workpiece or feature to create an angled surface, known as a chamfer, these are typically 45 degree angles and can be machined on the interior or exterior of a part following a straight or curved path.

Face milling creates a smooth finish by creating a flat surface on the workpiece, this is usually done by removing a small depth of material from the edge.

Drilling creates a hole with a diameter equal to that of the tool, extending through or partially through the workpiece.

Boring tools cut along an internal surface to form different features, often used after drilling to create more precise dimensions or enlarge the diameter of the hole.

Counterboring enlarges the top of an existing hole to the diameter of the tool providing space for a fastener head to sit flush with the workpiece surface.

Countersinking creates a cone-shaped opening in the top of an existing hole, creating space for a fastener head, like the top of a screw, to sit flush with the surface of the workpiece.

Reaming enlarges an existing hole to the diameter of the tool, it often removes a minimal amount of material and is performed to obtain a more accurate diameter and a smoother internal finish.

Tapping cuts internal threads in an existing hole, the threads may be cut to the full depth of the hole (through tap) or a specific depth (bottom tap).

Other Considerations

Possible defects in the finished pieces can be caused by incorrect cutting parameters, dull cutters, or unsecured workpieces.

Milling is one of the most commonly used processes for making custom parts to precise tolerances.

These tolerances include +/-.005” for local tolerances for most geometries, +/-.10” for plastics with variation dependent on the size of the part, 0.03” minimum wall thickness for metals, and 0.06” minimum wall thickness for plastics.

Article refrences:

https://www.custompartnet.com/wu/milling

https://en.wikipedia.org/wiki/Milling_(machining)

What is CNC?

Using a computer to aid in transforming a stock piece of material to a finished product is CNC.

CNC stands for computer numerical control, and started in the 1940’s and 50’s using punched tape or perforated paper tape.

It quickly transitioned to analog and then digital mediums, and now uses CAM or CAD files to give the instructions for the finished parts.

The computer files define the shape and sometimes give more information, like which layers to print and when for 3D printing, to the CNC machines.

Prototyping and other labor intensive mechanical processes can be shortened considerably by using CNC.

Often multiple tools are needed to make the cuts to process a part.

Basic machines use the x and y axis to position their tools, advanced machines use all three x,y,and z axes to interact with their materials.

Multi axis machines can even flip their materials to allow access to the underside of parts.

This eliminates steps that workers would have to perform, where they would flip the parts in between the machining done by the CNC machine.

Typically manual cuts do not have the accuracy of a computer cut, and they have a much higher chance of creating flaws and irregularities.

Finishing work and etching are often better performed by hand, as well as simple cuts that would otherwise take extensive design work to accomplish.

Conventional technologies for CNC include drills, lathes and milling machines.  

Although novel technologies like electrical or chemical machining or other cutting mediums, like laser cutting, use CNC as well.

Materials and uses

Materials like brass, aluminium, copper, steel, and titanium as well as wood, fiberglass, foam, and plastics are used, although almost any material can be cut with the right machines.

Rapid prototyping by hand was filled with large error margins before the use of CNC and after the technology took off, options for large and accurate productions of prototypes exploded.

CNC has a competitor in 3D printing, with advantages for each.

3D printing can create internal structures and complex shapes with greater ease than CNC.

CNC, on the other hand, has a wider selection of materials available, as 3D printing is limited by what can be adapted into filaments suitable for 3D printing.

CNC can also be adapted for niche manufacturing purposes with electrochemical machining as an example.

For one-off and medium-volume production CNC is reliable and cost effective.

Process step-by-step.

A 2D vector or 3D solid part file is needed to start the process of CNC, these are produced in CAD or computer aided design programs.

AutoCAD, Sketchup, Solidworks. Autodesk Inventor, CATIA, PTC Creo, FreeCAD, and OpenSCAD are all CAD programs.

Some of them are even freeware, like freeCAD, so finding a CAD solution is easy.

This file contains the measurements and coordinates of the parts, showing the space they occupy.

Designs have to be made with the restrictions of the CNC machine in mind.

For example most CNC tooling is cylindrical, so corners will be curved in the finished part.

Properties of the material, tooling design, and workholding capabilities of the machine further restrict the design possibilities.

Features like minimum part thickness, inclusion and complexity of internal parts and features, and maximum part size are all limited by these factors.

Once a compatible design is finished it is exported to a CNC-compatible file format.

Some common formats are AI, PDF, DXF, DWG for 2D and STL, OBJ, DXF, STEP, IGES, DWG, and 3DM for 3D.

Manufacturing the part:

The file is then run through a program, usually a CAM program, to analyse the geometry and produce the code that will ruin the machine and manipulate the tooling to cut the part.

Several programming languages are used, including M-code and G-code.  

G-code, general or geometric code, is the most well known.

It controls where, when, and how the machine tooling moves.  

This includes things like how fast to travel and in what direction, when to turn off or on and what overall paths to take across the material.

M-code, or Miscellaneous function code, controls the auxiliary functions of the CNC machine.

Automated processes are commonly M-coded, like the opening and closing of machine covers.

After the program is finished it is loaded into the CNC machine.

The machine has to be prepped before it can begin CNC production, with tasks like fixing the workpiece into the machine though spindles or vises.

Attaching or cleaning the tooling parts is also a common task.

After setup the program can be run.

The machine then executes the program, following the instructions of the file with its integrated computer.

Producing the desired part.

All of this can be produced in-house as long as the company has the CAD programs and CNC equipment.

Outsourcing to CNC machining service providers is also common.

Industries that use CNC in their manufacturing include aerospace, automotive, agriculture, commercial, defense, electronics, firearms, medical, and optical.

Types of CNC operations:

• Drilling
• Milling
• Turning

Discription of Operations

Drilling uses multi-point drill bits to create cylindrical holes in the workpiece.

The machine moves the drill bit perpendicularly to the workpiece surface plane.

Angular drilling can also be performed with more specialized machines and work holding devices.

Drilling can result in operations like tapping, countersinking, counterboring and reaming.

Milling rotates multi-point cutting tools to shave material from the workpiece.

CNC milling is performed opposite to the traditional method of milling, with the workpiece and the cutting tool moving in the same direction.

Operations performed by CNC milling include peripheral milling which cuts cavities, like slots and treads into the workpiece, as well as face milling which cuts shallow flat surfaces and flat-bottomed cavities into the workpiece.

Turning on a CNC machine uses a single-point cutting tool to remove material from a rotating workpiece.

This is usually performed on a lathe, removing material from the circumference of the workpiece until the desired diameter or shape is achieved.

Boring, facing, grooving, and thread cutting are all operations that CNC turning is capable of.

Some other CNC operations are broaching, sawing, grinding, honing, and lapping.

Article refrences:

https://www.thomasnet.com/articles/custom-manufacturing-fabricating/understanding-cnc-machining/

https://www.creativemechanisms.com/blog/everything-you-need-to-know-about-cnc-machines

https://www.millenniumprecision.com/7-key-industries-benefit-cnc-machining/

Laser cutting and other industrial cutting methods

Laser cutting uses a focused laser to cut materials and is commonly used industrially with sheet metal parts and products.

It can also be used to cut diamond, glass, silicon, wood, and plastics.

Older laser cutting machines used mirrors, but modern machines increasingly use fiber optics.  

There are two major types of laser cutting, ablative and fusion.

In ablative cutting material is removed layer by layer using a pulsating laser.  

Like a chizel it removes material bit by bit, essentially evaporating the material, and can be used in etching or engraving materials; as it can be stopped at a precise distance at any depth in the cut.  

Fusion cutting instead melts the material the laser is in contact with and uses a high-pressure gas stream to shear material away.  

Both processes produce intricate and high-quality parts with clean edge finishes.  

The cut also produces less waste, physical damage, and material contamination than other cutting processes like mechanical cutting, plasma cutting, or waterjet cutting.  

Mechanical cutting uses dies and pressure to cut pieces from base material and often leaves tool marks and scratches on the surface of your part.

Plasma cutting uses a heated channel of ionized gas to cut through material, but as the workpiece needs to be part of the electronic circuit it must be a conductor of electricity.

Water cutting uses a high-pressure stream of water and an abrasive to cut through material, it also has the highest operating cost among industrial cutting processes.  

Although these methods have some advantages over laser cutting in areas like large production runs, or in the thickness of the materials that they can process; overall laser cutting is extremely efficient.

This efficiency has led to it becoming the largest segment of the metal cutting machine market.  

How it works

Typical laser cutting machines have a laser resonator assembly, mirrors, and a laser cutting head.   

The laser cutting head is composed of a nozzle, a pressurized gas assembly, and a laser focusing lens.  

All stages of this head are critical to the execution of a precise cut, along with configuring the machine software and part file.

CO2 and fiber lasers are the most common types of laser cutters.

CO2 lasers use an electromagnetically stimulated gas, which can be helium, xenon, hydrogen, nitrogen, or carbon dioxide.  

Carbon dioxide is the most commonly used gas.  

These were the first laser cutters, and have only recently been overtaken by fiber laser cutters.

Initially CO2 lasers were far better for cutting thicker materials, and this has changed as fiber cutting technology was refined leading to a smaller advantage for CO2 lasers.  

This trend is strong enough to make many question whether the market of CO2 lasers will disappear.

Fiber lasers use rare-earth elements like erbium, ytterbium, neodymium, or dysprosium on an optical fiber as their focusing elements.  

This allows them to have a more focused beam and more power applied to the cut.

Reflectance and thickness of materials have been the limiting factors for this technology with 1in mild steel material and below resulting in the best cuts.  

Cut Efficiency

Cut efficiency also depends more on application of power and machine dynamics (acceleration and deceleration) than the overall power of the laser.  

Using a laser that cuts material at the maximum thickness possible at its power is also a bad idea as tolerance for errors and aftercut cleanup increase, requiring a more skilled technician.  

Overshooting the minimum power results in cleaner parts, and has less chance of flaws in the cuts allowing a less skilled technician to make high-quality parts.  

Having the most powerful laser can lead to more expensive operation if it is stuck moving slowly on small, intricate cuts as it cannot reach its full cutting speed.  

High speed cutting is becoming more common, with 2,000 inches per minute possible.  

This speed is impressive, but the machine needs to stop moving to create a new cut.  

Accelerating back to maximum speed is where time can be spent on multiple small parts, losing overall efficiency.  

Other factors in making a clean cut include factoring in the width of the cutting beam, usually 30-300 microns, and supporting small parts with tabs so they are not blown away by the pressurized gas.  

These tabs are kept small (0.2-0.4 mm wide) so that breaking them from the metal sheet is easy, aiding in post-processing.   

Less reflective materials are more efficient to cut as more of the laser is concentrated, creating a hotter cut.  

Some highly reflective materials like copper and aluminium can damage the laser machine as the beam can be bounced backwards into the lasers focusing components.

Maintenance also is a factor, with daily cleaning for nozzles and lens protection devices.  

The skill of the operator in everything from editing the computer cut files, programming the machine, and keeping the machine clean; allow the machine to operate capable of the cleanest cuts.

Overview of benefits and limitations:

Limitations:

• Selection of materials
• Material thickness
• Production rate inconsistent
• Metal hardening or cleaning can take more production time.
• High energy and power consumption
• Initial equipment cost
• Harmful gases produced when cutting materials like plastic

Article refrences:

https://www.thomasnet.com/articles/custom-manufacturing-fabricating/laser-cutting-technology/

https://www.engineering.com/AdvancedManufacturing/ArticleID/16808/An-Engineers-Guide-to-Laser-Cutting.aspx 

Parts of a Lathe

Lathes were first used around 1300 BC but without parts like the headstock and tailstock.  

They may have even been used in Mycenaean cities going back to the 13th or 14th centuries B.C.  

The first major innovations in lathes happened in 1751 when Jacques de Vaucanson invented a all-metal slide lathe, and when mechanized power was available to drive the shaft of the lathe and allow for faster, more accurate work.  

In the 1950’s CNC or computerized numerical control was added to lathe machines to allow for even more optimized work.

Parts of a lathe are:

The lathe bed is the main body of the machine, with all main components mounted on it.

Beds are usually made of cast iron, for its high compressive strength.

Chucks hold the workpiece, fastened on the spindle as they both rotate.

Four and three jaw chucks are used, according to machine requirements.

The holding device is called the headstock, placed at the left side of the bed.

Holding the tools in an accurate position is accomplished by the tool post, fastened on the carriage.

Lead screw, also known as power screw, is located at the bottom side of the bed and is used to move the carriage during thread cutting operations.

Located between the head and tailstock is the carriage.

It moves on guideways and holds and glides the toolpost horizontally and vertically.

Legs support the lathe and help prevent vibration.

Hanging over the front side of the lathe bed is the apron.

It provides power and hand feed capability to the carriage and cross-slide.

The movement of the carriage and tailstock is confined by the guideways.

Spindles hold and rotate the chuck.

On the right hand side of the bed is the tailstock, which locks the workpiece while drilling operations are performed.

It also supports the job when required.

The compound rest fixes the single point cutting tools.

A hand wheel is used to move the tailstock backward and forward.

Movement of the carriage along the lathe is managed by the feed rod.

Machine operations of a lathe

• Drilling
• Reaming
• Boring
• Counterboring
• Taper boring
• Tapping
• Undercutting
• Internal Thread cutting
• Parting-off

Turning is used to remove excess material and resize the material.

Straight turning uses a tool parallel to the lathe axis, producing a cylinder.

Rough turning is used to quickly remove material 2-4mm deep.

Turning produces a step from one diameter to another, working on this step is called shoulder turning.

Eccentric turning uses two separate axes of rotation, with the first axis offset to the second.

Taper turning produces a uniform cone from one diameter to another.

Reducing the length of the workpiece by moving a tool along the height of the center of the workpiece is facing, it produces a flat surface on the end of the piece.

Chamfering creates a bevelled surface at the edge of the workpiece, often used on bolt and shaft ends.

It helps to avoid damage to the sharp edges, and in the case of bolts helps fit nuts and screw them in place easily.

Knurling creates a diamond pattern on the workpiece, providing an improved grip for handheld items.

This operation is performed on the lowest speed settings on the lathe.

Threading like on screws is created by the thread cutting process.

Rotating the workpiece between two centers and moving a v shaped tool along it creates the helical grooves.

Filling is a finishing operation performed after turning, to remove burrs, feed marks, and sharp corners and remove a small amount of metal to bring the workpiece to size.

Polishing with emery cloth after filling creates a smooth, bright surface.

For filling the lathe is run at high speeds of 1500-1800m per min.

Grooving reduces the diameter of the workpiece over a narrow surface.

Shoulders or ends of threads are often used for grooving, as they leave a small margin.

Spinning forms a thin sheet of metal by pressing a headstock spindle against a quickly revolving workpiece.

Coiled springs can also be made by using a mandrel revolved on a chuck or between centers.  

The wire is fed through a small hole on the steel bar winding the spring as the lathe advances.

Turning a convex, concave or irregular shape is known as forming.

It can be accomplished by using forming tools, combining cross and longitudinal feeds, and tracing or copying a template.

Forming is not intended to remove most of the material and is used mainly for finishing.

Straight and circular tools are used for wider and circular surfaces respectively.

Drilling produces a cylindrical hole in a workpiece, by rotating a tool on the cutter side.

Reaming finishes and sizes a hole which has been already drilled or bored, and the reamer tool used has multi-plate cutting edges.

Boring enlarges a hole that has been already punched, drilled or forged.

The workpiece is revolved in a chuck or faceplate and the tools in the tool post are fed into the work.

Enlarging the end of the hole through a certain distance is counterboring.

Shoulder work in external turning is similar to counterboring.

Taper boring uses a boring tool to make a hole that includes a taper.

Cutting internal threads of a small diameter is tapping.

Undercutting is similar to grooving performed inside a hole.

It creates a groove or a large hole at a fixed distance from the end of a hole.

Lathes with special attachments can also perform grinding or milling operations.

Milling removes metal by feeding the work against a cutter with multiple cutting edges.

Grinding removes material by using a rotating abrasive wheel known as a grinding wheel.

Article Refrences:

https://www.theengineerspost.com/lathe-machine-operations

https://en.wikipedia.org/wiki/Lathe

https://engramritkumar.com/lathe-machine/