Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning.
Metal Turning: The Ultimate FAQ Guide
Metal turning is a popular metal machining processes you can use to make a range of parts and components.
However, you can only get high quality parts with right dimension if you follow the right process.
This guide covers everything you need to know about metal turning.
Let’s dive right in.
- What Is Metal Turning?
- What Are The Types Of Metal Turning Operations?
- On What Materials Can You Perform Metal Turning?
- What Are Some Design Rules To Consider When Conducting Metal Turning?
- What Equipment Do You Need To Perform Metal Turning?
- How Does A Metal Turning Machine Operate?
- What Machines Can You Use To Conduct Metal Turning?
- What Is The Process Cycle Within Metal Turning?
- What Defects Can You Encounter During Metal Turning?
- What Workholding Methods Are Available In Metal Turning?
- Do You Require Secondary Processes After The Running Process Cycle In Metal Turning?
- What Are The Cutting Parameters In Metal Turning?
- What Are Some Cost Drivers That You Should Consider During Metal Turning?
- What Are Some External And Internal Operations You Will Conduct During Metal Turning?
- What Equipment Will You Use During Metal Turning?
- What Components Will You Find In A Metal Turning Machine?
- How Does Metal Turning And Metal Milling Compare?
- How Does Manual And Automatic Metal Turning Compare?
- What Is Hard Turning In Metal Turning?
- What Are The Benefits Of Metal Turning?
- What Are The Disadvantages Of Metal Turning?
- What Certifications And Standards Should Metal Turning Comply With?
- What Tooling Will You Require When Performing Metal Turning?
- What Specifications Should A Metal Turning Machine Include?
- What Factors Will Affect The Cost Of Purchasing A Metal Turning Machine?
- What Safety Precautions Should You Undertake When Performing Metal Turning?
What Is Metal Turning?
Metal turning is the process of removing metal pieces using a cutting tool from a workpiece that rotates.
The aim of performing metal turning is to trim the workpiece to a suitable size and shape.
Besides, you can perform metal turning either externally on the surface or internally within the metal.
Different metal turning technique
What Are The Types Of Metal Turning Operations?
There are different types of metal turning operations you can perform.
They include the following:
This is the process you will use to enlarge a pre-drilled hole.
Besides, you will use a boring head or single-point cutting tools.
Boring is suitable when you need to obtain an accurate diameter of the holes and you can use it to make tapered holes.
Also, boring is the opposite of turning.
In this operation, the tool you use for cutting will axially follow paths using premade geometries.
Besides, you will pass the contouring tool severally to form a final product with a suitable shape.
This process is like step turning and will create square edge angle transitions between surfaces that contain varying turned diameters.
This is like parting, however, you will cut the grooves at predetermined depths and not sever the whole part from metal stocks.
The machinists can conduct grooving on the face, internal, or the external surface of the metal.
This process entails moving the appropriate cutting tool at a right angle to the axis of the rotation of the workpiece.
Besides, you will conduct facing by operating the cross-slide.
Here, you will conduct the initial process in the production of the workpiece, and mostly the last.
This process is suitable for materials whose Rockwell C level of hardness surpasses 45.
Hard turning happens after you heat treat the workpiece.
Besides, hard turning is replacing the dated grinding procedures.
Hard turning is suitable for metal parts that need roundness accuracy levels of between 0.5 μm and 12 μm.
Also, you can use it for metals that need the roughness of the surface to be between Rz 0.8 μm and 7.0 μm.
Examples of hard turning usages entail the following:
- Hydraulic parts
- Injection pump parts
- Gears, etc.
This is the process of eliminating metal pieces from the internal part of a workpiece.
Here, you will use a standard drill bit which you hold stationery within the tool turret of the turning machine.
This is the process of sizing a predrilled hole by eliminating small quantities of metals.
Reaming will allow you to obtain very accurate diameters of internal holes.
For instance, you can use a 7.98 drill bit when making an 8 mm hole, then achieve a precise dimension by reaming.
This process is also known as cutoff or parting off.
Parting will form deep grooves that eliminate a partially or fully completed part from its main stock.
In this process, you will cut serrated patterns on the surface of metal parts.
Besides, you will use the serrated pattern as a handgrip with the help of a knurling tool.
This is a process of machining non-circular design without disrupting the rotation of the raw materials.
This process will allow you to form conical surfaces by progressively increasing or reducing the diameter from cylindrical workpieces.
Tapered turning finds a lot of usages when constructing machines.
Almost every spindle of the machines contains taper holes.
Also, the taper holes will accept a tapered shank on a variety of tools and work gripping devices.
Tapered turning will produce transition ramps between the workpiece’s two surfaces with varying diameters.
The outcome happens because of the angled motion that exists between the cutting tools and the workpiece.
It is possible to metal turn non-standard and standard thread screws using the correct cutting device.
Besides, you can perform threading externally or within preexisting bores.
In this process, you will form two surfaces on the metal whose diameter changes abruptly.
The final product looks like a step.
This process enables you to produce a ball shape from the workpiece.
On What Materials Can You Perform Metal Turning?
Metal turning processes
There are various materials on which you can conduct metal turning, and they include the following:
- Stainless steel
- Carbon steel
- Cast iron
- Nickel, etc.
What Are Some Design Rules To Consider When Conducting Metal Turning?
Choose cost-effective materials.
Cheap workpieces nay lead to long cut times and wear of the tool, thereby increasing the overall cost.
Cut the workpiece to a suitable configuration before conducting the metal turning process as this will lower the turning time.
Ensure the surface area of the workpiece is large enough for the lathe to clamp it securely.
Also, there should be a clearance after clamping the surface to enable any cutting.
Ensure you avoid undercuts.
Decrease the setups necessary by making all the features accessible from a single setup.
Make sure you minimize the tools that you require for the process.
Lower costs by decreasing surface roughness and tolerance need if possible.
Design features that can operate with tools that are of standard sizes.
Make sure the depth you create does not surpass the tool length as this will eliminate the chance of the workpiece and tool holder contacting.
What Equipment Do You Need To Perform Metal Turning?
The process of metal turning needs the following:
- Lathe or turning machine
- Cutting tool
Workpieces are metal surfaces that you will secure to the fixture, while the fixture attaches to the turning machine and rotates at high velocities.
How Does A Metal Turning Machine Operate?
Metal turning illustration
The turning machine operates on the principle of rotating a workpiece against a fixed cutting device.
First, you will secure the workpiece between the center, which are two strong and sturdy supports, revolving faceplates, or within a chuck.
The lathe will eliminate unwanted metal as the workpiece rotates.
This occurs with the assistance of a traverse tool that operates across the work and you can feed it deep within the work.
The lathe will remove the metal in form of chips from a workpiece to form a desired size or shape.
What Machines Can You Use To Conduct Metal Turning?
These include the following:
Metal turning lathe machine
- Turret lathe
- Speed lathe
- CNC lathe
- Gap bed lathe
- Capstan lathe
- Engine lathe
- Vertical turret lathe
- Bench lathe
- Toolroom lathe
- Hollow spindle lathe
In short, lathe machine is popular in metal turning process.
What Is The Process Cycle Within Metal Turning?
This is the time it takes to make a certain quantity of components entailing the setup time and cycle time for every part.
The setup time encompasses the time for preparing the metal turning machine, movement plans, and installation of the fixture to the machine.
Besides, you can categorize the cycle time as follows:
Load Or Unload Time
This is the time it will take you to load the workpiece within the metal turning machine, secure it, and unload the final product.
This is the time it will take the metal turning machine to cut the workpiece in every operation.
This is the time you will conduct other processes not related to the workpiece.
Tool Replacement Time
This is the time it will take to replace worn-out tools.
What Defects Can You Encounter During Metal Turning?
The majority of defects in metal turning happen due to miscalculations in the dimension and surface roughness of the workpiece.
Here are some causes for such defects:
If you fail to secure the workpiece to the fixture, it may shift and change the outcome due to friction.
Blunt Cutting Tool
After a while, the cutting tool will wear off and become dull making it incapable of performing accurate cuts.
Bad Cutting Parameters
When the cutting parameters are too high, the workpiece surface will become rougher and may exhibit burn and scratch marks.
Besides, when the cut is too deep, it may cause the tool to vibrate thereby leading to inaccurate cuts.
What Workholding Methods Are Available In Metal Turning?
These include the following:
These are popular workholding methods and come in various types.
The variations are for round, irregular, and square stock shapes.
This is a pointed cone directed by a “dog” and is used for turning long cylinders and shafts.
These are suitable for use with small and round workpieces.
This is a spring-loaded or hydraulic teeth that will bit the ends of the workpiece.
Also, you can use it when you need to machine the whole length.
The faceplate, mandrel, and drive hog can be suitable for metal turning.
Do You Require Secondary Processes After The Running Process Cycle In Metal Turning?
It is possible to use secondary processes when you need to enhance the surface finish of the component.
What Are The Cutting Parameters In Metal Turning?
In metal turning, you can specify the motion and velocity of cutting tools in many parameters.
These include the following:
Cutting parameters in metal turning
This is the rotational velocity of the workpiece and spindle, whose measurement is in revolutions per minute.
Besides, the velocity of the spindle should change in relation to the diameter of the cut for it to maintain constant cutting velocities.
This is the distance that the workpiece or the cutting tool moves when the spindle moves in one revolution.
The measurement of cutting speed happens in inches per revolution.
Besides, there are instances when the workpiece will feed into the cutting tool, and vice versa.
For multipoint tools, cutting feed and feed per tooth are equal.
This is the velocity of the movement of the cutting tool in relation to the workpiece when it is cutting.
The measurement of feed rate is in inches per minute.
This is the workpiece surface velocity relative to the cutting tool edge when cutting.
The cutting speed is measured in surface feet per minute.
Axial Depth Of The Cut
This is how deep the cutting tool will go along the workpiece axis when cutting.
Large axial depths of cuts need low feed rates otherwise it will cause a high load on the cutting tool and decrease its longevity.
Radial Depth Of The Cut
This is how deep the cutting tool will go along the workpiece radius when cutting.
A cut with a large radial depth needs low feed rates otherwise it may lower the longevity of the tool.
What Are Some Cost Drivers That You Should Consider During Metal Turning?
These include the following:
The factors that affect this cost entail the overall number of the cutting tools and the cost of each tool.
Also, the number of tools you need depend on the required tools due to operations needed and the wear and tear they experience.
This cost pertains to overall production time and hourly rate.
The production time entails the following:
- Idle time
- Setup time
- Cut time
- Load time
- Tool replacement time
Lowering any of these factors decreases cost.
What influences the material cost is the material stock quantity needed and the price for each unit.
Factors that determine the stock amount include:
- Stock size
- Stock cutting technique
- Quantity of production
- Size of workpiece
Other factors that will affect material cost include costs related to cutting.
The shape and material of the workpiece will affect the cost of each material stock.
What Are Some External And Internal Operations You Will Conduct During Metal Turning?
Several operations may take place on the workpiece during the process cycle to give suitable results.
The operations are categorized as external and internal.
External operations affect outer diameter while internal operations affect inner diameter.
These entail the following:
Metal turning operations
What Equipment Will You Use During Metal Turning?
A lathe is a machine you will use when performing metal turning and they exist in various designs and configurations.
A majority of lathes exist in horizontal formats but vertical formats are sometimes applied especially for workpieces with large diameters.
Besides, lathes exist in manual and computerized versions.
What Components Will You Find In A Metal Turning Machine?
Several parts make up a metal turning machine enabling their optimal performance.
Some of these components include the following:
The bed is the large base where the metal turning machine sits.
It rests on a table or ground and will provide support to all the parts of the metal turning machine.
This part slides with the workpiece enabling the cutting tool to skim off the material during the movement.
The carriage sits on tracks laying on the metal turning machine bed known as ways.
Lead screws that receive power from a hand wheel or motor provide the sliding motion.
This is the front part of the metal turning machine that attaches to the bed.
The headstock assembly has a drive and motor unit that provides power to the spindle.
Besides, the spindle will rotate and support the workpiece which sits securely on the fixture.
Some versions of metal turning machines have turrets that will hold several cutting tools.
They also revolve the necessary tool in the right spot for the workpiece to be cut.
Besides, turrets move with workpieces and feed-cutting tools into the metal.
Whereas several cutting tools do not move, you can include live tooling.
Live tooling is powered enabling them to rotate, thereby cutting the workpiece.
Examples of live tooling include taps, mills, reamers, drills, etc.
This is the back part of the metal turning machine and it also attaches to the bed.
The tailstock assembly supports the opposite side of the workpiece and enables its rotation since it receives the rotational force from the spindle.
Other operations lack the support of the tailstock on the workpiece allowing you to remove the material from that side.
This part attaches to the upper part of the carriage enabling the tool to go away from or towards the workpiece while altering the cutting depth.
The cross handle gets power via a hand wheel or motor.
This part attaches above the cross slide and will offer support to the cutting tool.
Also, you will secure the cutting tool on a tool post that attaches to the compound.
The compound can revolve and change the cutting tool angle regarding the workpiece.
How Does Metal Turning And Metal Milling Compare?
Metal turning entails rotating a workpiece against cutting tools and will mainly use cylindrical stock bars when machining parts.
Metal milling entails spinning a cutting tool on stationary workpieces and will mainly use rectangular or square stock bars to form parts.
How Does Manual And Automatic Metal Turning Compare?
Manual metal turning entails employing operators to turn the handwheel.
Automatic metal turning uses computer numerical control [CNC] systems to independently perform the turning process.
Manual metal turning is time-consuming and requires more attention during operation.
Automatic metal turning is precise, consistent, efficient, and profitable.
With manual metal turning, you need more human labor which increases the overall production cost.
Automatic metal turning allows you to save cutting parameters thus increasing design uniformity.
Manual metal turning costs less for smaller productions.
Automatic metal turning machines cost more than manual metal turning machines.
What Is Hard Turning In Metal Turning?
Hard turning attributes to the lathe employing single-point turning devices to curve metals that have a hardness value exceeding 45 HRc.
The hardness usually ranges between 58 HRc and 68 HRc.
Some advantages of hard turning entail the following:
- Easy operation
- Environmentally friendly
- Machining flexibility
- Quick cycle and set-up times
What Are The Benefits Of Metal Turning?
Some of the advantages entail:
- The collection of chips is simple
- Achieves suitable surface finish
- It consumes less energy
- Short lead time
- Good tolerance levels
- Compatibility with all materials
- Requires no complex training
- Flexible material removal rate
- High-quality products
- Saves money
What Are The Disadvantages Of Metal Turning?
Some of the limitations include the following:
- High rate of tool wear and tear
- Suitable only for rotational components
- Defects occur due to dimensional features or roughness of the surfaces
- Large quantity of scrap
- High initial investment
- Components may need many operations and machines
What Certifications And Standards Should Metal Turning Comply With?
Metal turning products need to comply with a set of standards such as:
- ISO 5609
- TS 16949
- ISO 14001
- OHSAS 18001
- ISO 9001
- ISO 8062
- DIN 2768
- ISO 286-2
- DIN 1697
What Tooling Will You Require When Performing Metal Turning?
The tooling that you need for metal turning is normally a cutting tool that is sharp and pointed.
This can be one metal piece of long rectangular tools with sharp inserts on one end.
The inserts differ in shape and size but generally come in diamond, triangle, and square shapes.
Besides, you will attach the cutting tools in turrets and feed them to the revolving workpiece to slide away metal.
Some of the toolings you can find in the market include:
- Form tools
- Cutoff tools
- Style A whose lead-angle of the turning tool is at 0 degrees.
- Style B whose lead-angle of the turning tool is at 15 degrees.
- Style C whose square nose tool is at 0 degrees.
- Style D whose pointed-nose tool angle is at 80 degrees.
- Style E whose pointed-nose tool angle is at 60 degrees.
Furthermore, you can identify the tool as either left or right-handed which describes their movement when cutting the workpiece.
Also, you can use live tooling containing several cutting points with sharp teeth on the external part.
Here are some popular tool materials that you can use:
- Carbon steel
- Cobalt high-speed steel
- High-speed steel
What Specifications Should A Metal Turning Machine Include?
Include the following parameters when you are specifying the metal turning machine:
- The length that is between the two centers
This is the measurement of the total workpiece length that you can fix between the centers of the lathe.
- Pitch of the leadscrew
- The height of the center part
This is the distance that exists between the bed lathe and the axis lathe.
- The swing diameter above the bed
This is the maximum workpiece diameter that you can turn on the metal turning machine without it contacting the bed.
- The maximum diameter of the bar
This is the maximum workpiece diameter that you can fit via the hole within the headstock.
Other specifications that are worth considering include the following:
- Revolutions per minute and the motor horsepower
- Travel of the tailstock sleeve
- Metric thread pitch
- Shipping configurations such as length, height, width, and weight
What Factors Will Affect The Cost Of Purchasing A Metal Turning Machine?
These include the following:
Mini metal turning machines use less material compared to engine metal turning machines.
For this reason, the mini version is cost-effective while large versions are costly.
Also, ensure you select not the cheapest metal turning machine, but the one that will fit your work area.
The function that the metal turning machine supports is a vital factor to consider during purchasing.
A metal turning machine with several functions will fetch a higher price than those lacking such functions.
For instance, some contain the heat, gear, and cutting machines that are available in other metal turning machines and lack in others.
A more capable metal turning machine costs more than that with standard features.
What Safety Precautions Should You Undertake When Performing Metal Turning?
Metal turning product
Safety is an important factor to consider when operating a metal turning machine.
Here are some safety precautions to take:
Wear The Correct Gear
These entail safety goggles, ear protectors, gloves, etc.
Inspect The Guards And Shields
Ensure all parts are in good working condition before operating the machine.
Ensure The Tools Are Sharp
Dull tools are ineffective and hazardous to operate therefore, ensure they are always sharp.
Turn Off The Machine Before Making Adjustments
Never adjust the metal turning machine while it is still operating.
Remove the power source before maintaining the machine.
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