Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

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Similarly to casting, CNC machining can be a suitable option for producing large parts. This is because it requires less of a controlled environment than 3D printing and there’s a wide range of machine sizes available, in addition to lathes and milling machines capable of producing very large parts.

This is because casting benefits from higher economies of scale. As the quantity of parts increases, the fixed cost of producing a casting mould – which can be very expensive – can be allocated across many parts. With metal 3D printing variable costs are the main cost drivers, meaning the unit cost is not as dependent on the production quantities.

Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

Understanding these relationships and applying some creative thought can provide significant gains in efficiency. I will discuss how to take advantage of these relationships in my next column. CTE

Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.

Cutting speed calculations might well be the most important ones. They are easy to use and, with a little explanation, easy to understand. The cutting speed of a tool is expressed in surface feet per minute (sfm) or surface meters per minute (m/min.). Similar to mph for a car, sfm is the linear distance a cutting tool travels per minute. To get a better sense of scale, 300 sfm, for example, converts to 3.4 mph.

CNC printingservices

There’s no clear winner when comparing metal 3D printing with casting and CNC. Each technique has several pros and cons that need to be addressed concerning the task at hand.

So what is this telling us? Let’s say a 1"-dia. tool must run at 100 sfm. Based on the equation, that tool must turn at 382 rpm to achieve 100 sfm: 100 ÷ 1 × 3.82 = 382.

However, CNC machining still offers superior dimensional accuracy – capable of achieving tolerance of +/-0.001mm – which is significantly better than both casting and metal 3D printing. For this reason, both casted and printed parts often undergo post-process machining to achieve design specification requirements.

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In basic terms, casting is the manufacturing process where a liquid material is deposited into a mould of the desired shape then left to solidify. It’s a traditional method of manufacturing that dates back to the middle ages. We’ve compared casting with metal 3D printing based on several factors.

Metal 3D printing is still the best method when producing intricate parts with fine features. Not only this, but metal 3D printing can also produce lightweight structures and internal cavity profiles that would be impossible to produce using CNC machining.

Another way to consider this concept is to think about the distance the 1" tool would travel were it to make 382 revolutions across the shop floor. In that scenario, it would travel 100'; do it in 60 seconds and it would be traveling 100 sfm.

However, innovations within additive manufacturing could mean the size of parts produced by 3D printing could increase in time. Direct energy deposition (DED) is a 3D printing process that can print larger parts. Due to the use of a robotic arm, a DED printer isn’t limited to a specific part size. This could mean if a large, complex part is required, metal 3D printing could meet this need.

As metal 3D printing gains popularity throughout the manufacturing industry, many are beginning to wonder whether it’ll become the preferred choice above traditional methods, such as casting and CNC machining.

Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

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In general CNC machining is slower for producing smaller production batches compared to metal 3D printing. This is because more setup time is required and depending on the hardness of the working material, the cutting process may take longer. On the other hand, metal 3D printing prints the entire part in a single run and the hardness of the material is not a determining factor of the production process.

Casting involves a number of pre-production tasks, whereas 3D printing only requires a 3D model being uploaded to the printer. In addition to this, there are typically more post-process steps involved with casting to achieve the desired material density requirements.

The overall price depends on the number of parts produced. 3D printing will be the more cost-effective option for small production batches, especially if there is a degree of design variation involved. As that quantity increases, CNC machining becomes a cheaper option in terms of unit cost. When comparing the three methods, casting would be the most suitable method for the largest quantities.

Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.

The main benefit of CNC machining is that the final machined part usually only needs post-process heat treating. In contrast, 3D printing may require post-process machining to achieve the desired tolerances on certain features.

When producing large parts, casting would be the method to choose. Generally, traditional manufacturing methods are much better at producing larger parts. This is because 3D printed parts must be printed within a controlled environment and are limited to the size of the printer´s build volume.

Because the tool diameter is measured in inches, the “feet” in sfm must be converted to inches, and because there are 12 inches in a foot, multiply sfm by 12. In addition, the circumference of the tool is found by multiplying the tool diameter by π, or 3.14 to simplify. The result is: rpm = (sfm × 12) ÷ (diameter × π) = (sfm ÷ diameter) × (12 ÷ π) = (sfm ÷ diameter) × 3.82.

In our guide, we unpack the topic of metal 3D printing, focusing on the technologies, applications and processes, as well as discuss whether it’s the future for the manufacturing industry.

What rpm and feed rate should be programmed for a 4-flute, 1" endmill, running at a recommended cutting speed of 350 sfm and a recommended chip load of 0.005 inch per tooth (ipt)? Using the equation, rpm = sfm ÷ diameter × 3.82 = 350 ÷ 1.0 × 3.82 = 1,337, the feed rate = rpm × no. of flutes × chip load = 1,337 × 4 × 0.005 = 26.74 ipm.

What is chip load? When milling, it is the amount of material that the cutting edge removes each time it rotates. When turning, it is the distance the part moves in one revolution while engaged with the tool. It is sometimes referred to as chip thickness, which is sort of true. Chip thickness can change when other parameters like radial DOC or the tool’s lead angle change.

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However, metal 3D printing only uses the amount of material needed to create a part and any excess can usually be recycled into the next build. As the world becomes increasingly invested in sustainability, this could be a determining factor for some businesses.

Angle between the side-cutting edge and the projected side of the tool shank or holder, which leads the cutting tool into the workpiece.

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Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

Feed rate for milling is usually expressed in inches per minute (ipm) and calculated using: ipm = rpm × no. of flutes × chip load.

Before we compare metal 3D printing with CNC machining, many of the advantages and disadvantages will be similar to casting, as CNC machining and casting are both types of traditional manufacturing.

Here is where things get interesting, because by changing the values in the formula, the relationships of the different variables become evident. Try applying a 2" tool instead of the 1" tool. What happens? The rpm and feed rate decrease by half.

CNC machining is when automated cutters remove material from a solid block of material to achieve the final shape. It’s one of the most popular traditional manufacturing methods, as it offers repeatability and can be used with a wide range of materials.

Cost is often the biggest crunch point when deciding whether to use traditional manufacturing or metal 3D printing. One variable will affect this answer — the number of parts required.

When considering your project, it’s crucial to think about the quantity, complexity, cost and time to help you decide on the best method.

The following equation is used to calculate spindle speed: rpm = sfm ÷ diameter × 3.82, where diameter is the cutting tool diameter or the part diameter on a lathe in inches, and 3.82 is a constant that comes from an algebraic simplifica-tion of the more complex formula: rpm = (sfm × 12) ÷ (diameter × π).

3DprintingvsCNCcost

Toolmakers recommend cutting speeds for different types of workpiece materials. When a toolmaker suggests 100 sfm, it is indicating the outside surface of the rotating tool should travel at a rate of speed equal to 100 linear feet per minute. If the tool has a circumference (diameter × π) of 12", it would need to rotate at 100 rpm to achieve 100 sfm.

It’s also worth noting the waste involved in each process here, as waste material usually comes at an expense. CNC machining is a subtractive manufacturing process, meaning the material is cut away to achieve a final part, resulting in a large amount of material waste.

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.

Similar to 3D printing, CNC machining uses a digital file to create a part. However, unlike 3D printing, the machining operations need to be programmed into the CNC machine for each production run, which can take a lot of time.

Metal 3D printing excels in printing complex parts with fine details that are often challenging to achieve using casting methods. Moreover, LPBF (Laser Powder Bed Fusion) 3D printing provides a superior surface finish resolution compared to casting.

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

If time is of the essence, then metal 3D printing is the fastest method out of the two for small batch production. The overall process is much quicker, as 3D printing requires less set-up time and no special tooling is required to produce a part.

There’s no method that always comes out above another. To progress in the future, the idea is that traditional manufacturing techniques and metal 3D printing will complement each other, filling gaps where the other falls short.

About the Author: Christopher Tate is senior advanced manufacturing engineering for Milwaukee Electric Tool Corp., Brookfield, Wis. He is based at the company’s manufacturing plant in Jackson, Miss. He has 19 years of experience in the metalworking industry and holds a Master of Science and Bachelor of Science from Mississippi State University. E-mail: chris23tate@gmail.com.

Toolmakers publish chip load recommendations along with cutting speed recommendations and express them in thousandths of an inch (millimeter for metric units). For milling and drilling operations, chip load is expressed in thousandths of an inch per flute. Flutes, teeth and cutting edges all describe the same thing and there must be at least one, but, in theory, there is no limit to the number a tool can have.

LPBF 3D printed parts commonly display superior isotropic characteristics when compared to parts produced through CNC machining. This improved isotropy can be attributed to the consistent shape and distribution of the powder raw material utilized in 3D printing. Conversely, CNC machining, which utilizes forged bar stock as the working material, often yields denser parts that may exhibit potential anisotropic behaviour due to the grain structure of the starting material.

Lathes are different, of course, because the workpiece rotates instead of the cutter. Because the formula for cutting speed is dependent on diameter, as the diameter of the workpiece decreases, rpm must increase to maintain a constant surface speed. After each circular cut on the lathe, the workpiece OD decreases or the ID increases, and it is necessary for the rpm of the part to increase to maintain the desired cutting speed. As a result, CNC manufacturers developed the constant surface footage feature for lathe controls. This feature allows the programmer to input the desired cutting speed in sfm or m/min. and the control calculates the proper rpm for the changing diameter.

Although CNC machining is generally quicker than casting for lower production volumes, casting can be a more productive method for higher volume production.

This article compares metal 3D printing with casting and CNC machining to determine which, if any, is the best method to choose.

Chip load recommendations for turning operations are most often given in thousandths of an inch per revolution, or feed per rev. This is the distance the tool advances each time the part com-pletes one rotation.

While the tool or part is spinning, the machine must know how fast to travel while the cutter is engaged in the workpiece. Feed rate is the term that describes the traverse rate while cutting.

Therefore, you need to consider the types of parts you’re producing. Metal 3D printing would be better suited to smaller parts with intricate features, such as nozzles, small impellers or parts requiring lightweight structures. Casting is more suitable for larger parts where metal can more easily flow to all sections of the mold.

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

Surface feet per minute, chip load, undeformed chip thickness and chip thinning are familiar shop terms. Over the last few weeks, however, several occurrences in our shop have made me realize there are a lot of metalworking professionals who don’t understand these terms and the calculations that go along with them. Whether you work at a small job shop or a large contract manufacturer, it is important to understand cutting tool calculations and how to use them to help drive significant efficiency gains.

Casting would be the cheaper option when producing many parts. If your order size is smaller and has more complex requirements, then metal 3D printing would be the more cost-effective route.

CNC printingnear me

Notice the vertical lines, called tool marks, on the outside of the part being turned. As the feed rate increases, the distance between the lines also increases. The chip thickness is roughly equal to the feed.

Finally, you’ll need to consider the mechanical properties required for your parts. The mechanical properties achieved through metal 3D printing vary depending on the printing technology used. Parts produced using LPBF generally outperform casted parts, thanks to their higher densities and reduced risk of internal voids. However, it’s worth noting that practically any metal material can be cast, whereas the portfolio of materials for 3D printing is still limited.

Imagine the cutting tool as a rolling ring or cylinder. The distance traveled in one revolution times rpm is its surface speed. If the circle above had a diameter of 3.82", the circumference would be 12". As a result, every revolution would produce a linear distance of 1', and a spindle speed of 100 rpm would be a cutting speed of 100 sfm.

Cutting speeds are published in sfm because the ideal cutting speed for a particular family of tools will, in theory, be the same no matter the size of the tool. The engineer, programmer or machinist is expected to calculate the rpm needed to produce the proper cutting speed for each selected tool.