1. Overview

Material Removal refers to a group of manufacturing processes that create the desired shape, dimensions, precision, and surface quality by removing unnecessary material. While Forming creates shape by deforming material, Material Removal completes parts by removing material through cutting, grinding, electrical discharge, cutting-off, and related processes.

Material Removal is one of the most widely used process groups in machine-part manufacturing. It can produce many different geometries without molds or dies, and it can achieve high precision and good surface quality. For this reason, it is especially important for prototypes, low-volume production, precision parts, and post-machining operations.

Representative Material Removal processes include the following.

• Turning

• Milling

• Drilling

• Boring

• Reaming

• Tapping

• Broaching

• Grinding

• Electrical Discharge Machining

• Laser cutting

• Waterjet cutting

• Saw cutting

• Honing

• Lapping

The core of Material Removal is not simply “cutting material away.” It is a design-driven manufacturing process that requires simultaneous consideration of tool access, datum surfaces, clamping, cutting conditions, tool rigidity, machining sequence, surface roughness, tolerance, thermal distortion, chip evacuation, and inspectability.

2. Role of Material Removal

The core role of Material Removal is to secure the final geometry and precision of a part.

Parts made by Primary Shaping or Forming may already have a basic shape, but precision functional surfaces such as bearing mounting surfaces, shaft diameters, locating holes, sealing surfaces, and LM guide mounting surfaces often require additional machining. In such cases, Material Removal provides the accuracy required for functionally important surfaces.

The role of Material Removal can be summarized as follows.

• Creates the desired shape from raw stock.

• Post-machines functional surfaces of cast, forged, welded, or molded parts.

• Secures high dimensional accuracy and geometric accuracy.

• Creates datum surfaces, datum axes, and locating structures.

• Machines holes, grooves, slots, pockets, threads, planes, and cylindrical surfaces.

• Secures surface roughness and functional surface quality.

• Creates assembly references and inspection references.

• Responds flexibly to prototypes and low-volume production.

For example, a cast housing may have its outer form produced by casting, while bearing bores, bolting surfaces, and datum surfaces are finished by CNC machining. A welded frame may distort after welding, so LM guide mounting surfaces and reference surfaces are post-machined to secure precision.

Therefore, Material Removal is not merely a cutting process. It is a core manufacturing method that completes the functional accuracy of a part.

3. Basic Principle of Material Removal

Material Removal uses a tool or energy source to remove part of a material. Depending on the process, material may be cut, ground, melted, vaporized, or eroded.

The basic process flow is as follows.

Material preparation
→ Datum surface setup
→ Clamping
→ Application of tool or machining energy
→ Material removal
→ Formation of dimensions and surface
→ Deburring and cleaning
→ Inspection

Material preparation
→ Datum surface setup
→ Clamping
→ Application of tool or machining energy
→ Material removal
→ Formation of dimensions and surface
→ Deburring and cleaning
→ Inspection

Important elements in Material Removal are as follows.

The common principles of Material Removal are as follows.

• The tool must be able to access the area to be machined.

• The part must be clamped stably.

• Datum surfaces and datum axes must be clear.

• Deep and narrow features must consider tool rigidity and vibration.

• Internal sharp right-angle corners cannot be made directly with rotating tools.

• Dimensional accuracy and surface roughness must be specified within process capability.

• Burrs, chips, and contamination must be removed after machining.

4. Classification of Representative Processes

Material Removal can be divided into several processes according to material removal method and tool motion.

All of these processes remove material, but their applicable geometries and design criteria differ. Turning is suitable for rotationally symmetric shapes, while milling is suitable for planes and complex geometry. Grinding is used when precision and surface quality are required, and EDM is advantageous for hard materials or complex internal shapes.

5. Turning

Turning is a process that creates cylindrical geometry by rotating the workpiece and moving a cutting tool. It is widely used to manufacture rotational parts such as shafts, pins, bushings, pulleys, rollers, threads, and cylindrical housings.

Representative turning operations include the following.

• Outer diameter turning

• Inner diameter turning

• Facing

• Grooving

• Threading

• Parting

• Taper turning

• Combined turning operations

The advantages of turning are as follows.

• Very efficient for cylindrical parts.

• High concentricity and cylindricity can be achieved.

• Outer diameters, inner diameters, faces, grooves, and threads can be machined on one machine.

• Suitable for precision shafts and rotating parts.

The limitations of turning are as follows.

• Mainly suitable for rotationally symmetric geometry.

• Long parts may experience deflection and vibration.

• Thin-walled parts may deform during clamping.

• Complex non-rotational features require additional milling.

Designers should consider the following items.

• Chucking reference

• Possibility of center support

• Tool access direction

• Undercuts

• Edge radii

• Thread relief

• Machining sequence

• Vibration and deflection

• Concentricity and cylindricity

• Surface roughness

• Need for post-heat treatment and grinding

In shaft design, bearing mounting areas, seal contact areas, snap-ring grooves, keyways, and threaded sections each have different machining requirements. Bearing mounting areas may require precision tolerances and surface quality, while seal contact areas require proper roughness and hardness.

Long shafts are prone to deflection and vibration during machining, so center support, steady rests, and machining sequence must be considered.

6. Milling

Milling is a process that machines planes, grooves, pockets, slots, and three-dimensional surfaces using a rotating cutting tool. It is one of the most widely used Material Removal processes in CNC machining.

Representative milling operations include the following.

• Face milling

• End milling

• Pocket machining

• Slot machining

• Contour machining

• 3D surface machining

• Side machining

• 5-axis machining

The advantages of milling are as follows.

• Many different geometries can be machined.

• Complex parts can be produced without molds.

• Suitable for prototypes and low-volume production.

• High positional accuracy can be achieved.

• Multiple surfaces can be machined sequentially.

The limitations of milling are as follows.

• Internal features with poor tool access are difficult to machine.

• Internal sharp right-angle corners cannot be made with rotating tools.

• Deep and narrow pockets cause tool vibration and deflection.

• Multiple setups increase accumulated error.

• Long machining time increases cost.

Designers should consider the following items.

• Tool access

• Internal corner radius

• Pocket depth

• Slot width

• Clamping direction

• Datum surface setup

• Number of setups

• Tool length

• Chip evacuation

• Machining sequence

• Surface roughness

• Tolerance specification

One of the most important points in CNC milling design is the internal corner. An end mill is a round tool, so it cannot directly produce an internal sharp right-angle corner. Therefore, internal corners must have a radius equal to or larger than the tool radius.

Requirement for internal sharp right-angle corner
→ Not possible with ordinary end milling
→ EDM or additional process required
→ Machining cost increases

Requirement for internal sharp right-angle corner
→ Not possible with ordinary end milling
→ EDM or additional process required
→ Machining cost increases

Deep pockets require long tools, and long tools have low rigidity, making vibration and dimensional error more likely. Therefore, the ratio between pocket depth and width should be properly limited, and tool access directions should be simplified as much as possible.

7. Drilling, Boring, Reaming, and Tapping

Hole machining is a very important area in Material Removal. Most machine parts require holes for fastening, positioning, bearing mounting, fluid flow, wiring, or sensor mounting.

7.1 Drilling

Drilling is the basic process of creating holes using a drill tool.

Designers should consider the following items.

• Hole depth

• Hole diameter

• Through hole or blind hole

• Chip evacuation

• Drill entry surface

• Drill exit surface

• Positional accuracy

• Burr formation

Deep holes make chip evacuation difficult and can cause drill deflection. Therefore, holes with a large depth-to-diameter ratio must be reviewed for machinability.

7.2 Boring

Boring is a process that enlarges or improves the accuracy of an existing hole. It is used for bearing bores, precision internal diameters, and housing holes.

Boring is suitable under the following conditions.

• High positional accuracy is required.

• Internal diameter tolerance is important.

• Cylindricity and concentricity are required.

• Holes made by casting or drilling must be made more precise.

7.3 Reaming

Reaming is a process that improves the dimensional accuracy and surface quality of a drilled hole. It is used for locating pin holes and precision fitting holes.

Designers must leave appropriate machining allowance in the drilled hole before reaming.

7.4 Tapping

Tapping is a process that creates internal threads inside a hole. It is very important in bolted fastening structures.

Designers should consider the following items.

• Thread diameter

• Thread pitch

• Thread engagement length

• Extra depth for blind holes

• Possibility of tap breakage

• Tappability of the material

• Fastening direction

• Repeated disassembly

Blind tapped holes require additional drilling depth beyond the actual thread depth. In soft materials or plastics, insert nuts or helicoils may be required.

8. Grinding

Grinding is a precision machining process that removes material in small amounts using a high-speed rotating grinding wheel. It is used for parts requiring high dimensional accuracy, geometric accuracy, and surface quality.

Representative grinding processes include the following.

• Surface grinding

• Cylindrical grinding

• Internal grinding

• Centerless grinding

• Profile grinding

• Tool grinding

• Gear grinding

The advantages of grinding are as follows.

• High dimensional accuracy can be achieved.

• Good surface roughness can be obtained.

• High-hardness materials can be machined after heat treatment.

• Useful for improving cylindricity, flatness, and parallelism.

• Suitable for finishing precision functional surfaces.

The limitations of grinding are as follows.

• Material removal rate is not high.

• Machining time can be long.

• Damage from grinding heat may occur.

• Grinding burn, microcracks, and thermal distortion must be controlled.

• Proper grinding allowance is required.

Designers should consider the following items.

• Grinding allowance

• Required surface roughness

• Distortion after heat treatment

• Grinding datum surface

• Cooling conditions

• Grinding direction

• Edge treatment

• Geometric accuracy

• Measurement method

• Distinction between functional and non-functional surfaces

For example, the bearing mounting area of a heat-treated shaft is often turned first, heat-treated, and then ground to secure final dimensions and surface quality. LM guide mounting surfaces or precision sliding surfaces can also be ground to improve flatness and roughness.

9. Electrical Discharge Machining, EDM

Electrical Discharge Machining, EDM is a process that removes material using electrical discharges generated between an electrode and a workpiece. Because the tool does not mechanically cut the workpiece, EDM is advantageous for hard materials and complex shapes.

Representative EDM methods include the following.

• Wire EDM

• Sinker EDM

• Small-hole EDM

The advantages of EDM are as follows.

• Hard materials can be machined.

• Complex internal shapes can be produced.

• Narrow slots and precision contours can be machined.

• Mechanical cutting force is low.

• Suitable for machining heat-treated molds and precision parts.

The limitations of EDM are as follows.

• It is applicable only to conductive materials.

• Machining speed may be slow.

• A heat-affected layer may form on the surface.

• Electrode manufacturing may be required.

• Cost may be higher than ordinary cutting.

Designers should consider the following items.

• Electrical conductivity of the material

• Machining geometry

• Electrode access

• Wire start hole

• Corner radius

• Surface quality

• Heat-affected layer

• Need for post-polishing

• Machining time

• Cost

Wire EDM is suitable for mold plates, precision slots, gear profiles, and complex 2D contours. Sinker EDM is used for deep grooves, internal corners, and mold cavities that are difficult to produce with ordinary milling.

10. Broaching

Broaching is a process that removes material using a broach tool with multiple cutting teeth arranged progressively. With one linear motion, it can create keyways, splines, polygonal holes, and special internal profiles.

The advantages of broaching are as follows.

• Repeatability is good.

• Productivity is high.

• Suitable for internal keyways and splines.

• Surface quality is relatively good.

• Advantageous for mass production of identical shapes.

The limitations of broaching are as follows.

• Dedicated tool cost is high.

• Shape changes are difficult.

• It may be uneconomical for low-volume production.

• Tool length and machine size impose restrictions.

• Space is required for the broach to pass through.

Designers should consider the following items.

• Broach pass direction

• Machined profile

• Tool manufacturability

• Starting hole

• Cutting allowance

• Machinability of the material

• Burr formation

• Tool wear

• Production volume

Broaching is widely used for internal splines of gears, pulley keyways, coupling grooves, and precision repeated internal profiles. However, because a dedicated tool is required, it is economical only when production volume is sufficient.

11. Laser Cutting and Waterjet Cutting

11.1 Laser Cutting

Laser cutting is a process that cuts material by melting or vaporizing it with a high-energy laser beam. It is widely used for sheet cutting, complex 2D contours, and low-volume, high-mix production.

The advantages of laser cutting are as follows.

• Complex 2D shapes can be cut quickly.

• Cutting is possible without molds or dies.

• Kerf width is narrow.

• Automation is easy.

• It connects well with sheet-metal fabrication.

The limitations of laser cutting are as follows.

• A heat-affected zone occurs.

• Thick plates have limitations.

• Cut surface quality varies depending on material and thickness.

• Burrs or oxide layers may occur.

11.2 Waterjet Cutting

Waterjet cutting is a process that cuts material using high-pressure water and abrasive particles. Since it has almost no thermal effect, it can be applied to composites, rubber, plastics, ceramics, and metal sheets.

The advantages of waterjet cutting are as follows.

• Thermal effect is low.

• Various materials can be cut.

• Thick materials can be cut.

• Distortion is low.

• Useful for cutting composites.

The limitations of waterjet cutting are as follows.

• Cutting speed may be slow.

• Taper may appear on the cut surface.

• Precision may be lower than post-machining.

• Water and abrasive disposal must be handled.

Laser cutting and waterjet cutting are often used not as final precision machining processes, but as initial sheet cutting, flat-pattern part production, or preparation processes before welding.

12. Design Criteria for Material Removal

The first thing designers must consider in Material Removal is whether the tool can actually access the intended geometry.

The main design criteria are as follows.

12.1 Tool Access

If the tool cannot access the machining location, the geometry cannot be produced by ordinary machining. Deep internal grooves, blind internal corners, and long narrow pockets have poor machinability.

Tool access impossible
→ Ordinary machining impossible
→ Special process required
→ Cost increases
→ Lead time increases

Tool access impossible
→ Ordinary machining impossible
→ Special process required
→ Cost increases
→ Lead time increases

12.2 Internal Corner Radius

Rotating tools are circular, so they cannot produce internal sharp right-angle corners. Internal corners must have a radius equal to or larger than the tool radius.

12.3 Datum Surfaces and Datum Axes

In precision machining, datum surfaces and datum axes must be clear. If the datums are unclear, the machining sequence, inspection criteria, and assembly references become unstable.

12.4 Clamping

The part must be fixed so that it does not move under cutting forces during machining. Thin parts, long parts, and asymmetric parts require consideration of clamping deformation.

12.5 Number of Setups

As the number of setups increases, machining time and accumulated error increase. A structure that can be machined from one direction or with minimal setups is preferable.

12.6 Tolerance and Surface Roughness

Tolerance and surface roughness should be specified strictly only where function requires them. Unnecessary precision increases machining and inspection costs.

12.7 Chip Evacuation and Burr Removal

Chip evacuation is important in holes, grooves, and pockets. Burrs also occur after cutting, so deburring feasibility must be considered during design.

13. Cutting Conditions and Machining Quality

The quality of Material Removal is strongly affected by cutting conditions.

Representative cutting conditions include the following.

• Cutting speed

• Feed rate

• Depth of cut

• Tool material

• Tool geometry

• Coolant use

• Clamping rigidity

• Machine rigidity

• Tool wear condition

If cutting conditions are inappropriate, the following problems may occur.

• Poor surface roughness

• Dimensional error

• Increased tool wear

• Tool breakage

• Vibration

• Chatter marks

• Thermal distortion

• Work hardening

• Increased burr formation

Even if designers do not directly set cutting conditions, they must judge whether the design geometry makes cutting conditions difficult. For example, overly deep pockets, thin walls, long protrusions, and narrow slots can reduce tool rigidity and increase vibration.

14. Defects and Quality Issues

In Material Removal processes, various quality problems can occur due to cutting force, heat, vibration, tool wear, and clamping deformation.

Representative defects include the following.

These problems are not caused only by production-floor conditions. They are directly connected to design geometry, tolerance specification, datum setup, tool access, and clamping feasibility.

15. Material Removal and Post-Processing

After Material Removal, post-processing is often required to secure part function and quality.

Representative post-processing operations include the following.

• Deburring

• Cleaning

• Polishing

• Heat treatment

• Surface treatment

• Rust prevention

• Dimensional inspection

• Geometric inspection

• Surface roughness inspection

• Pre-assembly cleaning

After cutting, burrs and chips may remain. Especially in food machinery, hydraulic parts, pneumatic parts, bearing housings, and sealing components, residual chips and burrs can cause functional problems.

Machining completed
→ Deburring
→ Cleaning
→ Inspection
→ Surface treatment or assembly

Machining completed
→ Deburring
→ Cleaning
→ Inspection
→ Surface treatment or assembly

Post-processing feasibility must be considered during design. The inside of narrow grooves or blind holes is difficult to deburr and clean, so the structure should be designed to prevent contamination or chips from remaining.

16. Production Volume and Economic Feasibility

Material Removal is very suitable for prototypes, one-off parts, and low-volume production because it can be performed flexibly without molds or dies. However, since machining time is directly connected to cost, it can become expensive in mass production.

The relationship between production volume and Material Removal can be summarized as follows.

Low production volume
→ No mold or die cost
→ CNC machining is advantageous

High production volume
→ Machining time accumulates as cost
→ Primary shaping, forging, injection molding, or pressing followed by minimal machining is advantageous

Low production volume
→ No mold or die cost
→ CNC machining is advantageous

High production volume
→ Machining time accumulates as cost
→ Primary shaping, forging, injection molding, or pressing followed by minimal machining is advantageous

When selecting Material Removal, the following cost elements should be reviewed.

• Material cost

• Machining time

• Tool cost

• Setup time

• Machine usage cost

• Operator skill

• Inspection time

• Deburring and cleaning cost

• Required tolerance level

• Required surface roughness level

• Defect rate

• Post-processing cost

In the prototype stage, Material Removal is often the most reasonable method. However, when the same part is produced repeatedly, it may be more economical to create the basic shape by casting, forging, extrusion, or pressing, and then machine only the precision functional surfaces.

17. Application of Material Removal in Food Machinery

In food machinery and meat-processing machinery, Material Removal is widely used for stainless steel parts, food-grade plastic parts, shafts, housings, brackets, guides, nozzles, fastening areas, and sealing surfaces.

Representative applications include the following.

• Stainless steel shafts

• Food-grade POM and UHMW-PE guides

• Bearing housings

• Sealing surfaces

• Nozzles

• Cutter holders

• Brackets

• Locating pin holes

• Hygienic fastening areas

• Parts for disassembly and cleaning

When applying Material Removal to food machinery, the following should be considered.

• Surface roughness of food-contact surfaces

• Deburring feasibility

• Cleanability

• Prevention of residual chips

• Removal of sharp edges

• Precision of sealing surfaces

• Burrs and wear particles during plastic machining

• Surface discoloration and contamination after stainless steel machining

• Need for electropolishing or passivation

• Disassembly and maintainability

For food-contact parts, dimensional accuracy alone is not sufficient. If fine burrs or chips remain on the surface, they can cause foreign-material contamination and poor cleaning. Therefore, the design should include deburring, cleaning, and surface treatment after machining.

18. Connection with Other Knowledge Tracks

Material Removal is closely connected with other Knowledge Tracks.

18.1 Connection with Material

Machinability, tool wear, surface quality, burr formation, and thermal distortion vary depending on the material.

Material
→ Determines machinability, hardness, thermal conductivity, and burr formation characteristics

Material Removal
→ Secures geometry and precision with tools and machining conditions suitable for the material

Material
→ Determines machinability, hardness, thermal conductivity, and burr formation characteristics

Material Removal
→ Secures geometry and precision with tools and machining conditions suitable for the material

18.2 Connection with Mechanism & Motion

Moving parts require precise dimensions and surface quality. Shafts, bearing bores, sliding surfaces, cams, and gears strongly depend on Material Removal.

Mechanism & Motion
→ Defines rotation, linear motion, contact, and friction conditions

Material Removal
→ Secures dimensions and surface quality required for motion performance

Mechanism & Motion
→ Defines rotation, linear motion, contact, and friction conditions

Material Removal
→ Secures dimensions and surface quality required for motion performance

18.3 Connection with Assembly

Material Removal creates assembly datum surfaces, locating holes, fastening surfaces, and tapped holes. Therefore, it directly affects assembly and tolerance stack-up.

Material Removal
→ Forms datum surfaces, fastening surfaces, and locating holes

Assembly
→ Applies positioning, fastening, assembly sequence, and tolerance stack-up

Material Removal
→ Forms datum surfaces, fastening surfaces, and locating holes

Assembly
→ Applies positioning, fastening, assembly sequence, and tolerance stack-up

18.4 Connection with Manufacturing Quality

Material Removal directly determines dimensions, surfaces, and geometric accuracy, so it is closely connected with inspection criteria.

Material Removal
→ Generates dimensions, surface roughness, and geometric accuracy

Manufacturing Quality
→ Performs dimensional inspection, surface inspection, geometric inspection, and functional inspection

Material Removal
→ Generates dimensions, surface roughness, and geometric accuracy

Manufacturing Quality
→ Performs dimensional inspection, surface inspection, geometric inspection, and functional inspection

19. Core Thinking

The core thinking in Material Removal is as follows.

Removing material increases geometric freedom, but it also increases machining time and cost.

A shape that the tool cannot access cannot be made by ordinary machining.

Internal sharp right-angle corners cannot be directly machined with rotating tools.

Deep and narrow pockets create tool vibration and dimensional error.

Precision begins with datum surfaces and clamping.

The more setups are required, the more accumulated error and cost increase.

Tolerance and surface roughness should be strictly applied only where function requires them.

Burrs and chips after machining can cause functional failure and contamination.

Precision areas after heat treatment may require grinding or post-machining.

Material Removal is advantageous for prototypes and low-volume production, but in mass production it may be more economical to combine it with basic shaping processes.

Good Material Removal design considers machinability, datum setup, tolerance, surface quality, assembly, and inspectability at the same time.

20. Conclusion

Material Removal is a group of manufacturing processes that create the desired shape, dimensions, precision, and surface quality by removing unnecessary material. Processes such as turning, milling, drilling, boring, reaming, tapping, grinding, and EDM play a very important role in machine-part manufacturing.

However, Material Removal is not simply a process of cutting material away. Designers must consider tool access, datum surfaces, clamping, number of setups, internal corner radii, tolerances, surface roughness, chip evacuation, burr removal, thermal distortion, and inspectability together.

From the mechanical design perspective, the key points of Material Removal are as follows.

• Can the tool actually access the geometry?

• Can the part be clamped stably?

• Are datum surfaces and datum axes clear?

• Are internal corners and deep pockets machinable?

• Are the required tolerances and surface roughness within process capability?

• Can burrs and chips be removed after machining?

• Which process will finish the precision functional surfaces?

• Is the balance between production volume and machining cost appropriate?

Therefore, Material Removal is a core section in the Manufacturing Track for completing precision geometry and functional surfaces. It naturally connects with Primary Shaping, Forming, Surface Engineering, Finishing, Assembly, and Manufacturing Quality as part of a complete manufacturing knowledge system.