👷🏼‍♂️Intro to Mechanical Prototyping Unit 5 – Subtractive Manufacturing Techniques

Key Concepts

• Subtractive manufacturing involves removing material from a larger workpiece to create the desired shape or form
• Utilizes various cutting tools and machines to remove material through processes like milling, turning, drilling, and grinding
• Requires careful planning and design to ensure efficient material removal and minimize waste
• Suitable for a wide range of materials, including metals, plastics, and composites
• Enables the production of high-precision parts with tight tolerances and smooth surface finishes
• Offers flexibility in terms of part complexity and the ability to create internal features and cavities
• Requires skilled operators and technicians to set up and operate the machines and tools effectively

Historical Context

• Subtractive manufacturing has been used for centuries, with early examples including woodworking and stone carving
• The invention of the lathe in ancient times revolutionized the production of cylindrical parts and shapes
• The Industrial Revolution in the 18th and 19th centuries saw the development of more advanced machine tools like milling machines and drill presses
• The introduction of computer numerical control (CNC) in the 1950s and 60s greatly enhanced the precision and automation of subtractive manufacturing processes
• Advancements in cutting tool materials and coatings have improved the efficiency and capabilities of subtractive manufacturing over time
• The rise of additive manufacturing in recent decades has complemented subtractive manufacturing, but has not replaced it entirely

Types of Subtractive Manufacturing

• Milling involves using a rotating cutting tool to remove material from a workpiece, creating flat surfaces, slots, and complex shapes
  • Vertical milling machines have a vertically-oriented spindle and are used for general-purpose machining
  • Horizontal milling machines have a horizontally-oriented spindle and are often used for larger or heavier workpieces
• Turning uses a single-point cutting tool to remove material from a rotating workpiece, creating cylindrical and conical shapes
  • Lathes are the primary machines used for turning operations
  • Turning can produce parts like shafts, bushings, and threaded components
• Drilling creates cylindrical holes in a workpiece using a rotating drill bit
  • Drill presses are commonly used for manual drilling operations
  • CNC drilling machines offer automated and precise hole placement
• Grinding uses an abrasive wheel to remove small amounts of material and improve surface finish
  • Surface grinding creates flat surfaces
  • Cylindrical grinding is used for round parts
• Other subtractive processes include boring, broaching, and sawing

Tools and Equipment

• Cutting tools are the primary implements used in subtractive manufacturing to remove material from the workpiece
  • Milling cutters include end mills, face mills, and slot drills
  • Turning tools include single-point cutting tools made from high-speed steel or carbide
  • Drill bits come in various sizes and types, such as twist drills and core drills
• Machine tools are the powered machines that hold and move the cutting tools and workpiece
  • Milling machines, lathes, drill presses, and grinding machines are common examples
  • CNC machines are computer-controlled and offer high precision and automation
• Workholding devices secure the workpiece in place during machining operations
  • Vises, clamps, chucks, and fixtures are used depending on the part geometry and machine type
• Measuring tools ensure that parts are machined to the correct dimensions and tolerances
  • Calipers, micrometers, and gauges are used for manual measurements
  • Coordinate measuring machines (CMMs) provide automated and precise measurements

Materials and Properties

• Subtractive manufacturing can process a variety of materials, each with unique properties and machining requirements
• Metals are commonly machined using subtractive processes
  • Steels, aluminum alloys, and titanium are popular choices for their strength and durability
  • Machinability varies based on factors like hardness, ductility, and thermal conductivity
• Plastics can also be machined using subtractive techniques
  • Thermoplastics like acrylic, nylon, and polycarbonate are easier to machine than thermosets
  • Plastics may require special cutting tools and lower cutting speeds to avoid melting or deformation
• Composites, such as carbon fiber reinforced polymers (CFRP), can be machined but require careful consideration of fiber orientation and cutting parameters
• Ceramics and glass are more brittle and harder to machine, often requiring diamond-tipped tools and special techniques
• Material properties like hardness, toughness, and thermal stability affect the choice of cutting tools, speeds, and feeds

Process Overview

• Subtractive manufacturing begins with the creation of a digital 3D model of the desired part using computer-aided design (CAD) software
• The CAD model is then translated into machine-readable code, typically G-code, using computer-aided manufacturing (CAM) software
  • CAM software helps to plan the tool paths, cutting parameters, and machining strategies
• The workpiece material is selected and cut to the appropriate size for the machine tool being used
• The workpiece is securely fixed to the machine tool using workholding devices
• Cutting tools are selected based on the material, part geometry, and desired surface finish
  • Tools are mounted in the machine spindle or turret
• The machine tool is set up with the proper cutting parameters, such as spindle speed, feed rate, and depth of cut
• The machining process is initiated, and the cutting tool removes material from the workpiece according to the programmed tool paths
• Coolant may be used to manage heat and remove chips during the machining process
• After machining, the part is removed from the machine, cleaned, and inspected for accuracy and quality

Design Considerations

• Part geometry and complexity influence the choice of subtractive manufacturing processes and machines
  • Complex shapes may require multiple setups or specialized cutting tools
  • Internal features and cavities may be more challenging to machine than external features
• Tolerances and surface finish requirements affect the machining parameters and cutting tool selection
  • Tighter tolerances may necessitate slower cutting speeds and multiple passes
  • Smoother surface finishes may require finer cutting tools or additional finishing processes
• Material properties, such as hardness and machinability, impact the cutting tool selection and machining parameters
  • Harder materials may require more robust cutting tools and slower cutting speeds
  • Materials with poor machinability may produce more heat and wear on the cutting tools
• Design for manufacturability (DFM) principles should be applied to optimize parts for subtractive manufacturing
  • Avoid unnecessary complexity and tight tolerances where possible
  • Consider the limitations and capabilities of the available machine tools and processes
  • Incorporate features that facilitate workholding and tool access
• Cost and lead time are important factors to consider when designing for subtractive manufacturing
  • Simplifying part geometry and using standard tools and processes can help reduce costs and lead times
  • Minimizing material waste and optimizing tool paths can improve efficiency and sustainability

Applications and Examples

• Subtractive manufacturing is used in a wide range of industries, from aerospace and automotive to medical and consumer products
• In the aerospace industry, subtractive processes are used to create complex parts like turbine blades, landing gear components, and structural elements
  • Materials like titanium and high-strength alloys are commonly used
  • Tight tolerances and high surface quality are often required
• The automotive industry relies on subtractive manufacturing for engine components, transmission parts, and body panels
  • High-volume production and cost efficiency are key considerations
  • CNC machining centers and transfer lines are often employed
• Medical device manufacturing utilizes subtractive processes for implants, surgical instruments, and diagnostic equipment
  • Biocompatible materials like stainless steel and titanium are frequently used
  • Precision and surface finish are critical for patient safety and device performance
• Consumer products, such as electronics housings, sporting goods, and household items, are often produced using subtractive manufacturing
  • Plastics and aluminum are common material choices
  • Rapid prototyping and low-volume production are possible with CNC machining

Safety and Best Practices

• Proper personal protective equipment (PPE) should be worn when operating subtractive manufacturing equipment
  • Safety glasses, hearing protection, and closed-toe shoes are essential
  • Avoid loose clothing or jewelry that could get caught in moving parts
• Machine tools should be properly guarded and equipped with emergency stop buttons
  • Follow lockout/tagout procedures when performing maintenance or adjustments
• Cutting tools should be kept sharp and in good condition to ensure safe and efficient operation
  • Dull or damaged tools can cause excessive heat, vibration, and poor surface quality
• Workpieces should be securely clamped and supported to prevent movement during machining
  • Improperly secured workpieces can be ejected from the machine, causing injury or damage
• Coolant and lubricant systems should be maintained and used appropriately
  • Coolant helps to manage heat and remove chips, prolonging tool life and improving surface finish
  • Proper ventilation and filtration are necessary to minimize exposure to coolant mist and vapors
• Chips and debris should be regularly cleaned from the machine and surrounding area
  • Accumulation of chips can interfere with machine operation and pose a slipping hazard
• Follow manufacturer guidelines and recommended cutting parameters for each material and tool combination
  • Exceeding recommended speeds and feeds can lead to tool breakage, machine damage, and safety hazards

Advantages and Limitations

• Advantages of subtractive manufacturing include:
  • Ability to produce high-precision parts with tight tolerances
  • Wide range of materials can be processed, including metals, plastics, and composites
  • Suitable for both low-volume prototyping and high-volume production
  • Established and well-understood processes with a large knowledge base
  • Capable of creating complex geometries, internal features, and smooth surface finishes
• Limitations of subtractive manufacturing include:
  • Material waste can be significant, as material is removed rather than added
  • Some complex geometries and internal features may be difficult or impossible to create
  • Setup times can be lengthy, especially for complex parts or multiple operations
  • Skilled operators and technicians are required to program and operate machine tools
  • High capital investment in machine tools and equipment
  • Limited ability to create parts with variable material properties or gradients

Future Trends

• Integration of additive and subtractive manufacturing processes in hybrid machines
  • Combines the benefits of both technologies for greater design flexibility and efficiency
• Increased adoption of high-performance cutting tools and coatings
  • Improves machining efficiency, tool life, and surface quality
  • Enables the processing of harder and more challenging materials
• Advancements in machine tool design and performance
  • Higher spindle speeds, increased rigidity, and improved motion control
  • Multi-axis machines and multi-tasking capabilities for reduced setup times
• Expanded use of automation and robotics in subtractive manufacturing
  • Automated part handling, tool changing, and inspection
  • Collaborative robots working alongside human operators
• Growing emphasis on sustainable and eco-friendly machining practices
  • Minimizing energy consumption and waste generation
  • Recycling and reusing cutting fluids and metal chips
• Continued development of CAD/CAM software and simulation tools
  • Improved tool path optimization and collision avoidance
  • Integration of artificial intelligence and machine learning for process optimization