ABS CNC Machining FAQ

ABS is successfully machined using either CNC milling, turning, or drilling. The material is known for high impact resistance, rigidity, and great machinability. Inasmuch as it is relatively stable, parts with thin walls may require support to prevent vibration, deflection, or chatter during machining. See the full properties of ABS here.

PC makes up for the difficulty in machining through heat resistance. It can resist up to 138^oC, leading to better heat management during machining.

CNC machining can achieve tight tolerances of ±0.02mm, which is more precise than the standard injection molding tolerance of ±0.1mm.

1. Use light cutting depths (0.5 mm to 2 mm): To reduce cutting forces and minimize the heat generated during the process.
2. Avoid excessive clamping force: It can warp the ABS part. For thin sheets, use vacuum tables or tabs and properly support the part.
3. Use sharp, polished tools to lower burr formation and friction: The recommended tool is one with a positive rake angle of 10^o to 15^o and relief angle 5^o to 10^o.

Heat accumulation during cutting can cause material softening or distortion. Eventually, when the material cools, it can shrink or warp, leading to dimensional inaccuracy. On the other hand, surface defects like chatter lines, tool marks, and a hazy appearance can occur when machined with dull tools or at improper speeds. Since the material is soft, it can also be deformed by a tight clamping force.

Some of the applications of ABS CNC machining across different industries are as follows:

• Automotive industry: Instrument panels, ドアパネル, interior dashboards, exterior mirror housings.
• Consumer electronics: Computer keyboards, mouse casings, remote control shells.
• Medical devices: Medical device housings or equipment components that require high impact resistance.
• Toys: Manufacturing durable toys like LEGO.

The right cutting tool should have low flute counts (1 or 2) to minimize heat production and prevent melting.

Milling uses a rotating tool on a stationary block to create complex shapes. Turning spins the ABS block against a stationary tool to create a cylindrical part. Drilling uses a rotating drill bit to create holes.

Besides effective heat management, other factors that will affect the success of any ABS machining project include:

1. Material selection: select machine-grade ABS, which is specifically formulated with heat stabilizers to prevent warping.
2. Use the right cutting tools: The right tool should be sharp, have a positive rake angle, use single- or double-edge end mills, and should be uncoated or have diamond coating to minimize adhesive wear.
3. Optimize speed: This helps to balance heat generation during cutting.
4. Use effective coolants: ABS is sensitive to aromatic solvents. Therefore, coolant must either be compressed air or a water-soluble, plastic-specific coolant.
5. Optimize tool path: Use climb milling instead of conventional milling to lower tool deflection for better surface finish.
6. Care with securing the workpiece: Use low clamping pressures to avoid deformation.
7. Reduce internal stress: Anneal the raw material before machining to prevent deformation and improve dimensional stability.

High-Helix drills are plastic-specific drills that effectively pull chips out of the hole to reduce heat buildup. The table below highlights the recommended tools for milling, cooling, and workholding.

Take multiple shallow passes rather than one deep cut to minimize localized heat buildup, which can lead to part deformation. Tools with diamond-like carbon coatings prevent plastic from sticking and lower friction. In most cases, a strong blast of compressed air is sufficient to blow away chips and provide cooling without the mess associated with liquid.

Machining can create non-uniform wall thickness without risk of cosmetic flaws, uneven shrinkage, or warping, which are frequently encountered in injection molding when wall thickness is uneven, leading to uneven cooling.

Post-processing is used to achieve a polished finish to increase the part’s appeal to the end users. Post-machining is needed to:

• Improve aesthetics: Minimize glare, remove tool marks, or match color, making them more suitable for consumer electronics or goods.
• Enhance functionality: Smooth mating surfaces help to achieve air-tight or water-tight seals.
• Add coating: UV coatings help to prevent yellowing and brittleness if the part is exposed to direct sunlight.

ABS emits styrene fumes when heated and releases volatile organic compounds (VOCs) during chemical treatment. Therefore, chemical bonding of all sorts must be conducted in a well-ventilated area, preferably under a fume hood or with respiratory protection.
If sanding is used for finishing, start with coarse sandpaper (120 to 200 grit) to remove large imperfections. Then move to finer grit sizes (400 to 1000) for smoothing. Wet sanding is recommended to reduce toxic dust generation and to prevent the plastic from overheating and clogging the paper.

Sanding is used to remove tool marks, scratches, or burrs left behind by the cutting tool. It creates a smooth, polished, or semi-gloss finish. Sanding and priming improve paint adhesion, notwithstanding that ABS accepts paint very well. Other post-processing techniques include:

• Bead blasting: Fine glass beads under pressure are used to produce a consistent, uniform, matte, and textured appearance.
• Electroplating or vacuum metallization: Metal coatings can be applied to ABS for both decorative (chrome-look) and functional (shielding) purposes.
• Deburring and cleaning: This is the process of removing excess material or shavings from edges, often accompanied by cleaning to remove residual dust or oils.
• Thread insertion: Metal threads are inserted into pre-drilled holes for functional assembly.

Drilling or tapping: This process adds precision holes or threading after CNC drilling.

Acetone breaks down the surface polymer chains of ABS, causing them to flow and fill in gaps. When it re-solidifies, it gives a smooth, shiny surface. The two main techniques for achieving this are the vapor chamber method and the heated or portable method.
Vapor chamber method: The part is placed in a sealed, non-reactive container with acetone-soaked materials.
Heat or portable method: A heated container or a modified device is used to speed up the acetone evaporation and treatment time. It can be completed in minutes.

The rapid heating and cooling during machining can lock in uneven stresses, since ABS has poor thermal conductivity. The locked stresses can lead to dimensional instability over time. Annealing involves the gradual heating of the ABS part in an oven to around 70°C – 80°C for 2-4 hours and then cooling it down slowly to avoid introducing new thermal stresses.

Parts can be stored in airtight containers or bags to minimize exposure to moisture and oxygen. Place silica gel packets inside the storage containers to absorb any residual moisture.