How to Choose the Right Material for Robotic Grippers: Aluminum vs. Stainless Steel vs. Plastics

The performance of an automated robotic cell is entirely bottlenecked by its weakest link. More often than not, that weak link is the End-of-Arm Tooling (EOAT). If your gripper fingers deflect under load, wear out prematurely, or weigh too much, the robot's overall kinematic efficiency plummets.

Selecting the exact alloy for your EOAT components comes down to trading off mass against fatigue limits. Here is the raw data on the most common CNC materials used in industrial automation.

Quick Reference: Material Properties for EOAT

Skip the guesswork. Here is the mechanical baseline for materials commonly used in machined robot grippers. Treat these as starting points for engineering review, not replacements for your own load calculations or regulated-industry validation.

Application Matrix: What Should You Specify First?

The right material is rarely a single-material answer. Most reliable EOAT assemblies mix a lightweight structural body with harder or softer contact inserts.

Payload Penalty: Why Material Density Changes Robot Speed

For a simple 200 x 120 x 25mm gripper body, material choice can change the mass dramatically before you add cylinders, cups, sensors, or brackets.

This is why a "stronger" material can make the cell worse. If a 10kg payload cobot carries a 4.8kg stainless EOAT, nearly half the payload is gone before the robot picks the actual part. In many cases, an AL7075 body with replaceable hardened steel jaw inserts gives better total system performance.

1. Aluminum Alloys (The Industry Standard)

Aluminum is by far the most dominant material used in custom EOAT manufacturing. It strikes the perfect balance for industrial robotics: it’s lightweight, highly machinable, and exceptionally strong when alloyed.

AL 6061-T6

• Best For: General-purpose gripper bodies, structural adapter plates, and pneumatic manifolds.
• Why it works: AL6061 offers excellent corrosion resistance and accepts surface treatments (like Type II and Type III Hard Coat anodizing) beautifully. It's the default choice for 80% of automation components because it won't eat into the robot's payload capacity while maintaining rigid structural integrity. It is also highly economical to machine.

AL 7075-T6 (Aerospace Grade)

• Best For: High-stress linkage arms, slim gripper fingers, and high-speed moving parts.
• Why it works: AL7075 boasts a tensile strength nearly double that of AL6061—rivalling some mild steels—but at a fraction of the weight. When your robot requires ultra-fast acceleration (high G-forces) and minimal inertia, AL7075 is the premium choice to prevent deflection in extended gripper fingers.

2. Stainless Steel (The Heavy-Duty Defender)

While aluminum excels at being lightweight, it is relatively soft. When the EOAT needs to physically interact with abrasive environments, handle extreme impacts, or withstand harsh chemical washdowns, stainless steel steps in.

SUS 304 / 316L (Austenitic)

• Best For: Food-grade automation, medical packaging, and corrosive washdown environments.
• Why it works: Austenitic stainless steels are highly corrosion-resistant and non-magnetic. If your EOAT operates in a food-safe facility where it gets blasted with caustic cleaning agents (like sodium hydroxide) daily, 316L is mandatory. Note: It is heavy, so it should only be used where necessary to avoid payload penalties.

SUS 420 / 440C (Martensitic / Hardened)

• Best For: Gripper jaw contact faces, locating pins, and wear pads.
• Why it works: These martensitic stainless steels can be heat-treated to high Rockwell hardness (HRC 58-60). If your robot repeatedly grips unmachined castings, rough forgings, or glass, hardened stainless jaws give the contact surface a better chance of surviving high-cycle wear without losing the intended grip profile.

3. Engineering Plastics (The Gentle Touch)

Sometimes, metal is too harsh. When handling delicate, scratch-sensitive, or statically sensitive parts, CNC machined polymers are required.

POM (Delrin / Acetal)

• Best For: Suction cup mounts, electrical isolation blocks, and non-marring gripper fingers.
• Why it works: Delrin is highly machinable, dimensionally stable (it absorbs very little moisture), and has a very low coefficient of friction. If you are handling polished acrylic lenses, PCBs, or painted automotive trim, Delrin jaws provide firm clamping without scratching the payload.

PEEK (Polyether Ether Ketone)

• Best For: High-temperature environments, semiconductor handling, and vacuum chambers.
• Why it works: PEEK is an advanced, ultra-high-performance thermoplastic. It maintains its mechanical properties at temperatures exceeding 250°C (480°F) and resists harsh chemical solvents. It is frequently used in wafer-handling EOAT inside semiconductor fabrication plants. Due to its high material cost, it is usually reserved for extreme environments.

Material + Surface Treatment Compatibility

Surface treatment should be specified by function: corrosion protection, wear resistance, cleanability, color coding, or low friction. Do not apply every finish to every face.

Multi-Material EOAT Stack-Up

Summary: Designing for the Payload (The Golden Rule)

Every gram of weight you add to the end effector is a gram subtracted from the robot's maximum payload and a marginal decrease in acceleration speed.

The Golden Rule of EOAT Material Selection:

Actionable RFQ Checklist for Custom EOAT

When sending your 3D CAD files to a machining partner, ensure your 2D PDF drawings specify:

1. Exact Material Alloy: Don't just write "Aluminum". Specify "AL6061-T6" or "AL7075-T651".
2. Hardness Requirements: For steel jaws, specify the heat treatment target (e.g., "Harden to HRC 58-60").
3. Surface Treatment: Clearly label faces that require hard-coat anodizing, electroless nickel plating, or PTFE impregnation.
4. Cleanroom Prep: If applicable, state "No silicone-based cutting fluids" or "Ultrasonic clean before vacuum packaging".

Copy-Paste Material Specifications for RFQs

Use these as starting language for your 2D drawing or RFQ email, then adjust them to your company's standards.

(Want to lower your quotes even further? Read our 5 DFM Tips for Custom CNC Grippers).

By combining materials effectively, you can design an end effector that improves payload use, reduces unnecessary inertia, and gives maintenance teams clearer replacement-part rules.

Need help manufacturing your multi-material gripper assembly? Contact the EOAT Machining engineering team to discuss your material requirements, surface treatments, and CAD models.