Tombstone Fixturing on a CNC Machine: Purpose, Advantages, and Industry Applications

Tombstone fixturing is a critical component in the world of CNC machining, providing manufacturers with a way to optimize productivity and precision during the machining process. It is a specialized fixture used to hold parts securely during multi-axis operations on CNC machines. In this article, we will explore what a tombstone is, its purpose, the major brands that manufacture tombstones, how they help in the machining process, the advantages and disadvantages of tombstone fixturing, and the types of industries that benefit from using tombstones in their CNC operations.

What is a Tombstone in CNC Machining?

A tombstone is a workholding fixture used on CNC machines to hold multiple parts simultaneously for machining operations. The term "tombstone" comes from the fixture's shape, which resembles a vertical slab or monument. Tombstones are typically used on CNC vertical machining centers (VMCs), although they can be used on other machines as well. The fixture is mounted on the machine’s table, allowing for multiple parts to be loaded and machined at once.

Tombstone fixturing is particularly valuable for parts that require complex, multi-axis machining, as it allows for the efficient use of the machine’s capabilities.

The Purpose of a Tombstone

The primary purpose of a tombstone in CNC machining is to optimize workholding and maximize machine uptime. Here’s how tombstones achieve this:

• Multiple Parts in One Setup: Tombstones are designed to hold several parts simultaneously, reducing the need to re-fixture the part after every machining operation. This is particularly useful for high-volume production runs.
• Increased Efficiency: By enabling multiple setups in a single cycle, tombstones reduce the downtime between operations. CNC machines can continue to operate without requiring an operator to change parts frequently.
• Multi-Axis Machining: Tombstones enable the simultaneous machining of multiple sides or faces of a part, particularly in 4-axis or 5-axis CNC operations, which enhances flexibility and precision.
• Improved Accuracy: Since the parts are held securely and consistently across multiple operations, tombstone fixturing leads to improved part-to-part accuracy and repeatability.

Major Brands that Manufacture Tombstones

Several well-known brands specialize in the design and manufacturing of tombstone fixturing systems for CNC machines. Some of the top manufacturers include:

• Kurt Manufacturing: Known for producing high-quality workholding solutions, Kurt offers a variety of tombstone fixtures and workholding systems designed for high-precision machining.
• Röhm: A leading brand in workholding solutions, Röhm provides customizable tombstones made from durable materials such as cast iron and aluminum.
• Lang Technik: Specializes in flexible and modular workholding systems, including tombstones for CNC machines.
• Fipa: Offers a range of tombstone fixturing systems designed to maximize efficiency and precision for CNC machining centers.
• SCHUNK: Known for its advanced clamping and workholding technologies, SCHUNK produces tombstone fixtures that cater to high-end CNC machining applications.

These companies design tombstones that are compatible with various CNC machines and can be tailored to meet specific customer needs.

How Do Tombstones Help in CNC Machining?

Tombstone fixturing provides significant benefits in CNC machining by improving the production process. Here’s how tombstones help:

• Improved Productivity: By allowing for multiple parts to be machined in a single cycle, tombstones reduce the time spent loading and unloading parts, which increases the overall throughput.
• Enhanced Part Stability: Tombstones secure parts more firmly during machining, reducing vibrations and improving machining accuracy. This is particularly important for high-precision parts and high-speed operations.
• Flexibility in Setup: Many tombstone fixtures are modular, which means they can be easily customized for different part sizes and types. This allows for quick changeover between different parts in production.
• Cost Savings: With the ability to machine multiple parts at once, tombstones help reduce labor and machine time, leading to lower production costs, especially in high-volume manufacturing.

Advantages of Tombstone Fixturing

• Increased Efficiency: Tombstones reduce the number of setups required during machining, leading to faster cycle times and improved operational efficiency.
• Versatility: Tombstone fixtures can be configured for use with various CNC machines, including vertical and horizontal machining centers.
• Cost-Effective: By enabling multi-part machining in one cycle, tombstones can reduce labor costs and machine downtime, which ultimately lowers the cost per part.
• Enhanced Precision: The ability to hold multiple parts securely results in greater consistency in machining and better tolerances across parts.
• Time Savings: The use of tombstones eliminates the need for frequent re-fixturing, saving significant time during the production process.

Disadvantages of Tombstone Fixturing

• Complex Setup: While tombstones improve efficiency, setting up a tombstone fixture can be more time-consuming and complex compared to simpler workholding options.
• Space Limitations: Tombstones require a large machine workspace, which may not be ideal for smaller CNC machines or machines with limited table space.
• Initial Investment: Tombstones, especially customizable or modular ones, can represent a higher initial investment compared to other types of fixtures. However, this is often offset by long-term efficiency gains.
• Maintenance Requirements: Tombstone fixtures can require regular maintenance to ensure they remain in optimal condition. Any misalignment or damage to the fixture can affect part accuracy.

Types of Industries That Use Tombstones

Tombstone fixturing is beneficial for a wide range of industries that require high-volume, high-precision manufacturing. Industries that commonly use tombstone fixtures include:

• Aerospace: Precision machining of complex, lightweight parts is a staple in the aerospace industry. Tombstones are used to hold multiple parts during multi-axis machining of components like turbine blades, engine parts, and structural elements.
• Automotive: Manufacturers in the automotive industry often use tombstones to machine engine components, transmission parts, and other critical components efficiently.
• Medical Devices: For producing high-precision medical parts such as surgical instruments, implants, and diagnostic equipment, tombstones provide the stability and repeatability required for these critical parts.
• Mold and Die Making: In mold-making industries, where precision is essential, tombstones allow manufacturers to machine multiple cavities and components in a single operation, significantly increasing throughput.
• Defense and Military: Tombstones are often used to machine components for military vehicles, weapons, and equipment that require high precision and rapid turnaround times.

Conclusion

Tombstone fixturing is an essential technology for optimizing CNC machining processes, particularly when producing high-precision parts in high volumes. By allowing for multiple parts to be held simultaneously, tombstones help improve efficiency, accuracy, and cost-effectiveness, making them invaluable in industries like aerospace, automotive, and medical devices. While they may require a higher initial investment and more complex setup, the long-term benefits of using tombstones far outweigh the challenges. As manufacturing technology continues to evolve, tombstones will remain a key tool in advancing productivity and precision in the CNC machining world.