For deep-hole drilling, part-handling might be the most visible automation element, but it’s not necessarily the most impactful. Often, it’s internal process automation that yields the most significant results even with a manually loaded drilling machine.
19

Dec

Deep-Hole Drilling Automation Is More Than Part Load/Unload

BY ANTHONY FETTIG, CEO — UNISIG DEEP HOLE DRILLING SYSTEMS

For deep-hole drilling, part-handling might be the most visible automation element, but it’s not necessarily the most impactful. Often, it’s internal process automation that yields the most significant results even with a manually loaded drilling machine.

When it comes to automating deep-hole drilling, there are challenges unique to the process itself. These include fixturing complexities — where maintaining alignment requires elements such as guide bushings and tool supports not present in a conventional lathe or milling machine — and part attributes such as length and weight.

Long parts mean a long drilling cycle time, and maintaining production rates often requires multi-spindle, deep-hole drilling systems. Unfortunately, stopping a two- or four-spindle machine means two or four spindles sit idle until the parts are loaded and unloaded. So, in these instances, the more parts in the machine at one time, the more automation can actually inhibit cycle time while the machine is running.

Solving this problem in multi-spindle machines requires internal automation to achieve the objectives of lean manufacturing and one-piece flow. In-machine loaders singulate processes so that even within a small four-piece batch you maintain one-piece flow. The operator or automation device puts in a part and takes a part out, and the machine does a bit of maneuvering inside to sequence those four parts in such a way as to minimize spindle downtime while maintaining upstream and downstream processes for one-piece flow. For instance, parts could be loaded onto a smart conveyor, indexed, and lifted into chucks for the drilling cycle before robotic unloading on the out-feed side so that there are no bottlenecks to a steady production flow.

Tool life management is another form of internal automation. Getting feedback to the machine enables the deep-hole drilling process to adapt or halt, if necessary, before tools and parts are damaged.

Tool life management is built into a machine’s control, and the machine senses torque thrust and coolant. Chip condition is usually the first indicator of wear, which would otherwise require an operator present to detect, so the machine actually monitors the process and can predict tools starting to wear and identify when they need to be changed. A tool life management system also can count distances drilled and the number of cycles, then prompt  a tool change at the appropriate time.

That kind of in-machine automation smooths the path for external automation. As the process builds, highly standardized options for robot-ready machines such as an automatic door, workpiece-present sensors and programmable workpiece fixturing makes it easier to add a robot at a later date. These robot-ready machines also create efficiencies before they’re fully automated. Even with manual loading, the automatic doors and programmable clamping make the process more efficient.

In UNISIG’s experience, an embedded reamer tool changer enables manufacturers to manage significant throughput increases, even with an operator. With this technology, operators can maintain the pace of production loading the machine, while eliminating the task of inserting reaming tools for each cycle. This allows the operator to redirect efforts towards tasks such as additional quality checks and off-machine setups.

Commercial Tool and Die, plastic injection mold shop in Comstock Park, Michigan, highlights their capabilities in productive deep hole drilling, performed by Ingersoll Deep-Trio tools
15

Jun

Mold Manufacturer Highlights UNISIG’s Productivity Contribution

Commercial Tool and Die, plastic injection mold shop in Comstock Park, Michigan, highlights their capabilities in productive deep hole drilling, performed by Ingersoll Deep-Trio tools on their three UNISIG USC-M38 deep hole drilling and milling machines. The case study was featured in the June 2017 issue of Moldmaking Technology.

mold manufacturers using the UNISIG USC-M machine
Picture yourself facing knee surgery, under the care of a skilled orthopedic surgeon. Precision instruments, state-of-the-art monitoring equipment, and decades of experience
01

May

How to Drill Straighter: Concentricity in Deep Hole Drilling

Picture yourself facing knee surgery, under the care of a skilled orthopedic surgeon. Precision instruments, state-of-the-art monitoring equipment, and decades of experience are on hand, as they conduct a procedure that will ideally lead to more days on the court. The surgical team works patiently and carefully towards a successful outcome, relying on tools to guide their movements with exact precision, placing instruments exactly where they need to be in the body, and not even a half millimeter off. For deep holes in components to be accurate – including surgical tooling – they need to uphold tight concentricity tolerances, and in gundrilling, this happens best with counter-rotation. For a manufacturer, this is vitally important. For an end user, or in this case a patient facing surgery, it can make all the difference.

These precision parts are one of several applications that have deep holes, where concentricity is critical to the function of the part. Concentricity tolerances are achieved when the hole follows the desired axis of the part, eliminating drift from the point of entrance to the exit. In a round part with on-center drilling, this is easily illustrated; some applications may include deep holes which are off-center, or in non-round parts, but still have tight concentricity requirements.

Low concentricity in some applications can result in parts with weak sidewalls, mismatched holes, or even scrapped parts. In other cases, manufacturers may decline production of these components, because of perceived impossibility or unproductiveness. With the addition of a counter-rotating process on deep hole drilling equipment, critical concentricity tolerances can become both achievable and economical.

How Counter-Rotation Improves Concentricity

Drilling a deep hole is commonly achieved by rotating the cutting surface of a tool against the metal of a workpiece with two opposing spindles in a horizontal setup. Typically, this consists of a stationary workpiece and rotating tool, but can also be configured with a rotating workpiece and stationary tool, or a third option, with a counter-rotating tool and workpiece.

Common machining centers use a rotating cutting tool, such as a mill, and a fixtured, stationary workpiece. A lathe, alternatively, rotates a workpiece and cuts with a stationary tool. Much of the time, setups such as these are enough to achieve the goals and tolerances of a majority metal cutting tasks, but are limited when it comes to more extreme tolerances and depth-to-diameter ratios.

A tool-rotate configuration is the least accurate when it comes to concentricity. In this setup, gravity is believed to act on the base and shank of the tool, not the drilling tip, and along with the rotation of the tool. Because of the relative position of the tool and gravity to the workpiece, this configuration produces the poorest results. This tool-rotate process is common for shallower holes on a machining center, but as holes become deeper, and tolerances become tighter, this no longer works as a solution.

Workpiece-rotate-only setups produce holes that are approximately twice as concentric as tool-rotate. A rotating workpiece changes the relative force of gravity compared to the workpiece position, negating some of the effects on the finished hole. A rotating workpiece can be done on a lathe with limited capability, but is ideally performed on a dedicated deep hole drilling machine.

deep hole drilling diagramCounter rotating tool and workpiece improve significantly upon both of these, as the forces are never static – changing relative gravity and orientation will provide drilling conditions without a single constant net direction that the tool will follow. In this setup, the tool is restricted from drifting, and will produce a much more concentric finished hole.

Counter-rotation is easily achievable with the right equipment and setup, whether it is for smaller gundrilled holes, or larger, longer BTA drilled components.

Deep holes are typically classified as anything with a depth-to-diameter (D:d) ratio of approximately 10:1 or greater, and can even reach extreme ratios of 100:1. As deep holes approach ratios of 20:1 or greater, drilling with specialty tooling on dedicated equipment is optimal. Modern deep hole drilling machines are designed to maximize the potential of tools such as gundrill and BTA processes.

deep hole diagram

The Data

To represent the impact of counter rotation, a test was performed on a 4140HT workpiece, 30 inches in length, ¾” outer diameter and a ¼” drilled hole. The depth to diameter (D:d) of this test is 120:1. This part is easily representative of a power transmission shaft or aerospace linkage.

Drilling these test workpieces produced the following results (measured using ultrasound):

  • Rotating Tool, Stationary Work: 0.026 inch drift at 30 inches of drill length
  • Stationary Tool, Rotating Work: 0.015 inch drift at 30 inches of drill length
  • Rotating Tool, Counter Rotate Work: 0.009 inch drift at 30 inches of drill length
    *results may vary based on material, depth-diameter ratio, tooling, etc.

Drilling holes with a 40:1 or less depth-diameter ratio can be done with limited drift using standard drilling practices. Beyond 40:1, counter-rotation really begins to deliver benefits with minimal drift.

Total Drift Comparison, Drilling Methods

  • Rotating Tool - Stationary Workpiece
  • Stationary Tool - Rotating Workpiece
  • Counter-Rotating Tool and Workpiece

Getting Started with Counter-Rotating Deep Hole Drilling

Typical machining centers are often not capable of deep holes greater than a 20:1 D:d ratio, and are not configured for counter-rotation. Rather, dedicated deep hole drilling machines are a superior consideration because they are designed specifically to manage accurate counter-rotation in gundrilling and BTA processes.

Deep hole drilling machines that enable successful counter-rotation include the right components, machined and assembled to maintain superior alignment. These range from the machine base, to rotating bearing groups and spindles, to tool and workpiece support – all of which uphold alignment and work as a system. This allows the machine to maintain accuracy while moving, and hold concentricity tolerances throughout the depth of the hole.

rotating deep hole drilling workpieceFor deep hole machine builders, alignment considerations begin with the machine base. Each component is designed with alignment as a priority,as well as machining and environmental factors like temperature and gravity. Counter rotation may be possible on machines retrofitted with a second rotating group, but will often need to undergo an alignment improvement process which creates additional challenges. Equipment designed with this purpose will have the right combination of benefits to make concentricity tolerances manageable for nearly any operator.

On a counter-rotating drilling machine, a good operator interface will provide a full picture of process information, as well as allow control over process parameters, for fine-tuning and process repetition. Manufacturers can optimize their counter rotation application, and proceed into highly accurate and efficient production.

A general starting point for counter rotation is to allow one third of the total speed to come from the workpiece, and two thirds of the speed to come from the tool. This is a typically recommended starting point for counter-rotating drilling with confidence. Operators can adjust for their specific application, and work with industry partners for recommended parameters to meet deep hole drilling goals.

Productivity Considerations

The addition of counter-rotation in a deep hole drilling process gives operators an additional factor to optimize for both specification and production requirements. The ability to hold improved concentricity tolerances with counter-rotation allows feeds to be run at optimal rates, as well as extends tool life. Manufacturers can reliably produce more parts per hour, with fewer tool changes and improved tool consumption.

For applications where concentricity is indeed critical, the productivity benefits are significant, and easily justify the added capability. Counter-rotation consistently produces a more concentric drilled hole, typically with higher surface cutting speeds, offering clear benefits to manufacturers in both accuracy and efficiency.

Manufacturers can increase capability, improve hole tolerances, and optimize productivity, ultimately cutting costs and providing a competitive manufacturing advantage. With the right resources, drilling deep holes with extreme concentricity is economical, repeatable, and commercially viable.

Production deep hole drilling can seem complicated for manufacturers with multiple off-center holes, in multiple part families. UNISIG's UNI machine uses smart fixturing, seamlessly integrated automation, and X-Y positioning to manage this process, while upholding standards of both production and accuracy.
09

Mar

Off-Center Production Gundrilling Machine on the UNI-XY | Video

Production deep hole drilling can seem complicated for manufacturers with multiple off-center holes, in multiple part families. UNISIG’s UNI machine uses smart fixturing, seamlessly integrated automation, and X-Y positioning to manage this process, while upholding standards of both production and accuracy.

Continue reading“Off-Center Production Gundrilling Machine on the UNI-XY | Video”