Effective Hole Making Via Robotic Orbital Drilling
New technology may enable robotic drilling to be more commonplace in machine shops by overcoming the issue of limited robot rigidity.
The upside to using robots for drilling holes is that they have the maneuverability to reach multiple sides of a workpiece. The downside is that they sometimes lack the rigidity required to handle the high axial forces encountered during conventional drilling operations, especially in hard metals. However, Orbital Drilling end-effector technology from Novator (Spånga, Sweden) may make robotic drilling more commonplace in machine shops and manufacturing facilities by overcoming the issue of limited robot rigidity.
Orbital Drilling is similar to helical interpolation routines that enable machine tools to create holes of varying sizes using a single cutter. As a tool spins on its own axis, an eccentric spindle head rotates it to the offset required to produce the desired hole diameter. The spindle head contains a proprietary mechanism consisting of an inner and an outer eccentric body. These bodies are configured so that their mutual rotation enables continuous radial offset adjustment of the tool. The drilling cycle (feed rate, orbital speed and spindle speed) is fully programmable. This makes it possible to produce not only cylindrical, conical and countersunk holes of various sizes, but also holes with more complex shapes. Plus, Orbital Drilling produces lower thrust forces than conventional drilling to enable robots to effectively drill burr-free holes in materials ranging from carbon fiber reinforced plastic (CFRP) to titanium.
During Orbital Drilling, the tool has only partial and intermittent contact with the workpiece. That, together with efficient air cooling of the cutting tool and the hole surface, enables drilling to be performed dry or with minimum quantity lubrication (MQL). Efficient heat extraction also reduces the risk of matrix melting in composites and heat-affected zones in metals. Chips are small enough for efficient removal via an airflow extraction system.
Orbital Drilling is particularly effective for hole-making operations in stacked materials, such as CFRP/aluminum and CFRP/titanium used in aerospace applications. Both the wear factor and compensation curves are different for the stacked materials. To account for tool wear and differing material characteristics, the unit’s accompanying Orbital Manager software uses a compensation algorithm that enables it to dynamically adjust tool offset and other parameters during the drilling operation. According to the company, this makes it possible to drill a large number of holes to tight tolerances while significantly increasing tool life.
Novator’s E-D100 end-effector weighs approximately 130 kg and can create a maximum hole diameter of 25 mm. It offers a drill stroke length of 100 mm and uses a 9-kW, 30,000-rpm spindle.
The company also offers its PM Series of portable units for non-robotic applications. Available in 40- and 60-mm stroke lengths, these units are semi-automatic models with manually adjusted offset/eccentricity.
Reducing cutting fluid use offers the chance for considerable cost savings. Tool life may even improve.
Cutting holes by interpolating a face milling cutter may be a better process choice for many rough and even finish boring operations. Software improvements and better cutter designs allow expanding use of the versatile face mill for hole making.
Economic efficiency is an important consideration when choosing tools for challenging metals.