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Speed Up Setup, Improve Accuracy of All EDM Applications with Probing
By Brian Pfluger, EDM Product Line Manager at Makino
Manufacturers and shops of all sizes use probing technologies to reduce part setup time and validate accuracy for a wide variety of applications for wire, sinker and drilling electrical discharge machining (EDM).
Probing is an automatic machine cycle that establishes workpiece or electrode alignment data within the machine. In a recent webinar, I introduced the different standard and optional methods, discussed the advantages and disadvantages of the various probing technologies, and offered recommendations on how probing could improve your EDM processes.
In traditional milling, in-machine probing entails the use of a coordinate measuring machine (CMM)-style touch device, but this does not hold true for EDM. Instead, EDM machines can probe and establish location data using electrical touch sensing with an electrode (or the working tool), and most EDMs offer options for traditional CMM-style touch probe systems, too. Workpiece data can be determined for location and feature size, as well as the electrode size. The data can be used to establish a work coordinate system (WCS) value or origin point from which all work is based. In addition, this data can be used to calculate 2-D and 3-D offset values.
Rely on Wire to Probe Before Burning
For wire EDM applications, the wire itself can be used as a probe to establish workpiece locations and feature size, including workpiece rotation conditions. In order to establish reliable pick-up accuracy using the wire, the work piece must be clean and free of debris and burrs, and the wire itself must be clean and of high quality. Premium hard brass wire will generally provide the best pick up accuracy, as the special coatings used on most high speed coated/stratified wires degrade pick-up accuracy.
Most of the probing cycles to pick up locations can be incorporated into a program’s NC G-Code to automate production applications. On the Makino Hyper-i control, 12 probing cycles are preset, making them quickly available in the control’s main menu. To simplify setup operations, each probing cycle includes convenient how-to directions for the operator from the Hyper-i control’s touch screen. The measurements from each pick-up cycle can be recorded and exported out of the control in a Microsoft Excel format for statistical process tracking purposes.
Makino also offers a touch-probe option, which employs a high-accuracy Renishaw MP250 probe head. The probe is manually loaded and unloaded on the same centerline as the wire, enabling the probe to reach all areas within the machine stroke. All measurements captured by the probe system calculate an offset value within the machine based upon a calibration process between the probe and wire center line.
In Sinker EDM, Rely on Spindle and Table Balls
Just like on a wire EDM, the actual electrode on a sinker EDM can be used to probe the workpiece location and dimensions. However, this method may not produce precise measurements because the larger surface area of the electrodes makes them prone to inaccuracies caused by any debris between the workpiece and electrode in the work tank.
Use of a spindle ball tool holder is highly recommended for workpiece setup probing. The smaller contact area of the spindle ball makes this method faster and more precise. A table ball within the work tank is also recommended to probe the electrodes.
Sinker machines establish offset and location data between the workpiece and electrode through a correlation measure cycle between the spindle ball and table ball. The spindle ball is used on the Z-axis to establish workpiece locations as well as workpiece and feature sizes. The table ball measures electrode offsets and locations within the machine. Makino’s Hyper-i control can record and export this data for statistical process tracking, and provides helpful videos and tutorial information on the operation and function of each pick-up cycle to aid the operator in applying these time-saving features.
How to Improve EDM Drilling Probing Accuracy
EDM drilling machines can use the same spindle ball and table ball tooling and pre-set pick-up cycles as a sinker EDM to establish workpiece locations.
A spindle ball probe is recommended for establishing workpiece locations and alignments because using the actual small diameter electrode tube is unreliable due to movement and bending of the electrode the farther it is extended away from the die guide. The spindle ball tool holder can be a rigid probe or touch-probe system that is loaded and unloaded by the machine’s automatic tool changer (ATC).
The table ball setup for EDM drilling uses a half ball diameter for faster, more accurate electrode tube pickups. This configuration minimizes the distance the small-diameter electrode is extended from the die guide, and also allows for easier Z-depth and electrode length alignment.
Pros and Cons of EDM Probing
|Capture 2-D and 3-D workpiece data in some applications.
|Most in-machine probing capabilities are limited to capturing single data points and do not support 3-D scanning that full-blown CMMs provide.
|Reduce setup time in many applications by probing in the work tank.
|The time required for in-machine probing is time the machine is not adding any value to the part. Integrated off-line CMM’s should be considered for high-volume production applications.
|Improve and validate accuracy of workpiece location and dimension measurements.
|Debris in the work tank or on an electrode and poor workpiece condition can result in inaccurate probing measurements.
|Deliver regular correlation with master inspection device or calibrated standard.
|On-machine part inspection is one method to validate quality before removing the workpiece from the machine. This does not eliminate the need for final part inspection per ISO standards, but this machine data can be used as part of the overall quality standard system.
|Record and track data for statistical process control.
By watching the full webinar, you’ll gain a deeper understanding of the different probing capabilities for wire, sinker and drilling EDM applications.
In-machine probing offers many attractive advantages for manufacturers of all sizes by reducing setup time and providing more precise measurements of workpiece location and dimensions. I recommend using probing, especially when an EDM machine comes equipped with controls such as Makino’s Hyper-i, which provides preset cycles to simplify the probing and workpiece setup process.
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Learn more about Makino’s EDM probing technologies that reduce setup time for a wide range of applications from traditional die/mold parts aerospace and gas turbine blade and vane details.
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