CNC Walk-behind Micro-machining And Tools

In micro-machining, part sizes can be very small, and there are many options for which tools and machining programmes to use. As micro-machining faces a variety of challenges (e.g., very small dimensional tolerances, stringent quality requirements, difficult-to-machine materials, etc.), it is critical to choose the right machining method. By optimising the machining process for tiny parts, it is possible to save component material, shorten machining cycles, reduce tooling costs, reduce machine idle time and improve component machining quality. As technology continues to advance, it is important to have a reliable tooling partner who can provide application support and technical advice to help improve the productivity of small parts. Often, a good entry point for identifying cutting process improvements is based on the different industries and types of machining.

　　Manufacturing of electronic and telecommunication products

　　Due to increasing demands on component functionality, electronic products are increasingly manufactured from difficult-to-machine materials such as mild and alloy steels, which has become another barrier to machining these components. Microturning tools are suitable for the machining of many electronic parts (e.g., the fine structure of optical disc trays), which often involves internal turning, grooving, cut-offs and threading.

　　Medical Device Manufacturing

　　A common feature of many medical devices is the complexity of their thread profiles and the high level of dimensional accuracy required. The challenge of machining bone screws often lies in their large length-to-diameter ratio. The length of these screws is much greater than their diameter, making them more difficult to machine because the screws are prone to bending during the process. In addition, many of these screws now require a larger helix angle, making them more difficult to machine with single-edged threaded tools.

　　Thread spin milling (a milling process in which the cutting edge is located in the inner ring of the milling cutter rather than on the outer periphery) is a much more productive method of machining. The process is well suited to CNC walk-behind machines because the distance between the tool and the guide bush is shorter, which increases support and reduces vibration.

Machining of medical bone screws with the threaded rotary milling process. A threaded rotary milling cutter ring with inserts mounted in the inner ring rotates around the cylindrical workpiece and machines the threads. The smooth tangential cutting motion reduces the cutting forces and improves the metal removal rate.

　　In order to minimise machining chatter (a major problem that can occur with threaded rotary milling) and to extend tool life, manufacturers should choose a threaded rotary milling cutter ring with unequally spaced inserts. Because they are machining high-strength materials, milling inserts are subjected to high impact, so it is important to select a high-hardness, fine-grain insert substrate and apply a wear-resistant coating to extend tool life and improve surface finish.

　　Aerospace Manufacturing

　　In this industry, the suitability of the clamping system can greatly affect machining efficiency, especially when machining high strength materials. Due to the nature of the materials being machined, cutting operations in both the medical device and aerospace manufacturing industries require the use of a large number of inserts. Over time, the time consumed in changing inserts becomes a significant factor in productivity. In addition, the high-performance, long chip materials typically used in the machining of tiny parts in the aerospace manufacturing industry can cause chip breakage challenges.

　　The QS toolholding system with high precision cooling not only reduces tool loading and changeover times, but also improves chip breakage and machining performance. Its wedge design allows the operator to change inserts in seconds. Precision nozzles provide accurate coolant flow for improved part quality and chipbreaking performance. The benefit is a reduction in coolant pressure to 145 psi.

　　In aerospace manufacturing, productivity can be increased by applying helical milling (ramp milling) machining techniques. This technique uses milling cutters (rather than drills) to more efficiently machine a variety of holes and recessed features on curved and sloped surfaces common to many aerospace components. By using smaller depths of cut and higher cutting speeds, helical milling requires significantly less cutting force and machine power than drilling.

　　Automotive Manufacturing

　　Many automotive parts are formed from sheet metal that is processed through a punch die to form body components (e.g., doors, bonnets, wings, etc.). However, there are also many small automotive parts (e.g. drive shafts and gears) that are machined in large batches. Reducing the cost per part is the main goal of high volume machining of these parts. Key factors in achieving seamless production include process safety, cycle time and product quality.

　　In the machining of driveshafts and gears, steel turning dominates. However, careful selection of the right insert grade is essential for steel turning, as it paves the way for more efficient hard turning and, if the workpiece is still to be ground, the grinding allowance can be reduced, leading to a reduction in cost per part.

　　Tool and process selection

　　Micro-machining presents a unique set of challenges - not only because of the very small size of the workpieces, but also because the workpieces are mostly made of difficult-to-machine materials and have complex geometries in the industries that require these tiny parts. This challenge is accompanied by increasing competition and technological demands in the medical device, aerospace and electronics industries - requiring high volume machining and significant investment in tools and inserts.

　　While choosing the right tool and process may seem quite difficult, utilising the valuable resources available can help manufacturers with the machining of most tiny parts. Due to increasing competition, the ability to select tools and processes to increase productivity to stay ahead of the technology curve can make or break a company's manufacturing operations. And choosing the right tooling partner can also ensure successful machining.

　　Machining know-how

　　While different micro-machining operations require different cutting strategies and machining sequences, there are some know-how and machining guidelines that are applicable in many situations:

　　(1) When machining on a CNC walk-behind machine, drilling and internal turning should be performed first on the positive spindle, which improves machining stability as the guide bushings provide support for the bar.

　　(2) The second step should be external turning on the positive spindle. If possible, complete the full depth of cut in one pass to shorten the cutting time and thus improve machining stability.

　　(3) The third step should be milling. Preference should be given to face milling. Due to the limited stability and power of the rotary spindle, the smaller the cutting force, the better, and face milling can meet this requirement.

　　(4) in order to cut off the process before the outer diameter of the workpiece processing, usually using high productivity counter-turning processing, a tool to complete the processing to help reduce vibration.

　　(5) Cut-off is a process done on the positive spindle. The closer the two spindles are to each other, the smaller the overhang of the part, the better the surface finish.

　　(6) Finishing is then done on the secondary spindle. This process is usually the inner diameter processing, but can also be the outer diameter processing.